Reports: AC847231-AC8: Shapes, Scales and Spacing of Channel-belt Sand Bodies in Ancient and Experimental Avulsion-dominated Alluvial Basins

Paul L. Heller , University of Wyoming

Snehalata Huzurbazar , University of Wyoming

Chris Paola , University of Minnesota

The goal of this project is to describe the distributions and possible causes of apparent groupings of channel-belt sand bodies in natural and experimental alluvial basins. Clustering of sand bodies is a prominent feature of latest Cretaceous deposits in much of Wyoming, and has been observed elsewhere as well. Spatial groupings of similar character have been observed in fluvial experiments performed at the St. Anthony Fall Laboratory (University of Minnesota) with no changes in boundary conditions. These results suggest that extrinsic forcing is not a requirement for clustering and that such features may be an example of natural self-organization.

Much of the work for this project is now completed, graduate students have graduated or are finishing up, and publications are either out in Geology, in submittal to Geological Society of America Bulletin, or in preparation for submittal to American Association of Petroleum Geologists Bulletin. Besides preparing papers for publication, work over the past year have focused in two main areas. We are undertaking a study of controls on modern anastomosed river pattern development along the Little Laramie River, Wyoming. In some ways the river serves as an analog for the ancient clustered deposits that is the primary focus of the grant. The 2011 flooding of the river provides insight into how active channels develop across flood plains by a variety of mechanisms (head cut elongation, swale enlargement and reoccupation of abandoned flow paths). We have acquired airborne lidar imagery of most of the floodplain and begun hydrologic modeling of calculated stream power across developing channel threads. This study forms the basis of an M.S. thesis in the Department of Geology & Geophysics by Austin Andrus, expected to be completed during the summer of 2012.

We are also actively engaged in an Analysis of Object Data statistical study of sand-body clustering as seen in well log data or Late Cretaceous fluvial deposits in various basins of Wyoming. The Lance Formation is equivalent to the Ferris Formation, the primary focus of this study, and demonstrates clearly a non-random distribution of sand body size and spacing as seen in gamma ray data. We have compiled proxy lithologic data from this unit in the eastern part of the Wind River and parts of the Powder River basins for continued statistical analysis. This study will form part of a Ph.D. dissertation being done by Mr. Peter Marcy of the Department of Statistics at the University of Wyoming.

Students who have been, or will be, graduated that are partially supported from this grant include: Elizabeth Hajek (Ph.D. Geology and Geophysics, 2009, at present Assistant Professor of Geology at Pennsylvania State University); Austin Andrus (M.S, expected, summer 2012); Peter Marcy (Statistics, Ph.D. expected, 2012); Elizabeth Hajek (post-doc, University of Minnesota, 2010-2011).

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