Showing papers on "Foraminifera published in 1984"

Cenozoic marine sedimentation and ice-volume variation on the East Antarctic craton

Abstract: Recycled Cretaceous and Cenozoic marine microfossils have been recovered from samples of the Pliocene Sinus Formation. Samples were collected from outcrops in the Reedy, Beardmore, and Ferrar glacier areas of the Transantarctic Mountains between lat 77° and 86°S. The glaciogene sediments contained diatoms, foraminifera, calcareous nannoplankton, silicoflagellates, radiolarians, sponge spicules, palynomorphs, and ostracodes of Late Cretaceous, Paleocene, Eocene, late Oligocene, late Miocene, and Pliocene age. This suggests the presence of open marine basins on the East Antarctic craton during late Mesozoic and Cenozoic time. The apparent absence of early Oligocene and early through middle and earliest late Miocene assemblages suggests either that marine regression exposed the basin floors or that ice filled the basins during these times. The high-elevation setting of Sirius Formation outcrops suggests one of two hypotheses for their origin: (1) They are in situ Pliocene glaciomarine deposits that were uplifted 1,750–2,500 m with the Transantarctic Mountains to their present elevation; (2) the Sirius Formation deposits are a mixture of derived sediments stripped from sub-ice intracratonic basins and subsequently redeposited by ice flowing up the inland slope of the Transantarctic Mountains. We favor the second hypothesis, with transport to sites sometime within the past 3 m.y.

Radiocarbon measurements on coexisting benthic and planktic foraminifera shells: potential for reconstructing ocean ventilation times over the past 20 000 years

Abstract: In this paper the potential of AMS 14C dating of shells handpicked from deep sea sediments is explored. We show that while the age difference between planktonic (surface dwelling) and benthic (bottom dwelling) shells must carry information regarding paleocirculation rates, this message is likely obscured by effects associated with the coupling between bioturbation and dissolution and between bioturbation and abundance change. It is also possible that the 14C/12C ratio in planktonic shells was initially not identical to that in surface water and that the 14C/12C ratio in benthic shells was initially not identical to that in bottom water. These and other biases will plague all attempts to extract the desired information regarding circulation rate changes over the last 20000 years. However in sorting them out, much will be learned about the origin and history of the calcite particles found in deep sea sediments.

Sources of Periplatform Carbonates: Northwest Providence Channel, Bahamas

Abstract: Sources and quantities of periplatform carbonate sediments have been determined in Northwest Providence Channel, Bahamas, by an end-member method employing geochemical, textural, petrographic, and SEM data. The Holocene sediment over most of this open seaway, 200 to 2,000 m deep, between Great Bahama Bank and Little Bahama Bank, is a drape of largely fine grained lime mud 50 cm thick. Shallow platform sources contribute 75-90 percent; the remainder is planktonic foraminifera, pteropods, and coccoliths. Mud (< 62 µm) from each bank and the planktonic source are each geochemically distinct and can be quantified. The two shallow platform sources dominate sedimentation in the deep basin. Trend-surface maps of mud derived from each bank reveal no windward-leeward asymmetry in cont ast to reported sand-transport patterns. This indicates that the fines are swept off both platforms by storm and tidal exchange. Concentric distribution of fines relative to source indicates no offset by currents, suggesting that fecal pelleting must rapidly remove fine sediment from the water column. Canyon valleys and intercanyon highs have equal thicknesses of Holocene sediment, which indicates that pelagic processes of deposition presently dominate over gravity-flow processes. Confirmation of this depositional process is that the deposition rate increased from 2 cm/1,000 years to 10 cm/1,000 years when postglacial sea level flooded the bank tops. Thus 80 percent of the present sedimentation rate results from bank-top contribution. Furthermore, the calculated mass of mud traceable to Little Bahama Bank agrees excellently with the independent estimate of overproduction there. In cores, bank sediments resulting from the most recent sea-level highstand sharply overlie planktonic sediments, writing a sea-level history in alternating stable and unstable mineral suites.

