Conifer‐dominant palynoflora from the Lower Cretaceous in Ordos Basin, China: Biostratigraphical and palaeoclimatic implications

• Published in: Geological journal (Chichester, England) Vol. 56; no. 3; pp. 1549 - 1563
• Main Authors: Zhang, Mingzhen, Dai, Shuang, Zhang, Xianwen, Wang, Sen, Du, Zhen, Ma, Bo, Du, Baoxia
• Format: Journal Article
• Language: English
• Published: Hoboken, USA John Wiley & Sons, Inc 01.03.2021; Wiley Subscription Services, Inc
• Subjects: China; Climate; Climatic conditions; Conifers; Coring; Cretaceous; Early Cretaceous; Ferns; Humid climates; Ordos Basin; Palynology; Pollen; Sedimentary rocks; Spores; Zhidan Group; Ordos Basin; China
• ISSN: 0072-1050; 1099-1034
• DOI: 10.1002/gj.4015

Open oceanic and coastal marine sedimentary rocks provide abundant valuable records of Cretaceous greenhouse climates, but limited information is available regarding the Cretaceous continental climate regimes. This study presents a palynological report from the middle Zhidan Group based on the ZK1046 drillcore in the southwestern Ordos Basin of central China. A total of 52 types of palynomorphs including 15 genera of spores (20 species) and 24 genera of gymnosperm pollen (34 species) were recognized in the palynological assemblages. Upwards from the base, the palynomorph assemblages in the ZK1046 drill core were not very diverse. They were dominated by bisaccates and proto‐saccate pollen (around 80%), followed by some fern spores and a low content of Classopollis (below 10%). The overall characteristics of the palynomorph assemblages and some biostratigraphically significant palynomorph genera, such as Ephedripites, Jugella, and Rugubivesiculites, suggest that the middle Zhidan Group dates from the middle Early Cretaceous (probably Hauterivian). Vegetation reconstruction points to conifer‐dominated forests with subordinate pteridophyte, Taxodiaceae, and a few Cheirolepidiaceae plants, indicating a relatively stable, cold, and slightly humid environment. This climatic condition was a likely response to the relatively cool global climate during the middle Early Cretaceous. Climatic correlation in the Late Valanginian to Early Barremian indicated by the TEX86 palaeo‐temperatures , oxygen isotope values of bulk carbonate, changes of percentage of conifer pollen, and the generalized palynoflora in the Liupanshan Basin, the Northern Jiangsu Basin, the Zhidan Group (this study), the Tuchengzi Formation, and the Gongpoquan Basin