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.

摘要

The John Henry Member (JHM) of the Straight Cliffs Formation exposed along the Kaiparowits Plateau provides a record of ~5 my of coastal plain to marginal marine deposition. To better understand the mechanisms influencing the alluvial architecture of the fluvial JHM, a detailed quantitative characterization of the stratigraphic organization and stacking patterns of fluvial channel-belt sandstone bodies is performed. To this end, point pattern analysis techniques were applied on three datasets consisting of 136, 228, and 55 channel-belts collected from two fluvial outcrops in Bull Canyon and one fluvial outcrop in Rock House Cove, located 18 km to the west of Bull Canyon.;The results reveal two major trends in the spatial organization of channel-belts through time starting with (1) a trend of decreasing clustering and increasing regularity from the lower to middle stratigraphic interval followed by (2) a trend of increasing channel-belt clustering in the upper interval. Furthermore, up-section changes in channel-belt clustering exhibit strong similarities across the three outcrops as indicated by a correlation analysis based on dynamic time warping. Changes in channel-belt stacking patterns are interpreted to be primarily the product of changing basin boundary conditions given the existence of consistent clustering trends in Bull Canyon and Rock House Cove.;Correlation of clustering trends with previously measured architectural parameters and reconstructed paleo-hydraulic conditions suggest significant channel-belt clustering likely reflects the combined influence of three major factors. These include low aggradation rates driven by reduced accommodation, high avulsion frequency where channels are influenced by backwater hydraulics, and deposition downstream of a nodal avulsion point.;A scale-dependent clustering analysis using the K-function indicates channel-belts are clustered at small length scales, and uniform at larger length scales. The existence of different patterns at different length scales suggests the governing depositional processes operated at different scales. Small-scale clustering is interpreted to be the product of autogenic avulsion reoccupation, where abandoned channels that are preserved as topographic lows served as attractors to new avulsion paths and led to channel persistence. Conversely, the large-scale uniformity reflects periodic large-scale shifts in the local depo-center as a result of subsidence-controlled compensational stacking.