Early Cambrian microfossils from the cherts in carbonates of the Kuruktag area, the Tarim block

Abstract

The basal Cambrian is characteristic for the appearance of small shelly fossils and acanthomorphic acritarchs with relatively small vesicles. In the Tarim Block (NW China) and South China, this microfossil assemblage is dominated by small acanthomorphs and was referred to as the ‘Micrhystridium-Paracymatiosphaera-Megathrix’ (MPM) association, based on microfossils from the lower Cambrian Yurtus and Xishanblaq formations of the Tarim Block. This study provides the new early Cambrian microfossil assemblage preserved in cherts of carbonates in Tikebuladahuang section of the Kruktag area, Tarim Block. These early Cambrian microfossil assemblages come from upper part of the lower Cambrian Xishanblaq Formation in Tikebuladahuang section correlated with the Cambrian Stage 2, and the microfossil association dominated by Heliosphaeridium dissimilare, sponge spicules, Leiosphaeridia spp., and Siphonophycus sp. also occurs. The organic-walled microfossil assemblage found in this study can be compared with the microfossils in the early Cambrian Chert of the Yangtze plate. The Asteridium–Heliosphaeridium–Comasphaeridium (AHC) association in South China and the Tarim block may mix two fossil associations of different ages and fossil compositions.