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USGS1963

Cathedral Cliffs formation, the early acid Breccia unit of northwestern Wyoming

The name Cathedral Cliffs Formation is proposed for the rocks in the Clarks Fork area of northwestern Wyoming that have long been known by the informal designation "early acid breccia." In the Clarks Fork area the Cathedral Cliffs Formation is composed of tuffs, with lesser amounts of volcanic sedimentary rocks and breccias. Its thickness ranges from less than 100 feet to about 1500 feet but more commonly is 500-900 feet. The formation is tentatively considered to be late early Eocene or early middle Eocene. It is underlain by rocks ranging from Precambrian to early Eocene(?) and is overlain unconformably by the early basic breccia of middle Eocene age. Low-angle detachment faulting, which involved the Cathedral Cliffs Formation but not the overlying early basic breccia, has made recognition and correlation of the formation difficult. Blocks and masses of Madison Limestone of Mississippian age were emplaced locally on its upper surface by the Reef Creek detachment fault. The Cathedral Cliffs Formation and the Paleozoic carbonate rocks beneath it, as well as the Reef Creek fault masses on its surface, were then transported southeastward by the Heart Mountain detachment fault. As movement on the Heart Mountain detachment proceeded, the large fault mass broke up into smaller blocks, which separated as movement continued. Consequently the Cathedral Cliffs Formation was distributed in a pattern which gives the appearance of isolated occurrences and erosional remnants. The detached blocks of the Reef Creek fault on the upper surface of the Cathedral Cliffs also were scattered more widely than by their original movement on the Reef Creek fault. Soon after the fault-transported segments of the Cathedral Cliffs Formation ceased moving they were buried beneath the early basic breccia. The unconformity between the early acid breccia and the early basic breccia is thus substantiated in the Clarks Fork area; in the time interval represented, the Reef Creek and Heart Mountain fault masses were emplaced. The Cathedral Cliffs Formation is correlated with the early acid breccia in northern Yellowstone National Park and the upper part of the Reese Formation as mapped by Calvert west of Gardiner, Montana. The volcanic-source area probably is not in the central Yellowstone Park region, but somewhere to the north. © 1963, The Geological Society of America, Inc.

Wyoming↗

USGS1965

Structural geology of aconcagua province and its relationship to the central Valley Graben, Chile

Aconcagua Province is herein divided into three major structural provinces which, for the sake of simplicity, are named the Coastal Cordillera, Central Valley graben , and Andean Cordillera structural provinces to correspond to the three geomorphic provinces recognized farther south. The coastal structural province includes the Coastal Cordillera which is underlain mainly by layered sedimentary and effusive rocks that strike north and dip homoclinally to the east, range from Triassic to Late Cretaceous in age, and are intruded by Cretaceous granodioritic and dioritic rocks. Igneous and metamorphic rocks largely of Paleozoic age comprise the western coastal margin, Along the eastern edge of the province is the Los Angeles fault zone, a wide, poorly defined band of semiparallel, arcuate faults which show downward displacement to the east and which appear to have resulted mainly from intrusion and uplift on the west. The Coastal Cordillera, therefore, may be considered a large horst with an intrusive granodiorite core. The Central Valley graben is bounded on the west by the Los Angeles fault zone and on the east by the Pocuro fault zone. Between these two fault zones is an area 20-30 km wide in which volcanic rocks of Late Cretaceous age are flat lying to gently folded and block faulted. In places, pipelike stocks of andesitic to dioritic igneous rock intrude the area. The Pocuro fault zone is a prominent lineament that marks the eastern limit of the Central Valley at Santiago and has been traced northward for 150 km. It may, however, have a mappable length of more than 1200 km. Vertical displacement downward to the west has been measured near Los Andes to be at least 2000 m. Consequently, this fault zone may rank among the major faults of the world. The Andean structural province is subdivided into the Las Ollas and Juncal subprovinces. The Las Ollas is a mountainous front range that lies east of the Pocuro fault and extends eastward for about 25 km. Upper Cretaceous volcanic strata are gently warped into broad, open, north-trending folds, with local sharp flexures and faulted mainly by normal faults. The eastern part of the subprovince is cut by a narrow belt of Tertiary plutonic rocks, some of which are associated with porphyry copper deposits. The Juncal structural subprovince extends eastward into Argentina. It is typified by close, overturned folding, vertical bedding, and thrust faulting. In general, structural deformation increases in intensity from west to east, with imbricate overthrusting to the east in Argentina. Present evidence indicates that major graben formation began during early Tertiary (pre-Miocene) time as a result of tensional stress developed by strain release of earlier compressional forces that folded the Andes. Post-Miocene uplift of the central Andean region renewed tensional stress and opened deep-seated, north-striking fractures and reinitiated volcanism. Most of the active volcanos of Chile may be aligned along such fractures.

