M. Royhan Gani, PhD, University of New Orleans
Current sequence stratigraphic models deal with stratal packages mostly along depositional-dip. Although it is speculated that sequence stratigraphy will vary along depositional-strike, a well-documented example is largely lacking, particularly in the outcrops. The proposed study is investigating Shallow-marine to coastal-plain fluvial strata in depositional-strike-oriented outcrops in the Wasatch Plateau, which is contiguous with the dip-oriented and well-documented Book Cliffs outcrops, Utah. Much of the current and projected global hydrocarbon production remains in siliciclastic shallow- and marginal-marine reservoirs. Hence, this study is also motivated by the need to better understand the controls on shallow-marine and coastal-plain reservoir architecture using outcrop analogs, particularly along depositional-strike. Moreover, the findings of the proposed study can serve as a direct outcrop analog for producing tight-gas reservoirs in the adjacent Uinta and Piceance Basins.
This PRF funding has enabled PI to launch successfully a major research initiative at an early stage of his career in a tenure-track faculty position at a PhD granting institute. As part of this outcrop study, PI has developed effective collaborative efforts with Dr. Gary Hampson at Imperial College London and Dr. John Howell at University of Bergen. Under the supervision of PI, a number of students were and are actively pursuing research directly linked to this project.
Andrew Ranson has successfully defended his MS thesis in spring of 2012, and now has a full-time job at Chevron as a geologist. Previously, he also completed an undergrad senior thesis in PI’s lab. Hiranya Sahoo will defend his PhD dissertation during spring of 2013, and has completed an internship with Shell during summer of 2011. Undergrad student Corey Hinyup is currently conducting a senior thesis. Both of the graduate students have secured additional funding from external sources (AAPG, IAS, SEMP-Gulf Coast Section, and ExxonMobil Geoscience Grant) to support their ongoing research (field expenses, partial salary, etc.). This was made possible because of this PRF fund that initiated their graduate research.
Our target stratigraphic interval includes upper Cretaceous, shallow-marine Star Point Formation and overlying coastal-plain to continental-fluvial Blackhawk Formation, which are exposed in a large (c. 100 km), nearly-continuous section aligned subparallel to depositional-strike along the eastern edge of the Wasatch Plateau in central Utah. Each year, field work has been conducted to collect field and other (e.g. GPR, Lidar, 3D photorealistic outcrops) data. So far, we have collected low-angle aerial photographs of the entire outcrop belt (~100 km long; acquired on overview flights by a light airplane), 28 measured sections, ground penetrating radar data from a few mesa tops, and 15 outcrop photomosaic panels with facies architectural and sequence stratigraphic interpretation. One well core, ~300 m thick, were also logged at the Core Lab of Utah Geological Survey. As part of our collaborative effort with Bergen University, a team from Bergen University collected and processed helicopter-based lidar data (20 cm resolution) from a 3D cliff, ~5 km in length, located in our study area. Currently, we are generating virtual 3D outcrops of a few selected cliff faces using Sirovision technology.
This PRF-funded research has already resulted in numerous conference/meeting presentations and a number of peer-reviewed publications. Currently, a few manuscripts are also under submission and in preparation. Our results, interpreted so far, are briefly described below:
1) The late Santonian to early Campanian Star Point consists of five parasequences that predominantly comprise wave-dominated shoreface-shelf deposits. Along-strike variations in this trajectory pattern reflect increased tectonic subsidence towards the north combined with highly localized, large-volume, fluvial sediment supply near the northwestern limit of the study area during deposition of an areally extensive (>800 km2) fluvial-dominated delta front complex (Panther Tongue). Sequence stratigraphy of the Star Point Formation was summarized in more detailed in the previous report.
2) We have characterized facies and sequence stratigraphic complexity at the transition of the Star Point Formation to Blackhawk Formation. The nature of spatio-temporal transition of these two Formations is largely undocumented so far, particularly in the deposition-strike orientation. In the northern part of study area, the transition from marine to continental strata is expressed by complex intertonguing of marine and coastal-plain succession. Facies architecture of tidal channel strata reveals development of multiple IHS sets, as tidal channels migrated across the lower coastal plain. A depositional dip-oriented outcrop “window” shows abrupt updip pinchouts of two uppermost shallow-marine parasequences into coastal-plain deposits. This transitional complexity progressively decreases southward, the southern outcrops show a rather simple upward transition from shallow-marine strata to coastal-plain strata. At least two sequence boundaries (high frequency?) are correlated across the entire length of the studied outcrop belt, where each is represented as alternating incised-valley-floors and interfluve surfaces along depositional-strike.
3) For the entire Blackhawk Formation, early-to-middle Campanian in age, coastal-plain stratigraphic architecture and large-scale patterns of fluvial sandbody distribution have been analyzed using a large outcrop dataset. In general, the low-resolution stratigraphic architecture is marked by an upward increase in the size and abundance of channelized fluvial sandbodies, which coincides with a decrease in tectonic subsidence in the upper Blackhawk Formation and overlying Castlegate Sandstone.
4) The high-resolution stratigraphic framework of the lower Blackhawk Formation is defined by a series of laterally extensive coal zones, which formed on the coastal plain (up to 50 km from the coeval shoreline), generally during shoreline transgression. These coal-bearing strata contain large (up to 25 m thick, 1-6 km wide), multistorey, multilateral, fluvial channel-complex sandbodies that overlie composite erosion surfaces mapped at distinct stratigraphic levels. The large sandbodies are interpreted as fluvial incised valley fills. Other sandbodies in the lower Blackhawk Formation are significantly smaller, and lack apparent stratigraphic organization. Relative sea-level variations of modest amplitude (<30 m) are interpreted as the dominant control on stratigraphic architecture.
5) The upper Blackhawk Formation lacks clear, correlateable high-resolution stratigraphic markers. Channelized fluvial sandbodies within it display strikingly little stratigraphic organization. However, a small proportion (<10%) of these sandbodies occur in vertically-stacked and laterally-offset “clusters” that are not confined by a composite erosion surface. Autogenic processes are interpreted to dominate stratigraphic architecture, and “clustered” sandbodies may result from large-scale avulsion.