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Geology topics

C.D. Blome

Publications and source records attributed to C.D. Blome.

At least 19 recordsLinked to original sources
USGS2010

Tectonics of formation, translation, and dispersal of the Coast Range ophiolite of California

Data from the Coast Range ophiolite and its tectonic outliers in the northern California Coast Ranges suggest that the lower part of the ophiolite formed 169 to 163 Ma in a forearc or back arc setting at equatorial latitudes. Beginning about 156 Ma and continuing until 145 Ma, arc magmatism was superimposed on the ophiolite, and concurrently, a transform developed along the arc axis or in the back arc area. Rapid northward translation of this rifted active magmatic arc to middle latitudes culminated in its accretion to the California margin of North America at about 145 Ma. This Late Jurassic episode of translation, arc magmatism, and accretion coincided with the Nevadan orogeny and a proposed major plate reorganization in the eastern Pacific basin. The high rate of poleward motion necessary to translate the Coast Range ophiolite to middle latitudes during this time implies that the ophiolite traveled north on a fast-moving plate of the eastern Pacific basin, here termed plate X. Plate X probably was driven by a cryptic ridge east-northeast of the Pacific-Farallon-Izanagi ridge triple junction. Structural relations indicate that following Late Jurassic time, parts of the Coast Range ophiolite were displaced from the west side of the Great Valley province and incorporated into the Central belt of the Franciscan Complex along steep-dipping to low-angle reverse faults having dominant components of dextral shear. A northwest trending eastern zone of these right-laterally displaced outliers shows strong affinities to the main Coast Range ophiolite of the northwestern Sacramento Valley (the Elder Creek terrane), in that the outliers include ophiolitic breccias of Oxfordian to Kimmeridgian age. A southwestern zone of outliers lacks ophiolitic breccia and instead includes latest Oxfordian or Kimmeridgian to Tithonian, arc-derived volcanic rocks like those found in the Del Puerto and Stanley Mountain terranes of the main ophiolite. Whereas outliers of the northeastern outlier zone are right-laterally displaced no more than 260 km from the western side of the Sacramento Valley, outliers of the southwestern zone are displaced a minimum of 169 to 249 km. This displacement occurred between about 60 and 52 Ma. Ophiolitic rocks in the Decatur terrane of western Washington that have recently been correlated with the Coast Range ophiolite and the Great Valley sequence of California were apparently displaced at least 950 to 1200 km from the west side of the Great Valley between early Tertiary and Early Cretaceous time. Derived rates of northward translation for the ophiolite outliers in California are in the range of 1 to 4 cm/yr. Rates for the Decatur terrane are in the range of 2.5 to 4 cm/yr if translation was initiated 90 Ma, but as much as 11.9 to 15 cm/yr if it was not initiated until 60 Ma. The lower rates for the Decatur terrane are consistent with the rates derived for the California outliers and with the northward component of relative motion between the Farallon and North American plates from 90 to 50 Ma. The higher rates require northward transport on the Kula plate or on a fast-moving microplate. The higher translation rates derived for the Decatur terrane are also consistent with paleomagnetically determined rates for some limestones of the Central belt. This may indicate that outliers of the Coast Range ophiolite dispersed in the Central belt of the Franciscan Complex record only part of the total displacement which occurred along the Late Cretaceous to early Tertiary western margin of North America.

California↗
USGS2009

Bear Spray Safety Program

A bear spray safety program for the U.S. Geological Survey (USGS) was officially initiated by the Firearms Safety Committee to address accident prevention and to promote personnel training in bear spray and its transportation, storage, and use for defense against wild animals. Used as part of a system including firearms, or used alone for those who choose not to carry a firearm, bear spray is recognized as an effective tool that can prevent injury in a wild animal attack.

Fact Sheet↗
USGS1998

Phanerozoic stratigraphy of Northwind Ridge, magnetic anomalies in the Canada Basin, and the geometry and timing of rifting in the Amerasia Basin, Arctic Ocean

Cores from Northwind Ridge, a high-standing continental fragment in the Chukchi borderland of the oceanic Amerasia basin, Arctic Ocean, contain representatives of every Phanerozoic system except the Silurian and Devonian systems. Cambrian and Ordovician shallow-water marine carbonates in Northwind Ridge are similar to basement rocks beneath the Sverdrup basin of the Canadian Arctic Archipelago. Upper Mississippian(?) to Permian shelf carbonate and spicularite and Triassic turbidite and shelf lutite resemble coeval strata in the Sverdrup basin and the western Arctic Alaska basin (Hanna trough). These resemblances indicate that Triassic and older strata in southern Northwind Ridge were attached to both Arctic Canada and Arctic Alaska prior to the rifting that created the Amerasia basin. Late Jurassic marine lutite in Northwind Ridge was structurally isolated from coeval strata in the Sverdrup and Arctic Alaska basins by rift shoulders and grabens, and is interpreted to be a riftogenic deposit. This lutite may be the oldest deposit in the Canada basin. A cap of late Cenomanian or Turonian rhyodacite air-fall ash that lacks terrigenous material shows that Northwind Ridge was structurally isolated from the adjacent continental margins by earliest Late Cretaceous time. Closing Amerasia basin by conjoining sea-floor magnetic anomalies beneath the Canada basin or by uniting the pre-Jurassic strata of Northwind Ridge with kindred sections in the Sverdrup basin and Hanna trough yield similar tectonic reconstructions. Together with the orientation and age of rift-margin structures, these data suggest that (1) prior to opening of the Amerasia basin, both northern Alaska and the continental ridges of the Chukchi borderland were part of North America, (2) the extension that created the Amerasia basin formed rift-margin grabens beginning in Early Jurassic time and new oceanic crust probably beginning in Late Jurassic or early Neocomian time.

