Loess in eastern equatorial Pangea archives a dusty atmosphere and possible upland glaciation

Abstract Carboniferous–Permian strata in basins within the Central Pangean Mountains in France archive regional paleoequatorial climate during a unique interval in geological history (Pangea assembly, ice-age collapse, megamonsoon inception). The voluminous (∼1.5 km) succession of exclusively fine-grained red beds that comprises the Permian Salagou Formation (Lodève Basin, France) has long been interpreted to record either lacustrine or fluvial deposition, primarily based on a local emphasis of subaqueous features in the upper ∼25% of the section. In contrast, data presented here indicate that the lower-middle Salagou Formation is dominated by up to 15-m-thick beds of internally massive red mudstone with abundant pedogenic features (microscale) and no evidence of channeling. Up-section, limited occurrences of ripple and hummocky cross-stratification, and mudcracks record the intermittent influence of shallow water, but with no channeling nor units with grain sizes exceeding coarse silt. These data suggest that the most parsimonious interpretation for the Salagou Formation involves eolian transport of the sediment and ultimate deposition as loess in shallow, ephemeral lacustrine environments. Provenance analyses of the Salagou Formation indicate coarse-grained protoliths and, together with geochemical proxies (chemical index of alteration [CIA] and τNa) that correspond respectively to a low degree of chemical weathering and a mean annual temperature of ∼4 °C, suggest that silt generation in this case is most consistent with cold-weathering (glacial and associated periglacial) processes in the Variscan highlands. Together with previous studies that detailed voluminous Permian loess in western equatorial Pangea, this work shows a globally unique distribution of dust at low latitudes that can be linked either directly to glaciated alpine terranes or to reworked and deflated deposits of other types (e.g., fluvial outwash) where fine-grained material was originally generated from glacial grinding in alpine systems. These results further support a revised model for early Permian climate, in which extratropical ice sheets coexisted with a semiarid tropics that may have hosted significant ice at moderate elevation.

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Structure and Fabric on the Burroughs Glacier, South-East Alaska

Journal of Glaciology ◽

10.1017/s0022143000028331 ◽

1963 ◽

Vol 4 (36) ◽

pp. 731-752 ◽

Cited By ~ 20

Author(s):

Lawrence D. Taylor

Keyword(s):

Ice Age ◽

Coarse Grained ◽

Glacier Surface ◽

Ice Flow ◽

Fine Grained ◽

Glacier Terminus ◽

Basal Ice ◽

Differential Movement ◽

Slow Moving ◽

Optic Orientation

AbstractThe Burroughs Glacier, south-east Alaska, is a slow-moving remnant (14×3km.) of a much more extensive glacier. It is now entirely below the firn line; ablation has revealed ice structures and fabric once 300 m. or more below the glacier surface.At the present glacier surface three kinds of ice are identified—foliated ice, coarse-grained border ice and very coarse-grained basal ice.Two systems of fine-grained foliation are present. Differential movement in the glacier has caused recrystallization along closely spaced planes. At the glacier surface this produces a steeply dipping longitudinal foliation. A gently dipping foliation, having a regional trough-like structure, may be associated with former stratification planes or with former spoon-shaped shear surfaces.The optic orientation of crystals in the coarser layers of the foliated ice shows three weak maxima, and in the finer layers a single weak maximum, corresponding to one of the coarse layer maxima, and normal to the gently dipping foliation plane. The other maxima in the coarse layers are orientated close to the poles of principal fracture planes.In the coarse ice the fabric shows a pattern with three maxima similar to that obtained in torsion shear experiments. In the glacier the pattern may be formed by shear near the glacier bottom or along gently dipping foliation planes. Grain-size increases towards the glacier terminus, especially in the stagnant ice zone.Structural evidence suggests that in the early stages of the Little Ice Age the ice flow was from west to east. Later it was to east and west from an ice crest in the upper Burroughs Glacier. Structures produced by present movement have been superimposed on older structures.

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Is chemical index of alteration (CIA) a reliable proxy for chemical weathering in global drainage basins?

