Search

Abstract: Abundant data have been acquired on the lower Cambrian small shelly fossils (SSFs) of the Yangtze platform during the last three decades, demonstrating that these fossils are an important piece of evidence for the Cambrian radiation and are useful biostratigraphic tools for correlating the lower Cambrian. Here we report SSF associations from the Yanjiahe Formation in the Three Gorges area, South China. The Yanjiahe Formation is well exposed near the Yanjiahe village, and its 40-m-thick sequence can be subdivided on the basis of lithology into five stratigraphic intervals (beds). Small shelly fossils occur mainly in Beds 2 and 5, but abundant SSFs were discovered in thin sections of siliceous–phosphatic nodules from Bed 3 for the first time. No skeletal fossils were discovered in the basal siliceous rock interval (Bed 1), but the negative δ13Ccarb excursion and the occurrence of the acritarch Micrhystridium regulare indicate that it belongs to the basal Cambrian. The SSF associations are somewhat similar to those of East Yunnan, and can be differentiated into three biozones (in ascending order): the Anabarites trisulcatus–Protohertzina anabarica assemblage zone (Bed 2), the Purella antiqua assemblage zone (Bed 3), and the Aldanella yanjiaheensis assemblage zone (Bed 5). The occurrence of A. yanjiaheensis in Bed 5 probably indicates that Bed 5 belongs to Cambrian Stage 2, but the Stage 2/Stage 1 boundary is uncertain since Bed 4 lacks fossils. SSF biostratigraphy indicates that the Yanjiahe Formation is pretrilobitic Meishucunian in age (equivalent to the Nemakit–Daldynian to Tommotian of Siberia, Terreneuvian). Five SSF genera occur in Bed 2, more than six genera in Bed 3, and twenty-three genera in Bed 5. The stepwise increase in generic diversity through the Yanjiahe Formation is comparable with the global diversity increase through the Nemakit–Daldynian to early Tommotian interval. [Copyright &y& Elsevier]

Abstract: Small shelly fossils (SSFs) occur widely on the Yangtze Platform and have great potential for biostratigraphic subdivision of pre-trilobitic Early Cambrian strata. Based on the SSF record of the shallow water realm, five biozones can be recognized for the Meishucunian Stage. In ascending order the biozones are: Anabarites trisulcatus–Protohertzina anabarica Assemblage Zone; Paragloborilus subglobosus–Purella squamulosa Assemblage Zone; Watsonella crosbyi Assemblage Zone (formerly Heraultipegma yunnanensis Zone); poorly fossiliferous interzone; Sinosachites flabelliformis–Tannuolina zhangwentangi Assemblage Zone. In addition one SSF biozone is recognized for the overlying Qiongzhusian Stage: Pelagiella subangulata Taxon-range Zone. The formerly used Siphogonuchites triangularis–Paragloborilus subglobosus Zone and Heraultipegma yunnanensis Zone are discussed and redefined. Approximately 80 species of SSFs were screened for their spatial and temporal distribution on the Yangtze Platform. Variations in lithofacies and biofacies can be recognized throughout the Yangtze Platform, extending over an area of 2000×900 km. In a deeper water shelf setting the first zone is represented by the Protohertzina anabarica–Kaiyangites novilis Assemblage Zone, while younger zones are not recognized in the southern region. At the northern platform margin the Qiongzhusian is represented by the Ninella tarimensis–Cambroclavus fangxianensis Assemblage Zone and the Rhombocorniculum cancellatum Taxon-range Zone. The southeastern Shaanxi–western Hubei region followed a slightly different lithological and faunal development than the rest of Yangtze Platform, indicating a stronger similarity with parts of East Gondwana. Some taxa such as W. crosbyi, P. subangulata, R. cancellatum, Microdictyon effusum, A. trisulcatus, Protohertzina unguliformis, and P. anabarica occur nearly worldwide and support an international correlation of Early Cambrian sequences between the Yangtze Platform and smaller West Gondwanan blocks, Siberia, Newfoundland, and Australia. The six investigated zones of the Yangtze Platform comprise an interval spanning the early Nemakit–Daldynian to the late Atdabanian/early Botoman Stage on the Siberian Platform. Palaeobiogeographic analysis revealed a strong taxic similarity between the Yangtze Platform and the Tarim Platform. A smaller number of species are shared with other West Gondwanan platform fragments such as India and Iran. Palaeobiogeographic results do not support the previously reported position of the South China Block between Australia and Siberia during the Early Cambrian. [Copyright &y& Elsevier]

