Coupling of trace elements in brachiopod shells and biotic signals from the Lower Jurassic South-Iberian Palaeomargin (SE Spain): Implications for the environmental perturbations around the early Toarcian Mass Extinction Event

Geological and stratigraphical setting

The brachiopod-bearing outcrops are located in the Crevillente and Reclot mountains in Alicante province, SE Spain (Fig. 2A), which are integrated in the Eastern Subbetic Domain of the External Betic Zone. The Mesozoic sedimentary rocks of this area represent part of the South-Iberian Palaeomargin, located in the westernmost Tethys Ocean. During most of the Jurassic and Early Cretaceous, the Subbetic Domain was characterized by marine sedimentation with environments ranging from shallow carbonate platforms to pelagic troughs and swells (Azéma et al., 1979Azéma, J.; Foucault, A.; Fourcade, E.; García-Hernández, M.; González-Donoso, J.M.; Linares, A.; Linares, D.; López-Garrido, A.C.; Rivas, P. & Vera, J.A. (1979). Las microfacies del Jurásico y Cretácico de las Zonas Externas de las Cordilleras Béticas. Publicaciones Universidad Granada, 83 pp.; Vera et al., 2004Vera, J.A.; Martín-Algarra, A.; Sánchez-Gómez, M.; Fornós, J.J. & Gelabert, B. (2004). Cordillera Bética y Baleares, In: Geología de España (Vera, J.A., Ed.), SGE-IGME, 345-464.). In the Eastern Subbetic, the Lower Jurassic succession is typified by the Gavilán and Zegrí formations (e.g. García-Hernández et al., 1979García-Hernández, M.; Rivas, P. & Vera, J.A. (1979). Distribución de las calizas de llanuras de mareas en el Jurásico del Subbético y Prebético. Cuadernos de Geología Universidad Granada 10: 557-569.; Ruiz-Ortiz et al., 2004Ruiz-Ortiz, P.A.; Bosence, D.W.J.; Rey, J.; Nieto, L.M.; Castro, J.M. & Molina, J.M. (2004). Tectonic control of facies architecture, sequence stratigraphy and drowning of a Liassic carbonate platform (Betic Cordillera, Southern Spain). Basin Research, 16: 235-257. https://doi.org/10.1111/j.1365-2117.2004.00231.x ; Nieto et al., 2008Nieto, L.; Ruiz-Ortiz, P.A.; Rey, J. & Benito, M.I. (2008). Strontium-isotope stratigraphy as a constraint on the age of condensed levels: examples from the Jurassic of the Subbetic Zone (southern Spain). Sedimentology, 55: 1-39.) (Fig. 2B), which have been presented in the composite section herein arranged (Fig. 2C).

In the studied outcrops, the upper Sinemurian part of the Gavilán Formation consists of micritic and pseudo-oolithic whitish wackestone beds, showing lateral and upward transitions to oolithic grainstone/packstone levels with intraclasts and peloids. They were deposited in a proximal platform environment. The top of this lithostratigraphical unit shows intense extensional fissures. These were a consequence of an initial pre-rifting stage (Vera, 1988Vera, J.A. (1988). Evolución de los sistemas de depósito en el margen ibérico de la Cordillera Bética. Revista de la Sociedad Geológica de España, 1: 373-391., 1998Vera, J.A. (1998). El Jurásico de la Cordillera Bética: Estado actual de conocimientos y problemas pendientes. Cuadernos de Geología Ibérica, 24: 17-42.; Molina et al., 1999Molina, J.M.; Ruiz-Ortiz, P.A. & Vera, J.A. (1999). A review of polyphase karstification in extensional tectonic regimes: Jurassic and Cretaceous examples, Betic Cordillera, southern Spain. Sedimentary Geology, 129: 71-84. https://doi.org/10.1016/S0037-0738(99)00089-5 ) interpreted as the first tectonic pulses and related to the drowning of the westernmost Tethyan platforms in the framework of the Central Atlantic Ocean opening (Ruiz-Ortiz et al., 2004Ruiz-Ortiz, P.A.; Bosence, D.W.J.; Rey, J.; Nieto, L.M.; Castro, J.M. & Molina, J.M. (2004). Tectonic control of facies architecture, sequence stratigraphy and drowning of a Liassic carbonate platform (Betic Cordillera, Southern Spain). Basin Research, 16: 235-257. https://doi.org/10.1111/j.1365-2117.2004.00231.x ).

The upper member of the Gavilán Formation (upper Pliensbachian) overlies these shallow-water platform facies. It consists of red crinoidal grainstone beds with abundant glauconite. Brachiopods, benthic foraminifera, peloids, and intraclasts are also common. These layers often show irregular tops with condensed pavements interpreted as omission surfaces or hardgrounds with ammonoids, belemnites, and brachiopods.

The onset of the marly sedimentation is represented by the Zegrí Formation, which dominates throughout the early-middle Toarcian in the basin, suggesting a pelagic depositional environment. This formation is made up by alternating yellowish to greenish marl/marly mudstone beds with calcarenites interspersed at the base of the formation, showing towards the top a continuous increase in the marly content.

Brachiopod biochronostratigraphy

In the lowermost deposits (samples EFC3 to CC1.0), the analysed brachiopod shells predominantly belong to Calcirhynchia plicatissima (Table 1, Fig. 6), which shows a continuous record in these sediments. The acme of this species, together with that of Prionorhynchia regia and Gibbirhynchia curviceps, plus the first occurrence of multicostate zeilleriids and the genus Securina, typify the Assemblage 1 of brachiopods in the easternmost Subbetic (Baeza-Carratalá, 2013Baeza-Carratalá, J.F. (2013). Diversity patterns of Early Jurassic brachiopod assemblages from the westernmost Tethys (Eastern Subbetic). Palaeogeography, Palaeoclimatology, Palaeoecology, 381-382: 76-91. https://doi.org/10.1016/j.palaeo.2013.04.017 ). This assemblage is assigned to the Sinemurian-Pliensbachian transition (Raricostatum-Aenigmaticum zones).

In the middle part of the Lower Jurassic succession, the analysed shells are among the prevailing taxa of Assemblage 2 (Baeza-Carratalá, 2013Baeza-Carratalá, J.F. (2013). Diversity patterns of Early Jurassic brachiopod assemblages from the westernmost Tethys (Eastern Subbetic). Palaeogeography, Palaeoclimatology, Palaeoecology, 381-382: 76-91. https://doi.org/10.1016/j.palaeo.2013.04.017 ). Thus, several species of Prionorhynchia and Cirpa are selected for geochemical analyses (Table 1), since they occur profusely in the upper member of the Gavilán Formation. In these deposits, spiriferinides acquire great diversity and abundance as well, and they were selected for analyses only when multicostate rhynchonellides were not available. Data from ammonite faunas in these sediments range in age from the lower (Demonense Zone) up to the upper (Algovianum Zone) Pliensbachian (Braga, 1983Braga, J.C. (1983). Ammonites del Domerense de la zona Subbética (Cordilleras Béticas, S. de España). PhD Thesis Univ. Granada, 410 pp.; Iñesta, 1988Iñesta, M. (1988). Braquiópodos Liásicos del Cerro de La Cruz (La Romana, Prov. Alicante, España). Mediterránea Serie Geológica, 7: 45-64.; Tent-Manclús, 2006Tent-Manclús, J.E. (2006). Estructura y estratigrafía de las sierras de Crevillente, Abanilla y Algayat: su relación con la Falla de Crevillente. PhD Thesis, Universidad de Alicante, 970 pp., http://hdl.handle.net/10045/10414.).

The biochronological control of brachiopods prior to and after the Jenkyns Event is more accurate if the Subbetic record is correlated with that of the nearby Iberian basin, where an extensive succession of ammonites allows for a precise calibration. Thus, Lobothyris arcta is recorded prior to the Jenkyns Event in the Emaciatum-Polymorphum zones (García Joral et al., 2011García Joral, F.; Gómez, J.J. & Goy, A. (2011). Mass extinction and recovery of the Early Toarcian (Early Jurassic) brachiopods linked to climate change in northern and central Spain. Palaeogeography, Palaeoclimatology, Palaeoecology, 302: 367-380. https://doi.org/10.1016/j.palaeo.2011.01.023 , Baeza-Carratalá, 2013Baeza-Carratalá, J.F. (2013). Diversity patterns of Early Jurassic brachiopod assemblages from the westernmost Tethys (Eastern Subbetic). Palaeogeography, Palaeoclimatology, Palaeoecology, 381-382: 76-91. https://doi.org/10.1016/j.palaeo.2013.04.017 ) together with several spiriferinid (Calyptoria vulgata) and athyridide representatives (the so-called Koninckinid fauna; Fig. 6), which became extinct in the earliest Serpentinum Zone as an effect of the Jenkyns Event (Ager, 1987Ager, D.V. (1987). Why the Rhynchonellid Brachiopods survived and the Spiriferids did not: a suggestion. Palaeontology, 30: 853-857.; Vörös, 2002Vörös, A. (2002). Victims of the Early Toarcian anoxic event: the radiation and extinction of Jurassic Koninckinidae (Brachiopoda). Lethaia, 35: 345-357. https://doi.org/10.1080/002411602320790652 ; Comas-Rengifo et al., 2006Comas-Rengifo, M.J.; García Joral, F. & Goy, A. (2006). Spiriferinida (Brachiopoda) del Jurásico Inferior del NE y N de España: distribución y extinción durante el evento anóxico oceánico del Toarciense Inferior. Boletín Real Sociedad Española Historia Natural (Sec. Geológica), 101: 147-157.; Baeza-Carratalá et al., 2015Baeza-Carratalá, J.F.; García Joral, F.; Giannetti, A. & Tent-Manclús, J.E. (2015). Evolution of the last koninckinids (Athyridida, Koninckinidae), a precursor signal of the Early Toarcian mass extinction event in the Western Tethys. Palaeogeography, Palaeoclimatology, Palaeoecology, 429: 41-56. https://doi.org/10.1016/j.palaeo.2015.04.004 , 2018aBaeza-Carratalá, J.F.; García Joral, F.; Goy, A. & Tent-Manclús, J.E. (2018a). Arab-Madagascan brachiopod dispersal along the north-Gondwana paleomargin towards the western Tethys Ocean during the early Toarcian (Jurassic). Palaeogeography, Palaeoclimatology, Palaeoecology, 490: 256-268. https://doi.org/10.1016/j.palaeo.2017.11.004 ; Vörös et al., 2016Vörös, A.; Kocsis, Á.T. & Pálfy, J. (2016). Demise of the last two spire-bearing brachiopod orders (Spiriferinida and Athyridida) at the Toarcian (Early Jurassic) extinction event. Palaeogeography, Palaeoclimatology, Palaeoecology, 457: 233-241. https://doi.org/10.1016/j.palaeo.2016.06.022 , 2019Vörös, A.; Kocsis, Á.T. & Pálfy, J. (2019). Mass extinctions and clade extinctions in the history of brachiopods: brief review and a post-Paleozoic case study. Rivista Italiana di Paleontologia e Stratigrafia, 125(3): 711-724.). After this event, Soaresirhynchia bouchardi led the repopulation interval in many Western Tethyan basins (Fig. 6), constituting monospecific assemblages in the Elegantulum Subzone of the Serpentinum Zone (García Joral & Goy, 2000García Joral, F. & Goy, A. (2000). Stratigraphic distribution of Toarcian brachiopods from the Iberian Range and its relation to depositional sequences. Georesearch Forum, 6: 381-386.; García Joral et al., 2011García Joral, F.; Gómez, J.J. & Goy, A. (2011). Mass extinction and recovery of the Early Toarcian (Early Jurassic) brachiopods linked to climate change in northern and central Spain. Palaeogeography, Palaeoclimatology, Palaeoecology, 302: 367-380. https://doi.org/10.1016/j.palaeo.2011.01.023 ; Baeza-Carratalá et al., 2011Baeza-Carratalá, J.F.; García Joral, F. & Tent-Manclús, J.E. (2011). Biostratigraphy and palaeobiogeographic affinities of the Jurassic brachiopod assemblages from Sierra Espuña (Maláguide Complex, Internal Betic Zones, Spain). Journal of Iberian Geology, 37: 137-151. https://doi.org/10.5209/rev_JIGE.2011.v37.n2.3 , 2017Baeza-Carratalá, J.F.; Reolid, M. & García Joral, F. (2017). New deep-water brachiopod resilient assemblage from the South-Iberian Palaeomargin (Western Tethys) and its significance for the brachiopod adaptive strategies around the Early Toarcian Mass Extinction Event. Bulletin of Geosciences, 92: 233-256. https://doi.org/10.3140/bull.geosci.1631 ; Comas-Rengifo et al., 2013Comas-Rengifo, M.J.; Duarte, L.V.; García Joral, F. & Goy, A. (2013). Los braquiópodos del Toarciense Inferior (Jurásico) en el área de Rabaçal-Condeixa (Portugal): distribución estratigráfica y paleobiogeografía. Comunicaçoes Geológicas, 100: 37-42., 2015Comas-Rengifo, M.J.; Duarte, L.V.; Félix, F.F.; García Joral, F., Goy, A. & Rocha, R.B. (2015). Latest Pliensbachian-Early Toarcian brachiopod assemblages from the Peniche section (Portugal) and their correlation. Episodes, 38: 2-8. https://doi.org/10.18814/epiiugs/2015/v38i1/001 ). Therefore, Soaresirhynchia bouchardi was selected for geochemical analyses of this stratigraphic post-crisis interval (Table 1).

Finally, Telothyris pyrenaica is selected (Table 1) as representative for the lower-middle Toarcian, Serpentinum-lowermost Bifrons zones (García Joral & Goy, 1984García Joral, F. & Goy, A. (1984). Características de la fauna de braquiópodos del Toarciense Superior en el Sector Central de la Cordillera Ibérica (Noreste de España). Estudios Geológicos, 40: 55-60. https://doi.org/10.3989/egeol.84401-2650 , 2000García Joral, F. & Goy, A. (2000). Stratigraphic distribution of Toarcian brachiopods from the Iberian Range and its relation to depositional sequences. Georesearch Forum, 6: 381-386.; García Joral et al., 2011García Joral, F.; Gómez, J.J. & Goy, A. (2011). Mass extinction and recovery of the Early Toarcian (Early Jurassic) brachiopods linked to climate change in northern and central Spain. Palaeogeography, Palaeoclimatology, Palaeoecology, 302: 367-380. https://doi.org/10.1016/j.palaeo.2011.01.023 ; Baeza-Carratalá et al., 2016cBaeza-Carratalá, J.F.; García Joral, F. & Tent-Manclús, J.E. (2016c). Lower Jurassic brachiopods from the Ibero-Levantine sector (Iberian range): faunal turnovers and critical bioevents. Journal of Iberian Geology, 42: 355-369. https://doi.org/10.5209/JIGE.54666 ), signifying the re-establishment of the background conditions after the extinction event.

Trace element geochemistry and potential sources

Stratigraphic fluctuations

 ⌅

Concentration values of the trace elements and their distribution by samples have been displayed in box-plots Fig. 7 and Table 2. Mg, Al, and Fe are present in high values in the shells, followed by Sr. Among trace elements, Cr, Zn, and Ni show the highest values. The REEs show very low concentrations with the highest values corresponding to La, Ce, and Nd (Fig. 7). According to the brachiopod taxa analysed, the concentrations of elements are slightly different among the most common genera, Calcirhynchia and Prionorhynchia. Values of Ti, Cr, Fe, Co, Ni, Cu, Zn, Mo, Ba, and Pb are relatively higher in the shells of Calcirhynchia whereas Al, V, Mn, Th, and U show higher values in the shells of Prionorhynchia.

Figure 7.  Boxplot diagram representing the concentration of the trace elements in all the analysed samples. Boxes range from lower to upper quartiles, and the median is shown with a horizontal line inside the box, and whiskers denote minimum and maximum values unless they are considered outliers (denoted by crosses).

Table 2.  Chemical composition of studied specimens in ppm.

