Famennian phytoplankton from the Hongguleleng Formation of Western Junggar, NW China

Abstract

The Hongguleleng Formation is a stratigraphical unit in proximity to the Frasnian/Famennian and Devonian/Carboniferous boundaries within the Kazakhstan Palaeoplate. Nonetheless, the absence of conodont, ammonoid, and brachiopod assemblages in some significant stratigraphical horizons limits the precise subdivision of the formation. To address this issue, a new palynostratigraphical analysis was conducted at the Gennaren section, in order to provide additional data that would facilitate the delineation of biostratigraphical zones within the Hongguleleng Formation. In this study, a total of forty-one phytoplankton species belonging to 20 genera have been identified, including some in open nomenclature. The phytoplankton taxa can be separated into three assemblages. Of particular interest is the species Ammonidium levigatum, which exhibits potential as an index acritarch species for equivalents of the VCo miospore Zone in eastern Europe. The phytoplankton assemblage described here has its taxonomic composition closest to northeastern Europe (Poland) and belongs to the Laurussia Realm at a time of high cosmopolitanism. According to the percentage of marine and terrestrial palynomorphs observed in the Gennaren section, the sedimentary environment of the lower member of the Hongguleleng Formation is interpreted to have undergone a dynamic transformation, shifting initially from a coastal environment to a neritic one, subsequently shifting to a deep-water setting, and ultimately reverting back to a neritic environment.