The glacial-interglacial transitions of ice ages are associated with large, rapid changes in climate, which potentially can be reconstructed from stratigraphic profiles of the chemical index of ...alteration (CIA). Here, we present a case study based on high-resolution CIA profiles of Neoproterozoic glacial deposits from South China (paleolatitude ~30° N) as a record of the climate transition at the termination of the Sturtian Glaciation (~663 Ma). Drillcore ZK2115 (Gaodi Deposit) exhibits a progressive upsection increase in mean CIA over a ~50-m interval, from 58 (range 52–65; note: all ranges are given as 16th–84th percentiles) in the synglacial upper Tiesi'ao Formation to 67 (range 64–69) in the deglacial basal Datangpo Formation cap carbonates, and to 68 (range 66–70) in the postglacial Datangpo Formation black shales. A coeval section from the Lijiawan Deposit also exhibits an increasing CIA trend upsection within shallow-water Mn-carbonate facies. These CIA patterns show no relationship to lithology and are interpreted to reflect climatic warming and intensified chemical weathering during the Sturtian deglaciation. Similar large increases in postglacial CIA values are seen in Paleoproterozoic and Late Paleozoic successions, and at least moderate increases in CIA values are recorded during warm stages of the late Quaternary (e.g., the Bølling-Allerød and Holocene) relative to the cold stages (e.g., the Last Glacial Maximum and Younger Dryas). The rapidity of CIA changes in Quaternary systems (~1 to 10 kyr) suggests that weathering intensity may have changed at similarly rapid rates in more poorly dated deep-time glacial successions, with potential implications for Snowball versus Slushball models of Cryogenian glaciations. These examples show that CIA can be a robust proxy for climate changes (i.e., enhanced chemical weathering intensity) during glacial-interglacial transitions of both ancient and recent ice ages.
•Large increases in chemical index of alteration (CIA) during major deglaciations.•Case study of CIA changes in end-Sturtian deposits of Nanhua Basin (South China).•CIA increase from 59 ± 6 in synglacial Tiesi'ao Fm. to 66 ± 3 in postglacial Datangpo Fm.•CIA increase concentrated within terminal glacial deposits of uppermost Tiesi'ao Fm.•Similar CIA increases for glacial-interglacial transitions from Paleoproterozoic to Recent.
Silicic eruptive units can constitute a substantive component in flood-basalts-dominated large igneous provinces, but usually constitute only a small proportion of the preserved volume due to poor ...preservation. Thus, their environmental impact can be underestimated or ignored. Establishing the original volume and potential climate-sensitive gas emissions of silicic eruptions is generally lacking for most large igneous provinces. We present a case study for the ∼260 Ma Emeishan province, where silicic volcanic rocks are a very minor component of the preserved rock archive due to extensive erosion during the Late Permian. Modal and geochemical data from Late Permian sandstones derived from the province suggest that silicic volcanic rocks constituted some ∼30% by volume of the total eroded Emeishan volcanic source rocks. This volume corresponds to >3×104 km3 on the basis of two independent estimate methods. Detrital zircon trace element and Hf isotopic data require the silicic source rocks to be formed mainly by fractional crystallization from associated basaltic magmas. Based on experimental and theoretical calculations, these basalt-derived ∼104 km3 silicic eruptions released ∼1017 g sulfur gases into the higher atmosphere and contribute to the contemporaneous climate cooling at the Capitanian–Wuchiapingian transition (∼260 Ma). This study highlights the potentially important impact on climate of silicic eruptions associated with large igneous province volcanism.
•Minimum volume of silicic eruptions associated with Emeishan basalts is ∼1×104 km3.•Silicic rocks were formed mainly by fractional crystallization of basaltic magmas.•Emeishan silicic volcanism released ∼1×1017 g bulk sulfur into the atmosphere.•Silicic eruptions contributed to the cooling at Capitanian–Wuchiapingian transition.
Developments in Earth system research have led to widespread interest in multi‐sphere interactions that may have controlled bauxite formation. Although karst bauxite ores are abundant in the Tethyan ...Metallogenic Domain (TMD), their genesis and distribution are not yet fully understood. This study utilizes the Random Forest (RF) model to analyze geochemical data sets compiled from three bauxite provinces in the Tethys, including the Mediterranean, Central Asian, and Chinese provinces. Meaningful variables among the provenance, paleolatitude and tectonic setting that affected the formation of the bauxite deposits are identified. The Logistic Regression model is used to verify the importance of various factors. Our study shows that when RF model achieves the best classifier performance, TiO2 is the variable that has the greatest impact on the model. TiO2 content is the highest in the Central Asian Province. The high TiO2 content in bauxites indicates a provenance of magmatic origine associated with the Subduction Provenance Zone. Bauxites with TiO2 content similar to that of the continental basement are derived from siliciclastic and carbonate rocks, identified as the Orogenic Provenance Zone. This study illustrates a novel link between geochemical compositions (TiO2 content) of bauxites, provenance and regional tectonic setting.
