Small Shelly Fossils Research Articles

Chert-hosted small shelly fossils: expanded tool of biostratigraphy in the Early Cambrian

Small shelly fossils (SSFs) are widely utilized for Cambrian biostratigraphy of shallow-water carbonates. The apparent linkage of SSFs to carbonate facies reflects an observational bias. Our study on the deeper siliceous facies of the Yangtze Craton in Zhejiang and Hunan provinces (China) reveals that SSFs also can be extracted from cherts. For this purpose a quick-etching method with weak hydrofluoric acid is applied. SSFs extracted from cherts are comparable with those from carbonates. Energy-dispersive X-ray spectroscopy analyses indicate a primary composition of SSFs of organic carbon and apatite. Hydrofluoric acid-processing can provide valuable biostratigraphic data of SSFs that are complementary to standard methods.

Chancelloriid sclerites from theLowerCambrian (Meishucunian) of easternYunnan,China, and the early history of the group

AbstractChancelloriids are a group of enigmatic sessile animals that are covered with sclerites shaped as rosettes of spines, producing an appearance like that of a barrel cactus. They are known only fromCambrian rocks. Isolated sclerites of chancelloriids are widespread in small shelly faunas, but they have proven difficult to treat taxonomically due to the variation within and between individual animals. We report on large samples of chancelloriid sclerites from theMeishucunian (pre‐trilobiticLowerCambrian) of easternYunnanProvince,China, including material from theDahaiMember of theZhujiaqingFormation (theZhujiaqing section,Dahai,HuizeCounty) and theShiyantouFormation (theXiaotan section,YongshanCounty). The material from theDahaiMember appears to come from a single species,Chancelloriella irregularis. Statistical analysis of morphotype co‐occurrences in different samples suggests that several species are represented in the material from theShiyantouFormation, which we herein tentatively place in four species,Allonnia erromenosa,Allonnia tetrathallis,Archiasterella charmasp. nov. andArchiasterellacf.pentactina. We suggest therefore that careful study of large collections of isolated chancelloriid sclerites permits the identification of different species, opening the possibility of their use in evolutionary or stratigraphical studies. In particular, inSouthChina, it seems thatChancelloriella irregularisis characteristic of rocks of theParagloborilus subglobosus–Purella squamulosaAssemblageZone and theWatsonella crosbyiAssemblageZone, whilstArchiasterellaandAllonniafirst appear in the overlyingSinosachites flabelliformis–Tannuolina zhangwentangiAssemblageZone.C. irregularisis thus amongst the oldest well‐characterized chancelloriids, and the irregularity and poor organization of its sclerites relative to those of younger forms support the hypothesis that chancelloriid sclerites are compound structures arising from the fusion of originally separate elements, perhaps homologous with sclerites of halkieriids and other coeloscleritophorans. The similarity between the arrangement of rays in a chancelloriid sclerite and the arrangement of bubbles in small bubble clusters suggests that in many cases, aspects of the form of chancelloriid sclerites are the result of simple physical processes.

Phosphorus sources for phosphatic Cambrian carbonates

The fossilization of organic remains and shell material by calcium phosphate minerals provides an illuminating, but time-bounded, window into Ediacaran–Cambrian animal evolution. For reasons that remain unknown, phosphatic fossil preservation declined significantly through Cambrian Series 2. Here, we investigate the phosphorus (P) sources for phosphatic Cambrian carbonates, presenting sedimentological, petrographic, and geochemical data from the Cambrian Series 2–3 Thorntonia Limestone, Australia, some of the youngest Cambrian strata to display exceptional phosphatic preservation of small shelly fossils. We find that within Thorntonia sediments, phosphate was remobilized by organic decay and bacterial iron reduction, with subsequent reprecipitation largely as apatite within the interiors of small shelly fossils. We discuss the merits of bioclastic-derived, organic matter–bound, or iron-bound P as potential sources to these strata. Petrographic observations suggest that the dissolution of phosphatic skeletal material did not provide the P for fossil preservation. In contrast, high organic carbon contents imply significant organic fluxes of P to Thorntonia sediments. Sedimentology and iron-speciation data indicate that phosphorus enrichment occurred during times of expanded anoxic, ferruginous conditions in subsurface water masses, suggesting that phosphorus adsorption to iron minerals precipitating from the water column provided a second significant P source to Thorntonia sediments. Simple stoichiometric models suggest that, by themselves, neither organic carbon burial nor an iron shuttle can account for the observed phosphorus enrichment. Thus, we infer that both processes were necessary for the observed phosphorus enrichment and subsequent fossil preservation in the Thorntonia Limestone.

