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45453-B8
Structural, Sedimentologic, and Stratigraphic Study of Late Cretaceous Normal Faults and Syntectonic Sediments in the Kaiparowits Basin Region, Southern Utah
Project Overview:
Faults exposed on the western margin of the Kaiparowits sub-basin in southern Utah are hypothesized to have accumulated syntectonic growth strata during deposition of the Cretaceous Wahweap Formation. The faults either predate Laramide tectonism and represent faulting within the foreland of the Sevier thrust belt, or they signify an early onset of Laramide basement-involved deformation along the Kaibab uplift. If faults were active during and after Cretaceous sedimentation, they may have influenced the distribution of coal and the geometry of potential natural gas traps within the Kaiparowits basin. Evidence for syntectonic sedimentation should include systematic changes in structural style and orientations, local variations in sedimentation and stratigraphic thickness, and development of seismically-induced deformation or liquefaction features.
Scientific Progress:
We have documented strong evidence that localized seismogenic normal faulting affected sedimentation and soft-sediment deformation near the contact between the upper member and the overlying capping sandstone member of the Wahweap Formation. Features associated with the localized faulting include sag pond deposits, megaloads, sand blows, and clastic dikes and sills. The genesis of many structures was controlled by the initial interbedded lithologies, such that variations in rheological contrast produced different seismogenic structures. A qualitative scale was developed to rank the relative intensity of these seismogenic features, and a map of the intensity of soft-sediment deformation and liquefaction reveals increasing intensity in the immediate vicinity of a prominent fault within the field area. Systematic orientations of clastic dikes and deformation band shear zones that formed in the shallow subsurface parallel the local faults, and are consistent with Laramide stress fields. These data favor the hypothesis that faults within the field area originally formed as oblique outer-arc extensional faults on the steep limb of the developing Kaibab uplift during initial stages of the Laramide orogeny, during deposition of the Wahweap Formation.
A detailed stratigraphic section measured in the upper member of the Wahweap Formation between two of the suspected Late Cretaceous seismogenic normal faults contains abundant seismogenic features and unusually thick channel sand bodies. In subsequent field seasons additional sections will be measured and described at increasing distances from the faults; we hypothesize that stratigraphic thickness will decrease and sedimentological properties will change with increasing distance from the fault traces.
Four structural transects have been completed across the Wahweap Formation. Each transect combines accurate GPS locations with structural orientations and lithologic contacts in order to construct cross sections and calculate stratigraphic thickness of the Wahweap Formation and of its informal members. An undergraduate student will analyzie the structural data during the 2007-2008 grant year. In addition, two students are currently compiling subsurface data from the Utah Oil and Gas Commission's online database, which will be used to explore for other areas of potential growth strata in the Wahweap Formation within the Kaiparowits basin.
Career / Educational Progress:
During the 2006-'07 academic year, four undergraduate students analyzed preliminary sedimentological and structural field data. Each student published an abstract and presented a poster at a regional Geological Society of America meeting in May, 2007 in St. George, Utah. PRF funds assisted with students' travel and meeting expenses. A high school student member of our field team also presented a poster at the regional GSA meeting and won several prizes for her research at the Intel International Science Fair. Two abstracts were accepted for presentation at the national GSA meeting in Denver in October, 2007.
PRF funds provided stipends and travel expenses for two undergraduate researchers during the first summer of grant-supported field work (2007). In addition, PRF funds helped subsidize travel, camping and subsistence expenses for four additional fieldwork participants: a recent Kutztown graduate, a high school student, a high school science teacher, and a colleague from Central Connecticut State University (Dr. Mike Wizevich).
Finally, one of the principal investigators (Dr. Sarah Tindall) received tenure and promotion to Associate Professor. Establishment of an externally funded undergraduate-centered research program was a major factor in her success.
