Late Pleistocene to Holocene geomorphic and structural evolution of the Camarillo Fold Belt, California.

다국어 초록 (Multilingual Abstract)

The Camarillo Fold Belt (CFB) is composed of several south-verging anticlines, which comprise the western extent of the west-trending highly segmented Simi fault zone that extends from the northern Simi Valley to the city of Camarillo. Geologic mapping, GIS-based topographic analyses, optically stimulated luminescence (OSL) and radiocarbon dating, and subsurface well logs are integrated to bracket the relative timing of deformation on active faults, to develop a chronology of deformed surfaces, and to better constrain the age of the Saugus Formation in this part of the Western Transverse Ranges. New geochronology of the Saugus Formation exposed in the study area indicates that the strata are an order of magnitude younger than previously thought (∼20ka vs. 200ka). This chronologic revision has significant implications for the timing and rates of deformation, as well as for the seismic hazard in the study area.
Many of the Quaternary transpressional faults are reactivated Miocene high-angle (70-80°) transrotational faults. Where the age of deformed sediments is well-known, minimum vertical uplift rates on several of the active faults are ∼1.5 mm/yr, which is 3-times greater than most previous estimates based on paleoseismic investigations. Discrete structural domains are characterized by west-plunging anticlines, changes in the orientation and loci of active structures, and they are bound by fault segment boundaries that are often characterized by orthogonal north-striking faults. Structural relief and the age of deformation decrease from east to west across each successive north-striking fault. We interpret these relations to suggest that westward propagation of the fold belt occurred by punctuated lateral growth of the Simi fault due to the presence of north-trending faults. This style of deformation may be common in the Western Transverse Ranges and has important implications for seismic hazard assessment.
Geochronology of geomorphic surfaces indicates that the landscape evolution in the CFB was modulated by global climate change. A regionally extensive erosion surface in the study (45 km2) in the study area was cut during Marine Isotope Stage 2 (MIS2; 19-24 ka). Incision from 19-12 ka resulted in deep canyons cut throughout the study area, which were back-tilled following the Pleistocene Holocene transition (12-4 ka).