© ICDP, the International Continental Scientific Drilling Program, 1996-2020

www.icdp-online.org

Sevier Desert Basin Drilling Project

North America, U.S.A., Utah, Sevier Desert Basin

new workshop-proposal: ICDP-2007/09
for the funding-period starting 2007-01-15
by Nicholas Christie-Blick, Mark H. Anders, Georg Dresen, Gordon Stuart Lister, Gianreto Manatschal, Brian Philip Wernicke
Abstract
Low-angle normal faults or detachments are widely regarded as playing an important role in crustal extension and the development of passive continental margins. However, no consensus exists on how to resolve the mechanical paradox implied by such faults or on the general absence of evidence for seismicity. The purpose of proposed drilling in the Sevier Desert basin in the western United States is to test the extensional detachment paradigm through coring, downhole logging, biostratigraphic, isotopic and fission-track dating, magnetostratigraphy, and in situ measurement of pore pressure, permeability, fluid chemistry, temperature, and stress orientation/magnitude at an example for which evidence of large normal-sense slip on a detachment of particularly low dip (11°) is widely regarded as among the most convincing, and for which a case can be made for contemporary displacement. While no seismicity has been documented on the Sevier Desert detachment, its scale is consistent with earthquake magnitudes as large as M 7. Given a location ~150 km southwest of Salt Lake City, it rivals the more active but segmented Wasatch fault as a seismic hazard. We propose to hold an international workshop on “Scientific Drilling in the Sevier Desert Basin” in June or July, 2008. The purpose of the meeting is to flesh out objectives, strategies and operational details, with input from a much broader constituency of interested scientists than is represented by the PIs, and to develop a consensus on the location of a drill site. This will be informed by an already comprehensive evaluation of existing subsurface data, and by the need to balance optimal science against cost. The most important product of the workshop will be a full drilling proposal to be submitted to ICDP in January, 2009. Candidate drill sites are located east of a line along which the interpreted detachment passes from the contact between Paleozoic carbonate rocks and Cenozoic basin fill into deformed Neoproterozoic and Paleozoic rocks of the Mesozoic orogen on which the basin is superimposed. A compelling case can be made for a hole as deep as 4,000 m, at which depth fault rocks (both ductile and brittle) are most likely to be preserved. In interpreting basin evolution (and the history of displacement along the detachment), it will also be useful to sample as complete a stratigraphic record as possible. Compromise sites can be considered, but a borehole shallower than ~2,000 m risks not achieving important geological objectives.
Scientific Objectives
  • Geological studies in the proposed borehole are aimed at elucidating the character of the Paleozoic-Cenozoic contact and the long-term evolution of the basin – together constituting a new critical test of the detachment hypothesis. In situ measurements are aimed at determining the conditions under which displacement may have taken place, as recently as the Holocene, consistent with the generally accepted interpretation of the geology. Specific issues to be addressed include the following:
  • Evidence for ductile and/or brittle deformation vs an unconformable contact, recognizing that fault rocks may have been partially removed by erosion prior to burial, and that an originally unconformable contact may have been involved in faulting.
  • The history of sediment accumulation, and how the timing of basin development relates to exhumation of the hypothesized footwall of the detachment. A full suite of downhole logs (especially acoustic logging) will allow confident correlation with seismic reflection data.
  • In situ physical conditions along the detachment zone, including pore pressure, fracture permeability, fluid chemistry, temperature, the orientation of stress axes and the magnitude of differential stress. Employing methods developed and refined for the KTB and SAFOD drilling projects, particularly hydraulic fracturing tests and analysis of tensile and compressional (breakout) failures of the wellbore wall, it will be possible to estimate the complete stress tensor at depth along the detachment zone.
Keywords
Active faults, Drilling, Extensional detachment, ICDP-2007/09, SEVIER, Sevier basin, U.S.A., Utah
Location
North America, U.S.A., Utah, Sevier Desert Basin: 39.16667, -112.50000

© ICDP, the International Continental Scientific Drilling Program, 1996-2020

www.icdp-online.org