Unconformities in the mid-Late Proterozoic Pahrump Group: Stratigraphic evidence from the upper member Crystal Spring Formation
- City Coll. of New York, NY (United States). Dept. of Earth and Atmospheric Sciences
Deposition of the Pahrump Group rocks (Crystal Spring-Beck Spring-Kingston Peak Formations) in the Death Valley region of California post-dates 1.7 to 1.4 Ga gneissic basement rocks (Wright et al., 1976) and mostly predates the inferred 0.75 Ga glacial deposits of the Kingston Peak Formation. The 1.08 Ga age of the diabase sills in the middle Crystal Spring Formation provides an additional time constraint. Event though this time span is excessive when compared to better dated Phanerozoic successions, the Pahrump Group, nonetheless, has been assumed to be internally conformable. Results from the authors recent work invalidates that assumption. They have carefully measured 15 sections of upper member Crystal Spring Formation rocks and have mapped in detail the belt of exposures in the Saratoga, Saddle Peak, and Ibex Hills, and northern Kingston Range. Their data indicates that an unconformity of significant but unknown duration occurs within the upper member. Evidence for this unconformity includes: (1) local angular discordance of up to 20[degree]; (2) presence of an erosive-based breccia unit (0.10--30 m thick) that consists mostly of hornfelsic clasts derived from immediately subjacent rocks; and (3) erosional beveling and truncation of underlying rocks. In addition, the upward transition to Beck Spring deposition is marked by a disconformity (sequence boundary) that cuts down across and erosionally truncates strata of the upper member Crystal Spring Formation.
- OSTI ID:
- 5019828
- Report Number(s):
- CONF-9305259-; CODEN: GAAPBC
- Journal Information:
- Geological Society of America, Abstracts with Programs; (United States), Vol. 25:5; Conference: 89. annual meeting of the Cordilleran Section and the 46th annual meeting of the Rocky Mountain Section of the Geological Society of America (GSA), Reno, NV (United States), 19-21 May 1993; ISSN 0016-7592
- Country of Publication:
- United States
- Language:
- English
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