Geological Society of America Bulletin↗
USGS1996

Far-travelled Permian chert of the North Fork terrane, Klamath Mountains, California

Permian chert in the North Fork terrane and correlative rocks of the Klamath Mountains province has a remanent magnetization that is prefolding and presumably primary. Paleomagnetic results indicate that the chert formed at a paleolatitude of 8.6° ± 2.5° but in which hemisphere remains uncertain. This finding requires that these rocks have undergone at least 8.6° ± 4.4° of northward transport relative to Permian North America since their deposition. Paleontological evidence suggests that the Permian limestone of the Eastern Klamath terrane originated thousands of kilometers distant from North America. The limestone of the North Fork terrane may have formed at a similar or even greater distance as suggested by its faunal affinity to the Eastern Klamath terrane and more westerly position. Available evidence indicates that convergence of the North Fork and composite Central Metamorphic-Eastern Klamath terranes occurred during Triassic or Early Jurassic time and that their joining together was a Middle Jurassic event. Primary and secondary magnetizations indicate that the new composite terrane containing these and other rocks of the Western Paleozoic and Triassic belt behaved as a single rigid block that has been latitudinally concordant with the North American craton since Middle Jurassic time.

California↗
USGS1995

Radiolarian biostratigraphy of the Quinn River Formation, Black Rock terrane, north-central Nevada: correlations with eastern Klamath terrane geology

The Quinn River Formation, Black Rock terrane, Quinn River Crossing, is one of the few Nevadan sections of Permian and Triassic strata that are unaffected by Sonoman deformation. The formation consists of: 1) a basal tuff overlain by limestone and ferruginous dolomite, 2) interbedded radiolarian-bearing chert and argillite, 3) siltstone and carbonaceous shale, and 4) partly volcaniclastic rocks. All but the uppermost (barren) chert samples contain Late Permian radiolarian taxa. These radiolarians suggest that early Wordian conodonts reported from near the top of the chert and argillite unit are reworked. Poorly preserved Early(?) or Middle triassic radiolarians and Middle Triassic ammonites and pectenacid bivalves from the middle part of the volcaniclastic unit indicate the Early Triassic deposition cannot be documented at Quinn River. The ages of the Quinn River brachiopod, conodont, and radiolarian faunas resemble those of the Dekkas and Pit Formations, eastern Klamath terrane, northern California. The analogous Quinn River and eastern Klamath rock types and faunal ages, as well as similar hiatuses in their stratigraphic records, suggest that they may be lateral equivalents that formed in the same island-arc sedimentary basin. -from Authors

Micropaleontology↗
USGS1993

Acid processing of pre-Tertiary radiolarian cherts and its impact on faunal content and biozonal correlation

The numbers of radiolarians visible in thin sections of chert-rich rocks are commonly an order of magnitude greater than the numbers observed on the surfaces of fragments etched by hydrofluoric acid (HF) and typically orders of magnitude greater than the numbers of individuals found in HF-processed residues. Destruction of radiolarians during both diagenesis and HF processing severely reduces faunal abundance and diversity and affects the taxonomic and biostratigraphic utility of chert residues. The robust forms that survive the processing represent only a small fraction of the death assemblage, and delicate skeletal structures used for species differentiation, commonly preserved in limestone radiolarian faunas, are either poorly preserved or dissolved in many coeval chert residues. First and last occurrences of taxa in chert sequences are likely to be coarse approximations of their true stratigraphic ranges. Precise correlation is difficult between biozonations based solely on index species from cherts and those constructed from limestone faunas. Careful selection of samples in sequence, use of weaker HF solutions, and study of both chert and limestone faunas should yield better biostratigraphic information.

