A foraminiferal assemblage as a bioevent marker of the main Ladinian transgressive stage in the Betic Cordillera, southern Spain

Palaeogeography, Palaeoclimatology, Palaeoecology 224 (2005) 217 – 231 www.elsevier.com/locate/palaeo

A foraminiferal assemblage as a bioevent marker of the main Ladinian transgressive stage in the Betic Cordillera, southern Spain Alberto Pe´rez-Lo´peza,*, Leopoldo Ma´rquezb, Fernando Pe´rez-Valeraa a

Dpto. de Estratigrafı´a y Paleontologı´a, Facultad de Ciencias, Universidad de Granada, 18071 Granada, Spain b Dpto. de Geologı´a, Facultad de Biologı´a, Universidad de Valencia, 46100 Burjasot (Valencia), Spain Received 16 December 2003; received in revised form 18 October 2004; accepted 23 March 2005

Abstract The Betic Cordillera comprises the mountain range in the southern Iberian Peninsula that extends from Cadiz to Alicante, which displays typical features of alpine cordilleras. The Betic Cordillera includes two large geological tectonic domains, namely an External Zone, and an Internal Zone. The External Zone is essentially composed of epicontinental Triassic rocks that consist of the Buntsandstein, Muschelkalk and Keuper facies. The Buntsandstein facies rarely occur in outcrops, whereas the Keuper stratigraphic successions are truncated. The Muschelkalk facies frequently displays complete successions that are very useful for interpreting the Ladinian stage palaeogeography. The Muschelkalk facies consists of a lower carbonate member formed by three thick, massive limestone beds with intervals of thin-bedded marly limestone, and an upper marly member with intercalation of distinct beds of limestones and marls, where tempestites predominate. The first member has been interpreted as a transgressive systems track in which subtidal and ramp deposits can be identified. The second member is related to a highstand systems track, and consists of marine-platform and coastal deposits, which correspond to a shallowing-upward sequence. We describe and interpret a distinct bioclastic limestone bed with high concentrations of Involutinidae benthic foraminifers, that has been found in the Muschelkalk of several distant sections. This unusual bed is just above the third bed of massive Muschelkalk limestone, and consists of a bioclastic wackestone–packstone, up to 8 cm thick, with many Involutinidae of Ladinian age. The most abundant species are: Lamelliconus gr. biconvexus–ventroplanus, Lamelliconus cordevolicus and Triadodiscus eomesozoicus. These foraminiferal concentrations form a well-defined marker bed that may be related to a bioevent. The appearance of these foraminiferal taxa, which are also very common in the Triassic Alpine realm, coincides with the maximum flooding interval of a transgressive sequence. We surmise that these Tethyan foraminifers moved into newly developed coastal zones during maximum transgression and, at times, produced prolific shallow-water communities, which were reworked by storm currents that caused their unusual concentrations in deeper water. These concentrations thus generated the marker beds of foraminiferal packstones that can be found over distant outcrops in the region.

* Corresponding author. Tel.: +34 958243334; fax: +34 958 248 528. E-mail address: [email protected] (A. Pe´rez-Lo´pez). 0031-0182/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.palaeo.2005.03.036

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Similar involutinid foraminiferal assemblages occur in the upper Muschelkalk of the Iberian Ranges and Catalan Coastal Ranges, as well as in the upper part of the transgressive systems track of the UAA-2.2 third-order cycle identified in the Muschelkalk of the Pyrenees Basin. Thus, this foraminiferal assemblage can be considered as an extensive bioevent marker related to an important transgressive stage of Ladinian age. D 2005 Elsevier B.V. All rights reserved. Keywords: Foraminifers; Involutinidae; Betic Cordillera; Muschelkalk; Ladinian; Triassic

The Betic Cordillera comprises two distinct geologic domains that are differentiated as an External Zone and an Internal Zone (Fig. 1). The External Zone is composed of a non-metamorphic Mesozoic and Tertiary cover overlying a Variscan basement, and includes sediments deposited on the palaeomargin of the southern part of the Iberian plate before

1. Introduction and geological setting The Betic Cordillera is the mountain range that stretches from Cadiz to Alicante in the southern Iberian Peninsula (Fig. 1). This range, as well as the Rif (Northern Africa), is the westernmost segment of the alpine system.

