A.I. Levorson Award

Todd Greene Department of Geological and Environmental Sciences

The A.I. Levorsen award was given to Dr. Todd Greene for the best oral presentation at the Pacific Section-American Association of Petroleum Geologists (PS-AAPG) Annual meeting in Monterey, CA (April 2013). The title of Dr. Greene's presentation was: Fluvial architecture of a Cascades-sourced “paleo-Sacramento River” system within the Lower Tuscan Formation in the northern Sacramento Valley, CA.

Abstract. Although very little is known about deeper sources of groundwater (~500-1500 feet below ground surface) in the northern Sacramento Valley, interest in a potential “Lower Tuscan Aquifer” is growing stronger as greater stresses are imposed on surface and shallower groundwater systems. Using geophysical logs as well as sand grain analysis of well cuttings samples from 4 different wells, regionally mappable zones within the Lower Tuscan interval spanning an area approximately 130 square miles identify key areas where high percentages of porous sand (i.e. water-rich zones) exist within the Lower Tuscan. provenance differences in Coast Ranges-sourced sediment (metamorphic) from Cascades-sourced sediment (volcanic),

Results indicate a previously unrecognized north-south trending "paleo-Sacramento River" system (a 250-350 feet thick sand-rich zone within the Lower Tuscan) derived directly from Cascade-type volcanic source rocks. a sharp change occurs from a lower mixed source (Coast Ranges and Cascades-sourced) system to a predominantly Cascades-sourced sandy interval ("paleo-Sacramento") overlain by a return to a mixed sourced system. This "paleo-Sacramento River" has a sharp western boundary between Hamilton City and Interstate-5 and a more diffuse (less well control) eastern boundary.

This study represents the first step to better understand the stratigraphic architecture of the Lower Tuscan by developing a regionally consistent hydrostratigraphy that can serve as the foundation for groundwater models used to predict well water drawdrown effects from pumping within the Lower Tuscan.