NEOPROTEROZOIC GLACIATIONS: NEW DATA FROM QURUQTAGH, EASTERN CHINESE TIANSHAN

Geochronometric data suggest that at least three glacial intervals – Sturtian, Marinoan, and Gaskiers in geochronological order – occurred in the Neoproterozoic [1], yet few successions contain more than two intervals of glacial deposits. The slope-facies Quruqtagh Group in northwestern China is the only Neoproterozoic succession that has been cited to contain three intervals of glacial deposits (in geochronological order, the Baiyisi, Tereeken, and Hankalchough diamictites) in a single continuous succession. Our field observations confirm the glacial origin of the Tereeken and Hankalchough diamictites. The Baiyisi diamictite may also be glaciogenic, but unambiguous glacial evidence may have been obliterated by higher level of metamorphism. A carbonate unit between the Baiyisi and Tereeken formations is characterized by highly positive d¹³C values (up to +10.4‰ vs. PDB), comparable to those of pre-Marinoan but post-Sturtian carbonates. A pinkish cap limestone overlying the Tereeken diamictite shows a d¹³C chemostratigraphic pattern similar to the upper part of Marinoan cap carbonates in plat-form facies. A thin dolomite overlying the Hankalchough diamictite is characterized by variable but very negative d¹³C values. The d¹³C chemostratigraphic data suggest a likely Marinoan age for the Tereeken glaciation, and, by extension, a Gaskiers age for the Hankalchough diamictite.

[1] Bowring, S., Myrow, P., Landing, E., Ramezani, J., and Grotzinger, J., 2003, Geochronological constraints on terminal Neoproterozoic events and the rise of metazoans: Geophysical Research Abstracts, v. 5, p. 13219. (http://www.cosis.net/abstracts/EAE03/13219/EAE03-J-13219.pdf)