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Cretaceous Research 34 (2012) 268e283

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Cretaceous Research

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Stratal, sedimentary and faunal relationships in the Coniacian 3rd-order sequence of the Iberian Basin, Spain

José F. García-Hidalgo a, Fernando Barroso-Barcenilla a,b, Javier Gil-Gil a,*, Ricardo Martínez c, Jose Maria Pons c, Manuel Segura a a IBERCRETA UAH Research Team CCTE 2007/R23, Universidad de Alcalá de Henares, 28871 Alcalá de Henares, Spain b Departamento de Paleontología, Universidad Complutense de Madrid, 28040 Madrid, Spain c Departament de Geologia, Universitat Autònoma de Barcelona, 08193 Bellaterra, Spain article info abstract

Article history: The Coniacian 3rd-order sequence in the Iberian Basin is represented by a carbonate ramp-like open Received 3 August 2011 platform. The biofacies is mainly dominated by nekto-benthic (such as ammonites) and benthic Accepted in revised form 12 November 2011 organisms (such as bivalves, mainly rudists) with scarce solitary corals (hermatypics are absent), Available online 25 November 2011 showing major differences among the Transgressive System Tract (TST) and Highstand Normal Regres- sion (HNR). During the TST, platform environments were dominated by Pycnodonte, other oysters and Keywords: molluscs (with only subordinate rudists) and ammonites, which were represented by ornamented Depositional sequences platycones (Tissotioides and Prionocycloceras), and by smooth oxycones (Tissotia and Hemitissotia). During Ammonites Rudists the HNR, shallow water depositional areas were occupied by rudist-dominated associations. Storm- and Coniacian wind-induced currents and waves acting on these associations produced large amounts of loose Iberian Basin bioclastic debris that covered outer platform areas. This facies belt graded landwards into protected, Spain lower-energy settings (inner platform, lagoon and littoral environments). Rudist biostromes were preserved in seaward areas of these protected shallow environments of overall moderate to low hydrodynamic gradient, which was punctuated by storms. In this environment and landwards, large areas of marly substrate favoured the presence of gastropods, other bivalves, echinoderms, benthic foraminifera and solitary corals. Because of the input of siliciclastics and, probably, the lack of nutrients in suspension, the establishment of rudist communities was difficult in more landward areas of the lagoon and in tidal environments. This heterozoan carbonate factory was thus controlled by warm-water conditions and high energy levels, which were responsible for high-nutrient contents in suspension. Ó 2011 Elsevier Ltd. All rights reserved.

1. Introduction margins with the development of thick carbonate platforms (Segura et al., 1989, 2001; Floquet, 1998; Gräfe, 1999; García et al., The Upper Cretaceous carbonate platforms in the Iberian Basin 2004), in which dolomitization processes during early diagenesis are represented by successive transgressiveeregressive 3rd-order did not significantly affect carbonate facies; consequently, fossils sequences, suggesting the presence of extremely dynamic sedi- are common and relevant in both deep and open facies (Barroso- mentary systems over time in this basin. The stacking of these Barcenilla, 2006) and shallow platform facies (Gil et al., 2002, sequences generally shows a similar palaeogeographic pattern with 2009). These sequences are related to the globally recognised a siliciclastic facies belt at the coastal margin and an inner Cenomanian/Turonian boundary and late Coniacian eustatic carbonate platform facies in central areas of the basin (Gil et al., maxima (Haq et al., 1988; Hardenbol et al., 1998). 2006a, 2008; García-Hidalgo et al., 2007). In these facies, bio- Studies of the older sequence (Late CenomanianeEarly Turo- stratigraphically useful fossils are relatively poor because early nian) have been undertaken by Segura et al. (1989, 1993a, b), diagenetic processes (mainly dolomitization) obliterated primary García-Hidalgo et al. (2003, 2007), Barroso-Barcenilla (2006) and sedimentary structures and fossil content. Nevertheless, there are Barroso-Barcenilla et al. (2009, 2011) among others, and have two particular sequences displaying deep and open platform facies provided: (1) a deep understanding of its stratal and depositional in most of the basin, which flooded wide areas of the coastal framework, with a superimposed high-frequency depositional stacking pattern; (2) a detailed biostratigraphy based on ammonite * Corresponding author. Tel.: þ34 918854997; fax: þ34 918855090. faunas, allowing the revision of several ammonite families; and (3) E-mail address: [email protected] (J. Gil-Gil). an understanding of the geological history of this interval.

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In contrast, the palaeoenvironments along the entire basin of northeastern Iberia, the emerged Ebro Massif and different highs the second episode (Coniacian) are less well understood and separated the Iberian Basin from the Pyrenean Trough. Connection previous interest has mainly focused on rudist associations and with the Tethyan Realm occurred discontinuously along south- their vertical successions, fabrics and facies of shallow carbonate- eastern Iberia (García et al., 2004). platform settings (Gil et al., 2002, 2009, among others). In the During these times, the Iberian Microplate was located in the past, the detailed sedimentology and fossil content of the succes- tropical belt, south of a latitude of 30N(Dercourt et al., 2000), and sion were typically overlooked, although biotic communities are was exposed to the warm, circum-global Tethyan current and away particularly important for sedimentological analysis, because they from cold Boreal influences. This palaeogeographic location fav- record ecological and environmental conditions with many oured a warm, humid climate and the proliferation of benthic different features, determining accumulation rates and facies communities in the Tethyan peri-continental areas (Philip, 2003). distribution, thus controlling platform geometry (Pomar, 2001). As a consequence, significant carbonate production together with The Coniacian sequence (named here DS-2), which constitutes a remarkable widespread development of platforms took place in the main objective of this paper, is a superb example of a symmet- the basin. rical depositional event, with faunas and facies of both deep and The significant global eustatic sea-level rise during the Late shallow platform environments that retrogradate and progradate Cretaceous was the main factor controlling the depositional depending on the eustatic signal (system tract). Thus, the main aims episodes in the Iberian Basin (Rat, 1982; García et al., 1996, 2004; of this paper are to: (1) describe the stratal architecture of the Segura et al., 2001; Gil et al., 2004). Owing to the shallow char- sequence from distal platform environments to coastal margin acter of the Iberian Basin, it was particularly sensitive to any sea- areas; (2) identify the main stratigraphic reference surfaces in order level oscillation, registering even those of smaller amplitude to define the system tracts, describing the vertical succession of (high frequency) (Gil et al., 2006a, b; García-Hidalgo et al., 2007). facies in different areas of the basin; (3) describe the faunal Four 2nd order eustatic sea-level cycles have been described for the succession of ammonites, rudists and other bivalves, and their Late Cretaceous in the Iberian Basin (MS-1 to MS-4 megasequences; correlation from carbonate platform to coastal margin areas; (4) Segura et al., 2006). For the interval discussed in this paper, the relate their occurrence with the depositional stacking pattern; and DS-2 sequence represents the transgressive peak and the onset of (5) discuss their biostratigraphic and palaeoecological implications. the regressive phase of the upper Turonianelower Campanian megasequence (MS-2; Segura et al., 2006). 2. Geological setting Several of the stratigraphic sections discussed in this paper (Fig. 1B) have been previously studied by others. The ammonites of The deposition of Cretaceous strata on the Iberian Microplate the Cervera section were first studied by Wiedmann (1975), who took place in an intracratonic basin, with maximum subsidence and erected Hemitissotia celtiberica Wiedmann, 1975 here (for author sediment accumulation rates in the areas between the Hesperian names and dates of all species mentioned in the text, see Table 1); Massif and the Ebro Massif: the Iberian Basin (Fig. 1A). Reduced later the stratigraphy and sedimentology of this outcrop was subsidence in the west and southeast, and siliciclastic sediment described by Floquet (1991). The Castrojimeno section was first input, mainly derived from the Hesperian Massif, resulted in described by Alonso (1981), who reported ammonite and rudist deposition of the Coniacian sequence with an overall wedge- assemblages; more recently it has also been studied by Gil et al. shaped, westwards- and southeastwards-thinning geometry. In (2009), with a description and interpretation of the evolution of

