Early Neoproterozoic scale microfossils in the Lower Tindir Group of Alaska and the Yukon Territory

The Tindir Group is a <4-km-thick Neoproterozoic succession exposed in the Tatonduk inlier of east-central Alaska and the western Yukon Territory. The Tindir Group is informally divided into the Lower Tindir Group, which consists of <2 km of mixed carbonate and clastic rocks, and the overlying Upper Tindir Group, which contains two Cryogenian glacial deposits and an additional Ediacaran succession of mixed carbonate and clastic strata. Unique mineralized scale microfossils have been recovered from sections previously correlated with the Upper Tindir Group, and interpreted variously as Cryogenian to early Cambrian in age. Our remapping of the area indicates that these sections are stratigraphically below an early Cryogenian glacial diamictite, unit 2 of the Upper Tindir Group, and are actually part of the Lower Tindir Group. Carbon and strontium isotope correlations further suggest that the fossiliferous Lower Tindir Group is correlative with early Neoproterozoic strata of the northwestern Canadian Cordillera. This new age model is consistent with the accompanying microfossil assemblage and indicates that the diverse microfossils in the Lower Tindir Group can be added to the early Neoproterozoic record of eukaryotic evolution.