In the westernmost Tethys, the Early Jurassic involved critical environmental changes affecting marine ecosystems. Brachiopods were particularly affected in the South-Iberian Palaeomargin. A late Sinemurian-early Pliensbachian tectonic event led to the collapse of shallow platforms related to the Atlantic Ocean opening. Subsequently, the early Toarcian Extinction Event occurred during a carbon cycle perturbation and the development of oxygen-depleted conditions, mainly affecting benthic communities. In the Subbetic Domain, brachiopod dynamics concur with these major environmental perturbation events. Geochemical imprint of brachiopod shells from this area has been analyzed revealing a clear synchrony between oscillations of trace elements content, global trends in the C and O cycling, and faunal diversity dynamics around critical bioevents, allowing to validate global and regional models related to the platform collapse and the early Toarcian biotic crisis. In the Sinemurian-Pliensbachian turnover and the Toarcian crisis, the redox-sensitive trace metals, REEs, and Fe content in the brachiopod shells show positive excursions. Nevertheless, their trend together with brachiopod diversity patterns, the lower TOC values, and the sedimentary data, support that oxygen depletion must have played a secondary role as environmental stress factor for the benthic fauna. Instead, an increasing temperature gradient is invoked to have played a decisive role, as demonstrated by the main faunal turnover and replacement events correlating with the palaeotemperatures from the peri-Iberian platforms. Shifts on palaeoproductivity, continental influx, and hydrothermal input are also deduced by the increasing concentrations of several trace elements, interpreted as complementary triggering factors of these Early Jurassic bioevents in the westernmost Tethys Ocean.
En el Jurásico Inferior se registran diversos eventos críticos que influyeron significativamente en los ecosistemas marinos del Tethys occidental. Entre las comunidades bentónicas, en el Paleomargen Sudibérico, los braquiópodos se vieron particularmente afectados por dichos eventos. El episodio tectono-sedimentario distensivo asociado a la apertura del proto-Atlántico conllevó el colapso de las amplias plataformas someras imperantes en el Tethys hasta el Sinemuriense superior-Pliensbaquiense basal, con la consiguiente reorganización de los ecoespacios faunísticos. Posteriormente, el evento de extinción registrado en el Toarciense inferior, trajo consigo importantes alteraciones en el ciclo del carbono así como el desarrollo de condiciones anóxicas que afectaron principalmente a las comunidades bentónicas. En el dominio Subbético, la dinámica poblacional de los braquiópodos coincidió con estos importantes eventos de perturbación ambiental. Se ha analizado la impronta geoquímica registrada en conchas de braquiópodos del Subbético oriental, revelando una clara sincronía entre las oscilaciones del contenido en elementos traza, las tendencias globales en el ciclo del C y del O y la diversidad de la braquiofauna en torno a dichos eventos críticos, lo que permite validar modelos globales y regionales relacionados tanto con el evento de rifting incipiente de las plataformas someras en el Sinemuriense-Pliensbachiense, como con la crisis biótica global en torno al Toarciense inferior. En la renovación faunística verificada para el tránsito Sinemuriense-Pliensbachiense y para el evento de extinción del Toarciense, los metales traza sensibles a las condiciones redox, la concentración de REE y el contenido en Fe en las conchas de braquiópodos muestran excursiones positivas. Esta tendencia, junto a los patrones de diversidad de los braquiópodos, los bajos valores de TOC y las evidencias sedimentarias, sugieren que, en esta región, la anoxia debió representar un factor secundario como causa de estrés ambiental para la fauna bentónica. En cambio, se postula que el progresivo aumento de la temperatura jugó un papel determinante en las cuencas marginales del Tethys occidental, como se demuestra al correlacionar los principales eventos de renovación y sustitución faunística con las paleotemperaturas de las plataformas peri-ibéricas. Los cambios en la paleoproductividad, los aportes continentales y posibles contribuciones hidrotermales se relacionan asimismo con las oscilaciones de determinados elementos traza y se interpretan, por tanto, como factores coadyuvantes desencadenantes de estos bioeventos del Jurásico Inferior en el Tethys occidental.
