Palaeogeography, Palaeoclimatology, Palaeoecology 224 (2005) 186–199 www.elsevier.com/locate/palaeo Biotic changes linked to a minor anoxic event (Faraoni Level, latest Hauterivian, Early Cretaceous) Miguel Companya,*, Roque Aguadob, Jose´ Sandovala, Jose´ M. Taveraa, Concepcio´n Jime´nez de Cisnerosc, Juan A. Veraa aDepartamento de Estratigrafı´a y Paleontologı´a, Facultad de Ciencias, Universidad de Granada, 18002 Granada, Spain bDepartamento de Geologı´a, Escuela Universitaria Polite´cnica de Linares, Universidad de Jae´n, 23700 Linares, Spain cEstacio´n Experimental del Zaidı´n (CSIC), C/ Pedro Albareda, 1. 18008 Granada, Spain Received 19 January 2004; received in revised form 22 October 2004; accepted 23 March 2005 Abstract A conspicuous renewal in the ammonite faunas of the Mediterranean Tethys occurred in the latest Hauterivian. This faunal turnover took place following a stepwise pattern. The first step occurred at the boundary between the Pseudothurmannia ohmi Subzone and the Pseudothurmannia mortilleti Subzone, coinciding with the base of the so-called Faraoni Level. This is a Corg- rich interval that has been recognised in several basins of the Mediterranean Tethys and seems to be the expression of a short- lived oxygen-deficient event. It correlates with a well-documented second-order peak transgression. The oxygen depletion preferentially affected the deep nektic ammonites, which would explain the extinctions within this group around the Faraoni Level. On the contrary, an increase in the trophic resources in the photic zone favoured the diversification of epipelagic ammonites. Concurrently, an abrupt change took place at this level in the nannoconid assemblage composition. A minor second event, located at the base of the Pseudothurmannia picteti Subzone, was marked by the replacement of a few planktic ammonite species by closely related forms, and the structure of the ammonite assemblage was not substantially altered. The coincidence of this event with a further restructuring of the calcareous nannofossil assemblage suggests that some changes had to occur in the planktic ecosystem during the sea-level highstand subsequent to the peak transgression. The third and last stage of the renewal process started in the upper part of the P. picteti Subzone, coinciding with a drastic sea-level fall. It is characterised by the extinction of many of the species that had appeared in the two previous events, resulting in an extensive modification of the assemblage structure. The regression would probably cause a drop in the primary productivity and, consequently, an improvement in the oxygenation level of the sea bottom. This would explain the extinction of several planktic ammonite species and the appearance of new nektic and nektobenthic lineages. D 2005 Elsevier B.V. All rights reserved. Keywords: Biotic changes; Anoxic event; Ammonites; Calcareous nannofossils; Hauterivian; Mediterranean Tethys * Corresponding author. Tel.: +34 958243201; fax: +34 958248528. E-mail address: [email protected] (M. Company). 0031-0182/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.palaeo.2005.03.034 M. Company et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 224 (2005) 186–199 187 1. Introduction in sea level would have caused a severe telescoping of ammonite biotopes over the shelf edge, hence enhanc- The ammonite faunas of the Mediterranean Tethys ing selection pressure and extinction. underwent a remarkable turnover during the latest The start of this renewal process coincides with the Hauterivian and earliest Barremian. More than 90% so-called Faraoni Level, a Corg-rich stratigraphic in- of the species present in this interval were involved in terval, which has been recognised in several western the renewal, and taxa that had been major components Mediterranean basins and has been interpreted as the of the Hauterivian assemblages (like the Criocera- sedimentary record of a short-lived oxygen-deficient tites–Pseudothurmannia lineage or the genera Ple- event (Cecca et al., 1994; Baudin et al., 1999, siospitidiscus and Neolissoceras) disappeared at that 2002a,b). Moreover, marked changes in the microflo- time and were replaced by typical Barremian groups ral and microfaunal assemblages have also been (Barremites and the first representatives of Silesitidae, recorded within this interval (Coccioni et al., 1998). Holcodiscinae, and Leptoceratoidinae). Hoedemaeker In this paper, we analyse the extent and signifi- (1995a,b) previously documented this turnover, which cance of this ammonite faunal turnover, which we he related to a rapid eustatic sea-level fall. Such drop reinterpret in the context of the Faraoni event. 