Use of Clay Fabric to Distinguish Turbiditic and Hemipelagic Siltstones and Silts

O’Brien, Neal R.; Nakazawa, Keiji; Tokuhashi, Shuichi

doi:10.1002/9781444304473.ch18

Cited by 19 publications

(35 citation statements)

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“…Hemipelagic sediments are generally mottled owing to bioturbation, whereas parallel laminae are preserved in turbidites. Turbidite muds are often darker in color due to a greater amount of organic matter present (Piper, 1973;Hesse, 1977;O'Brian et al 1980). Despite the discontinuous sampling, inferences can be made about the depositional environment of the intervals studied in well G-287.…”

Section: Discussionmentioning

confidence: 99%

Cenozoic deep-water agglutinated foraminifera in the North Atlantic

Kaminski¹

1987

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Cenozoic (predominantly Paleogene) "flysch-type" agglutinated foraminiferal assemblages and their modern analogs in the North Atlantic and adjacent areas have been studied to provide an overview of their spatial and temporal distribution and utility for paleoenvironmental analysis. Over 200 species of agglutinated foraminifera have been recognized in Paleogene sediments from North Atlantic and Tethyan basins. This unified taxonomic data base enables the first general synthesis of biostratigraphic, paleobiogeographic and paleobathymetric patterns in flysch-type agglutinated assemblages from upper Cretaceous to Neogene sediments in the North Atlantic. The majority of taxa are cosmopolitan, but latitudinal, temporal and depth-related trends in diversity and species composition are observed among flysch-type assemblages.Modern deep-sea agglutinated foraminiferal faunas provide an analog to fossil flysch-type assemblages and serve as models for paleoecologic studies. Core-top samples from the Panama Basin, Gulf of Mexico and Nova Scotian continental rise were examined in order to determine the habitats of modern species of agglutinated foraminifera. The ecology of modern taxa provides constraints on the paleoenvironmental significance of fossil agglutinated assemblages in the North Atlantic, and their utility for paleoceanography.Towards this end, spade core samples from a 3912 m deep station in the Panama Basin were studied to determine abundance and microhabitat partitioning among living agglutinated foraminiferal populations and the preservation of dead assemblages. The genera Dendrophrya, Cribrostomoides and Ammodiscus have epifaunal habitats and the genus Reophax is predominantly infaunal. Species of Reophax are probably responsible for fine reticulate burrows observed in xradiographs. An experiment using recolonization trays in the Panama Basin was designed to identify opportunistic species of benthic foraminifera, and to assess the rate at which a population can colonize an abiotic substrate. The most successful colonizer at this site is Reophax, while Dendrophrya displays the lowest capability for dispersal. After nine months the abundance of living individuals in sediment trays was one-tenth to one-third that of background abundance, but the faunal diversity did not differ greatly from control samples. Recolonization by benthic foraminifera is more rapid than among macrofaunal invertebrates.Modern agglutinated assemblages from the Louisiana continental slope were examined to determine changes in species composition associated with hydrocarbon seeps. Organic-rich substrates are characterized by a decrease in astror--iihizids and an increase in trochamminids and textulariids. Highly organicenriched substrates with chemosynthetic macrofauna are dominated by Trochammina glabra and Glomospira charoides.The biostratigraphy of fossil agglutinated foraminifera in the North Atlantic is based on detailed analysis of 670 samples from 14 wells and one outcrop section, and examination of additional picked faunal...

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Section: Discussionmentioning

confidence: 99%

Cenozoic deep-water agglutinated foraminifera in the North Atlantic

Kaminski¹

1987

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“…S2-S4). Evidence for rapid entombment of soft-bodied fossils (16)(17)(18) within this facies is provided by randomly oriented clay microfabrics, indicating event-driven deposition of claystones from bottom-flowing density currents (19) (Fig. 2A and SI Appendix, Fig.…”