Specie	Sample Name	Ca	Li	Mg	Al	Ti	V	Cr	Mn	Fe	Co	Ni	Cu	Zn	As	Se	Rb	Sr	Mo	Cd	Sn	Sb	Ba	Pb	Bi	Th	U	La	Ce	Nd	Sm	Eu	Gd	Tb	Dy	Ho	Er	Tm	Yb	Lu	Tl
Telothyris pyrenaica	Z2C2-2g	2680	1,272	3119,207	576,110	1,511	2,527	14,428	85,239	947,400	1,547	8,069	2,298	8,893	0,568	0,417	1,285	385,260	0,398	0,108	0,289	0,060	4,390	1,398	0,142	0,862	0,537	3,724	6,373	5,479	1,168	0,260	1,377	0,180	0,925	0,172	0,462	0,058	0,352	0,056	0,072
Telothyris pyrenaica	Z2C2-1g	2466,44	0,516	2498,053	552,400	8,028	1,989	13,144	71,595	1084,134	1,309	7,791	1,492	9,078	0,606	0,461	1,130	235,970	0,445	0,131	0,628	0,104	8,180	4,914	0,022	0,877	0,343	3,210	5,191	4,689	1,083	0,210	1,218	0,150	0,790	0,134	0,371	0,042	0,258	0,040	0,021
Soaresirhynchia bouchardi	Z2C1-1g	754,52	0,367	2473,061	558,334	8,920	2,011	31,803	88,051	991,866	1,087	16,092	2,994	22,832	0,550	0,443	1,299	166,230	1,066	0,149	1,674	0,270	12,328	9,808	0,041	0,933	0,144	3,061	5,481	3,778	0,812	0,172	0,984	0,117	0,655	0,115	0,333	0,041	0,246	0,037	0,030
Lobothyris arcta	Z2B-2g	2070,00	0,746	2365,311	402,645	1,541	3,555	17,860	68,328	2017,471	0,760	7,680	3,085	18,939	0,774	0,341	0,986	230,876	0,373	0,103	0,324	0,045	4,514	1,218	0,089	0,730	0,270	3,636	4,558	4,367	0,748	0,161	0,852	0,108	0,544	0,101	0,274	0,037	0,231	0,039	0,041
Lobothyris arcta	Z2B-1g	539,99	1,757	3360,184	386,367	6,824	2,198	59,946	88,685	1157,010	1,067	29,775	4,948	54,127	0,442	0,552	1,081	365,554	1,982	0,116	2,723	0,291	7,699	4,516	0,045	1,334	0,413	3,217	4,559	3,563	0,742	0,160	0,947	0,110	0,628	0,110	0,326	0,040	0,255	0,037	0,028
Prionorhynchia aff. polyptycha	Z2A-2g	2660,00	0,719	2782,539	302,514	1,272	4,140	20,251	247,076	1016,647	0,921	5,691	1,179	13,260	0,307	0,255	0,639	231,469	0,300	0,143	0,198	0,018	4,000	1,531	0,048	0,306	1,190	1,923	1,529	1,539	0,283	0,070	0,360	0,049	0,269	0,055	0,159	0,022	0,149	0,026	0,008
Prionorhynchia aff. polyptycha	Z2A-1g	1985,39	0,852	2645,362	203,885	2,815	2,793	18,763	177,945	657,151	0,754	9,990	2,005	15,014	0,560	0,226	0,519	279,466	0,571	0,177	0,835	0,129	4,646	11,371	0,023	0,416	0,520	1,373	1,069	1,055	0,189	0,044	0,244	0,032	0,186	0,037	0,115	0,015	0,104	0,017	0,009
Prionorhynchia quinqueplicata	CC 2.9	3263,55	0,493	1047,500	143,051	1,742	0,457	9,969	32,149	145,314	0,425	4,605	1,951	4,828	0,106	0,128	0,225	167,856	0,331	0,138	0,484	0,084	2,787	1,275	0,010	0,164	0,033	0,827	0,575	0,584	0,110	0,026	0,145	0,018	0,113	0,021	0,066	0,009	0,057	0,009	0,005
Prionorhynchia quinqueplicata	CC 2.6-2g	2440,00	0,670	2410,213	378,689	1,430	0,873	17,640	131,913	316,998	1,003	9,999	2,176	3,733	0,191	0,276	0,742	199,025	0,548	0,204	0,334	0,011	3,402	0,905	0,036	0,279	0,038	0,904	1,270	0,914	0,187	0,043	0,239	0,032	0,168	0,032	0,089	0,012	0,074	0,012	0,007
Prionorhynchia sp.	CC 2.6-1g	1280,41	1,187	2486,321	588,409	8,367	1,308	27,748	56,876	473,038	0,901	16,626	2,912	10,723	0,534	0,393	1,414	174,186	0,989	0,220	1,509	0,231	4,204	1,860	0,051	0,877	0,062	2,348	2,825	2,496	0,544	0,113	0,636	0,082	0,428	0,081	0,239	0,031	0,182	0,026	0,033
Cirpa briseis	CC 2.5-1g	2325,84	0,435	736,626	187,437	2,465	0,471	12,524	16,299	170,529	0,566	6,441	1,230	3,492	0,301	0,091	0,251	214,208	0,468	0,077	0,725	0,145	2,071	0,729	0,026	0,221	0,025	0,547	0,533	0,537	0,108	0,025	0,124	0,016	0,093	0,017	0,053	0,007	0,041	0,007	0,016
Cirpa sp.	CC 2.4-2g	2230,00	0,621	2451,784	291,754	1,136	0,992	16,398	22,456	230,799	0,771	8,034	1,585	16,229	0,537	0,324	0,567	148,669	0,489	0,262	0,297	0,012	2,514	1,217	0,038	0,281	0,050	1,569	1,512	1,433	0,268	0,062	0,334	0,042	0,231	0,046	0,129	0,018	0,107	0,019	0,028
Cirpa sp.	CC 2.4-1g	920,77	0,360	1089,895	252,991	3,400	0,702	28,546	45,187	317,990	0,711	13,810	2,424	20,096	0,427	0,178	0,894	131,825	1,029	0,331	1,942	0,408	4,811	3,646	0,090	0,633	0,069	1,203	1,379	1,113	0,215	0,049	0,284	0,035	0,182	0,034	0,097	0,013	0,078	0,013	0,055
Cirpa sp.	CC 2.3-2g	2410,00	0,562	1733,885	314,556	1,208	0,683	14,652	23,851	228,440	0,815	7,442	1,448	3,819	0,416	0,378	0,500	263,572	0,466	0,205	0,289	0,014	2,742	0,829	0,023	0,192	0,035	1,157	1,014	1,111	0,224	0,055	0,277	0,037	0,200	0,039	0,110	0,015	0,088	0,015	0,014
Cirpa briseis	CC 2.3-1g	1138,59	1,046	2124,458	626,939	7,880	1,260	42,627	43,209	634,408	1,202	20,070	3,518	18,709	0,857	0,264	1,095	261,711	1,580	0,291	3,124	0,774	6,382	2,702	0,199	1,079	0,148	1,623	1,977	1,577	0,329	0,072	0,419	0,052	0,272	0,054	0,151	0,022	0,124	0,024	0,106
Prionorhynchia quinqueplicata	Z1B-2g		0,607	2565,395	224,262	3,512	6,891	13,748	222,814	1639,107	1,043	5,652	1,222	14,822	0,322	0,227	0,471	207,811	0,334	0,074	0,239	0,032	2,974	1,472	0,036	0,116	3,064	1,242	0,846	0,776	0,136	0,036	0,185	0,024	0,134	0,029	0,090	0,013	0,093	0,018	0,003
Prionorhynchia quinqueplicata	Z1B-1g	1204,45	0,837	2009,469	659,261	9,901	9,708	51,390	43,488	970,315	0,959	16,100	2,529	25,078	0,839	0,544	1,139	261,692	1,080	0,297	1,738	0,288	4,980	1,466	0,052	0,894	4,109	5,410	4,003	4,021	0,755	0,160	0,976	0,122	0,745	0,137	0,437	0,054	0,358	0,055	0,020
Cirpa briseis	CC 2.2-2g	2830,00	0,908	3586,443	464,002	2,425	1,780	20,569	49,325	417,371	1,292	12,778	1,906	26,007	0,688	0,439	0,760	332,723	0,776	0,314	0,629	0,019	9,846	1,212	0,033	0,380	0,095	2,608	2,045	2,281	0,440	0,111	0,529	0,071	0,393	0,080	0,225	0,031	0,195	0,035	0,010
Cirpa briseis	CC 2.2-1g	3584,54	0,301	834,531	41,038	0,545	0,136	10,382	12,825	88,774	0,431	4,878	0,818	4,129	0,107	0,103	0,050	228,592	0,411	0,068	0,953	0,264	1,329	0,307	0,050	0,288	0,033	0,347	0,167	0,295	0,051	0,012	0,064	0,009	0,051	0,010	0,030	0,004	0,024	0,005	0,016
Liospiriferina sp.	CC 1.11-1g	853,00	0,346	2551,152	381,971	5,614	1,287	49,954	64,397	583,388	0,863	30,042	3,159	16,945	0,473	0,539	1,493	328,847	1,712	0,216	2,105	0,329	4,351	1,279	0,016	0,888	1,233	3,669	4,193	4,987	1,085	0,207	1,090	0,136	0,732	0,123	0,330	0,035	0,215	0,033	0,015
Prionorhynchia quinqueplicata	CC 2.1-1g	1851,73	0,412	1559,939	160,748	2,135	0,385	16,224	45,212	233,793	0,567	7,694	1,273	6,201	0,306	0,126	0,367	169,645	0,649	0,097	1,888	0,627	1,846	0,729	0,122	0,852	0,053	0,743	0,786	0,771	0,161	0,033	0,197	0,025	0,147	0,027	0,086	0,011	0,069	0,011	0,009
Prionorhynchia aff. forticostata	CC 1.10-2g	2460,00	0,581	2025,128	293,435	0,894	0,925	9,378	35,902	200,755	0,634	6,929	1,146	4,448	0,348	0,290	0,610	148,428	0,316	0,227	0,201	0,005	3,250	2,013	0,016	0,251	0,062	2,017	1,450	1,804	0,345	0,082	0,401	0,055	0,299	0,059	0,166	0,022	0,134	0,024	0,012
Prionorhynchia aff. gignouxi	CC 1.10-1g	774,19	0,007	1242,296	88,918	1,272	0,369	29,937	34,070	262,466	0,464	19,089	2,174	6,582	0,151	0,098	0,160	125,042	0,981	0,085	1,339	0,133	2,107	0,891	0,011	0,354	0,041	0,746	0,769	0,651	0,123	0,030	0,171	0,021	0,129	0,023	0,081	0,010	0,065	0,010	0,007
Prionorhynchia sp.	CC 2.0-2g	3320,00	0,434	910,023	304,298	1,234	0,760	10,177	119,619	203,825	0,905	5,365	1,384	17,061	0,447	0,243	0,270	190,612	0,323	0,176	0,163	0,014	13,246	1,452	0,030	0,116	0,028	0,670	0,785	0,606	0,123	0,044	0,165	0,022	0,118	0,024	0,072	0,010	0,061	0,011	0,004
Prionorhynchia quinqueplicata	CC 2.0-1g	2355,41	0,173	548,274	37,772	0,492	0,145	7,708	25,354	75,924	0,264	3,946	1,603	1,241	0,074	0,045	0,041	92,366	0,417	0,073	1,759	0,797	0,566	0,510	0,252	1,664	0,040	0,240	0,457	0,262	0,051	0,011	0,076	0,009	0,048	0,009	0,029	0,004	0,026	0,004	0,002
Prionorhynchia gumbeli	CC 1.8-2g	3420,00	0,546	2185,185	205,858	1,008	0,554	10,229	23,395	191,984	0,715	5,222	1,279	3,718	0,215	0,271	0,414	271,498	0,313	0,184	0,219	0,011	2,256	0,963	0,012	0,163	0,084	1,446	1,346	1,294	0,251	0,059	0,312	0,043	0,226	0,046	0,131	0,017	0,104	0,020	0,004
Prionorhynchia gumbeli	CC 1.8-1g	789,97	0,887	1679,184	115,466	2,143	0,586	28,903	61,176	277,794	0,874	16,184	2,051	7,128	0,384	0,200	0,270	260,131	1,169	0,096	1,296	0,121	2,652	1,173	0,009	0,268	0,029	0,941	0,693	0,754	0,143	0,037	0,182	0,024	0,144	0,029	0,088	0,011	0,068	0,012	0,024
Liospiriferina sp.	CC 1.6-2g	2060,00	1,206	3925,997	765,832	3,292	1,989	23,618	43,219	724,987	1,283	12,252	2,703	13,049	0,685	0,600	1,429	289,931	0,649	0,220	0,427	0,029	12,216	2,258	0,025	0,563	0,478	2,909	2,909	2,913	0,593	0,149	0,732	0,099	0,534	0,104	0,289	0,038	0,232	0,041	0,011
Liospiriferina sp.	CC 1.6-1g	1432,11	0,798	3103,800	329,610	4,907	1,345	25,364	56,979	513,376	0,683	12,359	2,277	8,406	0,340	0,166	0,658	157,982	0,871	0,213	0,979	0,157	5,922	3,892	0,009	0,341	0,295	1,674	1,477	1,177	0,239	0,056	0,297	0,039	0,221	0,045	0,138	0,019	0,128	0,019	0,016
Calcirhynchia plicatissima	CC 1.1-2g	2170,00	0,744	1710,425	144,382	1,501	0,479	16,642	35,638	220,839	1,005	8,755	1,600	29,784	0,104	0,277	0,165	362,048	0,550	0,196	0,295	0,010	4,612	1,115	0,014	0,072	0,048	0,513	0,491	0,397	0,082	0,024	0,105	0,014	0,082	0,018	0,053	0,007	0,044	0,008	0,004
Prionorhynchia regia	CC 1.1-1g	866,61	0,579	745,207	38,901	0,944	0,346	37,632	10,586	247,396	0,564	20,865	3,042	69,914	0,088	0,129	0,075	377,770	1,221	0,051	1,602	0,153	2,662	0,988	0,015	0,295	0,019	0,077	0,039	0,070	0,013	0,004	0,017	0,003	0,017	0,004	0,012	0,002	0,010	0,002	0,009
Calcirhynchia plicatissima	CC.1.0-1g	789,97	0,595	750,643	35,751	1,033	0,288	30,357	11,521	214,929	0,444	15,000	2,403	22,741	0,075	0,082	0,091	271,973	0,981	0,050	1,282	0,147	2,604	1,375	0,008	0,238	0,024	0,162	0,181	0,153	0,032	0,008	0,043	0,005	0,034	0,007	0,020	0,003	0,020	0,004	0,007
Calcirhynchia plicatissima	BOL-1-1g	719,95	0,801	1320,683	87,094	2,199	0,646	41,483	20,888	360,102	0,712	20,619	3,064	28,901	0,190	0,178	0,131	415,005	1,581	0,072	1,790	0,193	3,548	1,202	0,000	0,212	0,031	0,535	0,373	0,394	0,080	0,023	0,101	0,014	0,084	0,018	0,061	0,007	0,055	0,009	0,006
Calcirhynchia plicatissima	BOL-2-1g	286,13	0,333	2132,527	1352,364	19,847	3,126	88,892	135,622	1538,479	1,964	42,947	6,642	45,284	0,859	0,625	2,020	98,378	3,071	0,531	3,515	0,277	25,849	15,303	0,031	1,059	0,065	6,877	9,031	6,018	1,247	0,272	1,470	0,174	0,916	0,147	0,425	0,048	0,314	0,043	0,032
Calcirhynchia plicatissima	EFC-0-1g	482,24	1,275	1516,373	145,575	2,466	0,638	62,941	24,329	460,403	0,853	30,451	5,315	30,108	0,167	0,390	0,329	223,175	1,965	0,156	2,500	0,274	4,269	1,804	0,010	0,450	0,046	0,535	0,552	0,493	0,106	0,027	0,142	0,019	0,112	0,021	0,074	0,009	0,063	0,012	0,021
Calcirhynchia plicatissima	EFC-1-1g	515,99	0,194	1180,938	123,855	2,394	0,595	62,859	18,277	452,778	0,828	30,297	5,008	35,334	0,299	0,246	0,178	300,356	2,172	0,156	2,452	0,167	8,012	1,221	0,007	0,365	0,026	0,232	0,373	0,253	0,057	0,021	0,074	0,011	0,066	0,014	0,033	0,004	0,028	0,005	0,013
Calcirhynchia plicatissima	EFC-2-1g	856,47	1,015	1606,679	38,215	1,119	0,264	38,048	12,918	267,023	0,538	18,264	2,667	31,274	0,068	0,144	0,090	216,659	1,368	0,128	1,600	0,093	1,897	0,886	0,001	0,204	0,028	0,342	0,264	0,243	0,038	0,011	0,081	0,010	0,068	0,014	0,053	0,007	0,050	0,008	0,006
Calcirhynchia plicatissima	EFC-3-1g	556,37	0,791	913,236	149,455	3,097	0,397	37,650	15,429	325,954	0,551	18,211	2,434	9,812	0,214	0,033	0,251	151,602	1,348	0,107	1,532	0,117	3,932	1,859	0,005	0,249	0,028	0,469	0,527	0,393	0,079	0,020	0,107	0,014	0,085	0,017	0,053	0,007	0,043	0,005	0,007

Selected trace element contents have been plotted against the stratigraphic composite section and the biochronostratigraphic framework (Figs. 8, 9) to elucidate the variation of contents over time, correlated with key events in the fossil and stratigraphic record. These selected trace elements are related to biological cycling or complexed in particulate organic matter (Mo, Ni, Zn, Cu, Co, Cd, and U) most of them representing redox-sensitive elements, and related to continental influx (Al, Fe, Ti, Cr, Pb, Ba, and REE) (e.g. Tribovillard et al., 2006Tribovillard, N.; Algeo, T.; Lyons, T. & Riboulleau, A. (2006). Trace metals as palaeoredox and palaeoproductivity proxies: an update. Chemical Geology, 232: 12-32. https://doi.org/10.1016/j.chemgeo.2006.02.012 ; Chester & Jickells, 2012Chester, R. & Jickells, T. (2012). Marine Geochemistry. John Wiley and Sons, 411 pp. https://doi.org/10.1002/9781118349083 ; Zaky et al., 2016Zaky, A.H.; Brand, U.; Azmy, K.; Logan, A.; Hooper, R.G. & Svavarsson, J. (2016). Rare earth elements of shallow-water articulated brachiopods: A bathymetric sensor. Palaeogeography, Palaeoclimatology, Palaeoecology, 461: 178-194. https://doi.org/10.1016/j.palaeo.2016.08.021 ).

Figure 8.  Stratigraphic distribution of trace elements from brachiopod shells regularly related to biological cycling or complexed in particulate organic matter, throughout the studied stratigraphic section. All concentration values are given in ppm.

Figure 9.  Stratigraphic distribution of trace elements from brachiopod shells, regularly related to continental influx, throughout the studied stratigraphic section. All concentration values are given in ppm.

A first positive excursion has been detected at the Sinemurian-Pliensbachian transition in the Calcirhynchia shells for Al, Fe, and Mg and trace elements such as Mo, Ni, Cr, Ba, Pb, Ti, and Cd (Figs. 8, 9) and for REE (Fig. 8). The redox sensitive elements (Cr, Co, Ni, Mo, and Cd) show a first increase followed by a decrease in the uppermost part of this interval ((Figs. 8, 9). Mg/Ca ratio increase close to the Sinemurian-Pliensbachian transition (Fig. 10). Subsequently, values are kept low for all the aforementioned elements upwards except for Mg (sample CC.1.6) in the Pliensbachian samples, up to the Pliensbachian-Toarcian transition (uppermost Emaciatum-lower Polymorphum zones), where several small positive peaks are detected in the pre-extinction interval (Mo, Ni, Cr, Zn, Ba, Ti, Fe, and U) in the shells of the genus Cirpa (Figs. 8, 9).

Figure 10.  Stratigraphic distribution of Mg/Ca ratio from brachiopod shells, throughout the studied stratigraphic section.

An important positive excursion for Mg, Fe, Mo, Ni, Cr, Zn, and Pb is recorded in Cirpa shells just in correspondence with the Z2B sampling level (first marly beds of the Polymorphum Zone) which can be related with the onset of the Jenkyns Event interval. The Mg/Ca ratio also increase in the base of the marls of the Toarcian (Fig. 10). The values obtained from Soaresirhynchia recorded in the marls of the base of the Serpentinum Zone evidence a clear enrichment in Ba and Pb and a decrease in Mo, Ni, Cr, and Zn. Then, element concentrations gradually go back to normal low values except for Fe, Co, and REE (Figs. 8, 9).

Principal Component Analysis

The Principal Component Analysis (PCA) establishes the structure of the variable dependence and therefore the correlations between the different trace elements. Three principal components axes (PC) were extracted which accounted for 83.13 % of the total variance. Fig. 11 and Table 3 display the trace elements grouping for the extracted principal components.

PC1 axis accounts for 61.37 % of the total variation and is associated with the Mg, Al, Ti, Fe, Co, Rb, Cd, Ba, Pb, and REEs. PC2 axis accounts for 15.22 % of the total variation and links Cr, Ni, Cu, Zn, and Mo, whereas PC3 axis includes V, Mn, and U with a total variation of 6.54 %.

