--> Abstract: Lacustrine-Swamp Systems In Strike-Slip Shear Zones: Potential Source Rock Accumulation And Structural Traps Generation, by L. Cabrera, B. Ferrus, and A. Saez; #90937 (1998)

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Abstract: Lacustrine-Swamp Systems In Strike-Slip Shear Zones: Potential Source Rock Accumulation And Structural Traps Generation

CABRERA, LLUIS, BERNAT FERRUS, ALBERTO SAEZ, University of Barcelona, Spain, (DGICYT Project PB94-0906)

Non marine, large scale strike-slip shear zones are often characterized by the generation of tectonic relieves and persistent subsidence, both related to the activity of neighboring and closely related compressional and extensional structures which may interplay in a complex way. Changes in local drainage conditions (shifted water divides, diverted or beheaded drainage) often give rise to poorly drained basins where thick alluvial and lacustrine-swamp related sequences may develop. Thus strike-slip shear systems are zones of potential interest where suitable lacustrine source rocks and structural and stratigraphic traps may develop. Better comprehension on general evolutionary trends and kinematics of these tectonosedimentary settings and the establishment of refined models can be undertaken either by producing mathematical models or by studying well constrained “natural labs” (i.e. small scale basins) where suitable base data are available.

This second approach was developed in the Tertiary As Pontes Basin (NW Spain), a km in scale dextral strike-slip zone where normal and reverse faults were active during early evolutionary stages. Later stages were characterized by the setting in motion of a restraining bend related to a master dextral strike-slip fault. The interaction between these structures resulted in the generation of lacustrine and swamp depocenters where organic matter rich shales (up to 12% of TOC) and liptinite rich subaqueous coals and coaly mudstones developed. These potential hydrocarbon sources occur closely interfingered and are overlain by alluvial successions which include well sorted fluvial channel and deltaic sandstones with diverse degrees of connection. Moreover the lacustrine an alluvial sequences were affected by coeval tectonic structures which resulted both in extensional and contractional culminations, liable to act as structural traps.

AAPG Search and Discovery Article #90937©1998 AAPG Annual Convention and Exhibition, Salt Lake City, Utah