Abstract: Synsedimentary Fault
Block Movements in the Early Triassic
Governing Fast Lateral Changes in Sand Body Geometry and
Composition
SEIDLER, LARS, University of Copenhagen, Dept. of General Geology, Oster Voldgade 10, DK- 1350 Copenhagen, Denmark.
The Scythian Wordie Creek Formation crops out on the east coast of Greenland and the working area covers c. 6000 km2. Data consists of detailed (1:100) sedimentary logs, photo sections, gamma ray logs and 3D mapping of sandbodies. In Late Permian and Early Triassic the basin was in a situation of thermal relaxation following extension and subsidence was mainly thermal (Surlyk, 1990). The thickness of the mainly marine succession varies between c. 170 m up to c. 700 m depending primarily on the location of the sections relative to synsedimentary faults trod subbasins exerting strong control on sedimentation.
The end-Permian eustatic sea level fall resulted in exposure of
Permian sediments in the relatively uplifted parts of the fault
blocks leading to incision of valleys up to 250 m wide. The P/T
boundary is at most localities an unconformity overlain by Triassic
fluvial or turbidite sandstones. In outcrop it is possible to trace
the lateral changes within a
fault
bounded subbasin from proximal
fluvial sedimentation to distal sedimentation by clinoform
progradation and submarine gravity flows. Distribution and
direction of submarine and fluvial channels seems to be controlled
chiefly by the
fault
lineaments in which the channels are situated
and eventually incise. At three localities the P/T is a conformable
shale-shale contact reflecting deposition in the deeper part of a
subbasin with continuos accommodation space. The frequency and
distribution of turbidite, tempestite and shoreface sandstones
varies within short distances due to this
fault
controlled
segregration of several subbasins.
AAPG Search and Discovery Article #90937©1998 AAPG Annual Convention and Exhibition, Salt Lake City, Utah