Date of Award:

2005

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Geology

Advisor/Chair:

Susanne U. Janecke

Abstract

We examine the transition between extension and strike-s lip in the San Felipe Hills, western Salton Trough, southern California using new and compiled geologic mapping, measured stratigraphic sections, magnetostratigraphy, and structural analysis. A 625 m measured section describes the Borrego, Ocotillo , and Brawley formations in the SE San Felipe Hills and constrains a regional disconformity and correlative angular unconformity at ~ 1 Ma. Sedimentation rates for the Brawley Formation above the disconformity range from 1.0 to 1.2 mm/yr, palcoflow was to the ENE. The Brawley Formation consists of three interbeddcd lithofac ics; (I) fluvial and fluvio-d eltaic, (2) lacustrinc, (3) and eolian depo sits. Changes in facies, provenance , and paleoflow , with deposition of Ocotillo and Brawley formations record onset and evolution of cross cutting strike- slip faults other than the San Jacinto fault zone in the western Salton Trough at ~ 1 Ma.

Since deposition of the Brawley Formation (~ 0.5 Ma), rocks of the San Felipe hills have been uplifted and complexly deformed. new data suggest that strands of the Clark fault persist SE of its previously mapped termination, transferring slip into folded rocks in the central and southern San Felipe Hills. Equivalent right lateral slip form folding for the Clark fault in the San Felipe Hills is 5.6 km. Minimum slip rates for the Clark strand are between 9 and 11 mm/year. Since ~ 0.5 Ma, evolving strands of the San Jacinto fault zone, including the Coyote Creek and Clark faults, have deformed rocks of the San Felipe Hills.

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