Palynological records from two cores in the Gongpoquan Basin, central East Asia: Evidence for floristic and climatic change during the Late Jurassic to Early Cretaceous

Current understanding of late Mesozoic greenhouse climates is mainly based on palaeoclimatic information from oceanic and coastal marine sedimentary rocks. In contrast, detailed information on the climatic evolution of continental interiors is comparatively rare. This study presents a palynomorph record based on two cores drilled in the Gongpoquan Basin of northwest China located in central Asia during Late Jurassic to Early Cretaceous times. Based on these palynomorph records (G2709 and K705 successions), a total of three stratigraphic sequences with long depositional gaps can be distinguished, consisting of the Lower Jurassic Shazaohe Formation, the Lower Cretaceous (Berriasian to Valanginian) Laoshuwo Group and the Lower Cretaceous (Aptian to Albian) Laoshuwo Group. The palynomorph data provides information on prominent changes of vegetation and climate during the late Mesozoic. During Oxfordian times, spore-producing ferns show a short-lived increase, followed by a long-lasting period of Classopollis dominance during the Late Jurassic, which points to the establishment of continuously dry and warm conditions. In contrast, a more humid and probably warmer climate is indicated by the composition and high diversity of the palynoflora in the Early Cretaceous (Berriasian to Valanginian). Comparison with palynofloras of the same age from other continental basins of northwest China shows a similar vegetation change from Late Jurassic Cheirolepidiaceae-dominated forests to Early Cretaceous mixed forests composed of conifers (including Taxodiaceae and Pinaceae), cycads and pteridophytes.