Deep-water agglutinated foraminifera from the Lower Cretaceous (Neocomian) ‘Complex à Aptychus’ Formation (Corridor de Boyar, Betic Cordillera, southern Spain)

The oldest deep-water sediments of the flysch units in the western part of the Betic Cordillera (southern Spain) arc red and green pelagic claystones with intercalated siliciclastic and carbonate turbidites, ranging from Berriasian to Barremian in age. Autochthonous and redeposited benthic foraminiferal assemblages were studied in outcrops of this ‘Complex à Aptychus’ Formation in the ‘Corridor de Boyar’ near Grazalema. The assemblage of the autochthonous red and green claystones is wholly comprised of agglutinated forms, reflecting deposition beneath the calcium carbonate compensation depth (CCD). Compared to coeval abyssal and deep bathyal assemblages from the NW Australian Margin (Eastern Tethys), the Polish Outer Carpathians and the North Atlantic, the assemblage from the Betic Flysch Zone is more related to its Tethyan equivalents and may represent a truly abyssal Early Cretaceous sub-CCD environment.


INTRODUCTION
Lower Cretaceous litho-and biofacies which are typical of a sub-calcium carbonate compensation depth (CCD) environment are poorly represented in the North Atlantic and western Mediterranean orogenic belt due to a relatively deep CCD in the Western Tethys at the time (deeper than 4 km according to Tucholke &. Vogt, 1979). Typical Lower Cretaceous sedimentary formations in this area are the Blake Bahama Formation (Jansa et al., 1979) in the North Atlantic and the rather similar Majolica Formation in the Western Mediterranean area, both ranging from late Tith0nia.n to Barremian in age. Pelagic limestone deposition prevailed thiroughout this time interval. Oxygenated seafloor-conditions persisted throughout the Berriasian, but beginning in the Valanginian there is evidence for increasingly common episodes of poorly oxygenated bottom water ('l'ucholke & Vogt, 1979). Owing to the dominance of pelagic limestones in deep-water sequences and the often poorly oxygenated conditions in intercalated shaly intervals occurrences of rich . benthic deep-water forminiferal assemblages from this time interval are exceptional curiosities. Lower Cretaceous abyssal and deep bathyal foraminiferal assemblages have so far been described from the Argo Abyssal Plain off the NW Australian Margin in the Eastern Tethys (Kuznetsova, 1974;Bartenstein, 1974;Riegraf & Luterbacher, 1989;Kaminski et a / . , 1992), the Cieszyn Limestone Formation in the Polish Outer Carpathians (Geroch & Olszewska, 1990), and the Blake-Bahama Fomation of the North Atlantic (Luterbacher, 1972;Maync, 1973;Kuznetsova & Seibold, 1977;Gradstein, 1978;Sigal, 1979;Sliter, 1980;Riegraf & Luterbacher, 1989).
During a re-examination of the oldest deep water sediments of the flysch units in the western termination of the Betic Chain and the Campo de Gibraltar, the so-called 'Compl'ex B aptychus' Formation (Didon et a / . , 1973), the so far oldest well-preserved andl diverse abyssal agglutinated foraminiferal assemblage of the Western Mediterranean was found i n the Corridor de Boyar Unit near Grazalerna. Eleven large bulk samples of 1-2 kg weight were removed from various lithologies in the 'Complex aptychus' formation in the Corridor de Boyar (western part of the Betic Cordillera. Andalousia). Six of these samples, which were removed from greyish marlstones and greenish claystones were completely barren or contained only non identifiable fine-grained carbonate detritus, indicating that these sediments represent fine-grained parts of turbiditcs. Four samples from coarse grained laminated and graded turbidity sequences are mainly made up by fragments of aptychii and contain rich redeposited assemblages of benthic foraminifera. This study mainly focuses on autochthonous abyssal agglutinated foraminifera from two large bulk samples of the multicolored claystone in the lower part of the 'Complex B aptychus' formation. The bulk samples have been split in several subsamples, completely desintegrated in diluted buffered hydrogen peroxide and anionic tensides and washed over a 6 3 p m sieve. Four replicate samples were completely picked for foraminifera. The assemblages of 400-800 specimens were mounted in Plummer-slides, determined and counted.
The two main objectives of this taxonomic and palaeoenvironrnental analysis of the autochthonous agglutinated foraminifera of the 'Complex B aptychus' Formation in the Corridor de Boyar are: (1) using benthic foraminiferal assemblages as a tool for the reconstruction of the Early Cretaceous palaeoenvironment and palaeobathymetric evolution of the Alboran Margin; (2) achieving a better understanding of the palaeogeographic position of the Corridor de Boyar deep-water basin by comparison of its benthic foraminiferal assemblages with coeval abyssal and deep bathyal assemblages from Argo Abyssal Plain (NW Australian Margin. Eastern Tethys), the Cieszyn Limestone Formation in the Polish Outer Kuhnt where autochthonous pelagic sediments of the 'Betic Seaway' (Subbetic Zone,Fig. 1.) interfinger with the flysch units of the Campo de Gibraltar (Fig. 1). Occurrences of this Berriasian-Barremian 'Complex B aptychus' formation are scarce in this area and generally covered by vegetation. However, outcrops in the surroundings of a small mountain pass, about 1 km NNW of the village of Grazalema (4071.800 N,288.300 E, sheet 14-44 Ubrique of the Mapa Militar de Espaila 150 000) allow not only sampling of the turbiditic beds but also the intercalated hemipelagic and pelagic multicolored claystones (position of the locality is indicated as 'Boyar' on Figs 1 and 2).
Carpathians, and the Blake-Bahama Fomation of the North Atlantic, and thereby evaluating the potential of Lower Cretaceous deep water agglutinated foraminifera1 (DWAF) assemblages for studies of Tethyan palaeobiogeography and palaeoceanography .

