FACTORS CONTROLLING THE SEDIMENTARY EVOLUTION OF THE KIMMERIDGIAN RAMP IN THE NORTH IBERIAN BASIN (NE SPAIN)

The aim of this paper is to summarize the present knowledge reached by the authors on the carbonate ramp which developed in the iberian basin during Kimmeridgian times. Our results were obtained from a combined field analysis and computer modelling carried out in the north Iberian Chain (NE Spain). Extensive field analysis in the Ricia area (Zaragoza, NE Spain), resulted in a detailed mapping of the transition from inner to outerramp facies on this carbonate rampo Three facies belts may be distinguished in this rampo The outer ramp facies consists of marls and mudstones rhythmic facies. The inner ramp facies, located aboye fair-weather wave base, are dominated by coral patch reef growing. The middle ramp facies are represented by marls and micrites bearing skeletal and oolitic tempestite levels which sharply grade into high-amplitude o'olitic sandwave. Factors such as resedimentation by storms, carbonate production and relative variation of sea level acting in the Kimmeridgian ramp are also quantiphied and discussed. Most of the mud accumulated in outer-ramp areas was produced in the coral «carbonate factory» located in inner areas. Off-shore resedimentation by storm was the main agent of basinward transport of this mudo The deduced accommodation curve consists of three elements: a linear rise which satisfactorily matches the normal subsidence figures observed in intracratonic basins; a third-order cycle, that may have a regional cause and higher order cycles in the Milanckovich band, that may be eustatic in origino


Introduction
Shallow epeiric seas covered most of the central and south european intracratonic basins during late lurassic times.Sedimentation in low-angle carbonate ramps dominated on these basins.The Iberian basin (NE Spain) was an intracratonic basin covered by a shallow epeiric sea.A very extensive carbonate ramp developed during Kimmeridgian times in the Iberian basin.The analysis of this ramp is constrained by two important features: excellent exposition, allowing accurate reconstruction of proximal to distal ramp sections, and time framework for correlation, provided by a well-defined ammonite biostratigraphy (Aurell, 1991).
Recent computer and outcrop modelling carried out in the Kimmeridgian of the north Iberian Chain provided sorne quantitative data on this carbonate rampo A cross-section 200 Km wide, extending from inner to distal outer of the ramp, has been recently modelled by Aurell et al. (1994) with the aid of the computer program CARBONATE introduced by Bosence and Waltham (1990).On the other hand, extensive field analysis in the Riela area (Zaragoza, NE Spain) resulted in a detailed mapping on the transition from rhythmic outer-ramp facies to oolitic and coral-reef inner ramp facies (Bádenas et a!., 1993).
The aim of this paper is to summarize the present knowledge reached by the authors on the carbonate ramp which developed in the Iberian basin during Kimmeridgian times.Extensive facies analysis and computer modelling resulted in the quantiphycation of a set of parameters as production rates, off-shore resedimentation or accommodation curve.This quantiphication, combined with the data provided from the sedimentological analysis of the Riela outcrops, gives sorne information which allow to further discuss on the factors which controlled the sedimentary evolution of the Kimmeridgian ramp in the north Iberian basin.

Geological setting and palaeogeographical remarks
The Iberian basin, located NE of Spain (fig.lA), was an intracratonic basin which was filled-up by sha-Ilow marine and continental sedimentary units during Mesozoic times.The evolution and amount of accommodation in the basin was mainly controlled by discontinuous tectonic activity, which involved the reactivation of sorne basement faults.Tectonicaly stable episodes are also detected alternating with theses episodes of tectonic activity and resulted in deposition of shallow-marine units in extensive, low-angle ramp setting.
Sedimentation in the Iberian basin took place in shallow and extensive ramp settings (several hundreds of kilometers) during late lurassic times.Phases of local activity of sorne basement faults occurred only at the Oxfordian-Kimmeridgian boundary and at the latest lurassic.These tectonic phases involved the uplift of the marginal areas and a correlative basinwards shift of coastal facies.
The late-Jurassic ramps opened towards the East, into the Tethys sea.However, during major flooding episodes (Le., middle Oxfordian and early Kimmeridgian) connection with boreal realms was possible across the so-called Soria seaway (fig.lA).At the onset of the late lurassic a series of palaeogeographic highs are detected, such as the so-called Ejulve high (Bulard, 1972;Salas, 1989;Aurell, 1990;Alonso and Mas, 1990;Aurell and Meléndez, 1993).

