INNER-SHELF TO LOWER-SHOREFACE HUMMOCKY SANDSTONE BODIES WITH EVIDENCE FOR GEOSTROPHIC INFLUENCED COMBINED FLOW, LOWER CRETACEOUS, WEST GREENLAND

Hummocky sandstone bodies were deposited on the margin of an Early Cre taceous rift basin in an overall progradational inner-shelf to lower-s horeface unit. Excellent outcrops of this unit permitted a detailed st udy of sedimentary structures and paleocurrents in relation to sandsto ne geometries. The sandstone bodies are lensoid and 0.5-4 m thick with lateral extensions from a few meters to more than 30 m. Laterally the y pinch into thin sandstone sheets that continue for at least 130 m al ong the entire outcrop or swell within a distance of 20-30 m to form a nother sandstone lens. The lower boundaries are sharp with local erosi onal relief up to 1 m. Hummocky cross-stratification, wave-ripple cros s-lamination, and low-angle cross-stratification are closely interbedd ed within the sandstone. Laminated mudstone beds (10-60 cm thick) sepa rate the sandstone bodies and are generally continuous over the entire length of the outcrop. Sedimentary structures in the sandstone bodies were produced by high-energy wave-generated oscillatory currents and unidirectional geostrophic currents, Vertical stratification successio ns from individual storm events reflect deposition during both increas ing storm-current velocity succeeded by waning-storm deposits and, mor e typically, waning-storm facies successions. Deposition of the unusua l vertical successions was probably controlled by an episodically high sediment supply. The local presence of the hummocky sandstone bodies on a regional scale was controlled by a paleogeographic setting where the bathymetric contours locally caused geostrophic currents to decele rate.