Vegetation changes and climate shift during the latest Ladinian to the early Carnian: Palynological evidence from the Yanchang Formation, Ordos Basin, China

Abstract

The Middle–Late Triassic climates have attracted the attention of paleontological and geological scientists for the Carnian pluvial event in the early Late Triassic. The event is well-documented in the pelagic and epi-continental marine deposits of the Tethys, Gondwana, and Laurasia. However, inland terrestrial deposits are less frequently depicted, with high-resolution palynological biostratigraphy constraints. In this study, we report the palynological records from the YC8-1 and YC7-3 sub-members of the Yunmeng profile in the Ordos Basin, China, where the YC7-3 was dated at 236.0–234.1 Ma. Two palynological assemblages were recognized and named the Lundbladispora watangensis–Taeniaesporites combinatus assemblage and Lundbladispora communis–Discisporites granulus assemblage for the YC8-1 and YC7-3 sub-members, respectively. Their ages were determined to be the latest Ladinian and early Carnian, respectively, for their stratigraphic correlations with the global boundary stratotype section and point (GSSP) of the base of Carnian in Europe and additional co-occurring floras with condonts in the Upper Triassic of South China. The coexistence of Cyathidites minor (Couper, 1953), Dictyophyllidites harrisii (Couper, 1958), Apiculatisporis bulliensis (Helby ex De Jersey, 1972), Aratrisporites xiangxiensis (Li and Shang, 2011), Piceaepollenites omoriciformis (Bolkh.) (Xu and Zhang, 1984), Podocarpidites ornatus (Pocock, 1962), Discisporites granulus (Zhang, 1984), and Classopollis (Pflug, 1953) is equivalent to the Carnian palynostratigraphic criterion reported in the North China palynofloristic realm. Vegetational changes, especially those occurring at the boundary between Ladinian and Carnian, account for approximately 70% of ferns and over 30% of gymnosperms lost. These were discovered and attributed to the strong seasonal arid climate, indicated by the emergence of Cheirolepidiaceae and Pinuspollenites. We thus know that the climate during the latest Ladinian and early Carnian was “hot house” with seasonal aridity. In addition, three strong monsoonal pluvial pulses were signaled by the humidity index of lowland plants. The present study will enable a better understanding the Carnian pluvial event in the Late Triassic inland basin.

Distinctive volcanic ash–rich lacustrine shale deposition related to chemical weathering intensity during the Late Triassic: Evidence from lithium contents and isotopes

“…On the basis of this age model, the onset time of the CPE event in this drill core interval is 234.0 Ma (Fig. 1C), broadly coinciding with the Carnian palynostratigraphic study of the drill core Y1011 and Yunmeng profile (28,32,33). Both the zircon U-Pb ages and the spore-pollen fossils of Chang 7 Member are comparable with those of Tanzhuang and Anyao Formations (232.9 ± 2.1 and 233.1 ± 1.3) in Jiyuan Basin (adjacent to the Ordos Basin), which systematically recorded the CPE (34,35).…”

High‐frequency temporal variability of provenance signal in the submarine fan with the narrow shelf: Insights from sediment delivery and formation of late Triassic Zhuoni fan in the northeastern Paleo‐Tethys Ocean

“…Cawood et al., 2012; Dickinson & Gehrels, 2009). The maximum depositional age of sample PY‐21 towards the upper part of the Panyuan section was 236.00 ± 3.31 Ma, calculated by the youngest grain cluster at 1δ (Figure S4), or 236.88 ± 4.25 Ma (Figure S5), calculated by the maximum likelihood algorithm (Coutts et al., 2019; Vermeesch, 2021), demonstrating that the true depositional age was dated to the early‐middle Carnian that was gradually influenced by monsoon‐induced precipitation and possibly even the subsequent Carnian Pluvial Episode (Li et al., 2023). In addition, the occurrence of Neocalamites in the hyperpycnites in the lower part of the Panyuan section also confirmed the late Triassic deposition (Li et al., 2019).…”

“…The late Triassic humid pulses within the overall hot and arid climate recorded in the surrounding area (e.g. the Ordos Basin by Chen et al, 2021;Li et al, 2023) could have been the main cause of the initiation of marine hyperpycnal flows. Furthermore, the narrow shelf configuration is also favourable for the plunge of marine hyperpycnal flows (Mulder et al, 2003).…”