Abstract
The Moreno Formation represents a base-of-slope to shelf-edge sedimentary sequence deposited along the central California continental margin during the late Maestrichtian to Danian (about 69-63 Ma). The formation consists of shales, mudstones, and siltstones with irregularly interbedded sandstones. The Marca Shale member of the Moreno Formation is particularly attractive as a potential petroleum source rock. The Marca contains sedimentologic, faunal, and geochemical evidence suggesting that it represents an anoxic depositional facies within the upper Moreno Formation. Submillimeter-scale depositional laminations are well preserved within the siliceous shale and diatomite of the Marca. Benthic foraminiferal biofacies are strikingly similar in patterns of abundance, dominance, and morphology to those found in Tertiary and Holocene sediments known or inferred to have been deposited under anoxic conditions. Also, total organic carbon (TOC) is as much as 7.25 wt.%. Laminated sediments contain kerogens of marine origin (Type II), whereas adjacent massive sediments contain organic matter dominated by kerogens of terrestrial origin (Type III). Data derived from this study indicate that the Moreno Formation has a significantly greater potential as a source of hydrocarbons than heretofore recognized. Rock-Eval pyrolysis and vitrinite reflectance data derived from core samples from a well near Coalinga show that the Marca shalemore » is marginally mature at relatively shallow depths. To the northeast, the Moreno is more deeply buried beneath late Tertiary and Quaternary basin-fill sediments, and has probably reached generative levels of maturity. Sands within the Moreno Formation are productive in at least two small fields in the western San Joaquin Valley. Thus, the Cretaceous of the San Joaquin basin may represent an exploration frontier in an otherwise mature basin.« less
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