Palaeontology, biostratigraphy and palaeoecology of the graptolites from the Hulo Formation (Darriwilian–Sandbian) in northwestern Zhejiang Province, East China
Creators: name: Ma, Xuan
Publisher: name: Zenodo
Year: 2023
Subjects: Graptolite Fauna
Hulo Formation
Palaeoecology
Northwestern Zhejiang
Middle–Late Ordovician
South China Block

description: Darriwilian (Middle Ordovician) to early Sandbian (Late Ordovician) is an<br> interval of critical transitions in global tectonics and sedimentary environments, and a<br> key period for the Great Ordovician Biodiversification Event (GOBE) and the rising<br> of the Paleozoic Evolutionary Fauna (PEF). As one of the predominant zooplanktons<br> of PEF, graptolites underwent a rapid phylogenetic evolution and burst of new forms,<br> and reached its taxonomic and morphological diversity acmes in Darriwilian.<br> Among the most significant turnovers is the replacement of dichograptids, a<br> fauna typified by its multiramous morphos and its predominance in the Early<br> Ordovician, by diplograptids, which first appeared in the early Middle Ordovician and<br> predominated in the entire Late Ordovician. Furthermore, a variety of morphological<br> types of graptolites appeared, including the tubaria of scandent, partially scandent,<br> non-scandent, single-stiped and rod-like forms, as well as some extraordinary<br> architectures of thecal morphology and arrangement, such as extremely elongated or<br> strongly deformed thecae, intensely compact proximal end by means of<br> obverse-reverse thecal superposition, or massive reduction of thecal walls. These<br> various kinds of new architectures of tubaria and thecal types represent a significant<br> functional and palaeoecological innovation in the evolutionary history of graptolites.<br> A study on the palaeontology, biostratigraphy and palaeoecology of diverse<br> Darriwilian to early Sandbian graptolite fauna with continuous biostratigraphic<br> occurrences, will enhance our understanding of graptolite macroevolution in response<br> to environmental changes during the GOBE. In the Jiangnan Region, Darriwilian to early Sandbian strata are continuous and<br> well-exposed, which are dominated by graptolitic shale facies, and yield abundant<br> planktonic and nektonic fossils. This is ideal for the study of the graptolite evolution<br> and palaeoecology. This dissertation deals with the systematic palaeontology,<br> biostratigraphy and paleoecology of Darriwilian to early Sandbian graptolites (Hulo<br> Palaeontology, biostratigraphy and palaeoecology of the graptolites from the Hulo Formation<br> (Darriwilian–Sandbian) in northwestern Zhejiang Province, East China Formation) from the region with a special reference to the driving mechanism of<br> graptolite macroevolution. During 2013-2018, over 3000 graptolite specimens were<br> collected from four sections of the Hulo Formation in the northwestern Zhejiang<br> Province, i.e. the Jiumulong and Lajichang sections in Anji County, and the Shengcun<br> and Songtian sections in Tonglu County. Based on the collection, 52 species of 25<br> genera belonging to 11 families and 1 subfamily are identified, and all of them are<br> systematically described, compared and discussed in the present dissertation.<br> A continuous graptolite biozonation comprising some six biozones is proposed<br> for the Hulo Formation in the two areas. Four graptolite biozones are identified for the<br> Hulo Formation in the Anji area, which are, in ascending order, the Acrograptus<br> ellesae Biozone, Nicholsonograptus fasciculatus Biozone, Pterograptus elegans<br> Biozone and Jiangxigraptus vagus Biozone, suggesting a Darriwilian age. For the<br> topmost Ningkuo Formation and the Hulo Formation in the Tonglu area, 5 graptolite<br> biozones and 1 subbiozone are identified, which are, in ascending order the<br> Undulograptus sinicus Subbiozone (of the Undulograptus austrodentatus Biozone),<br> Acrograptus ellesae Biozone, Nicholsonograptus fasciculatus Biozone,<br> “Hustedograptus teretiusculus Biozone” and “Nemagraptus gracilis Biozone”,<br> suggesting an age spanning Darriwilian to the earliest Sandbian. These biozones are<br> well correlated with those equivalent graptolite biozones in some other blocks or<br> regions of the world. By means of functional morphology and analogue analysis, the dissertation<br> attempts to understand the origination and functioning of some extraordinary<br> morphological features in Darriwilian, e.g. the extremely elongated thecae, intensely<br> compact proximal end of tubarium and the massive reduction of thecal walls. The<br> results show the appearances and development of these novel complexes of graptolite<br> morphology in the Darriwilian are resulted from the enhancement of feeding<br> efficiency and the protection and defense strategies, driven by the pressure derived<br> from consistently limited food sources and bursting planktonic organisms, and the<br> increasing predation pressure from giant predators such as the nautiloids during the<br> GOBE.
description: A dissertation submitted to the University of Chinese Academy of Sciences in partial fulfillment of the requirement for the degree of Doctor of Philosophy in Palaeontology and Stratigraphy