American Journal of Science ◽

10.2475/02.2010.03 ◽

2010 ◽

Vol 310 (2) ◽

pp. 111-127 ◽

Cited By ~ 69

Author(s):

C. Li ◽

S. Yang

Keyword(s):

Chemical Weathering ◽

Drainage Basins ◽

Chemical Index ◽

Chemical Index Of Alteration

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Mineralogy, micromorphology, geochemistry and genesis of a hydrothermal kaolinite deposit and altered Miocene host volcanites in the Hallaçlar area, Uşak, western Turkey

Clay Minerals ◽

10.1180/claymin.2011.046.3.421 ◽

2011 ◽

Vol 46 (3) ◽

pp. 421-448 ◽

Cited By ~ 7

Author(s):

H. Erkoyun ◽

S. Kadіr

Keyword(s):

Hydrothermal Process ◽

Volcanic Glass ◽

Relative Increase ◽

Coarse Grained ◽

Western Turkey ◽

Fine Grained ◽

Spectral Bands ◽

Chemical Index ◽

Infrared Spectral ◽

Hydrological System

AbstractThe Hallaçlar kaolinite deposit of the Uşak Province (western Turkey) is hosted by dacite, andesite and siliceous materials of the Miocene Karaboldere volcanites. Mineralogical zonation, such as the prevalence of kaolinite at the centre of the deposit, coexisting with silica polymorphs such as quartz and cristobalite along with feldspar and hornblende, and a relative increase of smectite, illite, chlorite, and Fe-oxide/-hydroxide phases outward and upward, demonstrate that hydrothermal-alteration processes resulted in kaolinization. Micromorphologically, kaolinite occurs as pseudohexagonal blocky kaolinite with coarse-grained quartz in microfractures, and the presence of relatively fine-grained vermiform kaolinite that edges volcanic materials indicates that kaolinite developed in several phases coexisting with goethite, lepidocrocite, hematite, pyrite, jarosite, alunite, and gypsum/anhydrite with smectite in fractures. The highly crystallized Hallaçlar kaolinite is identified by: (1) sharp reflections at 7.23 and 3.57 Å, with triplet and doublet non-basal reflections; (2) sharp infrared spectral bands at 3687, 3651 and 3620 cm-1; (3) well defined, pseudohexagonal and hexagonal kaolinite crystal growth; (4) a chemical index of weathering of 98.6-100; and (5) SiO2/Al2O3 ratios between 1.04 and 1.45. Enrichment of Sr and depletion of Rb+Ba, Ti, and HREE relative to LREE, with a distinct negative Eu anomaly, are responses to the fractionation of feldspar and hornblende by the hydrothermal fluid; these results are also supported by the O- and H-isotopic character and formation temperatures of the Hallaçlar kaolinite and smectite; namely, 134.1-183.4°C and 65.6°C, respectively. The negative δ34S (-20.7‰) value of gypsum/anhydrite reflects its formation from geothermal-water-derived sulphur. Under the influence of a tectonically controlled hydrothermal process, feldspar, hornblende and volcanic glass were altered, resulting in the conservation of Al and depletion of Si, Na, Ca, K, Mg and Fe in an open hydrological system such that formation of kaolinite in the central part of the deposit under acidic conditions and development of smectite and illite upward and outward under basic conditions were favoured.

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The effects of hydrodynamic sorting on the Ti isotope composition of sediments

10.5194/egusphere-egu2020-9329 ◽

2020 ◽

Author(s):

Martijn Klaver ◽

Pieter Vroon ◽

Marc-Alban Millet

Keyword(s):

