A diverse and abundant isolated sponge spicule assemblage of Late Ordovician age is first reported from the western margin of the Yangtze Platform in South China. The spicule assemblage was recovered from argillaceous limestone sampled for conodonts. It includes 14 types which can be split into two categories: hexactinellid spicules and demosponge spicules. The assemblage primarily comprises hexactines and their derivatives, including not only some distinctive types such as Kometia cruciformis, but also large numbers of morphotypes that are quite common and diagnostic for hexactinellids, e.g. swollen hexactines, curved hexactines, and stauractines. Demosponge spicule types are represented by tetraxons, and various desmas typical for lithistids also occur. A highly modified hexactine, Kometia cruciformis, is recovered from China for the first time. This record represents currently the only recovery of such spicules from strata outside of Australia, and is coeval to the assemblage known from the Malongulli Formation. The presence of such unique modified hexactines (Kometia) in both time-equivalent assemblages suggests that certain spicules may have potential importance in biostratigraphic correlations and palaeobiogeographical interpretations, demonstrating the dispersal of taxa and their migration along the peri-Gondwana shelf areas during the Ordovician, driven by ocean current systems. The Late Ordovician sponge spicule assemblage from the Yangtze Platform provides new perspectives for investigating phylogeny, biostratigraphy, and palaeobiogeography of Palaeozoic sponges, and promotes some understanding of macroevolution in siliceous sponges.

The Erdaopuzi section in the Baishan area of Jilin Province, northeast China, contains abundant late Tremadoc graptolites. However, there are some taxonomic controversies regarding the characters of the hand specimens that are difficult to identify. In this paper, we present our restudy of isolated graptolites from acid residue and discuss the taxonomic problems of the subgenus Clonograptus (Neoclonograptus) Zhao and Zhang. Four genera and six species were identified, including Adelograptus tenellus (Linnarsson), Ancoragraptus gracilis (Zhao and Zhang), Dictyonema sp., Psigraptus jacksoni Rickards and Stait, Psigraptus lenzi Jackson, Psigraptus arcticus Jackson. According to the significant evolution of morphological characters, two graptolite zones (from bottom to top) can be identified in ascending order in the study area, i.e. Adelograptus Zone and the Psigraptus Zone.

Strata equivalent to the majority of the Ordovician shallow-water sediments in South China occur in the western Yangtze region (present-day southwestern Sichuan and northeastern Yunnan, Southwest China), but remain to be properly documented largely due to their inaccessibility. Our research in the past decade has led to the recognition of spatial and temporal patterns, and hence a substantial stratigraphic revision of these rocks, with part of the results having been published in a series of papers. Here, we outline a unified and refined Ordovician stratigraphy of the region built chiefly on a summary of these new data, presenting a robust timeframe for exploring the environmental and biotic events during the Ordovician on a basin-wide scale in South China.

The new hexactinellid stiodermatid Turgidaspongia porosa gen. et sp. nov. is described from the Ordovician-Silurian boundary sequence in Beigong of Jingxian County, south Anhui Province, China. The spherical, thin-walled species possessed unique features including unusually large parietal gaps on the body wall, swollen hexactines as hypodermalia, and two different sizes of stauractines as dermalia and parenchymalia respectively. Based on the new material, the family Stiodermatidae is revised here, including five genera after reassessment, i.e., Rigbyella, Thoracospongia, Stioderma, Uralonema, and Turgidaspongia porosa gen. et sp. nov. The new species is well preserved with typical enlarged hypodermal hexactines with swollen rays and large, subcircular parietal gaps, giving an illuminating insight into the affinity between the new species and other taxa in Stiodermatidae. It also provides a link between the Cambrian stiodermatid lineage and late Palaeozoic stiodermatid lineage. The uneven distribution of the swollen dermalia in the new species may relate to the sloughing of the dermal spicules causing by the nutrient deficiency. The unique rigid skeleton structure and unusually large parietal gaps probably represent new attempts on the skeletal evolution of hexactinellids in the Palaeozoic.

