title: Quantitative analysis of Triassic-Jurassic pollen and spores for paleoenvironmental and paleoclimate reconstructions
Creators: name: Zhang, Jianguang
Publisher: name: UNSPECIFIED
Year: 2022

description: The eco-group classification based on the growth-form of plants (Eco-Plant model) is widely used for extant, Cenozoic, Mesozoic, and Paleozoic palaeoenvironmental reconstructions. However, for most Mesozoic dispersed sporomorphs, the application of the Eco-Plant model is limited, because either their assignment to a specific eco-group remains uncertain or the botanical affinities to plant taxa are unclear. A new database Sporopollen (http://www.sporopollen.com) focused mainly on Mesozoic sporomorphs is created. Currently, it has collected 100,610 sporomorph pictures, 59, 498 plant pictures, 31, 922 sporomorph descriptions. At the same time, from 63, 035 references, it has collected 2, 215, 162 occurrences for both sporomorph and non-sporomorph fossils. The collected plant data include 32, 972 genera from 946 families. The collected sporomorph pictures include 5, 857 genera. With the help of the database, 861 dispersed Mesozoic sporomorph genera of Bryophytes, Pteridophytes, and Gymnosperms are reviewed by comparing the unique outline and structure/sculpture of the sporomorph wall with that of modern plants and in situ fossil plants. The results show that 474 of them can be linked to their closest parent plants and Eco-Plant model at family or order level, but 387 of them can not because of the lack of detailed ultrastructure descriptions. The use of a light microscope (LM) for determination is one of the main reasons that some dispersed sporomorphs cannot be linked precisely to their parent plants. The presented eco-groups for disperse Mesozoic sporomorphs provide the possibility to identify detailed vegetation and palaeoenvironmental change in the Mesozoic, especially in the context of climate change. A new interface (http://www.sporopollen.com/sporemesozoicsegs.php?opencode=paper1) was created based on the reviewed result to quickly link the dispersed sporomorphs to past vegetation patterns and climatic changes. Users can upload their data to the database and in return get quick results. It can automatically link all of the Mesozoic and Cenozoic sporomorphs to their possible parent plants at phylum, order, or family level. It can also automatically link all of the Triassic and Jurassic sporomorphs to the Eco-Plant model to assess the effect of humidity (EPH) and the effect of temperature (EPT). By using 30 sporomorph samples from a 10 m thick lignite bed from the Upper Triassic Haojiagou Formation (Rhaetian) as an example, the palaeovegetation and palaeoenvironment of a peat-forming wetland near the Triassic-Jurassic boundary are discussed with the help of the Eco-Plant model. The results show that the palynoflora contains both Eurasian and Gondwanan elements, and is dominated by the spores and pollen of Bennettitales, Corystospermales, Ginkgoales, and Gleicheniales. At the Triassic/Jurassic boundary (Hettangian), the palynoflora significantly changes as Cyatheales spores become the dominant elements. We analyse assemblages in terms of an Eco-Plant model, which assigns the parent plants of the palynomorphs into five groups based on humidity and four groups based on temperature, and uses multivariate statistical analyses to infer palaeoclimate and palaeoenvironmental conditions. Results suggest that the palaeoclimate of the Rhaetian was generally wet and subtropical with short seasonal drought periods. Our analysis shows that an Eco-Plant model may be a useful tool to reveal past vegetation patterns and climate changes, applicable to other Mesozoic assemblages.