Eocene Porcellanites and Early Cretaceous Cherts from the Western North Atlantic Basin

Riech, Volkher; Rad, U. von

doi:10.2973/dsdp.proc.43.113.1979

Cited by 21 publications

(43 citation statements)

References 10 publications

(21 reference statements)

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“…The increased dissolution with depth of the opaline tests is consistent with the progression of silica diagenesis with burial (Riech and von Rad, 1979;Thein and von Rad, 1987). Opaline tests are evident until 490 mbsf; below this depth, ghosts predominate.…”

Section: Petrographymentioning

confidence: 53%

“…This diagenetic reaction involves the expulsion of substantial amounts of water of crystallization that leads to a subsequent volume reduction with formation of microfractures. Lower Eocene porcellanites have been well documented for the North Atlantic (Thein and von Rad, 1987;Wilkens et al, 1987;Riech and von Rad, 1979;McHugh et al, 1993). The front that marks the diagenetic transition from biogenic oozes to porcellanites has been identified and correlated throughout most of the western North Atlantic as the seismic reflection A c (Tucholke and Mountain, 1979;Poag, Watts, et al, 1987).…”

Section: Petrography Of Lower Eocene Sedimentmentioning

confidence: 97%

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Effects of relative sea-level changes on the diagenesis of Eocene sediment: New Jersey slope and coastal plain

McHugh¹

1997

Proceedings of the Ocean Drilling Program, 150X Scientific Results

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Eocene lithology recovered by the Ocean Drilling Program Legs 150 and 150X was studied to evaluate the effects of relative sea-level changes on the diagenesis of the sediment. Island Beach, Atlantic City, and Cape May boreholes were drilled on the coastal plain during Leg 150X, and Sites 902−904 and 906 were drilled on the continental slope (400-1200 m of water depth) during Leg 150. The shallow-to deep-water transect provides an opportunity to examine the diagenetic transformations of the sediment with increasing distance from the shoreline. Numerous episodes of diagenesis (with formation of micrite, sparry calcite, dolomite, and silica cements) typical of the near-shore, near-surface environment occurred in the coastal plain sediment. In contrast, less nucleation of crystallites, coarser crystal forms, and diagenesis below the bacterial sulfate reduction zone are characteristic of the upper slope Sites. Diagenesis is patchy at the middle slope, where some microfossils still maintain their primary cementation.Sediment adjacent to three main Eocene slope unconformities records physical and chemical changes that differ from those of the sediment within the sequences. The most extensive alterations occur in upper Eocene sediment beneath the contact with the upper Oligocene. This contact, marked by a seismic reflection that can be traced throughout the slope to the shelf and correlated to a sequence boundary, represents a major transition from an Eocene pelagic carbonate-dominated margin to an Oligocene hemipelagic siliciclastic-dominated margin. Lithologically, this transition is manifested in upper Eocene sediment by a decrease in the calcium carbonate and opal content and by an increase in detrital minerals. Diagenetic fluids transformed the unconformable surface of upper Eocene biosiliceous chalks into a mosaic of euhedral to subhedral dolomite rhombs that petrographic analyses suggest were deposited by highly saturated fluids at low temperatures. The upper Oligocene silty clays above contain abundant quartz, illite, kaolinite, and brown glauconites that indicate terrigenous sediment transport and reworking.More episodes of diagenesis, abundant former fluid migration routes, which suggest increased pore-fluid activity, and sediment reworking are associated with the two other Eocene unconformable surfaces. Energy dispersive X-ray analyses of former fluid pathways and the matrix of the sediment above and below these unconformable surfaces suggest that the sources for the fluids were local. These unconformities that separate the uppermost middle Eocene and the lower/middle Eocene have also been documented at other slope Sites and at the coastal plain, and appear to be widespread throughout the continental margin.

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Section: Petrographymentioning

confidence: 53%

Section: Petrography Of Lower Eocene Sedimentmentioning

confidence: 97%

Effects of relative sea-level changes on the diagenesis of Eocene sediment: New Jersey slope and coastal plain

McHugh¹

1997

Proceedings of the Ocean Drilling Program, 150X Scientific Results

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“…The classification and terminology of silicified sediments, designating sediments containing diagenetic silica constituents, is here based on the method proposed by von Rad et al (1978). Amounts of three silica-mineral polymorphs-opal A, opal CT, and diagenetic quartzwere estimated by thin-section and XRD analyses, and the sediments were classified as follows (Fig.…”

Section: Methods and Termsmentioning

confidence: 99%

“…Values of the rf(101) spacing of opal CT in silicified sediments were calculated by precise XRD, using silicon as the standard material and under the condition of slow 20-speed (1/4° per min.). Obstacle feldspars are very scarce in Leg 80 samples in general, so the XRD peak at 22° (CuKα) is considered to be attributable almost solely to opal CT.Diagenetic quartz was distinguished from clastic quartz grains by its characteristics in the matrix, such as its grain form, its texture (as in chalcedony aggregate), and its relation to fossil tests under the optical microscope; then its abundance was estimated mainly by visual means under the microscope, referring to XRD estimates and the background quartz contents of host sediments.The classification and terminology of silicified sediments, designating sediments containing diagenetic silica constituents, is here based on the method proposed by von Rad et al (1978). Amounts of three silica-mineral polymorphs-opal A, opal CT, and diagenetic quartzwere estimated by thin-section and XRD analyses, and the sediments were classified as follows (Fig.…”

