Great Valley Sequence
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| Great Valley Sequence | |
|---|---|
| Name | Great Valley Sequence |
| Type | Sedimentary sequence |
| Age | Late Jurassic–Cretaceous |
| Period | Mesozoic |
| Region | Central and Northern California |
| Country | United States |
| Namedfor | Great Valley |
| Thickness | up to ~10,000 ft |
| Extent | Sacramento Valley, San Joaquin Valley |
Great Valley Sequence The Great Valley Sequence is a thick Mesozoic turbidite-dominated sedimentary succession that crops out in the Central Valley of California and underlies much of the Sacramento Valley and San Joaquin Valley. It records deposition in a forearc basin adjacent to an active convergent margin, preserving linkages to plate tectonic processes, basin stratigraphy, and paleobiological assemblages associated with the Sonoma orogeny and later Cordilleran events. The succession has been studied in the contexts of regional geology, petroleum geology, paleontology, and tectonics by researchers from institutions such as the United States Geological Survey, Stanford University, University of California campuses, and the California Division of Mines and Geology.
Geologic Setting and Stratigraphy
The Sequence accumulated within a forearc basin bounded by the continental margin near the Sierra Nevada block and the oceanic plates of the Paleo-Pacific realm, with stratigraphic relationships tied to the Franciscan Complex, Sierra Nevada Batholith, and Coast Ranges. Stratigraphic frameworks developed by workers at the United States Geological Survey, California Geological Survey, Stanford University, and University of California, Berkeley subdivide the Sequence into informal stratigraphic units correlated with regional sections such as the Chico Formation, Martinez Formation, and Tejon Formation, and mapped across counties including Sacramento County, San Joaquin County, Contra Costa County, and Kern County. Correlative successions appear in the Klamath Mountains and the Diablo Range, and ties to the Franciscan accretionary complex and the Sierra Nevada plutons help constrain basin geometry and fill history documented in reports by the American Association of Petroleum Geologists and the Geological Society of America.
Lithology and Depositional Environments
Lithologies are dominated by thick turbiditic sandstone and interbedded shale, siltstone, chert, and conglomerate with localized limestone lenses; provenance signals implicate sources such as the Sierra Nevada and intra-oceanic arcs. Facies analyses published by researchers at Caltech, UC Santa Cruz, and the USGS describe channelized submarine fan systems, channel-levee complexes, mass-transport deposits, and hemipelagic intervals comparable to modern examples from the Cascadia margin and ancient analogs like the Monterey Formation and Flysch deposits of the Alps. Geochemical studies connecting detrital zircon populations, heavy-mineral suites, and stable-isotope work have been advanced by teams at the University of Arizona, Oregon State University, and the Geological Survey of Canada to infer sediment dispersal pathways and depositional rates.
Age, Correlation, and Tectonic History
Biostratigraphic and radiometric constraints place much of the Sequence from Late Jurassic through Cretaceous time, with ammonite and foraminiferal assemblages, along with U-Pb zircon dates from intercalated tuffs, providing age control utilized by paleontologists at the California Academy of Sciences and geochronologists at Princeton University and the University of California, Los Angeles. Correlations link the Sequence to coeval units in the Western Interior Seaway, the Sierra Nevada forearc, and the Insular Superterrane; tectonic interpretations invoke subduction of oceanic plates, accretionary processes akin to the Laramide and Sevier orogenies, and eventual interaction with transform systems such as the San Andreas Fault documented by researchers at the U.S. Geological Survey and the California Institute of Technology. Plate reconstructions published in journals like Earth and Planetary Science Letters and Tectonics integrate data from the Sequence with regional events including the Nevadan orogeny, Sevier deformation, and Pacific Plate movements.
Paleontology and Fossil Content
Fossil occurrences include marine invertebrates such as bivalves, ammonites, gastropods, echinoids, and benthic foraminifera recovered by paleontologists at the Smithsonian Institution, California Academy of Sciences, and the Natural History Museum of Los Angeles County. Vertebrate remains, rare plant fragments, and trace fossils provide additional paleoenvironmental constraints; collections and taxonomic work by researchers at UC Berkeley, UC Davis, and the American Museum of Natural History have documented species-level identifications that aid biostratigraphic zonation and paleobiogeographic comparisons with assemblages from the Western Interior, Baja California, and East Asia. Ichnological studies and paleoecological reconstructions have been conducted by teams affiliated with the Paleontological Society and Society of Vertebrate Paleontology.
Economic Importance and Natural Resources
The Sequence is important for hydrocarbon exploration in the San Joaquin Basin and Sacramento Basin, where sandstone reservoirs and shale source rocks have been assessed by petroleum geologists working for Chevron, ExxonMobil, Occidental Petroleum, and the California Department of Conservation. Aggregates, construction materials, and groundwater aquifers hosted in coarse clastic units supply resources to municipalities including Bakersfield, Stockton, Fresno, and Sacramento. Mineral occurrences such as placer gold and industrial minerals have been investigated by the U.S. Bureau of Land Management, California State Mining and Mineral Resources Division, and academic groups at UC Riverside.
Research History and Notable Studies
Foundational mapping and stratigraphic description began with state geologists and early 20th-century surveys by the California Division of Mines, expanded by mid-century syntheses from the USGS and papers by geologists affiliated with Stanford University, University of California, Berkeley, and California Institute of Technology. Landmark contributions include basin analysis syntheses in publications of the Geological Society of America, detailed sedimentologic work in the Journal of Sedimentary Research, and integrated tectono-stratigraphic models in Tectonics and Geological Society of America Bulletin by investigators such as John N. Huber, Eldridge Moores, and Christopher H. Chapman. Ongoing research incorporates detrital zircon provenance studies, seismic stratigraphy from the USGS and industry partners, and multidisciplinary projects at institutions including UC Santa Cruz, Caltech, and the Scripps Institution of Oceanography.