SAMPLE LOCALITY
Objective of this study is to examine the age and palaeoenvironment of the stratigraphically oldest formation within the 'Corridor de Boyar' Unit near Grazalema. This unit is situated in the western part of the Betic Cordillera, Main structural units of the Relic Cordillera (southern Spain). Compiled using data o f Azema rr d. (1979) and IGME, Geological Map 1:400 000.

GEOLOGICAL SETTING
The structural and palaeogeographical setting of the 'Corridor de Boyar' near the village of Grazalema has been a point of vigorous discussion since the classic works of Blumenthal (1927Blumenthal ( , 1935~4 19356, 1936 and Fallot (1930Fallot ( , 1948. At the Puerto de Boyar, west of Grazalema a Lower Cretaceous flysch type sedimentary sequence is tectonically sandwiched between a Penibetic carbonate platform sequence to the south and an Upper Jurassic carbonate platform sequence to the North (Sierra del Pinar). The origin and palaeogeographical position of this northern unit has been interpreted in very different ways. Hoeppener et al. (1964~. 6) preferred a reconstruction where the present arrangement of units corresponds to their former palaeogeographical position. Hoppe (1968) regarded the Sierra del Pinar as part of a large overthrusted mass, the root of which may have been south of the Penibetic, but regarded the flysch-type sediments of the Corridor de Boyar as autochthonous. More recent reconstructions (Dubois, 1971;Bourgois, 1978) suggested also for the Corridor de Boyar sequences a palaeogeographical origin south of the Penibetic and coinsidered the Sierra de Pinar units as part of the stratigraphic basement of the Corridor de Boyar sequence. Thurou (1987) suggested a close palaeogeographical relationship between the Median Subbetic units and the Corridor de Boyar sequences from similarities in the composition of their clastic components. Consequently the palaeogeographical position of these units is regarded as north of the Penibetic zone. In all these reconstructions surprisiingly little attention hils been paid to the possible influence of lateral movements on the present-day configuration of structural units. Leblanc & Olivier (1984) estimated a 400km dextral lateral displacement of the Alborati block along its northern margin (the North Betic Fault). Important lateral displacements may also have affected the more northerly palaeogeographical zones and it is quite possible, that the present day N-S transect across the Coirridor de Boyar includes units that were originally situated several hundred kilonietres to the east.
The theory of Bourgois (1978), that the sedimentation within the Corridor de Boyar is the stratigraphic continuation of the Sierra del Pinar sequence is now widely accepted (Duirand Delga, 1980;Thurow, 1987). The Sierra del Pin,ar is formed by a thick Liassic carbonate platform, which was drtowned during the late Dogger and early Malm (Bathonian?-Kimmeridgian), approximately coeval with the formation of the Mauretanian basin, the Betic seaway and the deep central North Atlantic. Durand Delga (1980) compmed the palaeogeographical position of the Corridor de Boyar series with the Djebel Moussa in Northern Morocco, which can be regarded as a deep part of the Alborati Margin (Predorsalien Unit in the sense of Olivier, 1984). Its strange present day position north of the Penibetic Unit can be explained by a northward transport of the unit by large-scale overthrusting or within gigantic olisthostromes (Bourgois, 1978) or, more likely, by dextral strike-slip and/or rotational movements parallel to the major dextral strike-slip zone which separates the internal and external Betic Zones (Durand Delga, 1980). In both cases, the Sierra del Pinar-Corridor de Boyar sedimentary sequence can be regarded as part of the late Jurassic-Cretaceous continental margin of the Alboran microcontinent (Fig. 2).