The late Jurassic depositional sequences
The late Jurassic of the Iberian basin consists of three depositional sequences (sensu Haq eta!., 1987), i.e., Oxfordian, Kimmeridgian and Tithonian-Berriasian sequences.These depositionai sequences were studied in the central part of the Iberian basin, by the measurement of 65 stratigraphic sections (Aurell, 1990).Further research on these sequences was carried out by Alonso and Mas (1990) in the northwest part of the basin, with additional measurement of 20 sections.Each depositional sequence developed different ramps which were successively dominated, in their middle and distal areas, by sponge and ammonite wackestone facies (Oxfordian sequence), thick rhythmic mudstones and marl alternation (Kimmeridgian sequence) and grain-supported oncolitic and skeletal facies (Tithonia-Berriasian sequence).
This report deals with the Kimmeridgian sequence.Sorne selected stratigraphic sections on figure 2 display the main lithological features of the Kimmeridgian sequence across the more complete transverse section, which is located at the north part of the basin (see fig. 1 for location).Systems tracts and facies distribution in this sequence have been described in detail by Aurell (1991) and Aurell and Meléndez (1993).Below we outline the facies distribution observed in the Kimmeridgian sequence.

Facies and systems tracts distribution in the Kimmeridgian sequence
The lower boundary of the sequence is represented by a subaereal exposure surface in western inner areas of the ramp, which were located in the shallo-  Aurell and Meléndez (1993) and Alonso and Mas (1990).
west realms of the Soria Seaway.In these areas (see fig. lB) the sequence boundary is an uneven ferruginous surface overlaying the shallowest siliciclastic and carbonate banks of the Oxfordian sequence.These contain numerous evidences for subaereal exposure, such as karstic surfaces or partly reworked edaphic layers (Alonso and Mas, 1990).In middle and outer areas of the ramp, a horizon rich in ferruginous particles with an associated hiatus affecting the upper part of the last Oxfordian biozone (i.e .. Planula zone, Planula subzone) separates the Oxfordian and Kimmeridgian sequences.No evidences for subaereal exposition associated to this surface have been found so far.
The lower part of the Kimmeridgian sequence or lowstand systems tract is formed by a sandy marly unit (Le., Sot de Chera Fm p.p.) which reach its maximum thickness in the middle areas of the ramp.where it can be up to 50 m thick (fig.lB).Based on both the thickness and facies distribution of the marls and sandstones at the bottom of the Kimmeridgian sequence, a tectonic origin for the Oxfordian-Kimmeridgian sequences boundary, and for the new accommodation created during deposition of this lowstand marls, was proposed in Aurell and Meléndez (1992).Tectonic quiet conditions were restored at the onset of the Kimmeridgian.The first marine flooding surface across the Kimmeridgian ramp or transgressive surface is earliest Kimmeridgian in age (Platynota zone, Desmoides subzone) and is clearly represented in the distal part of the ramp, where the lowstand marls are overlain by a series of ammonite wackestones via sharp, pianar surface.The overlaying ammonite facies or transgressive systems tract are earlY Kimmeridgian in age and are generally reduced in thickness.The areal extent of these condensed ammonitic facies in the outer part of the ramp is shown in figure lC, facies E.
In the middle part of the ramp a rhythmic alternation of marls and mudstones containing scattered benthic fossils (brachiopods, bivalvs, crionids) was deposited (fig.lC, facies D).These rhythmic series grades landward into marls containing evidences for deposition aboye storm wave base, as graded beds bearing sedimentary particles resedimented from proximal environments (fig.lC, facies C).Besides oolitic facies, in the more inner areas located to the north, coral rich facies are also observed (fig.lC, facies A and B).
The relative sea-level rise during the early Kimmeridgian produced a retrogradational facies geometry.Change to aggradational and progradational facies architecture at the early-late Kimmeridgian boundary implies a change from transgressive to highstand systems tract.A prominent hard-ground surface capping the earlY Kimmeridgian ammonitic facies in the distal part of the ramp is interpreted as the maximum flooding surface of the Kimmeridgian sequence.In outer areas of the ramp, this highstand unit contains ammonites ranging in age from late Kimmeridgian to earliest Tithonian (i.e., Hybonotum biozone, Atrops and Meléndez, 1985).The lateral component of the progradation during this highstand systems tract ranges between 25 to 40 Km (compare lateral extension of facies A and B in figs.lC and ID).In western, proximal are as of the basin, the upper boundary of the sequence is an angular unconformity (Aurell, 1991 ).

