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

Abstract

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.

Long‐term arid and hot climate during early Mid‐Cretaceous indicate by unvaried Cheirolepidiaceae‐dominant palynoflora from the Liupanshan Basin, China

“…The Zhidan Group in the middle Early Cretaceous in Ordos Basin is close to the study area. The group was dominated by conifers ascribed to Pinaceae, Podocarpaceae, and other ancient conifer types, accompanied by moderate levels of Cheirolepidiaceae and small amounts of ferns (Zhang et al, 2021). It indicates that the climate of the middle part of Zhidan Group was relatively stable, cool and slightly wet during the late Valanginian to early Hauterivian period (Zhang et al, 2021).…”

“…The group was dominated by conifers ascribed to Pinaceae, Podocarpaceae, and other ancient conifer types, accompanied by moderate levels of Cheirolepidiaceae and small amounts of ferns (Zhang et al, 2021). It indicates that the climate of the middle part of Zhidan Group was relatively stable, cool and slightly wet during the late Valanginian to early Hauterivian period (Zhang et al, 2021). In the earliest late Aptian period, Taxodiacean, Podocarpaceae and Pinaceae conifers were the most prominent features in the vegetation pattern of Huoshizhai section, while Cheirolepidiaceae was rare.…”