Showing papers on "Foraminifera published in 1977"

The oxygen isotope stratigraphic record of the Late Pleistocene

Abstract: Oxygen isotope measurements have been made in foraminifera from over 60 deep-sea sediment cores. Taken together with the oxygen isotope measurements published by Emiliani from Caribbean and Equatorial Atlantic cores, this comprises a unique body of stratigraphic data covering most of the important areas of calcareous sediment over the whole world ocean. The oxygen isotopic composition of foraminifera from cores of Late Pleistocene sediment varies in a similar manner in nearly all areas; the variations reflect changes in the oxygen isotopic composition of the ocean. The oceans are mixed in about 1 ka so that ocean isotopic changes, resulting from fluctuations in the quantity of ice stored on the continents, must have occurred almost synchronously in all regions. Thus the oxygen isotope record provides an excellent means of stratigraphic correlation. Cores accumulated at rates of over about 5 cm/ka provide records of oxygen isotopic composition change that are almost unaffected by post-depositional mixing of the sediment. Thus they preserve a detailed record of the advance and retreat of the ice masses in the northern hemisphere, and provide a unique source of information for the study of ice-sheet dynamics.

Deep-sea carbonate and the deglaciation preservation spike in pteropods and foraminifera

Abstract: The aragonite compensation depth fluctuated considerably during the last 20,000 yr. This fluctuation culminated in a preservation spike at about 14,000 yr BP. The aragonite preservation stratigraphy parallels that in calcitic foraminifera, and constitutes part of a worldwide phenomenon signalling considerable changes in ocean chemistry and providing a useful tool for correlation.

Calcareous plankton paleobiogeographic evidence for major climatic fluctuations in the early Cenozoic Atlantic Ocean

Abstract: It is only since the advent of the Deep Sea Drilling Project (DSDP) and the wider availability of older Cenozoic deep-sea core material that large-scale pre-Quaternary paleoenvironmental studies using marine microplankton could be attempted. The present study is one of the first attempts at mapping the early Cenozoic (65–24 m.y. B.P.) spatial and temporal distributions of calcareous plankton of the Atlantic Ocean using the DSDP cores and reconstructing the paleoclimatic History of the region from the resultant patterns. The early Cenozoic biogeographic patterns of calcareous nannoplankton (coccoliths and discoasters) and planktonic foraminifera have been delineated on the basis of quantitatively defined assemblages. These patterns show (1) that latitudinal differentiation among the calcareous planktonic groups existed during most of the early Cenozoic, with the exception of the earliest Paleocene (65–64 m.y. B.P.) when planktonic foraminiferal assemblages were essentially homogeneous through all latitudes, showing little provinciality, and when the floral gradients exhibited by nannoplankton were more closely related to near-shore and open ocean conditions and (2) that there have been major changes in the distributional patterns of both groups: those related to major latitudinal shifts with time and those due to evolution and disappearance of various forms. As is true in the present-day ocean, the early Cenozoic patterns are considered to be controlled mainly by the latitudinal thermal gradient (climate). Thus the temporal oscillations in the assemblages are interpreted as being caused by major climatic fluctuations. Four marked cooling episodes are recorded within the early Cenozoic Atlantic Ocean: those during the middle Paleocene (60–58 m.y. B.P.), the middle Eocene (46–43 m.y. B.P.), the earliest Oligocene (37–35 m.y. B.P.), and the middle Oligocene (32–28 m.y. B.P.). A particularly marked warming episode occurred during the late Paleocene-early Eocene (54–51 m.y. B.P.), and a second, less prominent warming trend began in the latest Oligocene (28 m.y. B.P.) and continued into the early Miocene.

Calcareous nannoplankton biostratigraphy of Middle and Upper Cretaceous deposits in Tunisia, Southern Spain and France

Abstract: The calcareous nannoplankton floras of sections in Tunisia, Southern Spain and France have been investigated leading to a succession of 17 biozones for the Middle and Upper Cretaceous, of which the Rucinolithus hayii Zone for the Middle Santonian is new. In order to correlate the zonation with the chronostratigraphic scale the calcareous nannofossil contents of the stratotypes of the commonly used European Middle and Upper Cretaceous stages have been investigated. The nannofloras of the Cenomanian and Turonian Stages have been published in earlier papers and the stratotype of the Coniacian Stage contains no calcareous nannofossils. From the samples used for the present study the planktonic foraminifera have also been studied to obtain a first order correlation between the zonations based on calcareous nannoplankton and planktonic foraminifera. Evolutionary trends have been recognized and are described in detail in the genera Ceratolithoides, Eiffellithus and Broinsonia. For the description of the calcareous nannofossils the generally accepted terminology is used, completed with some new terms. Remarks have been made on the observed taxa and several new combinations are proposed.

