Lower Upper Cretaceous standard section of the southern Münsterland (NW Germany): carbon stable-isotopes and sequence stratigraphy
Richardt, Nadine; Wilmsen, Markus
published: Apr 1, 2012
Two cores from two localities (Anröchte and Werl drill-holes) situated at the southeastern margin of the Münsterland Cretaceous Basin (MCB; NW Germany) have been logged bed-by-bed and sampled at 0.5 m-intervals for chemostratigraphic investigation. Detailed studies provide new data for establishing a standard section through the lower Upper Cretaceous (Lower Cenomanian - Middle Coniacian) of the “Haarstrang area. The Upper Cretaceous succession has a thickness of about 180 m in total - including an overlap of 7.00-8.70 m in the Middle Turonian interval - and overlies strata of Carboniferous age. The Anröchte core contains sediments of the Essen Greensand, Baddeckenstedt and Brochterbeck formations as well as the Büren and the lower part of the Oerlinghausen formations (Lower Cenomanian - lower Middle Turonian), while the Werl core penetrates the middle and upper part of the Oerlinghausen Formation, the Salder Formation developed in Soest Greensand facies, the Erwitte and lower Emscher formations (lower Middle Turonian - Middle Coniacian). The rather proximal depositional position of the cores has resulted in condensed lithofacies and relatively low thicknesses, especially for the Cenomanian. Moreover, new results require minor revisions of the established lithostratigraphic scheme. Based on carbon stable-isotope data, an overlap of the two core sections has been identified. All isotope events reported from contemporaneous successions (e.g., Baddeckenstedt, Halle/Westfalen, Oerlinghausen, Salzgitter-Salder and Dover) have been recognized and correlated inter-regionally. Through the Cenomanian, these are - in ascending order - the vaguely placed LCE I-III, the provisionally located Crippsi and Virgatus Beds events, the MCE I (only MCE Ib peak is present), the MCE sensu Ernst et al. as well as the P/B Break, MCE II, Jukes-Browne, Amphidonte Bed and Monument isotope events. The positive excursions of δ13C values during the Cenomanian Oceanic Anoxic Event MCE I and OAE 2/CTBE is also well represented. Furthermore, the Turonian interval shows the Holywell, Lulworth, Round Down, low-woollgari, Glynde, Pewsey, Lower and Upper Southerham, Caburn, Bridgewick, Hitch Wood and Navigation events. In the Coniacian, the Beeding, Light Point and East Cliff events are developed. Sequence boundaries of major significance are observed as omission and/or erosion surfaces followed by conspicuous, lithoclastic marl layers and are often characterized by abrupt facies changes. Major unconformities (SB Ce 1-5, SB Tu 1-5, SB Co 1) are related to eustatic 3rd-order sea-level falls and are well known from many Cretaceous localities, particularly in Europe.