PALEOMAGNETISM, GEOCHRONOLOGY, GLACIATION AND EDIACARAN(?) FOSSILS FROM LESSER KARATAU MICROCONTINENT, KAZAKHSTAN

The lesser Karatau microcontinent in Kazakhastan is one of myriad small blocks that make up the Central Asian Orogenic Belt (CAOB). The Central Asian orogenic belt (CAOB) is widely recognized as a locus of Asia’s main growth during the late Neoproterozoic – Paleozoic, but its evolution remains highly controversial. The views on the enigmatic, late Neoproterozoic to Cambrian stages, crucially depend on the views on the origin and subsequent kinematics of the numerous microcontinents with the Precambrian basement that are included in the mosaic structure of Kazakhstan, Tien Shan, Altai and Mongolia. Most of the so far published models are based mainly on the stratigraphic similarities between their late Neoproterozoic - early Paleozoic sections of the CAOB microcontinents. New geochronological, paleomagnetic and stratigraphic data can serve as an additional source of information the origin of these microcontinents and their subsequent history.

Here we present recent results from the Lesser Karatau microcontinent in Kazakhstan. Our work in this region focused on obtaining paleomagnetic and geochronologic data from the the Precambrian Kurgan Formation along with the description of Neoproterozoic glacial rocks overlying the Kurgan Formation. Paleomagnetic analyses of the Kurgan Formation yielded a pre-folding magnetization with a paleolatitude of 34.2° ± 5.3° N. A primary signature is supported by a positive intraformational conglomerate test. Zircons removed from a felsic tuff within the Kurgan yielded a U-Pb age of 766.4 ± 3.6 Ma. We also discovered within the Kurgan Formation (at a slighly lower stratigraphic level) discoidal fossils resembling Nimbia occlusa and Tirasiana disciformis. Unconformably overlying the Kurgan Formation is a glacial unit we call the Aktas tillite. Stable isotopic analysis along with other data suggest that this glacial deposit can be correlated to Marionoan-aged (~630 Ma) glaciations elsewhere in Asia.

We will discuss the significance of these results as they pertain to the Neoproterozoic history of the Central asian blocks, the Neoproterozoic glacial intervals and the evolution of metazoans.