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Fig. 1. Location and geologic setting of the Triassic outcrops in relation to the tectonic context of the Betic Cordillera (southern Spain). The epicontinental Triassic outcrops are composed of disrupted sections of Buntsandstein, Keuper and Muschelkalk facies. Localities of sections studied shown in Fig. 2 are also indicated.

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the alpine orogeny. The Internal Zone is made up of three nappe complexes that include rocks of different metamorphic grades, which are from bottom to top, the Nevado-Fila´bride, the Alpuja´rride and the lowgrade Mala´guide complexes (e.g. Azan˜o´n et al., 2002). The Internal Zone rocks were deposited in the Albora´n domain (Balanya´ and Garcı´a-Duen˜as, 1987), originally situated between the Iberian Peninsula and Africa. As a result of tectonism, Triassic rocks now occur notably displaced and fractured, thus displaying a mixture of different tectonic units. Triassic outcrops of the External Zone consist of shallow epicontinental facies sediments, which accumulated on the southern Iberian Continental Margin, and developed the three lithostratigraphic units equivalent to the classic German-type Triassic units (Buntsandstein, Muschelkalk and Keuper). The Triassic deposits in southern Spain belong to different facies according to the various Betic domains (External and Internal Zones) that experienced variable subsidence. Such interpretation is based on variations in thicknesses observed between the different stratigraphic sections where sedimentation depended on conditions controlled by the paleogeographic history of the given unit (e.g. Martı´n-Algarra, 1987; Martı´n-Algarra et al., 1995). In fact, several superposed rifting stages seem to have controlled the Mesozoic evolution of the External Zone, and basaltic volcanism in the Triassic rocks of the cordillera suggests that extension started in the Early Triassic (Morata, 1993). In the Iberian plate, the first important extensional stage associated with major subsidence and sedimentation began in the Middle Triassic (Lo´pez-Go´mez et al., 2002). Middle to Upper Triassic rocks are best represented, and are also the most studied of the Triassic System in southern Spain, because these rocks display rather complete successions, especially the Muschelkalk facies. Such successions have been very useful for interpreting Ladinian palaeogeography, and for this reason Ladinian carbonate rocks (Muschelkalk facies) are the object of this paper. However, there are constraints imposed by a lack of adequate index fossils, which makes it difficult to establish a detailed stratigraphic correlation between different sections. Ladinian carbonate rocks consist primarily of an alternation of marls, marly limestones and fossil-rich

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limestones. In many regions of Spain, Germany and France, these carbonate series form a large number of small-scale shallowing-upward cycles (e.g. Calvet et al., 1990; Lo´pez-Go´mez et al., 1993; Aigner and Bachmann, 1998), similar to the order that can be seen in the Betic Cordillera. Bivalves and other molluscs are very frequent in carbonate beds of Triassic Betic outcrops (Pe´rez-Lo´pez et al., 1991), and more specifically almost all tempestite beds consist of bivalve rudstones and floatstones. Generally, the epicontinental sea that was somewhat geographically isolated was inhabited by a fair number of very common bivalves, gastropods, echinoderms, brachiopods and arthropods (Hagdorn et al., 1998). Of special interest in the Muschelkalk facies studied is the presence of a distinct benthic foraminiferal assemblage that appears as a discreet unit in different stratigraphic sections of southern Spain (Figs. 1 and 2). This particular level rich in benthic foraminifers has been studied in detail in the sections at Las Vı´boras and at Canara, respectively. These sections are approximately 300 km apart (Fig. 1). The section at Las Viboras is located to the north of Rute (southern Cordoba Province) and the Canara section is to the north of Cehegı´n (northwest Murcia Region). To complement these sections, additional detailed observations were made in some sections of Calasparra (northern Murcia Region) and Jauja (southern Cordoba Province), which allowed for further interpretation of the sedimentary facies (Fig. 2). The present work focuses on the foraminifer-rich beds that are characterized by the presence of the Tethyan realm taxa, which have not yet been studied in southern Spain, although there are some references to these microfossils in others regions (Peybernes and Lucas, 1988; Ma´rquez et al., 1992; Ma´rquez-Aliaga et al., 1994). We further propose a sedimentary and stratigraphic interpretation of these beds, which we correlate with equivalent ones of different regions of the Iberian Peninsula. These beds are interpreted as significant foraminiferal marker beds, and are probably related to palaeogeographic and eustatic controls. We also suggest that these beds can be used to detect, as well as to correlate, sedimentary and biological events associated with the Ladinian stage in the region.

