Aptian bio-events - an integrated biostratigraphic analysis of the Almadich Formation, Inner Prebetic Domain, SE Spain

The Upper Barremian to Aptian Almadich Formation (Inner Prebetic Domain of the Betic Cordillera) is composed of hemipelagic sediments deposited on a d istal carbonate ramp in the southern Iberian Palaeomargin. Within this faci es we have found a thick interval of blue to black shales and marls that is interpreted as deposited under oxygen-depleted conditions. We think that t his interval, dated as early Aptian, represents the local record of Ocean A noxic Event la. The integrated biostratigraphic analysis of a section in th e Almadich Formation, by means of planktonic foraminifera, calcareous nanno fossils and ammonites, enables us to recognize most of the biostratigraphic units based on these three fossil groups and to correlate between them. Th e Sartousiana, Sarasini, Weissi, Deshayesi and Furcata (ammonite) Zones wer e identified for the Upper Barremian-Lower Aptian interval. By means of cal careous nannofossil biostratigraphy the Micrantholithus hoschulzii, Hayesit es irregularis and Rhagodiscus angustus Zones, plus several additional bioh orizons, were identified. A quantitative study performed on a set of 27 Low er Aptian samples has enabled the precise identification of the 'nannoconid crisis', the lower limit of which clearly precedes the main anoxic event, and its correlation with other bioevents. Planktonic foraminifera occur con sistently throughout the Lower to Upper Aptian of the Cau section and are m oderately well preserved. This fact allows us to use the most recent taxono mic framework, based on wall texture, to identify the Blowiella blowi, Scha ckoina cabri, Globigerinelloides ferreolensis, Globigerinelloides algerianu s, Hedbergella trocoidea and Ticinella bejaouaensis Zones. Coincident with the anoxic episode, the planktonic foraminiferal assemblages are composed o f a significant number of forms with elongated chambers and/or tubulospines assigned to the genera Claviblowiella, Lilliputianella, Leupoldina and Sch ackoina. Most of the planktonic foraminiferal and nannofossil taxa are illu strated. (C) 1999 Academic Press.