Stratigraphic Architecture of an Extensional Orogen: The Mojave Extensional Belt, Southern California.
Date of Award
Doctor of Philosophy (PhD)
Geology and Geophysics
Roy K. Dokka
Field-based studies and quantitative models provide new insights into the stratigraphic architecture of a developing continental extensional orogen. The early Miocene age Mojave Extensional Belt of southern California (MEB) exhibits a tripartite stratigraphy, consisting of (1) pre- to early synextension volcanic deposits, unconformably overlain by (2) syntectonic basement-derived megabreccia and breccia with local finer-grained units, overlain by (3) a posttectonic fining-upward sequence of gravel, sand, shale, and limestone. On a more local scale, stratigraphy and sediment dispersal within the MEB reflect the evolution of the major tectonic elements of the belt: (1) Breakaway zone. Strata of the western Newberry Mountains record a complex history of basin formation and dissection as the upper plate progressively broke up during extension. Sediment dispersal was dominated by drainage from unextended regions across the transfer boundary of the terrane. (2) Transfer zone. Strike-slip elements had a variable effect on patterns of sedirnent accumulation. Miocene sedimentary rocks exposed near the Kane Springs transfer zone were mostly derived from across the strike-slip boundary, but the Lane Mountain transfer zone appears to have had little effect on sedimentation patterns in the adjacent Mud Hills. (3) Core complex. Sedimentary rocks exposed in the Mud Hills record the topographic evolution of the Mitchel Range-Hinkley Hills-Waterman Hills metamorphic core complex. Syntectonic sedimentation in the Mud Hills was dominated by rock avalanches composed of upper plate erosional debris. The largely posttectonic Barstow Formation, however, is composed of alluvial fan, fluvial, and lacustrine strata and exhibits a minor component of metamorphic clasts derived from the adjacent core complex. Integration of stratigraphic, structural, metamorphic, and thermochronologic data provides new constraints on crustal-scale models for extension of this area. Quantitative models based on the assumptions of a linear dependance of sediment flux on slope and perfect sorting of sediment during deposition, predict many of the fundamental stratigraphic relationships observed in continental half graben. In addition, these models generate new insight into the controls of fault geometry, rates of faulting, and rates of erosion vs sediment transport on landscape evolution, sediment package geometry, and facies distributions.
Travis, Christopher John, "Stratigraphic Architecture of an Extensional Orogen: The Mojave Extensional Belt, Southern California." (1992). LSU Historical Dissertations and Theses. 5361.