The Aptian, Albian and Cenomanian of Roter Sattel, Romandes Prealps, Switzerland: a high-resolution record of oceanographic changes

Abstract

The Aptian–Lower Turonian hemipelagic sediments of Roter Sattel in the Swiss Prealps are well dated by planktonic foraminifera. Stacking pattern of the limestone-marl alternations and facies evolution allow the identification of sequence boundaries, transgressive surfaces, and maximum-flooding events or condensed sections on at least two hierarchical levels. Calibrated by a precise biostratigraphic framework, the major sequence boundaries can be correlated with those recognized elsewhere in European basins. Organic-rich black shales are generally confined to transgressive and/or condensed intervals and correspond to the oceanic anoxic events (OAE) 1a–d and 2. OAE 1a and OAE 2 show well-marked positive shifts in δ13C. High-resolution analysis of the Roter Sattel section shows that eustatic sea-level changes and fluctuations in the global carbon cycle are clearly recognizable. However, these were overprinted by regional changes of climate and availability of terrigenous source areas controlling nutrient input and hence organic productivity, and by regional and local tectonics shaping basin morphology and modifying the paths of oceanic currents. This led to facies changes, strongly varying sedimentation rates, and non-deposition or erosion during the Aptian Planomalina cheniourensis Zone. Despite this distortion of the sedimentary record, the Roter Sattel section may serve as a corner-stone for the study of basin-wide or global oceanographic, climatic, and evolutionary changes when correlated with sections in other palaeogeographical domains.