Chemical Weathering ◽

Isotope Composition ◽

Eastern Mediterranean ◽

Hf Isotope ◽

Passive Margin ◽

Coarse Grained ◽

Fine Grained ◽

Crustal Composition ◽

Mass Dependent ◽

Physical And Chemical

Detrital sediments provide a useful tool to investigate the composition of the continental crust through time. Mass-dependent (&#8220;stable&#8221;) isotope variations in Archaean to present-day sediments (shales, diamictites) have recently received much attention and Ti, in particular, holds significant promise as a novel tracer of crustal composition [1, 2, 3]. This approach is based on i) the contrasting Ti isotope composition of mafic versus felsic rocks as a result of the removal of isotopically light oxides during igneous differentiation; and ii) the chemical behaviour of Ti, a refractory and biologically inert element that should not fractionate during weathering and sedimentation. Hence, current interpretations of the Ti isotope detrital sediment record rely heavily on the assumption that it reflects the integrated composition of the source(s), and thus provides a record of the proportion of felsic to mafic rocks in that source.A potential caveat, however, is the hydrodynamic sorting of dense minerals in coarse, more proximal sediments [4]. This effect is well-known for zircon; coarser sediments tend to have higher Zr/Al2O3 and a less radiogenic Hf isotope composition due to the concentration of zircon grains [e.g., 5, 6]. Shales form the complementary zircon-depleted reservoir characterised by lower Zr/Al2O3 and a more radiogenic Hf isotope composition relative to the source. Common Ti-rich phases such as ilmenite and rutile are also resistant against physical and chemical weathering and could be concentrated together with zircon in coarse sediments.We examined a suite of Eastern Mediterranean passive margin sediments with well-constrained provenance [7] and found that Ti indeed behaves like Zr. Fine-grained samples have lower TiO2/Al2O3 compared to coarser, proximal deposits of identical provenance. The removal of Ti-rich phases with a light Ti isotope composition into coarse-grained sediments could thus bias the Ti isotope composition of shales towards isotopically heavier values. We will report on the &#948;49/47Ti isotope composition of these sediment samples, but a TiO2/Al2O3 mass balance suggests that a bias of more than 0.05 &#8240; in the &#948;49/47Ti of shales is possible. Understanding the consequences of hydrodynamic sorting for Ti isotopes in sediments is crucial for their use as a quantitative proxy of crustal composition and for reconciling the shale and diamictite Ti isotope records.[1] Greber et al. (2017) Science 357 1271-1274; [2] Deng et al. (2019) PNAS 116-4 1132-1135; [3] Saji et al. (2019) Goldschmidt abstract 2929; [4] Greber & Dauphas (2019) GCA 255 247-264; [5] Patchett et al. (1984) EPSL 69 365-378; [6] Carpentier et al. (2009) EPSL 287 86-99; [7] Klaver et al. (2015) GCA 153 149-168.

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Reconstructing chemical weathering during the Lower Mesozoic in the Western-Central Mediterranean area: a review of geochemical proxies

Geological Magazine ◽

10.1017/s0016756816001205 ◽

2017 ◽

Vol 155 (4) ◽

pp. 944-954 ◽

Cited By ~ 10

Author(s):

FRANCESCO PERRI

Keyword(s):

Rift Valley ◽

Chemical Weathering ◽

Mineralogical Composition ◽

Mediterranean Area ◽

Climatic Changes ◽

Central Mediterranean ◽

Geochemical Proxies ◽

Chemical Index ◽

Chemical Index Of Alteration ◽

Mineralogical Compositions

AbstractThe Triassic–Jurassic rift-valley stage of Tethyan rifting in the Western-Central Mediterranean area is characterized by a development of a puzzle of plates and microplates with the deposition of continental redbeds (in the internal domains of the Gibraltar Arc and Calabria–Peloritani Arc) that can be considered a regional lithosome. This paper aims to reconstruct the chemical weathering conditions of the Triassic–Jurassic boundary in the Western-Central Mediterranean area using the geochemical and mineralogical composition of continental redbed mudrocks of Mesozoic age. The mudrocks from the Calabria–Peloritani Arc show higher values of weathering (mobility) indices (αMg=(Al/Mg)sed/(Al/Mg)UCC;αK=(Th/K)sed/(Th/K)UCC;αBa=(Th/Ba)sed/(Th/Ba)UCC) than the Gibraltar Arc samples. Furthermore, the CIA (Chemical Index of Alteration) and MIA (Mineralogical Index of Alteration) values and the ‘Rb-type indices’ (e.g. Rb/Sr and Rb/K ratios) are higher for the Calabria–Peloritani Arc mudrocks than the Gibraltar Arc samples. All these geochemical proxies closely resemble each other and show similar variations suggesting climatic changes towards humid conditions through the Uppermost Triassic to Lowermost Jurassic that favoured chemical weathering conditions. This period is probably characterized by seasonal climate alternations corresponding to an increase in palaeoclimatic humidity. The mineralogical compositions of the Mesozoic mudrocks further confirm these indications as shown by a higher abundance of kaolinite, related to warm–humid conditions, in the Calabria–Peloritani Arc mudrocks than in those of the Gibraltar Arc.

