Asbestiform Minerals of the Franciscan Assemblage in California with a Focus on the Calaveras Dam Replacement Project

2020 ◽  
Vol 26 (1) ◽  
pp. 21-28
Author(s):  
R. Mark Bailey
Keyword(s):  
San Francisco ◽  
North American Plate ◽  
Tectonic Activity ◽  
Bay Area ◽  
The North ◽  
Rock Types ◽  
Selected Area Electron Diffraction ◽  
Transmission Electron ◽  
Naturally Occurring Asbestos ◽  
Asbestiform Minerals

ABSTRACT The San Francisco Bay Area is underlain by bedrock of the Franciscan Assemblage, which outcrops in numerous places. A significant portion of these outcrops consists of rock types that contain both regulated and unregulated asbestiform minerals, including ultra-mafic serpentinites, various greenstones, amphibolites, blueschist, and other schists (talc-tremolite, actinolite, etc.). These rocks are a legacy of tectonic activity that occurred on the west coast margin of the North American plate ∼65–150 MY ago during subduction of the East Pacific and Farallon plates. The Calaveras Dam Replacement Project (CDRP), located in Fremont, California, is an example of an area within the Franciscan Assemblage that is substantially underlain by metamorphosed oceanic sedimentary, mafic, and ultra-mafic rocks in a tectonic subduction zone mélange with highly disrupted relationships between adjoining rock bodies with different pressure/temperature metamorphic histories. In order to protect the health of workers and residents in the surrounding area, an extensive effort was taken to identify, categorize, and monitor the types, locations, and concentrations of naturally occurring asbestos at the site. Using a combination of geologic field observations and transmission electron microscopy, energy dispersive X-ray, and selected area electron diffraction analysis of airborne particulate and rock/soil samples, the CDRP was discovered to contain chrysotile-bearing serpentine. It also had as a range of amphibole-containing rocks, including blueschist, amphibolite schist, and eclogite, with at least 19 different regulated and non-regulated fibrous amphibole minerals identified. The extensive solid solution behavior of the amphiboles makes definitive identification difficult, though a scheme was created that allowed asbestos mineral fingerprinting of various areas of the project site.

Overview of Naturally Occurring Asbestos in California and Southwestern Nevada

2020 ◽  
Vol 26 (1) ◽  
pp. 9-14
Author(s):  
R. Mark Bailey
Keyword(s):  
Sierra Nevada ◽  
North American ◽  
Volcanic Belt ◽  
Island Arc ◽  
North American Plate ◽  
Mountain Range ◽  
The North ◽  
Rock Types ◽  
Naturally Occurring ◽  
Naturally Occurring Asbestos

ABSTRACT Naturally occurring asbestos (NOA) is being discovered in a widening array of geologic environments. The complex geology of the state of California is an excellent example of the variety of geologic environments and rock types that contain NOA. Notably, the majority of California rocks were emplaced during a continental collision of eastward-subducting oceanic and island arc terranes (Pacific and Farallon plates) with the westward continental margin of the North American plate between 65 and 150 MY BP. This collision and accompanying accretion of oceanic and island arc material from the Pacific plate onto the North American plate, as well as the thermal events caused by emplacement of the large volcanic belt that became today's Sierra Nevada mountain range, are the principal processes that produced the rocks where the majority of NOA-bearing units have been identified.

The Detection and Identification of Asbestos and Asbestiform Minerals in Talc

1976 ◽  
Vol 34 ◽  
pp. 618-619
Author(s):  
Harold D. Stanley
Keyword(s):  
Quantitative Detection ◽  
Chrysotile Asbestos ◽  
X Ray Diffraction ◽  
X Ray ◽  
Selected Area Electron Diffraction ◽  
Detection And Identification ◽  
Transmission Electron ◽  
Ore Bodies ◽  
Diffraction Peaks ◽  
Asbestiform Minerals

Concern with the health hazards associated with the presence of chrysotile asbestos and/or the asbestiform minerals in talc has prompted widespread investigation of methods of analysis which would be consistent with good analytical practicies. Of all the currently available techniques examined and evaluated, the two most reliable have been found by us to be Step Scanning X-ray Diffraction and Transmission Electron Microscopy, (TEM), with Selected Area Electron Diffraction, (SAED). The Step Scanning X-ray Diffraction technique allows quantitative detection and identification of tremolite and the asbestiform minerals down to 0.1% by weight. In the absence of chlorite it can detect and quantitatively determine chrysotile asbestos at the 0.5% level. Chlorite, however, is often associated with talc ore bodies. When present, chlorite will mask most of the main X-ray diffraction peaks of chrysotile. The X-ray diffraction technique cannot distinguish between fibrous and non-fibrous forms of the asbestiform minerals.

