Applying Chemostratigraphy to the Williams Fork Formation, Piceance Basin: an integrated stratigraphic approach

Jennifer Kharrazi, Milly Wright, and Jonathan Cantwell

The stratigraphic technique of chemostratigraphy relies upon recognizing changes in element concentrations through time and using those variations to model changes in geological features, such as paleoclimate, clay mineralogy and provenance. Although inorganic whole rock geochemical data have been used to define stratigraphic correlations in the petroleum industry for over a decade now, published accounts using this approach are largely focused on low-accommodation fluvial successions, where stratigraphic correlation using traditional techniques are often problematic (e.g. Ratcliffe et al., 2004, Ratcliffe et al., 2010, Wright et al., 2010 and Hildred et al., 2010). In this study cutting samples were collected from several wells penetrating the Williams Fork and over/underlying formations in order to test whether this technique could be used to produce a high resolution correlation framework within these complex fluvio-deltaic sequences. Samples were analyzed using ICP OES+MS techniques in order to acquired data for 50 major, trace and rare earth elements Regional well log correlations of the Williams Fork Formation in the Piceance Basin indicate significant changes in its stratigraphic architecture and depositional settings across the basin and through time. However, the predominantly non-marine nature of the Williams Fork Formation makes long distance correlations and sequence stratigraphic analysis difficult. By integrating this geochemical dataset with the existing sequence stratigraphic correlations through the study intervals, it has been possible to produce a refined, high-resolution correlation framework for the Williams Fork formation. The study intervals are divisible into several broad-scale geochemical 'packages' that are further divided into multiple higher resolution chemostratigraphic 'units'. These divisions are primarily based on changing K, Rb, Ti, Mg and Al values and are thought to relate to variations in sediment provenance and depositional environment both spatially and temporally.

AAPG Search and Discovery Article #90156©2012 AAPG Rocky Mountain Section Meeting, Grand Junction, Colorado, 9-12 September 2012