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At least 145 records · Page 8Linked to original sources
USGS2007

Sentinel Hill Core Test 1: Facies descriptions and stratigraphic reinterpretations of the Prince Creek and Schrader Bluff Formations, North Slope, Alaska

The Sentinel Hill Core Test 1 well penetrated an intertonguing sequence of (1) the marine Schrader Bluff Formation in the depth intervals 950–1,180 ft and 690–751 ft, which consists of shoreface and offshore deposits that accumulated along a storm-dominated, barred shoreline; and (2) the nonmarine Prince Creek Formation in the depth intervals 751–950 ft and surface to 690 ft, which consists of fluvial channel, crevasse splay, backswamp, and ash fall deposits. The strata range in age from early Campanian to early Maastrichtian. An erosional contact at a depth of 690 ft at the base of the upper unit of the Prince Creek Formation is interpreted as a major regional sequence boundary, and the overlying conglomeratic fluvial channel deposits are interpreted to have accumulated in a paleovalley. In its more proximal reaches along the Colville River, channels of this paleovalley cut down 75 ft into the lowermost Prince Creek Formation and the uppermost Schrader Bluff Formation. Farther offshore, the equivalent surface to the aforementioned paleovalley appears to be a subtle discontinuity between middle and lower Schrader Bluff Formation shelfal marine strata. Still farther offshore, the equivalent paleovalley surface is interpreted as a marine mass-wasting surface that locally cuts through the lowermost Schrader Bluff Formation and into the underlying Seabee Formation.

Alaska↗
USGS1994

Facies and age of the Oso Ridge Member (new), Abo Formation, Zuni Mountains, New Mexico

The Oso Ridge Member (new), at the base of the Abo Formation, nonconformably overlies Proterozoic rocks. The member consists of some 9m of conglomerate and arkose composed principally of fragments of the underlying Proterozoic metamorphic rocks; thin, fossiliferous limestone lenses are interbedded with the arkose. Biota from the lenses include a phylloid alga, foraminifers, conodonts, brachiopods, and molluscs. The age of the Oso Ridge Member is Virgilian Late Pennsylvanian) to Wolfcampian (Early Permian). -from Authors

New Mexico Geology↗
USGS2006

Ostracods and facies of the Early and Middle Frasnian at Devils Gate in Nevada: Relationship to the Alamo Event

In order to document the Alamo Event and to investigate its influence on shallow-marine environments, we undertook a study of ostracods, conodonts, and analysis of the sedimentology of the lower member of the type Devils Gate Limestone, Six major carbonate microfacies (MF1-MF6) ranging from open-marine environments below storm wave base to pre-evaporitic supratidal lagoons were recognized. The sedimentological study detected no important sedimentological changes during the Alamo Event; only an influx of detrital material and lithoclasts indicate that an unusual event had occurred. Ostracods are generally rare or absent in the lower member of the Devils Gate Limestone, and only 2,000 carapaces, valves and fragments were extracted; from these some 26 taxa were identified. Two new species, Voronina? eureka and Serenida dorsoplicata are proposed. The ostracods belong to the Eifelian Mega-Assemblage and their distribution was influenced by strong salinity variations. Because of the rarity and low diversity of ostracods and conodonts in samples collected from the lower part of the lower member of the Devils Gate Limestone it is not adequate to demonstrate conclusively an extinction event close to the Alamo Event Bed. Nevertheless the greater abundance and diversity of ostracods above this bed seems to indicate that the Alamo Event did not result in significant extinction of ostracod taxa in this shallow water setting. The ostracod fauna present in the lower member of the Devils Gate Limestone suggests faunal exchanges between Nevada and the Russian Platform via the Western Canadian platform.

Nevada↗
USGS2013

Preliminary stratigraphy and facies analysis of the Upper Cretaceous Kaguyak Formation, including a brief summary of newly discovered oil stain, upper Alaska Peninsula

The Alaska Division of Geological and Geophysical Surveys has an ongoing program aimed at evaluating the Mesozoic forearc stratigraphy, structure, and petroleum systems of lower Cook Inlet. Most of our field studies have focused on the Jurassic component of the petroleum system[this report.] However, in late July and early August of 2012, we initiated a study of the stratigraphy and reservoir potential of the Upper Cretaceous Kaguyak Formation. The Kaguyak Formation is locally well exposed on the upper Alaska Peninsula (fig. 25) and was named by Keller and Reiser (1959) for a sequence of interbedded siltstone and sandstone of upper Campanian to Maastrichtian age that they estimated to be 1,450 m thick.Subsequent work by Detterman and Miller (1985) examined 900 m of section and interpreted the unit as the record of a prograding submarine fan.This interpretation of deep-water deposition contrasts with other Upper Cretaceous rocks exposed along the Alaska Peninsula and lower Cook Inlet that are generally described as nonmarine to shallow marine (Detterman and others, 1996; LePain and others, 2012).Based on foraminifera and palynomorphs from the COST No. 1 well, Magoon (1986) concluded that the Upper Cretaceous rocks were deposited in a variety of water depths and environments ranging from upper bathyal to nonmarine. During our recent fieldwork west and south of Fourpeaked Mountain, we similarly encountered markedly varying lithofacies in the Kaguyak Formation (fig. 25), and we also found oil-stained rocks that are consistent with the existence of an active petroleum system in Upper Cretaceous rocks on the upper Alaska Peninsula and in lower Cook Inlet. These field observations are summarized below.