Tectonics and paleogeography of a post-accretionary forearc basin, Coos Bay area, SW Oregon, USA

2021 ◽  
pp. 187-243
Author(s):  
John M. Armentrout
Keyword(s):  
Sediment Transport ◽  
Middle Eocene ◽  
North American Plate ◽  
Coast Range ◽  
Forearc Basin ◽  
Oregon Coast Range ◽  
Susceptibility Data ◽  
Bay Area ◽  
The North ◽  
Coos Bay

ABSTRACT This field guide reviews 19 sites providing insight to four Cenozoic deformational phases of the Cascadia forearc basin that onlaps Siletzia, an oceanic basaltic terrane accreted onto the North American plate at 51–49 Ma. The field stops visit disrupted slope facies, prodelta-slope channel complexes, shoreface successions, and highly fossiliferous estuarine sandstones. New detrital zircon U-Pb age calibration of the Cenozoic formations in the Coos Bay area and the Tyee basin at-large, affirm most previous biostratigraphic correlations and support that some of the upper-middle Eocene to Oligocene strata of the Coos Bay stratigraphic record represents what was differentially eroded off the Coast Range crest during ca. 30–25 Ma and younger deformations. This suggests that the strata along Cape Arago are a western “remnant” of the Paleogene Tyee basin. Zircon ages and biostratigraphic data encourages the extension of the Paleogene Coos Bay and Tyee forearc basin westward beyond the Fulmar fault and offshore Pan American and Fulmar wells. Integration of outcrop paleocurrents with anisotropy of magnetic susceptibility data from the middle Eocene Coaledo Formation affirms south-southeast to north-northwest sediment transport in current geographic orientation. Preliminary detrital remanent magnetism data show antipodal directions that are rotated clockwise with respect to the expected Eocene field direction. The data suggest the Eocene paleo-shoreline was relatively north-south similar to the modern shoreline, and that middle Eocene sediment transport was to the west in the area of present-day Coos Bay. A new hypothesis is reviewed that links the geographic isolation of the Coos Bay area from rivers draining the ancestral Cascades arc to the onset of uplift of the southern Oregon Coast Range during the late Oligocene to early Miocene.

Upper plate deformation during blueschist exhumation, ancestral western California forearc basin, from stratigraphic and structural relationships at Mount Diablo and in the Rio Vista Basin

2021 ◽  
Author(s):  
Jeffrey Unruh
Keyword(s):  
San Francisco ◽  
Late Cretaceous ◽  
Normal Faults ◽  
Coast Range ◽  
Forearc Basin ◽  
Bay Area ◽  
The North ◽  
Early Tertiary ◽  
Local Equivalent ◽  
Structural Relief

