Fluctuation in the Past Rates of Carbonate Solution in Site 149: A Comparison with Other Ocean Basins and an Interpretation of Their Significance

Ramsey, A.T.S.; Schneidermann, Nahum; Finch, J.W.

doi:10.2973/dsdp.proc.15.122.1973

Cited by 6 publications

(4 citation statements)

References 8 publications

(9 reference statements)

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“…These studies show that discoasterids retain their identity better than all other genera during dissolution. Accordingly, Ramsay (1972Ramsay ( , 1977, and Ramsay et al (1973) suggested that the percentage of discoasterids in a given sample is an indicator of the intensity of the dissolution that the sample has undergone. Similarly, MacKenzie and Wise (1983) used the ratio of discoasterids to placoliths as a measure of dissolution.…”

Section: Taxonomic Methodsmentioning

confidence: 99%

Late Oligocene through Early Pleistocene Calcareous Nannofossils from Western Equatorial Indian Ocean (Leg 115)

Rio¹,

Fornaciari²,

Raffi³

1990

Proceedings of the Ocean Drilling Program

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The chronostratigraphy, the calcareous nannofossil biochronology, and the biostratigraphy of the Miocene and Pliocene sediments retrieved during Leg 115 in the equatorial western Indian Ocean are presented and discussed. Most of the zonal boundaries of the standard 1971 zonation of Martini and the 1973 zonation of Bukry are easily recognized in these low-latitude sediments. We also comment on the secondary events that are proposed in the literature to improve the biostratigraphic resolution provided by the standard zonations.The study of calcareous nannofossil biostratigraphy and taphonomy of sequences from the Northern Mascarene Plateau area, which was drilled to investigate the Neogene history of carbonate flux and dissolution, indicate that the accumulation of carbonates in this area results from a complex interplay among carbonate bioproductivity, carbonate removal by chemical dissolution and mechanical erosion, and carbonate addition by mass and current transport. In spite of these drawbacks, major changes and trends in carbonate accumulation can be recognized, most of which, if not all, correlate with major steps in the evolution of the Neogene climatic system.

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Section: Taxonomic Methodsmentioning

confidence: 99%

Late Oligocene through Early Pleistocene Calcareous Nannofossils from Western Equatorial Indian Ocean (Leg 115)

Rio¹,

Fornaciari²,

Raffi³

1990

Proceedings of the Ocean Drilling Program

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“…This scheme allows us to generate a quantitative estimation of dissolution similar to the one proposed by Dean et al (1981). Moreover, assuming that dissolution should increase the relative abundance of the more resistant forms, such as the asteroliths (Ramsay, 1972(Ramsay, , 1977Ramsay et al, 1973 Figure 11. Pseudoemiliania lacunosa accumulation rates at Sites 849 and 852 between 4 and 2 Ma.…”

Section: Nannofossil Preservation and Reworkingmentioning

confidence: 97%

Evolution of the Calcareous Nannofossil Assemblage as a Response to the Paleoceanographic Changes in the Eastern Equatorial Pacific Ocean from 4 to 2 Ma (Leg 138, Sites 849 and 852)

Flores¹,

Sierro²,

Raffi³

1995

Proceedings of the Ocean Drilling Program, 138 Scientific Results

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Variations in the accumulation rate and preservation of late Pliocene calcareous nannofossils from the eastern equatorial Pacific Ocean are studied. Increases in the accumulation rate of nannofossils, are related to changes in paleoproductivity which in turn are linked to paleoceanographic change. Maxima in fluxes of nannofossils observed from 3.50 to 3.40 and 3.10 to 2.65 Ma are interpreted as periods of high paleoproductivity. The nannofossil accumulation rate at Site 849, an area of oceanic divergence, on average is 10 times higher than that recorded at Site 852 (convergence area). Moreover, dissolution intensity is greater at Site 852. Times of greater dissolution at Site 852, characterized by high percentages of asteroliths, generally coincide with times of lower nannofossil accumulation rates at Site 849. Therefore, we assume that productivity and dissolution may be inversely related because the carbonate compensation depth (CCD) and the lysocline are deeper in the equatorial divergence region as a result of the higher carbonate supply in this region. The accumulation rate of asteroliths have a similar rank in both sites, allowing us to conclude that this group is relatively more abundant in the region of lower productivity, whereas it has been diluted in the higher productivity area. Aremarkable event is identified at 3.20 Ma in both sites. The reentry of the cool water species Coccolithus pelagicus coincides with a shoaling of the CCD, which may indicate a major paleoceanographic change in the eastern equatorial Pacific Ocean. Northward and southward currents may have been established or intensified at this age, introducing cool elements in the nannofossil assemblage at the same time that the Atlantic-Pacific connection become restricted through the Panamanian Corridor. The accumulation rate of Pseudoemiliania lacunosa follows a similar trend as that of C. pelagicus. Its high fluxes during globally recognized cool periods lead us to infer that it is linked to low-temperature surface waters. Between 4 and 2 Ma, a similar pattern of nannofossil accumulation rates is observed in the divergence and convergence areas, suggesting that a general model explains any variations in eastern equatorial Pacific Ocean.

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“…In this interval, we could not detect T A. amplificus. Because discoasterids are considered a solution-resistant form of nannofossil (Ramsay, 1972(Ramsay, , 1977Ramsay et al, 1973), we expected their abundance to increase in the dissolved assemblages encountered in the upper Miocene (i.e., the upper part of Core 138-845A-13H, just above a barren interval; Fig. 4).…”

Section: Site 845mentioning

confidence: 99%

Pleistocene through Miocene Calcareous Nannofossils from Eastern Equatorial Pacific Ocean (Leg 138)

Raffi¹,

Flores²

1995

Proceedings of the Ocean Drilling Program, 138 Scientific Results

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The calcareous nannofossil biostratigraphy of the sediments retrieved during Leg 138 in the eastern equatorial Pacific Ocean is presented and discussed. The sedimentary sequences stidoed, at 10 of the 11 sites drilled, span the stratigraphic interval from Pleistocene to upper (Sites 847 and 848) and middle Miocene (Sites 851, 852, and 853), and three extend to the upper part of the lower Miocene (Sites 844, 845, and 846). Most of the zonal boundaries of the 1973 zonation of Bukry and standard 1971 zonation of Martini are recognized and used for the biostratigraphic classification of these low-latitude sediments. Additional biostratigraphic events are discussed and in some intervals are used as secondary criteria for improving the biostratigraphic resolution. A further subdivision of upper Miocene Subzone CN9b of Okada and Bukry (1980) is proposed using the lowest and highest occurrences of Amaurolithus amplificus. Comments on the biochronology of calcareous nannofossils are given, with special reference to Miocene events, taking advantage of the very good magnetostratigraphy and orbitally tuned time scale produced for the Leg 138 sites. CNsl5 CN14b CN14a(?) CN13b(?)

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Fluctuation in the Past Rates of Carbonate Solution in Site 149: A Comparison with Other Ocean Basins and an Interpretation of Their Significance

Cited by 6 publications

References 8 publications

Late Oligocene through Early Pleistocene Calcareous Nannofossils from Western Equatorial Indian Ocean (Leg 115)

Late Oligocene through Early Pleistocene Calcareous Nannofossils from Western Equatorial Indian Ocean (Leg 115)

Evolution of the Calcareous Nannofossil Assemblage as a Response to the Paleoceanographic Changes in the Eastern Equatorial Pacific Ocean from 4 to 2 Ma (Leg 138, Sites 849 and 852)

Pleistocene through Miocene Calcareous Nannofossils from Eastern Equatorial Pacific Ocean (Leg 138)

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