First report of a Meishucun-type early Cambrian (Stage 2) ichnofauna from the Malyi Karatau area (SE Kazakhstan): Palaeoichnological, palaeoecological and palaeogeographical implications

A trace fossil assemblage from the early Cambrian phosphorites of the Aktugai and Koksu sections (Chulaktau Formation) of the Lesser Karatau area (= Malyi Karatau in the following text) in SE Kazakhstan is reported for the first time. Based on a rich and biostratigraphically significant Small Shelly Fossil (SSF) record, the ichnofauna can be attributed to the basal Cambrian (Terreneuvian: ?uppermost Fortunian to Stage 2).Along with rare vertical burrows, the ichnoassemblage yielded abundant simple worm-shaped epi- and infaunal burrows of various ichnotaxa being associated with branched traces and (pre-trilobitic) arthropod traces.The non-arthropod ichnofauna consists of hyporeliefs of large straight to slightly meandering traces belonging to Palaeophycus isp., and Psammichnites isp. type traces. This ichnofauna is accompanied by horizons with short inclined U-shaped burrows of the Planolites-type. The evidence of Treptichnus pedum-like simple branching (sub-) horizontal traces is proved for the Koksu section but remains problematic for the Aktugai section as they are poorly preserved and could be mixed up with Planolites-type traces. Additionally, a dark-brown coloured phosphoritic sandy dolostone band close to an iron- manganese rich stromatolite bed on the base of the Ushbas Member contains vertical funnel-shaped burrows of more than a decimetre in length which could be attributed to dwelling burrows of infaunal lingulid brachiopods (?Lingulichnus). Several short and larger (knob-shaped) vertical burrows in the surrounding phosphoritic dolostones occasionally display faintly preserved radial running and distally branching probes. They resemble star-shaped trace fossils from the Meishucun- and from the younger (Cambrian Stage 4) Guanshan sections of South China.The arthropod traces can be attributed to Rusophycus-type traces (probably R. avalonensis) as well as to Monomorphichnus-type and problematic primitive (?) Cruziana-type trackways. The arthropod traces are concentrated in the massive phosphorites of the Karatau Member (Upper Chulaktau Formation) of the Aktugai-I and the Koksu localities. Some of them are preserved as positive hyporeliefs on the subsurface of an overlaying greenish-grey coloured chert band (panel A of the fourth figure in this article).The ichnotaxonomic inventory, the facies, the lithology and the depositional regime of the hosting rocks as well as the trace preservation in the massive phosphorites resemble the situation in the some older (Fortunian Stage) Meishucun ichnofauna of southern Yunnan, South Chinese Yangtze Platform as well as in some aspects the ichnoassemblage from the much younger (Stage 4) Wulongqing Formation of Yunnan. The here reported type of early Cambrian ichnofauna could be characteristic for the abundant basal Cambrian phosphorite-dominated shelf deposits on the northwestern realm of Gondwana.

