scholarly journals Regional-scale correlations of accreted units in the Franciscan Complex, California, USA: A record of long-lived, episodic subduction accretion

2021 ◽  
Author(s):  
Francisco E. Apen ◽  
John Wakabayashi ◽  
Howard W. Day ◽  
Sarah M. Roeske ◽  
A. Kate Souders ◽  
...  
Keyword(s):  
San Francisco ◽  
Sierra Nevada ◽  
Detrital Zircon ◽  
Regional Scale ◽  
Northern Coast ◽  
Accretionary Complex ◽  
Central California ◽  
Franciscan Complex ◽  
Bay Area ◽  
History Of

ABSTRACT The Franciscan Complex of California, the type example of an exhumed accretionary complex, records a protracted history of voluminous subduction accretion along the western margin of North America. Recent geochronological work has improved our knowledge of the timing of accretion, but the details of the accretionary history are disputed, in part, due to uncertainties in regional-scale correlations of different units. We present new detrital zircon U-Pb ages from two sites on opposite sides of San Francisco Bay in central California that confirm previously proposed correlations. Both sites are characterized by a structurally higher blueschist-facies unit (Angel Island unit) underlain by a prehnite-pumpellyite-facies unit (Alcatraz unit). The Angel Island unit yields maximum depositional ages (MDAs) ranging from 112 ± 1 Ma to 114 ± 1 Ma (±2σ), and the Alcatraz unit yields MDAs between 94 ± 2 Ma and 99 ± 1 Ma. Restoration of post-subduction dextral displacement suggests these sites were originally 44–78 km apart and much closer to other Franciscan units that are now exposed farther south in the Diablo Range. Comparison with detrital zircon dates from the Diablo Range supports correlations of the Bay Area units with certain units in the Diablo Range. In contrast, correlations with Franciscan units in the northern Coast Ranges of California are not robust: some units are clearly older than those in the Bay Area whereas others exhibit distinct differences in provenance. Integration of age data from throughout the Franciscan Complex indicates long-lived and episodic accretion from the Early Cretaceous to Paleogene. Although minor, sporadic accretion began earlier, significant accretion occurred during the interval 123–80 Ma and was followed by minor accretion at ca. 53–49 Ma. Periods of accretion and nonaccretion were associated with arc magmatism in the Sierra Nevada–Klamath region, cessation of arc activity, and reorganization of paleodrainage systems, which implicates plate dynamics and sediment availability as major controls on the development of the Franciscan Complex.

Philip Tyson's 1849 study of California gold prospects

2017 ◽  
Vol 36 (1) ◽  
pp. 30-40
Author(s):  
K. R. Aalto
Keyword(s):  
San Francisco ◽  
Sierra Nevada ◽  
Cross Sections ◽  
Coast Range ◽  
Central California ◽  
Franciscan Complex ◽  
General Geology ◽  
Basement Rocks ◽  
Sierra Nevada Foothills ◽  
Fluvial Sedimentation

Philip Thomas Tyson (1799–1877) toured privately through central California, from San Francisco through the Sierra Nevada foothills gold prospects in 1849, to assess their potential and the general geology of the region. He produced the first regional map with geologic notations and several rough topographic/geologic cross-sections. He described Coast Range basement rocks, now described as Franciscan Complex mélange and broken formation, the stratigraphic configuration of the Great Valley, and general geology of the Sierra Nevada foothills. He recognized that the older Coast Range and Sierran basement were deformed prior to recent volcanism and extensive terrestrial fluvial sedimentation, likely Neogene in age.

scholarly journals High food insecurity in Latinx families and associated COVID-19 infection in the Greater Bay Area, California

BMC Nutrition ◽  
2021 ◽  
Vol 7 (1) ◽  
Author(s):  
Milagro Escobar ◽  
Andrea DeCastro Mendez ◽  
Maria Romero Encinas ◽  
Sofia Villagomez ◽  
Janet M. Wojcicki
Keyword(s):  
Food Security ◽  
Food Insecurity ◽  
San Francisco ◽  
Employment Status ◽  
The United States ◽  
Household Food Security ◽  
Bay Area ◽  
Household Food ◽  
History Of ◽  
The Impact

