Global Cycle Charts and Tertiary Stratigraphic Sequences of the San Joaquin Basin: Calibration and Constraints from a Tectonically Active Basin
Cari Johnson1, Stephan Graham2, and Roger B. Bloch3
1 University of Utah, Salt Lake City, UT
2 Stanford University, Stanford, CA
3 ExxonMobil Exploration Co, Houston, TX
Despite more than a century of petroleum exploration in the San Joaquin basin, California, public domain stratigraphic data, and derivative published interpretations of stratigraphic relationships, for the Tertiary basin fill are surprisingly limited. This results in confusing stratigraphic nomenclature; uncertainty of absolute ages of stratigraphic units and surfaces; problematic paleobathymetric curves; and difficulties in regional correlation of complex subsurface facies relations. Sequence stratigraphic analysis helps to mitigate these problems by emphasizing genetic facies relationships as a function of relative changes in sea level. However, explicit ties to global coastal onlap curves must await significant refinement of chronostratigraphic and biostratigraphic data from the San Joaquin basin. To illustrate this issue, an integrated outcrop and subsurface database is used to erect a framework of ten Eocene-Miocene stratigraphic sequences. Temporal uncertainty ranges placed on bounding units constrain the actual resolution of biostratigraphic data, which is rarely sufficient to warrant chronostratigraphic correlation to higher frequency cycles (e.g., 3rd order) on published global sea level charts. In part, this reflects problems inherent in calibrating biozones, particularly California benthic foraminifera stages, to chronostratigraphic time scales. Other limitations include time-transgressive biozones (e.g., Saucesian / Zemorrian stages, and Mohnian /Delmontian stages), as well as time-transgressive deposition of stratigraphic units (e.g., Domengine Formation, and Reef Ridge Shale). Furthermore, multiple examples of stratigraphic relations indicating coeval structural growth, including depositional systems tracts out-of-phase with published eustatic curves (e.g., Buttonbed Sandstone), indicate that regional/local tectonism played a critical role in development of the Tertiary stratigraphic architecture of the San Joaquin basin.