The Early Jurassic constituted a timespan that involved critical environmental perturbations affecting marine ecosystems. In the framework of the Central Atlantic Ocean opening, a late Sinemurian-early Pliensbachian tectonic event led to the collapse of the shallow-water platforms system well-established in the Western Tethys Ocean by rifting and subsequent drowning (
Note the negative carbon isotopic excursion (CIE) that correlated with the Jenkyns Event that includes the T-OAE. The isotopic curve is correlated with the sequence boundaries and the sea-level curve after
The evolution of the Early Jurassic depositional environments and ecological conditions in the South-Iberian Palaeomargin are well understood, evolving from shallow carbonate platforms to an epioceanic swell/graben system with changing environmental conditions and ecospaces for the marine communities (
Numerous high-resolution datasets of carbon and oxygen isotopes have been developed in order to elucidate episodes of warming and anoxia as the most probable causes for the early Toarcian biotic crisis (
Calcite and aragonite readily incorporate trace elements during precipitation (
Carbonate minerals are highly prone to incorporate significant amounts of trace elements (
Trace element content in the water column shows a variable vertical distribution and is controlled by a complex interaction involving source strengths, their removal rates and water circulation patterns (
For all the aforementioned reasons, geochemical analyses in shells can provide highly consistent proxies for the reconstruction of ancient palaeoenvironmental marine conditions (e.g.
The brachiopod-bearing outcrops are located in the Crevillente and Reclot mountains in Alicante province, SE Spain (
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 (
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.
Brachiopods were collected from the Lower Jurassic succession of four outcrops of the Eastern Subbetic in close proximity (SP: Sierra Pelada; CC: Cerro de la Cruz: CC1, CC2; Al: Algueda sections in
The Sierra Pelada section (coord. 38°21’29’’N, 0°55’07’’W) corresponds to the basal layers of the composite section, typifying the middle member of the Gavilán Formation. This unit mainly consists of massive micritic and oolithic wackestones, showing lateral and upward transitions to oolithic grainstone and packstone levels with intraclasts and micropellets. Faunal content mainly consists of brachiopod shell concentrations, sponge spicules, crinoids, and scarce gastropods and benthic foraminifera. Brachiopods are found in pocket-like accumulations and in thick cross-bedded deposits (
A. Skeletal concentrations made up of densely packed brachiopods of the Gavilán Formation in Sierra Pelada section. B. Crinoidal grainstone from the Gavilán Formation in the Cerro de la Cruz section 1 (CC-1) showing abundant crinoidal ossicles, brachiopods, and belemnite remains. C. Field view of the Cerro de la Cruz 2 section (CC-2) where the red crinoidal limestone beds rich in brachiopod crop out. d. Field view of the marl and marly limestone alternation beds of the Zegrí Formation (Serpentinum Zone), outcropping at the top of La Algueda section.
The basal layers of the Cerro de la Cruz outcrops are found in the CC-1 section (coord. 38°21’37’’N, 0°54’58’’W) and can be stratigraphically correlated with the uppermost interval recorded in the Sierra Pelada section, i.e., nests of brachiopod concentrations infilling extensional fissures within white massive limestone beds. Upwards, the upper member of the Gavilán Formation is extensively developed in both CC-1 and CC-2 (coord. 38°21’43’’N, 0°54’52’’W) sections (
In the Algueda section (coord. 38°15’35’’N, 0°54’57’’W;
These sections have been summarized in a composite stratigraphical section (
Taxonomic identification of brachiopods follow recent works on systematic data in the Subbetic Domain and neighboring basins of the Western Tethys (
Site | Level | Sample | Taxa | Author | Family | nL | ntL | Chronozone |
---|---|---|---|---|---|---|---|---|
Algueda | Z2 C2 | Z2 C2-2g |
|
Dubar, 1931 | Lobothyrididae | 14 | 17 | Serpentinum-lowermost Bifrons (LT-MT) |
Algueda | Z2.C2 | Z2.C2-1g |
|
Dubar, 1931 | Lobothyrididae | 14 | 17 | Serpentinum-lowermost Bifrons (LT-MT) |
Algueda | Z2.C1 | Z2.C1-1g |
|
Davidson, 1852 | Basiliolidae | 3 | 3 | Lower Serpentinum (LT) |
Algueda | Z2.B | Z2.B-2g |
|
Dubar, 1931 | Lobothyrididae | 3 | 7 | Uppermost Emaciatum-Polymorphum (UP-LT) |
