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Results for “Journal of Nannoplankton Research”

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8 recordsLinked to original sources
USGS2014

Catinaster virginianus sp. nov.: A new species of Catinaster from the middle Miocene Mid-Atlantic Coastal Plain

High-resolution analysis of sediments from four coreholes associated with the Chesapeake Bay impact crater has resulted in the identification of a new species, Catinaster virginianus. This species is similar to Catinaster coalitus coalitus, but differs in having a proximal stem. The first occurrence of C. virginianus is in Zone NN5, and is older than any previously identified Catinaster . This species has been identified previously as Catinaster sp. from the Gulf of Mexico and the Carpathian Foredeep and suggests both a global distribution and synchronous stratigraphic range. Morphologic similarities with Discoaster variabilis may suggest a taxonomic relationship to the D. variabilis lineage.

Chesapeake Bay↗
USGS2017

Biostratigraphic and morphometric analyses of specimens from the calcareous nannofossil genus Tribrachiatus

Biostratigraphic and morphometric analyses of calcareous nannofossil assemblages from one outcrop and two cored sections of lower Eocene sediments reveal the presence of two new species: Tribrachiatus lunatus sp. nov., and Tribrachiatus absidatus sp. nov. Differences between the new species and Tribrachiatus orthostylus are discussed. The first occurrence of the two new species is just below the calcareous nannofossil Zone NP11/NP12 boundary, close to the Chron 24r/23n boundary, and thus they are globally useful biostratigraphic markers.

Journal of Nannoplankton Research↗
USGS2006

The effects of the Chesapeake Bay impact on calcareous nannofossil assemblages: patterns from the Watkins School core, Newport News, Virginia (USA)

The goal of this study was to assess the effect that the Late Eocene Chesapeake Bay bolide impact had on local patterns of calcareous nannofossil species composition, richness and preservation. Although calcareous nannofossil assemblages have been described from a handful of coreholes drilled within the impact structure, this is the first study to examine the calcareous nannofossils from the Watkins School core , which was recovered along the outer rim of the crater. A detailed stratigraphic assessment of the calcareous nannofossil assemblages across the synimpact-postimpact boundary was performed to determine whether the impact produced any local extinction. The results obtained suggest that, despite its size, the Chesapeake Bay impact did not significantly affect the local calcareous nannoplankton community. Little or no change was documented across the synimpact-postimpact boundary in calcareous nannofossil species composition, richness or preservation quality. These findings do not support the existence of a calcareous nannofossil 'dead zone' in this particular core; however, the presence of impact-fractured calcareous nannofossils does attest to the tremendous pressures generated by the impact.

Virginia↗
USGS1983

New data on the age of Lepidocyclina in California

During the 1930's and early 1940's, controversy about the age of Lepidocyclina californica and faunas associated with it led to unreconcilable differences of opinion in the attempt to provide a standard stratigraphic framework for Cenozoic rocks of western North America. Two standards with significantly different series age assignments were provided, one based largelyon benthic foraminifers and the other on mollusks and echinoderms. Although both standards have more recently converged in regard to correlating faunas of the Pacific Coast with those in Europe, and although the age of Lepidocyclina has been more firmly established in various countries, the age of the California Lepidocyclina remains in doubt. We report here, for the first time, planktic foraminifers and calcareous nannoplankton associated with the Lepidocyclina . These floras and faunas correlate with the Helicosphaera ampliaperta Zone of Bukrv and Zone N 7 of Blow and indicate that Lepidocyclina californica is probably early Miocene. This revised age removes the basis for the significantly different series age assignments for the Pacific Coast standards.

Journal of Foraminiferal Research↗
USGS1999

Age and paleoenvironment of the imperial formation near San Gorgonio Pass, Southern California

Microfossiliferous marine sediments of the Imperial Formation exposed in the Whitewater and Cabazon areas, near San Gorgonio Pass, southern California, are late Miocene in age and were deposited at intertidal to outer neritic depths, and possibly upper bathyal depths. A late Miocene age of 7.4 to >6.04 Ma is based on the ranges of age-diagnostic benthic foraminifers (Cassidulina delicata and Uvigerina peregrina), planktic foraminifers (Globigerinoides obliquus, G. extremus, and Globigerina nepenthes; zones N17-N19), and calcareous nannoplankton (Discoaster brouweri, D. aff. D. surculus, Reticulofenestra pseudoumbilicata, Sphenolithus abies, and S. neoabies; zones CN9a-CN11) coupled with published K/Ar dates from the underlying Coachella Formation (10.1 ?? 1.2 Ma; Peterson, 1975) and overlying Painted Hill Formation (6.04 ?? 0.18 and 5.94 ?? 0.18 Ma; J. L. Morton in Matti and others, 1985 and Matti and Morton, 1993). Paleoecologic considerations (sea-level fluctuations and paleotemperature) restrict the age of the Imperial Formation to 6.5 through 6.3 Ma. Benthic foraminiferal assemblages indicate that the Imperial Formation in the Whitewater and Cabazon sections accumulated at inner neritic to outer neritic (0-152 m) and possibly upper bathyal (152-244 m) depths. Shallowing to inner neritic depths occurred as the upper part of the section was deposited. This sea-level fluctuation corresponds to a global highstand at 6.3 Ma (Haq and others, 1987). Planktic foraminifers suggest an increase in surface-water temperatures upsection. A similar increase in paleotemperatures is interpreted for the North Pacific from 6.5 to 6.3 Ma (warm interval W10 of Barron and Keller, 1983). Environmental contrasts between the Whitewater and Cabazon sections of the Imperial Formation provide evidence for right-lateral displacements on the Banning fault, a late Miocene strand of the San Andreas fault system. The Cabazon section lies south of the Banning fault, and has been displaced west relative to the Whitewater sections. The Cabazon section was deposited at greater depths, suggesting that it accumulated farther offshore than the Whitewater section. If the Salton Trough was a southward-opening, elongated northwest-southeast basin similar to the modern Gulf of California, the Cabazon sequence probably has been displaced right-laterally from a position farther southeast of the Whitewater sequence. This relation requires late Miocene displacements greater than the present 12 km cross-fault separation between the two Imperial sections in the San Gorgonio Pass area.

Journal of Foraminiferal Research↗