Foraminíferos del tránsito Cenomaniense-Turoniense en la sección de El Chorro, Cordillera Bética, sur de España

Abstract

A climatic, geological and biological global event resulted in sedimentation of black shales at the Cenomanian/Turonian (C/T) boundary, coinciding with the Oceanic Anoxic Event 2 (OAE2) or Bonarelli Event. We present an interdisciplinary analysis of the C/T transition at the Spanish El Chorro section (Betic Cordillera), and show the results of studies on planktic and benthic foraminifera, calcareous nannoplankton, radiolaria and environmental magnetic properties. The planktic foraminiferal biozones Rotalipora cushmani, Whiteinella archaeocretacea and Helvetoglobotruncana helvetica and the calcareous nannoplankton biozones NC11, NC12 and NC13 have been recognized. Diversity of the radiolarian assemblages gradually decreases from the upper Cenomanian towards the middle part of the OAE2 interval, where it reaches the lowest values, recovering above the OAE2. Oxygenation of the sea-bottom waters decreased towards the late Cenomanian, as inferred from a decrease in species size of benthic foraminifera 40 cm below the OAE2. Assemblages from the upper part of the section contain abundant and tiny epifaunal, trochospiral species and representatives of Tappanina, Pleurostomella and small buliminids. These data indicate that low oxygen conditions persisted towards the top of the section, 370 cm above the top of the OAE2 black shales