Microbial endoliths: a benthic overprint in the sedimentary record, and a paleobathymetric cross-reference with foraminifera

Abstract: Microbial endoliths occur commonly in tests of planktonic and benthic foraminifera, as in other types of skeletal and non-skeletal carbonate substrates in marine sediments. The modem sediments considered in this study were deposited in depths ranging from 200 to more than 4,000 meters. Microbial boring is a strictly benthic activity which afflicts carbonate particles after they have settled at the sediment/water interface. The trace-fossil record of microbial boring is thus a benthic overprint on the carbonate sedimentary record, regardless of its composition. A new morphologically characteristic endolith was found only in deep water sediments (between 2,000 and 4,000 m depths). Other modem heterotrophic endoliths appear to be less restricted in their depth distribution. There is no apparent correlation of occurrence between particular endolithic and foraminiferal taxa, indicating that the relationship is not a host-parasite one, and that any nutrient requirement by the heterotrophic endolith taxa studied is not specific for the organic product of any particular foraminiferal species. Some endolith species and assemblages of species are persistent through geological time (Cretaceous-Recent, Oligocene-Recent). As both microbial endoliths and their host substrates, the benthic foraminifera, have independent depth distributions, their co-occurrence provides a basis for a more refined cross-reference for paleobathymetric in-

End-cretaceous brachiopod extinctions in the chalk of denmark.

Abstract: The results of a detailed study of the brachiopods of the most complete Cretaceous-Tertiary boundary in Denmark, Nye Kl∅v, show an extinction pattern for this marine invertebrate group compatible with that reported for pelagic foraminifera and coccoliths and with the impact scenario. The extinction is abrupt, coinciding with the Maastrichtian-Danian boundary. There is no warning in the form of decreasing density, decreasing diversity, or early extinction of specialized groups. The basal few meters of the Danian are almost devoid of brachiopods, and a Danian brachiopod fauna starts almost as abruptly as the Maastrichtian fauna disappeared. The new fauna is similar to the Maastrichtian as regards density and diversity, and at maximum six species are common to both stages. The northwest European Masstrichtian chalk is composed mainly of the remains of coccoliths and pelagic foraminifera. The mass extinction of these groups led to a total cessation of chalk production. The chalk is overlain by a thin clay bed deposited partly under anoxic conditions. This combination of anoxia and clay deposition coupled with a cessation of productivity led to the extinction of specialized groups such as the chalk brachiopods. The surviving species included forms that could survive in well-aerated shallow marine waters on substrates other than chalk.

Benthic foraminifera as pollution indices in the marine environment of west coast of india

Abstract: Two ecosystems affected by acidic pollutants (Thana Creek, Bombay and inshore area of Trivandrum, Kerala) and two other ecosystems affected by alkaline pollutants (Cola Bay, Goa and inshore area of Karwar, Karnataka) were studied for pollution effects monitoring through Foraminifera. In the Thana Creek area, Bombay, the magnitude of corrosive effect, lower—than—normal ornamentation, deepening of grooves and sutural thickenings, enlargement of pores, widening of apertures in Foraminifera were taken as indices of pollution effect. In the, Cola bay area, Goa, the environment becomes hypertrophic resulting in large—sized, robust, mostly megalospheric forms of Ammonia. Elphidium and Florilus scaphum are recorded at the proximal zone near the discharge point; miliolids in the transitional zone and dominantly smaller—sized Nonionella, Fursenkoina pontoni, Bulimina marginata at the distal zone quite far from thc discharge point where pollutants are diluted and dissipated. In the Karwar area, Karnataka, pollutant causes reduced diversity with a decrease in foraminiferal population. Moreover, there is a reduction in size followed by test wall thinning in Nonion and Ammonia, increase of agglutinated forms near shore, and dispersal and dilution of the pollutants resulting in foraminiferal abundance. In the Trivandrum area, Kerala, the effluent effect presents morphological anomalies (Operculina, Cibicides), erosion along peripheries, induced growth in last few chambers, inferred dissolution and consequent destruction of small, thin—walled forms suggested by their absence, thus leaving only the larger ones in the entire area. Living/dead ratio is negatively oriented at all sites.

