Evaluating along-strike variation using thin-bedded facies analysis, Upper Cretaceous Ferron Notom Delta, Utah

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Abstract

Thin-bedded delta-front and prodelta facies of the Upper Cretaceous Ferron Notom Delta Complex near Hanksville in southern Utah, USA, show significant along-strike facies variability. Primary initiation processes that form these thin beds include surge-type turbidity currents, hyperpycnal flows and storm surges. The relative proportion of sedimentary structures generated by each of these depositional processes/events has been calculated from a series of measured sedimentological sections within a single parasequence (PS6–1) which is exposed continuously along depositional strike. For each measured section, sedimentological data including grain size, lithology, bedding thickness, sedimentary structures and ichnological suites have been documented. Parasequence 6–1 shows a strong along-strike variation with a wave-dominated 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 south-east. The lateral facies variations integrated with palaeocurrent data indicate that parasequence 6–1 is deposited as a storm-dominated symmetrical delta with a large river-dominated bayhead system linked to an updip fluvial feeder valley. This article 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. surge-type turbidity currents and hyperpycnal flows) and storm surges, and shows that there are significant interactions and linkages of these often paired processes.

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