Geological Society of America Bulletin↗

USGS1967

Stratigraphy and correlation of the precambrian belt supergroup of the southern Lewis and Clark Range, Montana

Several well-exposed and little-deformed Belt Supergroup sections have been studied in the southern Lewis and Clark Range . In the area studied, the Belt thins eastward or northeastward due both to primary sedimentation and to pre-Middle Cambrian erosion. These rocks can now be more precisely correlated with the well-known sections near Bonner, Helena, and Glacier National Park. In the western part of the area, the Missoula Group is thickest and lithologically intermediate between the sections at Bonner and Marias Pass. Formation names from these two sections are applied in the southern Lewis and Clark Range . The thin Belt sequence in the eastern part of the area includes the lower part of the Missoula Group and older formations that may be traced southward into the Helena, Empire, and Spokane Formations of the Helena area. Consequently, the Helena Dolomite of the Helena area, the Siyeh Formation of the Marias Pass area, and the "Newland Limestone" of the Bonner area are probably lateral equivalents.

Montana↗

USGS1970

Eocene age of the Adak ‘Paleozoic (?)’ rocks, Aleutian Islands, Alaska

In 1948, several specimens identified as the plant genus Annularia, a primitive horsetail of Pennsylvanian or Permian age, were found in tuffaceous sandstone exposed near the northern end of Adak Island, Alaska. These beds form the basal part of the Andrew Lake Formation, a newly named sequence of marine sedimentary rocks that is more than 850 m thick, and, in the main, consists of northwest-dipping tuffaceous sandstone, siltstone, shale, and siliceous siltstone and shale interbedded with basaltic flows or penecontemporaneous(?) sills (or both) a few tens of meters thick. This formation rests depositionally(?) on the Finger Bay Volcanics, the massive and intensely altered andesitic and basaltic flows and pyroclastic rocks that form the bulk of Adak Island. Mollusks, foraminifers, sponge spicules, and fish scales and skeletal remains occur in the lower 350 m of the section immediately overlying the basal “Annularia”-bearing beds. Included in this fauna is the pecten Pro-peamussium (cf. P. stanfordensis Arnold), of probable Eocene age; the associated foraminiferal fauna is provincially considered to be of late Eocene (Narizian) age, and the fish scales are similar to those found in the Narizian and Refugian (Eocene and Oligocene) of California. Examination of the matrix surrounding specimens of “Annularia” revealed a substantial dinoflagellate flora—establishing that the “Annularia”- bearing beds are themselves marine units of middle or late Eocene age. The Andrew Lake Formation probably accumulated in a perched basin along the crestal region of an early Tertiary Aleutian ridge. Accordingly, there is no evidence for a Paleozoic Aleutian ridge. There is only scant evidence that the ridge existed in Mesozoic time.

Alaska↗

USGS1971

Mesozoic granitic rocks in northwestern Nevada: A link between the Sierra Nevada and Idaho batholiths

Extensive areas in northwestern Nevada are underlain by granodiorite and quartz monzonite plutons, as well as less common smaller bodies of quartz diorite. Twenty-six K/Ar age determinations on rocks from this suite range from about 175 to 85 m.y., but most of the plutons are between 105 and 85 m.y. old. This Late Cretaceous intrusive epoch extending from 105 to 85 m.y. ago is here named the Lovelock intrusive epoch. Twenty-three whole-rock chemical analyses show that the granitic rocks of northwestern Nevada form a homogeneous differentiation series with a narrow range in major element distribution. The granitic plutons of northwestern Nevada are chemically and petrographically indistinguishable from granitic intrusives of equivalent age in the Sierra Nevada and Idaho batholiths, and form a link between these two major batholiths.

