Das Hilskonglomerat in der Unterkreide-zeitlichen Braunschweiger Bucht - Teil I: Die bioklastische Fazies des Hilskonglomerates als kartierbare Einheit und Klimazeuge
During the second great transgression in the early Lower Cretaceous, the Lower Saxony Basin was enlarged in the North onto the Pompeckj, in the South onto the Middle German, and in the East onto the Altmark Swells, respectively. At the turn of Valanginian to Hauterivian, the Braunschweig Bight developed between the Harz Mountains in the South and the Flechtingen-Roßlau Block in the North. This bay extended to the Subhercynian Basin of nowadays SE Lower Saxony during the following Cretaceous transgressions. The area is subdivided into Hercynian and Rhenian striking salt diapirs showing a strong correlation to tektonic structures in the premesozoic basement with a complex interrelation between tectonics and halokinesis. Southeast of Braunschweig, the Asse-Heeseberg salt diapir is bordered north by the Schöppenstedt and south by the Remlingen-Pabstorf Synclines, respectively. The Hauterivian transgression is represented here by the so-called Hilsconglomerate that crops out under soil at both sides of the range. Being a coarse and highly fossiliferous carbonate, it was investigated macro- and micro-facially. Due to diverse salt migration tendencies within the diapir, synsedimentary block tectonics differentiated the areas of shallow water life and accumulation. By means of statistic mappings, more than 20 perpendicular sections and over 70,000 gathering stones allowed the definition and localisation of these areas. Various energy levels are interpreted from the samples and collected fauna by means of different methods. Eight peaks of high energy can be traced over the areas bordering the Asse-Heeseberg range as well as to the western Lower Saxony Basin.