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Fig. 2. Stratigraphic columns of the main sections studied shown in Fig. 1. Distance between the Jauja–Las Vı´boras sections and the Calasparra– Canara sections is approximately 300 km. Partly shaded rectangle in the Calasparra section indicates the position of Fig. 8.

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2. Stratigraphy and palaeoenvironments In the epicontinental Triassic rocks (Fig. 3) of the External Zone (Betic Cordillera) it is possible to distinguish the following succession of facies, from oldest to youngest: a carbonate sequence of Muschelkalk facies (Majanillos Formation), five detrital evaporitic formations that constitute the Jae´n Keuper Group (Pe´rez-Lo´pez, 1991), and an upper carbonate sequence of Norian age (Zamoranos Formation; Pe´rez-Lo´pez et al., 1992). The Buntsandstein outcrops are rare, or at least difficult to recognize (Pe´rez-Valera et al., 2000), not only because these facies are very similar to the Keuper facies, but they are also mix due to regional tectonics and local diapirism (Pe´rez-Lo´pez and Pe´rez-Valera, 2003). The Buntsandstein facies were identified with certainty only

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below the Muschelkalk in the northernmost sector of the External Zone, near the Meseta (Palaeozoic of Iberian Massif), and in several places in the Murcia region. They consist of red and grey shales, thin layers of gypsum and sandstones with mud cracks, which should be considered as the upper part of the Buntsandstein, interpreted to represent deposits in a coastal plain (Pe´rez-Valera et al., 2000). The Muschelkalk facies consists of a carbonate succession (Majanillos Formation), generally dominated by marly beds towards the upper part. These beds display an overall thinning-upward trend. Two main members can be distinguished in the Majanillos Formation (Fig. 4): a lower Member, 20–40 m thick, consists of three thick massive limestone beds, with intervals of approximately 10 m of thin-bedded marly limestone; and an upper Member, up to 50 m thick,

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composed of a more marly succession with intercalations of thin beds of bioclastic limestone. The upper marls, with interbedded thin limestone beds, change upwards into Keuper gypsums and shales. The lower member has been generally interpreted to represent a deepening sequence in which subtidal and ramp deposits can be identified (Pe´rez-Lo´pez, 1998). The upper member presents a predominance of marly facies deposited on a shallow platform where there

are frequent storm deposits (tempestites). The uppermost facies display lagoonal and tidal-flat deposits which correspond to a muddy shallowing-upward sequence. The Keuper is characterized by multicoloured and red shales, sandstones, gypsum and sometimes by basaltic intrusive rocks. Although none of the outcrops display a complete section of Keuper, correlation between different outcrops allows to differentiate

