Microfossils from the Late Precambrian Altyn Formation of Montana

Abstract

SEDIMENTARY rocks of the late Precambrian Belt Supergroup are exposed in western Montana, Idaho, and adjacent parts of Canada. There are few reports of microfossils from the Belt Supergroup, although Metazoan ancestors may occur in the younger, upper Belt Missoula Group¹. Early this century Walcott² concluded that stromatolites found in the Belt were produced by blue-green algae. He reported pyritised blue-green algal filaments, associated with stromatolites, from the Newland Limestone of lower Belt age. Recent re-examination of this material supported Walcott's interpretation³. I report here the discovery of microfossils, which are older than 1,300 m.y., from the lower Belt Altyn Formation.