The axis PC1 reveals a strong interaction between Mg, Al, Ti, Fe, Co, Rb, Cd, Ba, Pb, and REEs, suggesting a common source for these elements (Fig. 11). PC2 and PC3 comprise the redox-sensitive trace elements. V and U are redox-sensitive elements in PC3 that present a common geochemical behaviour, different to that of other redox-sensitive trace metals found in PC2 (Zn, Mo, Ni, Cr, and Cu). In fact, U and V are reduced and can be eliminated from seawater under denitrifying conditions (Tribovillard et al., 2006Tribovillard, N.; Algeo, T.; Lyons, T. & Riboulleau, A. (2006). Trace metals as palaeoredox and palaeoproductivity proxies: an update. Chemical Geology, 232: 12-32. https://doi.org/10.1016/j.chemgeo.2006.02.012 ) whereas Ni, Cr, Cu, Zn, and Mo (represented in the PC2 axis, Fig. 11) are removed mainly under sulphate-reducing conditions (Tribovillard et al., 2006Tribovillard, N.; Algeo, T.; Lyons, T. & Riboulleau, A. (2006). Trace metals as palaeoredox and palaeoproductivity proxies: an update. Chemical Geology, 232: 12-32. https://doi.org/10.1016/j.chemgeo.2006.02.012 ). Fe is an element that is redox-sensitive as well but the PCA indicate a behaviour common with other elements typically derived from terrigenous detrital input such as Al, Ti and Rb (Hamroush & Stanley, 1990Hamroush, H.A. & Stanley, D.J. (1990) Paleoclimatic oscillations in East Africa interpreted by analysis of trace elements in Nile delta sediments. Episodes, 13: 264-269. https://doi.org/10.18814/epiiugs/1990/v13i4/006 ; Calvert, 1990Calvert, S.E. (1990). Geochemistry and the origin of sapropel in the Black Sea. In: Facets of Modern Biogeochemistry (Ittekkot, V; Kempe, S., Michaelis, W. & Spitzy, A., Eds.), Berlin, Springer, 326-352. https://doi.org/10.1007/978-3-642-73978-1_26 ; Calvert & Pedersen, 1993Calvert, S.E. & Pedersen, T.F. (1993). Geochemistry of recent oxic and anoxic marine sediments: implications for the geological record. Marine Geology, 113: 67-88. https://doi.org/10.1016/0025-3227(93)90150-T ; Chester & Jickells, 2012Chester, R. & Jickells, T. (2012). Marine Geochemistry. John Wiley and Sons, 411 pp. https://doi.org/10.1002/9781118349083 ; Reolid et al., 2012Reolid, M.; Rodríguez-Tovar, F.J.; Marok, A. & Sebane, A. (2012). The Toarcian oceanic anoxic event in the Western Saharan Atlas, Algeria (North African paleomargin): role of anoxia and productivity. GSA Bulletin, 124: 1646-1664. https://doi.org/10.1130/B30585.1 ; Rodríguez-Tovar & Reolid, 2013Rodríguez-Tovar, F.J. & Reolid, M. (2013). Environmental conditions during the Toarcian Oceanic Anoxic Event (T-OAE) in the westernmost Tethys: influence of the regional context on a global phenomenon. Bulletin of Geosciences, 88: 697-712. https://doi.org/10.3140/bull.geosci.1397 )

Brachiopod shells and geochemical record

Assessing possible disparities due to different vital effects in the incorporation of the trace elements in the shell of the most representative genera analyzed, i.e. Cirpa, Calcirhynchia, and Prionorhynchia, is important to discard possible interferences in the geochemical signals. Seemingly, these taxa are structurally influenced by similar factors with minor variations: external characters are practically comparable in outline, folding, ribbing multicostate pattern, and beak features, all of them showing minute pedicle foramen pointing to rhizo-pedunculate shells. Regarding the internal architecture, representatives of the Wellerellidae (Cirpa and Calcirhynchia) are typified by well-developed hamiform crural developments whereas Prionorhynchia shows a simpler raduliform crura. On the other hand, these taxa show differences in the microstructural pattern of the secondary layer of the shell. In Cirpa and Calcirhynchia microstructure is characterized by coarse calcite fibres forming the eurinoid pattern whereas Prionorhynchia shows thinner and anvil-like calcite fibres typifying the leptinoid pattern (Fig. 4). According to Simon et al. (2018)Simon, E.; Motchurova-Dekova, N. & Mottequin B. (2018). A reappraisal of the genus Tethyrhynchia Logan, 1994 (Rhynchonellida, Brachiopoda): a conflict between phylogenies obtained from morphological characters and molecular data. Zootaxa, 4471: 535-555. https://doi.org/10.11646/zootaxa.4471.3.6 the eurinoid type seemingly requires more metabolic energy and oxygenated habitats to construct coarser fibres than the leptinoid pattern. Thus, a theoretical approach could relate these differences among taxa to adaptive strategies or to dissimilar metabolism and feeding. However, these genera are recorded together virtually in the same ecospace and with similar body size, as inhabitants of the shallow platforms in the background conditions of the Sinemurian-Pliensbachian transition, and later in their Pliensbachian heyday under hemipelagic conditions (Baeza-Carratalá, 2013Baeza-Carratalá, J.F. (2013). Diversity patterns of Early Jurassic brachiopod assemblages from the westernmost Tethys (Eastern Subbetic). Palaeogeography, Palaeoclimatology, Palaeoecology, 381-382: 76-91. https://doi.org/10.1016/j.palaeo.2013.04.017 ).

Regarding the incorporation of trace elements in these taxa, there is not a great difference in the content of trace elements among the most analysed genera Cirpa, Calcirhynchia, and Prionorhynchia (Figs. 12, 13). The axis PC1 reveals a strong interaction between Mg, Al, Ti, Fe, Co, Rb, Cd, Ba, Pb, and REEs which could be related to continental influx (e.g. Chester et al., 1977Chester, R.; Baxter, G.B.; Behairy, A.K.A.; Connor, K.; Cross, D.; Elderfield, H. & Padgham, R.C. (1977). Soil-sized eolian dust from the lower troposphere of the eastern Mediterranean Sea. Marine Geology, 24: 201- 217. https://doi.org/10.1016/0025-3227(77)90028-7 ; Pye, 1987Pye, K. (1987). Aeolian dust and dust deposits. 334 pp. Academic Press, San Diego.; Tribovillard et al., 2006Tribovillard, N.; Algeo, T.; Lyons, T. & Riboulleau, A. (2006). Trace metals as palaeoredox and palaeoproductivity proxies: an update. Chemical Geology, 232: 12-32. https://doi.org/10.1016/j.chemgeo.2006.02.012 ; Chester & Jickells, 2012Chester, R. & Jickells, T. (2012). Marine Geochemistry. John Wiley and Sons, 411 pp. https://doi.org/10.1002/9781118349083 ; Zaky et al., 2016Zaky, A.H.; Brand, U.; Azmy, K.; Logan, A.; Hooper, R.G. & Svavarsson, J. (2016). Rare earth elements of shallow-water articulated brachiopods: A bathymetric sensor. Palaeogeography, Palaeoclimatology, Palaeoecology, 461: 178-194. https://doi.org/10.1016/j.palaeo.2016.08.021 ) whereas PC2 and PC3 are related to redox sensitive elements (e.g. Calvert & Pedersen, 1997; Tribovillard et al., 2006Tribovillard, N.; Algeo, T.; Lyons, T. & Riboulleau, A. (2006). Trace metals as palaeoredox and palaeoproductivity proxies: an update. Chemical Geology, 232: 12-32. https://doi.org/10.1016/j.chemgeo.2006.02.012 ).

The most common elements in the shells (excluding Ca) are Mg, Al, and Fe (Fig. 7). In marine environments these elements may be related to detrital inputs from emerged lands, mainly in the case of Al and Fe (Fig. 11). Brachiopod shells consist of low-Mg calcite, which explains the abundance of Mg in the shells compared to other elements (Fig. 7). Fe is included in the biological cycling (Bruland et al., 1991Bruland, K.W.; Donat, J.R. & Hutchins, D.A. (1991). Interactive influences of bioactive trace metals on biological production in oceanic waters. Limnology and Oceanography, 36: 1555-1577. https://doi.org/10.4319/lo.1991.36.8.1555 ; Morel & Price, 2003Morel, F.M.M. & Price, N.M. (2003). The biogeochemical cycles of trace metals in the oceans. Science, 300: 944-947. https://doi.org/10.1126/science.1083545 ; Smrzka et al., 2019Smrzka, D.; Zwicker, J.; Bach, W.; Himmler, T.; Chen, D. & Peckmann, J. (2019). The behaviour of trace elements in seawater, sedimentary pore water, and their incorporation into carbonate minerals: a review. Facies, 65: 41. https://doi.org/10.1007/s10347-019-0581-4 ), and is complexed in the particulate organic matter that is consumed by brachiopods. Iron is a micronutrient, and present high reactivity with oxygen as Fe²⁺ and low solubility as Fe³⁺ (and would not be incorporated into shell lattice except during diagenesis). Fe²⁺ facilitates electron transport in chloroplasts, mitochondria and bacteria. The Fe²⁺ can enter in the brachiopod metabolism through feeding and incorporate via coprecipitation because present octahedral coordination as Ca in calcite. The Sr is the following most abundant element in the studied shells, independently of the eurinoid or leptinoid microstructure pattern (Fig. 7). Sr and Mg replace Ca via adsorption of cations within the lattice with an initial surface uptake (Comans & Middelburg, 1987Comans, R.N.J. & Middelburg, J.J. (1987). Sorption of trace metals on calcite: applicability of the surface precipitation model. Geochimica and Cosmochimica Acta, 51: 2587-2591. https://doi.org/10.1016/0016-7037(87)90309-7 ; Stipp & Hochella, 1991Stipp, S.L. & Hochella, M.F.J. (1991). Structure and bionding envinronments at the calcite surface observed with X-ray photoelectron spectroscopy (XPS) and low energy diffraction (LEED). Geochimica and Cosmochimica Acta, 55: 1723-1736. https://doi.org/10.1016/0016-7037(91)90142-R ; Smrzka et al., 2019Smrzka, D.; Zwicker, J.; Bach, W.; Himmler, T.; Chen, D. & Peckmann, J. (2019). The behaviour of trace elements in seawater, sedimentary pore water, and their incorporation into carbonate minerals: a review. Facies, 65: 41. https://doi.org/10.1007/s10347-019-0581-4 ).

In the peri-Iberian platforms system, recent analysis performed in different macroinvertebrate taxa by Ullmann et al. (2020)Ullmann, C.V.; Boyles, R.; Duarte, L.V.; Hesselbo, S.P.; Kasemanns, S.A.; Kleins, T.; Lenton, T.M.; Piazza, V. & Aberhan, M. (2020). Warm afterglow from the Toarcian Oceanic Anoxic Event drives the success of deep-adapted brachiopods. Scientific Reports, 10: 6549. https://doi.org/10.1038/s41598-020-63487-6 provides a very comprehensive geochemical database for the upper Pliensbachian-lower Toarcian brachiopods derived from two stratigraphical sections from the Iberian Range (Spain) and the Lusitanian Basin (Portugal). The brachiopod taxa from the Subbetic, herein analysed, shows lower values in Sr and Mg if compared with their Portuguese or Central Iberian counterparts analysed by Ullmann et al. (2020)Ullmann, C.V.; Boyles, R.; Duarte, L.V.; Hesselbo, S.P.; Kasemanns, S.A.; Kleins, T.; Lenton, T.M.; Piazza, V. & Aberhan, M. (2020). Warm afterglow from the Toarcian Oceanic Anoxic Event drives the success of deep-adapted brachiopods. Scientific Reports, 10: 6549. https://doi.org/10.1038/s41598-020-63487-6 . It would be attributable to the different environmental conditions and ecological setting prevailing in the different Iberian palaeomargins (Rodríguez-Tovar & Uchman, 2011Rodríguez-Tovar, F.J & Uchman, A. (2011). Ichnofabric evidence for the lack of bottom anoxia during the lower Toarcian Oceanic Anoxic Event (T-OAE) in the Fuente de la Vidriera section, Betic Cordillera, Spain. Palaios, 25: 576-587. https://doi.org/10.2110/palo.2009.p09-153r ; Rodríguez-Tovar & Reolid, 2013Rodríguez-Tovar, F.J. & Reolid, M. (2013). Environmental conditions during the Toarcian Oceanic Anoxic Event (T-OAE) in the westernmost Tethys: influence of the regional context on a global phenomenon. Bulletin of Geosciences, 88: 697-712. https://doi.org/10.3140/bull.geosci.1397 ; Reolid et al., 2015Reolid, M.; Rivas, P. & Rodríguez-Tovar, F.J. (2015). Toarcian ammonitico rosso facies from the South Iberian Paleomargin (Betic Cordillera, southern Spain): paleoenvironmental reconstruction. Facies, 61: 22. https://doi.org/10.1007/s10347-015-0447-3 , 2018Reolid, M.; Molina, J.M.; Nieto, L.M. & Rodríguez-Tovar, F.J. (2018). The Toarcian Oceanic Anoxic Event in the Southiberian Palaeomargin, SpringerBriefs in Earth Sciences, 122 pp. https://doi.org/10.1007/978-3-319-67211-3 ). The depositional environment for the mainly Mediterranean Cirpa briseis (Pliensbachian) in the Subbetic consists of epioceanic and well-oxygenated platforms typified by crinoidal grainstone beds with abundant brachiopods, benthic foraminifera, peloids, and intraclasts. In addition, specimens of the Lusitanian Basin constitute a considerably younger occurrence than in the Subbetic area, since C. briseis is recorded in the Pliensbachian (Lavinianum-Emaciatum zones). On the other hand, the dataset of the Portuguese Cirpa fallax (lower Toarcian) collected by Ullmann et al. (2020)Ullmann, C.V.; Boyles, R.; Duarte, L.V.; Hesselbo, S.P.; Kasemanns, S.A.; Kleins, T.; Lenton, T.M.; Piazza, V. & Aberhan, M. (2020). Warm afterglow from the Toarcian Oceanic Anoxic Event drives the success of deep-adapted brachiopods. Scientific Reports, 10: 6549. https://doi.org/10.1038/s41598-020-63487-6 is the inhabitant of a low-energy, distal homoclinal ramp typified by hemipelagic sequences and organic matter rich facies (Duarte, 2007Duarte, L.V. (2007). Lithostratigraphy, sequence stratigraphy and depositional setting of the Pliensbachian and Toarcian series in the Lusitanian Basin (Portugal). In: The Peniche section (Portugal), Contribution to the definition of the Toarcian GSSP (Rocha, R.B., Ed.), International Subcomission on Jurassic Stratigraphy, 17-23.) where alternation of marlstone and argillaceous limestone beds prevailed (Duarte, 2007Duarte, L.V. (2007). Lithostratigraphy, sequence stratigraphy and depositional setting of the Pliensbachian and Toarcian series in the Lusitanian Basin (Portugal). In: The Peniche section (Portugal), Contribution to the definition of the Toarcian GSSP (Rocha, R.B., Ed.), International Subcomission on Jurassic Stratigraphy, 17-23.; Comas-Rengifo et al., 2013Comas-Rengifo, M.J.; Duarte, L.V.; García Joral, F. & Goy, A. (2013). Los braquiópodos del Toarciense Inferior (Jurásico) en el área de Rabaçal-Condeixa (Portugal): distribución estratigráfica y paleobiogeografía. Comunicaçoes Geológicas, 100: 37-42.; Ullmann et al., 2020Ullmann, C.V.; Boyles, R.; Duarte, L.V.; Hesselbo, S.P.; Kasemanns, S.A.; Kleins, T.; Lenton, T.M.; Piazza, V. & Aberhan, M. (2020). Warm afterglow from the Toarcian Oceanic Anoxic Event drives the success of deep-adapted brachiopods. Scientific Reports, 10: 6549. https://doi.org/10.1038/s41598-020-63487-6 ). Moreover, C. fallax is recorded in the Toarcian (Semicelatum Subzone, Polymorphum Zone) coevally with the representative components of the koninckinid fauna from the NW-European palaeobioprovince (Alméras et al., 1988Alméras, Y.; Elmi, S.; Mouterde, R.; Ruget, C. & Rocha, R. (1988). Evolution paléogéographique du Toarcien et influence sur les peuplements. 2nd International Symposium on Jurassic Stratigraphy, 2: 687-698, Lisbon., 1996Alméras, Y.; Mouterde, R.; Benest, M.; Elmi, S. & Bassoullet, J.-P. (1996). Les brachiopodes toarciens de la rampe carbonatée de Tomar (Portugal). Documents des Laboratoires de Géologie de Lyon, 138: 125-191. https://doi.org/10.1016/S0016-6995(97)80078-2 ; Alméras & Elmi, 1993Alméras, Y. & Elmi, S. (1993). Palaeogeography, physiography, palaeoenvironments and brachiopod communities. Example of the Liassic brachiopods in the Western Tethys. Palaeogeography, Palaeoclimatology, Palaeoecology, 100: 95-108. https://doi.org/10.1016/0031-0182(93)90035-H , Comas-Rengifo et al., 2013Comas-Rengifo, M.J.; Duarte, L.V.; García Joral, F. & Goy, A. (2013). Los braquiópodos del Toarciense Inferior (Jurásico) en el área de Rabaçal-Condeixa (Portugal): distribución estratigráfica y paleobiogeografía. Comunicaçoes Geológicas, 100: 37-42.), which is substantially different to the koninckinid fauna from the Mediterranean palaeobioprovince (Baeza-Carratalá et al., 2015Baeza-Carratalá, J.F.; García Joral, F.; Giannetti, A. & Tent-Manclús, J.E. (2015). Evolution of the last koninckinids (Athyridida, Koninckinidae), a precursor signal of the Early Toarcian mass extinction event in the Western Tethys. Palaeogeography, Palaeoclimatology, Palaeoecology, 429: 41-56. https://doi.org/10.1016/j.palaeo.2015.04.004 ). Therefore, differences in the Sr and Mg content between brachiopods from different Iberian palaeomargins may be related to different age, faunas and environmental conditions.

Following with the most abundant trace elements, Cr, Ni, and Zn, included in the PC2 axis (Fig. 11), usually present content < 60 ppm (Fig. 7). The concentration of these elements is slightly higher in Calcirhynchia shells (Fig. 12 and 13). Ni and Zn are micronutrients. Nickel constitutes a micronutrient required by phytoplankton growth in the photic zone (Calvert & Pedersen, 1993Calvert, S.E. & Pedersen, T.F. (1993). Geochemistry of recent oxic and anoxic marine sediments: implications for the geological record. Marine Geology, 113: 67-88. https://doi.org/10.1016/0025-3227(93)90150-T ; Dupont et al., 2010Dupont, C.L.; Buck, K.N.; Palenik, B. & Barbeau, K. (2010). Nickel utilization in phytoplankton assemblages from contrasting ocean regimes. Deep Sea Research I, 57: 533-566. https://doi.org/10.1016/j.dsr.2009.12.014 ) and, under oxic conditions, is dissolved as Ni²⁺ (Fig. 14). Zinc is required for biological cycling by eukaryotes and this element exhibits a nutrient-type profile in modern oceans with surface water depletion (Zhao et al., 2014 Zhao, Y.; Vance, D.; Abouchami, W. & de Baar, H.J.W. (2014). Biogeochemical cycling of zinc and its isotopes in the Southern Ocean. Geochimica and Cosmochimica Acta, 125: 653-672. https://doi.org/10.1016/j.gca.2013.07.045 ). Under oxic conditions Zn²⁺ appears as dissolved phase (Fig. 14).

The next most abundant elements in the brachiopod shells are Ti and Ba (< 10 ppm, Fig. 6), which are included in the PC1 axis related to continental influx (Figs. 11, 14). Among the elements with minority content (commonly < 5 ppm), the Cu, Pb, V, Co, Mo, Cd, U, and REE are remarkable (Fig. 7), most of them considered redox sensitive elements. Molybdenum species in oxic seawater is molybdate (MoO₄ ^2-) that is reduced and subsequently enriched in sediments in close association with dissolved sulfides (e.g. Helz et al., 2011Helz, G.R.; Bura-Nakic, E.; Mikac, N. & Ciglenecki, I. (2011). New model for molybdenum behavior in euxinic waters. Chemical Geology, 284: 323-332. https://doi.org/10.1016/j.chemgeo.2011.03.012 ) (Fig. 14). In oxygen depleted conditions, molybdenum is incorporated into pyrite. In oxic waters, molybdenum concentrations are controlled by co-precipitation and adsorption onto Fe and Mn (oxy)hydroxides (Algeo & Rowe, 2012Algeo, T.J. & Rowe, H. (2012). Paleoceanographic applications of trace metal concentrations data. Chemical Geology, 324-325: 6-18. https://doi.org/10.1016/j.chemgeo.2011.09.002 ). However, the correlation coefficient indicates a similar way of incorporation in the shell for Zn and Mo (R² = 0.64) in the brachiopod shells (Fig. 13), showing Zn a nutrient-type profile in marine environments (Zhao et al., 2014 Zhao, Y.; Vance, D.; Abouchami, W. & de Baar, H.J.W. (2014). Biogeochemical cycling of zinc and its isotopes in the Southern Ocean. Geochimica and Cosmochimica Acta, 125: 653-672. https://doi.org/10.1016/j.gca.2013.07.045 ).