Geology↗
USGS1992

Permian and early(?) Triassic radiolarian faunas from the Grindstone Terrane, central Oregon

Moderately well preserved Permian and Early(?) Triassic radiolarian faunas from sedimentary melange cherts of the Grindstone terrane in central Oregon are nearly identical to coeval chert faunas in Japan. Although several Oregon taxa have been reported from limestone sequences in the central United States, most of the Oregon forms have only been found in cherty rocks and nearly half have not previously been reported from North America. Forty-two taxa belonging to 19 genera are systematically treated. Co-occurrences of some species in Oregon indicate that their ranges in North America may differ from those in Japan. -from Authors

Journal of Paleontology↗
USGS1991

Evolution of a Permo-Triassic sedimentary melange, Grindstone terrane, east-central Oregon

The Grindstone terrane in east-central Oregon is one of the few areas in western North America where large blocks of unmetamorphosed Devonian, Mississippian, and Permian limestones are inter mixed with Permian and Lower Triassic radiolarian chert and Pennsylvanian?, Permian, and Triassic volcaniclastic rocks. Although originally described as parts of a coherent succession, we interpret the Grindstone rocks to be a sedimentary mélange composed of Paleozoic limestone slide and slump blocks that became detached from a carbonate shelf fringing a volcanic knoll or edifice in Late Permian to Middle Triassic time and were intermixed with Permian and Triassic slope to basinal clastic and volcaniclastic rocks in a forearc basin setting. Paleogeographic affinities of the Grindstone limestone faunas and volcaniclastic debris in the limestone and clastic rocks all indicate deposition in proximity to an island-arc system near the North American craton. The Grindstone terrane deposits are unconformably overlain by Upper Triassic to Middle Jurassic sequences of the Izee terrane. Although lithologic and faunal differences indicate that the Grindstone and Izee terranes together represent a tectonic block separate from the adjacent Baker terrane, all three terranes were juxtaposed by Late Triassic or Early Jurassic time.

Oregon↗
USGS1989

Reinterpretation of lower Mesozoic rocks on the Chilkat Peninsula, Alaska, as a displaced fragment of Wrangellia

The southern Chilkat Peninsula is underlain by low-grade metamorphic rocks consisting of a thick unit of greenstone, in part of Carnian age, that is locally overlain by an attenuated section of calcareous sedimentary rocks and chart of latest Carnian to late Norian age and a thick flysch unit of Jurassic and/or Cretaceous age. The Triassic part of this sequence has previously been inferred to be part of the Taku terrane. However, its lithology, age, fossils, and regional distribution indicate that it is probably a sliver of Wrangellia that was offset from the eastern Alaska Range to its present position by at least 350 km dextral displacement on the Denali fault.

Geology↗
USGS1988

Limestone and chert in tectonic blocks from the Esk Head subterrane, South Island, New Zealand

The Esk Head subterrane is a continuous belt, generally 10-20 km wide, of tectonic mélange and broken formation on the South Island of New Zealand. This subterrane separates older and younger parts of the Torlesse terrane which is an extensive accretionary prism composed mostly of quartzo-feldspathic, submarine-fan deposits ranging from Permian to Early Cretaceous in age. The Torlesse is the most Pacific-ward of several Permian and Mesozoic accreted terranes in New Zealand that record tectonic amalgamation and ultimate accretion against the Pacific-facing Gondwana margin. The Esk Head subterrane of the Torlesse is especially informative because it includes within it conspicuous tectonic blocks of submarine basalt and a variety of basalt-associated seamount and sea-floor limestones and cherty rocks thought to be representative of the subducted plate. Limestones in tectonic blocks are of Late Triassic and probably Jurassic ages and include (1) submarine-cemented, pelagic-bivalve, geopetal packstone-grainstone; (2) brachiopod-bryozoan encrinite; and (3) radiolarian, pelagic lime mudstone. Most of the Triassic blocks have been dated using conodonts which have remarkably low color alteration index (CAI) values (<1.5). An incomplete sampling of cherts in tectonic blocks and from Holocene gravels derived from the Esk Head subterrane yields radiolarian-based ages of Late Triassic, Early Jurassic, Middle Jurassic, and Late Jurassic. Paleogeographic inferences drawn from megafossils, bioclasts, and radiolarians, as well as from carbonate cements, indicate deposition of the oceanic sedimentary rocks at paleolatitudes somewhat lower than that of the New Zealand part of the Gondwana margin, but higher than paleoequatorial latitudes. These oceanic sediments and their basaltic substrates were evidently emplaced in the Torlesse accretionary prism following off-scraping from an extensive subducting oceanic plate, probably the Phoenix plate, which was obliquely convergent with the northwest-trending Gondwana margin during Late Jurassic and/or Early Cretaceous time.

Geological Society of America Bulletin↗
USGS1985

Carbonate concretions: an ideal sedimentary host for microfossils

Microfossils extracted from carbonate concretions tend to be better preserved, more abundant and diverse, and more likely to retain delicate and fragile structures than those extracted from the surrounding rocks. Enhanced preservation correlates with early diagenetic concretion formation at or near the sediment-water interface and with higher carbonate, organic material, and metallic cation content than in surrounding rocks. Early diagenetic growth is inferred by diverging sedimentary laminations and small-scale sedimentary structures in fossiliferous carbonate concretions. High initial concentrations of microorganisms or fecal pellets may commonly be responsible for incipient carbonate-concretion growth. Excellent preservation is demonstrated by radiolarians and palynomorphs extracted from a carbonate concretion from the Middle Jurassic Shelikof Formation, southern Alaska.

Geology↗