California, Idaho, Nevada↗

USGS1973

Miocene tholeiitic basalts of coastal Oregon and Washington and their relations to coeval basalts of the Columbia Plateau

Note: This paper is dedicated to Aaron and Elizabeth Waters on the occasion of Dr. Waters' retirement. Tholeiitic basalt flows and breccias of Miocene age in western Oregon and Washington form three distinct stratigraphic units. Each unit was erupted from coastal vents marked by dikes and sills of the same composition as associated extrusive rocks. The three coastal basalt units are interbedded with predominantly marine sedimentary rocks of middle to late Miocene age. These units are here named, from older to younger, the Depoe Bay Basalt, Cape Foulweather Basalt, and basalt of Pack Sack Lookout. The three units can be distinguished by their petrographic characteristics. The Depoe Bay Basalt is nonporphyritic; Cape Foulweather Basalt has sparse large labradorite phenocrysts; and Pack Sack basalt has labradorite phenocrysts with numerous pyroxene and glass inclusions as well as augite and olivine phenocrysts. Chemical analyses of basalts from these three units show that each has a distinct and uniform composition. The Depoe Bay Basalt is characterized by high SiO 2 content; the Cape Foulweather Basalt has high content of total iron, TiO 2 , and P 2 O 5 ; and Pack Sack basalt is marked by relatively high MgO and CaO content. The Depoe Bay Basalt, Cape Foulweather Basalt, and basalt of Pack Sack Lookout on the coast occur in the same stratigraphic order and are essentially the same ages as three basalt units that erupted on the Columbia Plateau. The plateau-derived units are the Yakima and late-Yakima petrographic types of Waters (1961) and the Pomona flow of Schmincke (1967). The virtual identity in chemical composition of the Depoe Bay Basalt and Yakima-type basalt, the Cape Foulweather Basalt and the late-Yakima–type basalt, and the Pack Sack basalt and the Pomona basalt flow indicate that each pair is consanguineous. Fissure vents for the plateau basalt are located in eastern Oregon and Washington and western Idaho more than 500 km east of the coastal vent areas. Thus, a regional mechanism of magma generation or emplacement is required. Three models of magma genesis considered in this report are: (1) partial melting of the subducted Juan de Fuca plate; (2) partial melting along a nearly horizontal shear zone at the base of the American plate; and (3) partial melting within the asthenosphere and fractionation during ascent of the magma.

Oregon, Washington↗

USGS1974

Buried Triassic basin in the central Savannah River area, South Carolina and Georgia

A basin filled with Triassic red beds, located on the South Carolina–Georgia line ∼32 km southeast of Augusta, Georgia, is buried beneath ∼350 m of Coastal Plain sediments. An extensive aeromagnetic survey, seismic refraction and reflection surveys, and geophysical logs and samples from three wells define the extent and character of the basin. This basin, herein named the Dunbarton Triassic basin, is ∼50 km long, 10 km wide, and trends northeast. The northwest margin of the basin is well defined by the aeromagnetic survey, a seismic reflection traverse, and a well that passed through 485 m of Triassic fanglomerate before entering the crystalline metamorphic rocks below. Near the center of the Triassic basin, a well passed through 902 m of maroon Triassic mudstone and sandstone of fluvial origin without penetrating the bottom of the basin. The permeability of the Triassic rock is extremely low, and water-transmitting fractures were not penetrated. Even slight water-level disturbances in the Triassic wells require many years to recover. Total dissolved solids of the water from the Triassic basin are about twice that in the crystalline metamorphic rocks that surround it. The inferred geologic history of this basin is similar to the history of Triassic basins that crop out in North Carolina.

