Middle–late Ordovician Chitinozoans from Drillcores in the Western Ordos Basin, North China

The Middle–Upper Ordovician black shale succession of the Wulalik Formation in the western Ordos Basin represents one of the key shale gas target intervals on the North China Block. Previous research has largely focused on evaluating its shale gas potential and identifying favourable target horizons within the formation. Here we conducted a systematic investigation on chitinozoans — critical index fossils for biostratigraphic and chronostratigraphic correlations — based on two drillcore samples in the Ordos Basin. Chitinozoans are documented from the Wulalik and its overlying Lashizhong formations, spanning the upper Darriwilian to Sandbian. A total of 26 species from 10 genera are identified, among which Belonechitina tuberculata and B. hirsuta have been designated as index fossils in Baltica and North America, enabling precise global biostratigraphical correlations. The chitinozoan assemblage also correlates closely with coeval successions in the Upper Yangtze Platform and Tarim Basin. As the first formal record of chitinozoans from the Ordos Basin, this work fills a long-standing gap in chitinozoan datasets in North China. It facilitates high-resolution biostratigraphic correlations across North China, Tarim and South China for this stratigraphic interval, provides robust paleontological support for temporal calibration, and thus advances the shale gas exploration in this area.