安徽石台地区柳树亭剖面是下扬子区中—晚奥陶世地层代表性剖面,本文对该剖面开展了详细的牙形类生物地层学研究.通过系统的样品采集分析,在柳树亭剖面的牯牛潭组和大田坝组自下而上识别出牙形类Lenodus antivariabilis带、Lenodus variabilis带、Yangtzeplacognathus crassus带、Dzikodus tablepointensis带、Yangtzeplacognathus jianyeensis带;宝塔组自下而上可识别出Baltoniodus alobatus带和Hamarodus brevirameus带.柳树亭剖面中—晚奥陶世牙形类生物地层序列可以在区域内乃至全球范围内进行较好的对比,但中—晚奥陶世之交缺失Eoplacognathus suecicus带、Yangtzeplacognathus foliaceus带和 Yangtzeplacognathus protoramosus带.

A robust stratigraphic framework and a coherent depositional ramp model for the Zitai, Dawan, Meitan and Ningkuo formations of Floian–Darriwilian age（Early–Middle Ordovician） in the Yangtze（Daoba, Xiangshuidong, Daling, Gudongkou and Honghuayuan sections） and Jiangnan regions（Nanba section） was created based on lithofacies and major element analysis. Three siliciclastic（LF1–3） and six carbonate（LF4–9） lithofacies are recognized representing sediments that were deposited in mixed siliciclastic and carbonate ramp environment. The intensity of mixed sedimentation and terrigenous input were evaluated using the elemental proxies Intensity of Mixed sedimentation（IM） and Aluminum Accumulation Rate（Al AR）, as well as their mean values during certain time intervals. Mixed sediments are most well-developed along the marginal Yangtze region, strongly impacted by recurrent influx of westerly derived terrigenous materials in response to global eustatic changes and regional tectonic movements, shaping the gently southeast-dipping morphology. Regular terrigenous influx resulted in periods of enhanced primary productivity on the Yangtze Ramp as evidenced by matching biodiversity peaks in planktonic organisms, i.e., chitinozoans and acritarchs. Brachiopods and other shelly fauna were also able to proliferate as new niches developed along the gently dipping ramp floor with substrate changes. The biodiversification patterns suggest that terrigenous influx controlled in part by regional tectonics played a more important role than previously thought in the development of Great Ordovician Biodiversification Event in South China.

The Lower and Middle Ordovician of the Yangtze Platform, China, is characterized by a sedimentary succession dominated by carbonate rocks. Three sections spanning the Nantsinkuan/Lunshan, Fenhsiang, Hunghuayuan, and Dawan/Zitai formations, corresponding to the Tremadocian–Dapingian in age, have been sampled for high-resolution δ 13 C chemostratigraphy (542 samples in total). Our new δ 13 C data reveal five tie-points with the potential for global correlation: (1) a positive δ 13 C excursion in the lower Nantsinkuan Formation within the Tremadocian Rossodus manitouensis Zone; (2) an excursion with two peaks roughly within the late Tremadocian Paltodus ‘ deltifer ’ Zone; (3) a positive δ 13 C shift in the lower Hunghuayuan Formation, within the early Floian Serratognathus diversus Zone; (4) a gradual positive δ 13 C shift in the late Floian, ranging from the uppermost S. diversus Zone to the basal Oepikodus evae Zone; (5) a minor negative shift in the lower Dawan/Zitai Formation, within the early Dapingian Baltoniodus triangularis Zone. These excursions are herein used for correlation of the Yangtze Platform strata with successions from South China, North China, the Argentine Precordillera, North America and Baltica. From a palaeogeographical perspective the Gudongkou, Xiangshuidong and Daling sections represent depositional environments along an inner to outer ramp profile. δ 13 C data from these sections show successively heavier (higher) δ 13 C values with increasing depositional depth. This is interpreted as due to remineralization of organic carbon within the carbonate rocks. Supplementary material: Carbon and oxygen isotope data are available at: https://doi.org/10.6084/m9.figshare.c.4767080

