Using Surface and Point Based Statistics to Evaluate Channel-Belt Clustering in the Fluvial lower Wasatch Formation, Uinta Basin, Utah.
The Eocene lower Wasatch Formation of the Uinta Basin contains exceptional outcrops of low net-sand content (37% sand) fluvial strata. This study quantitatively documents the stratigraphy of a 7 km wide by 300 meter thick strike-oriented outcrop in order to develop a quantitative database that can be used to improve our knowledge of how some fluvial systems evolve over geologic time scales. Data used to document the outcrop are: (1) 550 meters of decimeter scale stratigraphic columns that document grain size and sedimentary structures; (2) detailed photopanels used to document architectural style and lithofacies types; (3) thickness, width, and spatial position for all channel belts in the outcrop, and (4) directional measurements of paleocurrent indicators. Five different methods are used to document channel-belt clustering within the outcrop using both surface and point based statistics. These methods include: (1) ocular inspection, (2) Ripley's K function, (3) R3 Method, (4) channel density maps, and (5) the compensation index. Key upward and lateral characteristics of the outcrop are the following. First, the shapes of 243 channel belts are documented. The average width, thickness and aspect are 110 m, 7 m, and 16:1, respectively. Importantly, the size and shape of channel belts does not change upward. Second, channel belts are documented to spatially cluster. Key upward patterns in channel-belt clustering are a marked change from non-amalgamated isolated channel-belt clusters to amalgamated channel-belt clusters. Critically, stratal surfaces can be correlated from mudstone units within the clusters to time-equivalent floodplain strata adjacent to the cluster demonstrating that clusters are not confined within fluvial valleys. Finally, proportions of floodplain and channel belt elements underlying clusters and channel belts vary with the style of clusters and channel belts laterally and vertically within the outcrop.
AAPG Datapages/Search and Discovery Article #90193 © 2014 Rocky Mountain Section AAPG Annual Meeting, Denver, Colorado, July 20-22, 2014