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