Neoproterozoic Diamictites of the Middle Tianshan, Kyrgyzstan: Age, Depositional Environments and Provenance

The Upper Precambrian section in the Sandalash, Talas, and Chatkal ranges are studied to refine the age and genesis of Neoproterozoic diamictites of the Middle Tianshan. The results of detrital zircon dating show that diamictites were deposited in the Cryogenian and Ediacaran. The diamictites in the lower part of the Shorashu Formation comprise tillites, which were likely deposited at the end of the Cryogenian during the Marino glaciation (~640–635 Ma). In the upper part of the Shorashu Formation, the diamictites represent debris flows and grain flows associated with turbidites and, apparently, have nonglacial origin; their age is no 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 distribution of detrital zircon ages in the studied samples are characterized by the main peaks within the ranges of 700–800 and 1800–1900 Ma and subordinate peaks at 2400–2500 Ma and are almost identical to the distributions of ages in the Proterozoic sedimentary rocks of the Tarim Craton. The comparison of the studied sequences with the sections of the Kuruktag Range in the northeastern Tarim Craton suggests that the diamictites of the lower part of the Shorashu Formation are analogs of the Tereeken tillite, which deposited at the end of the Cryogenian, whereas the slope facies of the upper part of the section are correlated with turbidites of the Zhamokti and Yukkengol formations of the early Ediacaran.