Cherts and Porcellanites from the North Pacific, DSDP, Leg 32

Keene, J. B.

doi:10.2973/dsdp.proc.32.114.1975

Cited by 51 publications

(72 citation statements)

References 19 publications

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“…6E). Similar features have been described from DSDP sediments (e.g., Keene 1975). In the Waima River there are chert nodules c. 1-2 m long oriented perpendicular to bedding.…”

Section: Zone Isupporting

confidence: 59%

Sedimentology and petrography of early diagenetic chert and dolomite in the Late Cretaceous‐early Tertiary Amuri Limestone Group, eastern Marlborough, New Zealand

Lawrence

1993

New Zealand Journal of Geology and Geophysics

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The dominantly micritic Amuri Limestone Group of eastern Marlborough, New Zealand, consists of six regionally extensive units: the Mead Hill Formation, Teredo Limestone Formation, Lower Limestone Formation, Middle Limestone Formation, and the Lower and Upper Marl Formations, which were deposited in a northwest-trending trough. Six separate diagenetic zones (I-VI) are recognised, based on visually estimated proportions of chert, dolomite, or limestone. Zones I-V occur in the Mead Hill to Lower Limestone Formations, and Zone VI occurs in the Middle Limestone Formation. There is no chert or dolomite in the two Marl formations. The bulk of the chert and dolomite occurs in the basin centre (mainly in the Mead Hill Formation) where the limestone is thickest, but decreases in abundance stratigraphically upwards and towards the basin margins. Zone I consists almost entirely of chert which is either detrital rich or detrital poor. Zones II and IV consist of chert and dolomite in approximately equal proportions. Zones III and VI contain varying proportions of chert and limestone. Zone V is a thin, chertified, fine sandstone-mudstone of limited extent. Sulphide nodules, usually <10 mm in diameter, are common in all zones. Chert usually forms discontinuous nodular beds or nodules. Some elongated chert nodules which may be in excess of 2 m (chert bands) are found near the top of the chert sequence. Dolomite occurs as <1 mm diameter rhombohedra in discontinuous chert-cemented beds and lenses. The common pinch and swell morphology displayed throughout most zones results from differential compaction of relatively chert-free limestone, or dolomite, around chert nodules. Stylolites are generally absent, but where present they are deflected around chert nodules, indicating chert formation prior to stylolitisation.In thin section, Zone II dolomites contain inclusions arranged in cloudy-centre clear-rim patterns. Zone IV dolomite has inclusions arranged in diagonal planes. Both dolomite types are associated with abundant disseminated pyrite. All cherts consist of microcrystalline or cryptocrystalline quartz or chalcedony, with common disseminated pyrite. Petrographic evidence and δ 18 O data indicate that the Received 20 February 1992; accepted 19 November 1992 dolomite formed at temperatures <60°C, probably in the upper sediment column. The presence of pyrite suggests that dolomite formed in association with sulphate reduction. The δ 18 O composition of the chert is very similar to that of the dolomite, implying that chert formation may have occurred at similar depths and times in the sediment as the dolomite. The association of pyrite with chert suggests that sulphate reduction may also have promoted silica nucleation. Therefore, the sedimentological and petrographic evidence is consistent with the early nucleation of both chert and dolomite. G92009

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“…6E). Similar features have been described from DSDP sediments (e.g., Keene 1975). In the Waima River there are chert nodules c. 1-2 m long oriented perpendicular to bedding.…”

Section: Zone Isupporting

confidence: 59%

Sedimentology and petrography of early diagenetic chert and dolomite in the Late Cretaceous‐early Tertiary Amuri Limestone Group, eastern Marlborough, New Zealand

Lawrence

1993

New Zealand Journal of Geology and Geophysics

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“…There is approximately 2% FeMn-oxide present as coarse-silt-sized particles and stain. Carbonate analyses indicate about 85%-95% CaCO 3 in the chalks and 25%-50% CaCO 3 in the porcellanites (Bode, 1975;Keene, 1975). We estimate the bulk composition as 15% biogenic silica, 75% carbonate, and 8% clay.…”

Section: Sites 305 and 306 (Shatsky Rise)-berriasian Through Aptian Cmentioning

confidence: 90%

“…Despite the poor recovery, Matter et al (1975) recognized two Lower Cretaceous facies: a chert-bearing nannofossil chalk of Berriasian through earliest Barremian age (Cores 306-42R to -18R) and a calcareous porcellanite and chert-dominated radiolarian limestone of Barremian through Aptian age (Cores 306-17R to approximately -7R, and 305-68R to about -55R). The petrology of the cherts and porcellanites in these facies has been studied by Keene (1975).…”

Section: Sites 305 and 306 (Shatsky Rise)-berriasian Through Aptian Cmentioning

confidence: 99%

“…The light-tan siliceous limestones are bioturbation-homogenized with faint banding and gray chert or porcellanite nodules. Carbonate analyses average from 20% (Site 305) to 45% (Site 306) (Bode, 1975), and the calcareous-rich porcellanites are about 50% CaCO 3 (Keene, 1975). About a third of the radiolarians are silica-or calcitefilled molds; the rest are partially replaced ghosts.…”

Section: Sites 305 and 306 (Shatsky Rise)-berriasian Through Aptian Cmentioning

confidence: 99%

“…Most of the radiolarites within the clay-rich and carbonate-rich facies of the central Pacific have locally silicified horizons and concretions of porcellanite or chert Keene, 1975;Behl and Smith, this volume). Clay inhibits silica recrystallization of biogenic opal-A to diagenetic opal-CT and can preserve radiolarians during early diagenesis, whereas carbonate drives the reaction faster to quartz (Kastner et al, 1977).…”