Copper and vanadium are also essential nutrients for marine plankton as well (Smrzka et al., 2019Smrzka, D.; Zwicker, J.; Bach, W.; Himmler, T.; Chen, D. & Peckmann, J. (2019). The behaviour of trace elements in seawater, sedimentary pore water, and their incorporation into carbonate minerals: a review. Facies, 65: 41. https://doi.org/10.1007/s10347-019-0581-4 ) and they are constituents of numerous enzymes (Nalewajko et al., 1995Nalewajko, G.; Lee, K. & Jack, T.R. (1995). Effects of vanadium on freshwater phytoplankton photosynthesis. Water Air Soil Pollution, 81: 93-105. https://doi.org/10.1007/BF00477258 ; Moore et al., 1996Moore, R.W.; Webb, R.; Tokarczyk, R. & Wever, R. (1996). Bromoperoxidase and iodoperoxidase enzymes and production of halogenated methanes in marine diatom cultures. Journal of Geophysical Research, 101: 20899-20908. https://doi.org/10.1029/96JC01248 ) being as a dissolved phase under oxic conditions (CuCO₃, VO₂(OH)₃ ^2- and H₂VO₄ ^-) (Fig. 14). Vanadium (PC3) and molybdenum (PC2) show a high affinity for hydrogen sulfide and are co-enriched in anoxic sediments (e.g. Tribovillard et al., 2006Tribovillard, N.; Algeo, T.; Lyons, T. & Riboulleau, A. (2006). Trace metals as palaeoredox and palaeoproductivity proxies: an update. Chemical Geology, 232: 12-32. https://doi.org/10.1016/j.chemgeo.2006.02.012 ; Reolid et al., 2012Reolid, M.; Rodríguez-Tovar, F.J.; Marok, A. & Sebane, A. (2012). The Toarcian oceanic anoxic event in the Western Saharan Atlas, Algeria (North African paleomargin): role of anoxia and productivity. GSA Bulletin, 124: 1646-1664. https://doi.org/10.1130/B30585.1 ), but V is commonly present in the organic matter and absent in pyrite (Algeo & Maynard, 2004Algeo, T.J. & Maynard, J.B. (2004). Trace-elements behaviour and redox facies in core shales of Upper Pensylvanian Kansas-type cyclothems. Chemical Geology, 206: 289-318. https://doi.org/10.1016/j.chemgeo.2003.12.009 ) (Fig. 14). On the other hand, Co, Cr, and REE in sediments are derived from terrigenous detrital input (Fig. 14), but Cr appears in the PCA with a higher interaction with redox sensitive elements (PC2 axis, Fig. 11).

With respect to the Cd (PC1 axis), Tribovillard et al. (2006)Tribovillard, N.; Algeo, T.; Lyons, T. & Riboulleau, A. (2006). Trace metals as palaeoredox and palaeoproductivity proxies: an update. Chemical Geology, 232: 12-32. https://doi.org/10.1016/j.chemgeo.2006.02.012 stated that Cd, in contrast to Ni, Cu, and Zn (PC2 axis), presents one coordination state (Cd (II)) in the water column and sediments and has a nutrient-like role and, consequently, it implies a relatively short residence time in the water column. Cadmium is present as a dissolved phase (CdCl⁺) in the seawater, showing photic zone depletion and deep-water enrichment. It is primarily transported to sea bottom via CaCO₃ particles and associated to organic carbon particles. The phytoplankton and organic matter present high content of Cd compared with terrigenous material, thus making Cd a useful tracer for primary productivity (Gendron et al., 1996Gendron, A.; Silverberg, N.; Sundby, B. & Lebel, J. (1996). Early diagenesis of cadmium and cobalt in sediments of the Laurentian Trough. Geochimica and Cosmochimica Acta, 50: 741-747. https://doi.org/10.1016/0016-7037(86)90350-9 ; Piper & Dean, 2002Piper, D.Z. & Dean, W.E. (2002). Trace-element deposition in the Cariaco Basin, Venezuela Shelf, under sulfate-reducing conditions: a history of the local hydrography and global climate, 20 ka to the present. USGS Professional Paper No. 1670. https://doi.org/10.3133/pp1670 ).

With respect to the REE, the main sources to the modern oceans are river inputs and atmospheric dust (Greaves et al., 1994Greaves, M.J.; Statham, P.J. & Elderfield, H. (1994). Rare earth element mobilization from marine atmospheric dust into seawater. Marine Chemistry, 46: 255-260. https://doi.org/10.1016/0304-4203(94)90081-7 ; Holser, 1997Holser, W.T. (1997). Evaluation of the application of rare-earth elements to paleoceanography. Palaeogeography, Palaeoclimatology, Palaeoecology, 132: 309-323. https://doi.org/10.1016/S0031-0182(97)00069-2 ). Because the Al content in marine sedimentary environments is controlled by continental influx (Calvert & Pedersen, 1993Calvert, S.E. & Pedersen, T.F. (1993). Geochemistry of recent oxic and anoxic marine sediments: implications for the geological record. Marine Geology, 113: 67-88. https://doi.org/10.1016/0025-3227(93)90150-T ), the presence of Al in the shells has been plotted versus other elements (Fig. 10). Some elements present a high correlation coefficient with respect to Al, which is the case for REE (R²= 0.90) and Ba (R²=0.63), and lower correlation for Fe (R²=0.39). Other elements, such as Cr, Zn, and Ni have a very low correlation index (< 0.20, Fig. 12) which is congruent with the PCA (Fig. 11) where they are grouped along the PC3 axis group (redox sensitive elements). However, this approach takes into account the behaviour of the trace elements in the seawater using data of concentration in the brachiopod shells. But we cannot discard other factors which can influence the co-precipitation and absorption processes of these elements in the calcite structure.

Biotic and environmental changes reflected in the brachiopod diversity pattern

In the Eastern Subbetic domain, the brachiopod fauna shows a progressive diversification from the Sinemurian to the late Pliensbachian-early Toarcian interval, punctuated by several critical episodes that conditioned the diversity dynamics of this group in the basin. The homogeneous platform system, established in the Western Tethys during the earliest Jurassic, subsequently drowned related to the Central Atlantic Ocean opening (Bernoulli & Jenkyns, 1974Bernoulli, D. & Jenkyns, H.C. (1974). Alpine, Mediterranean, and Central Atlantic Mesozoic facies in relation to the early evolution of the Tethys. In: Modern and Ancient Geosynclinal Sedimentation (Dott, H.R. & Shaver, R.H., Eds.), SEPM Special Publications, 19: 129-160. https://doi.org/10.2110/pec.74.19.0129 ; Winterer & Bosellini, 1981Winterer E.L. & Bosselini, A. (1981) Subsidence and sedimentation on Jurassic passive continental margin, Southern Alps, Italy. AAPG Bulletin, 65: 394-421. https://doi.org/10.1306/2F9197E2-16CE-11D7-8645000102C1865D ). After an earlier diversification stage probably ongoing from the early Sinemurian (Baeza-Carratalá et al., 2018bBaeza-Carratalá, J.F.; Dulai, A. & Sandoval, J. (2018b). First evidence of brachiopod diversification after the end-Triassic extinction from the pre-Pliensbachian Internal Subbetic platform (South-Iberian Paleomargin). Geobios 51: 367-384. https://doi.org/10.1016/j.geobios.2018.08.010 ), a speciation burst and radiation event during the Sinemurian-Pliensbachian transition (Raricostatum-Aenigmaticum zones) led to a bloom in brachiopod diversity from the late Sinemurian onwards. This peak of prosperity was probably related to an incipient pre-rifting stage of the westernmost Tethyan platform system. In the Sinemurian, the initial tectonic pulses of disintegration of the South-Iberian Palaeomargin (Vera, 1988Vera, J.A. (1988). Evolución de los sistemas de depósito en el margen ibérico de la Cordillera Bética. Revista de la Sociedad Geológica de España, 1: 373-391., 1998Vera, J.A. (1998). El Jurásico de la Cordillera Bética: Estado actual de conocimientos y problemas pendientes. Cuadernos de Geología Ibérica, 24: 17-42.; Molina et al., 1999Molina, J.M.; Ruiz-Ortiz, P.A. & Vera, J.A. (1999). A review of polyphase karstification in extensional tectonic regimes: Jurassic and Cretaceous examples, Betic Cordillera, southern Spain. Sedimentary Geology, 129: 71-84. https://doi.org/10.1016/S0037-0738(99)00089-5 ) (Fig. 15) played an important role diversifying the ecological niches and facilitating the establishment and renewal of brachiopod communities (Baeza-Carratalá, 2013Baeza-Carratalá, J.F. (2013). Diversity patterns of Early Jurassic brachiopod assemblages from the westernmost Tethys (Eastern Subbetic). Palaeogeography, Palaeoclimatology, Palaeoecology, 381-382: 76-91. https://doi.org/10.1016/j.palaeo.2013.04.017 ). This event of speciation in the Sinemurian-Pliensbachian transition concurred with the clear disconnection of the Mediterranean/Euro-Boreal brachiopod bioprovinces in the Betic Domain, since the sudden increase of the bathymetry makes achievable the diversification not only for brachiopod communities but also for necto-planktic fauna (e.g. Sandoval et al., 2001Sandoval, J.; O’Dogherty, L. & Guex, J. (2001). Evolutionary rates of Jurassic ammonites in relation to Sea-level fluctuations. Palaios, 16: 311-335. https://doi.org/10.1669/0883-1351(2001)016<0311:EROJAI>2.0.CO;2 ). In other Tethyan basins this initial disintegration phase was also detected around the Sinemurian-Pliensbachian boundary, triggering greater diversification of depositional conditions in the late Sinemurian, which resulted in a great increase in diversity of the brachiopod fauna (cf. Hallam, 1981Hallam, A. (1981). A revised sea-level curve for the Early Jurassic. Journal of Geological Society, 139: 735-743. https://doi.org/10.1144/gsjgs.138.6.0735 ; Delance & Laurin, 1983Delance, J.H. & Laurin, B, (1983). Contròle de l’évolution des brachiopodes mésozoïques par les facteurs de l’environnement. Colloques internationaux du CNRS, 330: 91-99.).

The definitive extensional collapse of the platform system is evidenced in the South-Iberian Palaeomargin by faulting and blocks tilting (Rey, 1998Rey, J. (1998) Extensional Jurassic tectonism of an eastern Subbetic section (southern Spain). Geological Magazine 135: 685-697. https://doi.org/10.1017/S0016756898001277 ; Tent-Manclús, 2006Tent-Manclús, J.E. (2006). Estructura y estratigrafía de las sierras de Crevillente, Abanilla y Algayat: su relación con la Falla de Crevillente. PhD Thesis, Universidad de Alicante, 970 pp., http://hdl.handle.net/10045/10414.) (Fig. 13). The transition to more pelagic facies and the progressive establishment of epioceanic environments during the Pliensbachian produced changes in the environmental and depositional conditions. This also entailed alteration of the benthic biota, greatly influenced by substrate. A virtually complete renewal episode from the Sinemurian-Pliensbachian transition onwards meant the extinction of all endemic Sinemurian taxa together with several index-groups in the basin such as multicostate zeilleriids (Baeza-Carratalá, 2011Baeza-Carratalá, J.F. (2011). New Early Jurassic brachiopods from the Western Tethys (Eastern Subbetic, Spain) and their systematic and paleobiogeographic affinities. Geobios, 44: 345-360. https://doi.org/10.1016/j.geobios.2010.09.003 , 2013Baeza-Carratalá, J.F. (2013). Diversity patterns of Early Jurassic brachiopod assemblages from the westernmost Tethys (Eastern Subbetic). Palaeogeography, Palaeoclimatology, Palaeoecology, 381-382: 76-91. https://doi.org/10.1016/j.palaeo.2013.04.017 ; Baeza-Carratalá & García Joral, 2012Baeza-Carratalá, J.F. & García Joral, F. (2012). Multicostate zeillerids (Brachiopoda, Terebratulida) from the Lower Jurassic of the Eastern Subbetic (SE Spain) and their use in correlation and paleobiogeography. Geologica Acta, 10: 1-12.) and the replacement of the prolific Prionorhynchia regia and Calcirhynchia plicatissima stocks by new Pliensbachian multicostate rhynchonellides (Prionorhynchia spp., Cirpa spp.), herein selected for the analysis (Table 1, Fig. 6A). Haq (2018)Haq, B.U. (2018). Jurassic sea-level variations: a reappraisal. GSA Today, 28: 4-10. https://doi.org/10.1130/GSATG359A.1 proposed a maximum flooding episode in the Sinemurian/Pliensbachian transition, just between the JSi5 and JPl1 events. Thus, the replacement of the Pliensbachian assemblages of the Mediterranean bioprovince, better adapted to epioceanic environments, was produced by the continuous deepening of the basin around the Sinemurian/Pliensbachian boundary.

The late Pliensbachian interval coincides with the great speciation phase of the benthic biota in the Western Tethys as a whole (cf. Hallam, 1981Hallam, A. (1981). A revised sea-level curve for the Early Jurassic. Journal of Geological Society, 139: 735-743. https://doi.org/10.1144/gsjgs.138.6.0735 ). The decrease in the faulting activity allowed the irregularities of the sea floor to be smoothed out enabling the spreading of brachiopods. With the settlement of polyspecific and very prolific communities, with profusion of genera such as Prionorhynchia, Cirpa, and Liospiriferina, a maximum in biodiversity and abundance was reached in the Pliensbachian-Toarcian transition (Figs. 6B, C), due to the favourable environments and the arrival of taxa from closer Euro-Boreal basins (e.g. Lobothyris arcta). A similar significant turnover in the Pliensbachian/Toarcian boundary was also noticed in ammonoids (Sandoval et al., 2001Sandoval, J.; O’Dogherty, L. & Guex, J. (2001). Evolutionary rates of Jurassic ammonites in relation to Sea-level fluctuations. Palaios, 16: 311-335. https://doi.org/10.1669/0883-1351(2001)016<0311:EROJAI>2.0.CO;2 , 2012Sandoval, J.; Bill, M.; Aguado, R.; O’Dogherty, L.; Rivas, P.; Morard, A. & Guex, J. (2012). The Toarcian in the Subbetic basin (southern Spain): Bioevents (ammonite and calcareous nannofossils) and carbon-isotope stratigraphy. Palaeogeography, Palaeoclimatology, Palaeoecology, 342-343: 40-63. https://doi.org/10.1016/j.palaeo.2012.04.028 ) linked to a relative drop in the sea level (JPl8 regressive event in Haq (2018)Haq, B.U. (2018). Jurassic sea-level variations: a reappraisal. GSA Today, 28: 4-10. https://doi.org/10.1130/GSATG359A.1 ; Fig. 1), prior to the onset of the Toarcian transgression. This interval is also partly concurring with a global cooling episode during the late Pliensbachian (Suan et al., 2010Suan, G.; Mattioli, E.; Pittet, B.; Lécuyer, C.; Suchéras-Marx, B.; Duarte, L.V.; Philippe, M.; Reggiani, L. & Martineau, F. (2010). Secular environmental precursors to Early Toarcian (Jurassic) extreme climate changes. Earth and Planetary Science Letters, 290: 448-458. https://doi.org/10.1016/j.epsl.2009.12.047 ; Korte & Hesselbo, 2011Korte, C. & Hesselbo, S.P. (2011). Shallow-marine carbon- and oxygen-isotope and elemental records indicate icehouse-greenhouse cycles during the Early Jurassic. Paleoceanography, 26: PA4219. https://doi.org/10.1029/2011PA002160 ; Korte et al., 2015Korte, C.; Hesselbo, S.P.; Ullmann, C.V.; Dietl, G.; Ruhl, M.; Schweigert, G. & Thibault, N. (2015). Jurassic climate mode governed by ocean gateway. Nature Communications, 6: 10015. https://doi.org/10.1038/ncomms10015 ; Gómez et al., 2016Gómez, J.J.; Comas-Rengifo, M.J. & Goy, A. (2016). Palaeoclimatic oscillations in the Pliensbachian (Early Jurassic) of the Asturian Basin (Northern Spain). Climate of the Past, 12: 1199-1214. https://doi.org/10.5194/cp-12-1199-2016 ; Bougeault et al., 2017Bougeault, C.; Pellenard, P.; Deconinck, J.F.; Hesselbo, S.P.; Dommergues, J.L.; Bruneau, L.; Cocquerez, T.; Laffont, R.; Huret, E. & Thibault, N. (2017). Climatic and palaeoceanographic changes during the Pliensbachian (Early Jurassic) inferred from clay mineralogy and stable isotope (C-O) geochemistry (NW Europe). Global and Planetary Change, 149: 139-152. https://doi.org/10.1016/j.gloplacha.2017.01.005 ; De Lena et al., 2019De Lena, L.-F.; Taylor, D.; Guex, J.; Bartolini, A.; Adatte, T.; van Acken, D.; Spangenberg, J.E.; Samankassou, E.; Vernemann, T. & Schaltegger, U. (2019). The driving mechanisms of carbon cycle perturbation in the Pliensbachian (Early Jurassic). Scientific Reports, 9: art. 18430. https://doi.org/10.1038/s41598-019-54593-1 ; Storm et al., 2020Storm, M.S.; Hesselbo, S.P.; Jenkyns, H.C.; Ruhl, M.; Ullmann, C.V.; Xu, W.; Leng, M.; Riding, J. & Gorbanenko, O. (2020). Orbital pacing and secular evolution of the Early Jurassic carbon cycle. PNAS, doi:10.1073/pnas.1912094117. https://doi.org/10.1073/pnas.1912094117 ).

