Orbital forcing in a 'Boreal' Cretaceous epeiric sea: high-resolution analysis of core and logging data (Upper Albian of the Kirchrode I drill core -Lower Saxony basin, NW Germany)

A 245 in (0-245 in subsurface) core of Upper Albian marine sediments from N orth Germany (research well Kirchrode I) was studied to identify sequences and cycles of sedimentation and related forcing mechanisms on sedimentation in an epeiric sea of the (sub)-'Boreal' realm. The care consists of monoto nous gray marls with an exceptionally high sedimentation rate of 8-12 cm ka (-1). In total, it represents a period of approximately 2.5-4 Ma. A silty g lauconite-rich condensed layer marks a change in the succession at 132 in a nd is paralleled by the first occurrence of E. turriseiffelii and G. benton ensis. The lower part of the core shows lenticular bedding, siderite nodule s, average CaCO3 content of ca. 40% and an abundance of inoceramids (Inocer amus anglicus, Birostrina lissa, Actinoceramus sulcatus). The upper part is characterised by plane bedding, common siderite layers, an average CaCO3 c ontent of ca. 35% and an abundance of aucellinas (Aucellina gryphaeoides). According to lithology and ichnofacies, the succession represents a transgr essive-regressive cycle with distinct bimodality of lithology, fossil, and trace fossil content together with reworking and redeposition at the base a nd top. We studied well-log-data, sediment composition, sediment color, and carbona te content and applied various mathematical analysis techniques to these da ta (principal component analysis, spectral analysis (Fourier-transform), au tocorrelation). Spectral analysis revealed well-pronounced periodic cyclici ty in the upper part of the Upper Albian (12, 8, 4.5, 3.4, 1.7 in). The 12 m-eccentricity cycles are the most intense cycles reflecting periodic chang es in the terrigenous clastic supply. Chaotic transitional intervals occur around the Middle-Upper Albian, Upper Albian and topmost Albian parts of th e core. They are characterised by non-cyclic changes in litho- and biofacie s. Mathematically, these changes correspond to singularity points. They are preceded by non-orbital high-frequency variations in carbonate content and in gamma -ray. (C) 2001 Elsevier Science B.V. All rights reserved.