OF CRAZALEMA
The sedimentary succession within the Corridor de Boyar Unit was intially described by Bourgois (1978). A recent re-exaniination of the sequenc(e (Thurow, 1987) added more detailed sedimentologic descriptions and a precision of the biostratigraphy using radiolarian assemblages but did not substanlially change the initial stratigraphic subdivisions (Fig. 3 ) . This study concentrates on the stratigraphically deepest units (subunits A l -A3 according to Bourgois, 1978), which can be observed NNW of Grazalema in a tectonically disturbed but generally continuous succession from W-E. The oldest subunit ( A l ) is the only sequence where autochthonous deep-water foraminiferal assemblages have been obtained. A typical sedimentary sequence within this subunit comprises fine-grained carbonate turbidites with a maximum thickness of 20-30 cm, and hemipelagic and pelagic claystones with a thickness of a few tens of centimetres (Fig. 3). The whole sequence is intensely tectonically folded, and synsedimentary folding can also not be excluded. The overlying unit (A2) contains siliciclastic turbidites of up to SO cm in thickness and intercalated calcareous-marly sediments ('preflysch' of the French authors). Micropalaeontologic samples from the marly hemipelagic layers in this unit were barren, but samples from the bases of turbidites yielded rich redeposited assemblages of typical Tethyan outer shelf and slope benthic foraminifers of Berriasian to Barremian age. The following age-diagnostic species have been identified: 1966 Occasionally redeposited macro-invertebrates have been found, which allow a tentative dating of this subunit as Berriasian to Valanginian. Characteristic forms are (Bourgois, 1978 and sample E30/20): Larnellaptychus suhrnortilleti Trauth Punctaptychus ex gr. punctatus (Voltz).