Extensive information has been acquired on the occurrence of Lower Cambrian Small Shelly Fossils (SSF) in the shallow water sediments of the western fringe of the Yangtze Platform (eastern Yunnan and central Sichuan Provinces) during the last two decades. However, less is known on the temporal and spatial distribution of SSFs on the northern margin of the Yangtze Platform. Here we report SSF associations from Kuanchuanpu (Ningqiang County, southern Shaanxi Province), Shatan, and Xinli (both Nanjiang County, northern Sichuan Province) representing the Southwest Shaanxi region and from Sanlangpu, and Xiaowan (Xixiang County, southern Shaanxi Province) of the Southeast Shaanxi – Northwest Hubei region. The thickness of the Lower Cambrian SSF-bearing strata strongly decreases in this region from West to East and the stratigraphic hiatus increases. An earliest Cambrian hiatus is widely distributed on the northern margin of the Yangtze Platform. At the same time, a syngenetic brecciation occurred in wide shallow shelf settings. A tectonic mobilization, possibly related to the assembly of Gondwana following the breakup of Rodinia, may be responsible for this. In sections near Kuanchuanpu (Ningqiang County), the Meishucunian (equivalent to the Nemakit-Daldynian to Tommotian of Siberia) succession comprises ca. 55 m of dark phosphatic carbonates, siltstones, and cherts. The SSF associations are similar to those of East Yunnan and, in ascending order, can be discriminated into the Anabarites trisulcatus – Protohertzina anabarica Zone, the Watsonella yunnanensis Zone (previously mentioned as Heraultipegma yunnanensis Zone), and the Sinosachites flabelliformis – Tannuolina zhangwentangi Zone. The Siphogonuchites triangularis – Paragloborilus subglobosus Zone cannot be unambiguously detected in the Southwest Shaanxi region. The occurrence of embryos and eggs within the Anabarites trisulcatus – Protohertzina anabarica Zone, which has been reported earlier, is remarkable. The previously reconstructed life cycle and taxonomic treatment of Olivooides / Punctatus are re-discussed. The earliest SSF associations (Anabarites trisulcatus – Protohertzina anabarica Zone to Watsonella yunnanesis Zone) are missing in the Southeast Shaanxi – Northwest Hubei region and the Ninella tarimensis – Cambroclavus fangxianensis Assemblage Zone and Rhombocorniculum cancellatum Taxon Range Zone are introduced herein. [Copyright &y& Elsevier]

Abstract: Eggs, embryos, and hatchlings of olivooids are common and distinctive components of the earliest Cambrian small shelly fossil assemblage (Anabarites trisulcatus–Protohertzina anabarica Zone) at the northern and northwestern edge of the Yangtze Platform. Embryos are preserved in 3D as phosphatized permineralizations with superficial cellular structures. Nanofocus X-ray computed tomography reveals that diagenetic structures characterize the interior of most phosphatized eggs and embryos. The Olivooidae fam. nov. is herein distinguished from the possibly related hexaconulariids. Statistical size investigations and morphological studies indicate that at least three, but possibly five or more species of olivooids occur in the early Cambrian of South China. Fossilized smooth egg stages reflect a high biodiversity, encompassing 8–10 or more biological species. Eggs and embryos of Olivooides multisulcatus, Olivooides mirabilis and Quadrapyrgites quadratacris are represented by distinct and characteristic size clusters. The size ranges of embryonic parts of hatchlings roughly correspond to the size clusters of the embryos. From reconstruction of the developmental series of Olivooides multisulcatus it appears that the cleavage mode of olivooids was transitional between superficial and total cleavage. Late embryos and hatchlings of Olivooides multisulcatus and Olivooides mirabilis are characterized by pentaradial symmetry, whereas tubes of Quadrapyrgites quadratacris exhibit tetraradial symmetry. Tubular hatchlings of olivooids may represent larval or adult stages, or perhaps, nonfeeding larvae. Although the biological affinity of olivooids is weakely constrained, we hypothesize that they belong within an extinct clade of the Cycloneuralia. Their assignment to the Cnidaria is considered unlikely. [Copyright &y& Elsevier]