The impacts of bioturbation on the age difference between benthic and planktonic foraminifera in deep sea sediments

Abstract: Accelerator mass spectrometry offers for the first time the opportunity to date hand picked planktonic (surface dwelling) and benthic (bottom dwelling) foraminifera from deep sea cores. This opens up the possibility to reconstruct temporal changes in the rate of deep ocean ventilation. There is, however, a serious problem in interpreting such results. Bioturbation of the “soil” zone in the upper sediment has two subtle influences which lead to biases in the results. One has to do with changes with time in the abundances of the forams in newly deposited sediment. The other has to do with dissolution effects on the forams during their residence within the bioturbated layer. Mixing models are presented in this paper which illustrate the effects of these interactions on the 14 C age difference between benthic and planktonic species.

A Middle Permian calcisponge/algal/cement reef: Straža near bled, Slovenia

Abstract: Siddle Permian reef limestones exposed at the localities of the Straza quarry, Straza Hill and Bohinjska Bela near Bled (northwestern Slovenia) have been studied with respect to microfacies and paleontological criteria.

Amino acid epimerization implies rapid sedimentation rates in Arctic Ocean cores

Abstract: The palaeooceanography of the Arctic Ocean is less well known than any other ocean basin, due to difficulties in obtaining cores and in providing a secure chronological framework for those cores that have been raised. Most recent investigators have suggested that low sedimentation rates (0.05–0.1 cm kyr−1) have characterized the deep basins over the past 5 Myr (refs 1,2) despite the glacial–marine character of the sediment and proximity to major centres of shelf glaciation. These calculations have been primarily based on the down-core pattern in the inclination of magnetic minerals, supported by uranium-series, 14C and micropalaeontological evidence. Here we analyse amino acid diagnesis in foraminifera from two gravity cores raised from the floor of the Arctic Ocean, our results suggest that these cores span <200 kyr., conflicting with the earlier estimate of 3 Myr based on palaeomagnetic data. The chronology of other Arctic Ocean cores and previous palaeoenvironmental interpretations need re-evaluation.

Species duration and evolution: benthic foraminifera on the atlantic continental margin of north america.

Abstract: Average species durations were estimated for 131 commonly occurring modern species. The duration of species occurring at depths of less than 200 meters is 16 million years, while for those at greater than 200 meters and at all depths it is 25 to 26 million years. Species (less than 200 meters) distributed from Florida to Newfoundland and from Florida to Cape Hatteras have about the same durations (18 to 20 million years). The duration for species restricted to north of Cape Hatteras is only 7 million years. The data suggest that evolutionary rates are greater in shallower than in deeper depths and greatest in the shallower northern area.

Development of algal‐foraminiferal‐coral reefs in the Lower Carboniferous of Furness, northwest England

Abstract: Most carbonate buildups of Dinantian age are mud-mounds lacking direct evidence of abundant framework organisms. This contribution describes apparently unique structures containing abundant framebuilding organisms interpreted as true reefs. They occur in the Red Hill Oolite, part of the Carboniferous Limestone succession in the Furness area of northwest England. Reefs were initiated by the attachment of numerous Syringopora colonies to a firm substrate. Encrusting organisms, dominantly the supposed foraminifcr Aphralysia, colonised sediment and corallite surfaces leading to the development of a rigid framework. Thrombolites also assisted in the establishment of bindstone textures. During the later stages of reef growth, Syringopora became less common and its place in the reef was taken by upright, branching growths of solenoporoid algae. Rapid sedimentation and subsidence resulted in reefs with near vertical sides, but little topographic expression on the sea-floor during growth. The occurrence of these reefs cannot be attributed to any single environmental factor but probably resulted from an unusual combination of favourable circumstances. D Calcareous algae, Carboniferous, corals, Dinantian, foraminifera, reefs, thrombolites.

