Landform distribution on modern coastal distributive fluvial systems (DFSs) and predictions regarding ancient coastal plain progradational successions

Kelsey McNamara
University of New Mexico, Department of Earth and Planetary SciencesAlbuquerque, New Mexico, USA
[email protected]

Distributive fluvial systems (DFSs) are modern fluvial deposits of radial distributive channel patterns and encompass a continuum from small-scale alluvial fans to large-scale fluvial megafans. Given that DFSs have been shown to comprise most continental sedimentary basins, we hypothesize that these systems form fluvial deposits in sedimentary basins at the fluvial-marine interface.

Preliminary remote sensing and field data from the Gilbert River DFS in northern Australia reveals: 1) a radial channel pattern originating from an apex, 2) a down-DFS decrease in both channel and grain size (the latter inferred), 3) a lack of lateral channel confinement, 4) a broad fan shape, and 5) a distinct boundary between the tidally-influenced coastal plain and fluvial-dominated zones.

These observations ultimately lead to sedimentologic and stratigraphic predictions regarding coastal DFS deposits in the geologic record—namely Cordilleran foreland basin Cretaceous strata, such as the Williams Fork Formation and the John Henry Member of the Straight Cliffs Formation of Colorado and Utah, respectively. If these strata are DFS, then progradational successions should be characterized by basal shoreface strata, and exhibit a distal to proximal upsection increase in grain size, sand:mud ratios, and sandbody amalgamation.

Coastal plain fluvial and marginal marine progradational successions have proven to be important hydrocarbon and carbon dioxide sequestration reservoirs, coal accumulations, and aquifers. However, existing fluvial facies models used to predict sandbody distribution and connectivity are typically based on valley fill successions in dominantly degradational settings at the outcrop- to borehole-scale.

AAPG Search and Discovery Article #90157©2012 AAPG Foundation 2012 Grants-in-Aid Projects