Structure of Miocene Rocks in Sierra Madre, Northeastern Santa Barbara County, California: ABSTRACT

Abstract

Folds in Miocene rocks of the central Sierra Madre commonly are northwest-trending, curvilinear, concentric, and symmetrical; asymmetry and overturning occur in the vicinity of reverse faults. Fold hinges undulate across the area and in places bifurcate or merge. Disharmonic folds and sandstone dikes occur locally in the Monterey Shale. Faults are of three types: (1) along the northeastern edge of the range is a distributive fault zone consisting of parallel, longitudinal, reverse-slip faults which join both westward and downward and which have a subsurface distributive component that is now obscured by more recent deposits on the northeast; (2) southwest of the reverse-slip faults is a group of parallel, longitudinal, normal-separation faults; and (3) the remaining faults are mostly small, diagonal faults of different types; many are hinged at one or both ends and have slips or separations that indicate contemporaneous folding and faulting. Folding began during late Miocene or Pliocene while Miocene sediment was still unconsolidated and water laden. Diagonal faulting, intrusion of sandstone dikes, and possibly disharmonic folding accompanied early deformation. Asymmetrical and overturned folds formed later and large reverse-slip faults developed along their hinges. Normal-separation faults possibly formed last as lag faults. Northeast-southwest shortening of the area averages about 22%. End_of_Article - Last_Page 433------------