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five different lithostratigraphic units (Jae´n Keuper Group). Thicknesses and facies of these units vary from the southern palaeogeographic domains to the northern domains of the Betic External Zone. These units can be correlated with similar sequences that outcrop in the Eastern Iberian Peninsula (Ortı´, 1974). Despite their different denominations, in the present work the Keuper units have been assigned the following abbreviations: K1, K2, K3, K4 and K5 (Pe´rez-Lo´pez, 1991). Unit K1 (100–200 m) consists of multicoloured shales with thin intercalations of carbonates, gypsum and fine-grained sandstones (Fig. 3). The facies of this unit can be attributed to a fluvial–coastal systems tract, with ample development of lakes and salt pans (Pe´rez-Lo´pez and Lo´pez-Chicano, 1989). Unit K2 (25–60 m) is characterized by a predominance of thick sandstone beds with interbedded claystones. This unit corresponds to the deposits of a terminal alluvial system (Pe´rez-Lo´pez, 1991). Unit K3 (50–80 m) consists predominately of red claystone with red nodular gypsum. The deposits of this unit, essentially claystones with gypsums and some dolomites, are interpreted to represent a saline mud flat with environments of sabkha and lagoonal deposits (Pe´rez-Lo´pez, 1996). Unit K4 (5–30 m) consists of clay with a large percentage of red nodular gypsum, although laminated gypsum can be found locally. Because of the abundance of nodular gypsums and red clay, this unit can be interpreted as sabkha deposits of a coastal plain. Unit K5 (50–70m) consists of stratiform masses of white and grey laminar gypsums, and the upper part includes dolostones which can reach 25 m in thickness. This unit is similar in facies to the evaporitic deposits of the Upper Evaporitic Series of the Keuper facies (Ortı´, 1974), which also includes halite deposits in subsurface sections, and in certain outcrops (Ortı´ and Pe´rez-Lo´pez, 1994). The evaporites, claystones and dolostones of this unit correspond to deposits that accumulated in a coastal environment related to marshes, salt pans or saline lagoons, where precipitation of the evaporites and carbonates took place. A carbonate unit of variable thickness and facies that has been recognized in many outcrops of the External Zone overlies rocks of the Keuper facies (Fig. 3). It corresponds to the upper carbonate sequence of the Triassic also termed the Zamoramos Formation (Pe´rez-Lo´pez et al., 1992), which consists

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of bedded limestones and dolostones (25–45 m thick) with a peculiar red-coloured detrital intercalation (0.1–2 m thick) in the lowest part. These facies are interpreted to indicate shallow-platform and tidal-flat deposits with the red intercalation related to an emergent coastal–continental complex deposits: fluvial, mudflat and lake deposits with pedogenic processes. The Carcele´n Anhydrite Unit (Ortı´, 1987) overlies carbonates of the Zamoranos Formation, and consists of gypsums, carbonates and shales. This unit outcrops in several places of the central and eastern part of the External Zone, although it is very difficult to recognize because some of its facies are similar to those of Unit K5 (Pe´rez-Lo´pez et al., 1996). It has substantial development in the subsurface, as it has been observed in the eastern sector of the Betic Cordillera and, especially, in other adjacent basins such as the region of Valencia–Cuenca (Ortı´, 1990). In the subsurface, however, the Carcele´n Anhydrite Unit is composed of anhydrite, shales, and dolomite beds with important intercalations of halite. We interpret this unit to typify deposits in a palaeogeographic environment similar to that of the K5 unit related to coastal lagoons and sabkhas.

3. Biostratigraphy Our study of the Triassic epicontinental deposits of the Betic Cordillera has been carried out over a large number of sections, which consistently indicate a scarcity of adequate fossils, thereby limiting precise age correlation of the various lithostratigraphic units. In general, the fossil record is quite poor and the degree of preservation of the specimens is frequently deficient (Ma´rquez-Aliaga, 1985; Pe´rez-Lo´pez et al., 1991). Such constraint thus imposes limits to our ability to establish unequivocal stratigraphic correlation between the different units that have been recognized (Pe´rez-Lo´pez, 1998). Nevertheless, despite these constraints and the fact that many areas have not been sampled, or studied adequately, new age determinations in recent years have provided a better understanding of Triassic stratigraphy (Pe´rez-Lo´pez, 1998). Thus, the upper part of the Buntsandstein has been dated in the northern and eastern areas of the External

