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.

Minimal net incision of the northern Sierra Nevada (California, USA) since the Eocene–early Oligocene

Geology ◽  
2020 ◽  
Vol 48 (10) ◽  
pp. 1023-1027
Author(s):  
Emmanuel J. Gabet ◽  
Daniel P. Miggins
Keyword(s):  
Sierra Nevada ◽  
North American ◽  
Past Century ◽  
Mountain Range ◽  
Late Cenozoic ◽  
North American Cordillera ◽  
The Past ◽  
The North ◽  
Early Oligocene ◽  
Northern Half

Abstract Significant late Cenozoic uplift (>1000 m) of the northern half of the Sierra Nevada (California, USA), a mountain range in the North American Cordillera, has been a dominant paradigm over the past century. This paradigm has been supported by evidence suggesting that in response to this recent uplift, the range’s deep canyons were incised in the past 3–4 m.y. However, paleochannel elevations compiled from a mining report and geological maps demonstrate that while some modern rivers have incised 560 m below their Eocene–early Oligocene riverbeds, incision by others has been <300 m. For example, Eocene–early Oligocene fluvial gravels can be found just 161 m above the modern channel deep within the canyon of the South Fork American River. We conclude that the initiation of late Cenozoic incision was due to a resumption of a period of downcutting that was interrupted in the Eocene when the rivers were buried by fluvial sediment and by later volcanic deposits. This interpretation challenges the hypothesis that recent uplift was responsible for deep canyon incision. Correctly identifying the causes of recent incision in the northern Sierra Nevada has important implications for understanding the geological history of the North American Cordillera because the range is hypothesized to have been the western ramp of the Nevadaplano.

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.

Trends and Variability of North American Cool-Season Extratropical Cyclones: 1979–2019

2021 ◽  
Author(s):  
Robert Fritzen ◽  
Victoria Lang ◽  
Vittorio A. Gensini
Keyword(s):  
North American ◽  
Research Question ◽  
Weather Conditions ◽  
Extratropical Cyclones ◽  
Mountain Range ◽  
Cool Season ◽  
The North ◽  
Primary Driver ◽  
Regional Reanalysis ◽  
Log Linear

AbstractExtratropical cyclones are the primary driver of sensible weather conditions across the mid-latitudes of North America, often generating various types of precipitation, gusty non-convective winds, and severe convective storms throughout portions of the annual cycle. Given ongoing modifications of the zonal atmospheric thermal gradient due to anthropogenic forcing, analyzing the historical characteristics of these systems presents an important research question. Using the North American Regional Reanalysis, boreal cool-season (October–April) extratropical cyclones for the period 1979–2019 were identified, tracked, and classified based on their genesis location. Additionally, bomb cyclones—extratropical cyclones that recorded a latitude normalized pressure fall of 24 hPa in 24-hr—were identified and stratified for additional analysis. Cyclone lifespan across the domain exhibits a log-linear relationship, with 99% of all cyclones tracked lasting less than 8 days. On average, ≈ 270 cyclones were tracked across the analysis domain per year, with an average of ≈ 18 year−1 being classified as bomb cyclones. The average number of cyclones in the analysis domain has decreased in the last 20 years from 290 year−1 during the period 1979–1999 to 250 year−1 during the period 2000–2019. Spatially, decreasing trends in the frequency of cyclone track counts were noted across a majority of the analysis domain, with the most significant decreases found in Canada’s Northwest Territories, Colorado, and east of the Graah mountain range. No significant interannual or spatial trends were noted with bomb cyclone frequency.

A REVISION OF THE NORTH AMERICAN OMALIINAE (COLEOPTERA: STAPHYLINIDAE) 1. THE GENERA HAIDA KEEN, PSEUDOHAIDA HATCH, AND EUDECTOIDES NEW GENUS

1978 ◽  
Vol 110 (S106) ◽  
pp. 1-20 ◽  
Author(s):  
J. M. Campbell
Keyword(s):  
New Species ◽  
Sierra Nevada ◽  
North American ◽  
New Genus ◽  
The North ◽  
Two New Species

AbstractThe genera Haida Keen and Pseudohaida Hatch are revised and transferred from the tribe Coryphiini to the Anthophagini; the Palearctic genus Eudectus Redten bacher is also placed in the Anthophagini. Eudectus crassicornis LeConte is transferred to the new gents Eudectoides. Two new species are described, Haida bisulcata from the Sierra Nevada in California and H. insulcata from Oregon. Pseudohaida ingrata Hatch is transferred to Subhaida Hatch, a member of the tribe Coryphiini.The mouthparts and antenna are illustrated for each genus and the male aedeagus for each species. A key is included to aid in the identification of all the included taxa.

Bryozoa of the Mission Argillite (Permian), northeastern Washington

2000 ◽  
Vol 74 (4) ◽  
pp. 545-570 ◽  
Author(s):  
Ernest H. Gilmour ◽  
Edward M. Snyder
Keyword(s):  
New Species ◽  
Pacific Ocean ◽  
North American ◽  
Type Species ◽  
New Genus ◽  
Western Pacific ◽  
North American Plate ◽  
Western Pacific Ocean ◽  
Late Permian ◽  
The North

Fifteen species of Late Permian bryozoans occur in a biohermal bank in the Mission Argillite of northeastern Washington. These include two species conspecific with species described from Japan and 13 new species, one of which is the type species of a new genus. The presence of two species, Dyscritella iwaizakiensis Sakagami, 1961, and Hayasakapora cf. erectoradiata Sakagami, 1960, previously reported from Japan, and the similarity of new species with those previously described from Japan, China and Russia supports the idea that these rocks were originally deposited in the southeastern or central western Pacific Ocean and subsequently accreted to the North American Plate.Bryozoans and previously reported fusulinids indicate that the biohermal bank is latest Wordian (Kazanian).Newly described bryozoans include the new genus and type species Sakagamiina easternensis belonging to the Timanodictyidae. Other new species are Fistuliramus pacificus, Meekoporella inflecta, Neoeridotrypella missionensis, Coeloclemis urhausenii, Tabulipora colvillensis, Rhombotrypella kettlensis, Pamirella oculus, Pinegopora petita, Wjatkella nanea, Alternifenestella vagrantia, Polypora arbusca, and Mackinneyella stylettia.