Well-preserved graptolites of the genus Kiaerograptus are first reported from the upper Tremadocian Yinchupu Formation in the Nanba section, Yiyang, Hunan Province, South China, including four species, i.e., Kiaerograptus lauzonensis (Erdtmann, 1966), Kiaerograptus stoermeri (Erdtmann, 1965), Kiaerograptus cf. supremus? Lindholm, 1991, and Kiaerograptus sp., which are robust in form. Based on these new specimens, the Kiaerograptus biozone is established for the first time in South China, increasing the late Tremadoc graptolite biozones in South China from four to five, in ascending order as follows: the Adelograptus tenellus biozone, the Aorograptus victoriae biozone, the Kiaerograptus biozone, the Sagenograptus murrayi biozone, and the Hunnegraptus copiosus biozone. A review of the occurrence records for robust Kiaerograptus species worldwide reveals that the distribution is restricted to the Aorograptus victoriae biozone and Kiaerograptus biozone in the late Tremadocian. This limited stratigraphical distribution makes Kiaerograptus a valuable taxon for precise biostratigraphical correlation at both the regional and global scales.

A new halichondrid demosponge bubarid Ptilospongia hemisphaeroidalis gen.et sp.nov. is described from the latest Ordovician Beigong Biota in Jingxian County, Anhui Province, South China.The new taxon is well-preserved with a two-layer choanosomal skeleton structure (basal layer and erect monactines layer) and three different types of megascleres (styles, strongyles, strongyloxeas), providing an excellent insight into a bubarid affinity and indicating a previously unknown group.It probably represents the earliest known fossil record of bubarids, providing a more reliable calibration point currently available for taxonomic and molecular phylogenetic studies.

针对滇东北镇雄下蒿枝湾剖面晚奥陶世至志留纪兰多维列世过渡时期的沉积地层,本文进行了系统测制和地层古生物学研究,对其地层发育和对比进行了梳理与限定,首次发现该地晚奥陶世至志留纪早期地层自下而上可依次划分为大渡河组、"五里坡层"、龙马溪组底部和"龙马溪组中部".其中,大渡河组为一套沉积于内陆棚的泥质泥晶灰岩与钙质泥页岩,时代可与五峰组对比."五里坡层"是一套沉积于内陆棚的钙质粉砂岩地层,向上逐渐过渡为外陆棚相的龙马溪组底部黑色笔石页岩,两者构成了 Metabolograptus persculptus带中上部沉积.大渡河组与"五里坡层"呈平行不整合接触,之间缺失观音桥层及Hirnantia-Mucronaspis动物群,指示赫南特期全球性海平面下降."龙马溪组中部"以内陆棚的砂岩为起始,其中所产腕足动物化石指示其时代为志留纪鲁丹晚期.Edgewood-Cathay动物群缺失表明龙马溪组底部与"龙马溪组中部"之间存在不整合界面,体现了黔中古陆北缘的隆升.下蒿枝湾剖面奥陶纪—志留纪过渡时期的地层发育情况完整记录了在全球和区域事件的影响下滇东北沉积相和生物群的时空分布与发育的响应过程.

Diverse Telychian (Llandovery Series, Silurian System) conodont faunas have been documented from the South China Palaeoplate. Based on data from six selected sections in the Yangtze Platform, the spatial distribution of the Telychian conodont associations is investigated in detail by use of multivariate statistical methods. Two conodont biofacies are recognised within the Pterospathodus eopennatus Biozone: Dapsilodus-Decoriconus Biofacies and Apsidognathus-Galerodus Biofacies. The former is interpreted as representing a relatively deeper-water environment. The Apsidognathus-Galerodus Biofacies is widely distributed on the Yangtze Platform and is indicative of a shallower depositional setting. Vertical changes of conodont biofacies in the Baizitian and Xuanhe sections permit the recognition of transgressive-regressive patterns which are closely similar to published sea-level curves for the Early Silurian.

The Ordovician Lagerstätten record substantial amounts of excellent preservation and soft-bodied fossils during the Great Ordovician Biodiversification Event (GOBE). However, few Lagerstätten are known from the Lower Ordovician, most of which are preserved in restricted environments and high-latitude regions. Here, we report on a new tropical Lagerstätte, Liexi fauna, which has been recently discovered from a carbonate succession within the Lower Ordovician Madaoyu Formation in western Hunan, South China. It contains a variety of soft tissues, as well as rich shelly fossils, including palaeoscolecidan worms, possible Ottoia, trilobites, echinoderms, sponges, graptolites, polychaetes, bryozoans, conodonts and other fossils. The fauna includes taxa that are not only Cambrian relics, but also taxa originated during the Ordovician, constituting a complex and complete marine ecosystem. The coexistence of the Cambrian relics and Ordovician taxa reveals the critical transition between the Cambrian and Palaeozoic Evolutionary faunas. The unusual Liexi fauna provides new evidence for understanding Ordovician macroevolution and the onset of the GOBE.