Fig. 1. Location of the study area. A, palaeogeographical scheme of the Iberian Basin within the Tethyan Domain during the Coniacian, indicating main depositional environments and the cross-section of Fig. 7 (red line). B, geographical and geological scheme showing the cross-section of Fig. 7 (red line) and the location of the following reference key sections: 1, Cuevas de San Clemente; 2, Contreras; 3, Hoz de Silos; 4, Hortezuelos; 5, Casuar-Linares; 6, Castrojimeno-Castroserracín; 7, Barranco de las Cuevas; 8, Embalse de Entrepeñas; 9, Estrecho de Paredes. Modified from Gil et al. (2009). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.) Author's personal copy

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Table 1 northwards where it has been recognised as the Nidáguila Taxonomic list of species mentioned in text. Formation (Floquet et al., 1982; Floquet, 1998). The upper member Ammonoidea consists of nodular limestones (subfacies 11; Table 2) grading to Eulophoceras Hyatt, 1903 very thick- and poorly-bedded bioclastic and/or oolitic limestones Forresteria petrocoriensis (Coquand, 1859) (subfacies 22 and 23, respectively; Table 2) with thin marly inter- Hemitissotia Peron, 1897 calations (subfacies 1 or 3 ; Table 2), having a clear and distinctive Hemitissotia celtiberica Wiedmann, 1975 2 1 Hemitissotia turzoi Karrenberg, 1935 morphological expression in outcrops; the thickness of this upper Placenticeras Meek, 1876 member progressively increases southwards, reaching over 50 m, Plesiotissotia cantabria Karrenberg, 1935 (¼ H. turzoi) compensating for the loss of thickness of the middle marly ¼ Plesiotissotia dullai var. plana Karrenberg, 1935 ( H. turzoi) member. Prionocycloceras Spath, 1926 e Prionocycloceras iberiense (Basse, 1947) At the central reference area (sections 5 7inFig. 1B), the lower Pseudoschloenbachia Spath, 1921 member of the Hortezuelos Formation is almost absent (Fig. 3), Texanites gallicus Collignon, 1948 being occasionally represented by a thin set of bioclastic and oolitic Tissotia Douvillé, 1890 thin-bedded limestones (subfacies 22 and 23; Table 2). The thick- Tissotioides Reyment, 1958 ness of the middle marly member has decreased in favour of the Tissotiodes hispanicus Wiedmann, 1960 upper one, which is composed of an alternation of bioclastic, Hippuritoida micritic limestones with rudist buildups (subfacies 21e25; Table 2) Bournonia gardonica (Toucas, 1907) Bournonia fascicularis (Pirona, 1869) and yellow marls (subfacies 31; Table 2). The lower boundary of the Praeradiolites requieni (d’Hombres-Firmas, 1838) Hortezuelos Formation here is the top of the calcareous Caballar Biradiolites canaliculatus d’Orbigny, 1850 Formation, marked by a single hardground and a distinct litho- [Biradiolites angulosus (d’Orbigny, 1842)] logical change (Fig. 3 in Gil et al., 2009) from red tidal dolostones Radiolites sauvagesi (d’Hombres-Firmas, 1838) and stromatolites to inner platform deposits (subfacies 2 e2 ; Hippurites incisus Douvillé, 1895 1 5 [Hippurites resectus Defrance, 1821] Table 2). The overall trend of DS-2 in this area shows several [Hippurites vasseuri Douvillé, 1894] marlstone-limestone bundles (sedimentary cycles), grading from ’ Vaccinites giganteus (d Hombres-Firmas, 1838) outer platform facies (subfacies 11 and 12; Table 2) to inner platform Vaccinites moulinsi (d’Hombres-Firmas, 1838) facies (subfacies 21e25) or even restricted littoral deposits (subfa- Apricardia sp. cies 31; Table 2). In the basal cycles, outer platform facies Gryphaeidae predominate; whereas in the upper cycles, inner platform facies Pycnodonte Fischer von Waldheim (1835) followed by restricted littoral facies are predominant (Fig. 4). Inoceramidae In the SE reference area (sections 8 and 9 in Fig.1B) DS-2 pinches Cladoceramus undulatoplicatus (Römer, 1852) out to a 20-m-thick alternation of marls and dolostones, belonging to the upper half of Alarcón Formation (Fig. 5). DS-2 entirely consists here of restricted littoral sediments grading upwards from different rudist assemblages. Finally, the depositional, biostrati- green marls rich in organic matter (subfacies 43; Table 2) and thin- graphic and chronostratigraphic framework of different coastal bedded dolostones with ripples, wavy and flaser bedding, algal margin sequences at the Barranco de las Cuevas section has been laminations and ferruginous surfaces (subfacies 41; Table 2), to extensively investigated (Gil et al., 2002; Gil and García, 1996, several bed-sets of green marls (subfacies 43; Table 2) and thin- among others). bedded red dolostones (subfacies 41; Table 2) or intensively bio- turbated dolomitised breccias (subfacies 42). 3. Stratigraphic successions, facies and stratal stacking All of these sedimentary areas clearly show a trans- pattern gressiveeregressive depositional trend with a southeastward basal onlap. DS-2 is bounded by two major sequence boundaries (SB-2 Sequence DS-2 is a southeastward-thinning, 90e20 m thick, and SB-3, Figs. 2e5, 7), based on: (1) the presence of major sedi- marly and calcareous wedge. Eight reference sections have been mentary discontinuities and diagenetic overprints; (2) stratal studied in detail to create a composite NNWeSE cross-section relationships (onlap, offlap, toplap) with underlying and overlying (Fig. 1B). From NNW to SSE, DS-2 consists of the Hortezuelos 3rd-order sequences; and (3) the presence of the most important Formation (nodular limestones, bioclastic limestones and fossilif- breaks in the vertical succession of facies, reflecting major changes erous marls) and the upper half of the Alarcón Formation (green in the sedimentary trends below and above DS-2. All of these marls and thin-bedded dolostones) (Gil et al., 2004). Three distinct aspects suggest the existence of significant falls in the relative reference areas (NNW, central and SE), with slightly different sea-level in both cases. stratigraphic successions can be distinguished, owing to the inter- The lower sequence boundary (SB-2) is characterised by digitation of both formations and the presence of several members a widespread hardground with a well-developed lateritic crust and in the Hortezuelos Formation, showing a transition from outer boring structures (Fig. 6A, B), affecting the underlying sediments platform to littoral environments. Facies and subfacies described (DS-1; Gil et al., 2006a). Occasionally, it is also characterised by below, as well as their environmental interpretation, are also collapse dolomitic breccias related to early dissolution of evaporites summarised in Table 2. (Hoz de Silos section; Floquet, 1991; Fig. 4C in Gil et al., 2006b). The Hortezuelos Formation is lithologically subdivided in the From NNW to SE, also a progressively more intense ferruginization NNW reference area (sections 1e4inFig. 1B) into lower, middle and and early dolomitization of the underlying sediments occurred upper members (Fig. 2). The lower member consists of thin-bedded (Gil et al., 2009). Moreover, toplap relationships with at least three bioclastic limestones (subfacies 22) grading upwards to nodular, underlying 5th order parasequences (Gil et al., 2006a) and the basal fossiliferous and intensely bioturbated, micritic limestones (subf- onlap of DS-2 also suggest the existence of a sequence boundary acies 11), alternating with thin marly beds and clayey joints, (SB-2). Finally, a significant landward displacement of the showing a general thickening-upwards trend. The middle member carbonate platform facies belts occurred at this boundary, and mid- consists of fossiliferous grey marls and calcareous mudstones outer shelf carbonate facies (subfacies 23 and 12; Table 2) at the (subfacies 12); the thickness of this member progressively increases base of DS-2 rest on tidal carbonate facies (subfacies 41; Table 2)of Author's personal copy