FAUNAL CHARACTERISTICS AND PALAEOENVIRONMENT
Autochthonous benthic foraminiferal assemblages are exclusively made up of agglutinated foraminifera with organic, diagenetically silicified cement. Calcareous benthic foraminifera and agglutinated foraminifera with carbonate cement occur only in redeposited assemblages.
A striking characteristic of the Early Cretaceous abyssal agglutinated foraminifera1 assemblage is a small test size. Tests with a maximum length of more than 200 p m make up less than 1% of the total assemblage and forms larger than about 400 p m are virtually absent. This unusual size distribution can be either explained by slow growth rates due to limited resources, or by high reproduction rates which may have been triggered by short seasonal spikes in phytodetritus supply, as it can be observed in Recent oligotrophic deep-sea areas.
Tubular morphotypes with epifaunal habitat (e.g. Rhizammina indivisa) are generally rare. However, the fossilization potential of these forms is low and is probably dependent on sedimentation rates. Since sedimentation rates in the early Cretaceous of the Corridor de Boyar were undoubtedly low, a lack of epifaunal soft-walled agglutinated foraminifera such as rhizamminids is not surprising.
Significant differences are observed between assemblages from red claystones (referred here as type A assemblages), indicating oxic bottom water conditions and from green claystones (type B assemblages, mildly dysaerobic bottom waters, see Fig. 3 Bourgois, 1978) and typical sequence within the Subunit A1 of the 'Complex a aptychus' Formation. In the studied outcrop thesc sequences are now generally overturned and intensely folded. No autochthonous benthic foraminifera1 assemblages are so far known from the units D to F in the Corridor de Boyar area. These sequences may consist exclusively of redeposited material.
Verneuilinoides, Pseudoboliuina, Pseudoreophax and Bulbobaculites dominate in the red claystones (Table 1, Fig.  4). These four genera make up about 60% of the assemblage. Ammodiscids are mainly represented by the species Glomospira gordialis and Glomospira charoides, which occur as infauna in Recent deep sea sediments (Gooday, 1990;Kuhnt, Collins & Scott, unpublished observations). Planispiral ammodiscids also occur, but there is an unusual dominance of the genus Glomospirella, whereas true Ammodiscus have only been observed in single specimens. All these aspects of the 'red' assemblages point to a deep-water environment, which is largely sheltered from terrigeneous detritic flux, oxic (cool?) bottom water masses, generally low surface productivity, and possibly a pronounced seasonality in phytodetritus supply from primary production.
Assemblages from green claystones differ from the 'red' assemblages mainly in the distribution pattern of the genera Pseudoreophax, Bulbobaculites, Haplophragmoides, Glomospirella and Glomospira (Fig. 4). Pseudoreophax and Bulbobaculites are almost absent in the 'green' assemblage. Both these forms can be regarded as infaunal morphotypes which may be sensitive to a Redox-line close to the sediment surface. A similar occurrence restricted to red, oxic claystones has been observed for the Cenomanian-Turonian species Bulbobaculites problematicus in the Carpathians and the North Atlantic (Kuhnt & Kaminski, 1990). The genera Haplophragmoides, Glomospira and Glomospirella are significantly more abundant in 'green' assemblages (Fig. 4). These forms are characteristic representatives of Biofacies B assemblages (Kuhnt et al., 1989), which characterize environments under mildly oxygen-deficient conditions at the sea-floor and probably increased surface water productivity. Their life habitat has been interpreted as epifaunal detritus-feeders which can take advantage of enhanced food supply from phytodetritus and are less sensitive to oxygen deficiency.

PALAEOBIOGEOGRAPHICAL ASPECTS
The new observations on earliest Cretaceous deep-water agglutinated foraminifera in the Corridor de Boyar of the Betic Cordillera confirm the cosmopolitan distribution of these forms. Most of the 18 genera and 26 species observed in the Berriasian-Valanginian of the 'Complex i aptychus'  Quantitative composition of autochthonous deep-water agglutinated foraminifera1 assemblages from green and red claystones in the 'Complex i aptychus' unit. The plot is based on 1665 specimens counted from red claystones and 632 specimens counted from green claystones. Arrows indicate forms with significant differences in distribution between red and green claystones. unit seem to occur within the entire Tethys ocean. Occurrences of similar assemblages are known from the West Australian Margin (Indian Ocean = Eastern Tethys), the Polish Carpathians and the Central North Atlantic (= western termination of the Tethys ocean). However, this type of 'Tethyan' abyssal and deep-bathyal assemblages is not known from high latitude areas. It may be speculated that most of the forms observed in these assemblages have their ecological niche in deep-sea environments with restricted resources, and are unable to compete with other forms in more favourable environments.