Computer Modelling
Conventional sedimentological and stratigraphic analysis arrives at an understanding of facies, facies models and sequence stratigraphy.Computer modelling is probably the best technique by which the different controlling rates may be quantified, as it allows the quantitative analysis of the different controlling parameters.AIso the complex interaction of these effects can be studied in a logical way.It is important to remember that modeling only gives a rang of solutions, and that the results are not unique and therefore cannot be correct or prove any one solution (Aurell et al., 1994).
A cross-section reconstructed from the Kimmeridgian sequence of the northern part of the basin was modelled with the computer program CARBONA-TE introduced in Bosence and Waltham (1990).This section is 200 Km in length and expose facies from proximal to distal areas of the ramp (figs. 1 and 2).Facies, geometries and the decompacted thickness of this section is shown in figure 3.Because lowstand systems tract of the Kimmeridgian sequence is partly related to tectonic activity (see above), only transgressive and highstand systems tract were modelled.Bellow we summarize the results presented in Aurell et al. (1994).

Input data and results
In order to carry out the computer modelling and to generate the synthetic stratigraphies various data concerning the initial surface of ramp growth, the geometric and the temporal scaling of the ramp and the rates of sedimentological processes acting on the ramp are required.The thicknesses were corrected for decompaction prior to the modelling, because the current version of the computer model does not take into account compaction.Observed thicknesses were decompacted taking into account both the original textures and the burial depth of the sediments, according to the tables presented in Bond and Kominz (1984).On the other hand, the initial topographic surface at the bottom of the transgressive systems tract of the Kimmeridgian sequence is assumed to be a very low-angle slope surface, slightly dipping to the East, into the more open-marine realms.
The time scale for the deposition of these sedimentary units is based on a well-established ammonite biozonation (Atrops and Meléndez, 1985).To transform this biostratigraphic scale into geological time, we first assumed that the geological time covered for each Kimmeridgian ammonite biozone is equal.According to that, and assuming the time scale proposed in Harland et al. (1990), the length of the transgressive and highstand systems tracts of the Kimmeridgian sequence is 1.1 and 1.7 My respectively.
A local, relative sea-Ievel curve for the variation of accommodation was constructed for Kimmeridgian sequence (fig.4A).This curve includes, both a linear rise of 4 cm/Ky and a low-amplitude third order cycle (i.e., 15 m), and results in faster creation of accommodation during deposition of transgressive systems tract.To this accommodation curve a set of higher order cycles were introduced.The closests matches between synthetic and actual geometries from our modelling were obtained when cycles of 100 and 20 Ky with amplitudes of between 4-5 and 1-2 m respectively were input.These cycles were deduced from Crevello (1991) from the study of early Jurassic platforms of Morrocco.
A curve of variation of carbonate production rates with depth was also deduced by model matching the synthetic and the actual stratigraphies (fig.4B).For our modelling we increase production from a negative value in the intertidal to a maximum figure of 8 cm/Ky which is heId 1 to 10 m depth and then reduced to a straight line to a value of 2 cm/Ky at the depth of storm wave base, assumed to be located around 50 m.These values, which are 1 to 2 orders of magnitude lower than the production rates observed in the recent shallow-water open marine carbonate environments, are in coherence however with the figures observed in sorne recent restricted environments (minimum figures in the Florida Bay are 1 cm/Ky, Enos, 1991) or in open ramp (e.g., West Florida carbonate ramp-slope, around 5 cm/Ky; Roof et al., 1991).It should be also noted that these figures are comparable to values obtained from ancient carbonate platforms.Sedimentary rates in the four Jurassic platforms compiled by Enos (1991) range between 1.5 and 9.5 cm/Ky.Similar figures of carbonate production were obtained from computer modelling of carbonate ramps developed in ancient epeiric platforms (Aigner et al., 1990;Elrick and Read, 1991).Finally, erosion and redeposition was carried out in two ways in the programo First, muddy sediments are eroded at definable rates (average value of 10 cm/Ky) down to zero at a definable wave base (average value of 10 m).Second, mud produced in the shallow-proximal ramp was transported basinwards at a distance of 40 Km.This figure is based on both matching of the synthetic and the actual strati-graphies, and the observed facies distribution.In coherence with that, the belt defined by the facies containing mud transported from proximal domains of the ramp (i.e., rhythmic alternation of marls and mudstones, see discussion below) is 30 to 50 Km wide (facies D in figs.le and ID).