Section: Deep-ocean Pacific Radiolaritesmentioning

confidence: 99%

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Jurassic through Early Cretaceous Sedimentation History of the Central Equatorial Pacific and of Sites 800 and 801

Ogg¹,

Stattegger²,

Behl³

1992

Proceedings of the Ocean Drilling Program

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Sedimentation in the central Pacific during the Jurassic and Early Cretaceous was dominated by abundant biogenic silica. A synthesis of the stratigraphy, lithology, petrology, and geochemistry of the radiolarites in Sites 801 and 800 documents the sedimentation processes and trends in the equatorial central Pacific from the Middle Jurassic through the Early Cretaceous. Paleolatitude and paleodepth reconstructions enable comparisons with previous DSDP sites and identification of the general patterns of sedimentation over a wide region of the Pacific.Clayey radiolarites dominated sedimentation on Pacific oceanic crust within tropical paleolatitudes from at least the latest Bathonian through Tithonian. Radiolarian productivity rose to a peak within 5° of the paleoequator, where accumulation rates of biogenic silica exceeded 1000 g/cm 2 /m.y. Wavy-bedded radiolarian cherts developed in the upper Tithonian at Site 801 coinciding with the proximity of this site to the paleoequator. Ribbon-bedding of some radiolarian cherts exposed on Pacific margins may have formed from silicification of radiolarite deposited near the equatorial high-productivity zone where radiolarian/clay ratios were high. Silicification processes in sediments extensively mixed by bioturbation or enriched in clay or carbonate generally resulted in discontinuous bands or nodules of porcellanite or chert, e.g., a "knobby" radiolarite. Ribbon-bedded cherts require primary alternations of radiolarian-rich and clay-rich layers as an initial structural template, coupled with abundant biogenic silica in both layers. During diagenesis, migration of silica from clay-rich layers leaves radiolarian "ghosts" or voids, and the precipitation in adjacent radiolarite layers results in silicification of the inter-radiolarian matrix and infilling of radiolarian tests. Alternations of claystone and clay-rich radiolarian grainstone were deposited during the Callovian at Site 801 and during the Berriasian-Valanginian at Site 800, but did not silicify to form bedded chert.Carbonate was not preserved on the Pacific oceanic floor or spreading ridges during the Jurassic, perhaps due to an elevated level of dissolved carbon dioxide. During the Berriasian through Hauterivian, the carbonate compensation depth (CCD) descended to approximately 3500 m, permitting the accumulation of siliceous limestones at near-ridge sites. Carbonate accumulation rates exceeded 1500 g/cm 2 /m.y. at sites above the CCD, yet there is no evidence of an equatorial carbonate bulge during the Early Cretaceous. In the Barremian and Aptian, the CCD rose, coincident with the onset of mid-plate volcanic activity.Abundance of Fe and Mn and the associated formation of authigenic Fe-smectite clays was a function of proximity to the spreading ridges, with secondary enrichments occurring during episodes of spreading-center reorganizations. Callovian radiolarite at Site 801 is anomalously depleted in Mn, which resulted either from inhibited precipitation of Mn-oxides by lower pH of interstitial waters in...

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Methane seepage in a Cretaceous greenhouse world recorded by an unusual carbonate deposit from the Tarfaya Basin, Morocco

Smrzka

Zwicker

Kolonic

et al. 2017

The Depositional Record

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During the Cretaceous major episodes of oceanic anoxic conditions triggered large scale deposition of marine black shales rich in organic carbon. Several oceanic anoxic events (OAEs) have been documented including the Cenomanian to Turonian OAE 2, which is among the best studied examples to date. This study reports on a large limestone body that occurs within a black shale succession exposed in a coastal section of the Tarfaya Basin, Morocco. The black shales were deposited in the aftermath of OAE 2 in a shallow continental sea. To decipher the mode and causes of carbonate formation in black shales, a combination of element geochemistry, palaeontology, thin section petrography, carbon and oxygen stable isotope geochemistry and lipid biomarkers are used. The 13 Cdepleted biphytanic diacids reveal that the carbonate deposit resulted, at least in part, from microbially mediated anaerobic oxidation of methane in the shallow subseafloor at a hydrocarbon seep. The lowest obtained d 13 C carbonate values of À23Á5& are not low enough to exclude other carbon sources than methane apart from admixed marine carbonate, indicating a potential contribution from in situ remineralization of organic matter contained in the black shales. Nannofossil and trace metal inventories of the black shales and the macrofaunal assemblage of the carbonate body reveal that environmental conditions became less reducing during the deposition of the background shales that enclose the carbonate body, but the palaeoenvironment was overall mostly characterized by high productivity and episodically euxinic bottom waters. This study reconstructs the evolution of a hydrocarbon seep that was situated within a shallow continental sea in the aftermath of OAE 2, and sheds light on how these environmental factors influenced carbonate formation and the ecology at the seep site.

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Cherts and Porcellanites from the North Pacific, DSDP, Leg 32

Cited by 51 publications

References 19 publications

Sedimentology and petrography of early diagenetic chert and dolomite in the Late Cretaceous‐early Tertiary Amuri Limestone Group, eastern Marlborough, New Zealand

Sedimentology and petrography of early diagenetic chert and dolomite in the Late Cretaceous‐early Tertiary Amuri Limestone Group, eastern Marlborough, New Zealand

Jurassic through Early Cretaceous Sedimentation History of the Central Equatorial Pacific and of Sites 800 and 801

Methane seepage in a Cretaceous greenhouse world recorded by an unusual carbonate deposit from the Tarfaya Basin, Morocco

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