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Abstract: Depositional Remnants: Products of the Interplay Between Synsedimentary Tectonics and Changes in Relative Sea Level

MARTINSEN, RANDI S., University of Wyoming and LEE F. KRYSTINIK, Union Pacific Resources Company

Synsedimentary tectonic influence on the depositional record of stratigraphic intervals is well recognized throughout the Rocky Mountain region. For example, numerous studies document the occurrence of incised valley and fluvial-deltaic systems within fault bounded structural lows. However the extent to which erosion, especially that associated with ravinement, controls the preserved geometries of depositional systems is not widely recognized. Yet, structural lows, in addition to being favorable locations for the deposition of sediments, also favor their preservation. This is especially true in low accommodation settings wherein ravinement is capable of removing entire systems except for those parts lying within (structurally controlled) topographically low areas. In such settings, the preserved geometries of stratigraphic units can be very different from their original depositional geometries. In that geometry is an important component in the interpretation of ancient depositional environments, mistaking a preserved geometry for a depositional geometry can result in significant misinterpretations. For example, a sandstone with a sheet-like depositional geometry, if only preserved within linear half-grabens will appear to have a “bar” geometry if oriented parallel to the shoreline or a “channel” geometry if oriented more perpendicularly. Similarly, if only scattered portions of a once widespread depositional system are preserved, inaccurate paleogeographic reconstructions are likely. A depositional remnant may be small or very large depending on the size of the “container” in which it is preserved. We believe that depositional remnants are a common feature in the stratigraphic record of many basins and an important concept that can be utilized to open up new hydrocarbon plays.

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