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Table 2 Summary of main facies associations and subfacies of the DS-2 sequence (Coniacian) in the Iberian Basin, and their environmental interpretation.

Facies association Subfacies Lithofacies Biofacies and bioturbation Environmental interpretation

Outer carbonate 11 Nodular Nodular clayey limestones Gastropods, bivalves, bryozoans, Low-energy, open-marine setting platform limestones (mudstone to wackestone). discorbids, miliolids and green algae. with low sedimentation rate. Outer Poorly-bedded. Ferruginous Bioturbation common carbonate platform environment surfaces. below storm wave base

12 Fossiliferous Massive, grey marls and Oysters, ammonites, irregular echinoids, marls calcareous mudstones isocardiids and other bivalves, gastropods, brachiopods. Locally, oysters and ammonites are bioeroded, ferruginised and colonised by annelids.

Inner carbonate 21 Micritic Thin- to medium-bedded limestones Benthic foraminifera, gastropods, bivalves, Open-marine settings ranging from platform limestones (mudstone to wackestone). solitary corals, thin-shelled bivalve distal to proximal carbonate platform.

Grading-upwards to 22 and 23 fragments. Bioturbation and bioerosion Alternation of low-energy and shoal subfacies. Locally, hard grounds at top at top of beds is locally common settings between storm wave base

22 Bioclastic Coarsening- and thickening-upwards Oyster fragments in the lower part of and fair-weather wave base. limestones limestones (floatstones to rudstones); platform succession and rudist fragments angular to well rounded, and in the upper part. Bioeroded shells imbricated clasts. Reworked common. Rare bioturbation micritic intraclasts are common

23 Oolitic Oolitic and bioclastic limestones Radiolitids, gastropods, echinoderms, limestones (packstone-grainstone). Well-sorted bryozoans and red algae fragments, intraclasts and oolitised bioclasts. benthic foraminifera. Bioturbation Large through and planar absent cross-bedding or massive. Rarely quartz extraclasts

24 Rudist Rudist biostromes, open and Mono- and paucispecific associations boundstromes densely packed, autochthonous of radiolitids, biradiolitids, hippuritids (build-ups) and parautochthonous fabrics and vacinitids. Poorly-sorted rudist alternating with floatstones to fragments rudstones.

Lagoon 31 Yellow marls Yellow and ochre marls and nodular Radiolitids and hippuritids, isolated Lagoonal settings and low-energy clayey limestones. Silt layers. benthic foraminifera. Rudist and other subtidal ponds in back-barrier bivalve bioclasts. Organic matter-rich. ramp-coastal environments Abundant plants fragments and carbonaceous remains. Bioturbation common

Littoral 41 Thin-bedded Thin-bedded to fine laminated Moldic porosity. Plant fragments. Rare Intertidal to supratidal settings dolostones dolostones, red dolostones and sandy bioturbation at top of beds (including swamp and mangrove dolostones. Ripples and wavy bedding. environments) with common Fenestral structures. Pseudocolumnar, presence of acids meteoric waters laterally-linked stromatolites. and siliciclastic inputs Ferruginous surfaces.

42 Dolomitised Nodular to brecciated yellow and Intensive bioturbation breccias brown dolostones; chicken wire

43 Green marls Slaty green marls (yellow when are Organic matter-rich alterated)

Fig. 2. Field view of the upper Turonian 3rd-order sequence below (DS-1) and Coniacian 3rd-order sequence above (DS-2) in the Hoz de Silos section (3 in Fig. 1; Burgos). DS-2 is represented by the Hortezuelos Formation showing three clear lithosomes: a, lower calcareous member; b, middle marly and fossiliferous member; c, upper poorly-bedded calcareous member. *, collapse dolomitic breccias level associated with SB-2 and cited by Floquet (1991) and Gil et al. (2006a, b). Bar for scale is 20 m long. Author's personal copy