Facies analysis in the Riela area
Field evidences and computer modelling indicate that erosion and redeposition by storms were important processes acting on this Kimmeridgian rampo This supports evidence from other ramps described from ancient epeiric seas as storm dominated systems (e.g., Aigner, 1985).Storms and marine circulation produce significant erosion, transport and resedimentation to outer areas of the ramps.Basinward transport is favoured by the flat topography, with no physical barriers.
This general approach has sorne relevance in order to better understanding the origin of the rhythmic alternation of marls and mudstones covering wide areas of theKimmeridgian ramp in the Iberian basin.One point that should be addressed is the relationship between these micritic, outer-ramp facies and the coraline and oolitic facies which were originated and deposited in the shallow to inner realms of the rampo To answer this question, we carried out a detailed facies analysis in the outcrops near Ricia, west to Zaragoza (see section 3 in fig. 1 for location).These outcrops allow to examine the Kimmeridgian ramp in a key point.From them, a 6.5 Km long section nearly transversed to the ramp, showing the transition from outer ramp facies (Le., Loriguilla Fm) to inner ramp facies (Le., Torrecilla Fm, Riela Mb) may be examined in detail.
The Kimmeridgian sequence consists of three sedimentary units in the Riela outcrops: Sot de Chera Fm, Loriguilla Fm and Torrecilla Fm (see fig. 2, section 3).In Riela, the Torrecilla Fm consists of a wide spectrum of facies, ineluding cross-bedded oolitic grainstones, well cemented sandstones and microconglomerates, coraline boundstones, skeletal wackestones to packstones and mudstones, and was defined as a Riela Mb by Aurell et al. (1989).According to these authors, the Riela Mb is late Kimmeridgian in age and corresponds to the upper part of the highstand systems tract of the Kimmeridgian sequence.A detailed facies analysis has been presented in Bádenas et al. (1993).Bellow, we summarize the main results of this work.

Facies distribution on the Riela Member
Three facies associations were distinguished in the Riela Mb: 1. Association 1: The facies of this association can be grouped in two members; the lower member is mainly silielastic, whereas the upper one mainly consists of oolitic facies.In the transition between Loriguilla Fm and Riela Mb, a set of shallowing-upwar sequences (ca. 1 m thick) of bioelastic sandstones and trough cross-Iaminated microconglomerates is present.Sharply overlaying this silicielastic facies, an up to 20 m thick wedge-shaped-unid of oolitic facies is found.To the north the oolitic unit consistis of two stacked units, each one of them having a lower wellbedded burrowed marls, sandstones and oolitic grainstone facies, and an upper oolitic grainstones showing high-scale planar-cross bedding.The oolitic unit pinches out to outer areas of the ramp located to the south, and laterally grades into low-amplitud oolitic bars which are interbedded between the lower silicielastic facies.
2. Association 11: At the bottom of this association of facies a very continuous oncolitic level (Le., wackestones to packstones) is found.Oncoids are irregularly coated and have bioelastic cores (mainly corals).In northern areas, a set of patch-reef (c.1-3 m thick) rich in corals, chaetetids and red algae, overlies this oncolitic level.This coral facies grades to the south into well-bedded mudstones bearing in-tercalations of both rippled sandy levels, oolitic to bioclastic grainstones-packstones arranged in lowamplitude bars, and intraclastic grainstones composed of well-rounded clasts which generally display primary rim-cements.

Sedimentary evolution
The three aboye described facies assoclatlüns correspond to three episodes of the sedimentary evolution of the Kimmeridgian ramp in the Ricia area.
1. Episode 1 (Association 1): Fast progradation of a set of oolitic sandwaves over the subtidal facies of the Loriguilla Fm (fig.5.1).The onset of this episode is represented by the progressive shallowing of the facies of the Loriguilla Fm, resulting in both an increase of the siliciclastic input, and in the first nucleation of the oolitic bedforms.In an intermediate stage, development and growing of a set of megarippies and oolitic sandwaves took place.These bedforms prograded up to 3-4 Km over the low-angle ramp as a consequence of storm-generated waves.The last stage of this episode is represented by the stabilization of the sandwaves, which are covered by lower-amplitude oolitic bedforms.
2. Episode 2 (Association 11): Setting of the reef complex (fig.5.2).This second episode represents a sharp transition from the aboye described first episode and is characterized by the development of a reef complex in the inner ramp areas.The transition between the first and the second episode is marked by the presence of a widely distributed oncolitic bed, which was deposited under low sedimentary rates.This oncolitic bed laterally grades into the coral facies to the northern inner areas.These inner ramp areas, extensively colonized by coral and other benthyc fauna, are considered to be the main source of the mud accumulated in outer realms of the ramp, via storm resedimentation.Tempestite levels as graded beds, oolitic rippled levels, or skeletal and oolitic bars are commonly found in outer areas of the ramp, interlayered with well-bedded mudstones.Sorne resedimented grains on these tempestite levels have features developed under litoral environments (i.e., rounded grains, beachrock cements) and evidence the presence of beach environments, which would be located landward to the belt defined by the coral facies.M. AURELL.B. BADENAS 3. Episode 3 (Association I1I): Setting of the restricted lagoonar and palustrine environments (fig.5.3).The high carbonate productivity combined with the effectivity of the off-shore mud resedimentation, involved the progressive infilling of the accommodation in inner ramp areas and the increased restriction of the marine-circulation across the rampo Lagoonar and palustrine facies were deposited behind litoral environments.The main feature of this third episode is the fast progradation of these restricted environments over the aboye described coral and micritic facies which are successively overlain by litoral intraclastic facies, skeletal lagoonar facies and mudstones and plaustrine marls.