Georgia, South Carolilna↗

USGS1975

Chino Valley formation (Cambrian?) in northwestern Arizona

A thin persistent unit (maximum thickness 13 m) of probable Cambrian age in the Chino Valley region of northwestern Arizona consists of three laterally equivalent, mutually exclusive lithofacies. These are, from west to east, lithic sandstone, pebble to boulder conglomerate, and dolomite. The unit, named the Chino Valley Formation, is younger than middle Middle Cambrian and older than Devonian in age. A Late Cambrian age is probable, although no fossil evidence supports this conclusion. The lithic sandstone and conglomerate facies were derived from two apparently active source areas and were probably deposited in shallow marine water. Uplift to the south or southwest of the area almost reversed the regionally westward-dipping Cambrian paleoslope and exposed sedimentary rocks to erosion. Sediment derived from this terrain formed the lithic sandstone facies. Synchronous movement initiated erosion of the Mazatzal Quartzite (Precambrian) from which the conglomerate facies was derived. The dolomite facies is inferred to have accumulated on a mud flat in the supratidal zone.

Arizona↗

USGS1976

Obsidian hydration dating and correlation of Bull Lake and Pinedale Glaciations near West Yellowstone, Montana

The ages of the last two glaciations near West Yellowstone, Montana, can be calculated by obsidian hydration techniques that are calibrated by K-Ar dating of obsidian-bearing lava flows. The average age of glacial abrasion of obsidian in the Pinedale terminal moraines is about 30,000 yr, with most age measurements between 20,000 and 35,000 yr. For the Bull Lake moraines, it is about 140,000 yr, with most measurements between 130,000 and 155,000 yr. This age for the Bull Lake moraines is also supported by geologic relations that show that the moraines are older than a rhyolite flow dated by K-Ar as 114,500 ± 7,300 yr old (lσ). These obsidian hydration ages of the Pinedale and Bull Lake Glaciations correlate well with the last two cold intervals of the marine record. The age determined for the Bull Lake Glaciation near West Yellowstone antedates the last interglaciation of the marine record, which is commonly correlated with the Sangamon Interglaciation. Our results suggest correlation of the Pinedale Glaciation near West Yellowstone with much or all of the Wisconsin Glaciation and of the Bull Lake with the late Illinoian. This differs with the commonly accepted correlation of the Pinedale with the late (“classical”) Wisconsin and of the Bull Lake with the early Wisconsin. The correlation of Bull Lake with late Illinoian appears equally or more compatible with traditional criteria for correlation, namely comparative soil development and degree of preservation of morainal morphology.

Wyoming, Montana, Idaho↗

USGS1991

Anomalous folds associated with the east-central part of the Garlock Fault, southeast California

The east-central part of the left-lateral Garlock fault, in southeast California, is associated with three broad folds that trend and plunge northeast. The folds, which lie north, south, and astride the fault, postdate deposition of alluvial gravels that at one time formed a continuous northwest-sloping fan; the gravels rest conformably on lake beds that contain the Lava Creek B ash bed (0.62 Ma). The anticline, named after Christmas Canyon, has vertical relief of as much as 100 m. Topographic profiles suggest that the gravels exposed along the synclinal troughs to its southeast (Pilot Knob Valley syncline) and northwest (Teagle Wash syncline) lie at about the same elevations as they did when part of the originally active fan, implying that the synclines are passive results of the anticline development. If so, the original slope of the middle Pleistocene alluvial sediment sheet was about 0.6° northwest. The age and dimensional controls allow calculation of the rates of tilting and horizontal shortening. Corrected tilting rates vary from about 2.5° to 4.7°/m.y.; the total shortening of about 7.5 m developed at a minimum rate of 12.5 m/m.y.

California↗

USGS1994

Origin, transport, and emplacement of an exotic island-arc terrane exposed in eastern Kamchatka, Russia