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Fig. 3. Field view of the Coniacian 3rd-order sequence (DS-2) in Castroserracín section (6 in Fig. 1B), showing characteristic members of the Hortezuelos Formation (a, b and c, respectively) and the presence of a yellowish marly lithosome (d) of restricted littoral environments (subfacies 31 in Table 2) at top. the underlying sequence (Gil et al., 2009). Thus, the basal onlap and 4. Faunal succession displacement of facies belts suggest a major sea-level fall at the sequence boundary followed by a rapid rise during the subsequent The lower and middle members of the Hortezuelos Formation transgressive stage of the next depositional episode (DS-2). These are barren of rudists and contain ammonites, Pycnodonte and other observations suggest a stratigraphic gap at SB-2. oysters, inoceramids, gastropods and echinoderms. The upper The upper sequence boundary (SB-3) also represents an interval member of the Hortezuelos Formation contains, however, an of interruption of sedimentation with intermittent, minor episodes association of ammonites and rudists along with other bivalves, of subaerial exposure. The presence of the boundary is also shown gastropods and benthic foraminifera. Thus, two different fossil by a sudden, although less pronounced, change in the vertical facies assemblages can be distinguished in DS-2; the first is dominated by trend (first described by Floquet, 1991), and by the presence of ammonites and non-rudistid bivalves found in the TST and external a landward early dolomitization processes, also less intense than (deeper) facies of the HNR; the second is dominated by rudists and those related to SB-2. coincides with the internal (shallower) facies of the HNR. The Maximum Flooding Surface (MFS) of DS-2 is recognised within the middle marly member of Hortezuelos Formation 4.1. Ammonoidea (Figs. 2e4). Deeper water sediments of this member even reached areas of the Iberian Basin that were previously coastal environ- Three different ammonite associations can be distinguished ments in underlying sequences. As a consequence, a stratal stacking within DS-2. Ammonites in the lower association are scarce and pattern of two system tracts can be recognised (Fig. 7): (1) A represented by ornamented platycones (Tissotioides and Prionocy- Transgressive Systems Tract (TST) between SB-2 and MFS, showing cloceras); ammonites in the second association, however, are both a deepening-upwards and a retrogradational trend of facies common and characterised by smooth oxycones (Tissotia and belts, with a pronounced coastal onlap. This onlap geometry causes Hemitissotia). the MFS to be contained within SB-2 southeastwards, thereby Tissotioides hispanicus and Prionocycloceras iberiense have been increasing the hiatus contained in that boundary. (2) A Highstand identified in the first ammonite association. The former is a small to Normal Regression (HNR) (sensu Catuneanu et al., 2009) between intermediate-sized, involute species with a suboval or sub- MFS and SB-3, showing an aggradational and progradational trend. pentagonal compressed section, prominent and bullate umbilical

Fig. 4. Field view of the Coniacian 3rd-order sequence (DS-2) in Barranco de las Cuevas section (7 in Fig. 1B), showing the alternation between the upper calcareous member (c) of the Hortezuelos Formation and yellowish marly lithosomes of restricted littoral environments (d). Lower calcareous member (a in Figs. 2, 3) and middle marly member (b in Figs. 2, 3) are absent because of basal onlap. Author's personal copy

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Fig. 5. Field view of the Coniacian 3rd-order sequence (DS-2) in Embalse de Entrepeñas section (8 in Fig. 1B), showing the alternation between green marls (d) and thin-bedded tidal dolostones (e) belonging to Alarcón Formation. Sequence-boundary surfaces (SB-2 and SB-3) are out of the photograph.

tubercles, feeble, straight ribs, clavate ventrolateral tubercles, and H. turzoi were previously described and illustrated by Karrenberg relatively simple sutures with narrow, dentate lobes and wide, (1935), Bataller (1950), Wiedmann and Kauffman (1978), entire saddles (Fig. 8AeC). Specimens of T. hispanicus were previ- Wiedmann (1979), Martínez (1982) and Santamaría-Zabala (1991, ously described by Wiedmann (1960, 1964, 1979), Wiedmann and 1995). The forms Plesiotissotia dullai var. plana and Pleiotissotia Kauffman (1978) and Santamaría-Zabala (1991, 1995) and, cantabria, only established on the basis of small differences in the possibly, by Carretero-Moreno (1982); in the study area, this suture line, can be considered as synonyms of this species, as species has been found in Cuevas de San Clemente section. Prio- indicated by Santamaría-Zabala (1991, 1995). During the research nocycloceras iberiense is an intermediate-sized and involute to presented here, this species was identified in the Cuevas de evolute species, with a characteristic subrectangular compressed San Clemente, Contreras, Hortezuelos, Casuar-Linares and section, rounded umbilical tubercles and simplified sutures Castrojimeno-Castroserracín sections. (Fig. 8DeF). Specimens of P. iberiense were previously identified Stratigraphically above these two ammonite associations, the and figured by Basse (1947), Santamaría-Zabala (1991, 1995) and third association is composed of some poorly preserved specimens Gallemí et al. (2007); in the study area, this species has been with characteristics close to those of the genera Placenticeras, collected from the Contreras section. Eulophoceras and Pseudoschloenbachia. They have been collected The taxa Tissotia sp., Hemitissotia celtiberica and Hemitissotia from the Cuevas de San Clemente, Casuar-Linares and Castrojimeno- turzoi have been identified in the second ammonite association. Castroserracín sections. Tissotia sp. is an intermediate-sized and very involute taxon, with an inflated suboval compressed section, low tubercles and ribs during early ontogeny, and relatively complex sutures, with numerous 4.2. Hippuritoidea elements. Among them, first lateral saddles are divided into two equal intervals with few indentations, and entire saddles remain The second assemblage consists of rudist lithosomes that crop (Fig. 8GeI). Specimens similar to those identified here in the Cuevas out in the Castrojimeno-Castroserracín and Barranco de las Cuevas de San Clemente, Contreras and Hortezuelos sections, have been sections, which developed mainly in the upper part of the HNR of described by Santamaría-Zabala (1991, 1995). H. celtiberica is the DS-2. a discoidal and involute species with a subogival to suboval Bournonia gardonica (Fig. 9A) has only been identified in compressed section that reaches its maximum width close to the Barranco de las Cuevas section where it forms small, monospecific middle part of the flanks. During juvenile stages it shows an acute cluster reefs in fine micritic limestones, intercalated with bioclastic venter and, occasionally, some weak ornamentation that becomes limestones. The matrix was affected by early dolomitization, but rounded and disappears throughout ontogeny. It has pseudocer- the outer shell layer remained well preserved, showing both atitic sutures, with about three indented lateral lobes and three external morphological characters and shell structure. Knowledge rounded saddles per flank (Fig. 8JeL). Specimens of H. celtiberica of the shell structure of B. gardonica has been improved based on were previously described and figured by Wiedmann (1975, 1979) the study of these specimens (Gil et al., 2002). The species was first and Wiedmann and Kauffman (1978). This species has been described and figured by Toucas (1909) as Agria gardonica, from the identified in the Contreras, Hortezuelos, Casuar-Linares and Coniacian of Gatigues (Gard), together with other specimens from Castrojimeno-Castroserracín sections. Hemitissotia turzoi is very Piolenc (Vaucluse) and Beausset (Var), and reported also from similar to H. celtiberica. The only differences are that the former has Rochefort (Landes), all in France. It has also been reported from a completely smooth surface, a slightly more compressed and Istria in Croatia (Parona, 1926) and Cilento in southern Italy (Cestari involute section with a maximum width close to the inner third of and Pons, 2004) corresponding to the Coniacian event K in Cestari the flanks, an acute adult venter, and about two additional lateral and Sartorio (1995). lobes and saddles per flank (Fig. 8MeO). Although these two forms Bournonia fascicularis (Fig. 9B) has been identified in Cas- could be considered as mere synonyms, on the basis of these slight troserracín outcrops. The species was first described from the differences (although overlapping in certain cases), the morphology Coniacian of Colle di Medea (Friuli) and reported subsequently from and their temporal and geographical distribution suggest that it is many other localities in Italy (see Steuber, 2002). Toucas (1909) preferable to maintain the specific division. In Spain, specimens of figured specimens from the Coniacian of Gatigues (Gard), France. Author's personal copy

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Fig. 7. Dip cross-section of the Coniacian 3rd-order sequence (DS-2) in the Iberian Basin (see Fig. 1 for location), showing the depositional architecture of (1) the facies associations; (2) the faunal distribution; and (3) the system tracts and stratigraphic reference surfaces (sequence boundaries and Maximum Flooding Surface). SB-2, lower sequence boundary; SB-3, upper sequence boundary; TST, Transgressive Systems Tract; MFS, Maximum Flooding Surface; HNR, Highstand Normal Regression.