0 0 ALBACETE 1 0 Oliva 9 IBERIAN PENINSULA 8 Alcoy Elda 7 ALICANTE Elche Caravaca 3 5 4 0 38 6 MURCIA JAEN Huéscar 1 2 Lorca Cartagena Baza Lucena Iberian Massif Guadalquivir Bassin GRANADA Prebetic 370 ALMERIA Subbetic Internal Zones MALAGA Mediterranean Sea 0 50 100 150 Km Fig. 1. Simplified geological map of the Betic Cordillera and location of the studied Hauterivian/Barremian boundary sections: (1) Barranco de la Aguzadera (sections X.G and X.G1); (2) Ermita de Cuadros (section X.EC); (3) Rı´o Argos (sections X.Ag1, X.Ag4 and X.Ag5); (4) Barranco de Cavila (section X.Kv3); (5) Arroyo de Gilico (section X.V1); (6) Cerro del Tornajo (sections X.Tj1 and X.Tj2); (7) Sierra del Cid (sections X.A1 and X.A2); (8) Barranco de la Querola (section X.Q); (9) Cantera de l’Almuixic (section X.O). 188 M. Company et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 224 (2005) 186–199 2. Biostratigraphic framework et al., 2003) by establishing a subdivision of the zones classically admitted within this interval. Thus, the C. 2.1. Ammonite biostratigraphy balearis Zone is divided into four subzones defined by the consecutive appearance of four species belong- This study is based on the stratigraphic distribu- ing to the same Crioceratites lineage: C. balearis, C. tion of more than 5000 ammonites collected bed-by- binelli, C. krenkeli and C. angulicostatus. The P. ohmi bed from 14 sections located in different palaeogeo- Zone comprises three subzones characterised by three graphic domains of the Betic Cordillera, southeastern successive species of the genus Pseudothurmannia: P. Spain (Fig. 1). Widespread lithostratigraphic and ohmi, P. mortilleti and P. picteti. The lowermost biostratigraphic markers have enabled a precise cor- Barremian T. hugii Zone can in turn be divided into relation between those sections and the construction a lower T. hugii Subzone and an upper Psilotissotia of accurate composite ranges for the ammonite spe- colombiana Subzone. cies (Fig. 2). Published data from other areas (mainly Ammonites are scarce in the lower part of the C. SE France and Italy) have also been taken into balearis Zone. For this reason, we have limited our account. study to the interval between the upper part of that The stratigraphic interval analysed corresponds to zone and the lower part of the T. hugii Zone, where the uppermost Hauterivian and the lowermost Barre- ammonites are much more abundant and data are mian, including the Crioceratites balearis, Pseu- more consistent. dothurmannia ohmi and Taveraidiscus hugii Zones. The biostratigraphic scheme used in this paper is that 2.2. Calcareous nannofossil biostratigraphy proposed by Company et al. (2002, 2003), which improves the resolution of the current standard zona- The stratigraphic distribution of calcareous nan- tion (Hoedemaeker and Rawson, 2000; Hoedemaeker nofossils has been investigated in four selected sec- s latum bulum ficilis dius anum li e pseudomalbosi ohmi winkleri morloti guerini subgrasianum ras infundi nnia picteti ras nnia nnia mortilleti nnia s hugii interme subcylindrica jourdani fumisugina uhligi munieri thetys favrei vermeuleni neumayri mallada ” boutini dimboviciorensi tabarelli meriani obliquestrangu densifimbriatum spp. ceras thiollierei ceras koechlini sotia mazuca oceras pitidiscus subdif s atites angulicostatus atites binelli atites majoricensis atites krenke Sequence stratigraphy Subzone (adapted from Barremites Zone Anahamulina Anahamulina Originations Arnaudiella Psilotis Anahamulina Phyllopachyce Acrioceras ramkrishnai Acrioceras Pseudothurma Emerici Paraspinocera Emerici Acrioceras Discoidellia Phyllopachyce Plesios Lytoceras subfimbriatum Lytoceras Pseudothurma Hamulinites nicklesi Pseudothurma Silesite Abrytusites Discoidellia Pseudothurma Phylloceras Hamulinites Neoliss Lytoceras Barremites Paraspiticeras Criocer Extincions Criocer Taveraidiscus Criocer Criocer Taveraidiscus “ “Barremites” Hardenbolet al. 1998) STAGE . ) TS T. hugii My (p.p. BAR T.hugii 3 127.10 P. picteti SBHa7 2 P. mortilleti Faraoni Level P. ohmi p.p . 1 MFS 127.39 () P. ohmi C. anguli- TS costatus (p.p.) SBHa6 127.82 HAUTERIVIEN C. krenkeli MFS 128.10 C. binelli C. balearis ABCDE F TS 4 2 0 2 4 6 Fig. 2. Stratigraphic distribution, extinction and origination levels, and turnover steps (1,2,3) of the ammonite species throughout the Hauterivian/Barremian boundary interval in the Mediterranean Tethys. Inferred life-habit groups: (A) planktic drifters; (B) epipelagic vertical migrants; (C) epipelagic nekton; (D) mesopelagic vertical migrants; (E) mesopelagic nekton; (F) nektobenthic. M. Company et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 224 (2005) 186–199 189 tions (X.G1, X.EC, X.Ag1 and X.V1 in Fig. 1). untreated samples in order to retain the original Sampling was restricted to the marly interbeds, sample composition unaltered,