The early Toarcian mass extinction event (Fig. 6) was preceded by several biotic changes, especially noticeable in the brachiopod assemblages. The progressive warming of the seawater and sea-level rise from the latest Pliensbachian onwards (Danise et al., 2013Danise, S.; Twichett, R.J.; Little, C.T.S. & Clémence, M.E. (2013). The impact of global warming and anoxia on marine benthic community dynamics: an example from the Toarcian (Early Jurassic). PLoS ONE, 8: e56255. https://doi.org/10.1371/journal.pone.0056255 ) led to several brachiopod clades to perform global adaptive strategies also noticed in the Subbetic brachiopod occurrences. During the pre-extinction interval, assemblages suffered a replacement by taxa better adapted to warmer conditions, with L. arcta, C. vulgata, and Pseudogibbirhynchia? moorei as foremost representatives (cf. García Joral et al., 2011García Joral, F.; Gómez, J.J. & Goy, A. (2011). Mass extinction and recovery of the Early Toarcian (Early Jurassic) brachiopods linked to climate change in northern and central Spain. Palaeogeography, Palaeoclimatology, Palaeoecology, 302: 367-380. https://doi.org/10.1016/j.palaeo.2011.01.023 , Baeza-Carratalá, 2013Baeza-Carratalá, J.F. (2013). Diversity patterns of Early Jurassic brachiopod assemblages from the westernmost Tethys (Eastern Subbetic). Palaeogeography, Palaeoclimatology, Palaeoecology, 381-382: 76-91. https://doi.org/10.1016/j.palaeo.2013.04.017 ; Baeza-Carratalá et al., 2015Baeza-Carratalá, J.F.; García Joral, F.; Giannetti, A. & Tent-Manclús, J.E. (2015). Evolution of the last koninckinids (Athyridida, Koninckinidae), a precursor signal of the Early Toarcian mass extinction event in the Western Tethys. Palaeogeography, Palaeoclimatology, Palaeoecology, 429: 41-56. https://doi.org/10.1016/j.palaeo.2015.04.004 , 2018aBaeza-Carratalá, J.F.; García Joral, F.; Goy, A. & Tent-Manclús, J.E. (2018a). Arab-Madagascan brachiopod dispersal along the north-Gondwana paleomargin towards the western Tethys Ocean during the early Toarcian (Jurassic). Palaeogeography, Palaeoclimatology, Palaeoecology, 490: 256-268. https://doi.org/10.1016/j.palaeo.2017.11.004 ). On the other hand, koninckinid fauna (with Koninckella and Koninckodonta recorded together with the usually associated Nannirhynchia and Pseudokingena species) occurs in the Subbetic area prior to the sudden increase in temperature reached in the Jenkyns Event. In this biotic crisis, the worldwide global extinction of orders Athyridida and Spiriferinida (Vörös, 2002Vörös, A. (2002). Victims of the Early Toarcian anoxic event: the radiation and extinction of Jurassic Koninckinidae (Brachiopoda). Lethaia, 35: 345-357. https://doi.org/10.1080/002411602320790652 ; Comas-Rengifo et al., 2006Comas-Rengifo, M.J.; García Joral, F. & Goy, A. (2006). Spiriferinida (Brachiopoda) del Jurásico Inferior del NE y N de España: distribución y extinción durante el evento anóxico oceánico del Toarciense Inferior. Boletín Real Sociedad Española Historia Natural (Sec. Geológica), 101: 147-157.; García Joral et al., 2011García Joral, F.; Gómez, J.J. & Goy, A. (2011). Mass extinction and recovery of the Early Toarcian (Early Jurassic) brachiopods linked to climate change in northern and central Spain. Palaeogeography, Palaeoclimatology, Palaeoecology, 302: 367-380. https://doi.org/10.1016/j.palaeo.2011.01.023 ; Baeza-Carratalá et al., 2015Baeza-Carratalá, J.F.; García Joral, F.; Giannetti, A. & Tent-Manclús, J.E. (2015). Evolution of the last koninckinids (Athyridida, Koninckinidae), a precursor signal of the Early Toarcian mass extinction event in the Western Tethys. Palaeogeography, Palaeoclimatology, Palaeoecology, 429: 41-56. https://doi.org/10.1016/j.palaeo.2015.04.004 ; Vörös et al., 2016Vörös, A.; Kocsis, Á.T. & Pálfy, J. (2016). Demise of the last two spire-bearing brachiopod orders (Spiriferinida and Athyridida) at the Toarcian (Early Jurassic) extinction event. Palaeogeography, Palaeoclimatology, Palaeoecology, 457: 233-241. https://doi.org/10.1016/j.palaeo.2016.06.022 , 2019Vörös, A.; Kocsis, Á.T. & Pálfy, J. (2019). Mass extinctions and clade extinctions in the history of brachiopods: brief review and a post-Paleozoic case study. Rivista Italiana di Paleontologia e Stratigrafia, 125(3): 711-724.) is recorded in the Subbetic as well. In this sense, one of the last spiriferinid representatives (Calyptoria vulgata) suddenly appears in the Subbetic just prior to the Jenkyns Event, as a result of its long-term migration from the Arab-Madagascan margins to the epicontinental peri-Iberian ones triggered by increasing temperatures (Baeza-Carratalá et al., 2018aBaeza-Carratalá, J.F.; García Joral, F.; Goy, A. & Tent-Manclús, J.E. (2018a). Arab-Madagascan brachiopod dispersal along the north-Gondwana paleomargin towards the western Tethys Ocean during the early Toarcian (Jurassic). Palaeogeography, Palaeoclimatology, Palaeoecology, 490: 256-268. https://doi.org/10.1016/j.palaeo.2017.11.004 ).

The lowermost Serpentinum hyperthermal event coinciding with the biotic crisis (Reolid et al., 2021Reolid, M.; Mattioli, E.; Duarte, L.V. & Ruebsam, W. (2021). The Toarcian Oceanic Anoxic Event: where do we stand? Geological Society, London, Special Publications, 514, 1-12. doi:10.1144/SP514-2021-74 https://doi.org/10.1144/SP514-2021-74 ) led to the total demise of brachiopod fauna in the basin (Fig. 15). Rodrigues et al. (2019), also from outcrops of the Subbetic, proposed a decreased ¹³C fractionation during photosynthesis in C3 plants and arid environments from the Iberian Palaeomargin. Based on differences in the magnitude of the CIE recorded in land plants and marine substrates in the External Subbetic, Ruebsam et al. (2020)Ruebsam, W.; Reolid, M. & Schwark, L. (2020). δ¹³C of terrestrial vegetation records Toarcian CO₂ and climate gradients. Scientific Reports, 10: art. 117. https://doi.org/10.1038/s41598-019-56710-6 infer that the early Toarcian warming was paralleled by an increase in atmospheric CO₂ levels from ~500 ppmv to ~1000 ppmv. According to Rodrigues et al. (2019)Rodrigues, B.; Silva, R.L.; Reolid, M.; Mendonça Filho, J.G. & Duarte, L.V. (2019). Sedimentary organic matter and δ¹³Ckerogen variation on the southern Iberian palaeomargin (Betic Cordillera, SE Spain) during the latest Pliensbachian-Early Toarcian. Palaeogeography, Palaeoclimatology, Palaeoecology, 534: 109342. https://doi.org/10.1016/j.palaeo.2019.109342 and Ruebsam et al. (2020)Ruebsam, W.; Reolid, M. & Schwark, L. (2020). δ¹³C of terrestrial vegetation records Toarcian CO₂ and climate gradients. Scientific Reports, 10: art. 117. https://doi.org/10.1038/s41598-019-56710-6 the climatic belts in the South-Iberian Palaeomargin displaced to the north, turning more arid in this area.

After the Jenkyns Event, the repopulation began with Soaresirhynchia bouchardi as opportunistic taxa (García Joral & Goy, 2000García Joral, F. & Goy, A. (2000). Stratigraphic distribution of Toarcian brachiopods from the Iberian Range and its relation to depositional sequences. Georesearch Forum, 6: 381-386.; Gahr, 2005Gahr, M. (2005). Response of Lower Toarcian (Lower Jurassic) macrobenthos of the Iberian Peninsula to sea level changes and mass extinction. Journal of Iberian Geology, 31: 197-215.; García Joral et al., 2011García Joral, F.; Gómez, J.J. & Goy, A. (2011). Mass extinction and recovery of the Early Toarcian (Early Jurassic) brachiopods linked to climate change in northern and central Spain. Palaeogeography, Palaeoclimatology, Palaeoecology, 302: 367-380. https://doi.org/10.1016/j.palaeo.2011.01.023 ; Baeza-Carratalá et al., 2017Baeza-Carratalá, J.F.; Reolid, M. & García Joral, F. (2017). New deep-water brachiopod resilient assemblage from the South-Iberian Palaeomargin (Western Tethys) and its significance for the brachiopod adaptive strategies around the Early Toarcian Mass Extinction Event. Bulletin of Geosciences, 92: 233-256. https://doi.org/10.3140/bull.geosci.1631 ) probably related to its alleged low metabolic rate (Ullmann et al., 2020Ullmann, C.V.; Boyles, R.; Duarte, L.V.; Hesselbo, S.P.; Kasemanns, S.A.; Kleins, T.; Lenton, T.M.; Piazza, V. & Aberhan, M. (2020). Warm afterglow from the Toarcian Oceanic Anoxic Event drives the success of deep-adapted brachiopods. Scientific Reports, 10: 6549. https://doi.org/10.1038/s41598-020-63487-6 ). The subsequent post-Jenkyns Event recovery during the Serpentinum-Bifrons zones was due to the stabilization of temperatures, which facilitated the settlement of the so-called “Spanish Bioprovince” of brachiopods (García Joral & Goy, 1984García Joral, F. & Goy, A. (1984). Características de la fauna de braquiópodos del Toarciense Superior en el Sector Central de la Cordillera Ibérica (Noreste de España). Estudios Geológicos, 40: 55-60. https://doi.org/10.3989/egeol.84401-2650 , 2000García Joral, F. & Goy, A. (2000). Stratigraphic distribution of Toarcian brachiopods from the Iberian Range and its relation to depositional sequences. Georesearch Forum, 6: 381-386.; Alméras & Fauré, 1990Alméras, Y. & Fauré, P. (1990). Histoire des brachiopodes liasiques dans la Tethys occidentale: les crises et l’écologie. Cahiers de l’Université Catholique de Lyon Sciences, 4: 1-12.; García Joral et al., 2011García Joral, F.; Gómez, J.J. & Goy, A. (2011). Mass extinction and recovery of the Early Toarcian (Early Jurassic) brachiopods linked to climate change in northern and central Spain. Palaeogeography, Palaeoclimatology, Palaeoecology, 302: 367-380. https://doi.org/10.1016/j.palaeo.2011.01.023 ), with the herein analysed Telothyris gr. pyrenaica, characterizing the background conditions and the well-oxygenated environments.

Coupling of trace elements and biotic signals

The increase in concentration of the analyzed trace elements in brachiopod shells could be mainly related to: oxygenation degree, external inputs and productivity:

These possibilities are analyzed below.

The first option, enrichment in redox sensitive elements related to oxygen depleted conditions is herein discarded. In fact, macrobenthic organisms including brachiopods, disappear in suboxic and anoxic conditions but these conditions did not occur in the studied area. In addition, the prolific brachiopod-bearing Sinemurian to Pliensbachian facies in the Subbetic area consist of oolithic grainstone to packstone and crinoidal grainstone sediments, thus confirming current activity and oxygenation. The growth of brachiopod calcitic shells, like other marine organisms with mineral skeletons, is produced by epithelial secreting cells at the mantle margin that obtain the Ca²⁺ and CO₃ ^2- through metabolism (breathing and feeding). For this reason, increasing values of redox sensitive elements in the sediments detected in other Toarcian outcrops of the Iberian margins (Rodríguez-Tovar & Reolid, 2013Rodríguez-Tovar, F.J. & Reolid, M. (2013). Environmental conditions during the Toarcian Oceanic Anoxic Event (T-OAE) in the westernmost Tethys: influence of the regional context on a global phenomenon. Bulletin of Geosciences, 88: 697-712. https://doi.org/10.3140/bull.geosci.1397 ; Reolid et al., 2014Reolid, M.; Mattioli, E.; Nieto, L.M. & Rodríguez-Tovar, F.J. (2014). The Early Toarcian Oceanic Anoxic Event in the External Subbetic (Southiberian Palaeomargin, Westernmost Tethys): Geochemistry, nannofossils and ichnology. Palaeogeography, Palaeoclimatology, Palaeoecology, 411: 79-94. https://doi.org/10.1016/j.palaeo.2014.06.023 ) and related to precipitation under oxygen depleted conditions do not necessarily reach the metabolism of benthic organisms with the same intensity.

The biological cycling mostly affects to Mo, Cu, Ni, Zn, Cd, Co, Fe, and V (Bruland et al., 1991Bruland, K.W.; Donat, J.R. & Hutchins, D.A. (1991). Interactive influences of bioactive trace metals on biological production in oceanic waters. Limnology and Oceanography, 36: 1555-1577. https://doi.org/10.4319/lo.1991.36.8.1555 ; Morel & Price, 2003Morel, F.M.M. & Price, N.M. (2003). The biogeochemical cycles of trace metals in the oceans. Science, 300: 944-947. https://doi.org/10.1126/science.1083545 ; Smrzka et al., 2019Smrzka, D.; Zwicker, J.; Bach, W.; Himmler, T.; Chen, D. & Peckmann, J. (2019). The behaviour of trace elements in seawater, sedimentary pore water, and their incorporation into carbonate minerals: a review. Facies, 65: 41. https://doi.org/10.1007/s10347-019-0581-4 ), which are complexed in the particulate organic matter that is consumed by brachiopods, such as U typically related to organic matter (McManus et al., 2005McManus, J.; Berelson, W.M.; Klinkhammer, G.P.; Hammond, D.E. & Holm, C. (2005). Authigenic uranium: relationships to oxygen penetration depth and organic carbon rain. Geochimica and Cosmochimica Acta, 69: 95-108. https://doi.org/10.1016/j.gca.2004.06.023 ). Therefore, the active incorporation via co-precipitation during the growth of shells is facilitated for Co, Zn, and Fe that can enter in the metabolism through feeding and are ions with the octahedral coordination, the same as Ca in calcite (Fig. 12). Other elements usually present in calcitic shells such as Mg, Ba, Sr, and U (Delaney & Boyle, 1982Delaney, M.L. & Boyle E.A. (1982). Uranium and thorium isotope concentrations in foraminiferal calcite. Earth and Planetary Science Letters, 62: 258-262. https://doi.org/10.1016/0012-821X(83)90088-2 ; Russell et al., 1994Russell, A.D.; Emerson, S.; Nelson, B.K.; Erez, J. & Lea, D.W. (1994). Uranium in foraminiferal calcite as a recorder of seawater uranium concentrations. Geochimica and Cosmochimica Acta, 58: 671-681 https://doi.org/10.1016/0016-7037(94)90497-9 ; Thébault et al., 2009Thébault, J.; Chauvaud, L.; L’Helguen, S.; Clavier, J.; Barats, A.; Jacquet, S.; Pécheyran, C. & Amoroux, D. (2009). Barium and molydenum records in bivalve shells: Geochemical proxies for phytoplankton dynamics in coastal environments? Limnology and Oceanography, 54: 1002-1014. https://doi.org/10.4319/lo.2009.54.3.1002 ; Benito & Reolid, 2012Benito, M.I. & Reolid, M. (2012). Belemnite taphonomy (Upper Jurassic, Western Tethys) part II: Fossil-diagenetic analysis including combined petrographic and geochemical techniques. Palaeogeography, Palaeoclimatology, Palaeoecology, 358-360: 89-108. https://doi.org/10.1016/j.palaeo.2012.06.035 ; Pérez-Huerta et al., 2013Pérez-Huerta, A.; Etayo-Cadavid, M.F.; Andrus, C.F.T.; Jeffries, T.E.; Watkins, C.; Street, S.C. & Sandweiss, D.H. (2013). El Niño Impact on mollusk biomineralization: Implications for trace element proxy reconstructions and the paleo-archeological record. Plos One, doi:10.1371/journal.pone.0054274. https://doi.org/10.1371/journal.pone.0054274 ; Keul et al., 2013Keul, N.; Langer, G.; de Nooijer, L.J.; Reichart, G.J. & Bijma, J. (2013). Incorporation of uranium in benthic foraminiferal calcite reflects seawater carbonate ion concentration. Geochemistry, Geophysics, Geosystems, 14: 102-111. https://doi.org/10.1029/2012GC004330 ) have higher coordination number and substitute Ca via adsorption of cations within the lattice with an initial rapid surface uptake, followed by slower removal from solution (Comans & Middelburg, 1987Comans, R.N.J. & Middelburg, J.J. (1987). Sorption of trace metals on calcite: applicability of the surface precipitation model. Geochimica and Cosmochimica Acta, 51: 2587-2591. https://doi.org/10.1016/0016-7037(87)90309-7 ; Stipp & Hochella, 1991Stipp, S.L. & Hochella, M.F.J. (1991). Structure and bionding envinronments at the calcite surface observed with X-ray photoelectron spectroscopy (XPS) and low energy diffraction (LEED). Geochimica and Cosmochimica Acta, 55: 1723-1736. https://doi.org/10.1016/0016-7037(91)90142-R ). Live phytoplankton incorporate Ba by metabolic uptake or adsorption (Tribovillard et al., 2006Tribovillard, N.; Algeo, T.; Lyons, T. & Riboulleau, A. (2006). Trace metals as palaeoredox and palaeoproductivity proxies: an update. Chemical Geology, 232: 12-32. https://doi.org/10.1016/j.chemgeo.2006.02.012 ) and many studies have examined the link between primary productivity and biogenic Ba abundance (e.g. McManus et al., 1999McManus, J.; Berelson, W.M.; Hammond, D.E. & Klinkhammer, G.P. (1999). Barium cycling in the North Pacific: implication for the utility of Ba as a paleoproductivity and paleoalkalinity proxy. Paleoceanography, 14: 62-73. https://doi.org/10.1029/1998PA900007 ; Jeandel et al., 2000Jeandel, C.; Tachikawa, K.; Bory, A. & Dehairs, F. (2000). Biogenic barium in suspended and trapped material as a tracer of export production in tropical NE Atlantic (EUMELI sites). Marine Geochemistry, 71: 125-142. https://doi.org/10.1016/S0304-4203(00)00045-1 ; Prakash Babu et al., 2002Prakash Babu, C.; Brumsack, H.J.; Schnetger, B. & Böttcher, M.E. (2002). Barium as a productivity proxy in continental margin sediments: a study from the eastern Arabian Sea. Marine Geology, 184: 189-206. https://doi.org/10.1016/S0025-3227(01)00286-9 ; Reolid et al., 2012Reolid, M.; Rodríguez-Tovar, F.J.; Marok, A. & Sebane, A. (2012). The Toarcian oceanic anoxic event in the Western Saharan Atlas, Algeria (North African paleomargin): role of anoxia and productivity. GSA Bulletin, 124: 1646-1664. https://doi.org/10.1130/B30585.1 ).