Praeradiolites requieni (Fig. 9C) has been identified in the Cas- Radiolites sauvagesi (Fig. 9F) occurs in nearly all bioconstruction trojimeno and Castroserracín outcrops. Some specimens are conical types at Castrojimeno, and as isolated specimens at the Cas- (120 mm high, 70 mm wide), but others are remarkably flat (40 mm troserracín outcrops. Specimens represent a wide spectrum of shell high, 80 mm wide), lying reclined on their flat dorsal margin, growth conditions. Radial ribbing ranges from acute and narrow to particularly those from Castroserracín. The species has been rounded and broad. Spacing of growth lamellae is highly variable. reported from the Coniacian of Gatigues and Bagnols (Gard), The width of radial sinuses (always up-folds of growth lamellae) is Martigues (Bouches du Rhône), Noyères (Vaucluse), Nyons (Drôme) also variable. Inter-band down-fold is either simple, subdivided, or and Le Beausset (Var) in France (Toucas, 1907), and also from formed by three folds when radial sinuses are deep and their Montsec (Catalonia) in Spain (Pascual et al., 1989). margins well defined. The undivided inter-band fold was consid- Biradiolites canaliculatus (Fig. 9D, E) is the type species of the genus ered a primitive feature by Toucas (1908) justifying the erection of Biradiolites.Itwasfirst reported from the Coniacian of Martigues the species R. praesauvagesi, but it appears to be related to growth (Bouches du Rhône), Beausset (Var), Gatigues and Bagnols (Gard), all constraints and ecological factors. This species was first described in southeast France, and has been reported sporadically from other from the Coniacian of Gattigues (Gard) in southeast France and has localities including the southern Pyrenees, such as Montsec (Pascual been frequently reported from deposits of the same age all along et al., 1989). The species has traditionally been described as higher the Mediterranean Tethys margins. than wide. The specimens identified in the close cluster/frame reefs A Hippurites species occurs as a minor component, together with of Castrojimeno outcrop are extremely long and thin and develop radiolitids, in paucispecific close-cluster and segment reefs or in acute ribs (Fig. 9E), similar to those described for the Turonian monospecific close-cluster/frame reefs at Castrojimeno (Fig. 9G). It species B. angulosus, while those in the open cluster reefs of the has been identified as Hippurites incisus, which was first described as Castrocerracín outcrop, lying on their dorsal or anterior side, are a variety of H. resectus from the Coniacian of Espluga de Serra remarkably flat and expanded and, in some of them, the characteristic (southern Pyrenees), subsequently identified in other Coniacian inter-band fold develops downwards below the apex of the right localities in the Pyrenees (Pons, 1982) and reported later from other valve (Fig. 9D). This extreme intra-specific diversity is probably the distant areas. It is considered here to be the Coniacian species of cause of some misidentifications in literature. Toucas’ (1904) Hippurites canaliculatus Group; however, it is not

Fig. 6. Stratigraphic and biosedimentary features of the Coniacian 3rd-order sequence (DS-2). A, lower 3rd-order sequence boundary (SB-2) of DS-2 in Villaverde de Montejo Outcrop (near the Casuar-Linares section), showing a hardground surface and the boundary between the Muñecas Formation (below) and Hortezuelos Formation (above). B, detail of the same hardground surface in Casuar-Linares section (5 in Fig. 1B). C, large cross-bedding surfaces in thick-bedded sets of micritic to bioclastic limestones (subfacies 21 to 23 in Table 2) in the upper half of the HNR near the Contreras section (2 in Fig. 1B). D, densely packed autochthonous fabric of rudist boundstromes (subfacies 24 in Table 2), composed of specimens of R. sauvagesi, B. angulosus and scarce H. incisus; Castrojimeno-Castroserracín section (6 in Fig. 1B). E, alternation of micritic limestones (Subfacies 21) with benthic foraminifera and fenestral lamination (above) and bioclastic rudstones (Subfacies 22), composed of fine, well-sorted rudist fragments (above); note the irregular stratigraphic surface between both beds, pointing to intense bioeroding processes at the top of the previously lithified micritic bed; Barranco de las Cuevas section (7 in Fig. 1B). F, fine planar algal lamination within a set of thin-bedded yellowish dolostones; Embalse de Entrepeñas section (8 in Fig. 1B). G, detail of nodular to brecciated dolostones cropping out at the top of DS-2 at the southeastwards end of the transect; the nodular and brecciated aspect is a consequence of the intense bioturbation; Embalse de Entrepeñas section (8 in Fig. 1B). Author's personal copy

