Time-Space Variability of Paralic Strata Deposited in a High Accommodation, High Sediment Supply Setting: Example From the Cretaceous of Utah

Abstract

A previously unstudied section of the John Henry Member (Upper Cretaceous, Straight Cliffs Formation) preserves four stacked regressive-transgressive cycles of wave-dominated paralic strata from the Kaiparowits Basin in south-central Utah. The John Henry Member at Buck Hollow is unusually thick, suggesting deposition in a high accommodation, high sediment supply setting. Sixteen lithofacies are used to describe fourteen facies associations, which vary in both their internal sedimentology and geobody architecture. The facies associations (1s-10s m thick) are grouped into depositional environments (strandplain shoreface, wave-dominated delta, and estuary) which are stacked at the meso-scale (10s-100s m thick), showing the variability and change possible in one location over a short period (∼6.5 My). The unique location of Buck Hollow within the Kaiparowits Basin allowed for the preservation on distinct tidal facies (tidal channels, tidal bars, and flood-tidal deltas) within the estuarine back-barrier, as well as other transgressive geobodies (washover fans, distributary channels, bayhead deltas, and barrier islands). Correlations to nearby exposures of the Straight Cliffs Formation in the northern Kaiparowits Basin (Main Canyon (∼14 km southwest) and Left Hand Collet (∼40 km south)) show the paleogeographic variability up-dip and along-strike respectively. The section is 2-3 times thicker at Buck Hollow than Main Canyon, suggesting a local, dramatic increase in accommodation. Regional tectonics, eustasy, and climate likely played a role in determining relative base level shifts, but these regional-scale controls could not have caused the thickening observed within the northern Kaiparowits Basin. Rather, localized processes (erosion, differential compaction, and local tectonics) are considered. Backstripping was used to calculate the decompacted thicknesses the John Henry Member at Main Canyon (321 m) and Buck Hollow (802 m). Post-depositional decompaction and local erosion by fluvial incision can account for ∼13.5% of the total decompacted difference between the two localities. The remainder of residual local accommodation could have resulted from early compaction (<145 m, ∼30%) and structural controls (<578 m, ∼120%). Understanding the controls on accommodation lends insight into the preservation potential of paralic strata. This study provides a new outcrop example to improve predictive models for deposition and preservation in paralic settings.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016