Lower pleistocene dinoflagellate cyst, foraminiferal and pollen assemblages in four boreholes in the Southern North Sea

Abstract: Neogene and Lower Pleistocene stratigraphy in the Southern North Sea has been investigated in four I.G.S. boreholes between East Anglia and the Netherlands. The foraminifera of the Red Crag Formation in Borehole 81/51 are closely similar to Upper Pliocene assemblages in Holland. The overlying succession is clearly punctuated by unconformities in seismic profiles, separating four early Pleistocene formations in the boreholes, and indicating intervals of significant stratigraphic hiatus offshore. The Westkapelle Ground and Smith's Knoll Formations correlate with Thurnian and Antian Stage deposits in East Anglia. Pollen spectra in the Winterton Shoal and Yarmouth Roads Formations are similar to Baventian and Bramertonian assemblages in Britain. The autochthonous marine and allochthonous terrestrial microfauna and flora provide conflicting evidence of early Pleistocene palaeoclimate. The dinoflagellate cysts and foraminifera indicate that each formation was deposited in a warm temperate neritic environment. The pollen record, containing evidence of fluctuation between boreal and mixed coniferous–deciduous regional forest cover, suggests alternation between cool and warm temperate palaeoclimate.

Palaeoclimate of Baffin Bay from 300,000-year record of foraminifera, dinoflagellates and pollen

Abstract: Several different models1–5 have attempted to relate Quaternary marine and terrestrial records of ice-sheet growth in the North Atlantic region. The models are derived from either discontinuous terrestrial records, including marine fossils in raised shorelines1,2, or from deep-sea calcareous microfossils3,4. This study correlates Arctic marine and terrestrial data directly by comparing δ18O, foraminiferal, dinoflagellate and pollen records from a core taken in Baffin Bay. The core contains an almost continuous sequence of sediments deposited during isotope stages 1–10. Subarctic foraminifera and Atlantic dinoflagellates in early isotope stages 2, 4, 6 and 8 show that subarctic water entered southern Baffin Bay before the glacial maxima. Boreal–subarctic pollen suggest that Atlantic air flowed into Baffin Bay during the ice sheet growth phases. These data support models which postulate that open water in the Labrador Sea had an important role in supplying moisture to Laurentide and Greenland ice sheets.

Sessile invertebrate coelobite communities from reefs of Bermuda: Species composition and distribution

Abstract: Sessile invertebrate coelobite communities attached to the walls and roof of cavities in coralgal reefs on the annular rim of the Bermuda platform near North Rock (4 sites) and in the algal cup reef tract on the south shore (3 sites) have been studied by belt photo-transects and direct sampling. Irradiance measurements reveal a light gradient which appears to exert a strong influence on the composition, relative coverage and zonation of the attached biotic communities. Two main communities are recognised from cluster analysis and relative areal coverage data. Near the cavity entrances is a community dominated by crustose coralline algae, with subsidiary ascidians, demosponges, bryozoans and Foraminifera. Species richness is high and there is total biotic coverage of walls and roof. This community grades laterally into an exclusively animal community characterised by encrusting sponges and Foraminifera, with subsidiary bryozoans and unidentified branching organisms. Coverage varies from 100% to 30%, the substrate often exhibiting high micro-relief from the branching growth forms of the Foraminifera. Species richness is high at North Rock sites, less so on the south shore. The distribution of coelobite species is compared with that described from previous studies in Bermuda, Grand Cayman and Madagascar.

A Tertiary-Quaternary section at Sarsbukta, Spitsbergen, Svalbard, and its foraminifera

Abstract: Tertiary and Quaternary deposits outcrop in the coastal cliff of Balanusviken at Sarsbukta in Vest- Spitsbergen. The Tertiary deposits appear by their foraminifera to belong to the Middle to Upper Oligocene. The Quaternary deposits consist of an upper part of Late Pleistocene to Holocene age, and a lower part which had previously been considered Middle Weichselian of age. Its foraminiferal assemblages suggest a higher age (Late Saalian, Eemian?). This lower part of the Quaternary deposits is related to a series of raised beaches with an upper limit at 50 m above present day sea level. They were probably formed during the Eemian, and have not been distorted by later glaciation. The present study is based on sediment samples collected from the coastal cliff of Balanusviken, and particularly from that of Balanuspynten, Sarsbukta, Spitsbergen, during the summer expedition of Norsk Polarinstitutt in 1950.