Fluvial influence on high-frequency sedimentary cycle geometry: The transition from strandplain to deltaic deposition in the Cretaceous Point Lookout Sandstone, San Juan Basin, Colorado
Crandall, Gregg Armand
Dunbar, Robyn Wright
Master of Arts
The Point Lookout Sandstone undergoes an abrupt transition from strandplain-dominated to deltaic-dominated deposition in the northwestern part of the San Juan Basin near Durango, Colorado. The onset of deltaic deposition is preceded by a base level fall and development of a Type 2 sequence boundary as evidenced by a basinward shift in shoreline facies expressed as distributary channel sandstones overlying shoreface deposits. Deposition in the study area, therefore, represents late highstand systems tract progradation and subsequent shelf-margin systems tract deltaic deposition. Posamentier and Vail's (1988) model of deposition during base-level fail in the absence of fluvial incision predicts many of the stratigraphic relationships observed in the field, and provides the best sequence stratigraphic model for deposition within the study area.