Algueda | Z2.B | Z2.B-1g |
|
Dubar, 1931 | Lobothyrididae | 3 | 7 | Uppermost Emaciatum-Polymorphum (UP-LT) |
Algueda | Z2.A | Z2.A-2g |
|
Oppel, 1861 | Prionorhynchiidae | 8 | 15 | Lavinianum-Emaciatum (P) |
Algueda | Z2.A | Z2.A-1g |
|
Oppel, 1861 | Prionorhynchiidae | 8 | 15 | Lavinianum-Emaciatum (P) |
Algueda | Z1.B | Z1.B-2g |
|
Zieten, 1832 | Prionorhynchiidae | 49 | 168 | Lavinianum-Emaciatum (P) |
Algueda | Z1.B | Z1.B-1g |
|
Zieten, 1832 | Prionorhynchiidae | 49 | 168 | Lavinianum-Emaciatum (P) |
Cerro Cruz 2 | CC2.9 | CC2.9 |
|
Zieten, 1832 | Prionorhynchiidae | 7 | 136 | Lavinianum-Emaciatum (P) |
Cerro Cruz 2 | CC2.6 | CC2.6-2g |
|
Zieten, 1832 | Prionorhynchiidae | 5 | 64 | Lavinianum-Emaciatum (P) |
Cerro Cruz 2 | CC2.6 | CC2.6-1g |
|
Prionorhynchiidae | 1 | 64 | Lavinianum-Emaciatum (P) | |
Cerro Cruz 2 | CC2.5 | CC2.5-2g |
|
Gemmellaro, 1874 | Wellerellidae | 17 | 47 | Lavinianum-Emaciatum (P) |
Cerro Cruz 2 | CC2.5 | CC2.5-1g |
|
Gemmellaro, 1874 | Wellerellidae | 17 | 47 | Lavinianum-Emaciatum (P) |
Cerro Cruz 2 | CC2.4 | CC2.4-2g |
|
Wellerellidae | 27 | 141 | Lavinianum-Emaciatum (P) | |
Cerro Cruz 2 | CC2.4 | CC2.4-1g |
|
Wellerellidae | 27 | 141 | Lavinianum-Emaciatum (P) | |
Cerro Cruz 2 | CC2.3 | CC2.3-2g |
|
Wellerellidae | 26 | 197 | Lavinianum-Emaciatum (P) | |
Cerro Cruz 2 | CC2.3 | CC2.3-1g |
|
Gemmellaro, 1874 | Wellerellidae | 26 | 197 | Lavinianum-Emaciatum (P) |
Cerro Cruz 2 | CC2.2 | CC2.2-2g |
|
Gemmellaro, 1874 | Wellerellidae | 28 | 263 | Lavinianum-Emaciatum (P) |
Cerro Cruz 2 | CC2.2 | CC2.2-1g |
|
Gemmellaro, 1874 | Wellerellidae | 28 | 263 | Lavinianum-Emaciatum (P) |
Cerro Cruz 2 | CC2.1 | CC2.1-1g |
|
Zieten, 1832 | Prionorhynchiidae | 71 | 210 | Lavinianum-Emaciatum (P) |
Cerro Cruz 2 | CC2.0 | CC2.0-2g |
|
Prionorhynchiidae | 25 | 210 | Lavinianum-Emaciatum (P) | |
Cerro Cruz 2 | CC2.0 | CC2.0-1g |
|
Zieten, 1832 | Prionorhynchiidae | 110 | 210 | Lavinianum-Emaciatum (P) |
Cerro Cruz 1 | CC1.11 | CC1.11-1g |
|
Spiriferinidae | 2 | 34 | Lavinianum-Emaciatum (P) | |
Cerro Cruz 1 | CC1.10 | CC1.10-2g |
|
Böckh, 1879 | Prionorhynchiidae | 1 | 198 | Lavinianum-Emaciatum (P) |
Cerro Cruz 1 | CC1.10 | CC1.10-1g |
|
Jiménez de Cisneros, 1923 | Prionorhynchiidae | 3 | 198 | Lavinianum-Emaciatum (P) |
Cerro Cruz 1 | CC1.8 | CC1.8-2g |
|
Oppel, 1861 | Prionorhynchiidae | 111 | 392 | Lavinianum-Emaciatum (P) |
Cerro Cruz 1 | CC1.8 | CC1.8-1g |
|
Oppel, 1861 | Prionorhynchiidae | 111 | 392 | Lavinianum-Emaciatum (P) |
Cerro Cruz 1 | CC1.6 | CC1.6-2g |
|
Spiriferinidae | 20 | 38 | Lavinianum-Emaciatum (P) | |
Cerro Cruz 1 | CC1.6 | CC1.6-1g |
|
Spiriferinidae | 20 | 38 | Lavinianum-Emaciatum (P) | |
Cerro Cruz 1 | CC1.1 | CC1.1-1g |
|
Rothpletz, 1886 | Prionorhynchiidae | 11 | 311 | Raricostatum-Aenigmaticum (US-LP) |
Cerro Cruz 1 | CC1.0 | CC1.0-1g |
|
Quenstedt, 1852 | Wellerellidae | 29 | 87 | Raricostatum-Aenigmaticum (US-LP) |
Sierra Pelada | BOL-1 | BOL-1-1g |
|
Quenstedt, 1852 | Wellerellidae | 44 | 309 | Raricostatum-Aenigmaticum (US-LP) |
Sierra Pelada | BOL-2 | BOL-2-1g |
|
Quenstedt, 1852 | Wellerellidae | 123 | 198 | Raricostatum-Aenigmaticum (US-LP) |
Sierra Pelada | EFC-0 | EFC-0-1g |
|
Quenstedt, 1852 | Wellerellidae | 78 | 187 | Raricostatum-Aenigmaticum (US-LP) |
Sierra Pelada | EFC-1 | EFC-1-1g |
|
Quenstedt, 1852 | Wellerellidae | 139 | 323 | Raricostatum-Aenigmaticum (US-LP) |
Sierra Pelada | EFC-2 | EFC-2-1g |
|
Quenstedt, 1852 | Wellerellidae | 215 | 515 | Raricostatum-Aenigmaticum (US-LP) |
Sierra Pelada | EFC- 3 | EFC-3-1g |
|
Quenstedt, 1852 | Wellerellidae | 48 | 118 | Raricostatum-Aenigmaticum (US-LP) |
Ephebic/adult individuals were selected to avoid ontogenetic effect. Likewise, preservation of the shell was analysed near the mid-length. Possible signs of diagenetic alteration were studied on 45 samples with a binocular microscope and carried out by high-resolution microphotographs of acetate peels taken with a Nikon CFI60 600POL microscope. In addition, sections of the brachiopod shells were carbon coated and analysed with images of secondary electrons, cold cathodoluminescence and EDX (energy-dispersive X-ray spectroscopy) elemental mapping in a Merlin Carl Zeiss Scanning Electron Microscope (SEM) at the Centro de Instrumentación Científico-Técnica of the University of Jaén (Spain). Mn2+, Mn4+, Cr3+ and Pb2+ are the main activators of luminescence in carbonates (
