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
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Sedimentology of Paralic Reservoirs: Recent Advances
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Paralic reservoirs reflect a range of depositional environments including deltas, shoreline-shelf systems and estuaries. They provide the backbone of production in many mature basins, and contribute significantly to global conventional hydrocarbon production. However, the range of environments, together with relative sea-level and sediment supply changes, result in significant variability in their stratigraphic architecture and sedimentological heterogeneity, which translates into complex patterns of reservoir distribution and production that are challenging to predict, optimize and manage.
This volume presents new research and developments in established approaches to the exploration and production of paralic reservoirs. The 13 papers in the volume are grouped into three thematic sections, which address: the sedimentological characterization of paralic reservoirs using subsurface data; lithological heterogeneity in paralic depositional systems arising from the influence of tidal currents; and paralic reservoir analogue studies of modern sediments and ancient outcrops. The volume demonstrates that heterogeneity in paralic reservoirs is increasingly well understood at all scales, but highlights gaps in our knowledge and areas of current research.