PBS-SEPM 2025 September Luncheon - Kelly Hattori

"Refining models for the spatiotemporal evolution of mixed siliciclastic-carbonate systems of the Pennsylvanian Upper Strawn Group of the Eastern Shelf" - Kelly Hattori, Carbonate Geologist, STARR Research Group, Bureau of Economic Geology, UT Austin, Jackson School of Geosciences
 
Abstract
The Pennsylvanian Strawn Group of the Eastern Shelf of the Permian Basin, Texas, USA comprises a highly heterogeneous mosaic of siliciclastic and carbonate facies representing purely carbonate systems (e.g., “reefs”/buildups), purely siliciclastic systems (e.g., deltas), and a variety of mixed systems. Depositional environments range from intertidal/exposed to basinal deepwater settings. Because of rapid glacioeustatic fluctuations associated with this peak icehouse time, facies associated with any environment may be juxtaposed (laterally or vertically) with one another. Consequently, in the subsurface stratal relationships are difficult to resolve, and correlation becomes problematic. To highlight these challenges, we present a case study integrating core and wireline log data from three oil/gas fields along a 35 km transect in King County, TX. Bateman Ranch field (north) is composed of highly cyclic phylloid-algal boundstones, shallow-water wackestones, and deeper-water mudstones bounded by subaerial exposure surfaces. Katz field (south) contains tidally-modified deltaic deposits. Anne Tandy field (center) is characterized by interfingering silcicilastic- and carbonate-dominated deposits attributed to shoals, deltas, and deeper subtidal settings. Although biostratigraphic analyses indicate that the fields are broadly temporally correlative, they did not develop contemporaneously under the same depositional conditions. In this talk, we review key differences in lithologies and reservoir properties between these three fields, and show how core observations can be used to revise regional-scale depositional models to better explain the relationship of each field to one another. Traditional mixed-system models fail to adequately explain the distribution and spatiotemporal relationships of facies, which are strongly impacted by glacioeustatic fluctuations, tectonic activity, and the presence of a clastic point source. Thus, we incorporate elements of multiple models to develop a better-tuned model that includes consideration of the effects of high-frequency, high-amplitude sea level fluctuations and resultant underfilled accommodation, as well as the local structural setting which further impacts depositional systems. Incorporation of this icehouse climatic context illuminates the potential for preservation and recurrent reactivation of topographic features, which contributes significantly to a rugose bathymetric profile and development of extremely complex facies mosaics such as those observed on the Eastern Shelf.
 
Bio
Kelly Hattori is a carbonate geologist in the State of Texas Advanced Resource Recovery (STARR) research group at the Bureau of Economic Geology, Jackson School of Geosciences, University of Texas at Austin, Texas, USA. She holds Marine Biology and Geology bachelor degrees from the University of North Carolina at Wilmington, and a master's degree in Geosciences from the University of Texas at Austin. Her research focuses on stratigraphy and sedimentology of carbonate and mixed siliciclastic-carbonate systems of Paleozoic and Mesozoic formations of the American Southwest, including reconstruction of depositional systems and interactions of local, regional, and global controls on deposition.