A palynoflora of southern Xinjiang, China, and the proximity of the Tarim Plate to western Gondwana during the Llandovery (Silurian)

Abstract

The Tarim Plate, an independent continent during the Paleozoic, is of significance in understanding life and environment evolution, however, its paleogeography during the early Silurian is poorly known. Palynology, especially on land-derived palynomorphs, provides independent evidence for paleogeography as a supplement to paleomagnetic data. Here we recognize a Llandovery palynoflora from two sections (Arisu and East Dawangou) of the Kalpintag Formation in the northwestern Tarim Basin, Xinjiang, China, the paleontological evidence of which suggests that the Tarim Plate was proximal to western Gondwana during the early Silurian. The palynoflora consists of moderately diverse cryptospores with eight genera and twelve species, as represented by Laevolancis chibrikovae, Sphaerasaccus glabellus, Dyadospora murusdensa, Pseudodyadospora laevigata, P. petasus, and Tetrahedraletes medinensis. The monad S. glabellus reported herein is the first record from China. Other palynomorphs include a large number of sphaeromorph acritarchs, some tubes and cuticle-like sheets, and a few scolecodonts. The various kinds of meiosis process and predetermined diversity of older cryprospore producers in the Tarim Basin, together with ecological factors, contribute to the evolution of the Kalpintag cryptospore producers. By taxonomic comparisons of global coeval sporomorph records, combined with quantitative analyses (Cluster Analysis and Nonmetric Multidimensional Scaling Analysis), the Kalpintag palynoflora shows more closely related to those in northern Chad, northeastern Libya and central Saudi Arabia. The geographical zonation of sporomorph might emerge in the Llandovery. The geographical proximity of the Tarim Plate to western Gondwana during that time is also suggested.