--> Abstract: Re-Evaluating the Origin of Isolated Sandstones Encased in Marine Mudstone: The Cretaceous Prairie Canyon Member of the Mancos Shale at Hatch Mesa, East-Central Utah, by Kimberly M. Stevens, Donna S. Anderson, Michael H. Gardner, and John B. Wagner; #90039 (2005)

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Re-Evaluating the Origin of Isolated Sandstones Encased in Marine Mudstone: The Cretaceous Prairie Canyon Member of the Mancos Shale at Hatch Mesa, East-Central Utah

Kimberly M. Stevens1, Donna S. Anderson1, Michael H. Gardner1, and John B. Wagner2
1 Colorado School of Mines, Golden, CO
2 Nexen Petroleum, Dallas, TX

The Late Cretaceous Hatch Mesa sandstones, part of the Prairie Canyon Member of the Mancos Shale in the Book Cliffs of east-central Utah, have been interpreted as deposits of re-worked valley-fills, tempestites, mouthbars, and submarine fans. The 200-m thick Hatch Mesa succession consists of three main intervals: 1) a basal interval of isolated lenticular scour-fill deposits and unidirectional-ripple laminated sandstones encased in mudstone; 2) a middle interval of thick (10 m) sandstone sheets interbedded with mudstone sandstone; and 3) an uppermost marine mudstone correlative to the Kenilworth, Sunnyside and Grassy members of the Blackhawk Formation.

Facies and architectural-element analysis of the middle interval defines eight bedsets of offlapping sandstone sheets (average paleocurrent 080) that thin eastward. Sheets consist of structureless and soft-sediment deformed sandstone changing eastward within beds to parallel laminated sandstone, Bouma successions, and finally unidirectional rippled sandstone. Evidence for deposition within storm wave base is rare. A prominent easterly directed integrated scour network erodes the top of the thickest sandstone sheet. The scour network is discordantly filled with interlaminated mudstone and unidirectional-rippled sandstone facies, indicating later filling episodes. Regional correlations suggest that the Hatch Mesa sandstones were deposited at least 36 miles from the nearest coeval shoreline or delta. These observations and interpretations suggest that the Hatch Mesa sandstones formed from largely ignitive sediment gravity flows, below storm wave-base and far from the nearest delta front, placing them in a bottom-set position on a ramp-like clinoform.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005