A unique condition for early diversification of small shelly fossils in the lowermost Cambrian in Chengjiang, South China: Enrichment of phosphorus in restricted embayments

In the earliest Cambrian the major diversification of small shelly fossils (SSFs) was the first episode of the so-called Cambrian Explosion. In order to clarify the background environmental conditions of this event, we examined the lowermost Cambrian strata with bedded phosphorites in the Chengjiang area, South China. The lowermost Cambrian (the Zhongyicun Mb of the Zhujiaqing Fm) in eastern Yunnan is composed of bedded phosphorites and phosphatic limestones with diverse SSFs. We investigated 3 sections within the Chengjiang area at Hongjiachong, Maotianshan, and Xiaolantian. Detailed lithostratigraphic analysis of outcrops and drill cores at Hongjiachong indicates that the Zhongyicun Mb consists of 5 distinct units, A to E in ascending order. The presence of 15 genera of SSFs in 20 horizons shows that the Zhongyicun Mb yields two distinct SSF assemblages of Fortunian age (earliest Cambrian; 541–529Ma); i.e. the first assemblage with simple-shape SSFs (Anabarites, Protohertzina) from basal Unit A, and the second assemblage with various molluscan shells (Paracarinachites, Ocruranus–Eohalobia) from Units C–E. As well as abundant phosphate grains, all SSFs occur as clastic grains, suggesting that phosphorite was primarily formed in extreme shallow-water settings, as were the small shelly animals. We established that the first occurrence of the second SSF assemblage is at least 5m lower (ca. 1–2myr earlier in age) than previously reported in Chengjiang, and we speculate that the major diversification in SSF assemblage likely occurred during the Fortunian, at least before ca. 534Ma. Judging from the rift-related tectonic setting and relevant paleogeography of western South China, we further speculate that the Zhongyicun Mb was primarily deposited in restricted embayments in the Kangdian rift basin, and that the rapid SSF diversification in the Fortunian occurred in a unique setting in highly phosphorus-rich seawater.

Terreneuvian small shelly faunas of East Yunnan (South China) and their biostratigraphic implications

The study discusses the detailed composition of Terreneuvian small shelly fossil (SSF) assemblages of eastern Yunnan Province (Meishucun, Xianfeng and Huize regions). The described sections represent shallow water deposits of the Yangtze Platform that include a number of stratigraphical hiati. The reported SSF assemblages can be assigned to the regional SSF biozones I–III (Anabarites trisulcatus–Protohertzina anabarica Assemblage Zone; Paragloborilus subglobosus–Purella squamulosa Assemblage Zone; Watsonella crosbyi Assemblage Zone). Zones II and III are slightly redefined based on new data. Two subzones of Zone II are proposed here, namely, Annelitellus yangtzensis–Obtusoconus honorabilis Subzone and Maikhanella cambriana–Oelandiella korobkovi Subzone. Claviconchella qianyii gen. et sp. nov. and Bubiites simplex gen. et sp. nov. are reported. Here we also provide a critical revision of the SSF distribution for the well-known Meishucun section. The correlation scheme for East Yunnan documents the extent and duration of stratigraphical hiati. The distribution of SSFs and the lithological characterization indicate three major events of exposure of the carbonate platform resulting in sedimentary breaks and possible karstification. This prompts new consideration of the previously described stable isotope stratigraphy of shallow platform strata. Considering the complexity of the Terreneuvian Earth history as well as the uniqueness of SSF, an integration of sedimentology, geochemistry and paleontology is needed for future SSF study.

On the Lower Cambrian biotic and geochemical record of the Hetang Formation (Yangtze Platform, south China): evidence for biogenic silica and possible presence of Radiolaria

Abstract. Research on Lower Cambrian siliceous sedimentary rocks is important for understanding the origin and early involvement of polycystine Radiolaria in the silica cycle. During our study, thin sections and HF acid processing of black cherts and shales from the Hetang Formation that crops out in the Xintangwu section (west Zhejiang Province, south China) were made. We report on the presence of siliceous spherical microfossils (possibly Radiolaria) associated with sponge spicules and acritarchs. Their size and the presence of residual spines on some spherical siliceous microfossils observed in both residues and thin sections of cherts from the top of Member ‘a’ of the Hetang Formation argue for the possible presence of radiolarians. Based on the Small Shelly Fossil assemblages reported in previous studies, this interval should be considered as Qiongzhusian (Atdabanian–Early Botomian) in age. Finally, the values of the Ge/Si ratio measured on black cherts of the Hetang Formation point to a biogenic origin of the silica.