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J.F. García-Hidalgo et al. / Cretaceous Research 34 (2012) 268e283 277 definitively established whether this specific name should be The transgressive deposits reflect the flooding of the underlying reserved for the specimens with deeply folded growth lamellae, shallower sediments at the onset of the TST (Fig. 6A). The trans- producing acute ribs on the right valve surface, and having pustules gressive biotic associations are dominated by bivalves (mainly on the left valve, and those without these characteristics maintained Pycnodonte and other oysters, with the presence of banks of these as H. resectus, which is a Turonian cosmopolitan species but with molluscs being common), and gastropods; ammonites and echino- younger representatives that range up to the Maastrichtian. By derms are less common. accepting the last alternative, the stratigraphical distribution of The rise in sea-level during transgressive periods leads to the H. resectus would also reach the Coniacian, co-occurring in this stage influx of terrigenous sediments and nutrients (mainly silt, clay and with H. incisus and H. vasseuri; the latter species is currently related organic matter) from flooded coastal plains, allowing increased to the former but has characters that differentiate it. During the productivity and suggesting fluctuating environmental conditions course of our research the co-occurrence of different combinations (including possible short term salinity changes; Wilmsem and of two of the three species in different Coniacian fossil localities Voigt, 2006). The broad presence in these sediments of oysters from southern France and northern Spain has been revealed. well-adapted to resist prolonged environmental stress is indicative Vaccinites moulinsi (Fig. 9H) occurs in the Castroserracín expo- of both the transgressive nature of the sedimentation and the new sures. It was first reported from the Coniacian of Gatigues (Gard). environmental niches produced by the incursion of the sea onto the Until now it has only been reported from southern France and coast (Bauer et al., 2003; Pufahl and James, 2006). Oysters are northern Spain. Some misinterpretation of the tip of the ligament presently marine shallow-water inhabitants, and because they are ridge lead Douvillé (1895) to propose a new species, H. praemoulinsi, filter feeders, they can tolerate a wide range of environmental which was later considered invalid by Toucas (1904). conditions, ranging from tidal brackish settings (Stenzel, 1971; Vaccinites giganteus (Fig. 9I) occurs in the outcrops of both Cas- Pufahl and James, 2006) to subtidal, lagoonal environments trojimeno and Castroserracín. It has been reported previously from (Mahboubi et al., 2006; El-Azabi and El-Araby, 2007). The substrate the Coniacian of Gatigues (Gard), Noyères (Vaucluse), Nyons for oyster shells needs to be firm because they are sessile benthic. (Drôme), Martigues (Bouches du Rhône), Le Beausset (Var), and Fossil forms usually appear embedded in predominantly calcareous Bugarach (Aude) in France (Toucas, 1904), Espluga de Serra and sediments (Stenzel, 1971; Pufahl and James, 2006) whereas, other Pyrenean localities in Catalonia, Spain (Pons, 1982), and many Pycnodonte, a typical free-lying oyster, obtained stability on a soft other localities in the Adriatic area (see references in Steuber, 2002). substrate with its large, convex and thickened valve; their The specimens of Apricardia sp. collected at Castroserracín are appearance is usually related to marly substrates (Wilmsem and isolated individuals in which both valves are very similar in size, Voigt, 2006). coiling, and transverse section; the section is triangular, higher The tops of the carbonate beds are usually highly bioturbated than wide and carinate ventrally. Inner moulds show the impres- and red-stained, suggesting early lithification of substrates. These sion of the posterior myophore plate in both valves. They lithified sediments were probably unfavourable to the rudists, undoubtedly correspond to the genus Apricardia but its specific which are considered to have been partially buried in soft sedi- determination is doubtful. Late Cretaceous requieniids have ments (Cestari and Sartorio, 1995; Cestari and Pons, 2007); they are received less attention than Early (or mid) Cretaceous ones and almost completely absent from transgressive sediments. Corals little progress has been achieved since the nineteenth century. would have been able to grow on these firm substrates, but their Overall, this rudist assemblage is characteristic of the Coniacian absence implies that unstable environmental conditions probably of southern France and north-eastern Spain, although a few species inhibited their growth. In the Pyrenean Trough, however, they were have also been reported from other Mediterranean areas. commonly associated with rudists during the Coniacian (Booler and Tucker, 2002). 5. Relationships between stratigraphic patterns, sedimentary Regarding the ammonite distribution in the TST, the key indi- environments and biotic associations cators T. hispanicus and P. iberiense are restricted to the lower member of Hortezuelos Formation (lower set of DS-2 sequence; During the Coniacian, the Iberian Basin experienced a major Fig. 2) in the northern outcrops (Cuevas de San Clemente and transgressive event, resulting in the inundation of shallow areas, Contreras sections (1 and 2 in Fig. 1B). To date, these species have a phenomenon that usually causes changes in facies and biotic not been found in southern outcrops, suggesting that their absence associations on carbonate platforms (e.g. Pomar and Kendall, 2008). is owing to the onlap at the base of the formation related to the This transgression was also coincident with the beginning of the 3rd-order sea-level rise of the entire sequence (stratigraphic gap). maximum spreading and diversity of rudists in the Late Cretaceous During maximum transgression, around the Maximum Flooding (Cestari and Sartorio, 1995; Pomar and Hallock, 2008). It resulted in Surface (MFS), the basin was completely flooded and marly deep- the deposition of the bioclastic-rich limestones of the Hortezuelos water sedimentation occurred along the northern and central Formation resting upon the shallower Caballar and Muñecas parts of the Iberian Basin. During this late TST, the replacement of formations; siliciclastic influx was scarce and mainly derived from Tissotioides and Prionocycloceras by Tissotia and Hemitissotia took a crystalline Hercynian basement (Hesperian Massif), located to the place (Fig. 7); mostly, Tissotia sp. and H. celtiberica below the MFS, west of the study area (Fig. 1A). The sedimentary sequence reflects followed by H. turzoi. Comparing the morphology of these ammo- those of a carbonate ramp passing distally into a deep pelagic basin. nites, a clear change from platycones (Tissotioides and Prionocyclo- Along this sedimentary sequence, a change in biotic associations ceras), close to the morphogroup 9 of Batt (1989) and Westermann from transgressive to highstand deposits within a single deposi- (1996), to oxycones (Tissotia and Hemitissotia), close to the mor- tional sequence (DS-2) occurred. phogroup 11 of these authors, can easily be observed. This gradual

Fig. 8. Ammonite assemblage of the Coniacian 3rd-order sequence in the Iberian Basin. AeC, Tissotioides hispanicus, SC-S-985, Tissotioides hispanicus and Prionocycloceras iberiense zone of Cuevas de San Clemente, in A, ventral, B, lateral and C, apertural views. DeF, Prionocycloceras iberiense, CT-R-950, Tissotioides hispanicus and Prionocycloceras iberiense zone of Contreras, in D, apertural, E, lateral and F, ventral views. GeI, Tissotia sp., CT-R-980, Tissotia sp. zone of Contreras, in G, ventral, H, lateral and I, apertural views. JeL, Hemitissotia celtiberica, CT-S-954, Hemitissotia spp. zone of Contreras, in J, apertural, K, lateral and L, ventral views. MeO, Hemitissotia turzoi, CJ-S-924, Hemitissotia spp. zone of Castrojimeno, in M, ventral, N, lateral and O, apertural views. Scale bar represents 5 cm. Figured specimens to date are housed in the Coniacian Palaeontological Collection of the Universidad de Alcalá, Spain. Author's personal copy