Plain Language Summary
Abundant bauxite deposits formed in the Tethyan Metallogenic Domain are of great importance to bauxite research. However, previous studies generally focus on local bauxite occurrences formed over certain geologic time. A comprehensive understanding of the genesis and characteristics of bauxite deposits is hence essential. In this study, Machine learning methods (Random Forest and Logistic Regression) are applied to improve the understanding of Tethyan bauxite formation. Our research reveals that the TiO2 content in Tethyan bauxites is related to their provenance. The enrichment of TiO2 in bauxite deposits points to magmatic rock provenance that underwent subduction. Bauxites with a TiO2 content similar to that of continental basement are derived from siliciclastic and carbonate rocks exposed on orogenic belts. As such, this investigation elucidates a previously unexplored association between the geochemical characteristics (TiO2 content) of bauxite deposits, their provenance, and the regional tectonic context.
Key Points
Two Provenance Zones in the Tethys Domain are proposed: Subduction Provenance Zone and Orogenic Provenance Zone
High TiO2 content in bauxites resulted from magmatic rocks of the Subduction Provenance Zone
Ti in bauxites has the potential for tracing provenance and associated tectonic settings
Sandstone petrology, geochemistry, and detrital zircon U–Pb ages and trace elements are integrated to investigate the provenance of Middle Triassic strata from the Youjiang Basin, SW China. ...Variations in abundance of volcanic lithic fragments and ratios of Th/U, Zr/Sc and Th/Sc suggest that sandstones from the southwestern portion of the basin display less sedimentary recycling and have a lower felsic average source composition than time-equivalent strata from the central, eastern and northern portions of the basin. All sandstones exhibit an overall similar detrital zircon U–Pb age distribution pattern with major age groups at 1200–900Ma, 480–420Ma and 300–240Ma together with some Devonian–Carboniferous and Neoproterozoic grains. Combined with the compiled paleocurrents, the detrital zircon ages suggest multiple-sourced components. Pre-Devonian detrital zircons were likely derived from the recycled late Neoproterozoic–early Paleozoic clastic rocks and from magmatic and metamorphic rocks related to the early Paleozoic orogeny in the southeastern segment of the South China Craton. Late Paleozoic–Triassic detrital zircons together with the presence of well preserved volcanic lithic fragments were considered to indicate first-cycled detrital input from a subduction–collisional mountain belt to the southwest of the craton. These provenance data argue for an Indosinian mountain building event following the closure of a Paleo-Tethys branch ocean rather than for a thermotectonic reactivation event as recently proposed for the Indosinian orogeny in the southwestern China. In association with this orogeny the Youjiang Basin evolved into a foreland basin.
► We study the provenance of the Middle Triassic Youjiang turbidites in SW China. ► Major sources are related to the multiple orogenic cycles in South China. ► Indosinian orogeny in SW China is a mountain building event. ► The turbidites were deposited in a syn-orogenic basin.
The Cambrian–Ordovician boundary unconformity in the southern part of the South China Craton is spatially and temporally related to coeval orogenic activity along the Indian margin of east Gondwana. ...Detrital zircon age spectra from strata above and below the unconformity range in age from 3580–450Ma, with peaks in the late Mesoproterozoic and Neoproterozoic. The patterns are similar to time equivalent sequences elsewhere in South China and together with regional facies relationships and paleocurrent data indicate derivation from a Gondwana source. The disconformity at the base of the Ordovician succession forms part of a regional break that has also been documented in the Himalaya, Qiangtang, Lhasa, Sibumasu, and Western Australia. All these successions have similar detrital zircon age spectra suggesting derivation from common source(s). In South China the effects of this tectonic event are relatively mild and are represented by a local disconformity at the base of the Ordovician succession, but elsewhere in north Gondwana this event is marked by an angular unconformity with metamorphism of older units and relatively widespread magmatic activity. South China was likely located in a distal location to the northeast of the pulse of tectonic activity, which was focused in the Himalaya region, and was close to the continent–ocean boundary between northern Gondwana and the proto-Tethys.
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•South China was located along the northernmost margin of East Gondwana.•Early Paleozoic orogenic activity in north Gondwana affected South China.•Detritus from the Himalayan region accumulated in South China.•South China represents the distal portion of the northward facing synorogenic basin.
Whole-rock geochemistry and zircon trace element and U-Pb age data for Late Permian–early Middle Triassic volcanogenic sedimentary rocks in SW China show a change from Large Igneous Province to ...subduction-related sources immediately before the Permian–Triassic boundary. Zircons from Late Permian samples give identical within-error ages to the adjoining Emeishan Large Igneous Province (LIP). The bulk-rock geochemistry of these Late Permian units shows no depletion in high field strength elements and is similar to the high-titanium basalts of the Emeishan. Six samples of latest Permian–earliest Triassic tuff and two earliest Middle Triassic tuffs samples yield U-Pb zircon ages at of ~252Ma and ~247Ma, respectively. These tuffs and interstratified volcanogenic sedimentary rocks show significant depletion in high field strength elements, akin to magmatic arc-related rocks. Zircons from the tuffs have Nb/Hf, Th/Nb and Hf/Th ratios similar to those from arc/orogenic-related settings and distinct from the zircons from the Late Permian samples which display within-plate/anorogenic characteristics. Our data demonstrate that there is a compositional change of the volcanogenic sediments across the Permian–Triassic boundary in South China.
► We study the Late Permian-Middle Triassic volcanogenic sediments in SW China. ► A distinct compositional change across the Permo-Triassic boundary was found. ► Source changed from LIP to magmatic arc related volcanic rocks. ► Zircon trace elements are useful provenance indicator.
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