69 resultados para Paleoecology.


Relevância:

10.00% 10.00%

Publicador:

Relevância:

10.00% 10.00%

Publicador:

Resumo:

Benthic foraminifers were examined from the Paleogene of Ocean Drilling Program (ODP) Site 647 and Deep Sea Drilling Program (DSDP) Site 112 in the southern Labrador Sea. The Paleogene sequence of the deep Labrador Sea can be subdivided into seven assemblages, based on the ranges and relative abundance of characteristic taxa. The first occurrences (FOs) and last occurrences (LOs) of important benthic taxa are calibrated to a standard biochronology, by interpolating from our age model for Site 647. The biostratigraphy of Site 647 is used to improve the age estimates of Site112 cores. Fifteen microfossil events in Site 647 also are found in the sedimentary wedge along the Labrador Margin. A comparison of the probabilistic microfossil sequence from the Labrador Margin with that at Site 647 yields four isochronous benthic foraminifer LOs. Two new species are described from Sites 647 and 112: Hyperammina kenmilleri, Kaminski n.sp., and Ammodiscus nagyi Kaminski n.sp. Significant faunal turnovers are observed at the Ypresian/Lutetian and Eocene/Oligocene boundaries. The Ypresian/Lutetian boundary is characterized by a Glomospira-facies and is attributed to a rise in the CCD (carbonate compensation depth) associated with the NP14 lowstand in sea level. The Eocene/Oligocene boundary is delimited by the LO of Spiroplectammina spectabilis and Reticulophragmium amplectens. The change from an Eocene agglutinated assemblageto a predominantly calcareous assemblage in the early Oligocene took place gradually, over a period of about 4 Ma, but the rate of change accelerated near the boundary. This faunal turnover is attributed to changes in the preservationof agglutinated foraminifers, as delicate species disappeared first. Increasingly poorer preservation of agglutinated foraminifers in the late Eocene to earliest Oligocene reflects the first appearance of cool, nutrient-poor deep water in the southern Labrador Sea. The approximately coeval disappearance of agglutinated assemblages along the Labrador Margin was caused by a regional trend from slope to shelf environments, accentuated by the 'mid'-Oligocene lowstand in sea level.

Relevância:

10.00% 10.00%

Publicador:

Resumo:

Two hydraulic piston cores containing the total Quaternary suite were analyzed quantitatively in their planktonic foraminiferal contents. For the Early Pleistocene, the Caribbean standard zonation (BOLLI & PREMOLI-SILVA) can be adopted and refined by the introduction of an additional subzone at its base (the Globorotalia triangula subzone). Local substages are proposed for the Late Pleistocene because index fossils are missing. The use of the transfer-function technique resulted in paleotemperature and paleosalinity curves with a time resolution of cycles of about 4-68,000 years duration. The Early Pleistocene paleoenvironment is characterized by low oscillations of the surface water temperatures, followed by a distinct cooling trend during the Globorotalia viola subzone, a period of smoothed cycles during the Globorotalia hessi subzone and distinctly developed cycles during the late Pleistocene since the oxygen isotope termination III. Grainsize distribution and several dissolution indices gave evidence for current activities on the top of the Walvis Ridge, where the amount of fine grained components in the sediment is reduced in comparison with that of the flanks.

Relevância:

10.00% 10.00%

Publicador:

Resumo:

An original method of paleotemperature analysis on planktonic foraminifera is substantiated and actively used for stratigraphy of bottom sediments and paleoceanologic reconstructions. On the base of this method, as well as on lithological, geochemical, and oxygen isotope data, radiocarbon dating, constructions of other investigators, etc., the main features of dynamic Quaternary paleoceanology of the Atlantic Ocean is reconstructed. It is discussed in the context of global paleogeography. Paleotemperature field, climatic zonation, paleoecology of foraminifera, position of the main water masses, water fronts, currents, distribution of sea ice boundaries, upwelling activity, benthic circulation, processes of sedimentation are econstructed and analyzed.

Relevância:

10.00% 10.00%

Publicador:

Resumo:

This synthesis dataset contains records of freshwater peat and lake sediments from continental shelves and coastal areas. Information included is site location (when available), thickness and description of terrestrial sediments as well as underlying and overlying sediments, dates (when available), and references.

Relevância:

10.00% 10.00%

Publicador:

Resumo:

Mid-Cretaceous sediments recovered during Ocean Drilling Program Leg 183 (Cores 183-1138A-69R to 73R) on the central Kerguelen Plateau have been analyzed palynologically and paleobotanically to determine the age of the strata and to reconstruct vegetational development and paleoecology. The lower strata (Cores 183-1138A-71R to 73R), a dark, organic-rich silty claystone with many wood fragments and fern remains (sedimentary Unit VI), certainly of terrestrial origin, directly overlies the volcanic basement, which is dated as latest Albian (~95 to 103 Ma) to earliest Cenomanian. The age of the terrestrial strata can be determined by sporomorphs as late Albian to earliest Cenomanian as well. This shows that parts of the central Kerguelen Plateau must have been subaerial at least until the late Albian and were covered with a diverse high-latitude flora, probably dense conifer forest with various fern taxa in the undergrowth. Early angiosperms are also present. The vegetational character represented in Unit VI did not change significantly through time. However, varying percentages of several sporomorph groups seem to show recurring abundance variations, which might possibly be cyclic, caused by Milankovitch-type cyclic events. Cores 183-1138A-67R through 69R, of open marine origin, contain medium- to high-diversity dinocyst assemblages. Based on previous stratigraphic zonation schemes, the ages of these strata range within the Heterosphaeridium Superzone, from the Palaeohystrichophora infusorioides Zone to the Conosphaeridium striatoconus Zone, which correlates to the latest Cenomanian to Coniacian.

Relevância:

10.00% 10.00%

Publicador: