Facies Evolution, Carbonate Dissolution Cycles in Sediments from the Eastern South Atlantic (DSDP Leg 40) Since the Early Cretaceous

Melguen, Marthe

doi:10.2973/dsdp.proc.40.129.1978

Cited by 19 publications

(32 citation statements)

References 25 publications

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“…Inasmuch as the CCD is commonly several hundred meters deeper than the lysocline (Berger, 1976), we conclude that the middle Miocene (11-13 m.y.) CCD should have been about 3 km deep at 30°S latitude, and our estimate confirms the conclusion reached by Melguen (1978).…”

Section: Variations Of Ccd and Of Foraminiferal Lysoclinessupporting

confidence: 91%

“…The temporal variations of the lysocline and of the CCD in the South Atlantic show the same general trends as observed previously by Van Andel et al (1977) and by Melguen (1978). Two peaks in the CCD have been identified; the CCD was very shallow during the middle Eocene and the middle Miocene.…”

Section: Variations Of Ccd and Of Foraminiferal Lysoclinessupporting

confidence: 84%

“…The occurrences of several layers of Oligocene Braarudosphaera chalk were first discovered in the South Atlantic during the Leg 3 cruise and were subsequently reported from the Indian oceans (Roth, 1974) and from the African Atlantic margin (Melguen, 1978). The chalk is remarkable because one or two species of Braarudosphaera dominate the nannoflora, and the chalk layers may attain considerable thickness (e.g., 20 cm at Site 522).…”

Section: Paleoecological Evolutionmentioning

confidence: 96%

“…Hay, 1970;Berger and Roth, 1975;Van Andel et al, 1977;and Melguen, 1978). Melguen (1978) attempted to explain the first-order changes by the same mechanism as the second-order changes, and related the first-order rises of the CCD to intensified activity in the AABW. If the paleodepth of the first appearance of the N. umbonifera fauna is any indication, however, the difference in the AABW activities is small.…”

Section: Cause Of Ccd Variationsmentioning

confidence: 99%

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South Atlantic Cenozoic Paleoceanography

Hsü¹,

McKenzie²,

Oberhänsli³

et al. 1984

Initial Reports of the Deep Sea Drilling Project

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Several suites of undisturbed cores obtained by continuous hydraulic piston coring provided material for the investigation of Cenozoic paleoceanography. The faunal record is complete, except for the early Eocene. The isotope records have gaps in the early Eocene and in the early and middle Miocene. Hundreds of samples were studied and thousands of analyses were carried out. Detailed results and conclusions are presented in several separate chapters of this volume. This report is a synthesis.Studies of calcite dissolution in pelagic sediments indicate that calcite compensation depth (CCD) and lysocline underwent two types of changes during the Cenozoic. The first-order changes, which have a periodicity of some I0 7 yr., have amplitudes (depth difference from the medium) of more than 1,000 m. The Eocene and Miocene were epochs of high CCD. The deepening of the CCD in the late Eocene and early Oligocene was stepwise, but it was more abrupt in the early Pliocene. We attribute the higher CCD in the Eocene and Miocene to a relatively low production rate of calcareous plankton in the open oceans; during those epochs many of the nutrients had been consumed by phosphate deposition and by siliceous plankton. The second-order changes, which have a periodicity of I0 4 or I0 5 yr., represent CCD variations in response to changes from interglacial to glacial paleoenvironments during the Pliocene and Quaternary; the amplitude was a few hundred meters only. Evidence suggests that increased dissolution due to the more active bottom waters during the glacial stages in the Atlantic far overshadowed the effect of possible increases in fertility.The oxygen-isotope record shows an overall increase of δ 18 θ values since the middle Eocene, with a moderate reversal of the general trend during the late Oligocene and early Miocene. Whereas the early Paleogene trend of the Atlantic middle-latitude sites closely simulated that of the southern oceans, vertical and latitudinal gradients began to develop in the Oligocene and continued to steepen with time, so that the present thermal structure of the ocean waters above our sites is similar to that of the equatorial Pacific. The cause of the increased δ 18 θ values should have been related to increased ice volume on Earth and to temperature declines. However, the relative importance of the two different factors at any given time cannot be ascertained. We favor the hypothesis that the Antarctic Ice Cap started to form in the late Eocene and suggest that the early Oligocene ice volume was larger than it is today. The middle Miocene oxygen shift has also been registered at one of our sites, but its magnitude is smaller, and the corresponding environmental changes should have been less impressive, than those in the late Eocene and early Oligocene.The carbon-isotope record shows a parallel trend between the planktonic and benthic foraminifers since the beginning of the Oligocene and a divergent trend as well as a steeper gradient during the middle Eocene. Peak values of δ 13 C are found in ...