Therefore, a total of 38 specimens have been analysed assuming that biogenic calcite from the secondary layer of these brachiopod shells and consequently their shifts in trace elements content reflect variations in concentration in the water column. This is consistent with several studies (
Texturally well-preserved brachiopod shells (
Diagenetic alteration is absent as shown by the excellent preservation of the calcite fibres. A Microphotograph of a section performed in
Diagenetic alteration is discarded as shown by the absence of cathodoluminescence. The EDX elemental mapping only recognised C, O, Ca, Mg, Na, K and Si. Other elements are very scarce and they are only detected with ICP-MS. A. Secondary electron image. B. Cathodoluminiscence image. C - F. Selected EDX elemental maps for Ca, Mg, K and Si.
A statistical analysis was applied using SPSS vs. 26 (IBM). Descriptive statistics summarize features of trace elements in the brachiopod shells. Concentration profiles and variations of trace elements were plotted against the stratigraphical section. Finally, a Principal Component Analysis (PCA) applied to the database, as exploratory method for variable reduction, to establish the structure of the variable dependence and interrelationship between trace elements. PCA evaluates variable groupings within multivariate data by calculating principal components for a given percentage of the total variance. These components are computed by coefficients or scores, which include: (1) the absolute value of the coefficients (high values in several coefficients of the same principal component show a close relationship between them) and (2) the sign of the coefficients (the same or opposite sign of several coefficients shows the direct or inverse relationship between them).
In the lowermost deposits (samples EFC3 to CC1.0), the analysed brachiopod shells predominantly belong to
In the middle part of the Lower Jurassic succession, the analysed shells are among the prevailing taxa of Assemblage 2 (
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,
Finally,
Concentration values of the trace elements and their distribution by samples have been displayed in box-plots
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).
|
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 |
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
|
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 |
|
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 |
|
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 |
|
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 |
|
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 |
|
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 |
|
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 |
|
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 |
|
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 |
|
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 |
|
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 |
|
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 |
|
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 |
|
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 |
|
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 |
|
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 | |
|
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 |
|
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 |
|
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 |
|
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 |
|
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 |
|
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 |
|
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 |
|
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 |
|
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 |
|
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 |
|
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 |
|
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 |
|
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 |
|
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 |
|
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 |
|
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 |
|
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 |
|
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 |
|
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 |
|
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 |
|
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 |
|
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 (
All concentration values are given in ppm.
