Time–space variability of paralic strata deposited in a high accommodation, high sediment supply setting: example from the Cretaceous of Utah
Julia S. Mulhern, Cari L. Johnson, 2017. "Time–space variability of paralic strata deposited in a high accommodation, high sediment supply setting: example from the Cretaceous of Utah", Sedimentology of Paralic Reservoirs: Recent Advances, G. J. Hampson, A. D. Reynolds, B. Kostic, M. R. Wells
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A previously unstudied section of the John Henry Member (Upper Cretaceous, Straight Cliffs Formation) preserves four stacked regressive–transgressive cycles of paralic strata from the Kaiparowits Plateau in south-central Utah. Meso-scale (10–100 s m thick) shoreface, wave-dominated delta and estuarine depositional environments stack vertically and show the complexity of paralic facies in a single location through time. Correlations with nearby exposures show the palaeogeographical variability updip and along-strike over c. 6.5 myr. Such variability highlights the importance of high accommodation settings in preserving transgressive deposits, including landwards-stepping barrier island and lagoon systems. The Buck Hollow section is expanded two to three times compared with correlative successions only 15–40 km away. Tectonics, eustasy and climate contributed to relative shifts in base level, but these regional controls do not explain the dramatic local thickening observed. Local controls on accommodation were quantified through decompaction analysis. The results showed that the expanded thickness of the John Henry Member in Buck Hollow can be explained by differences in decompaction (c. 9%), local erosion by fluvial incision (c. 5%), early compaction (c. 30%) and local structures such as faults (c. 100–150%). This outcrop-based study illustrates facies variability within a thick paralic succession and investigates accommodation controls on the preservation of these strata with the goal of improving predictive models for analogous deposits.
Supplementary material:40Ar/39Ar age data methods and sample location available at https://doi.org/10.6084/m9.figshare.c.3277436.v1