Carbon cycle and sea-water palaeotemperature evolution at the Middle-Late Jurassic transition, eastern Paris Basin (France)

A very high-resolution carbon and oxygen stable isotope analysis (bulk-carbonate) of a bio-stratigraphically well-constrained Callovian-Oxfordian series is provided here for the first time. The homogeneity of the clayey series and the weak diagenetic alteration allow the isotopic signal variations to be considered as primary in origin. A prominent and brief negative excursion in the delta C-13 curve (-2 parts per thousand), occurring at the start of the Middle Callovian (Jason Zone - Obductum Subzone) and correlated regionally, suggests a possible methane release. The increasing delta C-13 values thereafter up to the Early Oxfordian, concomitant with a warming episode, highlight the burial of carbon in organic-rich layers which, in return, may have triggered a decrease in atmospheric pCO(2). At higher frequencies, observed fluctuations of the delta C-13 and delta O-18 values are orbitally driven (405-kyr and 100-kyr eccentricity cycles) and may correspond to the salinity and temperature variability recorded in sea water. The delta O-18 isotopic measurements from well-preserved diagenetically screened belemnites and bivalves along the series, compared to available data from Tethyan domains, agree with the scenario of a global cooling at the Middle-Late Jurassic transition. The well-dated delta O-18 isotopic curve suggests that the onset of this cooling event occurred at the end of the Coronatum Zone (Middle Callovian). (C) 2013 Elsevier Ltd. All rights reserved.