--> Abstract: The Iles Clastic Wedge in the Sand Wash Basin: High-Frequency Sequences and Shoreline Processes Within the Wedge, by Carolina A. Gomez-Veroiza and Ronald Steel; #90078 (2008)

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The Iles Clastic Wedge in the Sand Wash Basin: High-Frequency Sequences and Shoreline Processes Within the Wedge

Carolina A. Gomez-Veroiza and Ronald Steel
Geological Sciences, University of Texas at Austin, Austin, TX

The 3rd-order Iles Clastic Wedge was shed from the Cretaceous Sevier Thrust Belt to the NW. At its medial reaches in the Sand Wash Basin it can be divided into eleven 4th order regressive to transgressive sequences that cause shoreline excursions 22-85 km long into the basin. These high-order sequences can be followed from medial (shoreline) reaches in the Sand Wash Basin to proximal (alluvial) reaches in the Washakie Basin, for some 190 km. In the medial reaches, typical regressive-transgressive sequences are 20-95 m thick and from bottom to top, they can be recognized by (1) marine shales containing the maximum flooding surface, (2) marine deltaic sandstones that coarsen upwards from prodelta shales, (3) erosively-based (sequence boundary) tidal-estuarine channels, cutting into the underlying marine delta-front sandstones, (4) brackish to marine mudstones containing the sequence’s upper maximum flooding surface or eventually a few meters transgressive sandstone overlain by marine shale representing the maximum shoreline incursion.

Within the 3rd-order wedge the component shoreline tongues change their geometry through time. Within the thick regressive limb there are 3 cycles of progressively longer shoreline regression, each culminating in valley incision (capping Iles 3, 6 and 10), strongly suggesting punctuated forced regression and sediment bypass. In contrast with the long and continuous progradational tongues in the regressive 3rd-order limb, the shorelines within the transgressive limb are notably short and discontinuous.

 

AAPG Search and Discover Article #90078©2008 AAPG Annual Convention, San Antonio, Texas