Mapping key claystone units in the Plio-Pleistocene Tulare Formation: implications for structural and depositional model refinements of the southern San Joaquin Basin, Kern County, California

Abstract

In order to form a unified stratigraphy across multiple operating areas in the San Joaquin Basin within Kern County, California, a regional map of the Plio-Pleistocene Tulare Formation was created using well log correlation and two-dimensional seismic data interpretation. The Tulare Formation has two key claystone units, the ~2.2 Ma Amnicola Clay and the ~1.4 Ma Tulare Clay, that correspond to prominent seismic markers and can be mapped in the subsurface throughout the basin. Post-Miocene structural timing is constrained based on deformation of the Amnicola and Tulare clays and the unit thickness between the two clays. When unit thickness is consistent, tectonic hiatus is inferred; thinning or thickening of units between the key clays indicates structural growth and/or an increase in accommodation space. Deformation of the Tulare markers shows structural growth of anticlines on the western edge of the basin initiated after primary deposition of the Tulare Formation (3.4 Ma) but before ~2.2 Ma north of the Bakersfield Arch at Lost Hills and South Belridge. South of the Arch, tectonic hiatus occurred between 3.4 Ma and ~1.4 Ma, but swift subsidence and deformation began again after ~1.4 Ma, creating immense accommodation space and allowing for the deposition of a thick succession of Kern River sediments. The Kern River system influence on the Tulare Formation is limited to the eastern edge of the basin north of the Bakersfield Arch where the Amnicola and Tulare clay markers are disrupted in seismic and no longer correlatable in well logs. South of the Arch, the Kern River system is likely responsible for the deposition of a roughly 7,000-foot-thick sediment package that buries the prominent Tulare markers, which can be mapped at depth to the southeast until the seismic imaging degrades and well logs are not deep enough to confidently map the units. The thick succession deposited above the ~1.4Ma Tulare Clay marker indicates rapid sedimentation into a quickly developed accommodation space. Post ~1.4 Ma deformation of the Tulare Formation highlights rapid formation of structural traps on the southwestern boundary of the basin (e.g. Elk Hills and Buena Vista Hills) that coincide with rapid sedimentation and subsidence in the southern end of the basin. This new understanding of the Tulare Formation allows for timeline refinement of basin burial history, petroleum generation, and structural trap formation for the petroleum system in the southern San Joaquin Basin.

AAPG Datapages/Search and Discovery Article #90372 © 2020 AAPG Pacific Section Convention, 2020 Vision: Producing the Future, Mandalay Beach, Oxnard, CA, April 4-8, 2020 (Cancelled)