Dating the Cambrian Purley Shale Formation, Midland Microcraton, England

AbstractZircons from a bentonite near the base of the Purley Shale Formation in the Nuneaton area, Warwickshire, yield a 206Pb/238U age of 517.22 ± 0.31 Ma. Based on the fauna of small shelly fossils and the brachiopod Micromitra phillipsii in the underlying Home Farm Member of the Hartshill Sandstone Formation, trilobite fragments that are questionably referred to Callavia from the basal Purley Shale Formation, and the presence of trilobites diagnostic of the sabulosa Biozone 66 m above the base of the Purley Shale Formation, the bentonite likely dates an horizon within Cambrian Stage 3, at about the level of the Fallotaspis or basal Callavia Biozone. This is consistent with bentonite ages from other localities in southern Britain, which constrain the age of the lower and uppermost parts of Cambrian Stage 3. The new date provides additional chronological control on the earliest occurrence of trilobites in the Midland Microcraton, a date for the marine transgression at the base of the Purley Shale Formation, and is the first radiometric age from the Cambrian succession of Warwickshire.

Small shelly fossils from the early Cambrian Yanjiahe Formation, Yichang, Hubei, China

Abundant data have been acquired on the lower Cambrian small shelly fossils (SSFs) of the Yangtze platform during the last three decades, demonstrating that these fossils are an important piece of evidence for the Cambrian radiation and are useful biostratigraphic tools for correlating the lower Cambrian. Here we report SSF associations from the Yanjiahe Formation in the Three Gorges area, South China. The Yanjiahe Formation is well exposed near the Yanjiahe village, and its 40-m-thick sequence can be subdivided on the basis of lithology into five stratigraphic intervals (beds). Small shelly fossils occur mainly in Beds 2 and 5, but abundant SSFs were discovered in thin sections of siliceous–phosphatic nodules from Bed 3 for the first time. No skeletal fossils were discovered in the basal siliceous rock interval (Bed 1), but the negative δ13Ccarb excursion and the occurrence of the acritarch Micrhystridium regulare indicate that it belongs to the basal Cambrian. The SSF associations are somewhat similar to those of East Yunnan, and can be differentiated into three biozones (in ascending order): the Anabarites trisulcatus–Protohertzina anabarica assemblage zone (Bed 2), the Purella antiqua assemblage zone (Bed 3), and the Aldanella yanjiaheensis assemblage zone (Bed 5). The occurrence of A. yanjiaheensis in Bed 5 probably indicates that Bed 5 belongs to Cambrian Stage 2, but the Stage 2/Stage 1 boundary is uncertain since Bed 4 lacks fossils. SSF biostratigraphy indicates that the Yanjiahe Formation is pretrilobitic Meishucunian in age (equivalent to the Nemakit–Daldynian to Tommotian of Siberia, Terreneuvian). Five SSF genera occur in Bed 2, more than six genera in Bed 3, and twenty-three genera in Bed 5. The stepwise increase in generic diversity through the Yanjiahe Formation is comparable with the global diversity increase through the Nemakit–Daldynian to early Tommotian interval.

New biostratigraphical constraints on the Lower and lower Middle Cambrian of the Kharaulakh Mountains (northeastern Siberian Platform, Chekurovka anticline)

