Hydrochemistry, origin and evolution of sedimentary subsurface fluids: II. Early diagenetic pore-water evolution in high sedimentation-rate offshore basins

1987 ◽  
Vol 6 (1) ◽  
pp. 1-18
Author(s):  
Reinhard Hesse
Keyword(s):  
Pore Water ◽  
Sedimentation Rate ◽  
Origin And Evolution ◽  
High Sedimentation Rate ◽  
High Sedimentation

scholarly journals Origin and alteration of organic matter of the Oxford Clay Formation (U.K.) determined from bulk geochemical analyses

1992 ◽  
Vol 6 ◽  
pp. 163-163
Author(s):  
Fabien Kenig ◽  
Brian Popp ◽  
Roger Summons
Keyword(s):  
Organic Matter ◽  
Isotopic Composition ◽  
Water Column ◽  
Sedimentation Rate ◽  
Carbon Isotopic Composition ◽  
Deposit Feeder ◽  
High Sedimentation Rate ◽  
Carbon Isotopic ◽  
Shell Beds ◽  
High Sedimentation

To understand the processes controlling production, accumulation, and preservation of organic matter in the Lower Oxford Clay (LOC), we determined the hydrogen index (HI), the oxygen index (OI), the Tmax (from Rock-Eval), the content of total organic carbon (TOC), total carbon and total sulfur, and the carbon isotopic composition of bulk organic matter from 160 samples collected from 6 different quarries and one continuous core. With concentrations of TOC varying between 0.5% and 16.6%, the LOC is an organic-rich shale. For samples dominated by organic matter of phytoplanktonic origin, the hydrogen and oxygen indices and the Tmax (~418°) indicate low levels of maturity, and, thus, the shallow burial of the LOC through geologic time.Two main sources of organic matter can be distinguished: a major phytoplanktonic source with high HI and low OI and a minor terrestrial source with low HI and high OI. A third group, represented by samples with low HI and low OI, consists mainly of altered materials from the Middle Oxford Clay and the LOC. Selection of samples for chemical analysis was based on the macrofaunal assemblages defined by Duff (1975). These various biofacies are characterized by specific organic geochemical features indicating the relationship between conditions affecting faunal assemblages and those controlling accumulation and preservation of organic matter. For example, Duff's ‘deposit feeder shales', which are dominated by epifaunal bivalves and are depleted in infaunal organisms, exhibit the highest concentration and best preservation of marine organic matter, with an average TOC of 6.8% for 56 samples analyzed. The preservation of such organic matter requires a dysaerobic water column and a high sedimentation rate.Carbon isotopic compositions within the ‘deposit feeder shale’ biofacies (−27.6 to −23.2±) appear to have been controlled by the intensity of primary productivity. The highest-TOC, marine-dominated, 13C-rich samples reflect photosynthetic drawdown of dissolved-CO2 level, and, thus, originated in highly productive environments. On the other hand, variations in the carbon isotopic composition of organic matter in shell beds (−27.5 to −26±) probably reflect heterotrophic reworking of the organic matter, winnowing of the sediments, and mixing with a source of organic matter enriched in 13C, such as wood (δ13C from −25 to −23±). Such mixing phenomena may also explain the high variability of the carbon isotopic compositions of TOC-depleted and altered samples from the Middle and Upper Oxford Clay.The environment of deposition of the LOC would be characterized by the alternation of two major conditions: 1) periods of high productivity, dysoxic water column and high sedimentation rate leading to the development of organic-rich shales dominated by phytoplanktonic organic matter, and 2) periods of low productivity, oxic water column and high current activity implying winnowing and alteration of organic matter, and leading to the formation of shell beds where marine and terrestrial organic matter are mixed.

Evaluating Role of Leukocytosis and High Sedimentation Rate as Prognostic Factors in Acute Ischemic Cerebral Strokes

2012 ◽  
Vol 15 (8) ◽  
pp. 386-390 ◽  
Author(s):  
Masoud Nikanfar ◽  
Sheyda Shaafi ◽  
Maziyar Hashemilar ◽  
Daioush Savadi Oskouii ◽  
Mohamad Goldust
Keyword(s):  
Prognostic Factors ◽  
Sedimentation Rate ◽  
High Sedimentation Rate ◽  
High Sedimentation

Early diagenetic processes in deep Labrador Sea sediments: reactive and nonreactive iron and phosphorus

1994 ◽  
Vol 31 (1) ◽  
pp. 14-27 ◽  
Author(s):  
Marc Lucotte ◽  
Alfonso Mucci ◽  
Claude Hillaire-Marcel ◽  
Sophie Tran
Keyword(s):  
Sedimentation Rate ◽  
Extraction Procedure ◽  
Inorganic Phosphorus ◽  
Labrador Sea ◽  
Piston Core ◽  
Inorganic P ◽  
High Sedimentation Rate ◽  
High Sedimentation ◽  
Fluor Apatite ◽  
Redox Boundary

A sequential extraction procedure was applied to separate the oxides and lithogenous phases of iron and manganese and the organic and inorganic phosphorus phases in four box cores and one piston core from the slopes and rises of the Labrador Sea. Sedimentation rate, rather than the location in the basin, appears as a master variable of the diagenetic transformations of Fe, Mn, and P. High sedimentation rate, characteristic of two of the box cores, led to the creation of zones near the redox boundary of partial reprecipitation of dissolved Fe, Mn, and P released in the deeper reducing portions of the sediments. In contrast, surficial sediments from box cores with 10 times lower sedimentation rate only have sufficient reductive capacity to remobilize Mn hydroxides while leaving the Fe oxyhydroxides intact. Under these conditions, there is evidence for a redistribution of reactive inorganic P leading to the crystallization of carbonate fluorapatite in the top 30 cm of the cores. Gradual transformation of buried orthophosphate to authigenic apatite under suboxic conditions is also observed in the top 400 cm of the high sedimentation rate piston core. As in the box cores, the reaction is complete after several thousand years of burial and occurs in sediments characterized by low CaCO3 content. Depending upon the sedimentation rates, the carbonate fluor-apatite crystallization may be superimposed on the changes in detrital sedimentary fluxes accompanying the onset of deglaciation. A proxy indicator of paleo-redox conditions, and thus of biodegradable organic matter accumulation at the sediment–water interface, is given by the ratio of iron oxides to the reactive inorganic P (solid orthophosphate plus authigenic apatite).

Geophysical and palynological investigations of the Tell El Dabaa archaeological site, Nile Delta, Egypt

Antiquity ◽  
2001 ◽  
Vol 75 (290) ◽  
pp. 735-744 ◽  
Author(s):  
Salah Y. El Beialy ◽  
Kevin J. Edwards ◽  
Ahmed S. El-Mahmoudi
Keyword(s):  
Sedimentation Rate ◽  
Nile Delta ◽  
Archaeological Site ◽  
Geophysical Survey ◽  
Preliminary Results ◽  
High Sedimentation Rate ◽  
High Sedimentation ◽  
Palynological Study ◽  
Channel Deposits

The authors present preliminary results of geophysical and palynological reconnaissance at the Tell El Dabaa, eastern Nile Delta. The geophysical survey reveals the presence of floodbasins, levees and channel deposits. Low palynomorph concentrations probably result from the high sedimentation rate and mean that further work is needed on the methods for palynological study in the region.

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