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

ABSTRACT: Stratigraphic Controls on Permeability Variation Within Distributary Channel Sandstones, Cretaceous Ferron Sandstone, Utah

Detailed analysis of facies architecture and permeability structure reveals stratigraphic architecture is the fundamental control

on permeability variation within Ferron distributary-channel belts. In turn, facies architecture displays systematic changes in channel-belt interconnectedness, geometry, stacking pattern, and stratal diversity as a function of the stratigraphic position of the distributary-channel belt within in the upper Ferron clastic wedge.

The deltaic Ferron Sandstone was deposited during a regressive maximum of the Cretaceous Western Interior seaway and is divided into discrete depositional units bounded by time-significant surfaces representing deepening and landward shift of facies tracts. These units are arranged in a hierarchy of seaward-stepping vertically stacked and landward-stepping geometric patterns. Using this well-constrained chronostratigraphic framework, changes in facies architecture and permeability structure of Ferron distributary channel belts in seaward- and landward-stepping depositional units were compared.

The fundamental depositional unit in ferron distributary channel belts are macroforms-compound complex bars (e.g., side-attached bars in distributary channels). These units are several feet to tens of feet thick and tens to hundreds of feet across. Measurements of permeability using a minipermeameter show a close relationship between permeability and sedimentary facies type. Permeability patterns within the channel fill closely reflect the distribution and arrangement of macroforms. Distributary channel deposits coeval to seaward-stepping deltaic units are preserved as isolated, narrow, elongate sand bodies that deeply incise and crosscut preexisting distributary mouth-bar, delta-front, and interdistributary-bay deposits. Internally, these deposits are composed of a series of vertical y stacked, highly amalgamated macroforms. Dramatic permeability reductions characterize surfaces of amalgamation within and between macroforms. As a result, permeability displays a great deal of variation both vertically and laterally. Channel deposits coeval to landward-stepping deltaic units have a high width-to-depth ratio and are composed of a series of laterally stacked, poorly amalgamated macroforms. Vertical partitioning of stratal types produces a strong upward-decreasing permeability trend that may extend hundreds of feet laterally. This trend, however, is disrupted by thick, extensive, mudclast-bearing lags or fine-grained sediments that separate and compartmentalize individual macroforms.

AAPG Search and Discovery Article #90993©1993 AAPG Rocky Mountain Section Meeting, Salt Lake City, Utah, September 12-15, 1993.