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Abstract

The Upper Cretaceous sediments of the Blackhawk Formation of the Mesa Verde Group are interpreted as a complex of wave-dominated, prograding, siliciclastic shoreline parasequences. The Spring Canyon Member, of the Blackhawk Formation is representative of the shoreline deposits and was preserved in core of the Exxon Production Research Co. Price River "C" well. The core illustrates the trace fossil assemblages throughout the offshore to shoreface environments on a wave-dominated shoreline. The transition between the lower shoreface and the upper shoreface can be readily defined through the packaging of facies-dependent, diagnostic trace fossil assemblages. These assemblages allow the offshore and shoreface facies to be accurately divided into distal and proximal facies, providing a greater range of facies control for correlation between well logs. The development of opportunistic trace fossil assemblages, formed in response to storm sedimentation can be differentiated from the background resident trace fossil assemblages by interpreting the ethology of the individual traces as a response to increases in the rate of sedimentation, oxygenation and corresponding changes in the substrate.

Trace fossil assemblages can be used to define the flooding surfaces that bound parasequences, with deeper water facies resting sharply on more shallow water facies. There are no transgressive deposits, such as lags, that can be identified, associated with the sharp-based parasequence boundaries. Trace fossil assemblages can be used to identify and interpret key stratal surfaces. Recognition of the Glossifungites ichnofacies is important for delineating potential sequence boundaries.

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