Structural Interpretation and Modeling of the Santa Ynez Unit, Offshore Santa Barbara, California, with Implications for Transverse Range Tectonics
Steritz, J.W. and Harkins, N. W.
Our structural explanations and interpretations at the San Ynez Unit (SYU), offshore California, have been revised with improving seismic imagery and evolving Transverse Range rotation models. In particular, the role and relative importance of wrench structures, extension, and contractional inversion has varied with the large number of workers assigned to this asset over the last 30+ years. We summarize the evolution of past interpretations, our latest views, and explore implications for more area conservative rotation models with significant strike-slip along currently E-W trending panels vs. rotation of a more internally coherent Transverse Range block with late Cenozoic rifting and inversion, and significant crustal deformation external to the block. Critical tectonostratigraphic relationships within the field area are referenced in support of our general conclusions and models for the scale and timing of late Cenozoic uplift, extension and later contraction.
In structurally complex locations where reflection seismic imagery is non-diagnostic, structural geometric and mechanical modeling provides a quantitative means of evaluating competing subsurface interpretations. Here, we combine 3D faulted framework model construction with geometric and mechanical restoration techniques to both validate competing structural interpretations and describe the implications associated therein on distributed strain within the Cenozoic stratigraphy of the San Ynez Unit (SYU), offshore California. Well imaged growth patterns in the shallow stratigraphy, when considered in 3D along with generalized structural geometries observed in the poorly imaged deeper section, imply that the Hondo and Sacate culminations are developed at significant inversion structures. These structures are localized at an interpreted ramp in a deep detachment that extends under the entire SYU area. The complex strain history of this area is partitioned between early dip-slip normal faults that have been cut by younger and presently active predominantly dip-slip reverse faults and strike slip faults. Although complex, this strain history implies that significant internal deformation is generally lacking within the SYU, and in particular that large offset (km+) strike-slip faulting is not realized. Thus, this interpretation contrasts with previous interpretations of the culminations as transpressional flower structures. Importantly, an ‘inversion tectonics’ structural style holds significant and specific implications for the interpretation of Eocene reservoir geometry and fracture history within the Monterey.
AAPG Search and Discovery Article #90162©2013 Pacific Section AAPG, SPE and SEPM Joint Technical Conference, Monterey, California, April 19-25, 2013