--> Abstract: Permeability Variation in Distributary-Channel Deposits of Seaward- and Landward-Stepping Deltaic Depositional Units, Cretaceous Ferron Sandstone, Utah, by M. Barton and N. Tyler; #91013 (1992).

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ABSTRACT: Permeability Variation in Distributary-Channel Deposits of Seaward- and Landward-Stepping Deltaic Depositional Units, Cretaceous Ferron Sandstone, Utah

BARTON, MARK, and NOEL TYLER, Bureau of Economic Geology, University of Texas at Austin, Austin, TX

Permeability variation within distributary-channel deposits of landward- and seaward-stepping deltaic units of the Cretaceous Ferron Sandstone, East-Central Utah, were examined by use of a minipermeameter to investigate the response of permeability variation to different depositional styles.

Macroforms are complex compound bars (e.g., Point Bar). These units are several feet to tens of feet thick and tens to hundreds of feet across. Distributary-channel deposits of landward- and seaward-stepping deltaic units display different architectural and sedimentological characteristics. Channel deposits within landward-stepping genetic units have a high width-to-depth ratio and are composed of a series of laterally stacked, poorly amalgamated macroforms. Internally, the channel fill displays a variety of stratal types with thick (up to 3 ft) mudclast-bearing lag deposits or fine-grained sediments separating individual macroforms. Channel deposits within seaward-stepping

deltaic units have low width-to-depth ratios and are composed of a series of vertically stacked, truncated, and highly amalgamated macroforms. The channel fill is dominated by trough cross-stratified sandstone that displays a high degree of grain-size variation and numerous heavily hematite-cemented zones.

At the facies scale, permeability variation in both depositional settings is comparable and is controlled by similar factors, such as grain size, mineralogy, sorting, and stratification type. However, the different distribution and occurrence of these variables in each setting results in different styles of permeability variation. Within distributary channel deposits of landward-stepping deltaic units sigmoidal heterogeneities between macroforms, on the scale of several feet to tens of feet vertically and tens to hundreds of feet laterally, characterize the permeability variation. Connectivity between macroforms is very poor because of extensive, thick, mud-clast-bearing lags and fine-grained sediments that separate individual macroforms.

However, within an individual macroform small-scale heterogeneities are lacking. As a result, at this scale, permeability variation is low and connectivity high. Within seaward-stepping distributary-channel deposits small-scale heterogeneities within the macroform characterize the permeability variation. Although extensive mud-clast-bearing lags and fine-grained sediments are absent between these highly amalgamated macroforms, dramatic reductions in permeability characterize macroform boundaries. Further, small-scale heterogeneities (several inches to several feet vertically and several feet to several tens of feet laterally) within macroforms are abundant in the form of grain-size variation and the presence of hematite cemented zones. As a result, permeability variation is high and c nnectivity poor both within macroforms and across macroform boundaries.

 

AAPG Search and Discovery Article #91013©1992 AAPG Eastern Section Meeting, Champaign, Illinois, September 20-22, 1992 (2009)