The largest negative carbon isotope excursions in Neoproterozoic carbonates caused by recycled carbonatite volcanic ash

The late Ediacaran Shuram Excursion(SE)records the most prominent negativeδ^(13)C excursions(δ^(13)C=-12‰)during Earth’s history.It has been hypothesized to have resulted from oxidation of dissolved organic matter,diagenetic or authigenic precipitates.However,the origin of the SE remains enigmatic;current models face challenges regarding the significant amount of atmospheric oxygen needed to balance such extensive oxidation and sustained inputs of light carbon with extremely negative C isotope compositions.Here,we show that the Doushantuo Formation at the Jiulongwan section in South China,a key stratum recording the SE event,contains mineralogical and geochemical signatures related to igneous processes.Both the occurrence of ankerite,feldspar,moissanite and euhedral quartz in the SE samples and the relatively consistent Ce anomalies of carbonate and O isotopes of quartz indicate a contribution from an igneous source.In particular,the SE samples have trace element and C isotope compositions similar to those of recycled carbonatites formed by decarbonation and melting of sedimentary carbonate rocks.These observations suggest that the deep cycle of ancient carbonate rocks,which were subjected to decarbonation during subduction,melting and eruption related to the breakup of the Rodinia supercontinent,contributed to the SE.This igneous model for the SE may provide a connection between the deep and shallow carbon cycles of the Earth.

The Silurian-Devonian boundary in East Yunnan(South China)and the minimum constraint for the lungfish-tetrapod split

The Silurian-Devonian interval is an essential period in Earth history for witnessing the rise of sarcopterygian fishes and terrestrial vascular plants.In addition to its implication in global stratigraphic correlation,the precise location of the Silurian-Devonian boundary(SDB)in East Yunnan closely relates to the minimal and maximal estimated dates for the lungfish-tetrapod split.Several geochemical indicators including the values and curves ofδ^(13)C_(org),δ^(13)Ccarb and TOC are obtained from the continuous SDB sequence in Dahe,Yiliang County,East Yunnan.The results reveal the significant positiveδ^(13)C_(org) shifts in the upper part of the Yulungssu Formation and the lower part of the Xishancun Formation,and the peak value(−20.0‰)in the sample YD-25 from the lowermost of the Xishancun Formation,replicating theδ^(13)C_(org) variation trend from the uppermost Silurian to the lowermost Devonian worldwide.Theδ^(13)C_(org) variation across the SDB at the Dahe Section resembles the SDB curve from the borehole Klonk-1 drilled at the top of the Klonk GSSP in the Prague Basin,Czech Republic.As such,we place the SDB in the Dahe Area between the samples of YD-17 and YD-18 from the lowermost part of the Xishancun Formation.This SDB assignment is corroborated by new findings of Early Devonian thelodont Parathelodus from the lower part of the Xishancun Formation in Qujing Area.The resolution of the SDB in Dahe,coupled with available paleontological data and the biostratigraphic zonation in East Yunnan,has provided vital data for the geological ages of the fish-bearing strata in East Yunnan.The earliest rhipidistian Youngolepis from the Xishancun Formation(Lochkovian,Devonian)and earliest stem-sarcopterygian Psarolepis from the Kuanti Formation(Ludfordian,Silurian)in East Yunnan indicate that the split between lungfish and tetrapods occurred between 426.5 and 416.0 Ma.

Spatiotemporal variation in precipitation-economy correlations in eastern China over the past 1800 years

Research into climate change and the development of human societies has received considerable attention[1,2].By comparing paleoclimate records with major historical events in human society,previous studies have found that the development of human societies might be closely linked to climate change[3,4].In particular,large-scale hydrological changes caused by climate change have directly affected agricultural productivity and further caused population migration and social conflict.

Anoxia may delay biotic recovery from the Late Ordovician mass extinction

Diverse Ordovician marine ecosystems were abruptly terminated by the Late Ordovician mass extinction (LOME), when around 85%of species were eliminated. Previous studies thought early Silurian (~443–433 Ma) recovery of biotic diversity and ecosystem complexity [1] occurred relatively rapidly, in the first few million years of the Silurian [2].