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Small Shelly Fossils (SSFs) from the Cambrian are widely distributed and well known across different paleocontinents of the world. However, middle Cambrian SSFs from North China Platform have only rarely been documented until now. In this paper, we presented the first report on SSFs from bioclastic and oolitic limestones of the Zhangxia and Hsuzhuang formations of Henan province, North China. The carbonate-hosted fauna includes brachiopods (Micromitra sp., M. modesta, Eoobolus sp., and Schizopholis sp.), helcionellids (Oelandiellaaccordionata and O. aliciae), hyolithids, Hyolithellus sp., Chancelloriaeros, sponge spicules, echinoderm ossicles, and chancelloriid sclerites. In terms of preservation, the brachiopod shell valves of M. modesta appeared to be homogeneous, consisting of tightly packed phosphate grains. Eoobolus sp. is composed of primary layer and secondary baculate, both of which consist of tightly compacted phosphate grains. Schizopholis sp. has multiple-lamellar phosphatized microstructures that distinctly differ from the other brachiopods recovered from the Longwanggou section. A similar multiple-lamellar microstructure was also revealed in conchs of Hyolithellus, with tightly compacted phosphate grains. The argillaceous shell of Oelandiellaaccordionata and O. aliciae, and the calcitic inner molds of hyolith did not preserve any shell structure. The helcionellids O. accordionata and O. aliciae and the brachiopod M. modesta were reported for the first time from North China. The fauna is most similar to the middle Cambrian faunas of South Australia, in the brachiopod and mollusk components, it is also similar in composition of brachiopods and mollusks to coeval faunas from South China. The new fauna of SSFs in the Yiyang Longwanggou Section indicated that the Hsuzhuang and Zhangxia formations are late Drumian to middle Guzhuangian in age, most likely correlating with the Murrawong Creek Formation of South Australia.

The lower member of the Poleta Formation is well known for its abundant archaeocyaths, including an exceptionally preserved reef at Stewart’s Mill in Nevada. Large archaeocyath-bearing reefs are relatively uncommon, with most occurring as small nearshore patch reefs. Here, we describe a new 70 m-thick archaeocyath reef from the lower Poleta Formation, herein referred to as the Gold Point Reef, located near the townsite of Gold Point, Nevada. In spite of broad similarities with the Stewart’s Mill exposure, the Gold Point Reef shows an interplay between shoal and reef development over the ~ 70 m exposure that differs from what is observed at Stewart’s Mill. This reef also preserves a small shelly fauna in its uppermost 10 m, dominated by Hyolithellus. Three successive ecological stages of reef development are observed here: the pioneer stage characterized by a single rare frame-building species; the diversification stage involving about nine species of both frame-building and mud-sticking archaeocyaths; and the final foundering stage represented by one to two species of archaeocyaths and facies indicating reef demise, including abundant grainstone/packstone shoals and a silicified upper bed with a settlement of hyolitheminthes. During the apex of reef development here, there are large modular archaeocyaths, which were able to produce thick secondary skeletal tissue for a firm attachment; these archaeocyaths were capable of building large reefs in a variety of settings. Additionally, the carbon isotope profile recorded in the Gold Point Reef shows similarities to nearby exposures of the equivalent lower Poleta Formation, with the exception of a small negative downturn at the top of the reef that is not found in other locations. Combined with the documentation of facies changes over short lateral distances, the isotope data suggest that archaeocyathan reefs may have been time-transgressive across the shelf during deposition of the lower Poleta. Additionally, our work suggests that both here and globally, the specific biotic assemblage reflected the local influences of the environment on reef development, creating highly variable coeval paleocommunities even within a restricted area.

An assemblage of Late Precambrian macrofossils consisting of five species (Aspidella terranovica, Beltanelliformis brunsae, Nenoxites curvus, Palaeopascichnus renarius, and Suvorovella aldanica), was discovered in the type sections of the Yudoma Group of the Siberian Platform. A unique feature of the assemblage is the presence of carbonate discoidal remains of Suvorovella, formed as a result of secondary incrustation of basal structures, similar to Aspidella. The accumulations of redeposited fragments of Suvorovella formed the rock resembling the Phanerozoic shell beds. Except for this taxon, all members of the Yudoma assemblage have a wide geographic distribution. Their stratigraphic distribution tends to occur in the youngest deposits of the Upper Vendian, directly underlying the beds with small shelly fauna (SSF) of the Nemakit-Daldynian Stage, Cloudina tubes, and traces of the Treptichnus pedum Zone.