The Cambrian section of the western limb of the Chekurovka anticline was studied, with layer-by-layer collection of animal fossils. This permitted us to refine the biostratigraphic division of this section. Four biostratigraphic units (beds) with small shelly fossils were identified: Lapworthella tortuosa, Lapworthella bella, Mobergella radiolata, and Rhombocorniculum cancellatum. They characterize most of the Tommotian and Atdabanian Stages of the Lower Cambrian. The Lower Tyuser Subformation and the Sekten Formation were constrained by small shelly fossils for the first time. Numerous trilobite finds helped to reveal intervals correlating with the Delgadella anabara–Nevadella and Judomia–Uktaspis (Prouktaspis) Regional Zones in the upper Atdabanian.The upper Sekten Formation (black shales) forms the Kuonamka Formation. Within this interval, the following trilobites were found: Triplagnostus gibbus, Tomagnostus sibiricus, Pseudanomocarina sp., Eodiscus oelandicus, Paradoxides sacheri, and Ptychagnostus aff. atavus. They are widespread in the vast territory of the eastern Siberian Platform, within the Kuonamka Formation.Also, Korobovia khorbosuonica, Charaulaspis postprimus, and Hebediscus convexus trilobites were observed, which had been found earlier in the Khorbosuonka River section (Olenek uplift). This permits a detailed correlation between these localities.Similarity was observed between Triangulaspis annio trilobites and young Charaulaspis. This casts doubt upon the fact that the first Triangulaspis annio finds in the northeastern Siberian Platform belonged to the upper Atdabanian.

A pronounced negative δ13C excursion in an Ediacaran succession of western Yangtze Platform: A possible equivalent to the Shuram event and its implication for chemostratigraphic correlation in South China

A pronounced negative δ13C shift that can be potentially correlated with the Shuram excursion has been reported from middle Ediacaran strata in the Yangtze Gorges area of South China. Whether it represents a perturbation to the ocean carbon cycle or a record of post-depositional alteration is still open to debate. Resolving this controversy will help clarify if δ13C variations can be used for chemostratigraphic correlation of Ediacaran successions. To further understand the regional pattern of Ediacaran carbon isotopic excursions in the Yangtze platform, we carried out a detailed δ13C analysis of the Lianghong section in the western part of the Yangtze platform. The Ediacaran System at Lianghong is overlain by the Maidiping Formation yielding early Cambrian small shelly fossils and underlain by the Cryogenian Lieguliu Formation diamictite and tuffaceous siltstones. It comprises the Guanyinya and Hongchunping formations, which have been traditionally correlated with the Doushantuo and Dengying formations, respectively, in the Yangtze Gorges area. Two negative δ13C excursions occur in the Lianghong section. The lower one at the uppermost Guanyinya Formation, with a nadir at −8.6‰, may be correlated with the pronounced negative δ13C shift (EN3) in the uppermost Doushantuo Formation in the Yangtze Gorges area and possibly with the well known Shuram event in Oman. The upper negative δ13C excursion occurs in the upper Hongchunping Formation and may be correlated with negative excursions (EN4) near the Ediacaran/Cambrian boundary. Other negative δ13C excursions (e.g., EN1 and EN2) are not expressed in the Lianghong section because the lower Guanyinya Formation is dominated by siliciclastic rocks. Combined with previously published Ediacaran δ13C profiles, our results indicate that the EN3 excursion (likely a Shuram equivalent) may occur widely in South China and can be a useful chemostratigraphic feature for regional and global stratigraphic correlation.

Carbon and strontium isotope evolution of seawater across the Ediacaran–Cambrian transition: Evidence from the Xiaotan section, NE Yunnan, South China

