--> --> Abstract: Using GPS and Lasers to Map Subtle Tectonic Structures that Control Positions of Reservoir Sandstones in Foreland Basins, by Janok P. Bhattacharya, Jon Endresen, Xueming Xu, L. V. Carlos Aiken, and Brian J. Willis; #90914(2000)

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Janok P. Bhattacharya1, Jon Endresen1, Xueming Xu1, L.V. Carlos Aiken1, Brian J. Willis2
(1) University of Texas at Dallas, Richardson, TX
(2) SUNY, Oswego, NY

Abstract: Using GPS and lasers to map subtle tectonic structures that control positions of reservoir sandstones in foreland basins

The distribution of many sandstones in foreland basins appears to be controlled by subtle warping of the basin floor, but these structures are poorly documented because they are difficult to see and map in outcrop. Falling accommodation can align sands along these structures. The resulting linear sandstone bodies are not necessarily shore-parallel shoreface deposits, as is conventionally interpreted, but rather internally show a variety of tide- and river- influenced deltaic facies. Later truncation by marine erosion during renewed tectonic uplift tends to preserve smaller remnants of the once larger deltas aligned along these subtle structural features. Cretaceous examples from the Western Interior include the Panther Tongue delta in Utah, and the Frontier and Shannon sandstones in Wyoming.

Changes in the separation of continuously exposed regional bentonite beds at multiple horizons within the Frontier Formation provided us with an opportunity to map subtle changes in topography and deposition related to warping of the basin floor. Dips on fold limbs ( < 0.25°) are impossible to see in the field using conventional mapping techniques. We used real time Global Positioning System (GPS) to position a reflectorless laser rangefinder with centimeter precision. This allowed us to literally trace out the bentonite beds and sandstone tops in 3D with the laser. A highly accurate geometric map of these surfaces was completed with computer visualization and surface-fitting software (GOCADTM) to provide accurate 3D information on these structural features.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana