Vema Channel paleo-oceanography: Pleistocene dissolution cycles and episodic bottom water flow

Johnson, David A.; Ledbetter, Michael T.; Burckle, Lloyd H.

doi:10.1016/0025-3227(77)90079-2

Cited by 82 publications

(31 citation statements)

References 17 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

Section: Background and Objectivesmentioning

confidence: 99%

“…The upper part of the sediment pile was expected to include sediment eroded from the Vema Channel area and regions much farther south, then entrained in AABW flow and transported northward Le Pichon et al., 1971). Fluctuations in the strength and volume of AABW flow should relate to global climatic changes; and they should be represented in the sediments by changes in accumulation rate, depositional fabric, carbonate content, the proportion of reworked sediment (including volcanic and other terrigenous debris, and microfossils), and grain size (Johnson et al, 1977;Ellwood and Ledbetter, 1977).A consensus is developing that deep thermohaline convection began in the latest Eocene or earliest Oligocene and was responsible for greatly invigorating the oceanic thermohaline circulation (Benson, 1975;Savin et al, 1975;Kennett and Shackleton, 1976). Even if this is true for high southern latitudes, the northward movement of AABW into the Brazil Basin may have been delayed until much later by the presence of topographic barriers in the Falkland/Scotia Arc complex or in the Vema Channel itself.…”

mentioning

confidence: 99%

See 1 more Smart Citation

Site 515: Brazil Basin

Barker¹,

Carlson²,

Johnson³

1983

Initial Reports of the Deep Sea Drilling Project

View full text Add to dashboard Cite

.10Depth sub-bottom (m): 636.4 Nature: Zeolite-rich calcareous mudstone Age: early Eocene Measured velocity (km/s): 1.87 to 2.14 Principal results: Hole 515 was rotary drilled and washed to 55 m, but the drilling was terminated when the pressure core barrel jammed in the bottom-hole assembly. In Hole 515A, the hydraulic piston corer (HPC) was used to core to 107.9 m, with 89% recovery. Hole 515B was washed to 94.9 m, rotary drilled to 636.4 m, with 79% recovery. The lithologic section is divided into three lithologic units. 351 m of dark greenish gray biosiliceous mud and mudstone of middle Miocene to late Oligocene age with occasional nannoplankton-rich and rare foraminifer-rich horizons. Subunit 2b contains 84 m of dark greenish gray terrigenous mudstone of late Oligocene age, with only traces of siliceous micro fossils and evidence of silica diagenesis. Unit 3 is 20 m (minimum) of lower Eocene greenish gray calcareous zeolitic mudstone.Site 515 was chosen to study the onset and variability of the flow of Antarctic Bottom Water (AABW) through the Vema Channel into the Brazil Basin. The 22 Ma hiatus between Subunits 2b and 3 includes the Eocene/Oligocene boundary, which might correspond with the onset of AABW production. The lithologic boundary between Subunit 2b and Unit 3 corresponds precisely to a sharp and strongly discordant acoustic reflector, which extends throughout the Brazil Basin. The overlying sediments of Units 1 and 2 are fine grained.Early Eocene. Pelagic carbonates accumulated at normal rates of approximately 4 m/Ma during the early Eocene (Cores 515B-56 and 515B-57). Core 515B-56 grades upward from a pelagic carbonate to a dissolution facies consisting of a zeolitic clay with detrital mineral grains. The core contains thin laminations and cross laminations and a weak magnetic grain fabric aligned in a northnortheast direction, all evidence of active bottom currents beginning in the early Eocene.Early Oligocene to middle Miocene. Biosiliceous and terrigenous mudstones accumulated rapidly (approximately 40 m/Ma). Considerable amounts of detrital minerals and intermittent laminated intervals indicate persistent bottom-current activity. The cessation of siliceous sedimentation during the middle Miocene is an oceanwide event in the tropical and temperate Atlantic and reflects a major threshold event of paleocirculation. That event is probably related to the widening of Drake Passage and consequent deepening of the eastward circumpolar flow, which may in turn have shifted the South Atlantic circulation from a pattern of meridional flow to one of zonal flow. The initiation of strong eastward circumpolar flow may have blocked the entry of cold and productive Antarctic and sub-Antarctic waters into the South and central Atlantic, and siliceous sedimentation abruptly ceased in the lower and middle latitudes.Middle Miocene to middle Pleistocene. Terrigenous mudstones and intermittent layers of biogenic carbonate accumulated at rates of about 20 m/Ma. Absence of significant quantities of displaced Antarcti...

