Lower Cambrian Of South China Research Articles

Growth patterns and affinities of Huizenodus oligaspinosus (?Cnidaria) from the lower Cambrian of South China

Helmet-like small shelly fossils from the Cambrian Fortunian Stage of South China are a class of morphological taxa with uncertain affinities. Here, we redefine the genera Amoebinella and Huizenodus and consider Huizenodus oligaspinosus to be a senior synonym of Amoebinella echinata. In addition, we report two compound fossils of H. oligaspinosus for the first time from the Fortunian Zhangjiagou Lagerstätte in southern Shaanxi. Their multi-branched, dendritic, rigid structure is similar to the skeletons in several groups of colonial anthozoans, and thus, H. oligaspinosus may represent the skeletal structure of an ancestral anthozoan. H. oligaspinosus could have further constructed its skeleton by producing secondary individuals from the main branches or the sub-branches of the primary individuals to accommodate more polyps.

A new species of Decimoconularia (Cnidaria, Medusozoa) from the Lower Cambrian of South China

Hexangulaconulariids, a family of biradially symmetrical medusozoan cnidarians, have been widely reported from the Lower Cambrian of South China. The four currently recognized genera of hexangulaconulariids differ from each other mainly in the number of faces in the abapical region of the periderm. However, previously published illustrations of the monospecific type genus, Hexangulaconularia, clearly show two distinct morphotypes, one with six faces and the other with 10. Specimens with 10 faces are herein reassigned to the genus Decimoconularia. In addition, the new species D. anisfacialis is described from the Kuanchuanpu Formation (Cambrian Fortunian Stage) in the Kuanchuanpu and Shizhonggou sections in Ningqiang County, southern Shaanxi Province, China. Also described are additional specimens of H. formosa from the same formation in the Zhangjiagou section in Xixiang County, southern Shaanxi Province, and from Member 2 of the Yanjiahe Formation (Cambrian Fortunian Stage) in western Hubei Province. The discovery of D. anisfacialis extends the known stratigraphical range of Decimoconularia, now composed of two species, downward from Cambrian Stage 2 into the Fortunian Stage. Additionally, certain specimens previously assigned to H. formosa are reassigned to D. anisfacialis. The diagnoses of Hexangulaconularia, Decimoconularia, and Hexangulaconulariidae are emended accordingly. In accordance with the rule of time priority, the previously designated type genus and species, Hexaconularia He and Yang, 1986 and Hexaconularia sichuanensis He and Yang, 1986, are replaced herein by Hexangulaconularia He, in Xing et al., 1983.

Sclerite-bearing annelids from the lower Cambrian of South China

Cambrian annelids are strikingly diverse and reveal important details of annelid character acquisition. Their contribution, however, to a wider understanding of the evolution of the trochozoans (encompassing the annelids as well as such groups as the brachiopods and molluscs) remains limited. Thus the early annelids had been linked to a variety of cataphract Cambrian metazoans, notably Wiwaxia and the halkieriids, but recent work assigns such fossils to stem-group molluscs. Here we report two new annelids from the Lower Cambrian Chengjiang Lagerstätte, South China. Ipoliknus avitus n. gen., n. sp. is biramous with neurochaetae and notochaetae, but significantly also bears dorsal spinose sclerites and dorso-lateral dentate sclerites. Adelochaeta sinensis n. gen., n. sp. is unique amongst Cambrian polychaetes in possessing the rod-like supports of the parapodia known as aciculae. This supports phylogenetic placement of Adelochaeta as sister to some more derived aciculate Palaeozoic taxa, but in contrast Ipoliknus is recovered as the most basal of the stem-group annelids. Sclerites and chaetae of I. avitus are interpreted respectively as the remnants and derivatives of a once more extensive cataphract covering that was a characteristic of more primitive trochozoans. The two sets of chaetae (noto- and neurochaetae) and two sets of sclerites (spinose and dentate) suggest that in a pre-annelid an earlier and more complete scleritome may have consisted of four zones of sclerites. Other cataphract taxa from the Lower Palaeozoic show a variety of scleritome configurations but establishing direct links with such basal annelids as Ipoliknus at present must remain conjectural.