Section: Entombmentmentioning

confidence: 98%

Mechanism for Burgess Shale-type preservation

Gaines

Hammarlund

Hou

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

180

147

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Exceptionally preserved fossil biotas of the Burgess Shale and a handful of other similar Cambrian deposits provide rare but critical insights into the early diversification of animals. The extraordinary preservation of labile tissues in these geographically widespread but temporally restricted soft-bodied fossil assemblages has remained enigmatic since Walcott’s initial discovery in 1909. Here, we demonstrate the mechanism of Burgess Shale-type preservation using sedimentologic and geochemical data from the Chengjiang, Burgess Shale, and five other principal Burgess Shale-type deposits. Sulfur isotope evidence from sedimentary pyrites reveals that the exquisite fossilization of organic remains as carbonaceous compressions resulted from early inhibition of microbial activity in the sediments by means of oxidant deprivation. Low sulfate concentrations in the global ocean and low-oxygen bottom water conditions at the sites of deposition resulted in reduced oxidant availability. Subsequently, rapid entombment of fossils in fine-grained sediments and early sealing of sediments by pervasive carbonate cements at bed tops restricted oxidant flux into the sediments. A permeability barrier, provided by bed-capping cements that were emplaced at the seafloor, is a feature that is shared among Burgess Shale-type deposits, and resulted from the unusually high alkalinity of Cambrian oceans. Thus, Burgess Shale-type preservation of soft-bodied fossil assemblages worldwide was promoted by unique aspects of early Paleozoic seawater chemistry that strongly impacted sediment diagenesis, providing a fundamentally unique record of the immediate aftermath of the “Cambrian explosion.”

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“…The generation of acoustic anisotropy in the course of deposition in current-dominated environments has been described (Nacci et al, 1974, O'Brien et al, 1980. Comparing compositionally similar argillaceous sediments of hemipelagic and turbiditic origin from the Mississippi Fan, Wetzel (1986Wetzel ( , 1987 found clear differences in patterns of inferred strain and acoustic anisotropy.…”

Section: Acoustic Anisotropymentioning

confidence: 99%

Directional properties of P-wave velocities and acoustic anisotropy in different structural domains of the northern Barbados Ridge accretionary complex

Brückmann¹,

Moran²,

Housen³

1997

Proceedings of the Ocean Drilling Program, 156 Scientific Results

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Ocean Drilling Program (ODP) Leg 156 revisited the northern Barbados Ridge, where the previous Deep Sea Drilling Program Leg 78A and ODP Leg 110 studied the frontal part of this accretionary prism. Drilling and logging-while-drilling at Sites 947, 948, and 949 successfully identified major thrust faults and the décollement, which was the target of several downhole experiments. Two of the eight holes drilled were equipped with borehole observatories that will monitor temperature, pressure, and fluid flow over the next years. Coring at Hole 948C recovered 180 m of sediment, centered around the décollement, which was positively identified based on structural information. The aim of this study is the evaluation of the possible correlation of preferred orientation of acoustic properties and the direction of maximum compressive strain in the frontal part of the accretionary prism. For this purpose, shipboard P-wave velocities from Holes 948C and 949B were reoriented. This information was then used to compare the directional properties of accreted and subducted sediments. In Hole 948C, lowest transverse velocities (T min ) were observed to be consistently oriented perpendicular to the maximum horizontal compressive stress, believed to be parallel to the convergence vector. In the underthrust domain of Hole 948C, several preferred orientations for T min were detected, but no correlation with the geotectonic reference frame could be identified. Acoustic anisotropy does not show a comparable pattern in Hole 948C. It is concluded that the observed directional dependence of P-wave velocity in the accreted sediment domain in Hole 948B is the result of moderate to steeply inclined bedding, although this conclusion can not adequately be tested due to the lack of corrected structural data.

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Use of Clay Fabric to Distinguish Turbiditic and Hemipelagic Siltstones and Silts

Cited by 19 publications

References 0 publications

Cenozoic deep-water agglutinated foraminifera in the North Atlantic

Cenozoic deep-water agglutinated foraminifera in the North Atlantic

Mechanism for Burgess Shale-type preservation

Directional properties of P-wave velocities and acoustic anisotropy in different structural domains of the northern Barbados Ridge accretionary complex

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