Graduate Thesis Or Dissertation
 

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/79408265w

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  • The Ventura basin is an elongate sedimentary trough extending from the San Gabriel fault west into the Santa Barbara Channel. West of Ventura it contains over 4 km of severely deformed Pliocene and Pleistocene clastic strata. The north-dipping Red Mountain reverse fault system, which forms the northern boundary of the basin, has been active since the early Pliocene and has maximum reverse separation of 7300 m (23,900 ft). In the basin, the Grubb and Oak Grove faults were active in the early Pleistocene and were reactivated during late Pleistocene folding. Both are tear faults that dip steeply northeast and strike northwest, in contrast to the west-trending structural grain of the region. The Rincon anticline is the western extension of the Ventura Avenue anticline. Both anticlines formed approximately 200,000 years ago as rootless folds which die out in subjacent fine-grained Miocene strata. Above the Rincon anticline synchronous shortening occurred on the Javon Canyon/Padre Juan fault and San Miguelito anticline. The Padre Juan fault is a south-dipping reverse fault that flattens over the axis of the Rincon anticline and dies out to the north. Where it flattens, the Javon Canyon fault rises upwards and offsets 3500 year old marine terrace deposits at the surface. Maximum reverse separation across the Javon Canyon/Padre Juan fault is 2800 m (9200 ft). The steeply north-dipping to overfolded region between the Javon Canyon and Padre Juan faults constitutes a large portion of the north limb of the San Miguelito anticline. This anticline, constrained above the Padre Juan fault, is a complex example of a fault-propagation fold. Total shortening in the Ventura basin along a cross-section through the study area is approximately 7825 m (25,700 ft). For the last 200,000 years this north-south directed shortening has occurred at a rate of 12.5 to 22.3 mm/yr (0.49 to 0.87 in/yr). These values compare favorably with shortening values obtained at other locations in the basin, and support the concept of decreasing horizontal contraction from east to west across the basin for the last 200,000 years.
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