Paleomagnetic evidence of the Neoproterozoic age of the Purpol Formation of the Baikal-Patom Region

The Purpol Fm is distributed within the Baikal-Patom margin of Siberian Craton from middle reaches of the Chuya River to the Lake Nichatka. It represents the basal sedimentary unit of Siberia’s sedimentary cover, resting on the crystalline basement (mostly Paleoproterozoic, ca. 1.8–1.9 Ga). The Purpol Fm consists of mature red-bedded sandstones that are interpreted to have formed in a shallow sea environment. Sedimentary strata overlying the Purpol Fm and representing Siberia’s passive margin sequence are conventionally regarded as Riphean in age. Their age has been revised recently and is though to be younger. For example, tillites at the Lake Nichatka, which directly overly the Purpol Fm, were correlated with the Varanger Tillite. At present, there are no geochronological or paleontological data to constrain the age of deposition of the Purpol Fm. Thus, formally the age of the Purpol Fm can be anything between 1.8 and 0.7 (or 0.6) Ga.