Isoleucine epimerization for dating marine sediments: importance of analyzing monospecific foraminiferal samples.

Abstract: The rate of isoleucine epimerization in fossil planktonic foraminifera is strongly species-dependent. Alloisoleucine/isoleucine ratios of two species of the same age can vary by more than a factor of 2. This finding, in combination with the known temporal and spatial variability of foraminiferal assemblages, demonstrates the critical importance of basing geochronological studies of marine sediments on monospecific samples. One rapidly epimerizing species generates a calibration curve of potentially high precision for dating sediments between the ages of about 50,000 to 400,000 years.

Temporal changes in foraminiferal distributions in Miramichi River estuary, New Brunswick

Abstract: Distribution of foraminifera from surface sediments collected during September 1975 and February 1976 in Miramichi estuary are described and compared to similar data reported previously from the sa...

The stratigraphical zonation of the Albian sediments of north-west Europe, as based on foraminifera

Abstract: The previous zonation schemes for localised geographical areas within north-west Europe are reviewed. Individual sections as described by other workers are also incorporated into the proposed scheme. The new zonation scheme, which is predominantly applicable to the boreal realm, is directly correlative with the hoplitinid ammonite scheme. It is compared with the tethyan planktonic scheme of van Hinte (1976) . The new scheme uses the first appearance of selected species according to their abundance, associated assemblage and total range. It comprises nine zones and ten subzones: the zones being defined on foraminiferal assemblages with subzones on total stratigraphical range of individual species. Fifty-eight species are stratigraphically useful. Due to the rapid increase in diversity of foraminiferid species in the Upper Albian, the stratigraphical limits of individual zones and subzones are narrower and probably better here than the ammonite scheme. However, in the Lower and Middle Albian the ammonite scheme has greater refinement. In addition, cumulative percentage diagrams show the changes in benthonic foraminifera at superfamily level throughout the Albian. Also, the varying abundances of planktonic foraminifera are used not only for zonation, but as indicators of current circulation related to regional tectonism.

Cenozoic Foraminifera from the South Atlantic, DSDP Leg 36

Abstract: Cenozoic foraminifera occur in four sites drilled during Leg 36, one in the Drake Passage (Site 326), one in the Falkland Outer Basin (Site 328), and two on the eastern end of the Falkland Plateau (Sites 327 and 329). A calcareous section containing a well-preserved fauna was cored at Site 329. Planktonic foraminifera show that four Tertiary intervals were recovered, upper Paleocene-lower Eocene, Oligocene, lower Miocene, and upper Miocene. Some calcareous planktonics and benthonics are found in the Paleocene-lower Eocene of Site 327. The carbonate-free sediments of Site 328 only yielded an upper Cretaceous-lower Eocene arenaceous benthonic fauna. Planktonic species diversity and faunal composition at Site 329 indicate a progressive warming during the latest Paleocene culminating with the invasion of mid-latitude angular acarininids and keeled morozovellids. Species diversity of Oligocene assemblages is high relative to the latitudinal position of the site. Intense cooling is inferred from extreme low-diversity assemblages in the late Miocene with predominance of Globigerina bulloides. Four distinct benthonic assemblages occur in the Paleocene, lower Eocene, Oligocene, and upper Miocene. Comparison with low and mid-latitude assemblages from the South Atlantic suggests bathyal depth during the Paleocene. The remarkable stability of benthonic assemblages all through the Cenozoic with great similarities (on generic level) in faunal composition is a further indication for the absence of any substantial subsidence of the Falkland Plateau during the Cenozoic.

An estimate of the duration of the faunal change at the Cretaceous-Tertiary boundary

Abstract: A detailed analysis of sedimentation rates in the Upper Cretaceous–Paleocene section of pelagic limestones at Gubbio, Italy, based on the previously reported correlation of Gubbio magnetozones with the calibrated sequence of marine magnetic anomalies, suggests that the faunal overturn in planktonic foraminifera at the Cretaceous-Tertiary boundary may have happened rapidly, on the order of 10,000 yr or less.