The Ediacaran–Cambrian (E-C) transition witnessed dramatic tectonic, climatic, oceanic, and biological co-evolutions at the dawn of the ‘Cambrian explosion’. Although glaciations were reported in some mid-high-latitude continents during this interval, large uncertainties remain concerning timing and extent, as well as their effect on the entire Earth's surface system. We here report magnesium (Mg) isotopic compositions, along with chemical index of alteration (CIA), Al/Ti ratios from a time-dated, nonglacial E-C boundary section on the mid-low-latitude Yangtze Block, South China, to constrain chemical weathering intensity and associated climatic, oceanic and biological co-evolution during this critical interval. Our data demonstrate a rapid and significant negative δ26Mg excursion (from +1.28 to −0.34‰) along with similar CIA and Al/Ti decreases across the E-C boundary, reflecting an apparent attenuation in chemical weathering intensity likely in response to severe climate cooling. This finding further affirms the far-field glaciation reported in the mid-high-latitude continents during the E-C transition. Under this condition, the intense climate cooling could have enhanced oceanic circulation and/or upwelling, and simultaneously caused prominent variations of seawater geochemistry (including alkalinity elevation) and nutrient flux as well as ecological stresses on metazoans. All these could reasonably account for extensive deposition of phosphorites and organic-rich black shales, and faunal turnover (extinction of Ediacaran fauna and appearance of skeletonized small shelly fauna) across this interval. These novel datasets thus shed new insights into the climatic-oceanic-biological interactions and time-specific deposition around the E–C transition at the prelude of the Cambrian explosive bioradiation.

Animals with radial symmetry are abundant in the Cambrian Fortunian Stage of South China, but with relatively low diversity: representatives include Olivooides, Quadrapyrgites, carinachitiids, hexangulaconulariids and Pseudooides. Here, we report a new radial animal, Qinscyphus necopinus gen. et sp. nov., from the Fortunian small shelly fauna of southern Shaanxi Province, South China. Qinscyphus necopinus has a cup-shaped profile, with slightly raised annuli and five groups of triangular thickenings in pentaradial symmetry. This organism has a comparable morphology to, and thus a close affinity with, Olivooides and Quadrapyrgites, and is interpreted as a coronate scyphozoan. This discovery adds a new crown-group cnidarian to the Cambrian Explosion.

Widespread Ni-Mo sulfide mineralization in South China during the early Cambrian may have affected the seawater chemistry and biodiversity of this region, but its underlying causes are not well-understood. To better understand the formation of sulfide ores in early Cambrian marine systems, this study evaluated the paragenesis and sulfur isotopic composition (δ34S) of sediment-hosted Ni-Mo sulfide ores in the lower Cambrian Niutitang Formation of the Nanhua Basin of South China. Petrographic analysis revealed three types of sulfide aggregates: (1) ubiquitous framboidal and euhedral pyrite (Py-1), (2) a MoSC phase (i.e., Mo mineralization) that was cogenetic with larger pyrite cubes or nodules (Py-2), and (3) intergrown millerite (NiS), sphalerite (ZnS) and veined pyrite (Py-3) (i.e., Ni-Zn mineralization) characterized by laminated and veined textures. Alternating precipitation of Mo and Ni-Zn sulfides was caused by intermittent emission of Mo-Fe or Ni-Zn-rich hydrothermal fluids into euxinic mid-depth waters of the Nanhua Basin, representing a sedimentary exhalative (SEDEX) process. The different sedimentary ore textures are each associated with a characteristic δ34S distribution. At all study sites, the syngenetic Py-1 phase yields δ34S of −15.7 to + 1.9‰, consistent with a seawater sulfate source that was variably fractionated through microbial sulfate reduction (MSR). In the Nayong and Zunyi areas, δ34S values of −11.8 to +4.4‰ are associated with the MoSC phase, and −20.6 to −6.8‰ with the Py-2 phase. In the Zhangjiajie area, Py-2 yields similar values (−25.1 to −10.8‰) but MoSC higher and less variable values (+8.6 to +18.7‰). These phases are thought to contain a mixture of sulfur sourced from seawater sulfate (via MSR) and hydrothermal fluids in varying proportions. A mode of Ni-Zn sulfides δ34S values between −9.1 and +8.0‰ is likely to represent the isotopic composition of hydrothermal sulfur inputs to the Ni-Zn mineralization. As a consequence, both hydrothermal emissions and biogenic production of H2S had a significant influence on seawater chemistry, with consequences for contemporaneous evolution of early marine animal life (e.g., the small shelly fauna and Chengjiang Biota) in the early Cambrian Nanhua Basin.

