APTIAN DEPOSITS OF THE PROVENÇAL PLATFORM OF SOUTHERN FRANCE: EVIDENCE FOR LOW OXYGEN CONDITIONS AND THE INFLUENCE OF LOCAL PHYSIOGRAPHIC FACTORS

The Lower Cretaceous from Provence is represented by well-lithified light-yellow to white calcarenites with abundant rudist fragments, known as the Urgonian facies. In southeastern France, the Urgonian facies is succeeded by a rhythmic intercalation of bluish-gray, organic carbon-rich marls and marly limestones, beginning in the late early Aptian (late Bedoulian) and continuing through the mid-Aptian (Gargasian). The presence of abundant planktonic foraminifera and echinoid fragments in the bluish-gray marls, from the upper Bedoulian through the Gargasian, indicates influx of terrigenous material coincident with development of nerito-pelagic conditions that favored the accumulation of more organic-rich sediments. Nonetheless, the expression of the Selli-Goguel (OAE1a) event is not apparent in these sediments, and the relative timing of the onset of these special conditions is not yet well established.

Petrographic analyses together with characteristic benthic and planktonic foraminiferal assemblages, and high TOC contents (>1%), indicate that the Gargasian marls in southern France were deposited on the middle to outer shelf, under hypoxic conditions. Molecular biomarker (n-alkanes) distribution and clay mineral abundances further support depositional environments with fluctuating terrigenous inputs through time. Furthermore, common presence of micro-burrows, and the diversity of benthic faunas associated with some layers, indicate periods of increased oxygenation at the bottom that punctuated overall oxygen depleted waters. The absence of a conspicuous OAE signature implies that local physiography of the basin maintained ventilated conditions that overprinted the effects of global oceanic factors that led to anoxia in other basins.