Abstract: Dynamics of the SE-German Molasse basin: eustatic versus tectonic controls in a classical foredeep
ZWEIGEL, JANINE, and TOM AIGNER
The North Alpine
Molasse basin, as a classical foreland basin, was used as a natural laboratory
to study the effects of eustasy versus tectonics in the basin history.
The deposits are mainly derived from the raising Alps and form two classical
transgressive-regressive units: the Upper and Lower Marine and Freshwater
Molasse, respectively. The units are separated by an angular unconformity,
formed during the Early Miocene. A detailed sequence stratigraphic interpretation,
based on well and seismic
data, showed that the formation of sequence boundaries
was mainly controlled by eustatic sea-level falls which were able to outstrip
the subsidence. A subsidence analysis revealed that the geohistory of the
basin can be subdivided into four phases. Whereas, the interplay between
subsidence and sedimentation rates controlled the transgressive-regressive
cycles: 1) "flexural event" (Upper Eocene-uppermost Egerian, 38.6-22.3
Ma): increasing rates of subsidence and sedimentation related to the northward
advance and internal stacking of the Alpine nappes: first transgressive-regressive
cycle. 2) "visco-elastic reaction" (Uppermost Egerian - Eggenburgian, 22.3-19.5
Ma): decreased rates of subsidence at thrust front and uplift of distal
parts due to a visco-elastic reaction of the lower plate after cessation
of thrusting in the Eastern Alps - formation of angular unconformity; reduced
sediment input due to sudden reduction of relief in the orogen: second
transgression. 3) Ottnangian - end of Molasse sedimentation (19.5-8.5 Ma):
decreasing rates of subsidence and increasing rates of sediment input since
about 17.8 Ma: renewed regression. 4) "isostatic rebound" (Pannonian -
recent, 8.5-0 Ma): uplift. Stratigraphic
modeling
employing two different
modeling
softwares was attempted to quantify the influence of subsidence
and eustasy on the basin development.
AAPG Search and Discovery Article #90942©1997 AAPG International Conference and Exhibition, Vienna, Austria