Application of Chemostratigraphy to the Vaqueros, Tumey and Kreyenhagen Formations, Central California

The Miocene-Eocene Vaqueros, Tumey and Kreyenhagen Formations are located in the subsurface and in outcrop belts within the San Joaquin Basin of Central California. From Kettleman Middle Dome Northwest to the Coalinga Nose, these formations are associated with oil production in the subsurface. In nearby outcrops various unconformities within the section have removed significant intervals precluding accurate correlations of the stratigraphic sections from outcrop to subsurface sections. The primary goal of this study is to supply a framework to aid with these stratigraphic ties while gaining insights into the basin chemical changes during deposition of these interbedded source and reservoir rocks. This paper describes the use of chemostratigraphy to characterize these sequences in a single well in the Middle Dome Field area to test whether this technique is a viable characterization tool within these formations.

Chemostratigraphy is a tool that employs variations in inorganic whole rock geochemistry to enable the characterization and subsequent correlation of sediments. For this study, a total of 83 cuttings samples from the Vaqueros, Tumey, and Kreyenhaggen sections have been analyzed over a 2,600 ft interval. Whole-rock inorganic geochemical data were acquired for 50 elements by combining inductively coupled plasma - optical emission spectrometry and mass spectrometry analyses.

Using data derived from both claystone and siltstone lithologies, the study interval has been divided into a series of 7 broad-scale Geochemical Packages, which are sub-divided into a series of finer-scale Geochemical Units. Packages 1-3 comprise the Kreyenhagen Fm, Package 4 is broadly equivalent to the Tumey Fm and Packages 6 and 7 correspond to the Vaqueros Fm and younger section.

Changes in values of TiO2/Al2O3, Zr/Cr, K2O/Rb and TiO2/Nb ratios are thought to be related to changes in sediment provenance; with a significant move toward a more acidic/K-feldspar-rich provenance in the post-Tumey interval. Additionally, changes in ratios sensitive to changing paleo-environments such as the enrichment factor of vanadium (EFV) suggest that the Kreyenhagen Formation was deposited in an overall more anoxic environment compared to the overlying formations.

Following on from this test study it is hoped that equivalent formations may be sampled in adjacent fields and in outcrop in order to test the lateral extent of the geochemical characterizations seen in this section.
 

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California