INTERPRETATION OF PISTON CORE T-101, (32°05'S; 47°35'W) WITH CALCAREOUS NANNOFOSSILS-RIO GRANDE CONE, RIO GRANDE DO SUL, BRAZIL The present paper refers to the study of the calcareous nannofossils of the piston core T-101, placed in the Rio Grande do Sul Continental Elevation, latitude 32°05'S and longitude 47°35'W. The piston core presents 670cm of length and was obtained in a depth of 3.200m in the Rio Grande Cone area, during the accomplishment of the oceanography campaign GEOMAR VII, 1976. The analysis of these microfossils shows that they do not have a sequential distribution along the piston core, occurring concentrated at 670cm, 620cm and 580cm of the base and at 15cm of the top. Through the taxonomic identification of these microfossils, reworked material was detected in the base of the piston core mixing the early Pleistocene species with the Pliocene species. In the top, exist an assemblage of late Pleistocene. In the interval 580-15cm, calcareous nannofossils doesn't exist. Palaeoecologic and palaeoenvironmental inferences were presented. As the same time, took place the correlation of the top of the Zone Calcidiscus macintyrei of Gartner, 1977 of lower Pleistocene with the medium part of the magnetostratigraphic Matuyama unit and of the Zone Emiliania huxleyi of Gartner, 1977 with the superior part of the Brunhes unit.
The analyses of five piston cores (SG91-09/PC-01, SG91-14/PC-04, SG91-14/PC-06, SG91-14/PC08 e SG91- 14/PC09) sampled on Campos Basin - RJ, Brazil, permitted the systematic studies in Quaternary calcareous nannofossils and the description of the primary diagenesis effects on this microfossils using optical microscope and scanning electron microscope. The observation of “in situ” dissolution and reprecipitation of calcium carbonate recorded limitate the systematic studies of calcareous nannofossils and show the importance to use both optical and scaning microscope.
O estudo sobre os nanofósseis calcários do testemunho 43, localizado no Banco Maurice Ewing, Antártica, possibilitou o reconhecimento do taxon endêmico Chiasmolithus altus Bukry & Percival, 1971, exclusivo da região austral e do taxon cosmopolita Emiliania huxleyi (Lohmann, 1902) Hay & Mohler, 1967. Ao mesmo tempo foram reconhecidas parte de duas zonas bioestratigráficas: a Zona Chiasmolithus altus de Wise Jr., 1983 (Oligoceno inferior, parte superior) e a Zona Emiliania huxleyi de Wise Jr. & Wind, 1977 (Holoceno) e apresentada a distribuição dos taxa identificados através destas zonas. A grande quantidade de escudos distais de placolitos encontrados nos sedimentos correspondentes à Zona Chiasmolithus altus, e que caracterizam a zona mesolítica (uma subdivisão da Zona de profundidade de compensação da calcita), permitiu inferir que os mesmo foram depositados logo acima da lisóclina. Foi proposta uma correlação de parte da Zona Chiasmolithus altus de Wise Jr., 1983 com a Zona Sphenolithus distentus (base) e a Zona Sphenolithus ciperoensis (topo) de Burkry, 1973 correspondentes ao Oligoceno inferior (parte superior). Foram detectadas evidências de dissolução e indícios do clima frio, durante o Oligoceno, que afetaram mais a assembleia localizada na base do testemunho 43 do que a assembleia do topo, comprometendo o estado de preservação dos nanofósseis calcários. Foi observada, da mesma forma, a baixa diversidade das espécies nas duas assembleias analisadas.
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