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Section: Variations Of Ccd and Of Foraminiferal Lysoclinessupporting

confidence: 91%

Section: Variations Of Ccd and Of Foraminiferal Lysoclinessupporting

confidence: 84%

Section: Paleoecological Evolutionmentioning

confidence: 96%

Section: Cause Of Ccd Variationsmentioning

confidence: 99%

See 2 more Smart Citations

South Atlantic Cenozoic Paleoceanography

Hsü¹,

McKenzie²,

Oberhänsli³

et al. 1984

Initial Reports of the Deep Sea Drilling Project

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“…At Site 532, bottom sediments, which form the habitat of the benthic foraminifers, consist of marls dominated by: (1) terrigenous input deriving from the African continental margin, primarily from the embouchement of the Congo River; and (2) siliceous components produced in the fertile zone of the upwelling (Melguen, 1978). Leg 75 cores exuded significant amounts of biogenic gases on shipboard, attesting to bacterial activity and the high organic carbon contents (nearly 8%) of the sediments.…”

Section: Paleogeographic Settingmentioning

confidence: 99%

Pliocene Planktonic and Benthic Foraminifers from the Southeastern Atlantic Angola Margin: Leg 75, Site 532, Deep Sea Drilling Project

Boersma¹

1984

Initial Reports of the Deep Sea Drilling Project

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The evolution of Late Cretaceous deep‐ocean circulation in the Atlantic basins: Neodymium isotope evidence from South Atlantic drill sites for tectonic controls

Murphy

Thomas

2013

Geochem Geophys Geosyst

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The South Atlantic basins during the Late Cretaceous were characterized by overall expansion and the opening of deep‐water connections, eventually permitting deep‐ocean circulation with the Indian and North Atlantic basins. However, the evolving pattern of deep‐ocean circulation through the Late Cretaceous, particularly the timing of the connection between various basins, is not well constrained. Here we present new neodymium isotope data from five sites in the South Atlantic to reconstruct water mass chemistry and circulation patterns. The new data combined with previously published data indicate deep‐water formation occurred in the high‐latitude South Atlantic throughout the Late Cretaceous. Tectonic boundaries restricted the circulation of Southern Component Water until the opening of the Equatorial Atlantic Gateway and the subsidence of Rio Grande Rise between ∼79 and 75 Ma. Subsidence of these features permitted the northward flow of Southern Component Water, which then ventilated the deep North Atlantic. Nd isotope data indicate that the South Atlantic water column during the Cenomanian to Santonian was vertically stratified between intermediate and deep waters, with increased mixing evident during the Campanian and Maastrichtian.

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Facies Evolution, Carbonate Dissolution Cycles in Sediments from the Eastern South Atlantic (DSDP Leg 40) Since the Early Cretaceous

Cited by 19 publications

References 25 publications

South Atlantic Cenozoic Paleoceanography

South Atlantic Cenozoic Paleoceanography

Pliocene Planktonic and Benthic Foraminifers from the Southeastern Atlantic Angola Margin: Leg 75, Site 532, Deep Sea Drilling Project

The evolution of Late Cretaceous deep‐ocean circulation in the Atlantic basins: Neodymium isotope evidence from South Atlantic drill sites for tectonic controls

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