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Point Pattern Analysis of Channel Organization from the Cretaceous John Henry Member of the Straight Cliffs Formation, Kaiparowits Plateau, Southern Utah

Wassim Benhallam, Cari L. Johnson, Luke Pettinga, and Lisa Stright
University of Utah

The John Henry Member (JHM) of the Straight Cliffs Formation exposed along the Kaiparowits Plateau provides a record of ~6 my of coastal plain to marginal marine deposition. Understanding the mechanisms influencing stratigraphic trends throughout the basin requires elucidating the controls responsible for spatial changes in alluvial architecture. In particular, base-level driven change in accommodation is commonly hypothesized to be a major downstream control on fluvial systems. In this study, we test this hypothesis using the record of fluvial deposition preserved in the JHM that is coeval with known shoreline shifts in shoreface equivalents. Correlating the fluvial succession in the JHM with the mapped shoreline requires characterizing the spatial organization of channels across the multiple depositional units within the fluvial JHM. To this end, point pattern analysis techniques are applied on a dataset of fluvial channel sand bodies from the JHM. These techniques describe the channels' spatial organization as clustered, uniform, or random. The resulting variation in spatial organization is then correlated with relative sea-level fluctuations from the shoreline stratigraphy. Although a correlation may be established, this approach does not rule out the influence of other controls on the alluvial architecture. Three point patterns analysis techniques are used: quadrat method, nearest neighbor method, and K-function. Results indicate all depositional units are consistently classified by the three techniques. The correlation with onlap curves suggests channel clustering broadly corresponds to a basinward-shifting shoreline. Conversely, uniformity or randomness correlates with landward shifts of the shoreline. Furthermore, a moving window spatial analysis suggests the point pattern's history of spatial organization correlates even with the small scale fluctuations in relative-sea level.

AAPG Search and Discovery Article #90169©2013 AAPG Rocky Mountain Section 62nd Annual Meeting, Salt Lake City, Utah, September 22-24, 2013