Onset of oxidative weathering of continents recorded in the geochemistry of ancient glacial diamictites

Gaschnig, Richard M.; Rudnick, Roberta L.; McDonough, William F.; Kaufman, Alan J.; Hu, Zhaochu; Gao, Shan

doi:10.1016/j.epsl.2014.10.002

Cited by 62 publications

(71 citation statements)

References 76 publications

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“…Analyses were conducted on a PANalytical 2404 X-ray XRF vacuum spectrometer with a 4 kW super sharp X-ray tube. Major element results for the composite samples are new and reported in Table 2, whereas results for the individual samples were previously reported in Gaschnig et al (2014) and are provided here for completeness in Supplemental Table B.1. Trace elements by XRF are reported and discussed in the Supplemental material.…”

Section: X-ray Fluorescence Analysismentioning

confidence: 86%

“…Several geochemical indices have been used to recognize chemical weathering effects, the most popular of which is the chemical index of alteration. Fresh igneous rocks have CIA values ranging from 40 to 55 and pure kaolinite and chlorite have a value of 100, owing to their lack of Ca, Na, and K. Gaschnig et al (2014) noted that the majority of diamictites have CIA values elevated above those of igneous rocks; they also attributed the pervasive Sr depletion seen in the diamictites to the influence of chemical weathering.…”

Section: Identifying and Seeing Through The Effects Of Chemical Weathmentioning

confidence: 99%

“…This weathering signature appears to be inherited from the sediment source in most cases, rather than reflecting post-depositional changes or weathering during glacial erosion and transport (Gaschnig et al, 2014;Li et al, 2016).…”

Section: Identifying and Seeing Through The Effects Of Chemical Weathmentioning

confidence: 99%

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Compositional evolution of the upper continental crust through time, as constrained by ancient glacial diamictites

Gaschnig

Rudnick

McDonough

et al. 2016

Geochimica et Cosmochimica Acta

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108

101

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Section: X-ray Fluorescence Analysismentioning

confidence: 86%

Section: Identifying and Seeing Through The Effects Of Chemical Weathmentioning

confidence: 99%

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Compositional evolution of the upper continental crust through time, as constrained by ancient glacial diamictites

Gaschnig

Rudnick

McDonough

et al. 2016

Geochimica et Cosmochimica Acta

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108

101

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“…

AbstractGlacial diamictites, with ages ranging from $2900 to 0.01 Ma, record the changing composition of the upper continental crust through time (Gaschnig et al, 2014). Li concentrations and isotopic compositions, combined with Pb isotopic compositions, chemical index of alteration (CIA) values and relative Sr concentrations are used here to assess the degree of chemical weathering recorded in these deposits and the origin of this signature.

…”

mentioning

confidence: 99%

Influence of chemical weathering on the composition of the continental crust: Insights from Li and Nd isotopes in bauxite profiles developed on Columbia River Basalts

Liu

Rudnick

McDonough

et al. 2013

Geochimica et Cosmochimica Acta

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Glacial diamictites, with ages ranging from $2900 to 0.01 Ma, record the changing composition of the upper continental crust through time (Gaschnig et al., 2014). Li concentrations and isotopic compositions, combined with Pb isotopic compositions, chemical index of alteration (CIA) values and relative Sr concentrations are used here to assess the degree of chemical weathering recorded in these deposits and the origin of this signature. The d Li values of most of the diamictites (ranging from À3.9 to +3.5) are lower than those of mantle-derived basalts (+3.7 ± 2, 2r), and the low d7 Li values are generally accompanied by high CIA and low Sr/Sr * values (or Sr depletion factor, Sr/Sr * = Sr/(Ce * Nd) 0.5 ), reflecting a weathering signature that may have derived from pre-depositional, syn-depositional, and/or post-depositional weathering processes. Profiles through three glacial diamictites with relatively high CIA (a fresh road cut of the Neoproterozoic Nantuo Formation (CIA = 62-69), and drill cores through the Paleoproterozoic Timeball Hill (CIA = 66-75) and Duitschland Formations (CIA = 84-91)) do not show evidence of significant post-depositional weathering. High Th/U, reflecting loss of uranium during oxidative weathering, is seen in all Paleozoic and Neoproterozoic diamictites and a few Paleoproterozoic deposits. Pb isotopic systematics suggest that this signature was largely inherited from preexisting crust, although a subset of samples (the Neoproterozoic Konnarock, Paleozoic Dwyka, and several of the Paleoproterozoic Duitschland samples) appears to have experienced postdepositional U loss. Modern glaciomarine sediments record little weathering (CIA = 47, Sr/Sr * = 0.7, d7 Li = +1.8), consistent with the cold temperatures accompanying glacial periods, and suggesting that limited syn-depositional weathering has occurred. Thus, the chemical weathering signature observed in ancient glacial diamictites appears to be largely inherited from the upper continental crust (UCC) over which the glaciers traversed. The strength of this weathering signature, based on the CIA, is greatest in the Mesoarchean and some of the Paleoproterozoic diamictites and is weaker in the Neoproterozoic and Phanerozoic glacial diamictites. Combining these data with data for Archean shales and other types of post-Paleoproterozoic sedimentary rocks (i.e., shales, mudstones, etc.), it appears that post-Paleoproterozoic upper continental crust experienced less intense chemical weathering, on average, than Archean and Paleoproterozoic upper continental crust.

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“…Besides ore formations, these glaciogenic sediments also represent hydrocarbon source rocks (Bechstädt et al, 2009;Gaschnig et al, 2014).…”

Section: _______________ ___mentioning

confidence: 99%

Microbial activity records in Marinoan Snowball Earth postglacial transition layers connecting diamictite with cap carbonate (Otavi Group, NW-Namibia)

Gyollai¹,

Polgáry²,

Fintor³

et al. 2017

AJES

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This study concerns the microbial mat formation in postglacial layers of the Marinoan Snowball Earth glaciation. A high resolution investigation was carried out on the transition layers of Ghaub to Maieberg Formation (start of Keilberg Member) of the Otavi Group in NW-Namibia (Neoproterozoic). Macroscopic characterization, optical rock microscopy, XRD mineralogy, Raman spectroscopy investigations were done and geochemical (major and trace element content) as well as carbonate carbon isotopic data were collected. Three types of microbial contributions were determined: (1) primary, synsedimentary Fe-rich biomats; (2) secondary biomats from biodegradation of Fe-bearing minerals (pyrite, chlorite); and (3) pseudo-secondary structures coating on clasts. These microbial mats of iron-oxidizing bacteria consumed iron from different sources, such as hydrothermal solutions or ironbearing minerals. On the basis of the morphology of Fe-biomats, and the mineralogical and geochemical signatures, we suggest that the Marinoan postglacial transition layers (Ghaub-Maieberg boundary) formed under neutral, suboxic conditions in brackish water at the studied locality.____________________________________________________________________________________

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Onset of oxidative weathering of continents recorded in the geochemistry of ancient glacial diamictites

Cited by 62 publications

References 76 publications

Compositional evolution of the upper continental crust through time, as constrained by ancient glacial diamictites

Compositional evolution of the upper continental crust through time, as constrained by ancient glacial diamictites

Influence of chemical weathering on the composition of the continental crust: Insights from Li and Nd isotopes in bauxite profiles developed on Columbia River Basalts

Microbial activity records in Marinoan Snowball Earth postglacial transition layers connecting diamictite with cap carbonate (Otavi Group, NW-Namibia)

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