Rangely Turbidites and Their Linkage to Coeval Shallow-Water Succession, Rangely, Colorado

Sacerdoti, Raffaello and Piret Plink-Bjorklund
Colorado School of Mines, Golden, CO

     Isolated sand bodies within the Mancos shale of the Western Interior Basin are exposed below the Castlegate sandstone in the Rangely Anticline. These sand bodies have previously been interpreted as shoreface deposits associated with the Castlegate Formation. Detailed stratigraphic analysis has identified these deposits as turbidites. One of the objectives of this project is a further detailed analyses of the turbidite beds with the aim to document the architecture of this turbidite system, establish the type of feeder system (i.e. river-fed hyperpycnal flow turbidites vs. failure-initiated turbidites), and establish the paleo-water depth (i.e. deposition below or above the wave base). Considering the latter special attention is paid to signs of wave- or tide- influence in the turbidite beds. The second objective is to resolve the timing of the Rangely turbidite sandbody deposition, and whether it is associated with lowstand, falling-stage or highstand systems tract in the coeval shoreline complex. Previous correlations suggest that the Rangely turbidites are associated with the Desert interval of the Blackhawk Formation. Subsurface data and outcrop correlations are used to link the shallowwater deposits to the Rangely turbidites. Through linking the Rangely turbidites to their source, we hope to further understand what causes some systems to have an “attached” highstand, falling-stage and lowstand system, whereas in other systems the lowstand deposits are detached from their highstand shorelines.

AAPG Search and Discovery Article #90071 © 2007 AAPG Rocky Mountain Meeting, Snowbird, Utah