Facies Architecture, Paleo-hydraulics and Fluvial Style of a Falling Stage Terrace Deposit within a Compound Incised Valley System, Ferron Notom Delta, Utah



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Incised valley systems are important because they contain significant hydrocarbon reserves, provide clues into the geologic history of a region, and are crucial for sequence stratigraphic interpretations. The fluvial/deltaic Notom Delta component of the Turonian (Late Cretaceous) Ferron Sandstone Member of the Mancos Shale outcrops in south-central Utah providing an excellent opportunity to study a terrace deposit in both strike and dip orientations of a compound incised valley system. Using traditional field methods conducted during the summer of 2012, detailed cross sections and bedding diagrams were created that show a terrace deposit (Valley 3) that has been previously undescribed. This terrace deposit formed in response to multiple sea-level fluctuations. The presence of a tidal signature along with the proximity of the incised valley system to the coastal plain (parasequence 4) suggest the presence of a Coastal Plain Valley System. Fill from this incised valley deposit would also fall within the shorter, less preserved deposits of the segment 2 middle incised valley deposits of the idealized longitudinal incised valley model. Paleocurrent and bar accretion measurements taken from within individual channel belts of the incised valley generally showed accretion occurring at high angles to that of the paleocurrent direction. This suggests the fluvial style responsible for the formation of this incised valley system was meandering. Previous regional stratigraphic studies have shown that the incised valley system within the study area is a falling stage terrace deposit. This is incongruous with previous sequence stratigraphic models that early, falling stage valley fills are a result of braided rivers. Paleo-flow depths that were calculated based on cross-set thicknesses for Valley 3 indicate an average flow depth of 3.3 to 5.4 meters.



Incised valleys, Facies architecture, Fluvial style, Fluvial systems, Ferron sandstone, Paleo-hydraulics