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Sedimentary Petrology
Published in Supriya Sengupta, Introduction to Sedimentology, 2017
Near-surface diagenetic changes are caused by the interaction of minerals with interstitial pore fluids. This may lead to dissolution of the existing minerals and production of new (authigenic) minerals. Authigenic growths (‘overgrowths’) of quartz and feldspar are common features at this stage. The newly formed quartz is added to the detrital quartz grains maintaining the same crystallographic orientation (Fig. 4.21). Authigenic precipitation of feldspar takes place at a higher order of pressure and temperature than that provided by near-surface conditions. Excess potassium in the pore fluid is an essential condition for development of authigenic feldspar. Dissolution features in feldspars and production of kaolinite as pore-filling material are common at this stage.
Solid/solution relations of contaminants in surface waters
Published in W. Bechteler, Transport of Suspended Solids in Open Channels, 2022
Of the various processes taking place within an aquatic system that are potentially able to enrich toxic chemicals, particularly inorganic species, in the sediment, two groups of accumulative mechanisms can be distinguished according to their spatial and temporal occurrence (Jones & Bowser, 1978): Endogenic fractions refer to minerals originating from processes occurring within the water column in response to effects such as precipitation, sorption, enrichment in organisms, and organometallic interactions. Enrichtment of these minerals may be influenced by settling of particulates, filtering organisms, and flocculation. Endogenic processes exhibit a distinct temporal character, often as a result of the variation of the organic productivity, e.g. for carbonate precipitation.Authigenic (or diagenetic) fractions include those minerals which result from processes occurring within sediments once they have been deposited. Decomposition of organic matter, which is mediated by microorganisms, generally follows a definite succession in sediments depending upon the nature of the oxidizing agent (Berner, 1981): the successive events are oxygen consumption (respiration), nitrate reduction, sulfate reduction, and methane formation. Sedimentary constituents, particularly iron and manganese, are changed in their chemical form, involving new equilibrium between other solid and dissolved metal species.
Inorganic Sediment Chemistry and Elemental Speciation
Published in Renato Baudo, John P. Giesy, Herbert Muntau, Sediments:, 2020
Particles as substrates of pollutants originate from two major sources. Endogenic fractions of particulate matter include minerals that result from processes occurring within the water column (Jones & Bowser 1978). Enrichment of minerals generated by endogenic processes may be influenced by settling of particulates, filtering organisms, and flocculation. Endogenic processes exhibit a distinct temporal character, often as a result of the variation of the organic productivity. In lakes, the total particulate concentration of trace metals is generally lowest in the hypolimnion due to the decomposition of organic matter. Consequently, net biogenic flux, for example, of metals depends on the lake’s capacity to produce organic particulate matter and to decompose it before it is buried definitely in the sediment (Salomons & Baccini 1986). Authigenic (or diagenetic) fractions include minerals that result from processes within deposited sediments. Decomposition of organic matter, which is mediated by microorganisms, generally follows a finite succession in sediments depending upon the nature of the oxidizing agent (see Berner 1981); the successive events are oxygen consumption (respiration), nitrate reduction, sulfate reduction, and methane formation. The composition of interstitial waters in sediments is perhaps the most sensitive indicator of the types and the extent of reactions that take place between pollutant-loaded sediment particles and the aqueous phase that contacts them. The large surface area of fine-grained sediment in relation to the small volume of its trapped interstitial water ensures that minor reactions with the solid phases will be shown by major changes in the composition of the aqueous phase.
Formation mechanisms of calcite cements in tight sandstones of the Jurassic Lianggaoshan Formation, northeastern Central Sichuan Basin
Published in Australian Journal of Earth Sciences, 2019
Y. H. Qing, Z. X. Lü, J. Y. Wu, J. J. Yang, S. L. Zhang, C. H. Xiong, J. F. Liu
Cores of 22 wells from different local structures were selected to study lithology, sedimentary structure, mineralogy and fracture development. Seventy-two specimens, including core plugs and rock fragments, were sampled from 10 representative wells to study physical properties and rock-mineral determination. A total of 421 thin-sections were collected from 28 wells to study the authigenic minerals and their relationship with other diagenetic products using staining, cathodoluminescence, scanning electron and energy spectrometer, electron microprobe and X-ray diffraction techniques. Twenty-eight whole-rock samples with single composition and high content of carbonate were reacted with 100% phosphoric acid at 25°C, and the extracted gases analysed on a gas-source mass spectrometer following the analytical procedure of Li et al. (2008). The δ18O and δ13C values are reported in per mil relative to the V-PDB standard and the precision is better than 0.02‰. In addition, the influence of authigenic calcite on reservoir physical properties and the relationship between authigenic calcite and sedimentary microfacies were determined.
Diagenesis impact on a deeply buried sandstone reservoir (Es1 Member) of the Shahejie Formation, Nanpu Sag, Bohai Bay Basin, East China
Published in Australian Journal of Earth Sciences, 2019
M. Kashif, Y. Cao, G. Yuan, W. Jian, X. Cheng, P. Sun, S. Hassan
Mechanical compaction and quartz cementation are the primary elements that decrease the sandstone porosity whereas carbonate cementation affects the densification of sandstone through mesodiagenesis. Furthermore, pore-blocking and pore-lining authigenic clay minerals, which mostly developed at the early diagenetic stage, played an important role in destroying the reservoir quality.
Introducing palaeolithobiology
Published in GFF, 2021
Magnus Ivarsson, Henrik Drake, Anna Neubeck, Oona Snoeyenbos-West, Veneta Belivanova, Stefan Bengtson
A growing literature of fossils in deep igneous rocks identifies a previously unrecognized fossil record that holds novel information of Earth´s second largest biosphere of live biomass and its role throughout life´s history on Earth (Ivarsson et al. 2020a). Of particular interest is the fossil record prior to the plant colonization of land at 400 Ma, as the deep biosphere back then was necessarily the predominant reservoir of live biomass (McMahon & Parnell 2018). Indeed, its importance for the evolution of early life and biogeochemical processes on the early Earth as well as the distinctive nature of the deep endolithic record compared to traditional paleontology call for the creation of a specialized sub-discipline. The introduction of paleolithobiology as a distinct research area within paleobiology is based on the following unique precedents: 1) the fossils are preserved and mineralized in-situ, in their habitats, rather than post displacement in a depositional basin, 2) mineralization is either by inorganically or biologically produced authigenic minerals, or through biomineralization mediated by the metabolism of the organisms, 3) a major bulk of the fossils represent the deep biosphere, a part of Earth´s biosphere not included in the traditional fossil record, 4) paleolithobiology chiefly involves igneous crust in contrast to paleontology that almost exclusively investigates sedimentary rocks, 5) a substantial portion of the organisms are chemoautotrophs (or are indirectly dependent on chemoautotrophy) commonly preserved by the products of their own metabolism, thus the fossil record involves chemofossils (geochemical signatures of life) to a large extent, 6) the fossils are interpreted based on specific biogenicity criteria (Ivarsson 2006), 7) during their life-cycle the organisms were dependent on, and more engaged in interaction with the geosphere compared to organisms investigated within paleobiology as a whole, 8) the deep fossil habitat is uniformly represented through most of Earth’s history in contrast to habitats represented by the sedimentary fossil record (Bengtson et al. 2017).