The regional stratigraphy of eastern Kamchatka includes an exotic, Early-Late Cretaceous ophiolite and Late Cretaceous island-arc volcanic sequence. Integrating the existing geologic and geophysical data, we examine the origin, transport, emplacement, and postemplacement deformation of the island-arc terrane, which is named the Olyutorsky island arc. Results from several paleomagnetic studies consistently indicate that the island-arc terrane originated >1000 km to the south of where it is presently exposed. Although the formative paleolatitudes of the island-arc rocks approximately correspond to the location of the Izanagi-Farallon subduction zone, the age of the volcanic rocks postdates the cessation of Izanagi-Farallon convergence, thus indicating that an unnamed plate or back-arc basin existed in the northwest Pacific during Late Cretaceous time. We examine two possible models for northward transport of the island-arc terrane to Kamchatka: (1) infra-oceanic transport with the Pacific or Kula plates and (2) coastwise translation of the island-arc terrane after accretion to the Eurasian margin far to the south of Kamchatka. For both models, the dominant Eocene and Miocene deformation ages observed in eastern Kamchatka are used as two possible age limits for the cessation of northward transport. Although the observed paleolatitudes from paleomagnetic data correspond best with the infra-oceanic transport model, the provenance of the Paleogene "transport" stratigraphy indicates a near-shore sediment supply. Our preferred interpretation is that the island-arc terrane (1) accreted onto the Eurasian margin concurrent with cessation of island-arc volcanism (Maastrichtian-Danian) and (2) underwent northward coastwise translation along a major strike-slip fault zone ending by middle-late Eocene time (43-50 Ma). It is unclear whether the ophiolite was exposed during arc-continent collision or whether the ophiolite was obducted onto the island arc prior to collision. A consequence of either infra-oceanic transport or coastwise translation is that an open corridor between the western terminus of the Aleutian Arc and Kamchatka must have existed until middle to late Eocene time. Spreading within the Komandorsky Basin, subduction of sea-mounts, and collision of the Aleutian Arc with Kamchatka are proposed to have instigated the second Miocene phase of deformation, which uplifted and reexposed the island-arc terrane.

Kamchatka Peninsula↗

USGS1996

Recurrent eruption and subsidence at the Platoro caldera complex, southeastern San Juan volcanic field, Colorado: New tales from old tuffs

Reinterpretation of a voluminous regional ash-flow sheet (Masonic Park Tuff) as two separate tuff sheets of similar phenocryst-rich dacite erupted from separate source calderas has important implications for evolution of the multicyclic Platoro caldera complex and for caldera-forming processes generally. Masonic Park Tuff in central parts of the San Juan field, including the type area, was erupted from a concealed source at 28.6 Ma, but widespread tuff previously mapped as Masonic Park Tuff in the southeastern San Juan Mountains is the product of the youngest large-volume eruption of the Platoro caldera complex at 28.4 Ma. This large unit, newly named the “Chiquito Peak Tuff,” is the last-erupted tuff of the Treasure Mountain Group, which consists of at least 20 separate ash-flow sheets of dacite to low-silica rhyolite erupted from the Platoro complex during a 1 m.y. interval (29.5−28.4 Ma). Two Treasure Mountain tuff sheets have volumes in excess of 1000 km 3 each, and five more have volumes of 50–150 km 3 . The total volume of ash-flow tuff exceeds 2500 km 3 , and caldera-related lavas of dominantly andesitic composition make up 250-500 km 3 more. A much greater volume of intermediate-composition magma must have solidified in subcaldera magma chambers. Most preserved features of the Platoro complex-including postcollapse asymmetrical trap-door resurgent uplift of the ponded intracaldera tuff and concurrent infilling by andesitic lava flows-postdate eruption of the Chiquito Peak Tuff. The numerous large-volume pre-Chiquito Peak ash-flow tuffs document multiple eruptions accompanied by recurrent subsidence; early-formed caldera walls nearly coincide with margins of the later Chiquito Peak collapse. Repeated syneruptive collapse at the Platoro complex requires cumulative subsidence of at least 10 km. The rapid regeneration of silicic magmas requires the sustained presence of an andesitic subcaldera magma reservoir, or its rapid replenishment, during the 1 m.y. life span of the Platoro complex. Either case implies large-scale stoping and assimilative recycling of the Tertiary section, including intracaldera tuffs.