The early Cambrian (541–514 Ma) was a crucial interval for the evolution of life on Earth, popularly known as the “Cambrian Explosion”. Here, we report the timing of changes in hydrothermal and depositional inputs, as well as paleo-redox state, which may have influenced biogeochemical changes. According to high-resolution petrology, fossil distributions, isotopic records, and inorganic geochemistry, the lower Cambrian of the South China can be subdivided into four intervals: the lowermost Cambrian Zhujiaqing Formation (Cam-I); the Cambrian Stage 2 Shiyantou Formation (Cam-II); the lower part of the Cambrian Stage 3 Yu'anshan Formation (Cam-III); and the mid–upper Cambrian Stage 3 and the middle–upper part of the Yu'anshan Formation, continuing into the Canglangpu Formation (Cam-IV). Hydrothermal events are detected during the early Cam-I, Cam-II, and Cam-III intervals. During the early Cam-I and Cam-II intervals, these events coincided with extensive bottom water euxinia, which in turn may have restricted the spread or proliferation of Ediacaran fauna and small shelly fauna. Through the whole Cam-III interval, further hydrothermal events occurred concurrently with euxinic and ferruginous conditions, probably within a single spatially stratified water column, again plausibly restricting the spread of aerobic organisms. In conjunction with the cessation of hydrothermal events and the gradual lowering of sea level during the late Cam-III, oxic water environments gradually spread into relatively deep-water regions, concurrent with the emergence of the Chengjiang and Qingjiang faunas. These data suggest that periodic hydrothermal events may have had a significant impact on the spread, radiation and extinction of macroscopic fauna during the early Cambrian in South China.

Quadrapyrgites is a microfossil reported with embryonic and post-embryonic stages from the lower Cambrian small shelly fauna of South China, and is closely related to Olivooides. Their development mode and systematic positions are hot topics in palaeoembryology and evolutionary biology in recent years, but are still under debate. Here, we present a description on the growth pattern and post-embryonic development of Quadrapyrgitesquadratacris recovered from the lower Cambrian of South China. The growth zone of Q. quadratacris is situated at the oral end, and new terminal lobes are generated within the oral aperture. The terminal lobes are first in control of the opening and closure of the tubes, and later transferred to be crests, thus elongating the tubes. The post-embryonic development is characterized by a one-by-one addition of crests on the post-embryonic tissue, and an ontogenetic sequence with crest number from 1 to 17 is reconstructed. During the ontogeny, the embryonic tissue remains stable in size and morphology. The oral aperture is the only opening of the tubes, while a possible anus on the apical end does not occur. Quadrapyrgites was proposed to be the sister group of Olivooides, and now this is strengthened by the identical growth pattern and post-embryonic development. The comprehensive data from anatomy, growth pattern and post-embryonic development reject the stem-lineage cycloneuralian affinity for Quadrapyrgites and Olivooides, and instead support a coronate scyphozoan hypothesis.

