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R.Z. Poore

Publications and source records attributed to R.Z. Poore.

36 records · Page 2Linked to original sources
USGS1991

Pliocene sea surface temperatures of the North Atlantic Ocean at 3.0 Ma

Sea-surface temperature (SST) estimates based on quantitative analysis of planktic foraminifer faunas in North Atlantic deep sea cores suggest that high-frequency, low-amplitude variability related to orbital forcing was superimposed on long-term changes that delineate intervals within the Pliocene that were both warmer and cooler than today. SST estimates from several DSDP and ODP sites, as well as land sections, have been combined into a synoptic view of SST during a Pliocene warm interval centered at about 3.0 Ma. The Pliocene North Atlantic warm interval SST estimates show little evidence for warming in tropical regions whereas mid- to high-latitude areas show moderate to strong warming. SST estimates for the last interglacial (Isotope Stage 5e) show a similar pattern, but warming during the last interglacial was not as pronounced as the Middle Pliocene warming. The regional distribution of SST estimates during these past warm events suggests an increase in ocean circulation.

Quaternary Science Reviews↗
USGS1991

Neogene biostratigraphy and paleoenvironments of Enewetak Atoll, equatorial Pacific Ocean

Micropaleontologic analyses of Neogene sediments from Enewetak Atoll, Marshall Islands, provide data on the age of lagoonal deposits, stratigraphic disconformities and the paleoenvironmental and subsidence history of the atoll. Benthic foraminifers, planktic foraminifers, calcareous nannofossils and ostracodes were studied from six boreholes, the deepest penetrating 1605 feet below the lagoon floor into upper Oligocene strata. The Oligocene-Miocene boundary occurs at about 1200 ft below the lagoon floor. The early and middle Miocene is characterized by brief periods of deposition and numerous hiatuses. Ostracodes and benthic foraminifers indicate a shallow-marine reefal environment with occasional brackish water conditions. Upper Miocene and lower Pliocene deposits placed in calcareous nannofossil Zones NN9-15 and in planktic foraminifer Zones N16-19 contain species-rich benthic microfaunas which indicate alternating reefal and brackish water mangrove environments. The upper Pliocene contains at least two major depositional hiatuses that coincide with a major faunal turnover in benthic foraminiferal and ostracode assemblages. The Quaternary is characterized by benthic microfaunas similar to those of modern atoll lagoons and is punctuated by at least 11 disconformities which signify periods of low sea level. Atoll subsidence rates during the last 10 Ma averaged 30 to 40 m/m.y. ?? 1991 Elsevier Science Publishers B.V. All rights reserved.

Marine Micropaleontology↗
USGS1985

Apertural features and surface texture of upper Paleogene biserial planktonic foraminifers: links between Chiloguembelina and Streptochilus.

Several upper Paleogene species of Chiloguembelina have an internal apertural plate that is very similar to the internal plate typical of the Neogene genus Streptochilus. The type species of Chiloguembelina, C. midwayensis midwayensis (Cushman), however, lacks any internal apertural structure or modifications. Therefore, the following 'Chiloguembelina', which have an internal plate, are assigned to Streptochilus: S. cubensis (Palmer), S. martini (Pijpers) and S. sp.aff. S. martini. -Authors

Journal of Foraminiferal Research↗
USGS1984

Age and correlation of emerged pliocene and pleistocene deposits, U.S. Atlantic Coastal Plain

Paleontologic and paleomagnetic investigations were conducted on several hundred Pliocene and Pleistocene marine samples from five regions of the emerged Atlantic Coastal Plain: (1) the Delmarva Peninsula, (2) eastern Virginia, (3) central and northern North Carolina, (4) southern North Carolina and northeastern South Carolina, and (5) the Charleston area, South Carolina. Molluscan and ostracode interval and assemblage zonations, which are the primary means of regional correlation, have been calibrated using planktic biochronologic, paleomagnetic, radiometric and amino-acid recemization data. These multiple dating criteria were used to determine the age and, where possible, the duration of marine transgressive/regressive sequences. A correlation chart illustrates the age relationships of 27 formations from five regions. One important conclusion is some of the Yorktown Formation of Virginia and North Carolina (including the “Duplin” Formation), and some of the Raysor of South Carolina are late Pliocene in age. The late Pliocene Chowan River Formation of North Carolina is older than the early Pleistocene Waccamaw Formation of South Carolina, which in turn may be older than the James City Formation of North Carolina. During the last 1.0 million years, multiple marine transgressions occurred in each region, but the age of these middle and late Pleistocene formations often may differ from one area to the next. A significant result of the study is the evidence for the lack of time equivalence of formations in the five different regions; that is, the sequence of marine transgressions in one region does not necessarily correspond to that in another. This appears to be the result of differing subsidence and uplift histories, the patchiness of the depositional record, and the limitations of the dating techniques in light of the rapidity and frequency of sea-level fluctuations.