ABSTRACT Late Cenozoic growth of the Mount Diablo anticline in the eastern San Francisco Bay area, California, USA, has produced unique 3D exposures of stratigraphic relationships and normal faults that record Late Cretaceous uplift and early Tertiary extension in the ancestral California forearc basin. Several early Tertiary normal faults on the northeast flank of Mount Diablo have been correlated with structures that accommodated Paleogene subsidence of the now-buried Rio Vista basin north of Mount Diablo. Stepwise restoration of deformation at Mount Diablo reveals that the normal faults probably root into the “Mount Diablo fault,” a structure that juxtaposes blueschist-facies rocks of the Franciscan accretionary complex with attenuated remnants of the ophiolitic forearc basement and relatively unmetamorphosed marine forearc sediments. This structure is the local equivalent of the Coast Range fault, which is the regional contact between high-pressure Franciscan rocks and structurally overlying forearc basement in the northern Coast Ranges and Diablo Range, and it is folded about the axis of the Mount Diablo anticline. Apatite fission-track analyses indicate that the Franciscan rocks at Mount Diablo were exhumed and cooled from depths of 20+ km in the subduction zone between ca. 70−50 Ma. Angular unconformities and growth relations in the Cretaceous and Paleogene stratigraphic sections on the northeast side of Mount Diablo, and in the Rio Vista basin to the north, indicate that wholesale uplift, eastward tilting, and extension of the western forearc basin were coeval with blueschist exhumation. Previous workers have interpreted the structural relief associated with this uplift and tilting, as well as the appearance of Franciscan blueschist detritus in Late Cretaceous and early Tertiary forearc strata, as evidence for an “ancestral Mount Diablo high,” an emergent Franciscan highland bordering the forearc basin to the west. This outer-arc high is here interpreted to be the uplifted footwall of Coast Range fault. The stratigraphic and structural relations exposed at Mount Diablo support models for exposure of Franciscan blueschists primarily through syn-subduction extension and attenuation of the overlying forearc crust in the hanging wall of the Coast Range fault, accompanied by (local?) uplift and erosion of the exhumed accretionary prism in the footwall.

Taming the Wild West in the Late 1940s

2015 ◽  
Vol 92 (1) ◽  
pp. 27-52
Author(s):  
Christopher M. Sterba
Keyword(s):  
New York ◽  
San Francisco ◽  
Equal Opportunity ◽  
Political Conflict ◽  
Economic Security ◽  
Turn Of The Century ◽  
Lonely Crowd ◽  
The Great Depression ◽  
Bay Area ◽  
The North

In late 1945, a group of outraged citizens in the small city of El Cerrito formed a “Good Government League” to challenge the gambling and liquor interests who controlled City Hall. In the next few years the League achieved all of its agenda: a city manager plan, civil service reform, and the end of wide-open gambling. A movement like this was fairly typical of the Progressive Era. But the city in question was not a turn-of-the-century metropolis like New York or Chicago. These events happened in the late 1940s in a small bedroom community located just to the north of Berkeley. Within a few years, El Cerrito transformed its reputation from “Little Reno” to the squeaky-clean “City of Homes.” As a case study, the El Cerrito story is interesting for a number of reasons. Most importantly, it highlights how development in the San Francisco Bay Area has involved a regional periodization that differs from what we might traditionally associate with suburban growth. The city's Old West heritage was a major source of political conflict, while the activism of the city's new middle class contrasts with what sociologists called the politically quiescent “Organization Men” of the era's “Lonely Crowd.” The El Cerrito experience also lends insight into why the Bay Area has remained politically liberal since 1945. The city's reformers embraced much of the language and platform of the turn-of-the-century progressives. But they also lived through the Great Depression and the Second World War, and desired most of all to make public policy that would ensure economic security and equal opportunity. Their emphasis on an active public sector left a legacy that can still be felt today.

Serpentine Land Use and Health Concerns

2007 ◽  
Author(s):  
Earl B. Alexander ◽  
Roger G. Coleman ◽  
Todd Keeler-Wolfe ◽  
Susan P. Harrison
Keyword(s):  
Endangered Species ◽  
San Francisco ◽  
Plant Species ◽  
Road Construction ◽  
Serpentine Soils ◽  
Bay Area ◽  
Naturally Occurring ◽  
Private And Public ◽  
Naturally Occurring Asbestos ◽  
Ultramafic Substrates