Colorado↗

USGS2000

Late Holocene Peléan-style eruption at Tacaná volcano, Mexico and Guatemala: past, present, and future hazards

Tacaná volcano, located on the border between Mexico and Guatemala, marks the northern extent of the Central American volcanic chain. Composed of three volcanic structures, it is a volcanic complex that has had periodic explosive eruptions for at least the past 40 k.y. The most recent major eruption occurred at the San Antonio volcano, the youngest volcanic edifice forming the complex, about 1950 yr ago. The Peléan style eruption, issued from the southwest part of the dome, and swept a 30° sector with a hot block and ash flow that traveled about 14 km along the Cahoacán ravine. Deposits from this event are well exposed around the town of Mixcun and were therefore given the name of that town, the Mixcun flow deposit. The Mixcun flow deposit is, in the channel facies, a light gray, massive, thick (>10 m), matrix-supported unit with dispersed lithic clasts of gravel to boulder size, divisible in some sections into a variable number of flow units. The overbank facies is represented by a thin (<1 m), massive, matrix-supported unit. In both of these facies the deposit has disseminated charcoal, fumarolic pipes, and juvenile lithics with cooling joints. The Mixcun flow deposit contains clasts of (1) light gray, dense andesite, (2) dark gray, glassy and banded andesite, and (3) minor altered red andesite from the edifice, set in a matrix of sand and silt. The Mixcun flow deposit covers an area of at least 25 km 2 and has a minimum estimated volume of 0.12 km 3 . Basaltic-andesite inclusions (54% SiO 2 ) and various signs of disequilibrium in the mineral assemblage of the two-pyroxene andesitic products (60%–63% SiO 2 ) suggest that magma mixing may have triggered the eruption. Following deposition of the Mixcun flow deposit andesitic to dacitic (62%–64% SiO 2 ) lava flows were extruded and a dacitic dome (64.4% SiO 2 ) at the San Antonio summit formed. Syn-eruptive and posteruptive lahars flooded the main drainages of the Cahoacán and Izapa-Mixcun valleys in the area of the present city of Tapachula (population 250000) and the pre-Hispanic center of Izapa. Three radiocarbon ages date this event between A.D. 25 and 72 (range ±1σ, 38 B.C.–A.D. 216), which correlates with a halt in construction at Izapa (Hato phase of ca. 50 B.C.–A.D. 100), probably due to temporary abandonment of the city caused by lahars. Another similar event would produce extensive damage to the towns (population of about 68,000 people) now built upon the Mixcun flow deposit. The main summit of Tacaná volcano continues to show signs of fumarolic activity; the most recent period of activity in 1985–1986 culminated in a minor phreatic explosion.

Tapachula↗

USGS2003

Early neogene history of the central American arc from Bocas del Toro, western Panama

A newly discovered sequence of lower to middle Miocene rocks from the eastern Bocas del Toro archipelago, western Panama, reveals the timing and environment of the earliest stages in the rise of the Isthmus of Panama in this region. Two new formations, the Punta Alegre Formation (lower Miocene, Aquitanian to Burdigalian) and the Valiente Formation (middle Miocene, Langhian to Serravallian), are here named and formally described. The Punta Alegre Formation contains a diagnostic microfauna of benthic and planktic foraminifera and calcareous nannofossils that indicate deposition in a 2000-m-deep pre-isthmian neotropical ocean from as old as 21.5–18.3 Ma. Its lithology varies from silty mudstone to muddy foraminiferal ooze with rare thin microturbidite layers near the top. The Valiente Formation, which ranges in age from 16.4 to ca. 12.0 Ma, lies with slight angular unconformity on the Punta Alegre Formation and consists of five lithofacies: (1) columnar basalt and flow breccia, (2) pyroclastic deposits, (3) coarse-grained volcaniclastic deposits, (4) coral-reef limestone with diverse large coral colonies, and (5) marine debris-flow deposits and microturbidites. These lithofacies are interpreted to indicate that after ca. 16 Ma a volcanic arc developed in the region of Bocas del Toro and that by ca. 12 Ma an extensively emergent archipelago of volcanic islands had formed. 39 Ar/ 40 Ar dating of basalt flows associated with the fossiliferous sedimentary rocks in the upper part of the Valiente Formation strongly confirms the ages derived from planktic foraminifera and nannofossils. Paleobathymetric analysis of the two new formations in the Valiente Peninsula and Popa Island, in the Bocas del Toro archipelago, shows a general shallowing from lower- through upper-bathyal to upper-neritic and emergent laharic and fluviatile deposits from ca. 19 to 12 Ma. The overlying nonconformable Bocas del Toro Group contains a lower transgressive sequence ranging from basal nearshore sandstone to upper-bathyal mudstone (ca. 8.1–5.3 Ma) and an upper regressive sequence (5.3–3.5 Ma). A similar paleobathymetric pattern is observed from the Gatun to Chagres Formations (12–6 Ma) in the Panama Canal Basin area and in the Uscari, Rio Banana, Quebrada Chocolate, and Moin Formations (8–1.7 Ma) in the southern Limón Basin of Costa Rica.

