No abstract

Radiolarian skeletons are known from a limestone concretion collected from a black shale succession and from black cherts of the Yangtze Platform, China. Both occurrences are of earliest Cambrian age. The findings, reported in this paper, represent the oldest known fossil Radiolaria. Their spherical skeletons display a morphology typical of spherical radiolarians from Ordovician and younger faunas. This occurrence of radiolarians with radial symmetry and, most probably, a planktonic lifestyle can now be traced back into the earliest Cambrian. Thus, radiolarians have been part of the early oceanic plankton and likely played a significant role in the silica cycle of the oceans along with siliceous sponges.

The Cambrian Maotianshan Shale in Yunnan Province, China contains the well-preserved soft-body fossils of the Chengjiang Biota. The high quality preservation of the non-mineralizing biota (soft tissues and whole carcasses) shows regional and temporal differences, suggesting that paleogeography and local environmental conditions might have contributed to the taphonomy of these fossils. In this paper we present new results from petrographic, geochemical and detrital zircon analyses, and provide a new interpretation about the provenance of the Maotianshan Shale, as well as add to the understanding of the paleogeography of the South China Block during the Cambrian Stage 3. Results from petrographic analysis indicate that the provenance of the Maotianshan Shale is a recycled orogen overall, bordering the western and southwestern margin on the Yangtze Block. The most likely source of the terrigenous material is an exhumed area extending from the Kangdian paleoland to the southeast, paralleling the Song Ma fault zone. Minor regional differences in geochemical and petrographic proxies between the northwestern Jianshan/Ercai area and the southeastern Maotianshan/Xiaolantian area suggest influence of local sources. Sediments of the southeastern province are less mature and samples include minor elements commonly associated with mafic sources. Sediments from the northwestern province are more mature, largely lack mafic components and are enriched in Zr and Hf. The major population of the Maotianshan Shale detrital zircons group at ~800Ma. This crystallization age matches © 2015. This manuscript version is made available under the Elsevier user license http://www.elsevier.com/open-access/userlicense/1.0/well with the age of a widely spread felsic volcanic and intrusive event associated with the Neoproterozoic Kangdian rift, suggesting that these igneous rocks are most likely a major provenance for the Maotianshan sediments. The youngest zircon population yields consistent Concordia ages of ~520 Ma, representing a maximum age constraint on the timing of deposition of the Maotianshan Shale. The zircon crystals of the ~520 Ma populations are euhedral with magmatic zoning, indicative of short-distance transport. Volcanic activity along the Song Ma suture zone is a potential source for the ~520Ma detrital zircon suite.

Rare earth element (REE) contents and distribution patterns in the major rock-forming minerals (vesuvianite, wollastonite, garnet, pyroxene, hornblende, epidote and fluorite) from the Shizhuyuan W, Sn, Mo and Bi-containing skarn deposit of Hunan Province of South China have been determined. Three types of REE distribution patterns were found: 1) vesuvianite and wollastonite, formed at the ex pense of carbonates and shales of the Upper Devonian Shetianqiao Formation during thermal metamor phism stage, show linear light REE enrichment and small Eu anomalies; 2) garnet, the most abundant mineral in the skarn deposited at metasomatic stage, exhibits high REE enrichment and considerable negative Eu anomalies; 3) epidote and fluorite, precipitated during retrograde alteration stage, display very strong negative Eu anomalies. Comparison of relative REE abundances in these minerals with those in the carbonates and shales as well as in the Qianlishan Yanshanian granite suggests that REE compositions of the vesuvianite and wollastonite appear to have been inherited from precursor car bonates and shales, whereas REE contents and patterns in the metasomatic and the retrograde alteration products, such as garnet and epidote, seem to have been determined by the interactions between the reac ting minerals and hydrothermal solutions originated from Qianlishan granite.