Thesis
Non-volcanogenic Cenozoic gravel evolution of the Whitney Basin, Whitney 7.5' quadrangle, NE Oregon
Washington State University
Master of Science (MS), Washington State University
2012
Handle:
https://hdl.handle.net/2376/102644
Abstract
Geologic mapping and investigation of overlooked and underexplored Cenozoic gravels within and in relation to the Whitney Basin, southern Blue Mountains province, NE Oregon, reveal regional geomorphic and tectonic changes through time. The Whitney Basin is a small elliptical half-graben, ~7.5km long northwest axis and ~4.5km wide northeast axis, with a series of Andersonian northwest trending normal faults defining the northern margins. Early-Eocene to Middle-Eocene Tertiary gravels (Tg) are exposed just north of the basin and are composed of well to very well rounded pebble-boulder Elkhorn Ridge Argillite (ERA) and granitic Bald Mountain batholith clasts with at times a weakly consolidated, porous, sand-rich, often gold-bearing matrix. The extent and generally planar stratification of the Tertiary gravel deposits suggest it accumulated in either confined or broad braided channels that unconformably overlie ERA bedrock. Following deposition of Tg, a >1km thick succession of eastern Clarno Formation volcaniclastics, Tertiary volcaniclastics (Tvs), infill the basin from the middle-Eocene to the early-Oligocene. Erosion of the ERA and reworking of the Tvs and Tg created the late-Pliocene to Pleistocene, ERA clast dominated (~80%), Quaternary-Tertiary gravel (QTg) deposit. The QTg has prograded into the Whitney Basin and blanketed over 50 km2 of the Whitney and Sumpter 7.5’ quadrangles as a laterally extensive alluvial fan succession, with at least 50 m of loosely consolidated, sand- and silt-bearing, pebble-boulder gravel. In map view these deposits are concentrated in a broad, moderate sloped ~1.3°, pear shape, dissected by down cutting modern stream channels. The textural maturity and major/trace element X-Ray Fluorescence analyses of granitic gravel clasts in Tg strongly suggest they are multi-cyclic and recycled into the QTg. The Tg and QTg have been the focus of placer gold exploration and extraction for much of the past century.
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Details
- Title
- Non-volcanogenic Cenozoic gravel evolution of the Whitney Basin, Whitney 7.5' quadrangle, NE Oregon
- Creators
- Dale Preston Lambert
- Contributors
- David R. Gaylord (Degree Supervisor)
- Awarding Institution
- Washington State University
- Academic Unit
- Environment, School of the (CAHNRS)
- Theses and Dissertations
- Master of Science (MS), Washington State University
- Publisher
- Washington State University; [Pullman, Washington] :
- Identifiers
- 99900525389301842
- Language
- English
- Resource Type
- Thesis