The role of storms
Both the field analysis and the computer modelling results presented here rackets a set of parameters which model the sedimentological evolution of the Kimmeridgian ramp developed in the north Iberian basin.These data can be used to discuss the relative importance of the different factors controlling the development and facies distribution on the Kimmeridgian rampo A first process that can be evaluated is the off-shore resedimentation by storms.
Facies analysis of the Ricia outcrops clearly shows that storms were the main agent of off-shore transport and resedimentation.Evidences for fair weather wave or tidal reworking is scarce.This supports the general view of epeiric seas (Tucker and Wright, 1990), with the tides and waves being damped out by frictional effects over the very extensive shallow sea floor.The dominant processes affecting epeiric platform sedimentation would have been storms.
Based on recent environments (e.g., Hine, 1977), progradation of the oolitic sandwaves of Ricia was interpreted to be activated by storms (Bádenas et al., 1993).The seaward progradation of these sandwaves was very fast.Distances of progradation of nearly 4 Km during what it must be a short period of time can be measured in the Ricia outcrops.The rapid progradation rates of the Kimmeridgian ramp is a function not only of the erosion and resedimentation activated by storms but also of the shallow depth and low-angle depositional geometry.Storms are also dominant during the second and third sedimentary episode deduced from the Ricia outcrops.During deposition of the second distinguished episode, it is specially remarkable the relationship between the sha-1I0wer coral-facies and the outer mudstones.And intermediate spectrum of micritc facies with tempestite levels interlayered can be observed.These tem- pestite levels pinch out basinward and they grade into the mudstone facies.
In the Kimmeridgian ramp, basinward sediment transport distances of 40 Km are indicated from the distribution of storm beds, the occurrence of shallowwater allochems, and the model-matching known geometries.Storm wave-base depth considered in our computer modelling is SO m.This figure, which is consistent with the observed in recent partly enelosed basins such as the Persian Gulf, has also been deduced from computer modelling of Mississippian carbonate ramps (Elrick and Read, 1991).

Relationship between coraline and rhythmic mudstones facies
The presented data yield new information about the overall relationship between the inner, coraline facies of the Torrecilla Fm, and the outer, rhythmic mudstones of the Loriguilla Fm.The Riela outcrops only allow a partial view of the Kimmeridgian rampo However, taking into account the general distribution of the facies at the northern part of the basin (i.e., fig.ID), it elearly appears that the oolitic sandwaves of the Riela Mg are spread in an intermediated facies belt located between shallow ramp areas, dominated by coral growing, and relatively deep ramp areas, were deposition of carbonate-mud took place.These sandwaves would be placed in an intermediate depth, below fair weather wave-base, but aboye storm wave-base level.According to the elassification for carbonate ramps recently proposed in Burchette and Wirght (1992), these sandwaves would be located in the middle rampo The inner ramp areas, developed aboye fair weather wave-base, are represented by coraline, litoral and lagoonar facies.The outer ramp domains of the ramp, placed below storm wave-base, consists of a rhythmic alternation of mudstones and marls (fig.6).
Both the facies distribution and the aboye discussed role of the off-shore transport by storms, allow to state that most of the mud accumulated in outerramp areas was produced in the coral «carbonate factory» located in inner areas.Taking into account that storm episodes would be the main agent of basinward transport, it remains unanswered the question of how episodic storms and a single marl-mudstone couple are related.Observations in the Riela outcrops show that each single micritic bed (which grades landward intoc oral facies) may contain, in fact, more than one tempestite level.This observation probes that a single marl-mudstone couple records a complex depositional history, involving more than one storm episode.

