Metazoan fossils in the Gaojiashan Biota are famous for being well preserved and may provide new insights into the early evolution and skeletonization of Metazoans. We are studying the isotopic compositions of organic and carbonate carbon from a sequence of sedimentary rocks at the Gaojiashan section, northern Yangtze Platform, Shaanxi Province of China. Organic carbon isotope values display a range between -30.8%0 and -24.7%0 with clear stratigraphic variations. Carbonate carbon isotope data vary between 0.1%o and ＋6%0. Positive j13C values from sediments with Gaojiashan biota reflect temporal variations in carbon turnover, i.e. an increasing in photosynthetic carbon fixation followed by an increasing subsequent fractional organic carbon burial, and that related to bio- radiation such as increasing algae, bacteria, and original creatures productivity in biomass. These secular variations are interpreted to reflect perturbations of the regional carbon cycle, specifically changes in the fractional burial of organic carbon, and discuss the relationship between Gaojiashan biota and paleoenvrionmental variation.
贵州丹寨南皋在寒武纪属于扬子板块深水相区,最近在该区寒武系下部牛蹄塘组中上部黑色泥页岩中发现了大量保存完好的海绵动物化石,共9属10种。文中描述其中比较典型的海绵动物化石5属5种:赫兹海绵未定种Hintzespongia sp.,杯形对角海绵Diagoniella cyathiformis(Dawson,1889),密集鬃毛状海绵Saeta-spongia densa Mehl and Reitner in Steineret al.,1993,大坪三岔五射海绵Sanshapentella dapingi Mehl and Erdt-mann,1994和羽状光芒海绵Solactiniella plumata Mehl and Reitner in Steineret al.,1993。在这套整体缺氧的黑色泥页岩中有如此多而完整的海绵动物化石的保存,可能是由于上涌洋流、水流或海平面的变化等导致短暂的充氧事件,加上多幕次的热水沉积,提供大量食料,从而利于需氧量相对较低的原始后生动物--海绵动物的大量繁盛。
The Guanshan biota from eastern Yunnan(Cambrian Series 2,early Stage 4) is a Burgess Shale-type fossil biota with abundant exceptionally preserved soft-bodied fossils after the discovery of the well-known Cambrian Chengjiang fauna and Kaili biota in South China.The geological settings,sedimentology,taphonomy,and the fossil assemblage of the Guanshan biota are briefly summarized here.The Guanshan biota consists of about 60 taxa belonging to more than 10 metazoan groups and algae,among which the lobopods,eldonids,hyolithids with helens,and green algae are reported for the first time.The common occurrence of soft-bodied preservation in many groups,notably the trilobites and brachiopods,makes the Guanshan biota a significant fossil lagersttte for understanding the metazoan evolution during Cambrian explosion and taphonomy of the Burgess Shale-type fossils.
Based on previously published species data(228 species in over 18 phyla) and field sampling(114 species and 18406 individuals) in the Chengjiang-Haikou-Anning area,we analyzed quantitatively the paleocommunity composition and structure of the Cambrian Chengjiang biota(Cambrian Series 2,eastern Yunnan,China).Arthropods dominate the community both in species diversity(species:37%) and in abundance(individuals:51.8%).Priapulids(individuals:22.6%) and brachiopods(individuals:16.3%) follow in abundance rank.The arthropod Kunmingella douvillei(26.2%),the priapulid Cricocosmia jinning-ensis(15.4%),and the brachiopod Diandongia pista(11%) are the three most abundant species.Ecological analyses show that the community was dominated by epifaunal organisms(species:63%,individuals:68.4%) followed by infaunal organisms(species:11.9%,individuals:25.9%),nektobenthic organisms(species:11.5%,individuals:2.6%),and pelagic organisms(species:5.3%,individuals:3.1%).The diverse feeding strategies,dominated by suspension feeders(species:35.6%,individuals:26.1%) and hunter/scavengers(species:31.1%,individuals:40.4%),indicate the former existence of a complex food chain and intense competition.Epifaunal vagrant omnivores(28.2%),infaunal vagrant hunter/scavengers(19.8%),epifaunal sessile suspension feeders(17.7%),and epifaunal vagrant hunter/scavengers(15.3%) were the most abundant ecological groups,represented primarily by arthropods,poriferans,priapulids,and brachiopods.Ecological group analyses reveal that the early Cambrian Chengjiang biota is similar in community patterns and functional relations to modern biotas in shallow marine settings.
