EVALUATING ALONG-STRIKE VARIATION USING THIN-BEDDED FACIES ANALYSIS, UPPER CRETACEOUS FERRON NOTOM DELTA, UTAH
Li, Zhiyang 1991-
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This study evaluates the vertical and along-strike variability of thin-bedded delta-front and prodelta facies of the Upper Cretaceous Ferron Notom Delta Complex in Central Utah. Primary initiation processes that form thin beds include ignitive turbidity currents, hyperpycnal flows, and storm surges. The relative proportion of sedimentary structures generated by each depositional process/event has been calculated from a series of measured sedimentologic sections within a single parasequence (P6), which is continuously exposed along depositional strike. For each measured section, sedimentological data including grain size, lithology, bedding thickness, sedimentary structures, and ichnological suites have been documented. Parasequence 6 shows a strong along-strike variation with a completely wave-influenced environment in the north, passing abruptly into a fluvial-dominated area, then to an environment with varying degrees of fluvial and wave influence southward, and back to a wave-dominated environment further to the southeast. The depositional model of parasequence 6 is therefore interpreted as a storm-dominated symmetric delta with a large bayhead system. This study indicates that it is practical to quantify the relative importance of depositional processes and determine the along-strike variation within an ancient delta system using thin-bedded facies analysis. The wide range of vertical stratification and grading sequences present in these event beds also allows construction of conceptual models of deposition from turbidity currents (i.e. ignitive turbidity currents and hyperpycnal flows), storm surges, and the interactions between both flows.