Lagerstätte fossils from the Lower Cretaceous Yixian Formation of the Pingquan Basin, North China: stratigraphical correlation and palaeoenvironmental implications

Abstract

The Lower Cretaceous Yixian Formation in northeast China mainly contains the Jehol Biota. Notable investigations of the area have led to the discovery of feathered dinosaurs, angiosperms and numerous other exceptionally well‐preserved fossils. The Yixian Formation is mostly composed of basalts interbedded with siliciclastic sediments that can be divided into several beds (from lower to upper layers, the Jianshangou Bed, Dawangzhangzi Bed and Jinggangshan Bed). However, the stratigraphy and fossils of the Yixian Formation in the northern Hebei Province are less understood than those of the western Liaoning. This study carried out a sectional excavation on a lacustrine deposit outcrop of the Yixian Formation from the Pingquan Basin in northern Hebei (the Shimen section). This fieldwork resulted in a detailed lithostratigraphical description of 52 layers, including three abundant fossil layers found within a fine‐grained clastic deposit that is 15.48 m thick. A preliminary palaeontological record was also created from primary observations and from information from previous investigations. Representative fossils included the lizard Jeholacerta formosa, fish Lecoptera sp. tadpole shrimp Chenops yixianensis conchostracans Eosestheria, dragonfly Samarura and the palaeobotanical conifers Liaoningocladus boii and Schizolepis. Comparing the lithostratigraphy and biostratigraphy of this section with other Lower Cretaceous sections in the western Liaoning, the lacustrine strata of the Shimen section correlate to the lower part of the Yixian Formation's Dawangzhangzi Bed. Based on the analysis of the characteristics of the sediment and the typical types of the plants from this section, it is suggested that the Pingquan Basin is a small volcanic‐sediment basin, in temperate palaeoclimate during its deposition period.

Insect herbivory immediately before the eclipse of the gymnosperms: The Dawangzhangzi plant assemblage of Northeastern China

“…The Yixian Formation consists of deposits containing a series of tuffaceous strata that are interbedded with sedimentary facies (Fürsich et al ., 2007; Zhu et al ., 2007; Pott et al ., 2012a; Yang et al ., 2020), a stratigraphy also found in adjacent coeval basins (Qin et al ., 2019). Depositional environments of Yixian strata primarily consist of fluvial and lacustrine strata modified by layers of tuff (Zhu et al ., 2007; Yang et al ., 2020).…”

“…Fourth, was a community of emergent hydrophytes and plants of waterlogged soils consisting of horsetails and Archaefructus angiosperms. These plant communities typically are associated with particular assemblages of insects and arthropods (Zhou et al ., 2003; Matsukawa et al ., 2014), and strata of distinctive biofacies (Qin et al ., 2019).…”

First representative of the odonatan superfamily Triassolestoidea (Odonatoptera: Parazygoptera) from the Upper Triassic of the Korean Peninsula

“…The elongated body shape is of 'zygopteran-type', with three expanded gills at the apex of the abdomen resembling the 'Samarura-type', which is characterized by broad leaflike caudal gills (Nel & Paicheler 1994). 'Samarura-type' nymphs have been reported from Upper Triassic and Lower Cretaceous strata (Qin et al 2019), with Pritykina (1985) The Triassic isophlebiopteran Triassolestes epiophlebioides was identified from the Carnian section of the Ipswich Coal Measures in Queensland, Australia, which are coeval with the 'Samarura-type' nymph described by Rozefelds (1985). Similarly, the stratigraphical proximity of GNUE112004/ GNUE112005 to BCM2081 as a possible imago could indicate the referral of the nymph to Isophlebioptera.…”