Development characteristics and dominant factors of fractures and their significance for shale reservoirs: A case study from Є1b2 in the Cen'gong block, southern China

The Bianmachong Formation above the Niutitang Formation in the Lower Cambrian of South China, which was mainly deposited in a marine and transitional environment, has highly brittle characteristics and is an important shale layer for shale gas exploration, but the current level of exploration is low. This paper discusses in depth the development characteristics and dominant factors of fractures and their significance for the shale reservoir in Є1b2 (middle member of the Bianmachong Formation of lower Cambrian) of the Cen'gong block in Guizhou Province based on the observations of outcrops, cores, polished thin sections and scanning electron microscope chips, as well as statistics on the fracture characteristic parameters and a test data analysis of corresponding samples. The results show that overlaps of organic-rich shale and tight sandstone vertically have created favorable generation conditions for shale gas and tight sandstone gas in Є1b2 shale. Є1b2 shale has similar sedimentary environment, mineral composition and organic type as American marine shale but exhibits differences in terms of the abundance of organic matter and degree of thermal evolution. The TOC content of Є1b2 shale is mainly 1–2% and over-maturation. Multiple types and periods of fractures are abundant in Є1b2 shale. They are mainly structural fractures, such as high dip-angle shear, bedding, tension-shear, interlayer and slip fractures. The micro fractures are mainly interlayer fractures, grain boundary fractures and organic matter contraction fractures. Structure is one of dominant factors for the fractures development, but others also have a strong correlativity, such as the lithology, abundance of organic matter, formation thickness, mechanical properties and mineral content. Under the same structural background, the content of brittle minerals such as feldspar, pyrite and quartz is higher. The brittleness is higher in shale, and more fractures are generated, which contributes to reservoir heterogeneity. The TOC content of Є1b2 shale has positive correlations with the content of quartz and the total gas content, which is also positively correlated with fracture development in the cores, and the source of organic matter is siliceous organisms. For over-maturation and organic-rich shale, a high TOC content and a high silica content are beneficial for micro pores and fractures to be preserved. In addition, the fracture development is positively correlated with the total and free gas contents in Є1b2 shale. Micro pores and fractures exist in internal minerals, such as calcite, quartz, and pyrite, as well as in their intervals with fracture surfaces, which reduce the capacity of fractures to resist tension and shear. The fractures are prone to rupture again. In addition, filled fractures make a greater contribution to the reservoir space of Є1b2 shale through dissolution.

A highly redox-heterogeneous ocean in South China during the early Cambrian (∼529–514 Ma): Implications for biota-environment co-evolution

Abstract The “Cambrian Explosion” is known for rapid increases in the morphological disparity and taxonomic diversity of metazoans. It has been widely proposed that this biological event was a consequence of oxygenation of the global ocean, but this hypothesis is still under debate. Here, we present high-resolution Fe–S–C–Al-trace element geochemical records from the Jinsha (outer shelf) and Weng'an (outer shelf) sections of the early Cambrian Yangtze Platform, integrating these results with previously published data from six correlative sections representing a range of water depths (Xiaotan, Shatan, Dingtai, Yangjiaping, Songtao, and Longbizui). The integrated iron chemistry and redox-sensitive trace element data suggest that euxinic mid-depth waters dynamically coexisted with oxic surface waters and ferruginous deep waters during the earliest Cambrian, but that stepwise expansion of oxic waters commenced during Cambrian Stage 3 ( ∼ 521 – 514 Ma ). Combined with data from lower Cambrian sections elsewhere, including Oman, Iran and Canada, we infer that the global ocean exhibited a high degree of redox heterogeneity during the early Cambrian, consistent with low atmospheric oxygen levels ( ∼ 10 – 40 % of present atmospheric level, or PAL). A large spatial gradient in pyrite sulfur isotopic compositions (δ34Spy), which vary from a mean of − 12.0 ‰ in nearshore areas to + 22.5 ‰ in distal deepwater sections in lower Cambrian marine units of South China imply low concentrations and spatial heterogeneity of seawater sulfate, which is consistent with a limited oceanic sulfate reservoir globally. By comparing our reconstructed redox chemistry with fossil records from the lower Cambrian of South China, we infer that a stepwise oxygenation of shelf and slope environments occurred concurrently with a gradual increase in ecosystem complexity. However, deep waters remained anoxic and ferruginous even as macrozooplankton and suspension-feeding mesozooplankton appeared during Cambrian Stage 3. These findings suggest that the “Cambrian Explosion” in South China may have been primarily a consequence of locally improved oxygenation of the ocean-surface layer rather than of the full global ocean. Our observations are inconsistent with predicted changes in ocean chemistry driven by early Cambrian animals, suggesting that the influence of early Cambrian animals on contemporaneous ocean chemistry, as proposed in previous studies, may be overly exaggerated.

