High-resoltion geochemical and biotic records of the Tethyan 'Bonarelli Level' (OAE2, latest Cenomanian) from the Calabianca-Guidaloca composite section, northwestern Sicily, Italy

High-resolution micropalaeontological and chemostratigraphic records for the upper Cenomanian portion of the Calabianca-Guidaloca composite section (NW Sicily) provide new insight into the palaeoclimatic and palaeoceanographic evolution of the Tethys Ocean. The Bonarelli Level equivalent was identified on the basis of lithology and well constrained by calcareous plankton biostratigraphy and radiolarian assemblages, as well as by the delta(13)C curve showing a marked positive excursion (up to 4.7 parts per thousand). The Bonarelli Level equivalent deposition is characterized by highly eutrophic conditions as testified by radiolarian proliferation. Black shale samples from the Calabianca-Guidaloca composite section contain very high TOC (up to 26%) and moderate to high amounts of CaCO3 (on average 20%). Among the planktonic foraminifera, hedbergellids and globigerinelloids tolerated the environmental stress induced by the Oceanic Anoxic Event 2 (OAE2). The occurrence of some benthic foraminifera testifies to dysoxic rather than completely anoxic conditions at the sea floor during the deposition of some portions of the Bonarelli Level equivalent. Based on micropalaeontological results and geochemical proxies (delta(13)C, D*, Rb, Ti, V, Ni, Ba, Si, Cr), the Bonarelli Level equivalent is interpreted as a high-productivity event driven by increasingly warm and humid climatic conditions promoting an accelerated hydrological cycle. We propose that periodically increased riverine influxes, triggered by enhanced humidity, resulted in a sluggish circulation mode and consequent anoxic/euxinic conditions favotning the preservation of organic matter at the sea-floor. Spectral analyses performed on selected geochemical signals reveal within the main high productivity event a strong orbital- climatic forcing represented by a long-term eccentricity-steered humidity cyclicity that amplifies a short-term precession-controlled productivity fluctuation. (C) 2004 Elsevier B.V. All rights reserved.