Abstract: The study discusses the detailed composition of Terreneuvian small shelly fossil (SSF) assemblages of eastern Yunnan Province (Meishucun, Xianfeng and Huize regions). The described sections represent shallow water deposits of the Yangtze Platform that include a number of stratigraphical hiati. The reported SSF assemblages can be assigned to the regional SSF biozones I–III (Anabarites trisulcatus–Protohertzina anabarica Assemblage Zone; Paragloborilus subglobosus–Purella squamulosa Assemblage Zone; Watsonella crosbyi Assemblage Zone). Zones II and III are slightly redefined based on new data. Two subzones of Zone II are proposed here, namely, Annelitellus yangtzensis–Obtusoconus honorabilis Subzone and Maikhanella cambriana–Oelandiella korobkovi Subzone. Claviconchella qianyii gen. et sp. nov. and Bubiites simplex gen. et sp. nov. are reported. Here we also provide a critical revision of the SSF distribution for the well-known Meishucun section. The correlation scheme for East Yunnan documents the extent and duration of stratigraphical hiati. The distribution of SSFs and the lithological characterization indicate three major events of exposure of the carbonate platform resulting in sedimentary breaks and possible karstification. This prompts new consideration of the previously described stable isotope stratigraphy of shallow platform strata. Considering the complexity of the Terreneuvian Earth history as well as the uniqueness of SSF, an integration of sedimentology, geochemistry and paleontology is needed for future SSF study. [Copyright &y& Elsevier]

The lower Cambrian (Stage 3) Yu'anshan Formation in Yunnan Province, South China hosts the Chengjiang Lagerstätte , an exceptional window on the Cambrian Explosion. However, skeletal microfossils from this formation have long been neglected owing to the dominance of siliciclastics over carbonates. Here we characterize a new assemblage of small shelly fossils from the Maotianshan Shale Member of the Yu'anshan Formation. The assemblage consists of univalved mollusc, hyolith and brachiopod shells, trilobite and bradoriid carapaces, chancelloriid sclerites, sponge spicules, and echinoderm ossicles. Combining this information with taxonomic data previously tabulated for fossil assemblages from three other facies, we performed quantitative comparisons of the genus-level taxonomic diversity and modes of life and nutrition of four mutually equivalent, early Cambrian (Age 3) paleocommunities: (1) skeletal faunas of the inner shelf; (2) predominantly soft-bodied faunas of the intra-shelf basin; (3) archaeocyathan faunas of the carbonate shelf; and (4) sponge-dominated faunas of the slope to basin areas. The taxonomic and paleoecological distinctness of these four paleocommunities indicate possible low levels of competition within the communities and rapid expansion of habitat (ecospace) ranges, though with similarities in the taxonomic composition of poriferans and arthropods reflecting the rapid migration of these two groups into new habitats. The present, integrative study provides a more comprehensive portrait of metazoan diversification and paleocommunity evolution during the peak phase of the Cambrian Explosion than do investigations based on single communities. • New assemblage of skeletal fossils from the Cambrian Stage 3, South China. • The fauna is dominated by hyoliths, chancelloriids, bradoriids and molluscs. • The different paleocommunity compositions and structures are documented. • The paleocommunitites are highly facies-controlled. • The highest biodiversity of the Cambrian Explosion in South China [ABSTRACT FROM AUTHOR]