The origin of systems tracts and accommodation
The distribution of facies within systems tracts is considered to be the result of the interplay between the accommodation and sedimentary rates.The accommodation depends on eustacy and subsidence rates (Aurell, 1991).We have modeled a depositional sequence which correspond to a third-order cyele.Sequence boundary and lowstand systems tract of the Kimmeridgian sequence were related to a relative sea-Ievel fall produced by tectonic uplift (Aurell and Meléndez, 1993).Transgressive and highstand systems tracts were developed with smaller rates of accommodation.Transition from retrogradational transgressive systems tract to fast progradational highstand systems tract was satisfactory modeled by slightly decreasing the rates of accommodation, thus increasing the capacity of filling the accommodation with sedimento Computer modeling offers an elegant way to discuss about the interplay of eustacy and subsidence creating the accommodation.As exposed aboye, the more satisfactory modelling comes from the superposition of 20 and 100 Ky cyeles onto a both a linear rise of 4 cm/Ky and a low-amplitude third order cyele.The higher-order cyeles are in the Milanckovich band and may be eustatic in origino The magnitude of the linear rise satisfactorily matches the normal subsidence figures observed in intracratonic basins.The origin of third-order cyeles remains uncertain as their timespan and amplitude do not match the eustatic curves proposed by Haq et al. (1987) and Hallam (1988).Conclusions 1.This work offers a sedimentary model for the Kimmeridgian ramp in the north Iberian basin, showing its bathimetry and the distribution of its facies belts.The outer ramp facies, accumulated below storm wave base (i.e., ca.50 to 80 m depth), consists of marls and mudstones rhythmic facies (Le., Loriguilla Fm).The inner ramp facies, located aboye fairweather wave base (i.e., up to 10 m depth), are dominated by coral patch reefs (i.e., Torrecilla Fm).The middle ramp facies are represented by marls and micrites bearing skeletal and oolitic tempestite levels (Le., upper part of the sandy, Loriguilla Fm) which sharply grade into high-amplitude oolitic sandwaves (i.e., Riela Mb).
2. Resedimentation by storms was an important sedimentary process in the Kimmeridgian ramp and helped to maintain the low-angle ramp profile through time.Down-ramp transport distances were measured to be of around 40 Km.Fine-grained sediment produced in inner ramp areas accumulated in outer areas, below storm-wave base level, where micritic rhythmic series are recorded.
3. The deduced accommodation curve for Kimmeridgian sequence consists of three elements: a linear rise of 4 cm/Ky, a low-amplitude third order cyele and both a 20 and 100 Ky sea-Ievel cyeles.The magnitude of the linear rise satisfactorily matches the normal subsidence figures observed in intracratonic basins.The third-order cyele may have a regional cause as the timespan and amplitude of this cyele do not match the ones proposed in the published eustatic curves.The higher order cyeles are in the Milanckovich band and may be eustatic in origino Fig, l.-A) Locality map showing the palaeogeography of the Iberian basin during late Jurassie, B-D) Facies distribution during the successive systems tracts of the Kimmeridgian sequence, In B), open circles to the west indicates areas of no deposition (i.e" subareal exposure), the middle belt consists of marls and interbedded sandstones and the eastern belt is formed by marls (thickness variation is also indicated).Facies legend for C) and D): (A) oolitic grainstones; (B) coral boundstones; (C) marls bearing tempestite levels; (D) mudstones and marls (rhythmic series); (E) ammonite wackestones; (F) sandstonesand sandy mudstones to packstones.Compiled fromAurell and Meléndez (1993) andAlonso and Mas (1990).
Fig. 2.-Selected sections located in the north part of the basin (see fig. 1), indicating also the distribution of systems tracts and sequence boundaries.
Fig. 3.-Facies and thickness distribution (decompacted) for the transgressive and highstand systems tracts of the Kimmeridgian sequence in a section located and the north part of the basin.See figure 1 for location and 1egend of facies (modified fmm Aurell el al., 1994).
Fig. 4.--Curve of relative sea level variation (A) and curve of variation of production rates with depth (B) deduced from computer modelling of the section represented in figure 3 (modified from Aurell el al.• 1994).
Fig. 5.-Sedimentary model for the three successive episodes distinguished in the Kimmeridgian ramp in the RicIa area (from Bádenas el al., 1993).