Tommotiids are distinctive components of the early Cambrian small shelly fauna, almost invariably represented by isolated phosphatic sclerites derived from a multielement protective cover (scleritome). The unusual range of tommotiid sclerite morphologies and unknown construction of the scleritome have severely hampered our understanding of their phylogenetic affinities. However, recent description of rare, articulated scleritome material belonging to the tommotiid genera Eccentrotheca and Paterimitra support the hypothesis that some tommotiids fall within the stem group of the lophophorate phyla Phoronida and Brachiopoda and that at least some tommotiid sclerites are homologous precursors of the shells of organophosphatic brachiopods. Here we show that the shell microstructure of Eccentrotheca and Paterimitra share substantial similarities with paterinid brachiopods. While paterinids possess an overall brachiopod morphology, their microstructure appears more similar to Eccentrotheca and Paterimitra than to nonpaterinate lingulids. These findings strongly support the existence of a brachiopod total group that is solidly rooted within tommotiids, and identify the organophosphatic skeletal composition as plesiomorphic with calcareous shells as derived. The microstructural changes of the proposed tommotiid-brachiopod transition probably reflect an adaptation to fluctuating food and phosphorous intake that came with the switch to a sessile life style at the base of the tommotiid clade.

The Ediacaran to lowermost Cambrian successions of south-eastern Uruguay preserve an unusual and significant record of deposits generated during the Gondwana assembly (ca 590 to 535 Ma). This study presents a review of data obtained through extensive field-based mapping coupled with detailed sedimentology and stratigraphy of key formations. The geological units within the study area consist of the Maldonado Group (Playa Hermosa, Las Ventanas and San Carlos formations), the Arroyo del Soldado Group (Yerbal, Polanco Limestones, Barriga Negra and Cerro Espuelitas formations) and the Arroyo de la Pedrera Group (Piedras de Afilar and Cerro Victoria formations). The Maldonado Group is characterized by a glacially influenced volcanogenic-sedimentary sequence with ice-rafted debris and dropstones in the Playa Hermosa and Las Ventanas formations. The Arroyo del Soldado Group is a mixed siliciclastic-carbonate succession, mainly represented by an intercalation of basal pink dolostones, banded siltstones, rhythmites of dolostone-limestone, iron formations, cherts and conglomerates. Carbonates in the Polanco Limestones Formation are characterized by a negative δ13C excursion up to −3·26‰ PeeDeeBelemnite. The Arroyo de la Pedrera Group consists of quartz arenites and stromatolitic/oolitic dolostones. Preliminary data indicate that the Precambrian–Cambrian could be contained within or at the base of this group. The entire succession is almost 6000 m thick, and contains a rich fossil assemblage composed of organic-walled microfossils and small shelly fauna, including the index fossil Cloudina riemkeae. The stratigraphic and chemostratigraphic features are suggestive of a Gaskier age (ca 580 Ma) for the basal glacial-related units. In this scenario, the results show the importance of lithostratigraphic, biostratigraphic and chemostratigraphic data of these Ediacaran units in the global correlation of terminal Proterozoic sedimentary rocks.

A diverse and well-preserved fauna of shelly fossils from the upper Lower Cambrian Bastion and Ella Island Formations of North-East Greenland contains more than 90 species. The fauna is the most diverse shelly fauna yet discovered in the Lower Cambrian of Laurentia and includes many fossils previously known only from other continental blocks. It enhances correlation of the North-East Greenland succession into Laurentia, most notably with the Browns Pond Formation of New York State, but also with other important Early Cambrian continents, in particular with Australia, Antarctica, and Siberia. A middle Dyeran age is most probable for both the Bastion and Ella Island Formation, and the rich fossil assemblage facilitates correlation with the Botoman Stage of Siberia and its equivalents. One new taxon is described, the disc-shaped problematicum Tunudiscus duovittarius n. gen. and sp.

Attention is drawn to Nielsen's radical body plan concept, here named the 'brachiopod fold hypothesis', under which brachiopods and phoronids are recognized to be transversely folded across the ontogenetic anterior–posterior axis so that, to make useful comparisons with other phyla, these organisms must be conceptually unfolded. Under the hypothesis brachiopod brachial and pedicle shell valves are respectively 'anterior' and 'posterior' rather than 'dorsal' and 'ventral' as traditionally described. The hypothesis makes sense of the symmetry axes of the brachiopod shell, is consistent with various indications from fossil and Recent brachiopods, and gives rise to predicted patterns of axis–determining gene expression that differ from those obtaining under the traditional view of the body plan, whilst the variety of folding movements in different lineages implies that superficially dissimilar morphogenetic folds may be fundamentally homologous. Convergent folding patterns are noted in some other organisms. A previous conjecture that inarticulate linguloid brachiopods were derived from halkieriid–like ancestors is elaborated with proposals that recognize possible functional continuities of coelomic and marginal sclerite functions, and it is noted that an ancestrally facultative fold could have become incorporated by genetic assimilation into the brachiopod developmental program. An experimental approach is outlined to test the possibility that some members of the 'small shelly fauna' may have been members of the halkieriid–like brachiopod stem lineage and it is also suggested that buoyancy modification may have been an important function of mineralization amongst Lower Cambrian floaters and swimmers, since negative buoyancy would facilitate access to the benthic niche.

