Abstract
Abstract This study documented the architecture of a paralic succession using outcrops of the Upper Cretaceous John Henry Member of the Straight Cliffs Formation, southern Utah (USA). The 65 m thick interval of interest includes a basal succession of elongate tidal bars, which sits unconformably on the Calico Bed of the Smoky Hollow Member. These barforms are overlain by carbonaceous estuarine bay fill with tidal deposits, a bayhead delta and, ultimately, a coastal plain succession. The estuarine succession demonstrates a decreasing tidal influence through time and this is interpreted to reflect evolution from a mixed-energy to a wave-dominated estuary as a result of the changing morphology of the estuary and/or the migration of barrier islands across its mouth. The regional correlations are also discussed, with implications for sequence stratigraphic interpretations. A detailed interpretation of the ancient bayhead delta highlights the internal architecture and provides data for statistical comparison between this feature, which is dominated by inclined heterolithic strata, and a previously published study of fluvial point bar inclined heterolithic strata. The results emphasize distinct grain size trends from these two examples, as well as differences in the continuity and spatial distribution of mudstone drapes, which act as both baffles and barriers to fluid flow.
Published Version
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