Special attention is paid on the Mg concentrations (Fig. 7). This is a particularly important element in skeletal calcite because it varies with temperature, growth rate, and taxa (Buesing & Carison, 1992Buesing, N. & Carison, S.J. (1992). Geochemical investigation of growth in selected Recent articulate brachiopods. Lethaia, 25: 331-345. https://doi.org/10.1111/j.1502-3931.1992.tb01402.x ; see discussions on Pérez-Huerta et al., 2014Pérez-Huerta, A.; Aldridge, A.E.; Endo, K. & Jeffries, T.E. (2014). Brachiopod shell spiral deviations (SSD): Implications for trace element proxies. Chemical Geology, 374-375: 13-24. https://doi.org/10.1016/j.chemgeo.2014.03.002 ; and Clark et al., 2016Clark, J.V.; Pérez-Huerta, A.; Gillikin, D.P.; Aldridge, A.E.; Reolid, M. & Endo, K. (2016). Determination of paleoseasonality of fossil brachiopods using shell spiral deviations and chemical proxies. Palaeoworld, 25: 662-674. https://doi.org/10.1016/j.palwor.2016.05.010 ), as seen in the extant articulate brachiopods Terebratulina unguicula and Terebratalia transversa, where Mg increases as a response to higher growth rate and productivity. Experimental works have confirmed an increasing incorporation rate of other trace elements such as U into calcite with increasing growth rate of calcite crystals (Weremeichik et al., 2017Weremeichnik, J.M.; Gabitov, R.I.; Thien, B.M. & Sadekov. A. (2017) The effect of growth rate on uranium partitioning between individual calcite crystals and fluid. Chemical Geology, 450: 145-153. https://doi.org/10.1016/j.chemgeo.2016.12.026 ). Moreover, the U abundance in sediments usually shows a good correlation with the organic matter rain rate in the water column (McManus et al., 2005McManus, J.; Berelson, W.M.; Klinkhammer, G.P.; Hammond, D.E. & Holm, C. (2005). Authigenic uranium: relationships to oxygen penetration depth and organic carbon rain. Geochimica and Cosmochimica Acta, 69: 95-108. https://doi.org/10.1016/j.gca.2004.06.023 ). However, U content in the analyzed shells is very low (Figs. 7, 9). Cadmium presents a high affinity for adsorption onto calcite (Boyle, 1981Boyle, E.A. (1981). Cadmium, zinc, copper, and barium in foraminifera tests. Earth Planetary Sciences Lettters, 53: 11-35. https://doi.org/10.1016/0012-821X(81)90022-4 ; Papadopoulos & Rowell, 1989Papadopoulo, P. & Rowell, D.L. (1989). The reactions of copper and zinc with calcium carbonate surfaces. Journal of Soil Science, 39: 23-36. https://doi.org/10.1111/j.1365-2389.1988.tb01191.x ; Tesoriero & Pankow, 1996Tesoriero, A.J. & Pankow, J.F. (1996). Solid solution partitioning of Sr²⁺, Ba²⁺, and Cd²⁺ to calcite. Geochimica and Cosmochimica Acta, 60: 1053-1063. https://doi.org/10.1016/0016-7037(95)00449-1 ). Cd²⁺ and Ca²⁺ have similar chemical behavior and Cd²⁺ can replace Ca²⁺, forming surface complexes of CdCO₃ (otavite) that co-precipitate with calcite (Papadopoulos & Rowell, 1989Papadopoulo, P. & Rowell, D.L. (1989). The reactions of copper and zinc with calcium carbonate surfaces. Journal of Soil Science, 39: 23-36. https://doi.org/10.1111/j.1365-2389.1988.tb01191.x ). The affinity series for divalent metals with respect to calcite incorporation is Cd>Zn>Co>Ni>Ba (Reeder, 1996Reeder, R.J. (1996). Interactions of divalent cobalt, zinc, cadmium, and barium with the calcite surface during layer growth. Geochimica and Cosmochimica Acta, 60: 1543-1552. https://doi.org/10.1016/0016-7037(96)00034-8 ; Smrzka et al., 2019Smrzka, D.; Zwicker, J.; Bach, W.; Himmler, T.; Chen, D. & Peckmann, J. (2019). The behaviour of trace elements in seawater, sedimentary pore water, and their incorporation into carbonate minerals: a review. Facies, 65: 41. https://doi.org/10.1007/s10347-019-0581-4 ), but this does not correspond to the abundance of these elements in the analyzed shells (Fig. 6) since the concentrations of these elements in seawater are variable.

Therefore, the increasing values of trace elements in brachiopod calcitic shells are related to their increased content in seawater as dissolved phase and/or high primary productivity, the last one also favoured by high content of the dissolved phase of some trace elements (Figs. 14, 15). The high phytoplankton productivity implicates increasing food resources for brachiopods that feed on phytoplankton such as diatoms and dinoflagellates (Fürsich & Hurst, 1974Fürsich, F.T. & Hurst, J.M. (1974). Environmental factors determining the distribution of brachiopods. Paleontology, 17: 879-900.; Suchanek & Levinton, 1974Suchanek, T.H. & Levinton, J. (1974). Articulate brachiopod food. Journal of Paleontology, 48: 1-5.; Stanton & Nelson, 1980Stanton Jr., R.J. & Nelson, P.C. (1980). Reconstruction of the trophic web in paleontology: Community structure in the Stone City Formation (Middle Eocene, Texas). Journal of Paleontology, 54: 118-135.; McCammon, 1981McCammon, H.M. (1981). Physiology of the brachiopod digestive system. In: Lophophorates, Notes for a Short Course (Broadhead, T.W., Ed.), University of Tennessee, Dep. Geological Sciences. Studies in Geology, 5: 17G204. https://doi.org/10.1017/S0271164800000385 ; James et al., 1992James, M.A.; Ansell, A.D.; Collins, M.J.; Curry, G.B.; Peck, L.S. & Rhodes, M.C. (1992). Biology of living brachiopods. Advances in Marine Biology, 28: 175-387. https://doi.org/10.1016/S0065-2881(08)60040-1 ) and favored abundance of other trophic resources composing the seston as particulate organic matter, organic colloids and bacteria (Levinton & Suchanek, 1972Levinton, J. & Suchanek, T.H. (1972). The food of articulated brachiopod reconsidered. GSA Abstracts, 4: 575.; Suchanek & Levinton, 1974Suchanek, T.H. & Levinton, J. (1974). Articulate brachiopod food. Journal of Paleontology, 48: 1-5.; Steele-Petrovic, 1979Steele-Petrovic, H.M. (1979). The physiological differences between articulate brachiopods and filter feeding bivalves as a factor in the evolution of marine level bottom communities. Palaeontology, 22: 101-134.; James et al., 1992James, M.A.; Ansell, A.D.; Collins, M.J.; Curry, G.B.; Peck, L.S. & Rhodes, M.C. (1992). Biology of living brachiopods. Advances in Marine Biology, 28: 175-387. https://doi.org/10.1016/S0065-2881(08)60040-1 ) and dissolved organic matter (dissolved carbohydrates and aminoacids; James et al., 1992James, M.A.; Ansell, A.D.; Collins, M.J.; Curry, G.B.; Peck, L.S. & Rhodes, M.C. (1992). Biology of living brachiopods. Advances in Marine Biology, 28: 175-387. https://doi.org/10.1016/S0065-2881(08)60040-1 ) (Fig. 14). As well-known, brachiopods may be active/passive suspension feeders. There are experimental evidences on uptake of dissolved nutrients for brachiopods (McCammon & Reynolds, 1976McCammon, H.M. & Reynolds, W.A. (1976). Experimental evidence for direct nutrient assimilation by the lophophore of articulate brachiopods. Marine Biology, 34: 41-51. https://doi.org/10.1007/BF00390786 ; Doherty, 1981Doherty, P.J. (1981). The contribution of dissolved amino acids to the nutrition of articulate brachiopods. New Zealand Journal of Zoology, 8: 181-188. https://doi.org/10.1080/03014223.1981.10427960 ; Rosenberg et al., 1988Rosenberg, G.D.; Hughes, W.W. & Tkachuck, R.D. (1988). Intermediatory metabolism and shell growth in the brachiopod Terebratalia transversa. Lethaia, 21: 219-230. https://doi.org/10.1111/j.1502-3931.1988.tb02074.x ; Tkachuck et al., 1989Tkachuck, R.D.; Rosenberg, G.D.; Hughes, W.W. (1989). Utilization of free amino acids by mantle tissue in the brachiopod Terebratalia transversa and the bivalve mollusc Chlamys hastata. Comparative Biochemistry and Physiology, 92B: 747-750. https://doi.org/10.1016/0305-0491(89)90261-7 ). The lophophore and mantle can directly assimilate dissolved nutrients (McCammon & Reynolds, 1976McCammon, H.M. & Reynolds, W.A. (1976). Experimental evidence for direct nutrient assimilation by the lophophore of articulate brachiopods. Marine Biology, 34: 41-51. https://doi.org/10.1007/BF00390786 ; Doherty, 1981Doherty, P.J. (1981). The contribution of dissolved amino acids to the nutrition of articulate brachiopods. New Zealand Journal of Zoology, 8: 181-188. https://doi.org/10.1080/03014223.1981.10427960 ; see discussion in McCammon, 1981McCammon, H.M. (1981). Physiology of the brachiopod digestive system. In: Lophophorates, Notes for a Short Course (Broadhead, T.W., Ed.), University of Tennessee, Dep. Geological Sciences. Studies in Geology, 5: 17G204. https://doi.org/10.1017/S0271164800000385 ; Rosenberg et al., 1988Rosenberg, G.D.; Hughes, W.W. & Tkachuck, R.D. (1988). Intermediatory metabolism and shell growth in the brachiopod Terebratalia transversa. Lethaia, 21: 219-230. https://doi.org/10.1111/j.1502-3931.1988.tb02074.x ; Tkachuck et al., 1989Tkachuck, R.D.; Rosenberg, G.D.; Hughes, W.W. (1989). Utilization of free amino acids by mantle tissue in the brachiopod Terebratalia transversa and the bivalve mollusc Chlamys hastata. Comparative Biochemistry and Physiology, 92B: 747-750. https://doi.org/10.1016/0305-0491(89)90261-7 ) and surely related trace elements that work as micronutrients.

Sinemurian-Pliensbachian transition

From bottom to top, the first excursion in the geochemical signal recorded in the composite stratigraphical section occurred between the samples EFC2 and BOL1 in correspondence with the Sinemurian-Pliensbachian transition (Raricostatum-Aenigmaticum zones), where distribution of most of the trace elements (Mo, Ni, Cr, Ba, Pb, Ti, Al, Fe, Cd, and REE) marks a positive excursion in the Calcirhynchia shells (Figs. 8, 9). This excursion is mainly based in one data point corresponding to a well-preserved specimen of Calcirhynchia, but it is necessary to be cautious.

The diversity dynamics (burst in brachiopod species) and recent taphonomic assessment of these deposits (Baeza-Carratalá et al., 2014Baeza-Carratalá, J.F.; Giannetti, A.; Tent-Manclús, J.E. & García Joral, F. (2014). Evaluating taphonomic bias in a storm-disturbed carbonate platform. Effects of compositional and environmental factors in Lower Jurassic brachiopod accumulations (Eastern Subbetic basin, Spain). Palaios, 29: 55-73. https://doi.org/10.2110/palo.2013.041 ) provide a refined palaeoenvironmental setting, locating these shell beds in a shallow-water well-oxygenated bottom frequently affected by storms. In this context, the concentration values suddenly increase for most of the trace elements in this crucial timespan, decreasing upwards in most of the Pliensbachian samples to lower contents. The variations in content of trace elements in the shells are related to palaeotectonic events and climatic changes with incidence on the input of these elements to the sea from continental runoff and volcanic sources resulting on increased concentration in the seawater and primary productivity (Figs. 14, 15).

The geochemical perturbations in this timespan are concurrent with the initial tectonic pulses of rifting and drowning of the platform system developed in the South-Iberian Palaeomargin (Vera, 1988Vera, J.A. (1988). Evolución de los sistemas de depósito en el margen ibérico de la Cordillera Bética. Revista de la Sociedad Geológica de España, 1: 373-391., 1998Vera, J.A. (1998). El Jurásico de la Cordillera Bética: Estado actual de conocimientos y problemas pendientes. Cuadernos de Geología Ibérica, 24: 17-42.; Molina et al., 1999Molina, J.M.; Ruiz-Ortiz, P.A. & Vera, J.A. (1999). A review of polyphase karstification in extensional tectonic regimes: Jurassic and Cretaceous examples, Betic Cordillera, southern Spain. Sedimentary Geology, 129: 71-84. https://doi.org/10.1016/S0037-0738(99)00089-5 ; Ruiz-Ortiz et al., 2004Ruiz-Ortiz, P.A.; Bosence, D.W.J.; Rey, J.; Nieto, L.M.; Castro, J.M. & Molina, J.M. (2004). Tectonic control of facies architecture, sequence stratigraphy and drowning of a Liassic carbonate platform (Betic Cordillera, Southern Spain). Basin Research, 16: 235-257. https://doi.org/10.1111/j.1365-2117.2004.00231.x ) (Fig. 15), which diversified the ecological niches leading to a renewal of brachiopod communities (Baeza-Carratalá, 2013Baeza-Carratalá, J.F. (2013). Diversity patterns of Early Jurassic brachiopod assemblages from the westernmost Tethys (Eastern Subbetic). Palaeogeography, Palaeoclimatology, Palaeoecology, 381-382: 76-91. https://doi.org/10.1016/j.palaeo.2013.04.017 ). The abundance of the analysed trace elements in the calcite shells can be controlled by the transition to hemipelagic conditions and the change of current pattern favouring upwelling and increased productivity. The Cd content in brachiopod shells achieves the maximum values in a punctual excursion just concurring with the Sinemurian-Pliensbachian transition. Cadmium is a micronutrient and could favour an increase in productivity that may be in good accordance with the increasing in brachiopod diversity occurred in the Sinemurian-Pliensbachian transition (Figs. 6, 9).

The increased tectonic activity related to fragmentation of the South-Iberian Palaeomargin (García Hernández et al., 1989García-Hernández, M.; López-Garrido, A.C.; Martín-Algarra, A.; Molina, J.M.; Ruiz-Ortiz, P.A. & Vera, J.A. (1989). Las discontinuidades mayores del Jurásico de las Zonas Externas de las Cordilleras Béticas: Análisis e interpretación de los ciclos sedimentarios. Cuadernos de Geología Ibérica, 13: 35-52.; Vera, 2001Vera, J.A. (2001). Evolution of the Iberian Continental Margin. Mémoires du Musée National d’Histoire Naturelle Paris, 186: 109-143.) and the opening of Hispanic Corridor (Aberhan, 2002Aberhan, M. (2002). Opening of the Hispanic Corridor and Early Jurassic bivalve biodiversity. Geological Society London Special Publications, 194: 127-139. https://doi.org/10.1144/GSL.SP.2002.194.01.10 ; Korte et al., 2015Korte, C.; Hesselbo, S.P.; Ullmann, C.V.; Dietl, G.; Ruhl, M.; Schweigert, G. & Thibault, N. (2015). Jurassic climate mode governed by ocean gateway. Nature Communications, 6: 10015. https://doi.org/10.1038/ncomms10015 ; Schöllhorn et al., 2020Schöllhorn, I.; Adatte, T.; Van de Schootbrugge, B.; Houben, A.; Charbonnier, G.; Janssen, N. & Follmi, K.B. (2020). Climate and environmental response to the break-up of Pangea during the Early Jurassic (Hettangian-Pliensbachian), the Dorset coast (UK) revisited. Global and Planetary Change, 185: 103096. https://doi.org/10.1016/j.gloplacha.2019.103096 ; Storm et al., 2020Storm, M.S.; Hesselbo, S.P.; Jenkyns, H.C.; Ruhl, M.; Ullmann, C.V.; Xu, W.; Leng, M.; Riding, J. & Gorbanenko, O. (2020). Orbital pacing and secular evolution of the Early Jurassic carbon cycle. PNAS, doi:10.1073/pnas.1912094117. https://doi.org/10.1073/pnas.1912094117 ) would have favoured the sediment runoff due to uplift of emerged reliefs (Figs. 14, 15). We cannot discard alternative sources for the trace elements analysed related to hydrothermal sources, submarine volcanic outgases or eruptions (e.g. Tribovillard et al., 2006Tribovillard, N.; Algeo, T.; Lyons, T. & Riboulleau, A. (2006). Trace metals as palaeoredox and palaeoproductivity proxies: an update. Chemical Geology, 232: 12-32. https://doi.org/10.1016/j.chemgeo.2006.02.012 ) for example in the case of Cd, Zn, Cu, and Pb (Chester & Jickells, 2012Chester, R. & Jickells, T. (2012). Marine Geochemistry. John Wiley and Sons, 411 pp. https://doi.org/10.1002/9781118349083 ). Sinemurian alkaline submarine volcanism in the Subbetic area has been reported (Comas et al., 1986Comas, M.C.; Puga, E.; Bargossi, G.M.; Morten, L. & Rossi, P.L. (1986). Paleogeography, sedimentation and volcanism of the Central Subbetic Zone, Betic Cordilleras, Southeastern Spain. Neues Jahrbuch für Geologie und Paläontologie-Abhandlungen, 7: 385-404. https://doi.org/10.1127/njgpm/1986/1986/385 ; García-Hernández et al., 1989García-Hernández, M.; López-Garrido, A.C.; Martín-Algarra, A.; Molina, J.M.; Ruiz-Ortiz, P.A. & Vera, J.A. (1989). Las discontinuidades mayores del Jurásico de las Zonas Externas de las Cordilleras Béticas: Análisis e interpretación de los ciclos sedimentarios. Cuadernos de Geología Ibérica, 13: 35-52.; Portugal et al., 1995Portugal, M.; Morata, D.A.; Puga, E.; Demant, A. & Aguirre, L. (1995). Evolución geoquímica y temporal del magmatismo básico mesozoico en las Zonas Externas de las Cordilleras Béticas. Estudios Geológicos, 51: 109-118.; Olóriz et al., 2002Olóriz, F.; Linares, A.; Goy, A.; Sandoval, J.; Caracuel, J.E.; Rodríguez-Tovar, F.J. & Tavera, J.M. (2002). Jurassic. The Betic Cordillera and Balearic Islands. In: The Geology of Spain (Gibbons, W. & Moreno, M.T., Eds), Geological Society, London, 235-253.), which would be connected to the extensional palaeotectonic event of the first phase of the Atlantic Ocean opening that favoured the fragmentation of the western Tethys palaeomargins (Ruiz-Ortiz et al., 2004Ruiz-Ortiz, P.A.; Bosence, D.W.J.; Rey, J.; Nieto, L.M.; Castro, J.M. & Molina, J.M. (2004). Tectonic control of facies architecture, sequence stratigraphy and drowning of a Liassic carbonate platform (Betic Cordillera, Southern Spain). Basin Research, 16: 235-257. https://doi.org/10.1111/j.1365-2117.2004.00231.x ; Reolid et al., 2018Reolid, M.; Molina, J.M.; Nieto, L.M. & Rodríguez-Tovar, F.J. (2018). The Toarcian Oceanic Anoxic Event in the Southiberian Palaeomargin, SpringerBriefs in Earth Sciences, 122 pp. https://doi.org/10.1007/978-3-319-67211-3 ) and the reactivation of the Central Atlantic Magmatic Province (Ruhl et al., 2016Ruhl, M,; Hesselbo, S.P.; Hinnov, L.; Jenkyns, H.C.; Xu, W.; Riding, J.; Srom, M.; Minisini, D.; Ullmann, C.V. & Leng, M.J. (2016). Earth and Planetary Science Letters, 455: 149-165. https://doi.org/10.1016/j.epsl.2016.08.038 ; Storm et al., 2020Storm, M.S.; Hesselbo, S.P.; Jenkyns, H.C.; Ruhl, M.; Ullmann, C.V.; Xu, W.; Leng, M.; Riding, J. & Gorbanenko, O. (2020). Orbital pacing and secular evolution of the Early Jurassic carbon cycle. PNAS, doi:10.1073/pnas.1912094117. https://doi.org/10.1073/pnas.1912094117 ) (Fig. 15). Recent studies place the first clear evidences of volcanic activity and even the emplacement of the oceanic crust just in the late Sinemurian-earliest Pliensbachian, coinciding with the initial drifting stage (Sahabi et al., 2004Sahabi, M.; Aslanian, D. & Oliver, J.L. (2004). Un nouveau point de départ pour l’histoire de l’Atlantique central. Comptes Rendus Geoscience, 336: 1041-1052. https://doi.org/10.1016/j.crte.2004.03.017 ; Klingelhoefer et al., 2009Klingelhoefer, F.; Labails, C.; Cosquer, E.; Rouzo, S.; Geli, L.; Aslanian, D.; Olivet, J.L.; Sahabi, M.; Nouze, H. & Unternehr, P. (2009). Crustal structure of the SW-Moroccan margin from wide-angle and reflection seismic data (the DAKHLA experiment) Part A: Wide-angle seismic models. Tectonophysics, 468: 63-82. https://doi.org/10.1016/j.tecto.2008.07.022 ). Reolid et al. (2013)Reolid, M.; Nieto, L.M. & Sánchez-Almazo, I.M. (2013). Caracterización geoquímica de facies pobremente oxigenadas en el Toarciense inferior (Jurásico inferior) del Subbético Externo. Revista de la Sociedad Geológica de España, 26: 69-84. also linked volcanic activity with a higher tectonic activity episode in the Median Subbetic (Comas et al., 1986Comas, M.C.; Puga, E.; Bargossi, G.M.; Morten, L. & Rossi, P.L. (1986). Paleogeography, sedimentation and volcanism of the Central Subbetic Zone, Betic Cordilleras, Southeastern Spain. Neues Jahrbuch für Geologie und Paläontologie-Abhandlungen, 7: 385-404. https://doi.org/10.1127/njgpm/1986/1986/385 ; Reolid & Abad, 2014Reolid, M. & Abad, I. (2014). Glauconitic laminated crusts as a consequence of hydrothermal alteration of Jurassic pillow-lavas from Mediam Subbetic (Betic Cordillera, S Spain): a microbial influence case. Journal of Iberian Geology, 40: 389-408. https://doi.org/10.5209/rev_JIGE.2014.v40.n3.43080 ). Increased values of Zn, Cd, Cu, and Pb in the seawater for this interval could be related with these mechanisms due to their hydrothermal/volcanic origin in seawater (Chester & Jickells, 2012Chester, R. & Jickells, T. (2012). Marine Geochemistry. John Wiley and Sons, 411 pp. https://doi.org/10.1002/9781118349083 ).