The transition from the Neoproterozoic Nemakit-Daldynian 1 Krol-E dolomite to the Tommotian Lower Tal phosphorite-chert–black shale sequence denotes a period of drastic change in the depositional environment and the chemical milieu of the sedimentation basin. These changes are reflected by a marked negative excursion of carbon isotopes, phosphorus enrichment, trace-metal content, high organic carbon burial and notably the first appearance of prolific small shelly fauna and burrowing organisms. Recent studies have documented these changes along several stratigraphic profiles in the Mussoorie Hills of the Garhwal Himalaya for which a single profile from the Durmala phosphorite mine provides a key section discussed here.

General agreement exists that the position of the base of the Cambrian (Precambrian–Cambrian boundary) should coincide with a biostratigraphic marker that can be widely traced and is linked to the evolution of the small shelly fauna. On the Siberian platform the presence of distinct facies during the Vendian–Cambrian interval has made biostratigraphic correlation based on palaeontological data highly contentious. A solution to this problem appears to exist with the recognition of an almost uninterrupted profile in the Aldan–Uchur watershed where key sections expose the eastern and transitional facial region. On this basis we present a general biostratigraphic scheme for the Vendian–Cambrian across the southern Siberian platform that connects separate facies. Further correlation with key sections in northern Siberia leads to the recognition of three biostratigraphic zones for the Vendian–Cambrian interval. These are: Anabarites trisulcatus Zone; Purella antiqua Zone; Aldanocyathus sunnaginicus Zone. The abundance of Chinese-type small shelly fossils in the region of the eastern facies suggest correlation of the A. sunnaginicus Zone with the Siphogonuchites–Paragloborilus Zone of China, and the P. antiqua Zone with the Circotheca–Anabarites–Protohertzina Zone. In places, at the base of the Circotheca–Anabarites–Protohertzina Zone in China, analogies to the A. trisulcatus Zone can be identified. It is proposed that in Siberia the base of the A. sunnaginicus Zone (= base of Tommotian Stage) be taken as the base of the Cambrian. This would correspond with Marker B of the Meishucunian in China

Numerous spiniferous acritarchs, Baltisphaeridium, Micrhystridium, Coryphidium and Acanthodiacrodium , have been discovered in the lower Member of the Jiulaodong Fm of the lowest Cambrian Meishuucun Stage, in Maidiping, Emei, Sichuan, Southwestern China. Large (more than 20 μm) spiniferous acritarchs, Baltisphaeridium , etc., were discovered previously and described as taxa occurring contemporaneously with trilobites in Cambrian strata. The described Baltisphaeridium now has been found in sediments more than 120 m below the oldest trilobite bed. This is interesting for the following reasons: (1) the Baltisphaeridium evidently did not occur for the first time contemporaneously with trilobites, but already existed together with small shelly fauna in the early Meishucun or earlier; (2) the earliest trilobites possibly had occurred during the Meishucun Stage, but that is earlier than so far known; (3) the occurrence of Baltisphaeridium together with small shelly fossils in the Meishucun Fm not only increases the abundance and diversity of the Cambrian Meishucun fossil population and differentiates between the Cambrian and the Precambrian, but also raises the possibility of using Baltisphaeridium in determining the Precambrian-Cambrian boundary in the absence of small shelly fossils. The following taxa are described: Octaedryxium simplex n.sp., O. minutum n.sp., Baltispaeridium dictium n.sp., B. reticulum n.sp., B. jiulaodongense n.sp., Eomicrhystridium sp., Micrhystridium pseudozonale n.sp., M. maidipingense n.sp., Coryphidium sichuanense n.sp., Coryphidium sp., Acanthodiacrodium sp. and Cymatiosphaera sp.