The Devil Is in the Details: Challenges of Regional Correlation in Marine-Nonmarine Facies
The John Henry Member of the Cretaceous Straight Cliffs Formation (Kaiparowits Plateau, southern Utah) spans marine to continental landscapes and provides a unique opportunity to assess their relationship. By documenting each depositional regime separately and then linking them together, forced correlations can be avoided and true connections are revealed. The initial phase of the Straight Cliffs Project focuses on the marine and marginal marine realm in order to establish a sequence stratigraphic framework. The marginal marine system records a complicated pattern of alternating depositional systems including shoreface and lagoonal successions. Shoreface facies are interpreted as progradational (regressive) strandplain and storm wave-dominated open marine systems. Lagoonal facies include transgressive barrier and back barrier deposits. Transgressive deposits are of particular interest here, as they are accretionary and record process changes rather than characteristics of flooding 'surfaces' that have been traditionally emphasized in the literature. Preservation of transgressive deposits is enabled by steep shoreline trajectories and high sedimentation and accommodation rates typical of this part of the Western Interior Seaway and others including the San Juan Basin. Similarly, observed relationships between transgressive and regressive packages questions the identification of 'sequence boundaries' in this area, as basinward facies shifts are not always regional and could in fact represent autogenic influences. The identification of sequence boundaries is further complicated by higher subsidence rates, which mitigate erosion typically used to identify such surfaces. Despite the lack of obvious sequence boundaries, several transgressive-regressive cycles are identified within the marginal marine enabling a correlation into fluvial successions up-dip to the southwest. Outcrop, core and lidar data are utilized for comparison of fluvial architecture variations along depositional dip, strike and through time. Ongoing work includes reservoir modeling, quantitative characterization of fluvial architecture, and complete correlation from non-marine to marine environments using detailed facies analysis and large-scale depositional trends.
AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009