Neogene Disruption of Paleogene Depositional Facies in Western Transverse Ranges

DICKINSON, WILLIAM R., University of Arizona, Tucson, AZ

Paleomagnetic data imply that the western Transverse Ranges and nearby Channel Islands are composed of elongate fault-bounded crustal panels now oriented east-west but oriented north-south before Neogene clockwise rotation. Rotary motion within the complex strain field of the San Andreas transform system was accommodated by dextral strike slip along faults trending north-northwest between other crustal panels lying both north and south of the rotated region. Geometric analysis indicates that rotation was accompanied by some combination of the following complementary or alternate deformational mechanisms, adjusted mutually in relative magnitude to maintain areal balance of crustal segments involved: (1) sinistral strike slip on longitudinal panel-bounding faults internal to the array o rotating crustal panels, (2) longitudinal contraction followed later by longitudinal extension of individual rotating panels, (3) dextral strike slip followed later by sinistral strike slip along the northern (originally western) flank of the array of rotating panels, (4) sinistral strike slip followed later by dextral strike slip along the southern (originally eastern) flank

of the array of rotating panels, and (5) transtension followed later by transpression within belts of fault-bounded crustal panels oriented subparallel to the San Andreas trend both north and south (originally west and east) of the rotated region. The fragmented distribution of disrupted Paleogene depositional facies suggests that several of these deformational mechanisms were actually operative locally. Understanding the overall pattern of facies disruption in detail may afford fresh insight into the structural evolution of transrotational Neogene basins within and adjacent to the western Transverse Ranges.

AAPG Search and Discovery Article #91009©1991 AAPG-SEPM-SEG-SPWLA Pacific Section Annual Meeting, Bakersfield, California, March 6-8, 1991 (2009)