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The lower Proterozoic Fern Creek Formation, northern Michigan: mineral and bulk geochemical evidence for its glaciogenic origin

Canadian Journal of Earth Sciences ◽

10.1139/e01-086 ◽

2002 ◽

Vol 39 (4) ◽

pp. 481-492 ◽

Cited By ~ 3

Author(s):

Anne Argast

Keyword(s):

Rare Earth ◽

Chemical Weathering ◽

Chemical Index ◽

Quartz Arenite ◽

Bulk Chemical ◽

Chemical Index Of Alteration ◽

Rare Earth Mineral ◽

Chemical Trends ◽

Northern Michigan ◽

Bulk Chemistry

Bulk chemical data indicate the Fern Creek Formation (Early Proterozoic, Marquette Range Supergroup, Lower Chocolay Group) originated as a glacial till, resolving an old argument about the correct interpretation for diamictite-containing units within the formation. There are poor correlations among SiO2, Al2O3, and K2O, and the chemical index of alteration averages 55. These are qualities characteristic of tills and other sediments accumulated in the absence of chemical weathering and transport-induced sorting and inconsistent with an origin as a fluvial deposit (the principal alternate hypothesis). The Archean Carney Lake Gneiss might be the source for at least the lower portions of the Fern Creek Formation. Compositions are similar, and rare earth element trends in the Fern Creek Formation are consistent with derivation from an Archean high-grade terrane. Pegmatites in the gneiss could be the source for monazite, huttonite, and an unnamed fluor-hydroxy-rare earth mineral that occurs in the midsection of the Fern Creek Formation. In addition, mineral and bulk chemical trends are consistent with models involving deep erosion of a complex Archean source, similar to models previously developed for Gowganda tills in the Huronian Supergroup. Samples of the Sturgeon River Quartzite occurring above the Fern Creek Formation were also analyzed. The bulk chemistry is consistent with a well-sorted, supermature quartz arenite.

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Early-Holocene to present palaeoenvironmental shifts and short climate events from the tropical wetland and lake sediments, Kukkal Lake, Southern India: Geochemistry and palynology

The Holocene ◽

10.1177/0959683616660162 ◽

2016 ◽

Vol 27 (3) ◽

pp. 404-417 ◽

Cited By ~ 8

Author(s):

Vijayaraj Rajmanickam ◽

Hema Achyuthan ◽

Christopher Eastoe ◽

Anjum Farooqui

Keyword(s):

Tamil Nadu ◽

Chemical Weathering ◽

Warm Period ◽

Early Holocene ◽

Ice Age ◽

Terrestrial Plants ◽

Humid Forest ◽

Geochemical Composition ◽

Chemical Index ◽

Dry Spell

The Kukkal basin, Tamil Nadu, India, receives most of its rain from the southwest monsoon (SWM). A sediment core from Kukkal Lake preserves a continuous sediment record from the early-Holocene to present (9000 yr BP to present). The present lake is situated at an elevation of ~1887 m a.s.l., in a small basin that appears to have alternated between a and wetland depositional environment. Climate proxies, including sediment texture, total organic carbon (TOC), total nitrogen (TN), C/N, pollen and geochemical composition indicate a steady progression to wetter conditions, with two stepwise changes at about 8000, and between 3200 and 1800 yr BP. The change at 8000 yr BP appears to correspond to a brief (100–150 years) dry spell recorded elsewhere in India. The change at 3200–1800 yr BP consisted in a rapid intensification of the SWM, and may correlate with the initiation of the ‘Roman Warm Period’. There is no clear evidence of changes at the times of the ‘Medieval Warm Period’ (‘MWP’) and the ‘Little Ice Age’ (‘LIA’). The C/N ratio of the sediments ranges from 14.02 to 8.31, indicating that the organic matter originated from a mixture of lacustrine algae, vascular and terrestrial plants. Chemical weathering indices (Chemical Index of Alteration (CIA), Chemical Index of Weathering (CIW), and Plagioclase Index of Alteration (PIA)) are consistent with extreme silicate weathering. Pollen data show a development from savanna vegetation prior to about 8000 yr BP, followed by grassland with palms, the appearance of ferns just prior to 3200 yr BP and the establishment of the tropical humid forest between 3200 and about 1800 yr BP.