Delaware, Maryland, North Carolina, South Carolina↗
USGS1984

Oxygen isotope ranking of late Eocene and Oligocene planktonic foraminifers: Implications for Oligocene sea-surface temperatures and global ice-volume

Oxygen isotope analyses of late Eocene and Oligocene planktonic foraminifers from low and middle latitude sites in the Atlantic Basin show that different species from the same samples can yield significantly different isotopic values. The range of isotopic values observed between species is greatest at low-latitudes and declines poleward. Many planktonic foraminifers exhibit a systematic isotopic ranking with respect to each other and can therefore be grouped on the basis of their isotopic ranking. The isotopic ranking of some taxa, however, appears to vary geographically and/or through time. Isotopic and paleontologic data from DSDP Site 522 indicate that commonly used isotopic temperature scales underestimate Oligocene sea surface temperatures. We suggest these temperature scales require revision to reflect the presence of Oligocene glaciation. Comparison of isotopic and paleontologic data from Sites 522, 511 and 277 suggests cold, low-salinity surface waters were present in high southern latitudes during the early Oligocene. Low-salinity, high latitude surface waters could be caused by Eocene/Oligocene paleogeography or by the production of warm saline bottom water.

Marine Micropaleontology↗
USGS1983

Late cretaceous-cenozoic magnetostratigraphic and biostratigraphic correlations of the South Atlantic Ocean: DSDP Leg 73

DSDP Leg 73 sediment cores allow direct calibrations of magnetostratigraphy and biostratigraphy for much of the lates Cretaceous to Cenozoic in the mid-latitude South Atlantic Ocean. A complete record of the Cenozoic was not obtained, however, because strong dissolution, poor core recovery and intense core disturbance have masked the biostratigraphy or magnetostratigraphy over some intervals of all recovered sections. DSDP Leg 73 results show the following correlations: Early/middle Miocene in Chron 16 Oligocene/Miocene within Subchron C6N Eocene/Oligocene within Subchron C13R Middle/late Eocene top of Chron C17 Early/late Paleocene top of Subchron C27N Cretaceous/Tertiary within Subchron C29R

Palaeogeography, Palaeoclimatology, Palaeoecology↗
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↗
USGS1982

Post-middle Miocene accretion of Franciscan rocks, northwestern California.

Deformed sedimentary rocks assigned to the Franciscan assemblage in the King Range S of Cape Mendocino, N California, are dominantly deep-water argillite and sandstone occurring as thick- to thin-bedded, locally channelized marine turbidities of arkosic to andesitic volcaniclastic composition. The King Range appears to be a displaced terrane of oceanic basement overlain by Palaeogene(?) and Neogene sedimentary and igneous rocks of continental and oceanic derivation.-Authors

Geological Society of America Bulletin↗
USGS1981

Late Miocene biogeography and paleoclimatology of the central North Atlantic

Quantitative analyses of planktonic foraminiferal assemblages from Deep Sea Drilling Project (DSDP) Holes 334 and 410 demonstrate that subpolar and subtropical faunal provinces existed in the North Atlantic during the late Miocene. Climatic oscillations are clearly recorded in Hole 410 by variations in abundance of the Neogloboquadrina subpolar assemblage. These climatic oscillations have a period of about 1 m.y. Higher frequency oscillations with a periodicity of one to several hundred thousand years are evident from about 6.5 to 7.5 m.y. and are probably present throughout the entire late Miocene. A revised age of 7.0 m.y. is proposed for the first occurrence of the calcareous nannofossil Amaurolithus primus (the Amaurolithus datum).

Marine Micropaleontology↗
USGS1980

Tertiary δ18O record and glacio-eustatic sea-level fluctuations

Previous interpretation of the Tertiary δ 18 O record of plaiiktic and benthic foraminifers has emphasized comparison to the modern ocean, assumed an ice-free world prior to middle Miocene time, and thereby calculated surprisingly cool temperatures for the tropical sea surface. We propose an alternative interpretation, which compares Tertiary data to average late Pleistocene, assumes constant tropical sea-surface temperature, and thereby estimates global ice volume. This approach suggests that Earth has had a significant ice budget (and therefore glacio-eustatic sea-level fluctuations) at least since Eocene and perhaps even throughout much of Cretaceous time.

Geology↗