Alaska↗
USGS1992

Deep-water facies of the Lisburne Group, west-central Brooks Range, Alaska

Deep-water lithofacies of the Lisburne Group (chiefly Carboniferous) occur in thurst sheets in the western part of the foreland fold-and-thrust belt of the Brooks Range and represent at least three discrete units. The Kuna Formation (Brooks Range allochthon) consists mostly of spiculitic mudstone and lesser shale; subordinate carbonate layers are chiefly diagenetic dolomite. The Akmalik Chert (Picnic Creek allochthon) is mostly radiolarian-spiculitic chert; rare limy beds are calcitized radiolarite. The Rim Butte unit (Ipnavik river allochthon) consists chiefly of calcareous turbidites, derived from shallow- and deep-water sources, interbedded with spiculitic mudstone. Much of the material in the turbidites came from a contemporaneous carbonate platform and margin, but some fossils and lithic clasts were eroded from older, already lithified carbonate-platform rocks. All three units appear to be roughly coeval in the Howard Pass area and are chiefly late Tournaisian and early Viséan (late Early Mississippian) in age. Shallow-water lithofacies of the Lisburne Group exposed in the Howard Pass area (Brooks Range allochthon) are mostly of Viséan and younger (Late Mississippian) age. Thus, these carbonate-platform rocks were not the source of the calcareous turbidites in the Rim Butte unit. Rim Butte turbidites could have been derived from older carbonate-platform rocks such as the Utukok Formation of Tournaisian age (Kelly River allochthon) exposed mainly to the west of the Howard Pass quadrangle.

Alaska↗
USGS2020

Correlations along a 140 km transect in the westernmost Peach Spring Tuff, and tracing changing facies through depositional environments

Tephrochronology is the correlation of tephra beds and tuffs by various means, and it is an important tool in refining stratigraphic and structural interpretations. The 18.78 Ma Peach Spring Tuff (PST) is a large-volume ignimbrite that was deposited across a ~200 km x 360 km area of southeastern California, northwestern Arizona, and southern Nevada. The PST is a valuable stratigraphic marker in several stratigraphic sequences in this area. In this study, the field characteristics, mineral abundance, and feldspar composition of eight ignimbrite locations are examined along a 140 km swath across the northwestern extent of the PST in the Mojave Desert. Based on geochronologic or paleomagnetic data, five of the ignimbrites are PST, and three are possible PST ignimbrites do not have supporting geochronologic or paleomagnetic data. In 53 regionally dispersed locations of the PST, including the three possible PST ignimbrites in this study, the overlying and underlying sedimentary deposits are described in order to determine the depositional changes, if any, resulting from the geologically instantaneous deposition of the ignimbrite. Of the 53 locations, 37 locations allow interpretation of the pre- and post-PST depositional environments. Of the 37, 25 have an upward fining-thinning trend indicating that the deposition of the ignimbrite resulted in (1) disruption and change in local stream gradients and sediment supply, (2) a long period of time for depositional systems to propagate to and regenerate at a location, or (3) a lack of re-establishment of the pre-PST environments. However, 12 have no significant change, so there was minimal disruption to the depositional system.

Arizona, California, Nevada↗
USGS1978

Origin of two clay-mineral facies of the Potomac Group (Cretaceous) in the Middle Atlantic States

Sedimentary clay that crops out in the coastal plains of New Jersey, Delaware, the part of Maryland north and east of Washington, B.C., and the northeast half of Washington, D.C., in the nonmarine Cretaceous Potomac Group is predominantly kaolinite and illite. In contrast, in part of southeastern Maryland, the southwest half of Washington, D.C., and most of eastern Virginia, Potomac Group clay is predominantly montmorillonite. Kaolinite and illite were probably derived by intense acid weathering of metamorphic and granitic rocks to the west during the Cretaceous and were deposited in a well-drained basin. Montmorillonite was most likely produced by deep weathering of a mainly granitic source. Poor drainage and alkaline surface- and ground-water conditions probably accompanied the production, transportation, deposition, and burial of the montmorillonite. Kaolinization of the montmorillonite is taking place now at the surface in northern Virginia.

Delaware, Maryland, New Jersey, Pennsylvania, Virg↗