--> Abstract: Facies Assemblages on Distributive Fluvial Systems, by Stephanie Davidson, Adrian Hartley, Gary S. Weissmann, Gary Nichols, and Louis Scuderi; #90124 (2011)

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AAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA

Facies Assemblages on Distributive Fluvial Systems

Stephanie Davidson1; Adrian Hartley1; Gary S. Weissmann2; Gary Nichols3; Louis Scuderi2

(1) Geology & Petroleum Geology, University of Aberdeen, Aberdeen, United Kingdom.

(2) Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, NM.

(3) Department of Geology, Royal Holloway, University of London, Egham, United Kingdom.

Distributive fluvial systems (DFS) are likely to form a significant component of the continental rock record. Current facies models, however, as based on our understanding of tributary fluvial systems, are inadequate to interpret the downstream behaviour and signature of DFS. Analysis of DFS in aggradational continental sedimentary basins reveals that downstream channel and floodplain changes tend to behave in predictable ways to climate in the catchment and receiving basins. New generic models of facies assemblages derived from observations of remotely sensed imagery are presented. The distribution of sedimentary facies on modern DFS in a range of environmental settings and schematic predictions of downstream geomorphological response to external controlling variables were determined. Six generic models of facies assemblages were constructed based on the distribution and morphology of channels in plan-view on DFS, including; braided bifurcating; single braided; braided to sinuous; single major sinuous; single sinuous bifurcating, and multiple sinuous DFS types. Although there is great variation between and within the DFS planform types, with several exceptions behaving in a non-predictable fashion, our observations suggest that the vast majority conform to one of the generic models of facies assemblages. The facies associations are dependent on climate in the upstream catchment and downstream receiving sedimentary basin with the channel facies and architecture acting as distinguishing criteria for each major DFS planform type. DFS tend to terminate in a range of settings, such as eolian, playa, lacustrine, axial fluvial system, wetlands or marine environments. The termination types and floodplain facies as represented in the facies assemblage models are interchangeable depending on local conditions. Effectively, the new models suggest a novel way in which to view and interpret fluvial systems preserved in the rock record.