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Originaltitel: First Report of Small Skeletal Fossils from the Upper Guojiaba Formation (Series 2, Cambrian), Southern Shaanxi, South China
<p>A small skeletal fossil assemblage is described for the first time from the bioclastic limestone interbeds of the siltstone-dominated Guojiaba Formation, southern Shaanxi, China. The carbonate-hosted fossils include brachiopods (<em>Eohadrotreta zhujiahensis</em>, <em>Eohadrotreta zhenbaensis</em>, <em>Spinobolus</em> sp., <em>Kuangshanotreta malungensis</em>, <em>Kyrshabaktella</em> sp., <em>Lingulellotreta yuanshanensis</em>, <em>Eoobolus incipiens</em>, and <em>Eoobolus</em> sp.), sphenothallids (<em>Sphenothallus</em> sp.), archaeocyaths (<em>Robustocyathus</em> sp. and <em>Yukonocyathus</em> sp.), bradoriids (<em>Kunmingella douvillei</em>), chancelloriids sclerites (<em>Onychia </em>sp., <em>Allonnia </em>sp., <em>Diminia </em>sp., <em>Archiasterella pentactina</em>, and <em>Chancelloria</em> cf. <em>eros</em>), echinoderm plates, fragments of trilobites (<em>Eoredlichia</em> sp.), and hyolithelminths. The discovery of archaeocyaths in the Guojiaba Formation significantly extends their stratigraphic range in South China from the early Tsanglangpuian at least to the late Chiungchussuan. Thus, the Guojiaba Formation now represents the lowest known stratigraphic horizon where archaeocyath fossils have been found in the southern Shaanxi area. The overall assemblage is most comparable, in terms of composition, to Small skeletal fossil (SSF) assemblages from the early Cambrian Chengjiang fauna recovered from the Yu’anshan Formation in eastern Yunnan Province. The existing position that the Guojiaba Formation is correlated with Stage 3 in Cambrian Series 2 is strongly upheld based on the fossil assemblage recovered in this study.</p><p data-nested="1"><strong>Simple Summary</strong></p><p>Small skeletal fossils are reported for the first time from the early Cambrian Guojiaba Formation, southern Shaanxi, China. All specimens were recovered from bioclastic limestone interbeds and encompass a wide variety of skeletal clades, including brachiopods, sphenothallids, archaeocyaths, bradoriids, sponge spicules, echinoderm plates, and trilobite spines. The archaeocyaths described herein are considerably older than those described from the Xiannvdong Formation, which was previously assumed to contain the lowest archaeocyath-bearing horizons in South China. The brachiopod <em>Lingulellotreta yuanshanensis</em> is recorded for the first time from the Fucheng area, with previous records confined mainly to the Chengjiang Fauna-bearing Yu’anshan Formation in the lower Cambrian, the eastern Yunnan Province. Micro-morphological and elemental analyses of the small skeletal fossil assemblages were carried out using SEM, BSEM, and Micro X–ray fluorescence. The skeletal fauna in the Guojiaba Formation resembles the assemblages recovered from the upper Yu’anshan Formation (Chengjiang Fauna) in eastern Yunnan Province. Based on the recovered assemblage, the biostratigraphic age of the Guojiaba Formation correlates with the Chiungchussuan Stage (Stage 3 of Cambrian Series 2). </p>