Analysis of the depositional stratal geometry of the Fish Creek-Vallecito Basin in the northwest Salton Trough, southern California

Adan Silva
BS Candidate
Advisor: Dr. Rafael Almeida

Friday, May 4, 2023
9:30 am in CSL 422
watch Adan’s talk

The Fish Creek-Vallecito Basin (FC-VB) represents an uplifted and tilted 5.5-km-thick
sedimentary section (Dorsey et al., 2011). Deposited and filled on the hanging wall of the
Miocene-age West Salton detachment fault, the Fish Creek-Vallecito Basin is characterized by
marine and non-marine sedimentary units that range from late Miocene to early Pleistocene.
After deposition, the Fish Creek-Vallecito Basin was folded by 1.2 Ma NW-trending right-lateral
strike-slip faults caused by the tectonic reorganization of the San Andreas fault zone (Dorsey et
al., 2012), and broken up by cross-cutting NE-trending strike-slip, or transverse faults (Dibble,
1996). Published reconstructions of the basin propose that the strata within the Fish
Creek-Vallecito Basin remained horizontal throughout the entire life of the West Salton
detachment fault. However, in extensional regimes, strata deposited on the hanging wall of
normal faults generally have fanning dips that are formed as the older strata are tilted by
continued slip on the basin-bounding normal fault, in this case, the West Salton detachment fault.
For this thesis, I will carry out a detailed structural study of the stratal geometries of the Fish
Creek-Vallecito Basin in order to tease out the pre-deformation stratal geometries of the FC-VB
and attempt to gain a greater understanding of the deformational styles, either normal-faulting or
strike-slip faulting. To do this, I will compile existing structural measurements, measure where
there are few, digitize Dibblee’s maps of the FC-VB, and modify them according to satellite
imagery. I will also measure and characterize the stratigraphy along Sin Nombre Canyon in the
Coyote Mountains to document the transition from marine to continental deposition. Lastly, I
will construct a geologic section across the basin. By doing this, we hope to better constrain the
relationship between the West Salton detachment fault and the Fish Creek-Vallecito Basin.