Orbitally forced climate and sea-level changes in the Paleoceanic Tethyan domain (marl–limestone alternations, Lower Kimmeridgian, SE France)

Abstract

High-resolution analysis of multiple climatic proxies was carried out on a ∼ 8.5-m Lower Kimmeridgian interval of a pelagic marl–limestone succession at Châteauneuf-d'Oze (Vocontian Basin, southeastern France). The aim of the study was to characterize the orbitally controlled sedimentary cyclicity and to decipher paleoclimatic and paleoceanographic changes. All analysed proxies (magnetic susceptibility, carbonate content, manganese content, and bulk carbon and oxygen stable isotopes ( δ 13C and δ 18O) respond in synchrony to orbitally forced climate change. Precession index cycles modulated by short (∼ 100 kyr) eccentricity cycles are strongly expressed in magnetic susceptibility, carbonate and Mn contents but less so in δ 18O. Obliquity cycles are expressed in manganese and particularly in δ 13C. The orbital forcing was conferred to these rhythmic pelagic sediments via paleoclimatic and paleoceanographic changes as follows. Detrital input and marine carbonate production are recorded by the magnetic susceptibility and carbonate signals with strong precession cyclicity. Calcareous nannofossil analysis shows the omnipresence of coccoliths and debris of coccoliths in the marls and limestones, suggesting that the carbonate production was in largest part in situ. Precession index may exert oscillations in the antagonist marine surface productivity and detrital flux processes via solar radiation change. Oxygenation of the seafloor leading to redox cycles is detected in the manganese signal and supported by the δ 13C record, with a strong expression of the obliquity. Finally, paleotemperature variations were deduced from the δ 18O record, although this latter has been in part perturbed by diagenesis. In sum, the variations in the studied proxies suggest a depositional model of combined climate and sea-level cycles forced in concert by Earth's orbital parameters. In particular, the limestones represent warmer climates and higher sea-levels and the marls colder climates and lower sea-levels. This depositional model concurs with a previous depositional model of deep-water carbonates of the German Kimmeridgian, while is in opposition to a previous one of the same section in the Vocontian Basin.