show abstract

Section: Background and Objectivesmentioning

confidence: 99%

mentioning

confidence: 99%

Site 515: Brazil Basin

Barker¹,

Carlson²,

Johnson³

1983

Initial Reports of the Deep Sea Drilling Project

View full text Add to dashboard Cite

show abstract

“…There is no correlation (positive or negative) between the presence of displaced Antarctic diatoms, which have been shown to be excellent tracers of AABW (Johnson et al, 1977), and (Ruddiman and Glover, 1972). Similarity of these two records suggest CaCO 3 events in Hole 515A are bioturbated instantaneously deposited events.…”

Section: Discussionmentioning

confidence: 91%

“…Initially the spiky CaCO 3 record was thought to reflect changes in the intensity of AABW flow over the site, with less CaCO 3 indicative of more intense AABW production (more dissolution). One of the best and easiest AABW indicators to measure is the presence/absence or abundance change of displaced Antarctic diatoms (Johnson et al, 1977). Although there are clear changes in the distribution of displaced Antarctic diatoms within Hole 515A, there is no obvious positive or negative correlation with the CaCO 3 spikes (Fig.…”

Section: Discussionmentioning

confidence: 99%

“…Hole 515A was cored at a water depth of 4252 m. Previous studies of core top samples from this region have shown the carbonate lysocline to be at about 4050 m, and the carbonate content of sediments from depths in excess of 4200 m to be negligible as a result of the increase in CaCO 3 dissolution with depth (Melguen and Thiede, 1974;Johnson et al, 1977;Broecker and Takahashi, 1978). However, during routine analyses on Barker,P.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Carbonate Spikes and Displaced Components at Deep Sea Drilling Project Site 515: Pliocene/Pleistocene Depositional Processes in the Southern Brazil Basin

Shor¹,

Jones²,

Rasmussen³

et al. 1983

Initial Reports of the Deep Sea Drilling Project, 72

View full text Add to dashboard Cite

Late Pliocene to Recent sediments from the southern Brazil Basin (DSDP Hole 515A, hydraulic piston core) were analyzed for evidence of episodic flow of Antarctic Bottom Water (AABW) through the Vema Channel. Carbonate-enriched layers punctuate the post-Pliocene section, otherwise composed predominantly of terrigenous silt and clay. Carbonate enrichment is thought to result from rapid deposition of fine-grained calcareous turbidites, originating in canyons incised on the northern margin of the Rio Grande Rise. The composition of benthic foraminiferal assemblages and the presence of stratigraphically displaced discoasters is consistent with a turbidite origin. Based on the presence of displaced Antarctic diatoms, AABW flow through the Vema Channel apparently has had a major influence on this site for only four periods during the last 2.7 Ma (about 45 to 250; 375 to 430; 700 to 780; 1320 to 1345 thousand yr. ago).

show abstract

Geological Investigation of the Equatorial North Pacific Seafloor: A Discussion of Sediment Redistribution

Craig

1979

Marine Geology and Oceanography of the Pacific Manganese Nodule Province

View full text Add to dashboard Cite

Vema Channel paleo-oceanography: Pleistocene dissolution cycles and episodic bottom water flow

Cited by 82 publications

References 17 publications

Site 515: Brazil Basin

Site 515: Brazil Basin

Carbonate Spikes and Displaced Components at Deep Sea Drilling Project Site 515: Pliocene/Pleistocene Depositional Processes in the Southern Brazil Basin

Geological Investigation of the Equatorial North Pacific Seafloor: A Discussion of Sediment Redistribution

Contact Info

Product

Resources

About