Geologyhttp://hdl.handle.net/10211.3/2036072024-03-29T08:33:46Z2024-03-29T08:33:46ZMineralogical and geochemical characterization of the Miocene-Oligocene Santos Shale, Southern San Joaquin Valley, CaliforniaMitchell, Nicholas Jameshttp://hdl.handle.net/10211.3/2038072018-07-20T21:52:27Z2018-05-10T00:00:00ZMineralogical and geochemical characterization of the Miocene-Oligocene Santos Shale, Southern San Joaquin Valley, California
Mitchell, Nicholas James
The Santos Shale is a 29 - 20 Ma member of the Temblor Formation located in the southwest
corner of the San Joaquin Basin of California. It was deposited in an ocean basin along the slope
and the basin plain. The Santos outcrops in the Temblor Range along the western perimeter of
the San Joaquin Valley, where it dips and thins eastward into the subsurface under the valley.
The goal of the study is to characterize the Santos Shale through its mineralogical and
geochemical properties to better understand depositional environment and potential as a
source rock or fractured shale reservoir. Forty samples were used for this study from the wells
along the crest and the flank of the Belgian Anticline, ranging in depths of 1,061 feet in the west
and 14,970 feet in the east. XRD analyses revealed that the bulk composition of the average
Santos is composed of 45% clays, 29% quartz, 15% carbonates and 11% feldspar. In the clay size
fraction, the clays are on average composed of 45.5% smectite, 43.3% illite, 8.2% kaolinite and
3.0% chlorite. LOI reveals the Santos has an overall high TOC content that ranges from 1.4 to
15.8 wt-%, with an average of 7.7 wt-%. Geochemical analyses from XRF and ICP-MS indicate
the Santos was deposited in a well oxygenated marine environment based on relationships
between iron, TOC and total sulfur and low trace element ratios used as paleoredox proxies
such as Ni/Co vs. V(V+Ni), V/Sc vs. V(V+Ni), and V/Cr vs. Ni/Co. Redox conditions upon burial are
indicated by enrichment in Ni, V and U within the Santos samples. High TOC content is
attributed to the oxic ocean environment with productive paleo waters. The preservation of the
organic matter is due to redox conditions upon burial at the ocean-sediment interface where
the oxygen is quickly depleted from settling organic matter. High TOC values in the Santos imply
very good potential for fracture development.
2018-05-10T00:00:00Z