In addition to the palaeotectonic event, the palaeoclimatic changes had an important relevance around the Sinemurian-Pliensbachian boundary. A global warming episode, mainly developed in the late Sinemurian, has been recorded in the westernmost Tethyan basins, followed by a decrease in palaeotemperature in the early Pliensbachian (e.g. Hesselbo et al., 2000Hesselbo, S.P.; Gröcke, D.R.; Jenkyns, H.C.; Bjerrum, C.J.; Farrimond, P.; Morgans-Bell, H.S. & Green, O.R. (2000). Massive dissociation of gas hydrate during a Jurassic oceanic anoxic event. Nature, 406: 392-395. https://doi.org/10.1038/35019044 ; Korte & Hesselbo, 2011Korte, C. & Hesselbo, S.P. (2011). Shallow-marine carbon- and oxygen-isotope and elemental records indicate icehouse-greenhouse cycles during the Early Jurassic. Paleoceanography, 26: PA4219. https://doi.org/10.1029/2011PA002160 ; Gómez et al., 2016Gómez, J.J.; Comas-Rengifo, M.J. & Goy, A. (2016). Palaeoclimatic oscillations in the Pliensbachian (Early Jurassic) of the Asturian Basin (Northern Spain). Climate of the Past, 12: 1199-1214. https://doi.org/10.5194/cp-12-1199-2016 ). The increased values of Mg/Ca ratio is congruent with that global warming event that partly coincides with a perturbation in the oxygen and carbon cycles (excursions of the δ¹³C and δ¹⁸O) and remarkably with the trace elements herein analysed. The increased temperature and humidity reported for the Sinemurian-Pliensbachian transition (Korte & Hesselbo, 2011Korte, C. & Hesselbo, S.P. (2011). Shallow-marine carbon- and oxygen-isotope and elemental records indicate icehouse-greenhouse cycles during the Early Jurassic. Paleoceanography, 26: PA4219. https://doi.org/10.1029/2011PA002160 ; Schöllhorn et al., 2020Schöllhorn, I.; Adatte, T.; Van de Schootbrugge, B.; Houben, A.; Charbonnier, G.; Janssen, N. & Follmi, K.B. (2020). Climate and environmental response to the break-up of Pangea during the Early Jurassic (Hettangian-Pliensbachian), the Dorset coast (UK) revisited. Global and Planetary Change, 185: 103096. https://doi.org/10.1016/j.gloplacha.2019.103096 ) could facilitate the increase of continental weathering (Deconinck et al., 2003Deconinck, J.-F.; Hesselbo, S.P.; Debuisser, N.; Averbuch, O.; Baudin, F. & Bessa, J. (2003). Environmental controls on clay mineralogy of an Early Jurassic mudrock (Blue Lias Formation, southern England). International Journal of Earth Sciences, 92: 255-266. https://doi.org/10.1007/s00531-003-0318-y ) and the subsequent input of trace elements to the sea, where the concentration of the dissolved phases and of those incorporated to the biological cycling increased.

This timespan is typified by enrichment in most of the trace elements, especially in those related to be proxies of continental influx (PC1, Fig. 9) as Ba, Ti, Al, Fe, Pb, and REEs (Fig. 8). Therefore, the global warming event in the latest Sinemurian could have been the responsible for an increase in trace elements content in brachiopod shells by adsorption on the shell surface or co-precipitation via incorporation of these elements to the metabolism after feeding of phytoplankton, bacteria, organic detritus, colloidal material, and dissolved nutrients (i.e. trophic resources according to Rosenberg et al., 1988Rosenberg, G.D.; Hughes, W.W. & Tkachuck, R.D. (1988). Intermediatory metabolism and shell growth in the brachiopod Terebratalia transversa. Lethaia, 21: 219-230. https://doi.org/10.1111/j.1502-3931.1988.tb02074.x ; Tkachuck et al., 1989Tkachuck, R.D.; Rosenberg, G.D.; Hughes, W.W. (1989). Utilization of free amino acids by mantle tissue in the brachiopod Terebratalia transversa and the bivalve mollusc Chlamys hastata. Comparative Biochemistry and Physiology, 92B: 747-750. https://doi.org/10.1016/0305-0491(89)90261-7 ; James et al., 1992James, M.A.; Ansell, A.D.; Collins, M.J.; Curry, G.B.; Peck, L.S. & Rhodes, M.C. (1992). Biology of living brachiopods. Advances in Marine Biology, 28: 175-387. https://doi.org/10.1016/S0065-2881(08)60040-1 ). Thus, weathering of the continental crust is the ultimate source of REE in the water reservoirs, whereas riverine discharge and aeolian deposition are the primary fluxes (Zaky et al., 2016Zaky, A.H.; Brand, U.; Azmy, K.; Logan, A.; Hooper, R.G. & Svavarsson, J. (2016). Rare earth elements of shallow-water articulated brachiopods: A bathymetric sensor. Palaeogeography, Palaeoclimatology, Palaeoecology, 461: 178-194. https://doi.org/10.1016/j.palaeo.2016.08.021 , and references therein).

The brachiopod diversity peak and turnover episode, with the demise of endemic Sinemurian fauna (e.g. Cincta peiroi, Praesphaeroidothyris cisnerosi; Baeza-Carratalá, 2013Baeza-Carratalá, J.F. (2013). Diversity patterns of Early Jurassic brachiopod assemblages from the westernmost Tethys (Eastern Subbetic). Palaeogeography, Palaeoclimatology, Palaeoecology, 381-382: 76-91. https://doi.org/10.1016/j.palaeo.2013.04.017 ) and their replacement by deeper Mediterranean Pliensbachian fauna, correlates with a regressive-transgressive cycle (Hallam, 1988Hallam, A. (1988). A re-evaluation of Jurassic eustasy in the light of new data and the revised Exxon curve. In: Sea-level Changes: An integrated approach (Wilgus, C.K.; Hastings, B.S.; Posamentier, H.; Van Wagoner, J.; Ross, C.A. & Kendall, C.G.S., Eds.), Society of Economic Paleontologists and Mineralogists Special Publications 42, 261-273. https://doi.org/10.2110/pec.88.01.0261 ; O’Dogherty et al., 2000O’Dogherty, L.; Sandoval, J. & Vera, J.A. (2000). Jurassic Ammonite faunal turnover tracing sea-level changes during the Jurassic (Betic Cordillera, southern Spain). Journal of the Geological Society London, 157: 723-736. https://doi.org/10.1144/jgs.157.4.723 ; Sandoval et al., 2001Sandoval, J.; O’Dogherty, L. & Guex, J. (2001). Evolutionary rates of Jurassic ammonites in relation to Sea-level fluctuations. Palaios, 16: 311-335. https://doi.org/10.1669/0883-1351(2001)016<0311:EROJAI>2.0.CO;2 , 2012Sandoval, J.; Bill, M.; Aguado, R.; O’Dogherty, L.; Rivas, P.; Morard, A. & Guex, J. (2012). The Toarcian in the Subbetic basin (southern Spain): Bioevents (ammonite and calcareous nannofossils) and carbon-isotope stratigraphy. Palaeogeography, Palaeoclimatology, Palaeoecology, 342-343: 40-63. https://doi.org/10.1016/j.palaeo.2012.04.028 ; Schöllhorn et al., 2020Schöllhorn, I.; Adatte, T.; Van de Schootbrugge, B.; Houben, A.; Charbonnier, G.; Janssen, N. & Follmi, K.B. (2020). Climate and environmental response to the break-up of Pangea during the Early Jurassic (Hettangian-Pliensbachian), the Dorset coast (UK) revisited. Global and Planetary Change, 185: 103096. https://doi.org/10.1016/j.gloplacha.2019.103096 ).

This interpretation is congruent with the absence of black shales and oxygen depleted conditions in the studied area during the Sinemurian-Pliensbachian boundary that would limit the brachiopod survival as well as favour the co-precipitation of some trace elements with iron sulfides (Mo, Ni, and Cu) and fixation to buried organic matter (U, Cd, Zn, and V) but not an increase in their content in the brachiopod shells. Oxygen-depletion should be therefore reasonably excluded to explain trace elements variations in this timespan.

Variations around the Jenkyns Event

The return to the standard conditions in the Pliensbachian shows a very slight decreasing trend in the trace elements analyzed subsequently (CC1.1 to CC2.2 samples). After that, the next main perturbation imprints on the trace elements are located in the uppermost Pliensbachian-lowermost Toarcian (Emaciatum-Polymorphum zones), with several pulses showing positive excursions from CC2.2 to Z2B samples and a peak in Z2B, just prior to the extinction boundary. If we compare this interval with the δ¹³C and δ¹⁸O curves (Gómez & Goy, 2011Gómez, J.J. & Goy, A. (2011). Warming-driven mass extinction in the Early Toarcian (Early Jurassic) of northern and central Spain. Correlation with other time-equivalent European sections. Palaeogeography, Palaeoclimatology, Palaeoecology, 306: 176-195. https://doi.org/10.1016/j.palaeo.2011.04.018 ; García Joral et al., 2011García Joral, F.; Gómez, J.J. & Goy, A. (2011). Mass extinction and recovery of the Early Toarcian (Early Jurassic) brachiopods linked to climate change in northern and central Spain. Palaeogeography, Palaeoclimatology, Palaeoecology, 302: 367-380. https://doi.org/10.1016/j.palaeo.2011.01.023 ; Gómez et al., 2016Gómez, J.J.; Comas-Rengifo, M.J. & Goy, A. (2016). Palaeoclimatic oscillations in the Pliensbachian (Early Jurassic) of the Asturian Basin (Northern Spain). Climate of the Past, 12: 1199-1214. https://doi.org/10.5194/cp-12-1199-2016 ; Ruebsam et al., 2020Ruebsam, W.; Reolid, M. & Schwark, L. (2020). δ¹³C of terrestrial vegetation records Toarcian CO₂ and climate gradients. Scientific Reports, 10: art. 117. https://doi.org/10.1038/s41598-019-56710-6 ;) (Fig. 1), a high correlation between general trends of trace element perturbations and the C and O cycling oscillations can be deduced. Their occurrence in the pre-extinction interval of the Jenkyns Event really suggests a multi-phased stage in this biotic crisis (Figs. 4, 15), which started earlier in the latest Pliensbachian as deduced by several authors (cf. Little, 1996Little, C.T.S. (1996). The Pliensbachian-Toarcian (Lower Jurassic) extinction event. GSA Special Paper, 307: 505-512. https://doi.org/10.1130/0-8137-2307-8.505 ; Macchioni & Cecca, 2002Macchioni, F. & Cecca, F. (2002). Biodiversity and biogeography of middle-late liassic ammonoids: implications for the Early Toarcian mass extinction. Geobios, M.S. 24: 165-175. https://doi.org/10.1016/S0016-6995(02)00057-8 ; Wignall & Bond, 2008Wignall, P.B. & Bond, D.P.G. (2008) The end-Triassic and Early Jurassic mass extinction records in the British Isles. Proceedings of the Geologists’ Association, 119: 73-84. https://doi.org/10.1016/S0016-7878(08)80259-3 ; Dera et al., 2010Dera, G.; Neige, P.; Dommergues, J.L.; Fara, E.; Laffont, R. & Pellenard, P. (2010). High resolution dynamics of Early Jurassic marine extinctions: the case of Pliensbachian-Toarcian ammonites (Cephalopoda). Journal of the Geological Society London, 167: 21-33. https://doi.org/10.1144/0016-76492009-068 ; Caruthers et al., 2013Caruthers, A.H.; Smith, P.L. & Gröcke, D.R. (2013). The Pliensbachian-Toarcian (Early Jurassic) extinction, a global multi-phased event. Palaeogeography, Palaeoclimatology, Palaeoecology, 386: 104-118. https://doi.org/10.1016/j.palaeo.2013.05.010 ; Arias, 2013Arias, C. (2013). The Early Toarcian (Early Jurassic) ostracod extinction events in the Iberian Range: The effect of temperature changes and prolonged exposure to low dissolved oxygen concentrations. Palaeogeography, Palaeoclimatology, Palaeoecology, 387: 40-55. https://doi.org/10.1016/j.palaeo.2013.07.004 ; Rita et al., 2016Rita, P.; Reolid, M. & Duarte, L.V. (2016). The incidence of the Late Pliensbachian-Early Toarcian biotic crisis from ecostratigraphy of benthic foraminiferal assemblages: new insights from the Peniche reference section, Portugal. Palaeogeography, Palaeoclimatology, Palaeoecology, 454: 267-281. https://doi.org/10.1016/j.palaeo.2016.04.039 ; Baeza-Carratalá et al., 2017Baeza-Carratalá, J.F.; Reolid, M. & García Joral, F. (2017). New deep-water brachiopod resilient assemblage from the South-Iberian Palaeomargin (Western Tethys) and its significance for the brachiopod adaptive strategies around the Early Toarcian Mass Extinction Event. Bulletin of Geosciences, 92: 233-256. https://doi.org/10.3140/bull.geosci.1631 ). In the analyzed samples, the onset of these perturbations is coincident with the first record of koninckinid fauna in the Subbetic (CC 2.2 sample onwards) which was considered as precursor signal of the Jenkyns Event (Baeza-Carratalá et al., 2015Baeza-Carratalá, J.F.; García Joral, F.; Giannetti, A. & Tent-Manclús, J.E. (2015). Evolution of the last koninckinids (Athyridida, Koninckinidae), a precursor signal of the Early Toarcian mass extinction event in the Western Tethys. Palaeogeography, Palaeoclimatology, Palaeoecology, 429: 41-56. https://doi.org/10.1016/j.palaeo.2015.04.004 , 2017Baeza-Carratalá, J.F.; Reolid, M. & García Joral, F. (2017). New deep-water brachiopod resilient assemblage from the South-Iberian Palaeomargin (Western Tethys) and its significance for the brachiopod adaptive strategies around the Early Toarcian Mass Extinction Event. Bulletin of Geosciences, 92: 233-256. https://doi.org/10.3140/bull.geosci.1631 ).

The maximum positive excursion in trace elements is reached in the sample Z2B, just in the base of the marls of the Polymorphum Zone (lower Toarcian, Figs. 8, 9). An anoxic event is a recurrent factor used to explain the mass extinction occurring in the early Toarcian (e.g. Jenkyns, 1988Jenkyns, H.C. (1988). The Early Toarcian (Jurassic) anoxic event: stratigraphy, sedimentary and geochemical evidence. American Journal of Science, 288: 101-151. https://doi.org/10.2475/ajs.288.2.101 ; Bassoullet & Baudin, 1994Bassoullet, J.P. & Baudin, F. (1994). The Early Toarcian: a period of crisis in basins and carbonate platforms from Northwestern Europe and Tethys. Geobios, 27 (Sup. 3): 645-654. https://doi.org/10.1016/S0016-6995(94)80227-0 ; Harries & Little, 1999Harries, P.J. & Little, C.T.S. (1999). The Early Toarcian (Early Jurassic) and the Cenomanian-Turonian (Late Cretaceous) mass extinctions: similarities and contrasts. Palaeogeography, Palaeoclimatology, Palaeoecology, 154: 39-66. https://doi.org/10.1016/S0031-0182(99)00086-3 ; Pálfy & Smith, 2000Pálfy, J. & Smith, P.L. (2000). Synchrony between Early Jurassic extinction, oceanic anoxic event, and the Karoo-Ferrar flood basalt volcanism. Geology, 28: 747-750. https://doi.org/10.1130/0091-7613(2000)028<0747:SBEJEO>2.3.CO;2 ; Wignall et al., 2005Wignall, P.B.; Newton, R.J. & Little, C.T.S. (2005). The timing of paleoenvironmental change and cause-and-effect relationships during the Early Jurassic mass extinction in Europe. American Journal of Science, 305: 1014-1032. https://doi.org/10.2475/ajs.305.10.1014 ; Mailliot et al., 2006Mailliot, S.; Mattioli, E.; Guex, J. & Pittet, B. (2006). The early Toarcian anoxia; a synchronous event in the Western Tethys? An approach by quantitative biochronology (Unitary Associations), applied on calcareous nannofossils. Palaeogeography, Palaeoclimatology, Palaeoecology, 240: 562-586. https://doi.org/10.1016/j.palaeo.2006.02.016 ; Ruebsam et al., 2020Ruebsam, W.; Reolid, M. & Schwark, L. (2020). δ¹³C of terrestrial vegetation records Toarcian CO₂ and climate gradients. Scientific Reports, 10: art. 117. https://doi.org/10.1038/s41598-019-56710-6 ). However, in the Subbetic area, neither sedimentary evidence (black shales) nor TOC content points to the anoxia as the primary factor for the biotic crisis. Maximum TOC values from the Subbetic area in the basal Serpentinum Zone are around 0.4-0.9 wt.% (for the biotic crisis. Maximum TOC values from the Subbetic area in the basal Serpentinum Zone are around 0.4-0.9 wt.% (Reolid et al., 2013Reolid, M.; Nieto, L.M. & Sánchez-Almazo, I.M. (2013). Caracterización geoquímica de facies pobremente oxigenadas en el Toarciense inferior (Jurásico inferior) del Subbético Externo. Revista de la Sociedad Geológica de España, 26: 69-84., 2014Reolid, M.; Mattioli, E.; Nieto, L.M. & Rodríguez-Tovar, F.J. (2014). The Early Toarcian Oceanic Anoxic Event in the External Subbetic (Southiberian Palaeomargin, Westernmost Tethys): Geochemistry, nannofossils and ichnology. Palaeogeography, Palaeoclimatology, Palaeoecology, 411: 79-94. https://doi.org/10.1016/j.palaeo.2014.06.023 ; Rodríguez-Tovar & Reolid, 2013Rodríguez-Tovar, F.J. & Reolid, M. (2013). Environmental conditions during the Toarcian Oceanic Anoxic Event (T-OAE) in the westernmost Tethys: influence of the regional context on a global phenomenon. Bulletin of Geosciences, 88: 697-712. https://doi.org/10.3140/bull.geosci.1397 ; Rodrigues et al., 2019Rodrigues, B.; Silva, R.L.; Reolid, M.; Mendonça Filho, J.G. & Duarte, L.V. (2019). Sedimentary organic matter and δ¹³Ckerogen variation on the southern Iberian palaeomargin (Betic Cordillera, SE Spain) during the latest Pliensbachian-Early Toarcian. Palaeogeography, Palaeoclimatology, Palaeoecology, 534: 109342. https://doi.org/10.1016/j.palaeo.2019.109342 ; Ruebsam et al., 2020Ruebsam, W.; Reolid, M. & Schwark, L. (2020). δ¹³C of terrestrial vegetation records Toarcian CO₂ and climate gradients. Scientific Reports, 10: art. 117. https://doi.org/10.1038/s41598-019-56710-6 ) instead of the 5-15 wt.% present in the NW-European basins (e.g. Röhl et al., 2001Röhl, H.J.; Schmid-Röhl, A.; Oschmann, W.; Frimmel, A. & Scwark, L. (2001). The Posidonian Shale (Lower Toarcian) of SW-Germany: an oxygen-depleted ecosystem controlled by sea level and paleoclimate. Palaeogeography, Palaeoclimatology, Palaeoecology, 165: 27-52. https://doi.org/10.1016/S0031-0182(00)00152-8 ; Bucefalo-Palliani et al., 2002Bucefalo Palliani, R.; Mattioli, E. & Riding, J.B. (2002). The response of marine phytoplankton and sedimentary organic matter to the Early Toarcian (Lower Jurassic) oceanic anoxic event in northern England. Marine Micropaleontology, 46: 223-245. https://doi.org/10.1016/S0377-8398(02)00064-6 ; Mailliot et al., 2006Mailliot, S.; Mattioli, E.; Guex, J. & Pittet, B. (2006). The early Toarcian anoxia; a synchronous event in the Western Tethys? An approach by quantitative biochronology (Unitary Associations), applied on calcareous nannofossils. Palaeogeography, Palaeoclimatology, Palaeoecology, 240: 562-586. https://doi.org/10.1016/j.palaeo.2006.02.016 ; McArthur et al., 2008McArthur, J.M.; Algeo, T.J.; van de Schootbrugge, B.; Li, Q. & Howarth, R.J. (2008). Basinal restriction; black shales; Re-Os dating; and the Early Toarcian (Jurassic) oceanic anoxic event. Paleoceanography, 23: PA4217. https://doi.org/10.1029/2008PA001607 ; Baroni et al., 2018Baroni, I.R.; Pohl, A.; van Helmond, N.A.G.M.; Papadomanolaki, N.M.; Coe, A.L.; Cohen, A.S.; van de Schootbrugge, B.; Donnadieu, Y. & Slomp, C.P. (2018). Ocean circulation in the Toarcian (Early Jurassic): A key control on deoxygenation and carbon burial on the European Shelf. Paleoceanography and Paleoclimatology, doi:10.1029/2018PA003394. https://doi.org/10.1029/2018PA003394 ; Thibault et al., 2018Thibault, N.; Ruhl, M.; Ullmann, C.V.; Korte, C.; Kemp, D.; Gröcke, D.R. & Hesselbo, S.P. (2018). The wider context of the Lower Jurassic Toarcian oceanic anoxic event in Yorkshire coastal outcrops, UK. Proceedings of the Geologists’ Association, 129: 372-391. https://doi.org/10.1016/j.pgeola.2017.10.007 ; Fantasia et al., 2019aFantasia, A.; Föllmi, K.B.; Adatte, T.; Spangenberg, J.E. & Mattioli, E. (2019a). Expression of the Toarcian Oceanic Anoxic Event: New insights from a Swiss transect. Sedimentology, 66: 262-284. https://doi.org/10.1111/sed.12527 ). Moreover, under oxygen depleted conditions most of the trace elements would be incorporated to the bottom as sulfides (Fe, Mo, Ni, Cu, Pb) and complexed in the particulate organic matter (U, Mo, Cu, Cd, Zn, Co, Ni, V), instead in dissolved phase in the sea water. On the contrary, under oxic conditions, Zn, Ni, and Cu are strongly complexed by dissolved organic matter. Moreover, Zn, Mo, Cr, Cu, and Ni are related in the PC2 axis as redox sensitive elements, usually dissolved in the seawater under oxic conditions (Tribovillard et al., 2006Tribovillard, N.; Algeo, T.; Lyons, T. & Riboulleau, A. (2006). Trace metals as palaeoredox and palaeoproductivity proxies: an update. Chemical Geology, 232: 12-32. https://doi.org/10.1016/j.chemgeo.2006.02.012 ).