This study reports a high-resolution carbon and strontium isotope profile for the Ediacaran–Cambrian Xiaotan section, situated in northeastern Yunnan, South China. Xiaotan section represents a more distal setting than the more condensed Meishucun section in eastern Yunnan, and is, biostratigraphically and chemostratigraphically, the best constrained section on the Yangtze platform covering the Ediacaran–Cambrian interval. The carbonate carbon isotopic ratios of the late Ediacaran, upper Dengying Formation to the early Cambrian, Zhujiaqing Formation, exhibit a large negative excursion (N1, −12.2‰) in the Daibu Member, just below the first appearance of small shelly fossils (SSF) at the base of the Zhongyicun Member, and a sustained pre-‘Tommotian’ positive excursion (P4, δ13C up to +7.3‰) which coincides with the occurrence of the Heraultipegma yunnanensis (=Watsonella crosbyi) Assemblage SSF in the Dahai Member. Least altered strontium isotope ratios, based on sequential acid leaching of limestones as well as dolostones and phosphorites following rigid petrographic and geochemical selection, reveal a systematic decreasing trend from 0.7085–6 in the latest Ediacaran (Daibu Member) to about 0.7082–3 by the FAD of Watsonella crosbyi in China (Dahai Member). The carbon and strontium isotope features of the Xiaotan section can be correlated with those from sections in Morocco, Mongolia and Siberia, and confirm a decrease in seawater 87Sr/86Sr during Cambrian Stage 1 accompanied by C-isotope oscillations, which together may assist global stratigraphic correlation of the early Cambrian. As previously intimated by C-isotopes and biostratigraphy, this new Sr-isotope evidence confirms a depositional gap during the pre-Tommotian in the Aldan River area of SE Siberia. The decreasing trend of 87Sr/86Sr in the Cambrian Stage 1 marks a temporary (∼16Myrs) reversal of the overall increasing trend during the Ediacaran and Cambrian periods, and potentially records a short-term decrease in continental weathering within a prolonged interval of generally increasing weathering rates. Other factors, such as increased submarine hydrothermal alteration, ocean spreading rates and/or chemical weathering of volcanic provinces and young carbonate dissolution might also have affected this decrease in seawater 87Sr/86Sr.

A refined chronology for the Cambrian succession of southern Britain

Abstract: Three dated (U–Pb, zircon) ash beds from biostratigraphically constrained Avalonian successions of Shropshire (England) and Pembrokeshire (Wales) delimit the traditional ‘Lower'–‘Middle' Cambrian boundary and resolve a problematic regional correlation. In Shropshire, a date of 514.45 ± 0.36 [0.81 including tracer calibration and 238 U decay constant errors] Ma from near the top of the Lower Comley Sandstone Formation provides a maximum age for the boundary between Cambrian Stages 3 and 4, and a date of 509.10 ± 0.22 [0.77 including tracer calibration and 238 U decay constant errors] Ma from the basal Quarry Ridge Grits, Upper Comley Sandstone Formation, provides a minimum age for the boundary between Cambrian Stages 4 and 5 (and thus Series 2 and 3). These dates offer a calibration of early metazoan evolution by directly constraining the age of the intervening Comley Limestones, which contain diverse small shelly fossils in addition to trilobites, and also a key early occurrence of exceptional, three-dimensionally preserved arthropods. In Pembrokeshire, an ash bed from the Caerfai Bay Shales Formation dates to 519.30 ± 0.23 [0.77 including tracer calibration and 238 U decay constant errors] Ma, equivalent to a horizon low in the Lower Comley Sandstone Formation of Shropshire, possibly around the level at which trilobites make their first local appearance. Supplementary material: Appendix 1, a table of isotope data, is available at http://www.geolsoc.org.uk/SUP18444 .

Early Cambrian epibolic gastrulation: A perspective from the Kuanchuanpu Member, Dengying Formation, Ningqiang, Shaanxi, South China

The Cambrian explosion is marked by the apparent sudden appearance of diverse metazoan skeletal fossils and an increase in the complexity of both body and trace fossils. Among them, fossil eggs and embryos from the Lower Cambrian Kuanchuanpu Member of the Dengying Formation at Ningqiang in southern China provide a unique window for investigating the ontogeny of metazoans. Gastrulation is the cell migration stage after cleavage, and can be viewed as the embryonic analog of the transition from protozoan to metazoan grades of complexity. As an example, the embryonic developmental sequences of Punctatus emeiensis is well-documented because of the stellate spines covering the body surface, that are shared with embryonic stages represented by Olivooides and their growth stages represented by P. emeiensis. Although Olivooides was considered to be a taxonomic mixture, consideration of its variation was neglected. A specific type of embryo with zigzag blastopore lips that differs from typical candidate embryos for P. emeiensis is identified; its gastrulation process is reconstructed and is comparable to the epibolic gastrulation of extant metazoans. Both the embryos and adults of this ‘type’ display radial symmetry, that suggests an affinity distinct from that of echinoderms. Moreover, the body plan of penta-radial symmetry seen widely in Early Cambrian ‘Small Shelly Fossils’ (SSF's) was probably deep rooted in the Ediacaran.

