Tianzhushania spinosa and other large acanthomorphic acritarchs of Ediacaran Period from the Infrakrol Formation, Lesser Himalaya, India

Abstract

Covering a time span from Ediacaran (base of Blaini pink carbonates) to Early Cambrian (base of Tal Group), the Krol belt in the Lesser Himalaya (India), occurs as a series of synclines from Solan, Himachal Pradesh in the north-west to Nainital, Uttarakhand in the south-east. Various lithostratigraphic divisions of this belt reveal many palaeobiological entities, namely cyanobacteria, algae, acritarchs, small shelly fossils and trace fossils. Globally, large acanthomorphic acritarchs of the Ediacaran Period are used as significant biostratigraphic tools for global correlation. In the Krol belt, reports of acanthomorphic acritarchs from the Infrakrol and Krol ‘A’ formations of the Krol Group have further supported this notion. This paper reports well-preserved microfossils including acanthomorphic acritarchs, sphaeromorphic acritarchs, coccoids namely Tianzhushania spinosa, T. polysiphonia, Papillomembrana compta, Schizofusa sp., Gloeodiniopsis lamellosa, Sphaerophycus medium, and the unnamed forms A, B and C from the chert nodules of the Infrakrol Formation exposed in the Nainital Syncline of the Kumaun Lesser Himalaya. A biostratigraphic correlation based on acanthomorphic acritarchs suggests that the Infrakrol Formation is coeval to the lower Tianzhushania assemblage zone of the Doushantuo Formation of south China. Tianzhushania and Papillomembrana are significant additions to the previous record of the Ediacaran acanthomorphic acritarchs from the Lesser Himalaya of India and provide an independent evidence for construction of both biozonation scheme and paleogeography.