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Anatomy of an Extensive, Low-accommodation Clastic Wedge: Insights from Isopach Maps and Regional Correlation in the Uinta-Piceance Basins

Aschoff, J.L. and R.J. Steel
Jackson School of Geosciences, University of Texas at Austin, Austin, TX

     Despite recent advances in foreland basin research, the response of clastic wedges to tectonics remains contentious. Several studies demonstrate that clastic wedge progradation is coincident with structural development, whereas others show that progradation lags behind. Delineating architectural and geometric variation within clastic wedges can help resolve these discrepancies because different wedges may record tectonics differently. Three distinct clastic wedges are present in Campanian strata exposed at the southern Uinta-Piceance Basin margin. The upper and lower clastic wedges are thicker (>0.6 km), less extensive (130-150m), and have risingshoreline trajectories characteristic of higher-accommodation settings. The middle wedge is thinner (< 0.3km), much more extensive (>250km), and has flat-to-falling shoreline trajectories characteristic of lower-accommodation settings. We describe the anatomy of the middle clastic wedge because it is anomalously-extensive, architecturally-complex, and developed very rapidly (250 km progradation in <500 ky). Units within the middle clastic wedge include the Sego Sandstone, Neslen Formation, Anchor Mine Tongue, Bluecastle Tongue and Iles Formation. This wedge consists of 8-12, thin (10-25 m), 50-100 km-long, transgressive-regressive sandstone tongues. Regressive tongues have narrow (10-20 km), fluvial-dominated proximal zones, wide (25-50 km), tidallyinfluenced central zones with numerous incisions, and narrow (10-20 km), mixed-energy distal zones. Transgressive tongues are thinner (<20 m) and less extensive than regressive tongues. They typically have narrow, fluvial-dominated proximal zones (<20 km), broad (25- 50 km), tidally-influenced central zones, and broad (>50 km), wavedominated distal zones. We highlight clastic wedge variability, and propose that different clastic wedges record tectonics differently-some may be syntectonic and others post-tectonic.


AAPG Search and Discovery Article #90071 © 2007 AAPG Rocky Mountain Meeting, Snowbird, Utah