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Zone with an assemblage of Ladinian palynomorphs (Besems, 1983; Pe´rez-Valera et al., 2000). Cephalopods (Goy et al., 1996), conodonts, foraminifers, as well as an assemblage of bivalves typical of the Ladian age, have been found in the upper part of the Muschelkalk carbonates of the Majanillos Formation (Pe´rez-Lo´pez et al., 1991). Shales, sands and evaporites of the K1 and K3 units from the Keuper facies contain plant debris (Equisetites arenaceus Brong) and pollens (Camerosporites secatus Leschik, Patinasporites densus Leschik, and Vallasporites ignacii Leschik) attributable to the Carnian. Furthermore, we infer that Unit K5 may be placed in the Norian based on its stratigraphic position, and on the occurrence of pollens assigned to the Norian in the superjacent carbonate unit, or Zamoranos Formation. Finally, part of the shales from the Carcele´n Anhydrite has been dated as Rhaetian. A fossil record, therefore, exists from the Ladinian to the Rhaetian, although it needs further accuracy. So far no identifiable fossil record has indicated Anisian age taxa associated with deposits neither of the Buntsandtein nor of the middle Muschelkalk. Peculiarly, a number of shale outcrops occurring below the Muschelkalk carbonates contain pollens of Carnian age, which clearly indicate tectonic reversal of the stratigraphic position of the Keuper facies below the carbonate unit.

4. Sequence stratigraphy of Majanillos formation (Muschelkalk carbonates) The carbonate sequence from the lower member of the Majanillos Formation includes tidal and ramp facies, thus it has been interpreted to indicate sediments of a transgressive depositional system (Pe´rezLo´pez, 1998, 2001). The upper member consists of marine-platform sediments grading upward into coastal facies (Fig. 4), therefore it corresponds to a highstand depositional system. These highstand sediments enclose numerous bioclastic beds with erosional bottoms, lags and sedimentary laminae, sometimes

wave ripples, which are interpreted as tempestite beds. Of significant stratigraphic importance is the fact that all the sections studied show a marked upward change from the top of the lower carbonate member. Clearly, the upper member is also lithologically much more variable than the lower member, and the variations depend on the sections (Fig. 2). We argue that these lithofacies changes show a record of the development of the carbonate ramp into a restricted platform, where sediments of the upper member accumulated (Pe´rez-Lo´pez, 1998). The upper member displays a shallowing-upward sequence, which we interpret as a progradation of the sedimentary environments and the uppermost Muschelkalk represents a gradual transition from marine to continental deposits (Keuper facies). The lower member of the Majanillos Formation has two levels rich in benthic foraminifers that occur at the top of the first and third massive limestone beds. These levels contain taxa characteristic of the Tethys realm. The upper foraminifer-rich level is more distinct and in some sections it also overlies a hardground, as found in the Calasparra section (Fig. 4).

5. The foraminiferal assemblage Unusually high concentrations of benthic foraminifers that characterize the top of the first and third massive limestone beds within the lower part of the Majanillos Formation (Fig. 4) consist of abundant Involutinidae of great size (about 0.5 mm). These levels also contain frequent crinoid, gastropod and bivalve fragments. In the most notable samples from the Canara and Las Vı´boras sections, the following involutinid foraminifers have been identified (Fig. 5): (A) In the Canara section (Cehegı´n, Murcia; Sample CN1-02-1): Lamelliconus gr. biconvexus–ventroplanus, Lamelliconus cordevolicus (Oberhauser), Triadodiscus eomesozoicus (Oberhauser); (B) In the Las Vı´boras section (Rute, Cordoba; Sample VIB-02-2): Lamelliconus gr. biconvexus–ventroplanus, L. corde-

Fig. 5. Ladinian foraminifers of the marker bed from the Las Vı´boras section (Rute, Cordoba Province) and the Canara section (Murcia Region). Scale bar is 100 Am. (1 and 2) Lamelliconus cordevolicus (Oberhauser), CN1-02-1. (3 and 5) Lamelliconus gr. biconvexus–ventroplanus, CN102-1. (4) L. cordevolicus (Oberhauser), VIB-02-2. (6) Endotriadella cf. wirzi (Koehn–Zaninetti), VIB-02-2. (7 and 8) Triadodiscus eomesozoicus (Oberhauser), CN1-02-1. (9) Trochammina jaunensis Bro¨nnimann and Page, VIB-02-2.