Geological Society of America Bulletin↗

USGS2003

SHRIMP U-Pb geochronology of Neoproterozoic Windermere Supergroup, central Idaho: Implications for rifting of western Laurentia and synchroneity of Sturtian glacial deposits

In central Idaho roof pendants, a northwest-trending belt of metamorphosed strata, correlative with the Windermere Supergroup, links northern and southern segments of the western Laurentia Neoproterozoic rift belt. Nine newly named formations within the Gospel Peaks sequence-A through Gospel Peaks sequence-D record Cryogenian preglacial, rift-glacial, and postglacial events as well as Neoproterozoic III glacial and rift events. The Edwardsburg Formation of Gospel Peaks sequence B includes interfingered bimodal rift-related volcanic and glaciogenic diamictite strata. Zircons from a rhyodacite flow in the lower Edwardsburg Formation and from a rhyolite flow at its top, dated by using the sensitive high-resolution ion microprobe (SHRIMP), yielded a weighted average of 685 ± 7 Ma and 684 ± 4 Ma. Reevaluation of geochronology and correlations indicates that Cryogenian rifting may have been (1) protracted between 780 and 685 Ma, (2) diachronous along the Cordillera, and/or (3) stepwise with a Cordilleran-wide event at ca. 685 Ma that initiated the formation of the Cordilleran miogeocline and set its geometry. Reevaluation of the Cryogenian glacial record indicates that (1) two associated ca. 685 Ma glacial intervals in the Edwardsburg Formation correlate with the Rapitan glaciation, (2) the Sturtian snowball Earth event must be reevaluated on the basis of revision of Rapitan glaciation from 750–700 Ma to ca. 685 Ma, and (3) there were older Cryogenian glaciations or Cryogenian glaciations were not globally synchronous. New dates and correlations significantly impact the number and synchroneity of possible snowball Earth events and the paleolatitudes of Cryogenian glaciations. Western Laurentian events at ca. 685 Ma particularily affect Neoproterozoic paleocontinental reconstructions by indicating diachronous and multi step breakup of supercontinent Rodinia.

Idaho↗

USGS2003

The early Mesozoic Birdsboro central Atlantic margin basin in the Mid-Atlantic region, eastern United States

The early Mesozoic Birdsboro basin (new name) was a single, elongate depositional trough in the present Mid-Atlantic area of the eastern United States, extending north-eastward from central Virginia across Maryland, Pennsylvania, and New Jersey into southern New York. What now remains after erosion comprises the Barboursville, Culpeper, Gettysburg, and Newark remnants. Some 7?? km of late Triassic and early Jurassic continental sediments of varying provenances entered and spread across in the Birdsboro basin in several depositional environments. The five resulting sedimentary lithosomes include feldspathic sandstone, quartzose sandstone, red silty mudstone, gray shale, and fanglomerate. The extensive interbedding, intertonguing, and lateral gradation among these lithosomes suggest that they were contemporary and closely interrelated. The feldspathic sandstone lithosome contains sediment with a southeastern provenance that accumulated in a bajada environment extending the length of the southeastern side of the basin. Sediment in the quartzose sandstone lithosome had a northwestern provenance-the coarse-grained fraction formed regional alluvial fans at the mouths of four major input centers. The finer-grained fraction was deposited in the distal reaches of these fans and in the playa environments in the interfan areas; this fraction formed the red silty mudstone lithosome. Gray/black shales and argillites of the gray shale lithosome accumulated in lacustrine environments in the interfan areas. The fanglomerate lithosome comprises numerous small, lobate deposits of poorly sorted sediment along both basin margins. The location and time of activity of the northwest input centers largely determined the distribution and areal extent of the various depositional environments and consequent lithosome along the length and across the width of the basin. The Birdsboro basin was deformed (tilted, faulted, and folded) sometime after the deposition of the youngest preserved rocks (early Sinemurian). The deformation varied along the length of the basin, producing differences in the amount of tilting, structural elevation, and subsequent erosion. The present erosional remnants create the illusion of four originally separate depositional basins.