Indeed, the maximum brachiopod diversity is reached just prior to the timing of this biotic crisis, dated in the westernmost Tethys in the lowermost Serpentinum Zone. Thus, in the Subbetic Domain, we can invoke from the biotic signals an alternative triggering mechanism as a primary responsible factor in this biotic crisis, such as an increasing temperature gradient. Firstly, koninckinid beds early appear in the basin just in the levels showing several trace elements perturbations (sample CC 2.2 upwards). This brachiopod clade (Athyridida) became extinct during the Jenkyns Event (Vörös, 2002Vörös, A. (2002). Victims of the Early Toarcian anoxic event: the radiation and extinction of Jurassic Koninckinidae (Brachiopoda). Lethaia, 35: 345-357. https://doi.org/10.1080/002411602320790652 ; Baeza-Carratalá et al., 2015Baeza-Carratalá, J.F.; García Joral, F.; Giannetti, A. & Tent-Manclús, J.E. (2015). Evolution of the last koninckinids (Athyridida, Koninckinidae), a precursor signal of the Early Toarcian mass extinction event in the Western Tethys. Palaeogeography, Palaeoclimatology, Palaeoecology, 429: 41-56. https://doi.org/10.1016/j.palaeo.2015.04.004 ; Vörös et al., 2016Vörös, A.; Kocsis, Á.T. & Pálfy, J. (2016). Demise of the last two spire-bearing brachiopod orders (Spiriferinida and Athyridida) at the Toarcian (Early Jurassic) extinction event. Palaeogeography, Palaeoclimatology, Palaeoecology, 457: 233-241. https://doi.org/10.1016/j.palaeo.2016.06.022 ) and their record in the Subbetic area (South-Iberian Palaeomargin), as results of their adaptive strategies, was considered as precursor signal of the Jenkyns Event (Baeza-Carratalá et al., 2015Baeza-Carratalá, J.F.; García Joral, F.; Giannetti, A. & Tent-Manclús, J.E. (2015). Evolution of the last koninckinids (Athyridida, Koninckinidae), a precursor signal of the Early Toarcian mass extinction event in the Western Tethys. Palaeogeography, Palaeoclimatology, Palaeoecology, 429: 41-56. https://doi.org/10.1016/j.palaeo.2015.04.004 ). On the other hand, the sudden occurrence in the basin of Calyptoria vulgata and Lobothyris arcta (Baeza-Carratalá, 2013Baeza-Carratalá, J.F. (2013). Diversity patterns of Early Jurassic brachiopod assemblages from the westernmost Tethys (Eastern Subbetic). Palaeogeography, Palaeoclimatology, Palaeoecology, 381-382: 76-91. https://doi.org/10.1016/j.palaeo.2013.04.017 ; Baeza-Carratalá et al., 2018aBaeza-Carratalá, J.F.; García Joral, F.; Goy, A. & Tent-Manclús, J.E. (2018a). Arab-Madagascan brachiopod dispersal along the north-Gondwana paleomargin towards the western Tethys Ocean during the early Toarcian (Jurassic). Palaeogeography, Palaeoclimatology, Palaeoecology, 490: 256-268. https://doi.org/10.1016/j.palaeo.2017.11.004 ), typical of warmer regions (García Joral et al., 2011García Joral, F.; Gómez, J.J. & Goy, A. (2011). Mass extinction and recovery of the Early Toarcian (Early Jurassic) brachiopods linked to climate change in northern and central Spain. Palaeogeography, Palaeoclimatology, Palaeoecology, 302: 367-380. https://doi.org/10.1016/j.palaeo.2011.01.023 ; Baeza-Carratalá et al., 2018aBaeza-Carratalá, J.F.; García Joral, F.; Goy, A. & Tent-Manclús, J.E. (2018a). Arab-Madagascan brachiopod dispersal along the north-Gondwana paleomargin towards the western Tethys Ocean during the early Toarcian (Jurassic). Palaeogeography, Palaeoclimatology, Palaeoecology, 490: 256-268. https://doi.org/10.1016/j.palaeo.2017.11.004 ), suggests a thermal maximum around the Z2B sample, in the Polymorphum Zone, just prior to their total extinction, not surpassing the hyperthermal event of the Serpentinum Zone.

Many authors have proposed a global warming related to the negative CIE of the Jenkyns Event and the correlative T-OAE (e.g. Suan et al., 2010Suan, G.; Mattioli, E.; Pittet, B.; Lécuyer, C.; Suchéras-Marx, B.; Duarte, L.V.; Philippe, M.; Reggiani, L. & Martineau, F. (2010). Secular environmental precursors to Early Toarcian (Jurassic) extreme climate changes. Earth and Planetary Science Letters, 290: 448-458. https://doi.org/10.1016/j.epsl.2009.12.047 ; Korte & Hesselbo, 2011Korte, C. & Hesselbo, S.P. (2011). Shallow-marine carbon- and oxygen-isotope and elemental records indicate icehouse-greenhouse cycles during the Early Jurassic. Paleoceanography, 26: PA4219. https://doi.org/10.1029/2011PA002160 ; Korte et al., 2015Korte, C.; Hesselbo, S.P.; Ullmann, C.V.; Dietl, G.; Ruhl, M.; Schweigert, G. & Thibault, N. (2015). Jurassic climate mode governed by ocean gateway. Nature Communications, 6: 10015. https://doi.org/10.1038/ncomms10015 ; Them et al., 2017Them, T.R.; Gill, B.C.; Selby, D.; Grocke, D.R.; Friedman, R.M. & Owens, J.D. (2017). Evidence for rapid weathering response to climatic warming during the Toarcian Oceanic Anoxic Event. Scientific Reports, 7: 5003. https://doi.org/10.1038/s41598-017-05307-y ; Ruebsam et al., 2019Ruebsam, W.; Mayer, B. & Schwark, L. (2019). Cryosphere carbon dynamics control early Toarcian global warming and sea level evolution. Global and Planetary Change, 172: 440-453. https://doi.org/10.1016/j.gloplacha.2018.11.003 ; Baghli et al., 2020Baghli, H.; Mattioli, E.; Spangenberg, J.E.; Bensalah, M.; Arnaud-Godet, F.; Pittet, B. & Suan, G. (2020). Early Jurassic climatic trends in the south-Tethyan margin. Gondwana Research, 77: 67-81. https://doi.org/10.1016/j.gr.2019.06.016 ; Reolid et al., 2020Reolid, M.; Mattioli, E.; Duarte, L.V. & Marok, A. (2020). The Toarcian Oceanic Anoxic Event and the Jenkyns Event (IGCP-655 final report). Episodes, 43: 833-844. https://doi.org/10.18814/epiiugs/2020/020051 ) (Figs. 1, 15). The Mg/Ca values at the beginning of the lower Toarcian increase respect to the Pliensbachian and confirm the global warming related with the Jenkyns Event. The enhanced weathering related to this climate change (Montero-Serrano et al., 2015Montero-Serrano, J.C.; Föllmi, K.B.; Adatte, T.; Spangenberg, J.E.; Tribovillard, N.; Fantasia, A. & Suan, G. (2015). Continental weathering and redox conditions during the early Toarcian Oceanic Anoxic Event in the northwestern Tethys: Insight from the Posidonia Shale section in the Swiss Jura Mountains. Palaeogeography, Palaeoclimatology, Palaeoecology, 429: 83-99. https://doi.org/10.1016/j.palaeo.2015.03.043 ; Fu et al., 2017Fu, X.G.; Wang, M.; Zeng, S.Q.; Feng, X.L.; Wang, D. & Song, C.Y. (2017). Continental weathering and palaeoclimatic changes through the onset of the Early Toarcian oceanic anoxic event in the Qiangtang Basin, Eastern Tethys. Palaeogeography, Palaeoclimatology, Palaeoecology, 487: 241-250. https://doi.org/10.1016/j.palaeo.2017.09.005 ; Them et al., 2017Them, T.R.; Gill, B.C.; Selby, D.; Grocke, D.R.; Friedman, R.M. & Owens, J.D. (2017). Evidence for rapid weathering response to climatic warming during the Toarcian Oceanic Anoxic Event. Scientific Reports, 7: 5003. https://doi.org/10.1038/s41598-017-05307-y ) drove to the subsequent detrital and nutrient input to the marine basin (Rodríguez-Tovar & Reolid, 2013Rodríguez-Tovar, F.J. & Reolid, M. (2013). Environmental conditions during the Toarcian Oceanic Anoxic Event (T-OAE) in the westernmost Tethys: influence of the regional context on a global phenomenon. Bulletin of Geosciences, 88: 697-712. https://doi.org/10.3140/bull.geosci.1397 ; Danise et al., 2015Danise, S.; Twichett, R.J. & Little, C.T.S. (2015). Environmental controls on Jurassic marine ecosystems during global warming. Geology, 43: 263-266. https://doi.org/10.1130/G36390.1 ; Fantasia et al., 2019bFantasia, A.; Thierry, A.; Spangenberg, J.E.; Font, E.; Duarte, L.V. & Follmi, K.B. (2019b). Global versus local processes during the Pliensbachian-Toarcian transition at the Peniche GSSP, Portugal: A multi-proxy record. Earth-Science Reviews, 198: art. 102932. https://doi.org/10.1016/j.earscirev.2019.102932 ; Kemp et al., 2019Kemp, D.B.; Baranyi, V.; Izumi, K. & Burgess, R.D. (2019). Organic matter variations and links to climate across the early Toarcian oceanic anoxic event (T-OAE) in Toyora area, southwest Japan). Palaeogeography, Palaeoclimatology, Palaeoecology, 530: 90-102. https://doi.org/10.1016/j.palaeo.2019.05.040 ) and the increase as dissolved phase where oxygen depleted conditions did not develop. This increased primary productivity also favoured the labile organic matter (particulate, colloidal and dissolved organic matter) for suspension-feeders such as brachiopods, with the subsequent increase of some trace metals in the shells (Fe, Cr, Zn, Ni, Mo, and Cu).

After reaching the maximum concentration values in the Jenkyns Event interval, the content of most trace elements slowly decreases progressively towards the top of the stratigraphical succession, although showing higher values than prior the Jenkyns Event. Thus, the repopulation interval just starts with the record of the opportunistic Soaresirhynchia bouchardi (Z2C1 sample) in the Serpentinum Zone (usually recorded in the Elegantulum Subzone) where the trace elements values start their decreasing trend. The reestablishment of the background conditions is reached from this sample upwards (Z2C1- Z2C2), in coincidence with the recovery of the brachiopod diversity led by the “Spanish Bioprovince” of brachiopods (García Joral & Goy, 1984García Joral, F. & Goy, A. (1984). Características de la fauna de braquiópodos del Toarciense Superior en el Sector Central de la Cordillera Ibérica (Noreste de España). Estudios Geológicos, 40: 55-60. https://doi.org/10.3989/egeol.84401-2650 , 2000García Joral, F. & Goy, A. (2000). Stratigraphic distribution of Toarcian brachiopods from the Iberian Range and its relation to depositional sequences. Georesearch Forum, 6: 381-386.; Alméras & Fauré, 1990Alméras, Y. & Fauré, P. (1990). Histoire des brachiopodes liasiques dans la Tethys occidentale: les crises et l’écologie. Cahiers de l’Université Catholique de Lyon Sciences, 4: 1-12.; García Joral et al., 2011García Joral, F.; Gómez, J.J. & Goy, A. (2011). Mass extinction and recovery of the Early Toarcian (Early Jurassic) brachiopods linked to climate change in northern and central Spain. Palaeogeography, Palaeoclimatology, Palaeoecology, 302: 367-380. https://doi.org/10.1016/j.palaeo.2011.01.023 ).

Some trace elements such as Ti, Fe, and REE, considered as reliable proxies of possible continental influx (Figs. 11, 14) (Zaky et al., 2016Zaky, A.H.; Brand, U.; Azmy, K.; Logan, A.; Hooper, R.G. & Svavarsson, J. (2016). Rare earth elements of shallow-water articulated brachiopods: A bathymetric sensor. Palaeogeography, Palaeoclimatology, Palaeoecology, 461: 178-194. https://doi.org/10.1016/j.palaeo.2016.08.021 ; Smrzka et al., 2019Smrzka, D.; Zwicker, J.; Bach, W.; Himmler, T.; Chen, D. & Peckmann, J. (2019). The behaviour of trace elements in seawater, sedimentary pore water, and their incorporation into carbonate minerals: a review. Facies, 65: 41. https://doi.org/10.1007/s10347-019-0581-4 , and references therein), reach their highest values in the brachiopod shells during the Jenkyns Event interval and just in the onset of the repopulation interval (Z2C1 sample). Other typical elements such as Al, Ba, and Pb show a short increase delayed respect to the peak of Ti, Fe, and REE (Fig. 8).

Summarizing, in the South-Iberian Palaeomargin redox fluctuations in the seawater does not appear to have been a primary cause for oscillation of trace elements concentration in brachiopod shells. In fact, the record of benthic fauna is quite continuous, and this would not be the case in an anoxic environment. Other factors related to the global change induced by the Jenkyns Event (global warming, enhanced weathering, and subsequent changes in primary productivity) had impact on both assemblage structure and shell composition (with increasing content on some trace elements). In this sense, seawater temperature must be invoked to play a decisive role in this mass extinction event, as it is deduced by the biotic signals correlated with the palaeotemperatures deduced for the peri-Iberian platform system (García Joral et al., 2011García Joral, F.; Gómez, J.J. & Goy, A. (2011). Mass extinction and recovery of the Early Toarcian (Early Jurassic) brachiopods linked to climate change in northern and central Spain. Palaeogeography, Palaeoclimatology, Palaeoecology, 302: 367-380. https://doi.org/10.1016/j.palaeo.2011.01.023 ; Sandoval et al., 2012Sandoval, J.; Bill, M.; Aguado, R.; O’Dogherty, L.; Rivas, P.; Morard, A. & Guex, J. (2012). The Toarcian in the Subbetic basin (southern Spain): Bioevents (ammonite and calcareous nannofossils) and carbon-isotope stratigraphy. Palaeogeography, Palaeoclimatology, Palaeoecology, 342-343: 40-63. https://doi.org/10.1016/j.palaeo.2012.04.028 , Gómez et al., 2016Gómez, J.J.; Comas-Rengifo, M.J. & Goy, A. (2016). Palaeoclimatic oscillations in the Pliensbachian (Early Jurassic) of the Asturian Basin (Northern Spain). Climate of the Past, 12: 1199-1214. https://doi.org/10.5194/cp-12-1199-2016 ; Rosales et al., 2018Rosales, I.; Barnolas, A.; Goy, A.; Sevillano, A.; Armendáriz, M. & López-García, J.M. (2018). Isotope records (C-O-Sr) of late Pliensbachian-early Toarcian environmental perturbations in the westernmost Tethys (Majorca Island, Spain). Palaeogeography, Palaeoclimatology, Palaeoecology, 497: 168-185. https://doi.org/10.1016/j.palaeo.2018.02.016 ; Ullmann et al., 2020Ullmann, C.V.; Boyles, R.; Duarte, L.V.; Hesselbo, S.P.; Kasemanns, S.A.; Kleins, T.; Lenton, T.M.; Piazza, V. & Aberhan, M. (2020). Warm afterglow from the Toarcian Oceanic Anoxic Event drives the success of deep-adapted brachiopods. Scientific Reports, 10: 6549. https://doi.org/10.1038/s41598-020-63487-6 ).