Thin-bedded Facies Analysis of a Ferron Storm-dominated Delta Front and Prodelta: Cretaceous Ferron Sandstone, Utah
Seepersad, Darsel 1986-
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This study examines thin-bedded facies within shelf and prodelta deposits of the Cretaceous Ferron Notom Delta in central Utah. Thin beds may be the result of storms (tempestites), ignitive turbidity currents, or hyperpycnal flows. This study quantitatively evaluates the proportion of each facies types within heterolithic strata at the base of the sandier lithofacies to better characterize the relative proportion of formative processes. Mud along shelves has traditionally been linked to suspension settling. This study also quantitatively compares structures initiated by traction deposition to those linked to suspension settling in an attempt to show that most mud deposited offshore is due to reworking by waves and storms, and hyperpycnal flows. Primary data were derived from well-exposed outcrops of parasequences 5a, 5b, 6, 11, and 16b, within the Notom deltaic wedge, which represent a spectrum of wave-dominated shorefaces to river-dominated deltas. Parasequences 5a and 5b are comprised of over 60% HCS beds with subordinate amounts of wave-rippled strata. Parasequence 5a represents a high-energy wave environment. Parasequence 5b also reflects a wave-dominated environment, however, a greater proportion of massive to planar interbeds suggests fluvial and wave mixing. Parasequence 6 contains predominantly normal and inverse graded units with numerous Bouma sequences and starved ripples. Parasequence 6 is river/flood dominated, containing both ignitive turbidites and hyperpycnites. Parasequence 11 is dominated by graded bedding, and shows the highest degree of river/flood dominance with the highest evidence of hyperpycnal deposits seen within the three parasequences. Parasequence 16 is dominated by massive units, along with graded beds, Bouma sequences, and rare HCS. Parasequence 16b shows evidence of all three processes, although ignitive turbidite deposits seem to dominate. Over 90% of all parasequences were represented by bedload deposits as opposed to suspended sediment settling. Tempestites, ignitive turbidites, and hyperpycnites likely occur within the same system, interacting with each other, producing deposits which have remnant signatures of each. Results show it is possible to document the relative proportion of formative processes within heterolithic sequences, as well as to quantify them in terms of wave versus fluvial versus tidal dominance, as well as bedload versus suspended load transport.