Abstract Background Food insecurity impacts nearly one-in-four Latinx households in the United States and has been exacerbated by the novel coronavirus or COVID-19 pandemic. Methods We examined the impact of COVID-19 on household and child food security in three preexisting, longitudinal, Latinx urban cohorts in the San Francisco Bay Area (N = 375 households, 1875 individuals). Households were initially recruited during pregnancy and postpartum at Zuckerberg San Francisco General Hospital (ZSFG) and UCSF Benioff prior to the COVID-19 pandemic. For this COVID-19 sub-study, participants responded to a 15-min telephonic interview. Participants answered 18 questions from the US Food Security Food Module (US HFSSM) and questions on types of food consumption, housing and employment status, and history of COVID-19 infection as per community or hospital-based testing. Food security and insecurity levels were compared with prior year metrics. Results We found low levels of household food security in Latinx families (by cohort: 29.2%; 34.2%; 60.0%) and child food security (56.9%, 54.1%, 78.0%) with differences between cohorts explained by self-reported levels of education and employment status. Food security levels were much lower than those reported previously in two cohorts where data had been recorded from prior years. Reported history of COVID-19 infection in households was 4.8% (95% Confidence Interval (CI); 1.5–14.3%); 7.2% (95%CI, 3.6–13.9%) and 3.5% (95%CI, 1.7–7.2%) by cohort and was associated with food insecurity in the two larger cohorts (p = 0.03; p = 0.01 respectively). Conclusions Latinx families in the Bay Area with children are experiencing a sharp rise in food insecurity levels during the COVID-19 epidemic. Food insecurity, similar to other indices of poverty, is associated with increased risk for COVID-19 infection. Comprehensive interventions are needed to address food insecurity in Latinx populations and further studies are needed to better assess independent associations between household food insecurity, poor nutritional health and risk of COVID-19 infection.

History of geological investigations of Mount Diablo, Contra Costa County, California

2021 ◽  
Author(s):  
Gregory W. Bartow
Keyword(s):  
San Francisco ◽  
Focal Point ◽  
San Francisco Bay Area ◽  
University Of California ◽  
General Description ◽  
Mountain Building ◽  
Structural Interpretation ◽  
Bay Area ◽  
History Of ◽  
The University

ABSTRACT Over the past 150 years, Mount Diablo has served as a window into the evolving understanding of California geology. In the 1800s, geologists mapped this easily accessible peak located less than 100 km (62 miles) from the rapidly growing city of San Francisco and the geology departments at the University of California at Berkeley and Stanford University. Later, the mountain served as a focal point for investigating San Francisco Bay area tectonics. The structural interpretation of the up-thrusting mechanisms has evolved from a simple compressional system involving a few local faults to a more complex multifault and multiphase mountain-building theory. The stratigraphic interpretation and understanding have been advanced from a general description of the lithologies and fossils to a detailed description using sequence stratigraphy to define paleogeographic settings and depositional regimes.

Late Pleistocene Glaciations in the Northwestern Sierra Nevada, California

2002 ◽  
Vol 57 (3) ◽  
pp. 409-419 ◽  
Author(s):  
L. Allan James ◽  
Jon Harbor ◽  
Derek Fabel ◽  
Dennis Dahms ◽  
David Elmore
Keyword(s):  
Sierra Nevada ◽  
Late Glacial ◽  
Lateral Moraine ◽  
Riparian Ecosystems ◽  
Glacial Ice ◽  
Central California ◽  
Minimum Age ◽  
History Of ◽  
Ice Retreat ◽  
Moraine Ridge

AbstractPleistocene fluvial landforms and riparian ecosystems in central California responded to climate changes in the Sierra Nevada, yet the glacial history of the western Sierra remains largely unknown. Three glacial stages in the northwestern Sierra Nevada are documented by field mapping and cosmogenic radionuclide surface-exposure (CRSE) ages. Two CRSE ages of erratic boulders on an isolated till above Bear Valley provide a limiting minimum age of 76,400±3800 10Be yr. Another boulder age provides a limiting minimum age of 48,800±3200 10Be yr for a broad-crested moraine ridge within Bear Valley. Three CRSE ages producing an average age of 18,600±1180 yr were drawn from two boulders near a sharp-crested bouldery lateral moraine that represents an extensive Tioga glaciation in Bear Valley. Nine CRSE ages from striated bedrock along a steep valley transect average 14,100±1500 yr and suggest rapid late-glacial ice retreat from lower Fordyce Canyon with no subsequent extensive glaciations. These ages are generally consistent with glacial and pluvial records in east-central California and Nevada.

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