Abstract: Paleogeographic Relations of Paleogene Depositional Systems in the Western Transverse Ranges
William R. Dickinson
Paleogene depositional systems in the western Transverse Ranges included a varied assemblage of alluvial fans and fluvial braid plains, marine deltas and complex strandlines, shelf-slope associations, and turbidite fans and ramps. These strata were deposited within a residual fore-arc basin across the crustal joint between granitic and metamorphic basement to the east and deformed subduction complex to the west. Robust paleomagnetic data from at least three laboratories indicate that Neogene transrotational tectonism has rotated the Paleogene facies tracts up to 90° clockwise, and broken them up by associated faulting into partly disconnected structural domains.
Kinematic analysis of the transrotation suggests that the western Transverse Ranges contain rotating fault-bounded panels that are divided longitudinally into linked segments, with greater rotation of western than eastern segments. The rotation of the panels was accompanied by sinistral strike slip along faults now oriented east-west in the Transverse Ranges, and by nonrotational dextral strike slip between northwest-trending sliding blocks of the Coast and Peninsular Ranges and the offshore continental borderland.
The pinned model for transrotational deformation implies that Miocene phases of rotation were accompanied by transtensional strain, whereas subsequent rotation has been accompanied by transpressional strain. Specific predictions of fault offsets and total Neogene shortening within the western Transverse Ranges are closely matched by reported observations. The transrotational model thus seems adequate to describe the disruption of Paleogene depositional systems in detail, and to reconstruct their original paleogeographic relationships along the continental margin.
AAPG Search and Discovery Article #90981©1994 AAPG Pacific Section Meeting, Ventura, California, April 27-29, 1994