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This research is focused on defining sedimentary facies architecture and reservoir potential in the Cretaceous John Henry Member (JHM) of the Straight Cliffs Formation, southern Utah. We are conducting a field-based analysis of shallow marine and nonmarine clastic deposits, with an emphasis on developing well-controlled facies models to improve reservoir prediction in analogous subsurface reservoirs. The study area around the Kaiparowits Plateau features high-quality, three-dimensional exposures of these strata. It is therefore possible to physically track facies transitions in all directions, as well as the major surfaces bounding stratigraphic packages. Our results bear directly on fundamental principles of sequence stratigraphy and their applications to energy exploration. Key findings to date  include:

1.      Documentation of T-R cycles in shallow marine strata reveals unusual and perhaps under-recognized preservation of transgressive deposits. Accurate interpretations of these cycles is critical to understanding their stratigraphic architecture and sequence-stratigraphic context.  A careful study of paralic facies near Rogers Canyon has defined two distinctive facies associations found in close proximity to one another: transgressive and regressive. Transgressive deposits include marine shell-rich lagoonal shales, tidal inlets, back barrier bioturbated sandstones and washover fans. Regressive deposits are shallowing upward, storm dominated shoreface facies. Between these T-R cycles, four surface manifestations are described that form two types of bounding surfaces or elements. Flooding surfaces and wave ravinement surfaces are observed at the base of regressive shoreface facies. A process change and coaly intervals are found at the base of transgressive facies. These bounding elements generate two T-R cycle architectures: 1) regressive, tabular, shallowing-upward marine parasequences, and 2) transgressive and regressive wedges that thin basinward and landward.

The recognition of these surfaces and different T-R cycles preserved due to accretionary transgressive deposits are critical to achieving accurate sequence stratigraphic interpretations of fourth-order cycles. Additionally, sequence boundary formation within this setting (high accommodation/sedimentation rates) does not follow standard models. Two surfaces within the John Henry Member record the deposition of tidal deposits over wave deposits. The first is composed of an unconformity, however it records a minor basinward shift in facies and is not interpreted as a result of a relative sea level fall. The second surface is conformable, however because of a significant basinward shift in facies, it is interpreted as forming during a slow relative sea level fall. These two surfaces demonstrate that an unconformable surface and a significant relative sea level fall are not always related.

2.      We are conducting careful outcrop and subcrop correlation of these higher-order shoreline shifts into nonmarine strata. Field work near the Kelly Grade defines fluvial facies architecture, guided by a ‘new’ approach to fluvial stratigraphy, and tests whether existing sequence-stratigraphic models for fluvial response to base level change are appropriate for this case study.

New outcrop and subcrop data illustrate regional nonmarine-marine stratigraphic correlations and address sequence stratigraphic models based on such correlations. Three measured sections and two logged cores (each >230 m), 2367 paleocurrent measurements, and examinations of lateral facies relationships were made in the John Henry Member. This data stratigraphically correlates to 43 measured sections and logged cores from previous work in the region. Three facies associations identified in fluvial and paralic sections correlate to downdip marine and shoreline equivalents as follows: Facies association 1 (FA-1, the lowermost interval) consists of tidally influenced, laterally restricted fluvial channel belts, coastal mire, and shoreface sandstone. FA-1 correlates to a lower marine package that shows net progradation and consists of vertically thick, laterally extensive regressive shoreface sandstones intercalated with transgressive lagoonal deposits. Facies association 2 (FA-2, the middle interval) consists of laterally restricted, highly sinuous fluvial channel belts, lagoonal and estuarine coastal plain mires, bay-head deltas, isolated distributary channels and tidal channels. FA-2 correlates downdip with a middle marine package shows net transgression and consists of vertically thin, laterally restricted regressive shoreface deposits intercalated with thick transgressive lagoonal deposits and barrier island sandstone. Facies association 3 (FA-3) consists of laterally extensive, low sinuosity fluvial channel belts and vertically amalgamated fluvial channel belt complexes, and floodplain overbank. The marine equivalent of FA-3 shows net progradation and consists of vertically thick, laterally extensive regressive shoreface sandstones intercalated with transgressive lagoonal deposits. Preserved within each marine package are multiple transgressive-regressive cycles, but the fluvial architecture does not appear to respond to this scale of cyclicity. The observed evolution of fluvial systems and the inferred relationship to relative sea level change is distinct from previous interpretions of these strata. Autogenic or allogenic trunk channel avulsion may exert a primary control on the overall relationships between marine, paralic and fluvial stratigraphy in the John Henry Member.Thus, preliminary interpretations of  more proximal (relative to Rogers Canyon) JHM deposits show fluvial facies shifting in tandem with the higher amplitude T-R cycles observed in the marginal marine sections (or at least, fluvial packaging at the about the same temporal scale and stratigraphic interval), although true sequence boundaries within the John Henry Member are not evident.

3.      Terrestrial lidar can provide user-friendly and even cost-effective datasets with direct economic and training applications for the petroleum industry. A large lidar dataset was acquired near Rock House Cove to aid facies documentation in nonmarine JHM strata, including quantitative and spatial definition of architectural elements, reservoir prediction, and to form the basis of several learning modules for geosciences education, which we suggest modifying for industry use. Two new students have initiated M.S. projects that will focus on fluvial strata landward of the Kelly Grade, including facies documentation, regional correlation with our other work in the area, and different applications of the lidar dataset. We seek to build predictive reservoir models, and we are also testing educational and training aspects of the combined virtual and ‘real’ outcrop data. We are significantly aided by collaboration with a local company, Intelisum, that has resolved many of the software issues experienced by other Lidar users in the past.