New biostratigraphical constraints on the lower Cambrian Ratcliffe Brook Formation, southern New Brunswick, Canada, from organic-walled microfossils

Organic-walled microfossils from the Ratcliffe Brook Formation of southern New Brunswick enable recognition of the three lowest Cambrian acritarch-based zones established in southeastern Poland and on the East European Platform. This is the first record of these zones in Avalonia. The distribution of acritarchs of the Asteridium tornatum-Comasphaeridium velvetum, Skiagia ornata-Fimbriaglomerella membranacea, andHeliosphaeridium dissimilare-Skiagia ciliosa zones leads us to propose a revised correlation of sections of the Ratcliffe Brook Formation, in which an ash bed dated at 531 Ma now predates rather than postdates an assemblage of small shelly fossils that had been previously attributed to the Watsonella crosbyi Zone. The small shelly fossils are here suggested to belong to a younger biozone as they occur with acritarchs of the Skiagia ornata- Fimbriaglomerella membranacea Zone, the base of which is currently thought to approximate in time to the global appearance of trilobites. The occurrence of acritarchs of the Heliosphaeridium dissimilare-Skiagia ciliosa Zone close to the top of the Ratcliffe Brook Formation suggests that the upper part of this formation and the overlying Glen Falls Formation are younger than previously thought and that their correlationwith strata in Newfoundland is in need of revision.Biostratigraphic constraints are currently insufficient to position the 531Maash bedwith precisionwith respect to the Watsonella crosbyi Zone in Newfoundland, but it is likely that the date is within this zone.

Chapter 23 Glacial deposits of the Bokson Group, East Sayan Mountains, Buryatian Republic, Russian Federation

Abstract The Bokson Group (Gr.) forms the platform cover in northern part of the Tuva-Mongolian Massif, south of the East Sayan Mountains. Widespread diamictites occur in the lower part of the Bokson Gr., in the Zabit Formation (Fm.). These contain erratic, faceted and striated stones along with dropstones. They have disconformable or gradual lower boundaries and conformable or transitional upper boundaries with overlying deposits. The isotopic δ 13 C crb curve records some maximum and minimum values as a background of insignificantly varying values (from –3 to 2‰). Maximum values (up to 5.5‰), are recorded in deposits underlying diamictites, whereas the overlying beds of the Zabit Formation (Fm.) yielded three peaks or minima down to −4‰. A fourth negative anomaly derived from the middle part of the Bokson Gr. in the lower part (close to base) of the Tabinzurt Fm. is as low as –5.7‰. The deposits underlying the diamictites contain Ediacaran (Vendian) microfossils. Cloudina sp. was discovered in the granule of diamictites, whereas beds just above include small shelly fossils (SSF) of the Nemakit-Daldynian type ( Cambrotubulus decurvatus Miss., Anabarites trisulcatus Miss.), which is overlain by a member with abundant fossils of the Tommotian assemblage. The diamictites represent glaciomarine deposits formed in the uppermost Ediacaran or lowermost Cambrian stage (Upper Vendian).

The coral Cothonion from the lower Cambrian of North Greenland

Originally described from the Coonigan Formation of New South Wales, Australia, a second occurrence of the operculate coral Cothonion sympomatum is here described from the Paralledal Formation of North Greenland. Both finds are of late early Cambrian age, Series 2, Stage 4 in the emerging fourfold classification of the Cambrian. The new find supports widespread distribution patterns seen in early Cambrian Small Shelly Fossils, although associated trilobites belong to traditional redlichiid (Australia) and olenellid (Greenland) realms, respectively.

