Detailed Lithostratigraphic Characterization of the Monterey Formation at Chico Martinez Creek, California

Mosher, Annie; Guillaume, Jonathan; and Behl, Richard J.
[email protected]

Chico Martinez Creek, located in the foothills of the Temblor Range, southwestern San Joaquin basin, has served as a stratigraphic reference section for the Miocene Monterey Formation for nearly 100 years because of its great thickness (>6000 feet) and its close proximity to major oil fields. The Monterey succession includes the Gould, Devilwater, McDonald, and Antelope Shales. Much of the previous work from the 1930’s to 1980’s was proprietary and focused on identifying lithostratigraphic and biostratigraphic intervals for subsurface correlation in the western San Joaquin basin. In spite of numerous field guides with general or very localized descriptions, a continuous, detailed lithostratigraphic characterization of the section has not been published. To rectify this, % lithology will be described in 5-foot increments through the entire Monterey and handheld spectral gamma-ray data will be acquired at 2-foot intervals. To obtain consistent, high-quality results through covered intervals, approximately 2500 stratigraphic feet of trenches were dug or reopened by backhoe. The gathered data will be compiled into a mudlog-type format consistent with presentation of subsurface logs to aid in basin-wide correlation. These data will be integrated with existing industry-provided biostratigraphy for the Chico Martinez Creek section to provide chronostratigraphic context. To refine age control across the poorly dated McDonald Shale, 33 dolostone beds were cored and analyzed to identify magnetic reversals in the Upper Miocene succession. Magnetostratigraphic and biostratigraphic data will provide additional age constraint, allow for more accurate determination of sediment and geochemical mass accumulation rates, and make chronostratigraphic correlation with other Neogene sections possible. Ultimately, this new detailed reference section will be of value to geoscientists working on the Monterey in the subsurface of the San Joaquin basin and throughout California.

AAPG Search and Discovery Article #90162©2013 Pacific Section AAPG, SPE and SEPM Joint Technical Conference, Monterey, California, April 19-25, 2013