(Table 1) Radiolarians in the Oligocene-Miocene at DSDP Hole 72-515B
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| Formato: | Dataset Open Access |
| Lenguaje: | en |
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PANGAEA
1983
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| _version_ | 1867168142123335680 |
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| author | Johnson, David A |
| author_facet | Johnson, David A |
| collection | Datos científicos de ciencias marinas y ambientales |
| contents | The Neogene of the southwestern Atlantic is virtually barren of biogenic silica. Of the four sites drilled on Leg 72, only two contained identifiable radiolarian specimens. In the southwestern Brazil Basin (Site 515), radiolarians are present only from the upper Oligocene (Anomaly 8, about 28 Ma) to the middle Miocene (Zone NN8, about 11.5 Ma). On the Rio Grande Rise (Site 516), radiolarians are present only within a short interval of the lower Miocene (Zones N5-N6, about 18-20 Ma). The abrupt cessation of silica deposition in the upper middle Miocene is characteristic of many drill sites in the tropical and temperate Atlantic and implies that a major oceanographic "threshold" was exceeded at this time, allowing the Atlantic waters to become either less productive or relatively silica deficient. Siliceous microfossils are notably more abundant in Oligocene-Miocene sediments of deep regions where carbonate preservation is poor (Site 515) than in equivalent carbonate-rich strata nearby (Site 516). This discrepancy suggests that the presence of calcareous microfossils may act to enhance post-depositional dissolution of biogenic silica tests by elevating the pH of the surrounding pore waters. Carbonate-free clays, by contrast, may provide a more favorable chemical environment for silica preservation. |
| format | Dataset Open Access |
| id | pangaea_https___doi_org_10_1594_PANGAEA_811702 |
| institution | PANGAEA |
| language | en |
| publishDate | 1983 |
| publisher | PANGAEA |
| record_format | pangaea |
| spellingShingle | (Table 1) Radiolarians in the Oligocene-Miocene at DSDP Hole 72-515B Johnson, David A 72-515B; Artophormis gracilis; Botryopyle dictyocephalus; Calocycletta cf. costata; Calocycletta robusta; Calocycletta virginis; Cannartus bassanii; Cannartus prismaticus; Cannartus tubarius; Carpocanopsis bramlettei; Carpocanopsis cristatatum; Carpocanopsis favosa; Centrobotrys petrushevskayae; Clathrocanium sphaerocephalum; Cyclampterium leptetrum; Cyclampterium milowi; Cyclampterium pegetrum; Cyrtocapsella cornuta; Cyrtocapsella elongata; Cyrtocapsella japonica; Cyrtocapsella tetrapera; Deep Sea Drilling Project; Dendrospyris bursa; Dicolocapsa microcephala; Dorcadospyris alata; Dorcadospyris ateuchus; Dorcadospyris papilio; Dorcadospyris simplex; Dorcadospyris triceros; DRILL; Drilling/drill rig; DSDP; DSDP/ODP/IODP sample designation; Eucyrtidium cienkowskii; Eucyrtidium diaphanes; Eucyrtidium punctatum; Glomar Challenger; Gorgospyris schizopodia; Histiastrum martinianum; Leg72; Lychnocanoma elongata; Radiolarian preservation; Radiolarians abundance; Radiolarian zone; Sample code/label; Siphostichartus corona; South Atlantic/BASIN; Stichocorys armata; Stichocorys delmontensis; Stichocorys peregrina; Stichocorys wolfii; Theocorys spongoconum; Theocyrtis annosa The Neogene of the southwestern Atlantic is virtually barren of biogenic silica. Of the four sites drilled on Leg 72, only two contained identifiable radiolarian specimens. In the southwestern Brazil Basin (Site 515), radiolarians are present only from the upper Oligocene (Anomaly 8, about 28 Ma) to the middle Miocene (Zone NN8, about 11.5 Ma). On the Rio Grande Rise (Site 516), radiolarians are present only within a short interval of the lower Miocene (Zones N5-N6, about 18-20 Ma). The abrupt cessation of silica deposition in the upper middle Miocene is characteristic of many drill sites in the tropical and temperate Atlantic and implies that a major oceanographic "threshold" was exceeded at this time, allowing the Atlantic waters to become either less productive or relatively silica deficient. Siliceous microfossils are notably more abundant in Oligocene-Miocene sediments of deep regions where carbonate preservation is poor (Site 515) than in equivalent carbonate-rich strata nearby (Site 516). This discrepancy suggests that the presence of calcareous microfossils may act to enhance post-depositional dissolution of biogenic silica tests by elevating the pH of the surrounding pore waters. Carbonate-free clays, by contrast, may provide a more favorable chemical environment for silica preservation. |
| title | (Table 1) Radiolarians in the Oligocene-Miocene at DSDP Hole 72-515B |
| topic | 72-515B; Artophormis gracilis; Botryopyle dictyocephalus; Calocycletta cf. costata; Calocycletta robusta; Calocycletta virginis; Cannartus bassanii; Cannartus prismaticus; Cannartus tubarius; Carpocanopsis bramlettei; Carpocanopsis cristatatum; Carpocanopsis favosa; Centrobotrys petrushevskayae; Clathrocanium sphaerocephalum; Cyclampterium leptetrum; Cyclampterium milowi; Cyclampterium pegetrum; Cyrtocapsella cornuta; Cyrtocapsella elongata; Cyrtocapsella japonica; Cyrtocapsella tetrapera; Deep Sea Drilling Project; Dendrospyris bursa; Dicolocapsa microcephala; Dorcadospyris alata; Dorcadospyris ateuchus; Dorcadospyris papilio; Dorcadospyris simplex; Dorcadospyris triceros; DRILL; Drilling/drill rig; DSDP; DSDP/ODP/IODP sample designation; Eucyrtidium cienkowskii; Eucyrtidium diaphanes; Eucyrtidium punctatum; Glomar Challenger; Gorgospyris schizopodia; Histiastrum martinianum; Leg72; Lychnocanoma elongata; Radiolarian preservation; Radiolarians abundance; Radiolarian zone; Sample code/label; Siphostichartus corona; South Atlantic/BASIN; Stichocorys armata; Stichocorys delmontensis; Stichocorys peregrina; Stichocorys wolfii; Theocorys spongoconum; Theocyrtis annosa |
| url | https://doi.org/10.1594/PANGAEA.811702 |