New conodont and stable isotope data are presented from the classical Baizitian section in the Yanbian County of Sichuan Province, South China. The Telychian to Sheinwoodian strata were sampled and studied for carbon isotope stratigraphy and conodont biostratigraphy. The paired δ13Ccarb and δ13Corg data reveal a pronounced positive excursion, the Manitowoc carbon isotope excursion (Manitowoc CIE, 'Manitowoc Excursion') spanning the upper Pterospathodus eopennatus Zone and the lower Pterospathodus amorphognathoides amorphognathoides Superzone, with an increase of ca. 2‰ in δ13Ccarb and ca. 5‰ in δ13Corg. Well-bracketed by conodont biostratigraphy, the Manitowoc CIE is an essential tie-point for correlation between the Baizitian succession and the Telychian strata of Baltica and Laurentia. Our new δ13Ccarb and δ13Corg data imply that the carbon isotope excursion previously recognized as the 'Ireviken Excursion' (Early Sheinwoodian Carbon Isotope Excursion) at Baizitian should be revised as being the Manitowoc CIE. The Δ13C data presented in this study further suggest a slight concurrent drop of atmospheric CO2, and thus add evidence for a perturbation of the global carbon cycle during the middle Telychian. Based on the combined information from the conodont apatite oxygen isotope records from Estonia and the significant stratigraphic gaps recognized at the Baizitian section, we propose that the latter stratigraphic gaps should correlate with the Telychian Valgu and the early Sheinwoodian glaciation.

Middle to Late Ordovician carbonates were collected in South China (Anhui Province) from the Kuniutan, Datianba, and Pagoda formations in the Dingxiang and Daling sections and analysed for high‐resolution carbon isotope chemostratigraphy. An increase by 0.4‰ in δ13Ccarb is observed in the upper part of the Kuniutan Formation (Eoplacognathus pseudoplanus Biozone), representing the rising limb of the Middle Darriwilian Isotopic Carbon Excursion (MDICE). In the upper part of the Datianba Formation, positive shifts of ca. 1‰ are recorded in the studied section which compare with the carbon shifts reported in North America and Baltoscandia. A pronounced positive δ13Ccarb excursion of ca. 1.5‰ from the lower part of the Pagoda Formation can be correlated with the global Guttenberg Isotopic Carbon Excursion (GICE). The documentation of three carbon isotope shifts in this study provides new evidence for changes in the global carbon cycle from Darriwilian to Early Katian which could have been influenced by changes in global climate and primary productivity.

Rossellids are geographically widespread in the modern deep-water sponge community. They are referred to Lyssacinosida, characterized by hypodermal pentactines and choanosomal megascleres of hexactines and diactines or the latter only. The fossil records of rossellids are usually found in the Cenozoic, with the earliest existence known from the Upper Cretaceous, later than the molecular phylogenetic result. A new lyssacinosan hexactinellid, Palaeorossella sinensis gen. et sp. nov., is described from the uppermost Ordovician of Anhui, South China. The sponge shows a saccular, globular or oval form with relatively thick wall. The skeleton is lyssacine type mainly composed of hexactines and stauractines, with the outer margin reinforced by hypodermal pentactines, which usually protrude the periphery as prostalia lateralia. The new species is well-preserved with typical hypodermal and prostalia pentactines as well as an articulated skeleton, giving some tentative insights into the affinity between the new species and other taxa in Rossellidae. It represents the oldest record of rossellids, providing new information for understanding the phylogeny of rossellids and on the evolution of modern Hexactinellida.