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Fig. 10. Sedimentological model for the HNR of the DS-2 sequence in the Iberian Basin (for explanation of subfacies, see Table 2). replacement by more hydrodynamic and less ornamented forms can very shallow and coastal waters have been reported previously also be perceived in the evolution of the more abundant genus (Hewitt and Westermann, 1989; Kauffman, 1990) The presence of (Hemitissotia): its earlier representatives have low, rounded oxycones in these near-coast environments could be increased by umbilical tubercles and a moderately compressed section, and are onshore transport of shells as a result of post-mortem drift progressively replaced by completely smooth and tightly (Wilmsem and Mosavinia, 2011). compressed later specimens. During the early HNR, platform facies and their biotic commu- Similar morphological transitions have been reported and nities started to recover, but they were different from those of the related to changes in the marine environment of the depositional TST. In this case a complete transect from deeper marls to tidal basins (deepening-upwards cycles), among others, in the Middle facies can be observed (Fig. 10). Jurassic of Germany (Bayer and McGhee, 1984), and the Upper Deeper environments are similar to those of the MFS, being Cretaceous of the Western Interior of the USA (Jacobs et al., 1994), characterised by marls (subfacies 12) and nodular limestones Germany and Iran (Wilmsem and Mosavinia, 2011). (subfacies 11); inoceramids and ammonites were common in this The morphologic transformations observed in these ammonite facies in northward sections (Fig. 10; Gallemí et al., 2007). The inner faunas appear to be hydrodynamic adaptive responses to sea-level ramp facies are characterised by skeletal packstones very rich in changes (ecophenotypic variations), because in terms of hydrody- rudist fragments and oolitic grainstones (subfacies 22 and 23). They namics, a compressed, smooth form usually has a lower drag are interpreted as high-energy facies, reflecting the development of coefficient and faster, more efficient locomotion than a robust one. sandy (bioclastic or oolitic) shoal sediments (Fig. 10). No rudist Consequently, platycones (more abundant in the TST) reflect build-ups or shells have been observed in these facies except comparatively shallower near-shore (proximal) environments, locally; all fragments are worn and rounded, indicating abrasion with higher energy, whereas oxycones (more numerous in the and transport before deposition. Thus, this bioclastic fraction was MFS) correspond to relatively deeper open marine (distal) waters swept off to the external platform areas, where the skeletal debris (Wilmsem and Mosavinia, 2011), being well-adapted to a nekto- commonly accumulated forming the bulk of the skeletal compo- benthic lifestyle (Chamberlain, 1980). nent. The basal beds of the early HNR contain the smallest amounts Two lines of evidence suggest that Hemitissotia oxycones were of rudists; however, as long as low-energy, unconsolidated related to these open marine and lower energy environments. substrates developed, these substrates allowed rudist communities Firstly, they are present in deeper, quiet-water marly and nodular to recover and substitute previous biotic associations. limestone facies (subfacies 11 and 12), with inoceramids (Gallemí Large cross-bedding (up to 10 m thick) has been observed locally et al., 2007) and echinoderms rather than in high energy facies. (Fig. 6C), but this is not indicative of the flanks of steep-sided, high- Secondly, in many of the intervals studied, Hemitissotia is the only relief build-ups, because no evidence of reef-flat to reef-slope ammonoid present, occurring as scattered, isolated specimens in sediments has been found. These beds were thus deposited from benthos-poor strata. The fact that Hemitissotia so commonly occurs shoals with a relatively gentle relief (Fig. 10). in strata devoid of both benthic fauna and other ammonoids Although rudists could have been spread over all inner shelf suggests a pelagic habit in the upper levels of the water column sectors, they have only been preserved in growth position over (as proposed for other oxycone ammonites by Tsujita and different substrata on the leeward sides of the shoals and in lagoonal Westermann, 1998), where water oxygenation was probably areas (Fig. 10). Scarce, poorly preserved ammonites (possibly higher and more or less constant. Both pieces of evidence support Placenticeras, Eulophoceras, Pseudoschloenbachia) have also been the idea that most oxyconic ammonoids were well-adapted to found, which unlike open marine Hemitissotia, have more depressed a predatory lifestyle (Westermann, 1996), mainly by short chase shells, probably reflecting shallower but quiet environments. anywhere in the water column (Tsujita and Westermann, 1998). In Rudists grew in soft sediments giving rise to laterally limited and fact, the incursions of predatory oxycones, such as Hemitissotia,to scattered rudist-rich lithosomes (see below), which were of low

Fig. 9. Rudists of the Coniacian 3rd-order sequence in the Iberian Basin. A, Bournonia gardonica, transverse section of right valve, PUAB-43933, Barranco de las Cuevas. B, Bournonia fascicularis, ventral posterior view of right valve, PUAB-75899, Castroserracín. C, Praeradiolites requieni, ventral posterior view of both valves, PUAB-74442, Castroserracín. D, E, Biradiolites canaliculatus. D, ventral posterior view of both valves, PUAB-74455, Castroserracín. E, transverse section of right valve, PUAB-43735, Castrojimeno. F, Radiolites sauvagesi, ventral views of two right valves from the same bouquet, PUAB-43748, Castrojimeno. G, Hippurites incisus, transverse section of several right valves from a thicket, PUAB-43745, Castrojimeno. H, Vaccinites moulinsi, transverse section of right valve, PUAB-74426, Castroserracín. I, Vaccinites giganteus, transverse section of right valve, PUAB-74419, Castroserracín. J, Apricardia sp., inner mould of both valves, posterior view, PUAB-74463, Castroserracín. PB, posterior radial band; PML, posterior myophore lamina; VB, ventral radial band. Scale bar represents 10 mm. Figured specimens are housed in the Palaeontological Collections of the Universitat Autònoma de Barcelona (PUAB). Author's personal copy

