NEOPROTEROZOIC DIAMICTITES OF THE MIDDLE TIANSHAN, KYRGYZSTAN: AGE, DEPOSITIONAL ENVIRONMENTS AND PROVENANCE

With the aim to improve our understanding of the age and genesis of the Neoproterozoic diamictites of the Middle Tianshan of Kyrgyzstan, we studied the late Precambrian strata of the Sandalash, Talas and Chatkal Ranges. The results of detrital zircon dating indicate that diamictites were deposited in the Cryogenian and Ediacaran. Diamictites in the lower part of the Shorashu Formation comprise tillites and were likely deposited during the Marino glaciation ca 640–635 Ma. Diamictites in the upper part of the Shorashu Formation represent debris flows and grain flows associated with turbidites and, apparently, have non-glacial origin; their age is not older than the early Ediacaran 616 ± 7 Ma. The pinching out of the Shorashu Formation to the north and the predominantly southerly directions of sediment transport in turbidites indicate that a non-depositional uplift located north of the basin. The distributions of detrital zircon ages in the studied samples are characterized by large peaks at 0.7–0.8 and 1.8–1.9 Ga and small peaks at ca 2.4–2.5 Ga and are almost identical to the age distributions in the Proterozoic sediments of the Tarim Craton. Comparison of the studied strata with key sections of the Kuruktag Range in the NE Tarim suggests that the diamictites of the lower part of the Shorashu Formation are analogues of late Cryogenian Tereeken tillites, and the slope facies of the upper part of the section are analogues of the early Ediacaran turbidites of the Zhamokti and Yukkengol Formations.