All concentration values are given in ppm.
A first positive excursion has been detected at the Sinemurian-Pliensbachian transition in the
An important positive excursion for Mg, Fe, Mo, Ni, Cr, Zn, and Pb is recorded in
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.
Trace elements scores clustered in terms of their possible source.
PC1 | PC2 | PC3 | |
---|---|---|---|
Mg |
|
-0.316 | 0.048 |
Al |
|
0.064 | -0.083 |
Ti |
|
0.374 | 0.077 |
V | 0.562 | -0.307 |
|
Cr | 0.441 |
|
0.203 |
Mn | 0.35 | -0.253 |
|
Fe |
|
-0.095 | 0.431 |
Co |
|
0.078 | 0.006 |
Ni | 0.408 |
|
0.061 |
Cu | 0.48 |
|
0.055 |
Zn | 0.237 |
|
0.273 |
Rb |
|
-0.027 | -0.115 |
Mo | 0.355 |
|
0.066 |
Cd |
|
0.259 | -0.094 |
Ba |
|
0.394 | -0.064 |
Pb |
|
0.342 | 0.033 |
U | 0.346 | -0.33 |
|
La |
|
-0.061 | 0.029 |
Ce |
|
-0.006 | -0.139 |
Nd |
|
-0.14 | -0.141 |
Sm |
|
-0.121 | -0.181 |
Eu |
|
-0.125 | -0.174 |
Gd |
|
-0.12 | -0.153 |
Tb |
|
-0.158 | -0.162 |
Dy |
|
-0.152 | -0.129 |
Ho |
|
-0.207 | -0.119 |
Er |
|
-0.191 | -0.074 |
Tm |
|
-0.237 | -0.056 |
Yb |
|
-0.225 | -0.005 |
Lu |
|
-0.292 | 0.008 |
% varianza | 61.37 | 15.22 | 6.54 |
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 (
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.
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
Fe, REE, and Ba present a high correlation coefficient, congruent with an origin from detrital input from continental influx but also with a same behaviour in the incorporation to the brachiopod shell. Ni, Zn, and Cr present a different way of incorporation to the shell compared to Al as indicated by the low correlation coefficients. There is not a clear differentiation according to the taxa, except for a slight variation for
The most common elements in the shells (excluding Ca) are Mg, Al, and Fe (
In the peri-Iberian platforms system, recent analysis performed in different macroinvertebrate taxa by
Following with the most abundant trace elements, Cr, Ni, and Zn, included in the PC2 axis (
Continental input (affected by tectonic events as well as climate changes) would be the main supplier of trace elements to the ocean (included micronutrients). Volcanism as that recorded in the Median Subbetic (
The next most abundant elements in the brachiopod shells are Ti and Ba (< 10 ppm,
Copper and vanadium are also essential nutrients for marine plankton as well (
With respect to the Cd (PC1 axis),
With respect to the REE, the main sources to the modern oceans are river inputs and atmospheric dust (
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 (
The extinction interval of the early Toarcian is preceded by environmental perturbations, as recorded in the content of trace elements in the shells during the so-called pre-extinction phase. Maximum values of trace elements in the shells are also related to: a) palaeotemperature-weathering interaction (blue for cooling and orange for warming;
The definitive extensional collapse of the platform system is evidenced in the South-Iberian Palaeomargin by faulting and blocks tilting (
The late Pliensbachian interval coincides with the great speciation phase of the benthic biota in the Western Tethys as a whole (cf.
The early Toarcian mass extinction event (
The lowermost Serpentinum hyperthermal event coinciding with the biotic crisis (
After the Jenkyns Event, the repopulation began with
The increase in concentration of the analyzed trace elements in brachiopod shells could be mainly related to: oxygenation degree, external inputs and productivity:
Oxygen depleted conditions: Some of these trace elements are redox sensitive and are related to sulfides and organic matter, which preservation is favoured under reduced conditions;
External inputs: The higher concentration in the seawater as dissolved phase would result from increased inputs from emerged areas or proliferation of submarine volcanic activity;
Increase in productivity: Some of these trace elements are strongly complexed by dissolved organic matter and particulate organic matter used for brachiopod feeding.