280 J.F. García-Hidalgo et al. / Cretaceous Research 34 (2012) 268e283 relief on the surrounding sea bed and limited to the last generation Santonian) in Riu de Carreu and Prat de Carreu (Gallemí et al., of specimens (Fig.10). Storm- and wind-induced currents and waves 2004), and Villamartín (Gallemí et al., 2007) sections in northern repeatedly mobilised the rudist-supporting loose sediments; as Spain. This low stratigraphic position for these genera could not be a consequence, a well-sorted and rounded bioclastic fraction was confirmed by the present work, because C. undulatoplicatus has not reworked to the external platform areas; meanwhile toppled shells been identified in the sections studies. Nevertheless, this research were very abundant landwards. Only in deposits reflecting the more seems to confirm the presence of some ammonite genera internal and protected shelf sectors can the growth-related commonly attributed to the Santonian in lithosomes strati- arrangement of the rudist shells be easily observed. graphically below or coincident with those containing the charac- Inner platform areas (Casuar-Linares and Castrojimeno- teristic Coniacian rudist assemblage. Castroserracín sections; Fig. 7; 5 and 6 in Fig. 1B) are characterised The stratigraphic and sedimentologic analysis shows that the by an alternation of mudstones-wackestones with a highly diverse entire sequence DS-2 in the Iberian Basin was deposited on benthic fauna (solitary corals, chaetetids, echinoderms, brachio- a carbonate ramp (Fig. 10). The palaeogeographic reconstructions of pods and benthic foraminifera), alternating within rudist elevator the basin during this interval suggest that sedimentation took place biostromes (Fig. 10). These biostromes show both open and densely in tropical waters (Fig. 1A), a typical environment for photozoan packed autochthonous fabrics (Fig. 6D), parautochthonous fabrics, assemblages. Biotic assemblages, however, show the presence of and bioclastic levels of reworked rudist fragments with floatstone a mollusc-dominated diverse association during the TST, but a low- to rudstone textures (Gil et al., 2002, 2009). These fabrics and diversity association of rudists, which were heterotrophic suspen- textures correspond to matrix-supported cluster and segment sion feeders (Scott, 1995), during the HNR. These can be considered reefs, and even skeleton-supported frame reefs, according to the as heterozoan skeletal assemblages, which tend to be related to structural categories of organic reefs of Riding (2002). cooler waters of temperate to polar latitudes (Lees and Buller, 1972; In the innermost platform areas (Barranco de las Cuevas section, James, 1997). The upper Coniacian heterozoan assemblages cannot, Fig. 7;7inFig. 1B), rudists and benthic foraminifera inhabited low to however, be strictly interpreted as foramol facies (sensu Lees and medium energy muddy bottoms, where the rudists formed limited Buller, 1972) because firstly, organisms such as rudists, solitary build-ups in restricted lagoon areas (Fig. 10). These shallow water corals, gastropods, chaetetids and benthic foraminifera are gener- limestones rich in rudists contain a preponderance of skeletal ally considered to have flourished in warm seawater environments components (molluscs and benthic foraminifera) and lack non- and secondly, cool-water (pectinid bivalves, among others) and skeletal grains. The most prominent sediments are rudist-dominated infaunal molluscs were extremely scarce and even totally absent fine- to coarse-grained rudstones (Fig. 6E). The sediments were within these carbonates. These data altogether with the absence of generated in situ on protected areas where rudists were the primary evaporites suggest that changes in temperature (or too high sediment producers. These sediments were subsequently moved by temperatures) and salinity can be excluded as major factors storms, waves and currents. The finer fractions were probably controlling sedimentation; the presence, however, of monospecific winnowed out and deposited in deeper waters. oyster assemblages indicates that sedimentation in lagoonal areas Finally, an alternation of green marls with plant debris, massive was punctuated by salinity crises (Wilmsem and Voigt, 2006). or stromatolitic dolostones (Fig. 6F), well-bedded dolomitised Similar heterozoan assemblages in warm-water conditions have mudstones/wackestones locally with benthic foraminifera, and been recognised in several Coniacian carbonate platforms of the dolomitised breccias (Fig. 6G), characterise the more landwards Tethys (Simone et al., 2003; Philip and Gari, 2005); meanwhile, in outcrops (Embalse de Entrepeñas and Estrecho de Paredes sections, other Tethyan areas, rudists occurred in close association with Fig. 7; 8 and 9 in Fig. 1B), where they rhythmically alternate and corals (Pyrenees, Booler and Tucker, 2002; Alps, Sanders and Pons, testify to deposition in tidal-flat environments (Fig. 10). 1999). Some of these occurrences were interpreted to imply that DS-2 contains several ammonite and rudist assemblages. The the sediments formed under deeper, darker, and more eutrophic first assemblage is dominated by Middle Coniacian ammonites conditions than typical, present-day tropical, coral-bearing (Tissotioides hispanicus and Prionocycloceras iberiense); the second, carbonates (Philip and Gari, 2005). The close association with characteristic of the Upper Coniacian, is mainly composed of corals, however, might be interpreted as reflecting deposition in Tissotia sp., Hemitissotia celtiberica and H. turzoi. On the other hand, lighter, shallower environments, although Cretaceous corals prob- the DS-2 sequence can be clearly correlated with (1) UC9/10 and ably flourished in deeper water than their modern equivalents UC10/11 sequences of Gräfe (1994) and Gräfe and Wiedmann (Pomar et al., 2005). This supports the former interpretation, but (1998); (2) DS Co II and DS Co III of Wiese and Wilmsen (1999), adds a further complication to the interpretation of carbonates and (3) DC8 depositional cycle of Floquet (1998), suggesting that its dominated by this skeletal association. base is probably upper Lower Coniacian in the northern outcrops An alternative interpretation, which is preferred here, points to where a hiatus at the base of DS-2 existed, as shown by the pres- the existence of a strong sedimentary and trophic control on the ence of collapse breccias (Fig. 2) and hardground development biotic assemblages, as suggested for other Coniacian platforms (Fig. 6A, B). This hiatus in deposition was longer in the southern (Carannante et al., 1995). Nutrients, high hydrodynamic gradients, outcrops, where sediments of the entire TST are missing (Fig. 7). mobile substrates, and the presence of siliciclastics were probably A third assemblage, which can be identified in the southern the factors that controlled the development of these biotic associ- sections, is dominated by rudists that are usually attributed to the ations in the Iberian Basin. Rudists in life position occupied a narrow Upper Coniacian (Biradiolites, Praeradiolites, Radiolites, Apricardia, fringe mainly located on the seaward side of lagoonal areas. Facies in Hippurites, Vaccinites). The upper part of DS-2 has a poorly seaward areas of this fringe were composed of high-energy bars; preserved ammonite assemblage, some of whose representatives although rudists were able to occupy mobile substrates (Pomar (Placenticeras, Eulophoceras, Pseudoschloenbachia) are commonly et al., 2005), they have not been found in life position in these facies. attributed to the Santonian, coexisting with Coniacian rudists, The high rates of erosion related to these environments with highly which raises a problem concerning the precise age of the top of this mobile substrates suggests the existence of large amounts of nutrients sequence. On this point, it should be mentioned here that several in suspension, allowing the predominance of nutrient-tolerant, possible representatives of this upper assemblage have been suspension feeder groups of calcareous organisms, such as rudists. located below the FAD (first appearance datum) of the inoceramid The presence of high-nutrient levels might not be the cause of rudist Cladoceramus undulatoplicatus (index species for the base of the development, but a consequence of the high energy environment. In Author's personal copy

J.F. García-Hidalgo et al. / Cretaceous Research 34 (2012) 268e283 281 quieter, shallower, landward areas rudists are absent (Embalse de Acknowledgements Entrepeñas and Estrecho de Paredes sections; Fig. 7;8and9inFig.1B); probably, because of both the absence of abundant nutrients in This study has been carried out within the projects CGL2007- suspension and higher siliciclastic input. In fact nutrients may have 60054, CGL2008-03112/BTE, and CGL2009-12008/BTE of the been abundant, but the presence of siliciclastics would have strongly Dirección General de Investigación y Gestión del Plan Nacional diluted (and thus reduced) the nutritional values of the suspended I+D+i Spanish Ministerio de Ciencia e Innovación, and PEII11-0237- particulate matter (Witbaard et al., 2001); thus, today in such 7926 of the Junta de Comunidades de Castilla-La Mancha, Spain. We circumstances nearshore communities may be impoverished and/or gratefully acknowledge Markus Wilmsen, Christopher J. Wood and characterised by the presence of smaller individuals. As on other David J. Batten for their valuable comments, constructive review platforms, the relationships between rudists and siliciclastics suggest and assistance in revising the English text, which helped to improve that moderate siliciclastic influxes controlled neither the presence the initial version of the manuscript. and absence of rudists, nor the composition of rudist associations (Sanders and Pons, 1999). However, substrate colonization by rudists was probably more difficult, or even impossible in the shallowest References areas with low nutrients and higher siliciclastic input (landwards), Alonso, A., 1981. El Cretácico de la provincia de Segovia (borde Norte del Sistema and in outer platform areas under frequent shifting of the bioclastic Central). In: Seminarios de Estratigrafía, Serie Monografías, 7, 271 pp. substrates. Barroso-Barcenilla, F., 2006. 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