ROSS, WILLIAM C., and DALE E. WATTS, Marathon Oil Company, Littleton, CO; KEITH N. SHANLEY, Shell Development Company, Houston, TX; and MICHAEL H. GARDNER, Bureau of Economic Geology, Austin, TX

ABSTRACT: Alluvial Architecture as a Function of Base-Level Dynamics: Implications for Stratigraphic Modeling

Stratigraphic modeling programs must develop strategies for simulating basin-fill geometries and facies distribution. Basin-fill geometries can be numerically modeled by varying sediment supply in conjunction with the relative rise and fall of laterally continuous base-level surfaces. These base-level surfaces represent the upper limit to which sediments can be deposited in marine and nonmarine environments for a given profile of equilibrium. Sediments transported along a given facies tract are deposited and preserved as these continuous base-level surfaces rise relative to an initial surface of deposition.

Facies modeling requires strategies for differentially distributing available sand:mud mixtures below these rising base-level surfaces for each environment. Alluvial architecture, shoreline positions, shelf widths, and the occurrence of basinal (turbidite) sands are modeled by budgeting sand:mud distributions in fluvial environments for varying rates of relative base-level rise.

Variations in nonmarine sand:mud ratios and/or alluvial architectural styles are related to changing rates of aggradation (i.e., relative base-level rise). In the current model channel-sand interconnectedness and sand:mudratios increase with decreasing rates of aggradation (i.e., relative base-level rise). Quantitative estimates of this relationship from nonmarine sections (the Campanian-aged Blackhawk, the Santonian-aged John Henry, and Turonian-aged Ferron Formations of Utah) along with the modeling implications of these data will be presented.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.