Spatial Analysis of Channel-Belt Stacking Patterns: Metrics to Discriminate Between Local and Regional Controls on Deposition in the Fluvial John Henry Member of the Straight Cliffs Formation, Southern Utah

Abstract

The John Henry Member (JHM) of the Straight Cliffs Formation exposed along the Kaiparowits Plateau provides a record of ~4 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 this study, we use the record of fluvial deposition preserved in the JHM to investigate the stratigraphic organization and distribution of fluvial channel-belt sand bodies. To this end, point pattern analysis techniques are applied on two datasets of 136 and 55 channel-belts collected from two outcrops in east Bull Canyon and northwest Rock House Cove, respectively (10 miles apart). These techniques classify the spatial organization of channel-belts as clustered, uniform, or random. Three point patterns analysis techniques are used - quadrat method, nearest neighbor method, and K-function - and all yield consistent classification of the spatial organization of channel-belts in all depositional units. A moving window spatial analysis is also performed on the two datasets to (1) describe the up-section changes in the stratigraphic arrangement of channel belts, (2) relate these changes to local trends in fluvial morphology, and (3) compare channel-belt stacking patterns between the two fluvial outcrops to discriminate between regional and local/autogenic controls on deposition. The analysis reveals three major trends in channel belt spatial organization starting with an increase in clustering throughout the lower stratigraphic interval, a progressive decline in clustering and increase in regularity in the middle interval, and a final trend of increasing randomness. Three roughly time-equivalent trends are also observed in the shoreline trajectory: progradation, retrogration, and aggradation, in this order. These trends, combined with data on channel-belt architecture, suggest long-term trends of increasing clustering are linked to trends of decreasing accommodation space. This interpretation is also supported by comparable stacking patterns of channel-belts in Bull Canyon and Rock House Cove, suggesting deposition in both locations was controlled by allogenic/regional processes. However, higher frequency clustering cycles are likely the result of autogenic processes such as compensational avulsion where small systems with limited lateral mobility require a higher avulsion frequency to build topography.

AAPG Datapages/Search and Discovery Article #90216 ©2015 AAPG Annual Convention and Exhibition, Denver, CO., May 31 - June 3, 2015