Problems in Paleogene and Neogene correlations based on planktonic foraminifera

Abstract: Paleogene and Neogene world-wide distribution patterns of planktonic foraminifera are discussed. Differences in environmental conditions, mainly changing water temperatures, are regarded as the principal factors controlling the occurrence and distribution of individual species. Species associations caused by natural barriers, such as the Isthmus of Panama, may also develop at similar latitudes. Furthermore, anomalous distribution patterns, resulting from the exclusion of certain species at the expense of others are also known within the same area. As a result of all these differing species distributions numerous zonal schemes were proposed, some of which are herein shown on figures 1 and 6. Correlation problems that necessarily arise from this are discussed for a number of selected areas and sections. For the Paleogene, examples are discussed from the Caucausus-Crimea and eastern Mediterranean, where faunal differences are caused by climatic and facies changes. In the Neogene of the Caribbean-Atlantic and Indo-Pacific, different faunal developments and distribution patterns may occur at similar latitudes. A good example of temporary exclusion of certain species is found within the Caribbean, where during the presence of Globorotalia miocenica Palmer, G. exilis, and G. pertenuis Beard in the Middle Pliocene, Pulleniatina sp. and to a large degree also Globorotalia menardii (d'Orbigny) have disappeared, to return only after the extinction of the first named group of species. Problems in Paleogene and Neogene correlations based on planktonic foraminifera*

Comparison of Lower and Middle Cretaceous Palynostratigraphic Zonations in the Western North Atlantic

Abstract: Cretaceous palynomorph zonations, based respectively on the stratigraphy of dinoflagellate cysts and sporomorphs, are presented for six Deep Sea Drilling Project sites in the western North Atlantic. Eight dinoflagellate zones and four sporomorph zones are described from the reference section at site 105, which ranges in age from Berriasian (core 30) to Cenomanian (core 9). Published nannofossil and planktonic foraminifera studies of site 105 permit the direct comparison of part of the palynomorphic zonations with a published geochronological scale. The sporomorph zonation is compared with that published for the largely nonmarine Lower Cretaceous facies of the adjacent U. S. Atlantic coastal plain.

Long Distance Transport of Foraminiferal Tests by Wind in the Thar Desert, Northwest India

Abstract: In the Thar Desert, northwest India, aeolian sand grains were sampled from late Pleistocene dunes and the presence of marine Foraminifera was noted. The frequency of Foraminifera declines in a progressive fashion with distance from the sea, but they are found at least up to 800 km from the nearest point downwind on the coast. This indicates that Foraminifera have been susceptible to long distance transport by the wind, that the coast has been an important source area for the sands of the Thar Desert, and that the presence of Foraminifera in aeolian sediments does not necessarily imply former close proximity to the sea.

Vertical distribution of foraminifera in the Indian River, Florida

Abstract: In the Indian River, Florida, four cores were taken simultaneously from a subtidal flat consisting of silty sand. Each centimeter of each core was sampled to a depth of 10 cm. Ammonia beccarii, Elphidium mexicanum, and the total number of living individuals have significant differences in the mean number of individuals between depth, but not between cores. Quinqueloculina has a significant difference between cores, but not between depths. The data indicate abundant foraminifera occur to a depth of 6-7 cm. All species are positively correlated, and exhibit no vertical stratification.

Mesozoic Foraminifera – Western Atlantic

Abstract: Planktic foraminiferal zonal control of Upper Cretaceous sequences is provided by species of the genera Globotruncana, Marginotruncana, Rotalipora, Hedbergella, Rugotruncana, Archeoglobigerina, Abathomphalus , and Ventilabrella. Many of these species are tethyan so that recognition of tethyan biostrati-graphic zones is apparent for the most part. Other species, however, are strictly boreal. Consequently, a zonal framework for this region reflects tethyan and boreal water as they influenced the region during specific time intervals of the Cretaceous. Due to preservational factors a planktic zonation for the Lower Cretaceous is at present incomplete. Benthic foraminiferal assemblages are known from a few Lower Cretaceous and Upper Jurassic sections. They are sparse but apparently belong to shelf to abyssal facies. Upper Cretaceous assemblages occur in shelf, slope, and abyssal facies. Shelf assemblages include species of the genera Coryphostoma, Globulina, Guttulina, Gaudryina , and Gavelinella in addition to a number of lagenid species. Slope assemblages are characterized by species of the genera Gyroidinoides, Praebulimina, Pullenia, Osangularia, Gavelinella, Bolivinoides. Dorothia and others. A number of these species also occur in abyssal planktic oozes. Biostratigraphic control is rather general being useful for the recognition of state intervals. The Bolivinoides zonation is the one exception and it complements the planktic zonation in the Santonian, Campanian, and Maestrichtian.