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volicus (Oberhauser), T. eomesozoicus (Oberhauser), Trochammina jaunensis Bronnimann and Page, Endotriadella cf. wirzi (Koehn–Zaninetti). The chronostratigraphic range of involutinid taxa such as (L. gr. biconvexus–ventroplanus, L. cordevolicus and T. eomesozoicus) extends from the Ladinian to the Carnian (Trifonova, 1993), while E. wirzi indicates an Anisian–Ladinian age (Rettori, 1995). On the other hand, T. jaunensis has been reported in the Middle and Upper Triassic (Trifonova, 1992). Based on these reported ranges, these different foraminifers indicate an overall Ladinian age for the occurrence of the foraminiferal event. This date assignment is further corroborated by the presence of the conodont Pseudofurnishius murcianus (Boogaard) in adjacent beds (Pe´rez-Lo´pez, 1991). The Involutinidae fauna indicated above is habitual for the Tethys realm, and also appears in some basins (Ma´rquez, 1994) of the Iberian Peninsula, such as the Pyrenean basin (Ma´rquez et al., 1992), the Iberian basin (Pe´rez-Arlucea and Trifonova, 1993) and in one of the Balearic Islands (Minorca; Vachard et al., 1989). The importance and consequences of the presence of Tethyan fauna in the Spanish Triassic have been amply discussed by Budurov et al. (1993), and will be addressed in a subsequent paragraph.

Some unidentified bivalves, and scattered ceratites are occasionally associated with these foraminifers, and Goy and Pe´rez-Lo´pez (1996) found Ptychitidae and Proarcestes spp. (Ladinian ammonoids) in an equivalent stratigraphic interval of the Tethys realm.

6. Facies of the foraminiferal marker bed and sedimentary interpretation In the sections at Las Vı´boras, Jauja, Canara and Calasparra (Figs. 2 and 4), carbonates of the lower member of the Majanillos Formation include two levels with unusual concentrations of benthic foraminifers. These levels rich in foraminifers will be referred to hereafter as bforaminiferal marker bedQ (Figs. 2 and 4: F.M.). As pointed out earlier, these levels appear distinctly at the top of the first and third thick massive limestone beds, but the latter is the most important (Fig. 4), because it also accentuates the limit between the two members, where the stratigraphic succession begins to become steadily more clayey. The main foraminiferal marker bed is about 10 cm thick, and appears as a nodular bioclastic limestone (wackestone–packstone) with Involutinidae (Figs. 6 and 7) recorded in sparry calcite by means of a neomorphic process or mineralogical inversion (Fer-

Fig. 6. Detail of nodular limestone bed with recrystallized foraminifers. Note the darker grey dots which correspond to the foraminifers.

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Fig. 7. Microfacies of the foraminiferal marker bed. Photomicrograph (crossed nicols) showing some molluscs (black arrows) and foraminifers (white arrows) recorded in sparry calcite (wackestone–packstone). Scale bar 1 mm.

na´ndez-Lo´pez, 1998). The lower boundary of the bed is characterized by an erosional surface, whereas the top is irregular and sharp, overlain by thin marl and marly-limestone beds of the upper member. In some outcrops (e.g. Jauja section), the foraminiferal marker bed can include a substantial amount of bivalve fragments. In fact, this marker bed can extend laterally to a bioclastic bed (packstone) comprised exclusively of recrystallized bivalve shells (Calasparra section). Despite its lateral variation and apparent localized discontinuity, this layer is a viable event bed that can be recognized in outcrops at distances over hundreds of kilometres (Figs. 1 and 2), such as at the Canara and Las Vı´boras sections. Components of the foraminiferal assemblages associated with the marker bed, and especially the abundance of Involutinidae, are characteristic of restricted and rather shallow, warm-water environments (Zaninetti, 1976; Trifonova, 1993; Rettori, 1995). However, the foraminiferal marker bed is associated with muddy deposits (marls and thin-bedded marly limestones with ceratites) which are relatively deep within a carbonate ramp (Pe´rez-Lo´pez, 2001). Furthermore, the foraminiferal bed sometimes displays, like other bioclastic beds found in the upper part of the sequence, features of interlayered tempestites in

