Evidence for syntectonic activity during alluvial deposition, Yucca Flat, Nevada
Downhole movies in four large diameter drillholes show a shallowing of bedding dip with increasing distance above the alluvium-tuff contact. The holes are located on the downthrown side of an east dipping normal fault. In each hole the dip of the strata decreases from 20/sup 0/ to 30/sup 0/ at total depth to nearly horizontal at a depth of 150 to 200m. From this depth to the surface the bedding is nearly (<5/sup 0/) horizontal. In emplacement hole U4ar, the alluvial section is divided into 5 stratigraphic units. The three lowest units have a specific range of bedding attitude. The upper two units occur in the same zone of horizontal dip. The borehole film of U4ar as well as a dipmeter log from exploratory hole UE4ah, indicates the attitudes of the volcanic tuff beds below the alluvium-tuff contact are the same as those of the basal alluvial unit. The conformable contact suggests that block rotation and thus fault displacement began after the initial alluvial deposition. Contemporaneous sedimentation and deformation continued until the sediments now at about 150 m depth were deposited. At this time, the fault activity decreased significantly. The uphole decrease in dip is consistent with block rotation along a listric fault. A seismic reflection survey through the area supports the proposed listric nature of the fault. Similar growth faults in the Gulf Coast result from contemporaneous sediment deposition and deformation. However, at the NTS the faults are a result of tectonic processes rather than sedimentary loading. 6 refs., 13 figs.
- Research Organization:
- Lawrence Livermore National Lab., CA (USA)
- DOE Contract Number:
- W-7405-ENG-48
- OSTI ID:
- 5024247
- Report Number(s):
- UCRL-93405; CONF-850953-13; ON: DE86001650
- Resource Relation:
- Conference: 3. symposium on containment of underground nuclear explosions, Idaho Falls, ID, USA, 10 Sep 1985
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
58 GEOSCIENCES
ALLUVIAL DEPOSITS
TECTONICS
NEVADA
STRATIGRAPHY
BOREHOLES
GEOLOGIC FAULTS
NEVADA TEST SITE
SEISMIC SURVEYS
TUFF
CAVITIES
FEDERAL REGION IX
GEOLOGIC DEPOSITS
GEOLOGIC FRACTURES
GEOLOGIC STRUCTURES
GEOLOGY
GEOPHYSICAL SURVEYS
NATIONAL ORGANIZATIONS
NORTH AMERICA
SURVEYS
US DOE
US ORGANIZATIONS
USA
450201* - Military Technology
Weaponry
& National Defense- Nuclear Explosions & Explosives- Containment
580203 - Geophysics- Geophysical Survey Methods- (1980-1989)
580201 - Geophysics- Seismology & Tectonics- (1980-1989)