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confidence: 99%

Silicified Sediments and Silica Diagenesis in the Goban Spur Area of the Northeast Atlantic, Leg 80

Otsuka¹

1985

Initial Reports of the Deep Sea Drilling Project

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X-ray powder diffraction and optical and scanning-electron microscope analyses of sediment samples taken from four sites drilled in the Goban Spur area of the northeast Atlantic show variable diagenetic silicification of sediments at several stratigraphic horizons. The results are as follows:1. The silicified sediments are middle Eocene at Site 548, Paleocene to lower Albian at Site 549, upper to lower Paleocene at Site 550, and lower Turanian at Site 551.2. There are three types of these silicified sediments: nodular type in carbonate-rich host sediments, bedded type in clayey host sediments, and a type transitional between the other two.3. Silica diagenesis is considered to progress as follows: dissolution of siliceous fossils; precipitation of opal CT in pore spaces and transformation of biogenic silica (opal A) to opal CT, development of opal CT cement; chalcedonic quartz precipitation in pore spaces and replacement of foraminiferal tests by chalcedonic quartz; and finally, transformation of opal CT to quartz, and cementation. But the strong influence of host-sediment types on diagenetic silica fades is recognized. Bedded-type silicified sediments in a clayey environment indicate a lower grade of silica diagenesis. Only very weak chalcedonic quartz formation is recognized, and there is no opal CT cementation, even in Lower Cretaceous bedded-type clayey silicified sediments.4. The rf(101) spacing of opal CT shows two distinct trends of ordering or decrease with burial depth; one is a rapid change, in the case of nodular silicified sediments, and the other is a more gentle shift, found in bedded silicified sediments.5. Diagenetic silica facies of the nodular type develop as irregular concentric zones around some nodule nuclei. Also, quartz-chert nodule formation occurs at rather shallower horizons, and is discordant with the trend of decreasing d(101) spacing in opal CT.6. Silicified sediments at Site 551 are shallower than at the other sites. The diagenetic silica facies suggest the probable erosion of 300 m or more of sediment at this site.7. The zeolites clinoptilolite and phillipsite were found in the sediment samples recovered on Leg 80. Clinoptilolite occurs from the shallower levels to the deepest horizons of diagenetically silicified zones, suggesting that clinoptilolite formation is related to diagenesis of biogenic silica. Phillipsite at Site 551 (Section 551-5-2) may originate from volcanogenie material. INTRODUCTIONDetailed studies of silicified sediments from DSDP samples have clarified the worldwide distribution of cherts and other silicified sediments in ocean basins. These studies have yielded many new insights regarding the occurrence and the nature of various siliciffed sediments. They have also revealed very diverse features of silica diagenesis and the formation of cherts and other siliceous sediments, such as porcellanites and diatomites (Heath, 1973;Garrison et al., 1975;Keene, 1975;Kelts, 1976;Kagami, 1979;Pisciotto, 1980;Riech, 1980;Grehin et al., 1981;Hein et al., 1981; Riech, ...

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“…Downhole through this front, there is a generally marked increase in the acoustic impedance, in association with a marked reduction in porosity as bioclastic silica (opal-A) is reprecipitated as interstitial cement (opal-CT) (e.g., Weaver and Wise, 1974;Riech and von Rad, 1979;Wilkens et al, 1987). In sequence stratigraphy, seismic reflections are usually produced along bedding surfaces and unconformities and are significant chronostratigraphically.…”

Section: Diagenetic Boundariesmentioning

confidence: 99%

Seismic-to-Well Correlation of Seismic Unconformities at Leg 150 Continental Slope Sites

Lorenzo¹,

Hesselbo²

1996

Proceedings of the Ocean Drilling Program, 150 Scientific Results

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Seismic-to-well correlation at Ocean Drilling Program (ODP) continental slope Sites 902, 903, 904, and 906 identifies 19 Pleistocene-Eocene unconformable surfaces and reflectors. Seismic features on 120-channel, tuned, air-gun seismic data are tied to borehole depths via one-dimensional synthetic seismogram models. Reprocessed migrated seismic profiles along Maurice Ewing Lines 1005 and 1027 reveal clear images of two middle Miocene canyon-cutting surfaces and Pleistocene slumpbounding unconformities. At Site 904, good-quality compressional-wave velocity and density values allow models to match seismic facies. A high-amplitude continuous seismic facies between Miocene unconformities q and w can be attributed to distal toe-of-delta clinoforms containing alternating glauconite-rich and -poor sedimentary facies. A seaward-thinning Oligocene interval downlaps the upper Oligocene/upper Eocene, producing reflectors resolvable only through ties to biostratigraphic and lithologic borehole data. A silica-indurated diagenetic front within the middle Eocene produces reflectors that do not have chronostratigraphic significance and can mislead sequence stratigraphic interpretations.

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Eocene Porcellanites and Early Cretaceous Cherts from the Western North Atlantic Basin

Cited by 21 publications

References 10 publications

Effects of relative sea-level changes on the diagenesis of Eocene sediment: New Jersey slope and coastal plain

Effects of relative sea-level changes on the diagenesis of Eocene sediment: New Jersey slope and coastal plain

Silicified Sediments and Silica Diagenesis in the Goban Spur Area of the Northeast Atlantic, Leg 80

Seismic-to-Well Correlation of Seismic Unconformities at Leg 150 Continental Slope Sites

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