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Evaluating Along-Strike Variation Using Thin-Bedded Facies Analysis, Upper Cretaceous Ferron Notom Delta, Utah


The Upper Cretaceous Ferron Sandstone consists mainly of fluvial-Previous HitdeltaicNext Hit deposits. Within Previous HitdeltaicNext Hit Previous HitenvironmentsNext Hit, thin beds commonly occur, especially in delta front and prodelta. Primary initiation processes to form thin beds include ignitive turbidity currents, hyperpycnal flows and storm surges. Ignitive turbidites are characterized by the classical fining upward Bouma sequence. Hyperpycnites can show either inversely graded or normally graded bedding. Storm deposits (tempestite) are fining upward and are characterized by the hummocky cross stratification (HCS) and wave ripples. All these three processes are common in Previous HitdeltaicNext Hit systems. Ignitive turbidity currents and hyperpycnal flows indicate fluvial-dominated depositional Previous HitenvironmentsNext Hit, whereas tempestites directly linked to wave/storm dominated Previous HitenvironmentsTop. With the fully-developed sequence stratigraphic framework across the study area, the relative amount of sedimentary structures generated by each depositional process can be calculated from a series of measured stratigraphic sections within a single parasequence (Parasequence 6) which is continuously exposed along depositional strike. For each measured section, important sedimentological data including grain size, lithology, bedding thickness, sedimentary structures and ichnological suites have been documented in a millimeter to centimeter scale. The thin-bedded prodelta and distal delta front facies within Parasequence 6 show a strong along-strike variation with completely wave-dominated facies in the north, passing into river-dominated facies southward, then to river-dominated, wave-influenced facies south to southeastward, and a wave/storm-dominated facies further to the southeast. Results show that it is practical to quantify the relative importance of formative processes and determine the along-strike variation within Parasequence 6 of the ancient Notom Delta system using thin-bedded facies analysis.