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 (
The biological cycling mostly affects to Mo, Cu, Ni, Zn, Cd, Co, Fe, and V (
Special attention is paid on the Mg concentrations (
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 (
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
The diversity dynamics (burst in brachiopod species) and recent taphonomic assessment of these deposits (
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 (
The increased tectonic activity related to fragmentation of the South-Iberian Palaeomargin (
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.
This timespan is typified by enrichment in most of the trace elements, especially in those related to be proxies of continental influx (PC1,
The brachiopod diversity peak and turnover episode, with the demise of endemic Sinemurian fauna (e.g.
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.
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 (
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.
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 (
Many authors have proposed a global warming related to the negative CIE of the Jenkyns Event and the correlative T-OAE (e.g.
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
Some trace elements such as Ti, Fe, and REE, considered as reliable proxies of possible continental influx (
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 (
Trace element contents have been analysed on brachiopod shells derived from Lower Jurassic deposits from the South-Iberian Palaeomargin (Eastern Subbetic) revealing significant fluctuations throughout the late Sinemurian-early Toarcian (Raricostatum-Serpentinum zones).
The Sinemurian-Pliensbachian transition reveals the first main positive excursions of trace elements (Mo, Ni, Cr, Ba, Pb, Ti, Cd, Zn), REEs, and Fe content in brachiopod shells. This excursion is concurrent with a palaeotectonic event, the initial pulses of drowning of the South-Iberian platform system, a global warming episode, and a renewal and burst of brachiopod communities, which correlates with an enhanced weathering and submarine volcanism and delivered trace element to the marine basin. As a consequence, these trace elements were present as dissolved phases in the seawater, incorporated to phytoplankton, complexed in particulate organic matter, and subsequently incorporated to the shells through brachiopod metabolism. Facies analysis excludes major oxygen depletion and thus enrichment of brachiopod shells in these elements is not linked to pulses of oxygen depleted conditions in the South-Iberian Palaeomargin.
Several positive excursions of trace elements in brachiopod shells (Mo, Ni, Cr, Zn, Pb, REE) are recorded in the upper Pliensbachian-lower Toarcian (Emaciatum-Polymorphum zones), with a peak just in correspondence with the onset of the Jenkyns Event, prior to the extinction boundary of this biotic crisis. These pulses show a high correlation with global trends in the C and O cycling oscillations, suggesting a multi-phased stage in this biotic crisis, and concurring with the first record of the koninckinid fauna, regarded as precursor of the Jenkyns Event. Sedimentary evidences, low TOC content, and the maximum brachiopod diversity reached just prior to the Jenkyns Event do not point to sea-bottom waters deoxygenation as the primary factor for this crisis in the South-Iberian Palaeomargin. Newly, global warming and correlative enhanced weathering and subsequent input of terrigenous and nutrients to the seawater can be reflected in the trophic resources of brachiopods and manifested in the shell composition.
The sudden occurrence of warmer brachiopod assemblages suggests a thermal maximum around the uppermost Emaciatum-Polymorphum zones, just prior to their total extinction, not surpassing the hyperthermal event of the Serpentinum Zone. On the other hand, increase on reliable proxies of higher primary productivity (e.g. Cd and Zn) in the pre-Jenkyns Event interval and just in the onset of the repopulation interval is in good accordance with the increasing brachiopod diversity.
Trace element contents gradually decrease during the post-Jenkyns Event interval, coinciding with the repopulation led by the opportunistic
The correlation of the geochemical imprints with critical brachiopod bioevents and the episodes of evolution of the westernmost Tethyan basins allows increasing fidelity of the record of major environmental shifts around the Sinemurian-Pliensbachian boundary and the Jenkyns Event in the South-Iberian Palaeomargin and for a more detailed reconstruction of changes in the main palaeocological parameters.
This research is a contribution to the IGCP-655 (Toarcian Oceanic Anoxic Event: Impact on marine carbon cycle and ecosystems), and was supported by projects CGL2015-66604-R, CGL2015-66835-P and PID2019-105537RB-100 (MINECO, Government of Spain) and P20_00111 (Junta de Andalucía), and the Research Groups VIGROB-167 (University of Alicante) and RNM-200 (University of Jaén). Authors expres gratitude to all who performed analytical research and technical and human support provided by the CICT of Universidad de Jaén. This contribution has benefited by the constructive comments by two reviewers (Dr. M. I. Benito and one anonymous).