Abstract:
The Russell Ranch oil field is located in the southern Coast
Ranges west of Bakersfield, California. Detailed subsurface
mapping shows that a northwest-oriented right-lateral wrench-fault
system was active from possibly latest Oligocene to Pliocene time.
The effects of Quaternary thrusting were superimposed on, and influenced
by, structures associated with the older wrench tectonic
regime. The right-lateral shear system produced a complex pattern
of right-stepping en echelon folds, dip-slip faults with normal
separation, and strike-slip faults with both normal and reverse
separation. Deformation along the wrench system began during deposition
of the late Oligocene-early Miocene Soda Lake Shale and
Painted Rock Sandstone members of the Vaqueros Formation, producing
elongate en echelon submarine troughs and highs. Northerly
trending growth faults of early Miocene age caused thickening of
the late Saucesian-early Relizian Saltos Shale Member of the
Monterey Formation and may have initiated growth of the Russell
Ranch anticline. Northeast- to northwest-trending normal faults
and northwest-trending strike-slip faults of the Russell fault
system were active during deposition of a sequence tentatively
correlated with the Branch Canyon Sandstone and Santa Margarita
Formation of middle and late Miocene age. Strike-slip faulting
produced a complex interleaving of fault slices and juxtaposed
slices of contrasting lithologies and orientations. Subsequent
minor movement along the wrench system folded the base of the
Morales Formation, of Pliocene-Pleistocene age, into elongate en
echelon folds.
The north-dipping Whiterock and Morales thrusts brought
Miocene and younger strata southward over deposits as young as
late Pleistocene. The Whiterock thrust changes southward from a
southeasterly to an easterly strike. The upper plate was thrust
southward, and structures in the lower plate apparently controlled
the geometry of the developing fault plane. The thrust ramps
as it overrides the normal and strike-slip faults of middle Miocene
age; rootless folds similar to those found in the Caliente
Range are present in the upper thrust plate above the tectonic
ramps.
Wrench-related faulting in the Cuyama basin predates similar
movement along the San Andreas fault to the northeast and may
represent a strand of the proto-San Andreas fault. Quaternary
thrusting in the basin was influenced by and now obscures the
structures of the older wrench fault system; thrusting activity
was probably contemporaneous with thrust faulting in the Transverse
Ranges to the south.
