RECORD OF EDIACARAN COMPLEX ACANTHOMORPHIC ACRITARCHS FROM THE LOWER VINDHYAN SUCCESSION OF THE CHAMBAL VALLEY (EAST RAJASTHAN), INDIA AND THEIR BIOSTRATIGRAPHIC SIGNIFICANCE

摘要

Abundant and well-preserved Ediacaran complex acanthomorphic acritarchs are recorded from the Lower Vindhyan succession in the recently drilled wells of CH-A, PL-A and SK-A in the Chambal Valley part of Vindhyan Basin. Important complex acanthomorphs recorded include various species of Apodastoides, Appendisphaera, Cavaspina, Ceratosphaeridium, Densisphaera, Gyalosphaeridium, Knollisphaeridium, Sinosphaera and Tanarium. Other significant forms are the species of Lophosphaeridium, Obruchevella, Schizofusa and Vandalosphaeridium. In addition, three new acanthomorph taxa, viz. Archaeoacanthodiacrodium, Chambalasphaeridium and Triloboacanthosphaeridium are identified. The above-mentioned complex acanthomorphs first appear in the basal part of the Lower Vindhyan Group, become abundant in the middle and finally disappear in the upper part of the Lower Vindhyan Group within the lower Suket Shale, suggesting an early Ediacaran age for the above succession. The middle and upper parts of the Suket Shale are dominated by Lophosphaeridium rarum, Obruchevella spp. and Leiosphaeridia spp. along with abundant filamentous microfossils, suggesting late Ediacaran age. The uppermost part of the Suket Shale and the overlying Upper Vindhyan succession are marked by the occurrence of Asteridium tornatum, Comasphaeridium sp., Cristallinium cambriense, Dictyotidium birvetense and Lophosphaeridium tentativum of Early Cambrian age.