The Barremian–Aptian interval in NW Germany: A review

Abstract

A multidisciplinary research group has studied marine sediments of Barremian–early Aptian age in NW Germany. Disciplines and aspects involved include sedimentology, palaeogeography, calcareous nannofossils, calcispheres, palynomorphs, mineralogy, and organic and inorganic geochemistry. The objectives of this multidisciplinary study were to test the interaction of biota and sediments during this critical interval and to evaluate regional and global processes which may have caused the deposition of Barremian and early Aptian muds in NW Germany, now preserved as black shales.Both biota and sediments show similar trends throughout the Barremian and lowermost Aptian. Endemic evolution of marine biota (calcareous nannofossils, foraminifera, belemnites and ammonities) coincides with the deposition of black clays and laminated sediments in the Barremian. These patterns reflect restricted conditions in a marginal epicontinental sea. The laminated sediments of the Barremian and earliest Aptian, which are rich in Corg, were deposited under anoxic conditions. Palaeotological and geochemical data indicate a major oceanographic change well before the deposition of the final laminated horizon, the Fischschiefer (early Aptian,Deshayesites deshayesiZone). A turnover of planktonic and nektonic organisms from endemic associations to homogenous cosmopolitan forms occurred in earliest Aptian times.The Barremian laminated sediments are believed to have been caused by a thermally induced stable water stratification. The early Aptian Fishschiefer is interpreted as an anoxic sediment of a stagnant environment, having been caused by a slight reduction in the salinity of surface waters. Despite the stratigraphic correlation of the Fischschiefer with the global ‘Ocean Anoxic Event 1a’ (OAE1a), we believe that the deposition of the Fischschiefer was controlled by regional factors.