fair-weather muddy deposits: e.g. erosional base, graded beds, lags, etc. Based on these observations, these high concentrations of foraminifers are interpreted as shells that were transported seaward during storms. In some cases the foraminiferal beds also consist of packstone–wackestone and display burrows filled with foraminiferal grainstone. Reworking related to these concentrations is further supported by the fact that some gastropods that are associated with the foraminifers contain sediment infill different from the micrite matrix, which is a characteristic of redeposited shells. Also, thin layers formed by skeletal packstones of bivalves undoubtedly related to storm deposits appear just above the level rich in foraminifers. Tempestites occurring 2 m above the foraminiferal marker bed consist of ooid packstone–grainstone, and tempestites still further above that level have shells of bivalves, as shown in Fig. 8 of a partial tempestite succession that displays upward thickening. Therefore, as the foraminiferal marker bed is the lower tempestite of this shallowing-upward sequence, it can be interpreted to have been deposited below a fair-weather wave base (at the lower zone of the shoreface), where the most powerful storms affected the sea floor only on certain occasions. Powerful storms would have caused the sediment to reach the

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FMB

Thick ening upwa Shall rd se owing quen ce upwa rd se quen ce

Tempestite grains

50 cm

Hardground

Packstone/grainstones (Tempestite)

FMB: Foraminiferal Marker Bed Bivalves Ooids Ceratite Foraminifers Wave ripples Fig. 8. Sedimentary sequence of tempestite in the upper member of the Majanillos Formation. Stratigraphic position is given in Fig. 2.

deepest zones of the shoreface by the ebbing storm currents.

7. Significance of the involutinid foraminiferal marker bed as a bioevent and discussion Since most beds of the Triassic system have low diversity (Pe´rez-Lo´pez et al., 1991), we can deduce that ecological conditions of the shallow seas of the southern Continental Iberian Margin must not have been favourable for most of the fauna. Therefore, the presence of abundant fossils from the Tethys in certain beds punctuates changes in the environments related to major sea-level rises that resulted in a connection with the Tethys Sea. For example, it has been argued that the presence of the bivalve Daonella, in a section of a Alpuja´rride unit of the Internal Zone of the Betic

Cordillera (Pe´rez-Lo´pez et al., 2003), implies that the Tethys was connected with the Betic Basin. This taxon is, indeed, typical of Alpine Triassic Wengen beds from Italy (Dolomites, southern Alps) and is of Ladinian age (Capoa Bonardi, 1970). In Spain, Daonella specimens are found in the Majorca and Minorca Islands (Llompart et al., 1987), in the Catalonian Coastal Ranges (Virgili, 1958; Ma´rquez-Aliaga, 1985), and in the Iberian Range (Ma´rquez-Aliaga, 1985; Arche et al., 1995). The record shows that the Involutinidae foraminifers are common in the Tethys realm (Zaninetti, 1976; Salaj et al., 1983; Trifonova, 1978, 1984, 1993; Rettori, 1995) as reported, for instance, in the Polish Muschelkalk (Gazdzicki et al., 1975). Characteristic foraminiferal assemblages similar to the ones found in the study area have been cited in the northern Pyrenees (Peybernes and Lucas, 1988; Frechengues et al., 1990), as well as in the southern Pyrenees (Ma´rquez et al., 1992). Calvet et al. (1990) interpreted these assemblages as being representative of the upper part of the Transgressive Systems Tract of the UAA2.2 third-order cycle of Haq et al. (1987) in the Triassic Catalan Basin. Ma´rquez-Aliaga et al. (1994) also pointed out that the involutinid assemblage (Aulotortus sp. and Triadodiscus sp., among others) indicates environments of greater marine influence related to periods of greatest advance of the sea during the middle Ladinian transgression. The implied highstand episode based on the involutinid foraminifers is further corroborated by other taxon groups, as Aigner and Bachmann (1992) indicated that the assumed maximum flooding interval in southern Germany (for the lower Muschelkalk sequence) contains characteristic Tethyan fauna, including the ammonite Beneckeia buchi and the brachiopod Dielasma ecki (Schwarz). Thus, it appears that the Tethys sea was connected to all the epicontinental basins during major sea-level rises. The importance of the influence of the Sephardic province fauna has been reported throughout the shallowest areas of the southernmost domains of the Betic basin (Hirsch, 1977; Hirsch et al., 1987; Ma´rquez-Aliaga and Hirsch, 1988; Pe´rez-Lo´pez et al., 2003). Thus, the presence of these Alpine foraminifers in the Muschelkalk carbonates is striking and indicates a connection during the Ladinian transgressive stage between the Tethys sea and the northern-