Geological Society of America Bulletin↗

USGS2003

Life and death of the resurrection plate: Evidence for its existence and subduction in the northeastern Pacific in Paleocene-Eocene time

Onshore evidence suggests that a plate is missing from published reconstructions of the northeastern Pacific Ooean in Paleocene- Eocene time. The Resurrection plate, named for the Resurrection Peninsula ophiolite near Seward, Alaska, was located east of the Kula plate and north of the Farallon plate. We interpret coeval near-trench magmatism in southern Alaska and the Cascadia margin as evidence for two slab windows associated with trench-ridge-trench (TRT) triple junctions, which formed the western and southern boundaries of the Resurrection plate. In Alaska, the Sanak-Baranof belt of near-trench intrusions records a west-to-east migration, from 61 to 50 Ma, of the northern TRT triple junction along a 2100-km-long section of coastline. In Oregon, Washington, and southern Vancouver Island, voluminous basaltic volcanism of the Siletz River Volcanics, Crescent Formation, and Metchosin Volcanics occurred between ca. 66 and 48 Ma. Lack of a clear age progression of magmatism along the Cascadia margin suggests that this southern triple junction did not migrate significantly. Synchronous near-trench magmatism from southeastern Alaska to Puget Sound at ca. 50 Ma documents the middle Eocene subduction of a spreading center, the crest of which was subparallel to the margin. We interpret this ca. 50 Ma event as recording the subduction-zone consumption of the last of the Resurrection plate. The existence and subsequent subduction of the Resurrection plate explains (1) northward terrane transport along the southeastern Alaska-British Columbia margin between 70 and 50 Ma, synchronous with an eastward-migrating triple junction in southern Alaska; (2) rapid uplift and voluminous magmatism in the Coast Mountains of British Columbia prior to 50 Ma related to subduction of buoyant, young oceanic crust of the Resurrection plate; (3) cessation of Coast Mountains magmatism at ca. 50 Ma due to cessation of subduction, (4) primitive mafic magmatism in the Coast Mountains and Cascade Range just after 50 Ma, related to slab-window magmatism, (5) birth of the Queen Charlotte transform margin at ca. 50 Ma, (6) extensional exhumation of high-grade metamorphic terranes and development of core complexes in British Columbia, Idaho, and Washington, and extensional collapse of the Cordilleran foreland fold-and-thrust belt in Alberta, Montana, and Idaho after 50 Ma related to initiation of the transform margin, (7) enigmatic 53-45 Ma magmatism associated with extension from Montana to the Yukon Territory as related to slab breakup and the formation of a slab window, (8) right-lateral margin-parallel strike-slip faulting in southern and western Alaska during Late Cretaceous and Paleocene time, which cannot be explained by Farallon convergence vectors, and (9) simultaneous changes in Pacific-Farallon and Pacific-Kula plate motions concurrent with demise of the Kula-Resurrection Ridge.

Geological Society of America Bulletin↗

USGS1971

Palynology, age, and correlation of the Wanship Formation and their implications for the tectonic history of northeastern Utah

Although never formally introduced, the stratigraphic name Wanship Formation has become entrenched in the literature; recently, misunderstanding of its age and correlation has led to invalid interpretations of the structural evolution of northeastern Utah . The basal Wanship conglomerate has been erroneously correlated with a conglomerate within the Frontier Formation at Coalville. The Coalville section has been dated as Cenomanian-Coniacian. The Wanship Formation at its "type locality" is Campanian-Maestrichtian in age , as determined by its palynomorph content, and is not correlative with the Coalville section. The Wanship is correlative with the lower Evanston Formation . Recognition of these relationships obviates the need for a hypothesized episode of folding and faulting during middle Cretaceous time in northeastern Utah .

Utah↗