Soils developed from serpentine (ultramafic) substrates are noted for their meager and strange biomass. The chemical infertility is the main controlling factor in the development of plants in serpentine soils (Proctor and Woodell 1975, Kruckeberg 1984, Brooks 1987). Botanists have recognized the unusual nature of the endemic plants and this has led to preserving serpentine tracts that contain rare plant species. The evolution of plant species that are restricted to serpentine has produced remarkable adaptations to survival on serpentine substrates. Kruckeberg (1984) pointed out that the long-term habitat attrition on these rare natural serpentine ecosystems requires conservation initiatives to insure their preservation. In California, private and public land managers are required to develop environmental impact studies before disturbing tracts containing serpentine bedrock and its overlying soils (Clinkenbeard et al. 2003). The U.S. Fish and Wildlife Service (USFWS 1998) carried out a recovery plan for 28 species of plants and animals that occur exclusively or primarily on serpentine soils and grasslands in the San Francisco Bay area. The strategy was to provide detailed actions needed to achieve self-sustaining populations of endangered species so they will no longer require protection under the Endangered Species Act. Serpentine land tracts within metropolitan areas have come under closer regulation, as there is concern of releasing naturally occurring asbestos during construction disturbances. Typical examples of disturbance would be construction sites, new road construction, and quarry excavation. Of particular concern are the large amounts of dust produced in quarry operations or unpaved gravel roads consisting of crushed serpentine rock. The dust from such sites may contain airborne asbestos fibers released from the serpentine. This asbestos-bearing dust may pose a toxic threat to the construction workers and to later occupants of homes, schools, and office buildings occupying serpentine tracts. Asbestos is the blanket term for a group of naturally occurring silicate minerals that can be separated into fibers. The fibers are strong, durable, and resistant to extreme heat. Because of these qualities, asbestos has been used in industrial, maritime, automotive, scientific, and building products.

scholarly journals Migration patterns of San Francisco Bay Area Hermit Thrushes differ across a fine spatial scale

2016 ◽  
Vol 3 (1) ◽  
pp. 1-13 ◽  
Author(s):  
Allison R. Nelson ◽  
Renée L. Cormier ◽  
Diana L. Humple ◽  
Josh C. Scullen ◽  
Ravinder Sehgal ◽  
...  
Keyword(s):  
British Columbia ◽  
San Francisco ◽  
San Francisco Bay ◽  
San Francisco Bay Area ◽  
Spatial Scales ◽  
Geographic Variations ◽  
Migration Patterns ◽  
Bay Area ◽  
The North ◽  
Connectivity Patterns

AbstractEffective conservation of short-distance migrants requires an understanding of intraspecific variation in migratory patterns across small spatial scales. Until the advent of ultra-light geolocation devices, our knowledge of the migratory connectivity of songbirds was limited. For the Hermit Thrush (Catharus guttatus), subspecies delineations and connectivity patterns have been unclear in the portion of their breeding range in western North America from southeastern Alaska to northwestern Washington, where individuals wintering in the San Francisco Bay Area of California purportedly breed. To determine breeding locations and migratory timing of the Bay Area’s wintering Hermit Thrushes, we deployed geolocators at sites to the north and south of the San Francisco Bay. We compared results from these two regions to one another and to connectivity patterns suggested by subspecies definitions. We collected morphometrics to identify regional differences. Hermit Thrushes that wintered in the North Bay had a wider and more southerly breeding distribution from the British Columbia coast to northwestern Washington, whereas South Bay thrushes migrated to southeastern Alaska and the British Columbia coast. In general, North Bay thrushes departed wintering grounds and arrived on breeding grounds earlier than South Bay thrushes, but we cannot eliminate sex as a factor in these differences. Regional morphology differed only in bill length. Intraspecific isolation in glacial refugia during the Late Pleistocene may explain these fine-scale geographic variations in migration patterns and morphology.

scholarly journals The Possibilities and Potential Pitfalls of Contemporary Global Environmental(ist) Imaginaries: The Human/Nature Project and Philip Krohn’s EARTH Sticker

2010 ◽  
Vol 1 (2) ◽  
Author(s):  
Micha Gerrit Philipp Edlich
Keyword(s):  
Human Nature ◽  
San Francisco ◽  
Cultural Production ◽  
Institutional Conditions ◽  
Bay Area ◽  
The North ◽  
Works Of Art ◽  
Cry For Help ◽  
Global Environmental ◽  
American Artist