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most Betic epicontinental platform. Such connection must have occurred on several occasions, because similar associations of foraminifers occur at different levels in the stratigraphic succession (Fig. 2). We emphasize the importance of these high concentrations of foraminifers rich in Tethyan taxa, particularly at the stratigraphic level that coincides specifically with the boundary between the two members of the Majanillos Formation (Pe´rez-Lo´pez, 1998). That level is interpreted as sediments deposited during a main stage of sea-level rise, because it occurs on top of a transgressive sequence. This remarkable boundary bed that defines a maximum flooding surface can be equated to a similar level that occurs in the Pyrenees (Ma´rquez et al., 1992). Although the foraminifer-rich bed is not recognized as such in the Calasparra section, an equivalent bed composed of bivalve rudstone is situated just on top of a hardground developed over an oolitic limestone. Therefore, the bioclastic accumulation associated with this marker bed can be interpreted as the first deposit after a major transgression and, on some occasion, after a hiatus. For example, it is worth noting that in Germany also the maximum flooding interval associated with the upper Muschelkalk is marked by bfirmgroundsQ colonized by brachiopods (Aigner and Bachmann, 1992), when the rate of subsidence was more rapid than the rate of sedimentation. The record thus implies that when the sea covered extensive areas during the Ladinian maximum transgression, foraminifers of the Tethys migrated to occupy the new coastal habitats that had just developed in the shallower zones of the Betic domain. These newcomers gave rise to communities that became at times very numerous, which supplied skeletal grains to finer-grained, thin, and distinct tempestite units. The occurrence of such bioevent in the southern Iberian Continental Margin was recorded in concentrations of foraminiferal shells in distal tempestites. The benthic foraminifers were carried from the shallowest zones to the deepest zones of the platform by the ebbing currents related to storms. It is this mechanism that gave rise to the distinct foraminiferal marker bed that has been the main focus of this study. Such an becostratigraphicQ marker bed reflects a btaphoeventQ, and the related bioevent can thus be considered isochronous, as corroborated by its distinct spatial continuity in different sections (Figs 1 and 2).

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8. Conclusions In the present study we further confirm the presence of a foraminiferal marker bed just at the limit between two depositional carbonate sequences of the Muschelkalk facies (Majanillos Formation). This bed constitutes a guide level to establish correlations among different stratigraphic sections of Middle–Triassic carbonates around the Betic Cordillera. It can be defined as an becostratigraphicQ marker bed, also termed the foraminiferal marker bed, which is related to a storm-induced foraminifer deposit in the lower zone of the shoreface of the northernmost Betic platform. The appearance of the same foraminifer deposit on top of the transgressive systems tract, at different locations of the Iberian Peninsula, suggests that it is a bioevent related to a global transgressive stage. This major rise in sea level favoured the migration and development of Tethyan benthic fauna that occupied many coastal and lagoon environments. These foraminifer beds in southern Spain, which are situated where there is a substantial change in the lithofacies evolution, corroborate that these deposits may be related to the upper limit of the transgressive sequence when the sea-level rise stabilized during the Ladinian.

Acknowledgements The authors would like to thank P. Plasencia, of the University of Valencia, for his assistance with the conodont study. This investigation was carried out within the Junta de Andalucı´a Research Group RNM 0163 and was supported by Project BTE 2002-00775 of the DGESIC, Ministerio de Educacio´n y Cultura, Spain. This study was part of an international project (IGCP 467: Triassic Time).

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