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

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 a dataset of 136 channel-belts collected from a 220 m thick and 2000 m wide outcrop in east Bull Canyon. 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 same dataset to (1) describe the up-section changes in the stratigraphic arrangement of channel belts and (2) relate these changes to local trends in fluvial morphology and basin-wide trends in accommodation space.

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. 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. This is evidenced by the presence of strong clustering signals in low net-to-gross units characterized by straight fluvial styles and laterally-restricted channel-belts.