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:
During the last two years we have accumulated compelling field evidence that localized seismogenic normal faulting affected sedimentation and soft-sediment deformation, and stratigraphic thickness in the upper capping sandstone members of the Wahweap Formation. Isoseismal maps based on analysis of widespread, traceable seismite horizons reveal the effects of local, intrabasinal faulting superimposed on broader regional trends of earthquake activity. Our work demonstrates the utility of mapping seismites in detail to distinguish the effects of regional versus local tectonic activity in a foreland basin setting.
This year, three new detailed stratigraphic sections were measured in the upper member of the Wahweap Formation on the hanging and foot walls of two of the Late Cretaceous seismogenic normal faults within the field area. Hanging wall sections contain abundant seismogenic features and anomalously thick channel sand bodies, particularly compared with observations of deposits in more distal parts of the Kaiparowits basin. From preliminary analysis of data, hanging wall sedimentation shows much greater seismic intensity than the footwall section. All sections proximal to the faults display greater intensity of soft-sediment deformation than our more distal section. In addition, hanging wall sections show a different style of fluvial preservation with greater thicknesses of heterolithic beds. Measured sections, structural transects and cross sections display a significant increase in overall sediment wedge thickness on the proximal hanging walls of faults, confirming the presence of syntectonic growth strata. During the next field season, additional sections will be measured and described at still greater distances from the faults; we hypothesize that stratigraphic thickness will decrease and sedimentological properties, intensity of soft-sediment deformation, and fluvial preservation style will continue to change with increasing distance from the fault traces.
Career / Educational Progress:
During the 2007-’08 academic year, two undergraduate students and a high school student analyzed sedimentological and structural field data. Principal investigators and students presented abstracts at the National Geological Society of America Meeting in Denver, CO in October, 2007, and at the combined Cordilleran - Rocky Mountain Section GSA meeting in Las Vegas, NV in March, 2008. PRF funds assisted with students’ travel and meeting expenses, as well as 2008 summer field work. A high school student member of our research team also presented posters at these GSA meetings.
PRF funds also helped subsidize travel, camping and subsistence expenses for five additional 2008 summer field work participants: a recent Kutztown University graduate, a high school student, a colleague from Central Connecticut State University (Dr. Mike Wizevich), and two of Dr. Wizevich’s undergraduate students.
A paper based on this PRF-supported research is currently in press in Palaeogeography, Palaeoclimatology, Palaeoecology. In addition to the principal investigators, the paper includes two Kutztown University student authors as well as a high school student and high school teacher.
