scholarly journals A Robust Chemical Weathering Index Applicable to a Wide Range of Sedimentary Rocks

2020 ◽  
Author(s):  
Tenichi Cho ◽  
Tohru Ohta
Keyword(s):  
Chemical Weathering ◽  
Sedimentary Rocks ◽  
Weathering Index ◽  
Wide Range

scholarly journals The Relationship between Fluid Flow, Structures, and Depositional Architecture in Sedimentary Rocks: An Example-Based Overview

Geofluids ◽  
2020 ◽  
Vol 2020 ◽  
pp. 1-19 ◽  
Author(s):  
Vilde Dimmen ◽  
Atle Rotevatn ◽  
Casey W. Nixon
Keyword(s):  
Fluid Flow ◽  
Sedimentary Rocks ◽  
Structure Type ◽  
Mineral Dissolution ◽  
Rock Properties ◽  
Hydrocarbon Migration ◽  
Geological Processes ◽  
Wide Range ◽  
Depositional Architecture ◽  
The Relationship

Fluid flow in the subsurface is fundamental in a variety of geological processes including volcanism, metamorphism, and mineral dissolution and precipitation. It is also of economic and societal significance given its relevance, for example, within groundwater and contaminant transport, hydrocarbon migration, and precipitation of ore-forming minerals. In this example-based overview, we use the distribution of iron oxide precipitates as a proxy for palaeofluid flow to investigate the relationship between fluid flow, geological structures, and depositional architecture in sedimentary rocks. We analyse and discuss a number of outcrop examples from sandstones and carbonate rocks in New Zealand, Malta, and Utah (USA), showing controls on fluid flow ranging from simple geological heterogeneities to more complex networks of structures. Based on our observations and review of a wide range of the published literature, we conclude that flow within structures and networks is primarily controlled by structure type (e.g., joint and deformation band), geometry (e.g., length and orientation), connectivity (i.e., number of connections in a network), kinematics (e.g., dilation and compaction), and interactions (e.g., relays and intersections) within the network. Additionally, host rock properties and depositional architecture represent important controls on flow and may interfere to create hybrid networks, which are networks of combined structural and stratal conduits for flow.

3. Sedimentary rocks

2016 ◽  
pp. 29-50
Author(s):  
Jan Zalasiewicz
Keyword(s):  
Sedimentary Rock ◽  
Chemical Weathering ◽  
Sedimentary Rocks ◽  
Chemical Environment ◽  
Combined Effects ◽  
Star System ◽  
The Earth ◽  
Different Types ◽  
Physical And Chemical

The Earth has the greatest abundance and variety of sedimentary strata in our star system, dating back some 3.8 billion years. ‘Sedimentary rocks’ describes the processes that create different types of sedimentary rocks, which form a key guideline in reconstructing Earth’s history. Particles are created by both physical and chemical weathering. These particles are then moved by different modes of transport and sorted by size, which affect the resulting sedimentary rock. Sedimentary layers can remain as soft muds or loose sands for millions of years, but most buried sedimentary layers harden and turn into rock, under the combined effects of increasing heat and pressure, and of changes in chemical environment.

Deconvolution of the composition of fine-grained pyrite in sedimentary matrix by regression of time-resolved LA-ICP-MS data

2020 ◽  
Vol 105 (6) ◽  
pp. 820-832 ◽  
Author(s):  
Aleksandr S. Stepanov ◽  
Leonid V. Danyushevsky ◽  
Ross R. Large ◽  
Indrani Mukherjee ◽  
Irina A. Zhukova
Keyword(s):  
Trace Elements ◽  
Regression Analysis ◽  
Trace Element ◽  
Sedimentary Rocks ◽  
Trace Element Composition ◽  
Element Composition ◽  
Silicate Matrix ◽  
Time Resolved ◽  
Icp Ms ◽  
Wide Range

