Stratigraphy, depositional history, and hydrocarbon source-rock potential of the Upper Cretaceous - Lower Tertiary Moreno Formation, Central San Joaquin Basin, California

The Moreno Formation is a marine sedimentary sequence deposited in the central San Joaquin basin, California, during late Maastrichtian to middle Paleocene time (ca. 70-61 Ma). Facies sequences within the formation contain the following elements: a base-of-slope turbidite and channel sandstone facies; an oxygen-deficient lower to middle slope shale facies; an upwelling-related anoxic upper slope diatomaceous shale facies; and an upper slope to outer shelf sandstone and shale facies. Hence, the Moreno Formation records the shoaling of the south-central portion of the Great Valley forearc basin to shelf depths during latest Cretaceous to early Tertiary time.;Subsurface stratigraphic sections and isopach maps derived from study of borehole data reveal that a major shift in sediment supply to the basin accompanied the beginning of Moreno Formation deposition. Syndepositional uplift along the western margin of the basin accompanied the onset of the Laramide orogeny (ca. 75-45 Ma). The unique composition of a sandstone unit exposed in outcrop reveals the earliest known influx of Franciscan-derived detritus into the western San Joaquin basin, and suggests that portions of the uplifted western basin margin were exposed to erosion by mid-Maastrichtian time. The southward progradation of deltaic/shelf complexes resulted in the filling of the basin to shelf depths by middle Paleocene time.;Geochemical analyses of well core samples reveal a discrete partitioning of hydrogen-rich organic matter into fine-grained, laminated sediments within the Moreno sequence, whereas more oxidized organic matter characterizes non-laminated sediments. Organic facies favorable for the generation of liquid hydrocarbons exist within the Moreno in the southwestern portion of the study area, but maturity data are inconclusive. Biomarker analysis of oils from five producing wells in the San Joaquin basin and Vallecitos areas suggest that Moreno sediments were the source of at least two known petroleum accumulations.;Consideration of models of climate and oceanic circulation for the Late Cretaceous suggest that wind-driven, seasonal upwelling was responsible for increased diatom productivity in the San Joaquin basin in latest Cretaceous time, and was a major contributing factor in the development of anoxia in the basin.