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

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.