Abstract Pyrite is a common mineral in sedimentary rocks and is the major host for many chalcophile trace elements utilized as important tracers of the evolution of the ancient hydrosphere. Measurement of trace element composition of pyrite in sedimentary rocks is challenging due to fine-grain size and intergrowth with silicate matrix and other sulfide minerals. In this contribution, we describe a method for calculation of trace element composition of sedimentary pyrite from time-resolved LA-ICP-MS data. The method involves an analysis of both pyrite and pyrite-free sediment matrix, segmentation of LA-ICP-MS spectra, normalization to total, regression analysis of dependencies between the elements, and calculation of normalized composition of the mineral. Sulfur is chosen as an explanatory variable, relative to which all regressions are calculated. The S content value used for calculation of element concentrations from the regressions is calculated from the total, eliminating the need for independent constraints. The algorithm allows efficient measurement of concentrations of multiple chalcophile trace elements in pyrite in a wide range of samples, including quantification of detection limits and uncertainties while excluding operator bias. The data suggest that the main sources of uncertainties in pyrite composition are sample heterogeneity and counting statistics for elements of low abundance. The analysis of regression data of time-resolved LA-ICP-MS measurements could provide new insights into the geochemistry of the sedimentary rocks and minerals. It allows quantification of ratios of elements that do not have reference material available (such as Hg) and provides estimates on the content of non-sulfidic Fe in the silicate matrix. Regression analysis of the mixed LA-ICP-MS signal could be a powerful technique for deconvolution of phase compositions in complex multicomponent samples.

scholarly journals Provenance and weathering index of the Upper Cretaceous São Carlos Formation and its tectonic significance in the eastern Bauru Basin, SE Brazil

2019 ◽  
Vol 19 (3) ◽  
pp. 77-94
Author(s):  
Lara Ferreira Neves ◽  
Alessandro Batezelli
Keyword(s):  
Trace Elements ◽  
Chemical Weathering ◽  
Upper Cretaceous ◽  
Source Area ◽  
Sedimentary Basins ◽  
Major And Trace Elements ◽  
Published Data ◽  
Weathering Index ◽  
Se Brazil ◽  
Eastern Border

Geochemistry of major and trace elements has been used as an important tool for the study of provenance and tectonic and climatic evolution of sedimentary basins. The São Carlos Formation is an Upper Cretaceous unit that lies on the eastern border of the Bauru Basin. Despite the paleontological and paleodepositional studies performed in this unit in the last years, little is known about the correspondence between tectonic and climatic conditions acting during the first stages of sedimentation. The hypothesis of this paper is to evaluate São Carlos and Araçatuba formations and understand the evolution of the eastern border of the basin. Thus, were conducted geochemical studies using X-ray fluorescence on sandstones, siltstones, and shales from the São Carlos Formation. According to the chemical weathering index, which presented values ranging from 57.12 to 71.58%, the oxides of major elements indicate that moderate weathering processes affected the source area, possibly associated with the arid-semiarid climate. Alkaline rocks, granites, gneisses, and metasediments were the main lithotypes of the source area. Ternary diagrams show that the tectonic environment was equivalent to the passive continental margin, coinciding with the Serra do Mar and, secondarily, Alto Paranaíba Uplift regions. Based on major and trace elements, their ratios, and published data on the basin, was elaborated a paleogeographic model of the eastern border of the Bauru Basin, concluding that the source area of the sediments was constituted by intermediate and felsic rocks, sometimes recycled by sedimentary processes.

New winter crane flies (Insecta: Diptera: Trichoceridae) from the Jurassic Daohugou Formation (Inner Mongolia, China) and their associated biota

2006 ◽  
Vol 43 (1) ◽  
pp. 9-22 ◽  
Author(s):  
Junfeng Zhang
Keyword(s):  
New Species ◽  
Middle Jurassic ◽  
Inner Mongolia ◽  
Late Jurassic ◽  
Sedimentary Rocks ◽  
New Genera ◽  
Crane Flies ◽  
Geological Age ◽  
Wide Range ◽  
Biostratigraphic Correlation

Four extinct new species referable, respectively, to three extinct new genera within Trichoceridae have been recovered from the Jurassic Daohugou Formation in Ningcheng, Chifeng, Inner Mongolia, China: Archaeotrichocera ephemera gen. et sp. nov., Tanyochoreta integera gen. et sp. nov., Tanyochoreta chifengica sp. nov., and Sinotrichocera parva gen. et sp. nov. The specimen described earlier as trichocerids from China, Mesotrichocera laiyangensis Hong and Wang 1990, does not belong to this family. The Daohugou biota comprises a wide range of vertebrate and invertebrate organisms that inhabited, a small lake, luxurious everglade, streams, and forest with volcanoes nearby. The Daohugou Formation can be compared to the Karabastau and Haifanggou formations based on biostratigraphic correlation. The geological age for trichocerid-bearing nonmarine volcano-sedimentary rocks may be latest Middle Jurassic (Callovian) or earliest Late Jurassic (Oxfordian) rather than early–middle Middle Jurassic or Early Cretaceous.

