Asymmetric geometry of a half-graben basin as indicated by sediment character: An example from the Diligencia Basin, southeastern California
- Virginia Polytechnic Inst. and State Univ., Blacksburg, VA (United States). Dept. of Geological Science
Sedimentation on the northern side of the basin is characterized by the development of a large scale apron of coallesced alluvial fan deposits. The northern part of the apron is composed of gently dipping, matrix supported, oligomictic granite boulder breccias. Traced southwards, these deposits appear to pass into well-rounded clast-supported cobble-boulder conglomerates containing lensoidal sandbodies as well as examples of clast alignment and imbrication. In contrast, on the southern margin of the Diligencia Basin the steeply dipping Diligencia Formation is composed of fluvial cross-bedded sandstones with minor pebble-cobble conglomerates. The deposits exhibit a notable along-strike grain size variation. The very coarse nature of the sediments on the northern margin indicates deposition along an extremely steep elevation gradient. Some of the blocks may measure tens to hundreds of meters in dimension and represent catastrophic gravity glide events. On the southern side of the basin, although much of the fans have been removed by subsequent erosion, the coarsest deposits are debris flow deposits which must represent a relatively proximal position on the fan. The contrasting character of the lower units of the Diligencia Formation suggests the primary geometric asymmetry of a developing, half-graben basin. The high-gradient deposits in the north are interpreted to represent deposition along the escarpment of a basinward-dipping detachment fault system, whereas the finer sediments of the southern margin must represent low-gradient alluvial fans forming on the gently sloping hanging wall of the half-graben.
- OSTI ID:
- 6137161
- Report Number(s):
- CONF-921058-; CODEN: GAAPBC
- Journal Information:
- Geological Society of America, Abstracts with Programs; (United States), Vol. 24:7; Conference: 1992 annual meeting of the Geological Society of America (GSA), Cincinnati, OH (United States), 26-29 Oct 1992; ISSN 0016-7592
- Country of Publication:
- United States
- Language:
- English
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