Monday, September 18, 2014 AGS Luncheon Topic:

"Recognition and Significance of Bayhead Delta Deposits: Implications for Oil/Gas Exploration and Basin Dynamics"

Noon Luncheon 11:30-1:00 pm

ABSTRACT:

Detailed sedimentology and sequence-stratigraphic context of ancient bayhead delta (BHD) deposits in the Book Cliffs, UT provides insight into BHD development, and helps predict reservoir distribution using the transgressive trajectories they define. Estuaries are common features of transgressive coastlines with high preservation potential due to their position within incised valleys. Despite advances in estuarine facies models over the last 20 years, bayhead delta deposits are not widely recognized or utilized in the stratigraphic record, and their geometries/reservoir characteristics are not well known. Bayhead deltas develop at the innermost part of bays within wave-dominated and mixed-energy estuaries.  Deposits of bayhead deltas can be important reservoirs for oil and gas.  However, their true value is that they record the high-frequency turn-around from transgression to regression; in turn, this delineates the long-term trajectory of transgression and assists with facies prediction up- and down-dip of the estuarine facies tract. The following criteria for bayhead delta identification are herein proposed: (1) overall coarsening-up pattern, (2) presence of small-scale clinoforms (5-15 m height; 100-1000 m length) showing a down-clinoform decrease in grain-size and paleocurrent energy, (3) increasing abundance of mud interbeds toward the clinoform toe, (4) basinward- directed paleocurrents  generated mainly by fluvial input with strong tidal overprint, (5) greatest tidal influence in the intertidal zones of the inactive delta front and better preservation of turbidites at clinoform toes, (6) brackish trace and body fossils and (7)  located within a transgressive interval, especially near transgressive maximum. Recognition of bayhead delta deposits in the Book Cliffs, UT aided regional correlation and defined the transgressive trajectory within a retrogradational sequence set.  The rising transgressive trajectory defined herein helps to explain the high proportion of well-preserved tidal deposits within the middle Castlegate Sandstone and downdip equivalents.  Utilization of bayhead delta deposits in other basin-scale studies provides a useful tool for reconstructing transgressive shoreline trajectories that can better predict reservoir distribution, and aids interpretation of long- and short-term drivers on clastic wedge development.

SPEAKER:

Jennifer Aschoff, PhD
Associate Professor, Stratigraphy, Department of Geological Sciences, University of Alaska, Anchorage
jaschoff@uaa.alaska.edu

Education
2008    Ph.D., University of Texas at Austin, Geology
2003    M.S., New Mexico State University, Geological Sciences
2000    B.S., Montana State University, Earth Sciences

Research Interests
The formation, fill and economic resource potential of ancient sedimentary basins is the primary focus of my academic research.  To understand the linkages between tectonics, sedimentary process and basin dynamics I use an integrated approach using a range of datasets.  Depending on the hypothesis I’m testing, I use a mixture of outcrop, seismic, well-log, core and geochemical data.  The methods I use include detailed sedimentology, sequence stratigraphy typically integrating well logs, geologic mapping, provenance analysis, and paleocurrent analysis.  Core research themes that I have developed are:

  1. Understanding basin dynamics and their fill- especially the role of dynamic subsidence,
  2. Applied stratigraphy and sedimentology as it pertains to the oil and gas industry.

Recent Positions Held
2011-2014    Assistant Research Professor (part-time), Stratigraphy, Dept. Geology and Geological Engineering, Colorado School of Mines (Golden, CO) (split with BP-America)
2011- 2014   BP America Sed/Strat Specialist (split with part-time Research Professor at CSM)
2008-2011       Assistant Professor, Stratigraphy, Dept. Geology and Geological Engineering, Colorado School of Mines (Golden, CO)

Selected Recent Publications
(1) Valora, P.M. and Aschoff, J.L., 2012, Geologic map and sections of the Thistle 7.5 Quadrangle: Insights into tectono-stratigraphic development of the Southern Provo Salient, Utah: UGS Miscellaneous Publication #12-1.
(2) Aschoff, J.L. and Steel, R.J., 2011, Anomalous clastic wedge development during the Sevier-Laramide transition in the Cordilleran Foreland Basin, USA: GSA Bulletin; DOI: 10.1130/B30248.1
(3) Steel, R.J., Plink-Bjorklund, P. and Aschoff, J.L., 2011, Tidal deposits of the Campanian Western Interior Seaway, Wyoming, Utah and Colorado, in Principles of tidal sedimentology, by Richard A. Davis Jr. & Robert W. 621 pp.
(4) Aschoff, J.L., and Steel, R.J., 2011, Anatomy and development of a low-accommodation clastic wedge, Upper Cretaceous, Cordilleran Foreland Baisn, USA: Sedimentary Geology; DOI: 10.1016/ j.sedgeo.2010.10.006
 (5) Aschoff, J.L, 2010, Preliminary regional sequence-stratigraphic framework and characterization of potential fluvial reservoirs of the Upper Mesaverde Group, Uinta Basin, Utah: UGS Open File Report #569.

Recent Service to Geological Community
2015- Session chair for AAPG Annual Meeting, Denver, CO
2014- Reviewer J.Sedimentary Research, Sedimentology, Basin Research, GSA Special Publication
2013- Session chair GSA Annual Meeting, Denver, CO
- Reviewer Sedimentology, Basin Research, GSA Special Publication
      -Session chair AAPG Annual Meeting, Pitsburgh, PA

Teaching
Depositional Systems and Dynamic Stratigraphy, UAA
Numerous Courses at CSM, and several at BP

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