RERIK - Hochauflösende seismische Analyse der Mecklenburger Bucht
|Das Untersuchungsgebiet RERIK liegt im
nördlichen Zentralteil des Norddeutschen Beckens zwischen
Rostock und Lübeck. Ein zur Erdöl-Erdgas Exploration
in den 80er-Jahren aufgenommener seismischer Datensatz bestehend aus
einem sehr dichten streng orthogonalen Netz seismischer Linien mit
einer Gesamtlänge von mehr als 1800km bildet die Basis der
Untersuchung. Hauptziel des interdisziplinären Projektes ist
die Erstellung und Interpretation von hochauflösenden
Laufzeit- sowie Mächtigkeitskarten zur Untersuchung der
strukturellen Entwicklung dieses Gebietes seit dem Rotliegenden.
Das Verständnis der vor-alpidischen Strukturgeschichte erfordert eine Charakterisierung der Deformation durch Störungskartierungen und Bestimmung von Absenkungs- und Sedimentationsraten über verschiedene geologische Zeiträume.
The geological evolution of the North German Basin can be separated into four distinct periods in the Rerik study area. During Late Permian and Early Triassic evaporites and clastics were deposited. Salt movement was initiated after the deposition of the Middle Triassic Muschelkalk. Salt pillows, which were previously unmapped in the area, are responsible for the creation of smaller subsidence centers and angular unconformities in the Late Triassic Keuper, especially in the vicinity of the fault-bounded Grimmen High. In this area, partly Lower Jurassic sediments overlie the Keuper unconformably. The change from extension to compression in the regional stress field remobilized the salt, leading to a major unconformity marked at the base of the Late Cretaceous.
The interpreted seismic sections and the thickness maps of the Top Zechstein map show accumulation of Zechstein salt in salt pillows, striking NW-SE as a result of salt tectonics. The maximal thickness of two previously unmapped salt pillows reaches approximately 1800 m.
At the Base Zechstein we can observe a system of NW–SE and E-W striking faults with little vertical displacement. The number of faults increases towards the east. The fault in the central part of the area cuts the entire Mesozoic sedimentary sequence. Significant unconformities were found between the Middle Keuper horizons and below the Base Upper Cretaceous.
After a long period of subsidence and sedimentation from Permian to Middle Triassic, periods of erosion in Middle Keuper and late Lower Cretaceous with strong tectonic influence followed, before a time of quiescent subsidence began with the Late Cretaceous.
No major tectonic activity is observed during the deposition of the Bunter and Muschelkalk of Early and Middle Triassic age. However, the Grimmen High area acted as a local basin with significant higher sedimentation rates and enhanced subsidence during the Early Triassic (Bunter).
Enhanced tectonic activity followed with periods of erosion in Middle Keuper and late Lower Cretaceous. The Middle/Upper Keuper unconformity is most probably caused by tectonic stress impulses of the Kimmerian phase (Beutler, 1982; Krauss, 1994). During this time interval first vertical salt movements are delineable for the salt pillows in the NE part of the study area. The very prominent erosional unconformity below the base Cenomanian (Albian) is a result of the sea level high-stand and the subsequent basin inversion starting around that time. Such may be correlated with the development of the Central North Sea Dome due to plutonic activity (Ziegler, 1990, Underhill and Partington, 1993).
In this period Lower Liassic sediments and portions of the Upper Keuper deposits were eroded. Only in the Grimmen High region and in depressions in between the salt pillows were remains of Jurassic sediments preserved. Then, with beginning of the Upper Cretaceous sequence, an interval of subsidence began, characterized by weak tectonic activity. Later in the Late Cretaceous the onset of basin inversion is observed.