CONCLUSIONS
The Cretaceous turbiditic sequences of the Corridor de Boyar unit were deposited in a deep continental margin setting close to the western termination of the Alboran Block. Sediments and autochthonous benthic foraminiferal assemblages within the Corridor de Boyar basin represent a truly abyssal sub-CCD environment as early as in Berriasian-Valanginian times. The foraminiferal assemblage is composed of cosmopolitan forms, fairly diverse (26 species) and not dominated by single species. Red sediment colour and the presence of numerous infaunal benthic foraminiferal morphotypes indicate well-oxygenated bottom-water conditions within the basin. From these observations can be concluded that during Berriasian-Valanginian times the Corridor de Boyar flysch basin was connected to the belt of Lower Cretaceous flysch basins within the western Tethys (Durand Delga, 1980) and had deep-water connections to the Tethys ocean and the central North Atlantic abyssal basin. The main subsidence phase of this part of the western Alboran margin was already terminated in the Berriasian-Valanginian and probably took place within a short time interval in the latest Jurassic. This Late Jurassic subsidence phase coincides with the first formation of oceanic crust on the Tagus Abyssal Plain (Mauffret ef ul., 1989). Transform directions associated with this old spreading ridge are WSW-ENE (Malod, 1989) and thus in agreement with the general trend of the northern margin of the Alboran block at this time (compare Fig. 2). Kinematic reconstructions of the Iberian plate (Malod, 1989) predict a significant extension between Africa and Iberia during the Late Jurassic rifting. It may be speculated that the abyssal Corridor de Boyar basin was formed along a transform-margin of the Alboran block during a Late Jurassic extensional phase, which affected not only the Explanation of Plate 1 Brady (1884), sample E30/10, X170. Fig. 2. Rhubdummina cylindricu Glaessner 1937, sample E30/10, X 170. Fig. 3. Hyperamminu gaultina Ten Dam 1950, sample E30/10, X170. Fig. 4. Hyperammina cf. difurata Grzyhowski 1x96, sample E30/10, X170.  (Berthelin 1880), sample E30/10, X 125. Figs 12-13. Glomospira irregularis (Grzybowski 1898), sample E30/10, X170. Fig. 14. Saccamminu grzybowskii (Schubert 1902), sample E30/10, X 170.

Kuhnt
Tagus abyssal plain but also the southern Iberian margin and Alboran block.

Haplophragmoides sp. A
Remark. Test small, smooth, with four to five chambers in the last whorl and a rounded periphery. Remarks. This form resembles Haplophragmoides kirki Wickenden, a shallow-water form from the Upper Cretaceous of Alberta, in its planispiral test with four or five globular chambers in the last whorl. Haplophragmoides sp. B is kept separate here because of its significantly smaller size, and its different stratigraphic and environmental distribution. Vasicek, 1947 (Pl. 1, fig. 5 Vasicek;Geroch & Nowak: 228, pl. 1, fig. 7, pl. 5, fig. 4-5. 1986 Hippocrepina depressa Vasicek; Bartenstein & Bolli:

Hippocrepina depressa
1989 Jaculella depressa (Vasicek);Riegraf & Luterbacher: 1085-1986 Remarks. H. depressa is a very characteristic species of the Lower-to Mid-Cretaceous 'flysch' and pelitic series of the Polish Carpathians and the Gibraltar Arch area. Specimens of Leg 50 DSDP in the eastern North Atlantic belong to a deep-sea foraminifera1 assemblage of Berriasian(?)-Valanginian age with water depths of 2000m and more (Sliter, 1980 specimens are generally compressed, whereas other foraminifers in the same assemblages are not compressed (Loeblich & Tappan, 1988).
Pseudobolivina cf. rnunda Krasheninnikov, 1973Krasheninnikov, 1973 cf. Pseudobolivina munda Krasheninnikov: 210, pl. 2, Remarks. Differs from the typical Late Cretaceous P. munda in possessing a slightly twisted initial portion. Differs from P. uariabilis Vasicek 1947 in possessing an apertural neck. Morphologically similar forms of the genus Plectinella do not possess a terminal aperture produced on a short neck.
Pseudobolivina sp. A (Pl. 4, figs 9-11) Remarks. After an initial regular biserial stage with a tendency to becoming uniserial with the last 3 chambers. Differs from Pseudobolivina variabilis Vasicek 1947 in its tendency to a uniserial final stage and in a twisted chamber arrangement.

Trochammina quinqueloba
Remarks. The test is coiled in a somewhat irregular low trochospire. Finely agglutinated wall with a mooth surface.

ACKNOWLEDGEMENTS
The study of the palaeoecology and biogeography of deep-water benthic foraminifera in various basins of the Western Mediterranean is part of the ALKAPECA-project at the University of Tiibingen which is supported by the Deutsche Forschungsgemeinschaft. I am grateful to all members of the working group, especially Thomas Pletsch, Klaus Reicherter and Jost Wiedmann for their support and stimulating discussion. I also want to thank Jiirgen Thurow (University of Bochum) for joint field-work in the 'Corridor de Boyar' and for providing additional sample material. Stanislaw Geroch (Jagiellonian University, Krakow) and