scholarly journals Chemical weathering east and west of the emerging Caledonides in the Silurian – Early Devonian, with implications for climate

2016 ◽  
Vol 53 (8) ◽  
pp. 774-780 ◽  
Author(s):  
Enli Kiipli ◽  
Tarmo Kiipli ◽  
Toivo Kallaste ◽  
Tiiu Märss
Keyword(s):  
Chemical Weathering ◽  
Sedimentary Rocks ◽  
Clay Fraction ◽  
Climatic Conditions ◽  
Chemical Compositions ◽  
Tropical Zone ◽  
Early Devonian ◽  
Marine Carbonates ◽  
Latitudinal Position ◽  
Mountain Chain

The late Llandovery (Silurian) – early Lochkovian (Devonian) climate of the tropical zone is tracked considering orogenesis, global glaciation events, and cratonic drift. Mineral and chemical compositions of clay fractions of Canadian (the Franklinian Basin) and Estonian (the Baltoscandian Basin) sedimentary rocks from different sides of the emerging Caledonides were studied, using clay as an index of climatic conditions of the provenance area. Illite is the main clay mineral, with addition of orthoclase, muscovite, and chlorite in both regions. Authigenic chert is present in some Canadian sections. The similarity of clay minerals and elemental composition in the two regions suggest common chemical weathering conditions. Nevertheless, the Al/Ti ratio of the <1 μm clay fraction, the proxy for climate’s aridity–humidity and weathering intensity, reveals differences. The Franklinian Basin in Laurentia shows a shift of climate from humid to semi-humid in pace with the uplift of the Caledonides. The sub-meridional mountain chain in the east reduced the amount of rainfall and, therefore, caused drier climate than could have been expected from the low latitudinal position of the area. The material from the Baltoscandian Basin reveals semi-arid and arid climate for most of the Silurian. Although the southern part of the Fennoscandian Shield was situated in desert latitudes, the evidence from the provenance of clay suggests that the climate was not fully arid. In Baltoscandia, covariation between low Al/Ti of clay and negative shifts of δ13C of marine carbonates is recorded at some stratigraphical levels, suggesting a link between humid climatic episodes in mainland and waning of glaciers at the South Pole.

scholarly journals Digital ultraviolet petrography: approaches and applications

2020 ◽  
pp. 86-94
Author(s):  
Vladimir P. Samodurov ◽  
Alena A. Vasilionak ◽  
Yuriy N. Yalenski ◽  
Anastasia M. Erohovets
Keyword(s):  
Chemical Elements ◽  
Sedimentary Rocks ◽  
Optical Resolution ◽  
Quantum Yields ◽  
Thin Sections ◽  
Methodical Approach ◽  
Wide Range ◽  
Geochemical Condition ◽  
Major Chemical ◽  
Reflectance Microscopy

Integrated data on the approaches and applications of the rock fluorescent macro- and micropetrography is presented. Fluorescence in minerals is caused not by the major chemical elements but a wide range of chemical impurities (activators). As a result, fluorescence cannot be used for the mineral identification in the different deposits because of the different activators prevailing in the different localities. Nevertheless, fluorescence is the reliable typomorphic feature because the minerals with specific fluorescence forms in the same geochemical condition. This methodical approach is based on the combination of the epifluorescent microscopy and multifocal petrography of the rocks. Ultraviolet (UV) investigations by the reflectance microscopy method reveal some advantages, mostly in the sedimentary rocks studying – improving an optical resolution of the images, avoiding the microparticles overlapping inside the thin sections. On the contrary to the classical petrography which uses light source, fluorescent minerals are the source of light themselves, and this feature improves the optical resolution of this method as well. Ultraviolet investigations of the samples of Starobin UpperDevonian bed reveal polygenic processes of their forming. Silt-sized minerals with the different fluorescence features, small and high quantum yields, have been brought from the different sources. Prevailing marls, consisting of the clay minerals and dispersed calcite reveal invisible for the other methods structures – colloform aggregates, metasomatic replacement of the marls in the fracture zones of the rocks. Fluorescent features let to define hydrothermal and chemogenic minerals in the sedimentary rocks. For example, fluorescent borates in the salt formations of the evaporates. Nevertheless, complex methodical approach, such as XRD and XRF, needs for the accurate mineral definition.

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