Located at the gradually emerging juncture between the current discourses on the global and art in ecocritical scholarship, this article explores how contemporary works of art such as EARTH Sticker (2005) by the North American artist Philip Krohn and artist residency and exhibition projects such as Human/Nature: Artists Respond to a Changing Planet (2008) parse, represent, and imagine the political, socioeconomic, cultural, and especially ecological implications of globalization. EARTH Sticker and two contributions to Human/Nature, the sculptures Sapukay: Cry for Help and Teko Mbarate: Struggle for Life by the Portuguese artist and current San Francisco Bay Area resident Rigo 23, present different environmental imaginaries that challenge and simultaneously rely on the material contexts and conditions on which the increasingly globalized production of art is always predicated. As Krohn and Rigo 23 demonstrate, even art that is created in an environmentalist context (Human/Nature) or with an ostensible activist purpose (EARTH Sticker) cannot escape this double bind. To identify this dilemma is not to dismiss these works of art as self-contradictory failures, but to highlight precisely Krohn’s and Rigo 23’s important insights with regard to this embedment for other global environmental imaginaries and particularly for further ecocritical analysis. Emphasizing the material and institutional conditions, current means and sites of cultural production, and technologies for the dissemination of information, these works of art thus foreground and perform what is often erased from the equation and from critical analysis.ResumenSituado en la poco a poco emergente coyuntura entre los discursos sobre lo global y sobre el arte en la ecocrítica, este artículo examina cómo trabajos de arte contemporáneo como EARTH Sticker (2005), del artista norteamericano Philip Krohn, y residencias de artistas y proyectos de exposiciones como Human/Nature: Artists Respond to a Changing Planet (2008) analizan, representan e imaginan las implicaciones políticas, socieconómicas, culturales y especialmente las ecológicas, de la globalización. EARTH Sticker y  dos contribuciones a Human/Nature, las esculturas Sapukay: Cry for Help y Teko Mbarate: Struggle for Life del artista portugués Rigo 23, actual residente del área de la bahía de San Francisco, presentan diferentes imaginarios medioambientales que desafían y al mismo tiempo dependen de los contextos y las condiciones materiales en las que se fundamenta la producción de arte, cada vez más globalizada. Como Krohn y Rigo 23 demuestran, incluso el arte creado en un contexto medioambiental (Human/Nature) o con un propósito aparentemente activista (EARTH Sticker) no puede escapar esta coyuntura. Identificar este dilema no es desestimar estas obras de arte como fallos contradictorios, sino precisamente poner de manifiesto las importantes apreciaciones de Krohn y Rigo 23 en lo referente a esta inclusión para otros imaginarios medioambientales y en particular para un mayor análisis ecocrítico. Poniendo énfasis en las condiciones materiales e institucionales, los actuales medios y sitios de producción cultural, y las tecnologías para la difusión de información, estas obras de arte ponen de relieve y representan lo que a menudo se elimina en la ecuación y en el análisis crítico.

HRTEM study of valleriite, a hydroxide-bearing copper sulfide

1990 ◽  
Vol 48 (4) ◽  
pp. 462-463
Author(s):  
S. Wang ◽  
P. R. Buseck
Keyword(s):  
Electron Microscope ◽  
High Resolution ◽  
Copper Sulfide ◽  
Carbonaceous Chondrite ◽  
Structural Data ◽  
Basic Structure ◽  
Long Period ◽  
Selected Area Electron Diffraction ◽  
Transmission Electron ◽  
Wavy Structure

Valleriite is an unusual mineral, consisting of intergrowths of sulfide layers (corresponding in structure to the mineral smythite - Fe9S11) and hydroxide layers (corresponding to brucite - Mg(OH2)). It has a composition of approximately 1.526[Mg.68Al.32(OH)2].[Fe1.07Cu.93S2] and consists of two interpenetrating lattices, each of which retains its individual structural and diffraction characteristics parallel to the layering. The valleriite structure is related to that of tochilinite, an unusual iron-rich mineral that is of considerable interest for the origin of certain carbonaceous chondrite meteorites and to those of franckeite and cylindrite, two minerals that are of interest because of their unique morphological and crystallographic properties, e.g., the distinctive curved form of cylindrite and the perfect mica-like cleavage with unusual striations and the long-period wavy structure of franckeite.Our selected-area electron diffraction (SAED) patterns and high-resolution transmission electron microscope (HRTEM) images of valleriite provide new structural data. A basic structure and a new superstructure have been observed.

A Qualitative Study of Ecstasy Sellers in the San Francisco Bay Area

2004 ◽  
Author(s):  
Sheigla Murphy ◽  
Paloma Sales ◽  
Micheline Duterte ◽  
Camille Jacinto
Keyword(s):  
Qualitative Study ◽  
San Francisco ◽  
San Francisco Bay ◽  
San Francisco Bay Area ◽  
Bay Area
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