Abstract: The Söhlde Formation (Upper Cenomanian-lower Upper Turonian) of Lower Saxony and Sachsen-Anhalt is characterized by an alternation of red and white limestones of a pelagic biosedimentary system, deposited ca. 200 km distant from the nearest coastline on the European Cretaceous shelf sea at a paleolatitude around 45° N. Seven sedimentary cycles of ca. 430 ky duration can be recognized, each of which is separated by discontinuities and/or significant facies changes. White limestones and marl–limestone alternations were deposited mainly in intrashelf depressions and/or during relative sea–level highs. The red limestones were deposited on intrashelf swells above and shortly below storm wave base. Storm-and current-induced advective pore-water flow associated with low accumulation rates in a nutrient-depleted intrashelf swell setting (low C org flux into the sediment) resulted in an excess of oxygen in the sediment column and an early diagenetic window, in which ferric iron minerals were generated, causing the red pigmentation. The source of the iron was most likely clay minerals, inasmuch as a positive correlation between clay content and red pigmentation is observed. No trace of microbial activity associated with the genesis of the red color can be confirmed yet.

Abstract During the Cretaceous (145.5-65.5 Ma; Gradstein et al. 2004 ). Central Europe was part of the European continental plate, which was bordered by the North Atlantic ocean and the Arctic Sea to the NW and north, the Bay of Biscay to the SW, the northern branch of the Tethys Ocean to the south, and by the East European Platform to the east ( Fig. 15.1 ). The evolution of sedimentary basins was influenced by the interplay of two main global processes: plate tectonics and eustatic sea-level change. Plate tectonic reconfigurations resulted in the widening of the Central Atlantic, and the opening of the Bay of Biscay. The South Atlantic opening caused a counter-clockwise rotation of Africa, which was coeval with the closure of the Tethys Ocean. Both motions terminated the Permian-Early Cretaceous North Sea rifting and placed Europe in a transtensional stress field. The long-term eustatic sea-level rise resulted in the highest sea level during Phanerozoic times ( haq et al. 1988;Hardenbol et al. 1998 ). Large epicontinental shelf areas were flooded as a consequence of elevated spreading rates of mid-ocean ridges and intra-oceanic plateau volcanism, causing the development of extended epicontinental shelf seas and shelf-sea basins ( Hays & pitman 1973 ; Larson 1991 ). A new and unique lithofacies type, the pelagic chalk, was deposited in distal parts of the individual basins. Chalk deposition commenced during middle Cenomanian-early Turanian times. Chalk consists almost exclusively of the remains of planktonic coccolithophorid algae and other pelagic organisms, and its great thickness reflects a high rate of production of the algal tests. The bulk of the grains are composed of lowmagnesium calcite, representing coccolith debris with a subordinate amount of foraminifers, calcispheres, small invertebrates and shell fragments of larger invertebrates ( Håkansson et al. 1974 ; Surlyk & Birkelund 1977 ; Nygaard et al. 1983 ; Hancock 1975 , 1993 ).