From a fossil assemblage to a paleoecological community---Time, organisms and environment based on the Kaili Lagerstatte (Cambrian), South China and coeval deposits of exceptional preservation.

摘要

Complex, multicellular life underwent a global adaptive radiation in the lower to middle Cambrian (∼542 Ma). The fossil record is dominated by hard part fossils, but rarely a site of exceptional preservation allows study of both organisms with hard parts and organisms composed of soft, non-mineralized tissue. The Burgess Shale Biota was the first fully described fossil assemblage in the Cambrian that contains a relatively complete picture of an ancient living benthic community. More and more Burgess Shale-type (BST) fossil assemblages have been discovered since then and are ready to be utilized to test hypotheses about the paleoecology of the Cambrian explosion, which is the most important event in the evolution of metazoans. The Kaili Biota is the primary focus of this dissertation, but other Proterozoic, Cambrian, and Ordovician material was also studied.; The first part of my Kaili research includes literature review, sequence stratigraphy, and biostratigraphy. Although the research on Kaili Formation began in 1960s, Kaili is not well known to all Western scientists because most of the Kaili studies (at least 116 papers) were published in Chinese and in Chinese journals that have limited circulation. Therefore, a comprehensive review on the discovery, significance, and social impact of the Kaili Biota is provided here for English-speaking readers. Based on my field work, the lateral extent of both the Kaili Biota and the newly discovered Balang Biota of Guizhou and their sequence stratigraphic context is now better understood. In addition, a compilation of all geological studies on the Kaili Formation is completed to reinforce its potential as a global stratotype.; The second part of my Kaili research focuses on the taphonomy of well-preserved fossils. Based on additional occurrences of trilobite soft-part preservation, Olenoides trilobites are not considered deposit feeders based on the mud-free and sclerite-free gut content. Taphonomic considerations of Chinese echinoderms include entombment patterns, decay sequences, individual-specific diagenetic histories, unusual burial postures, selective disarticulation patterns, and postmortem elongation. Chemical analyses reveal that carbon, calcium, manganese, and iron are the major elements responsible for the variety of colors exhibited by Guizhou gogiid echinoderms. Three-dimensional stereomic microstructure occurs on the external surfaces of thecal plates in two gogiid species. Stereom preservation in calcite suggests that the dissolution of calcareous echinoderm plates, yielding characteristic moldic preservation, is sub-Holocene. Kaili also contains intact egg clusters. Unlike previous studies on the Cambrian embryos based on the Orsten-type deposits, Kaili embryo material is preserved in a fine-grained siliciclastic setting; thus, it provides a new taphonomic window for egg/embryo preservation.; The third part of my Kaili research is to understand its paleoecology. A new hypothesis on trilobite dispersal is proposed based on local population of trilobite larvae and juveniles. Echinoderm-substrate relations are documented in detailed. This study suggests that substrate availability is a crucial factor forcing on local echinoderm populations. Based on unusually preserved specimens, a reasonable model of gogiid echinoderms attaching to live brachiopods is reconstructed. Based on multiple occurrences of egg clusters, the depositional environment of Kaili Biota is regarded as a suitable spawning ground for benthic metazoa. The association of body fossils and trace fossils exemplified by Kaili material allows us to understand the effect of bioturbation on the formation of BST deposits. The paleoecologic information preserved in the Kaili Biota outlined here provides a roadmap to understand better the essential architectural elements of BST communities. It serves as a stepping stone to gain a more complete understanding of Cambrian life through the window of BST deposits.; I