Zooproblematica and mollusca from the Lower Cambrian Meishucun section (Yunnan, China) and taxonomy and systematics of the Cambrian small shelly fossils of China

The monograph presents the results of the study of the Cambrian small shelly fossil fauna of the Meishucun Locality (east of Yunnan Province, China), the reference section for the Cambrian stratigraphy and paleontology of China and the stratotype of the Meishucunian Regional Stage. This publication contains a monographic description of 66 species and 52 genera of zooproblematica and mollusks and an annotated checklist of the small shelly fossil species of the Cambrian of China. The checklist includes 744 nominal species (among them 508 species names are zooproblematica, 220 species names are mollusks, and 16 names represent other groups of organisms). A taxonomic revision of all mollusk and zooproblematic taxa that have ever been described from the Cambrian of China is made at the species and generic levels. We propose that, of the 508 checklisted species of zooproblematica, 221 species should be considered valid, 80 of them are considered as tentatively valid, whereas of the 220 checklisted species of mollusks, 92 species can be considered valid. It was found out that 28 species names of zooproblematica and 7 species names of mollusks should be considered as nomina nuda, since their descriptions do not satisfy the availability criterion. We have to consider 20 species of mollusks and 18 species of zooproblematica as nomina dubia, because these taxa have been described based on unsatisfactory or fragmentary preserved material lacking any diagnostic features. Based on taxonomic work, it has been shown that the great number of synonymous taxa resulted in a more than double overestimation of the real value of the nominal species biodiversity of the Cambrian small shelly fossil fauna of China. The following new taxa are described, i.e. genera: Hexagonellus Demidenko, gen. nov.; Asiapatella Parkhaev et Zhegallo, nom. nov.; Dorispira Parkhaev, gen. nov.; and species: Platyspinites elegans Demidenko, sp. nov.; Mongolodus sulcus Demidenko, sp. nov.; Hexagonellus kuzminae Demidenko, sp. nov.; Halkieria wangi Demidenko, sp. nov.; Asiapatella sinuata Parkhaev, sp. nov.; Pseudoscenella levigata Parkhaev, sp. nov.; Trifistulella tortilis Demidenko, sp. nov. Based on the analysis of biostratigraphic and chemostratigrahic data, we propose the correlation of the Upper Precambrian-Lower Cambrian boundary deposits of the Siberian Platform and Yangtze Platform. According to this correlation, the base of the Tommotian Stage corresponds to the level within the middle of the Zhongyicun Member of the Zhujiaqing Formation. The monograph contains an extensive bibliography of 379 publications on the subject.

Early Cambrian brachiopods and other shelly fossils from the basal Kinzers Formation of Pennsylvania

An assemblage of seventeen species of Small Shelly Fossils, dominated by the brachiopod Eothele tubulus and species of the mollusk Yochelcionella, is described from the basal Kinzers Formation of Thomasville, Pennsylvania. The occurrence extends southwards the distribution of an Early Cambrian fauna (Cambrian Series 2, Stage 4) that is otherwise characteristic of the eastern shelf of Laurentia from New York to Greenland. The poorly known acrothelid brachiopod Eothele tubulus is redescribed based on large collections of ventral valves. The shell structure of E. tubulus is characterized by orthogonal baculae, and represents the oldest known example of a baculate shell structure, indicating that this type of shell structure evolved already in the Early Cambrian.

Early Cambrian brachiopods and other shelly fossils from the basal Kinzers Formation of Pennsylvania

An assemblage of seventeen species of Small Shelly Fossils, dominated by the brachiopod Eothele tubulus and species of the mollusk Yochelcionella, is described from the basal Kinzers Formation of Thomasville, Pennsylvania. The occurrence extends southwards the distribution of an Early Cambrian fauna (Cambrian Series 2, Stage 4) that is otherwise characteristic of the eastern shelf of Laurentia from New York to Greenland. The poorly known acrothelid brachiopod Eothele tubulus is redescribed based on large collections of ventral valves. The shell structure of E. tubulus is characterized by orthogonal baculae, and represents the oldest known example of a baculate shell structure, indicating that this type of shell structure evolved already in the Early Cambrian.