湖北兴山发现晚元古代灾变事件的证据──微球粒和碳同位素负异常

在湖北省兴山县白果园银—钒矿层中发现钾长石微球位和碳同位素负异常，是扬子地台上晚元古代地球灾变事件的证据。在银—钒矿层底部（陡山沱组上部）粘土层及以上黑色页岩中发现了化学成分与冲击成因的玻陨石相似的含钾微球粒，夹于黑色页岩中的碳酸盐岩薄层（主要为白云岩）的δ（１３）Ｃ和δ（１８）Ｏ趋向于最大负值（分别为８．６２‰和６．０８‰ＰＤＢ），黑色页岩中还有微量元素和ＲＥＥ异常。灾变事件的原因可能与地外冲击或火山喷发有关。

EVIDENCE FOR THE LATE PROTEROZOIC CATASTROPHIC EVENTS IN XINGSHAN COUNTY:MICROSPHERULES AND NEGATIVE ANOMALIES OF CARBON ISOTOPES

K-feldspar microspherules and negative anomaly of carbon isotopes are found in silvervanadium ore beds in the Baiguoyuan ore district, Xingshan County, Hubei Province, whichare evidence of Late Proterozoic catastrophic events on the Yangtze platform. At the bottomof the Ag-V ore beds,there is a boulder clay layer marking the beginning of the events. ManyK-bearing microspherults are found within the layer as well in black shales above it,whosechemical composition is comparative to that of tektite of impact origin. The thin carbonatebeds （mainly dolomite） intercalated in the black shales show the tendency of δ18O and δ13Ctowards the largest negative values （δ13C=-8. 62‰, PDB and δ18O=-6. 08‰ PDB）. Thereare anomalies of trace elements and REE in the black shales too. The cause of the catastrophic events might be due to extraterrestrial impact or volcanic eruption.