Abstract: Rotliegend Basin Evolution, German North Sea - Effects on Gas Accumulation

SZATAI, JOHN E., and G. A. SZATAI

The ancestral Rotliegend Basin is an asymmetrical megagraben extending NW all along the deepest, axial region of a lower Rotliegend Autunian Rift Zone. It is bounded by and contains regional strike slip faults. Between these are numerous tilted blocks, created by movements along NNW-trending secondary faults. Grabens and half grabens, among these, are filled with synrift strata and volcanics. The central, deepest, 40- 60-km-wide band of the rift contains a dune field. Here, the tilted blocks are covered and draped by eolian-blanket, Schneverdingen dune sands. Renewed fault movements accentuated structures thus formed. The entire dune field was subsequently covered by salt and mudstone deposits of the Rotliegend lake providing good seals over the structures. The lake expanded with time reaching a length and width over 1000 km and 200 km, respectively.

Intermittent differential subsidence related to movements along the major faults, climaxing during Jurassic, caused development of the giant German North Sea Arch, the Horn Graben and the Gluckstadt Graben, perpendicular to the Rotliegend Basin. The Schneverdingen sands are now in a perched position on the Arch; they dip from 5000 meters to over 8000 meters into the Horn and Gluckstadt grabens.

The central 40-60-km, NW-trending band, overlying the ancestral Rotliegend basin, is probably the best prospective area for gas in the German North Sea due to its evolution and location. Numerous structures, which contain porous eolian Schneverdingen sands, were formed early, are located above Carboniferous source rocks, and are over a rift "kitchen." They probably received the first methane-rich gas-generation products, which ascended along numerous, short, fault migration routes.

AAPG Search and Discovery Article #90942©1997 AAPG International Conference and Exhibition, Vienna, Austria