Systematics and Paleoecology of Norian (Late Triassic) Bivalves from a Tropical Island Arc: Wallowa Terrane, Oregon

1987 ◽  
Vol 61 (S22) ◽  
pp. 1-83 ◽  
Author(s):  
Cathryn R. Newton ◽  
Michael T. Whalen ◽  
Joel B. Thompson ◽  
Nienke Prins ◽  
David Delalla
Keyword(s):  
North American ◽  
Island Arc ◽  
Late Triassic ◽  
Small Scale ◽  
Long Distance ◽  
Tropical Island ◽  
North American Cordillera ◽  
The North ◽  
Wallowa Terrane ◽  
Hells Canyon

Early Norian silicified bivalves from Hells Canyon in the Wallowa terrane of northeastern Oregon are part of a rich molluscan biota associated with a tropical island arc. The Hells Canyon locality preserves lenses of silicified shells formed as tempestites in a shallow subtidal carbonate environment. These shell assemblages are parautochthonous and reflect local, rather than long-distance, transport. Silicification at this locality involved small-scale replacement of original calcareous microstructures, or small-scale replacement of neomorphosed shells, without an intervening phase of moldic porosity. This incremental replacement of carbonate by silica contrasts markedly with void-filling silicification textures reported previously from silicified Permian bivalve assemblages.The bivalve paleoecology of this site indicates a suspension feeding biota existing on and within the interstices of coral-spongiomorph thickets, and inhabiting laterally adjacent substrates of peloidal carbonate sand. The bivalve fauna is ecologically congruent with the reef-dwelling molluscs associated with Middle Triassic sponge-coral buildups in the Cassian Formation of the Dolomites (Fuersich and Wendt, 1977). Hells Canyon is a particularly important early Norian locality because of the diversity of substrate types and because the site includes many first occurrences of bivalves in the North American Cordillera. These first occurrences include the first documentation of the important epifaunal families Pectinidae and Terquemiidae in Triassic rocks of the North American Cordillera.The large number of biogeographic and geochronologic range extensions discovered in this single tropical Norian biota indicates that use of literature-based range data for Late Triassic bivalves may be very hazardous. Many bivalve taxa formerly thought to have gone extinct in Karnian time have now been documented from Norian strata in this arc terrane. These range extensions, coupled with the high bivalve species richness of the Hells Canyon site, suggest that the Karnian mass extinction in several literature-based compilations may be an artifact of incomplete sampling. Even for the Norian, present compilations of molluscan extinction may have an unacceptably large artifactual component.Thirty-five bivalve taxa from the Hells Canyon locality are discussed. Of these, seven are new: the mytilid Mysidiella cordillerana n. sp., the limacean Antiquilima vallieri n. sp., the true oyster Liostrea newelli n. sp., the pectinacean Crenamussium concentricum n. gen. and sp., the unioid Cardinioides josephus n. sp., the trigoniacean Erugonia canyonensis n. gen. and sp., and the carditacean Palaeocardita silberlingi n. sp.

The southern Mexico block: main boundaries and new estimation for its Quaternary motion

2008 ◽  
Vol 179 (2) ◽  
pp. 209-223 ◽  
Author(s):  
Louis Andreani ◽  
Xavier Le Pichon ◽  
Claude Rangin ◽  
Juventino Martínez-Reyes
Keyword(s):  
North American ◽  
Triple Junction ◽  
Strike Slip ◽  
North American Plate ◽  
Southern Mexico ◽  
Active Deformation ◽  
Lateral Strike Slip ◽  
Counterclockwise Rotation ◽  
The North ◽  
Slip Partitioning

Abstract Numerous studies, mainly based on structural and paleomagnetic data, consider southern Mexico as a crustal block (southern Mexico block, SMB) uncoupled from the North American plate with a southeast motion with respect to North America, accommodated by extension through the central Trans-Mexican volcanic belt (TMVB). On the other hand, the accommodation of this motion on the southeastward boundary, especially at the Cocos–Caribbean–North American triple junction, is still debated. The boundary between the SMB and the North American plate is constituted by three connected zones of deformation: (1) left-lateral transtension across the central TMVB, (2) left-lateral strike-slip faulting along the eastern TMVB and Veracruz area and (3) reverse and left-lateral strike-slip faulting in the Chiapas area. We show that these three active deformation zones accommodate a counterclockwise rotation of the SMB with respect to the North American plate. We specially discuss the Quaternary motion of the SMB with respect to the surrounding plates near the Cocos–Caribbean–North American triple junction. The model we propose predicts a Quaternary counterclockwise rotation of 0.45°/Ma with a pole located at 24.2°N and 91.8°W. Finally we discuss the geodynamic implications of this counterclockwise rotation. The southern Mexico block motion is generally assumed to be the result of slip partitioning at the trench. However the obliquity of the subduction is too small to explain slip partitioning. The motion could be facilitated by the high thermal gradient and gravitational collapse that affects central Mexico and/or by partial coupling with the eastward motion of the Caribbean plate.

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