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Assessing sediment pollution by applying some geochemical indices for Al-Wind River banks/ East of Iraq

Iraqi Journal of Science ◽

10.24996/ijs.2019.60.8.8 ◽

2019 ◽

pp. 1711-1719

Author(s):

Iman A. Al-Ali

Keyword(s):

Enrichment Factor ◽

Chemical Weathering ◽

Contamination Factor ◽

Anthropogenic Pollution ◽

Sediment Pollution ◽

Pollution Indices ◽

Polluted Sediments ◽

Chemical Index ◽

Chemical Index Of Alteration ◽

Cu And Zn

15 sediment samples were collected; 8 samples from the eastern bank, and 7 samples from the western bank of Al-Wind River in Diyala governorate to assess the sediment pollution in some trace elements such as Fe, Ni, Cd, Zr, Zn and Cu in addition to some oxides such as Al2O3, CaO, Na2O and K2O to find the effect of anthropogenic pollution and the industrial production on the sediment closed especially Naftkhana by using some geochemical pollution indices such as: geoaccumulation factor (I-geo), enrichment factor (EF),contamination factor (CF), pollution loud index (PLI) and to evaluate the degree of weathering by Applying the Chemical Index of Alteration (CIA)in both banks of Al-Wind River. The results of general contamination factors indicate that the eastern bank of Al-Wind River especially that closed by Naftkhana area having quite more concentrations of trace element and oxides from the western bank. The results of I-geo presents unpolluted sediment with Pb and Fe and slightly polluted with Zn, Cu, and Ni in both banks, while the western bank in some locations recorded of moderately polluted sediments with Ni and slightly to moderately polluted sediments with Cu and Zn and reach moderately severely polluted in the eastern bank. The contamination factor (CF) for Ni and Zr classified as class 2 which indicate moderately contamination to severely pollute in both banks, while Fe, Pb, Cu and Zn conbankred unpolluted in both banks. Enrichment factor (EF) for Fe, Pb, Zr and Cu are conbankred deficiency to low enrichment the range of natural variability, while Ni record high values reached to 6.4 indication of anthropogenic inputs. Pollution load Index (PLI) is perfection and classified as class 0 in both banks. Chemical index of alteration (CIA) reflecting the chemical weathering intensity especially for the western bank.

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Structure and Fabric on the Burroughs Glacier, South-East Alaska

Journal of Glaciology ◽

10.3189/s0022143000028331 ◽

1963 ◽

Vol 4 (36) ◽

pp. 731-752

Author(s):

Lawrence D. Taylor

Keyword(s):

Ice Age ◽

Coarse Grained ◽

Glacier Surface ◽

Ice Flow ◽

Fine Grained ◽

Glacier Terminus ◽

Basal Ice ◽

Differential Movement ◽

Slow Moving ◽

Optic Orientation

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Potassium-metasomatism in Anthracite: A Cluster of Geochemical Evidences

10.21203/rs.3.rs-832423/v1 ◽

2021 ◽

Author(s):

Santanu Ghosh ◽

Anwita Ojha ◽

Atul Kumar Varma

Keyword(s):

Source Rock ◽

Chemical Weathering ◽

Bituminous Coal ◽

Climatic Conditions ◽

Rock Composition ◽

Thrust Belts ◽

Chemical Index ◽

Parent Rocks ◽

Chemical Index Of Alteration ◽

The Fourier Transform

Abstract The present study focuses on the inorganic geochemical features of the bituminous coal samples from the Raniganj and the Jharia Basin, as well as the anthracite samples from the Himalayan fold-thrust belts of Sikkim, India. The SiO2 content (48.05 to 65.09 wt% in the ash yield of the bituminous coal samples and 35.92 to 50.11 wt% in the ash yield of the anthracite samples) and the ratio of Al2O3/TiO2 (6.97 to 17.03 in the bituminous coal samples and 10.34 to 20.07 in the anthracite samples) reveal the intermediate igneous source rock composition of the minerals. The ratio of the K2O/Al2O3 in the ash yield of the bituminous coal samples (0.03 to 0.09) may suggest the presence of kaolinite mixed with montmorillonite, while its range in the ash yield of the anthracite samples (0.16 to 0.27) may imply the presence of illite mixed with kaolinite. The chemical index of alteration values may suggest the moderate to strong chemical weathering of the source rock under sub-humid to humid climatic conditions. The plot of the bituminous coal samples in the A-CN-K diagram depicts the traditional weathering trend of parent rocks, but the anthracite samples plot near the illite field and are a bit offset from the weathering trend. This may imply the plausible influences of the potassium-metasomatism at post coalification stages. The Fourier transform infrared spectra further reveal the hydroxyl stretching intensity of the illite in the anthracite samples substantiating the effect of the epigenetic potassium-metasomatism. The decrease in total kaolinite intensity/compound intensity of quartz and feldspar may provide additional evidence towards this epigenetic event.

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