Kreda północnosudecka a wschodniobrandenburska

Abstract

RELATION BETWEEN THE NORTH-SUDETIC AND EAST-BRANDENBURG CRETACEOUS FORMATIONSSummaryThe paper deals with the mutual relation between the East-Brandenburg and North-Sudetic Cretaceous formations. Towards south-east the Cretaceous deposits rest on the older and older series, from Jurassic in north-west, to Older Palaeozoic in south-east. This is the first uniform basin, in which two zones may be distinguished: a south-western near-shore zone, characterized by distinct continental influence (sandstones, siltstones, marls), and a north-eastern off-shore zone, where the influence of the Sudetic islands already disappears (clay marls, limestones). The accumulation of these deposits corresponds to a rhythm of transgression – regression. The uniformity of the basin is also proved by an almost similar fauna composition of the two present-day depressions. Marine transgression took place at the Upper Cenomanian time (horizon Acanthoceras rhotomagense), and the sea retreated at the Lower Santonian time (horizon Inoceramus cordiformis) or at the lower part of the Upper Santonian (horizon I. pinniformis). The transgression cycle lasted up to the end of the Lower Turonian time, and the regression began at the Upper Turonian time. In the basement rocks of the Cretaceous formation more or less labile areas may be distinguished. A narrow zone, stretching along the macroaxis of the North-Sudetic Cretaceous basin proved to be the most labile area here. This zone existed already at the Upper Turonian time. Its maximum development was in Coniacian, and the development continued still at the Lower Santonian. The thickness of the Cretaceous deposits in this zone exceeds 1100 m, whereas that of the East-Brandenburg Cretaceous deposits, found to occur in a lesser sinking area, amounts to 500 m. The deepening of the North-Sudetic basin took place during the deposition of the Cretaceous formations. Thus, it may be said here that this area constitutes a synsedimentary marginal trough.