A detailed study of the graptolite fauna from the Lower to Middle Ordovician Ningkuo Formation in the Nanba section, Yiyang, Hunan Province, reveals variable but generally increasing diversity during the Floian–Dapingian, peaking in the Corymbograptus deflexus Biozone. The diversification trend of graptolites in the Nanba section is broadly consistent with that in the Jiangnan region of South China and Avalonia, but is delayed compared with that in the Yangtze region of South China, Australasia, and Baltica. Furthermore, the first peak in diversity of graptolites in the Nanba section slightly post-dates that of brachiopods and conodonts, but is earlier than that for trilobites and acritarchs. Comparison of diversity trends with the sea-level curve for the Yangtze Platform reveals that the Early and Middle Ordovician graptolite radiation coincided with a transgression. Graptolite diversity trends through this interval initially reflect replacement of Anisograptid fauna by Dichograptid fauna and subsequent commencement of evolution within the Dichograptid fauna.

There are few sponges known from the end-Ordovician to early-Silurian strata all over the world, and no records of sponge fossils have been found yet in China during this interval. Here we report a unique sponge assemblage spanning the interval of the end-Ordovician mass extinction from the Kaochiapien Formation (Upper Ordovician-Lower Silurian) in South China. This assemblage contains a variety of well-preserved siliceous sponges, including both Burgess Shale-type and modern type taxa. It is clear that this assemblage developed in deep water, low energy ecosystem with less competitors and more vacant niches. Its explosion may be related to the euxinic and anoxic condition as well as the noticeable transgression during the end-Ordovician mass extinction. The excellent preservation of this assemblage is probably due to the rapid burial by mud turbidites. This unusual sponge assemblage provides a link between the Burgess Shale-type deep water sponges and the modern forms. It gives an excellent insight into the deep sea palaeoecology and the macroevolution of Phanerozoic sponges, and opens a new window to investigate the marine ecosystem before and after the end-Ordovician mass extinction. It also offers potential to search for exceptional fossil biota across the Ordovician-Silurian boundary interval in China.

A new locality exposing T remadocian ( E arly O rdovician) graptolitic shales in H unan P rovince, S outh C hina, has yielded an exceptionally well‐preserved annulated worm. This palaeoscolecidan is described as W aflascolex changdensis gen. et sp. nov. and reveals extremely fine detail of the cuticle organization and plating array. The new taxon is characterized by three critical characters: incomplete plate rows that occur only on the posterior end of the worm (except in the posterior‐most area) and do not extend over the entire circumference or along the entire trunk; a regular rhomboidal array of platelets around intercalations; and reduced cuticular organization at the posterior termination. The unique cuticular organization and platelet ornamentation in the new taxon offer insight into functional differentiation of plates in the scleritome. Palaeoscolecid distribution through the early P alaeozoic is reviewed, showing that the worms were widespread in the C ambrian and O rdovician, but became more restricted during the S ilurian. Ordovician palaeoscolecidans are diverse in scleritome architecture, and strikingly different from C ambrian taxa, indicating that this group diversified as part of the G reat O rdovician B iodiversification E vent.

Discovery of well-preserved specimens from the Nanba section in Yiyang, Hunan Province, in combination with a literature review, enabled us to re-evaluate and revise the graptolite genusAncoragraptus. This is a genus of biradiate, multiramous anisograptids with horizontal to reclined rhabdosomes and free lower part of the metasicula and slightly isolated autothecal apertures. According to the revised definition, two species are included inAncoragraptus, i.e.,Ancoragraptus bulmani(Spjeldnæs, 1963) andAncoragraptus psigraptoidesCho, Kim, and Jin, 2009. It is the first time thatA. bulmanihas been reported from China. The occurrences ofAncoragraptusreported worldwide are reviewed in the present study and found to be restricted to the lower upper Tremadocian. The restriction ofAncoragraptusin stratigraphical distribution makes it a taxon with a high potential for precise biostratigraphical correlation at both regional and global scale.

Chitinozoans and acritarchs are reported from the Late Tremadocian to early Floian graptolitic shales in the Nanba Section of the Yiyang area in the Hunan Province.Three chitinozoan biozones and three acritarch assemblage zones are distinguished.The co-exsiting of graptilites,chitinozoans together with acritarchs allows precise calibration between the chitinozoan biozones and acritarch assemblages versus the reference graptolite biozones.The succession of the Late Tremadocian-early Floian chitinozoans and acritarchs from the Jiangnan Slope not only allows precise correlation at both regional and global scale,but also has some palaeogeographical implication refers to this time interval.