--> --> Abstract: Complex Transition of Shallow-Marine Star Point Formation to Coastal-Plain Blackhawk Formation, Wasatch Plateau, Utah, by Andrew M. Ranson, Royhan Gani, Gary Hampson, Nahid D. Gani, and Hiranya Sahoo; #90124 (2011)

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Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA

Complex Transition of Shallow-Marine Star Point Formation to Coastal-Plain Blackhawk Formation, Wasatch Plateau, Utah

Andrew M. Ranson1; Royhan Gani1; Gary Hampson2; Nahid D. Gani1; Hiranya Sahoo1

(1) Earth and Environmental Sciences, University of New Orleans, New Orleans, LA.

(2) Department of Earth Science and Engineering, Imperial College, London, United Kingdom.

Using cliff-face photomosaics, measured sections, GPR (ground penetrating radar), and core data, this outcrop study characterizes facies and stratigraphic complexity at the transition of marine to non-marine depositional environments as preserved in the stratigraphic transition of the late Cretaceous Star Point Formation to Blackhawk Formation that superbly crops out in the north-eastern Wasatch Plateau, Utah. Data from seven “windows” of the outcrop, including GPR profiles through selected sandbodies, and one coal-mining core demonstrate this complexity at a range of scales. The youngest two sandbodies (i.e. parasequences) of the Star Point Formation constitute an overall wave-dominated shoreface environment with hummocky to swaley cross-stratification, dune cross-bedding, and marine trace fossils. The lower Blackhawk Formation constitutes an overall coastal-fluvial environment, which contains a number of facies representing various sub-environments, including: (1) thin to thick coal beds with Teredolites burrows, (2) fluvial channel deposits with dune cross-bedding and lateral-accretion surfaces, (3) tidal channel deposits with IHS (inclined heterolithic stratification), and (4) coastal to bay-fill mudstones.

In the northern part of study area (Wattis Road location), the complex transition from marine to continental strata is expressed by intertonguing of marine and coastal-plain strata. Facies architecture of the tidal channel strata reveals development of multiple IHS sets, as tidal channels migrated across the coastal plain. A depositional dip-oriented section shows up-dip pinch-outs of two shallow-marine parasequences into coastal-plain Blackhawk deposits. A prominent incised valley (~10 m thick) was also observed that eroded the upper part of this shallow-marine sandstone. At the same stratigraphic level, more incised valleys were documented in other outcrop “windows” that erosionally overly the uppermost marine sandstone, indicating the existence of a sequence boundary. Transitional complexity progressively decreases southward; the Cottonwood Canyon outcrop shows a rather simple upward transition from shallow-marine strata to coastal-plain strata.