La Jolla Group

La Jolla Group
Name	La Jolla Group
Type	Geological group
Age	Late Cretaceous to Paleogene
Period	Cretaceous
Region	Southern California
Country	United States

La Jolla Group is a lithostratigraphic assemblage of sedimentary and volcanic units exposed in coastal Southern California. It has been the focus of regional stratigraphic correlation, paleontological study, and resource assessment involving institutions such as the United States Geological Survey, University of California, San Diego, and historical surveys by the California Geological Survey. The Group crops out near cities and localities including La Jolla, San Diego, Torrey Pines State Natural Reserve, Point Loma, and parts of Orange County, California and Los Angeles County, California.

Overview and definition

The name was applied during early 20th‑century mapping by investigators associated with the United States Geological Survey and state surveys; it groups together coastal strata correlated with regional units mapped by geologists from the California Division of Mines and Geology and academics at Stanford University and the Scripps Institution of Oceanography. Correlations have been drawn with formations described by researchers at Princeton University, Harvard University, and the American Association of Petroleum Geologists publications. The unit has been discussed in context with the Peninsular Ranges Batholith, the San Andreas Fault, and the tectonic framework emphasized by authors affiliated with the Geological Society of America and the Seismological Society of America.

Stratigraphy and lithology

Stratigraphic descriptions differentiate members and formations within the Group, a practice used by cartographers from the USGS National Geologic Map Database and field geologists from California State University San Marcos. Lithologies include sandstones, siltstones, conglomerates, mudstones, and local tuffs and basaltic flows documented in reports by the Society of Economic Paleontologists and Mineralogists and regional theses at the University of California, Berkeley. Studies reference stratigraphic principles developed by figures associated with James Hutton heritage and methods used by stratigraphers of the International Commission on Stratigraphy. Key mapped units are juxtaposed against units such as the Torrey Sandstone and correlatives noted in mapping by the San Diego Association of Governments.

Age and geochronology

Biostratigraphic and radiometric constraints place parts of the assemblage across the Maastrichtian to Danian interval, with isotopic work reported by laboratories at the California Institute of Technology and Scripps Institution of Oceanography. Chronologies incorporate fossil calibration from taxa described in monographs from the Smithsonian Institution and U.S. museum collections tied to the Natural History Museum, London. Geochronologic techniques cited in regional studies include K–Ar and Ar–Ar analyses developed in laboratories at Argonne National Laboratory and chronostratigraphic frameworks used by the International Union of Geological Sciences. Correlations have been drawn to marine successions known in the Pacific Northwest and to global events such as the Cretaceous–Paleogene extinction event.

Depositional environment and paleoenvironment

Sedimentary structures and facies analysis indicate nearshore to shallow marine depositional settings, with estuarine and deltaic influences analogous to coastal successions studied along the Pacific Coast Ranges and the Gulf of Mexico margins. Paleoenvironmental reconstructions utilize analogs from research by paleoclimatologists at the National Oceanic and Atmospheric Administration, palynological datasets compared with cores curated by the British Geological Survey, and sequence stratigraphic models promoted by the European Association of Geoscientists and Engineers. Tectonic influences from the Pacific Plate–North American Plate boundary and subsidence related to the Peninsular Ranges have been invoked to explain accommodation and sediment supply patterns, following paradigms set out in works sponsored by the National Science Foundation.

Fossil content and paleontology

Fossil assemblages include marine invertebrates, microfossils, and vertebrate remains recorded in collections at the San Diego Natural History Museum and comparative series at the American Museum of Natural History. Taxa reported in the literature encompass mollusks, echinoderms, foraminifera, and rare shark teeth comparable to specimens cataloged by researchers at the Natural History Museum of Los Angeles County and universities such as University of California, Los Angeles. Paleontological methods used mirror those from monographs published by the Paleontological Society and case studies in journals produced by the Society of Vertebrate Paleontology. Fossil occurrences have been used for biostratigraphic zonation tied to global biozones recognized by the International Commission on Stratigraphy.

Economic uses and resources

Units within the Group have been evaluated for groundwater resources by the San Diego County Water Authority and for construction aggregate by local firms and regulatory agencies including the California Department of Conservation. Historical quarrying and coastal bluff erosion have influenced land‑use planning coordinated with the City of San Diego and conservation efforts involving the California Department of Parks and Recreation. Environmental assessments referencing the Group have been produced under auspices of the Environmental Protection Agency and regional planning bodies such as the San Diego Association of Governments.

Category:Geologic groups of California Category:Geology of San Diego County, California