New occurrences of Sphenothallus in the lower Cambrian of South China: Implications for its affinities and taphonomic demineralization of shelly fossils

Sphenothallus , a tubular fossil that occurs in Paleozoic strata around the world, may be related to cnidarians or ‘worms,’ but its affinities remain controversial due to preservational variations among localities. Here, to test hypotheses regarding Sphenothallus taphonomy and affinities, we investigate the preservation of new fossils from the lower Cambrian Shuijingtuo Formation at Heziao and Jijiapo (Hubei Province) and the equivalent Niutitang Formation at Siduping (Hunan Province) in South China. Morphology and allometry suggest that the fossils represent a single species, and their biostratinomy and authigenic mineralization indicate that they underwent similar pre-burial and early diagenetic processes, particularly transport and focused degradation via microbial sulfate reduction. However, the compositions and microstructures of the tests vary among localities. The Heziao tests consist of lamellar phosphatic material covered interiorly and exteriorly by layers of carbonaceous material. In contrast, the Siduping tests consist of non-lamellar phosphatic material associated with carbonaceous material, and the Jijiapo tests consist entirely of carbonaceous material. Based on these observations and experimental taphonomic data—which show that hydrochloric acid treatment of Heziao samples produces fossils that compositionally and microstructurally resemble the Jijiapo specimens—we propose that the new tests constitute a taphonomic continuum between shelly and carbonaceous preservation. This taphonomic model suggests that the preservation of shells as carbonaceous fossils results from kerogenization of the organic matrixes and subsequent or concomitant demineralization of the biomineralized microstructures of the shells. Hence, variations in Sphenothallus test composition and microstructure among localities may reflect varying extents of test demineralization, and the carbonaceous layers in Heziao specimens may have formed via demineralization of the tests' exterior and interior phosphatic lamellae. Our reconstruction based on this model indicates that pristine Sphenothallus tests consist of exteriorly sculptured and interiorly unsculptured organophosphatic lamellae. Thus, Sphenothallus microstructurally resembles and may be related to conulariids, and potentially, cnidarians. • Sphenothallus fossils in Shuijingtuo and Niutitang formations of Hubei and Hunan. • We provide data on their taphonomy, allometry, compositions, and microstructures. • Data illuminate Sphenothallus affinities and taphonomic diversity of Cambrian shells. • Sphenothallus microstructurally resembles conulariids and may be a cnidarian. • Data support taphonomic model for preservation of shells as carbonaceous fossils.

The earliest species ofBurlingiaWalcott, 1908 (Trilobita) from South China: biostratigraphical and palaeogeographical significance

AbstractBurlingia balangensissp. nov. from the lower Cambrian of South China represents the earliest species of this genus, and suggests that the genus may have originated in South China. A revision of the genus shows thatB. primitivaandB. obscuracan be used in order to indentify the base of the Cambrian Stage 5 when other trilobites are absent because their last appearance datum (LAD) coincides with the first appearance datum (FAD) ofOryctocephalus indicus. Available palaeogeographic and palaeoclimatic models suggest five major palaeocurrents during Cambrian times which could control the migration patterns of theBurlingiaclade from South China to Baltica.

Quadrapyrgites from the lower Cambrian of South China: growth pattern, post-embryonic development, and affinity

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.

Experimental mineralization of crustacean eggs: new implications for the fossilization of Precambrian–Cambrian embryos

Abstract. Phosphatized globular microfossils from the Ediacaran and lower Cambrian of South China represent an impressive record of early animal evolution and development. However, their phylogenetic affinity is strongly debated. Understanding key processes and conditions that cause exceptional egg and embryo preservation and fossilization are crucial for a reliable interpretation of their phylogenetic position. We conducted phosphatization experiments on eggs of the marbled crayfish Procambarus that indicate a close link between early mineralization and rapid anaerobic decay of the endochorional envelope. Our experiments replicated the different preservational stages of degradation observed in the fossil record. Stabilization of the spherical morphology was achieved by pre-heating of the eggs. Complete surface mineralization occurred under reduced conditions within one to two weeks, with fine-grained brushite (CaHPO4 · 2H2O) and calcite. The mechanisms of decay, preservation of surface structures, and mineral replacement in the experiment were likely similar during fossilization of Cambrian embryos.

Ontogeny of the trilobite Estaingia sinensis (Chang) from the Lower Cambrian of South China

Ontogeny of the trilobite Estaingia sinensis (Chang) from the Lower Cambrian of South China

Ontogeny of the eodiscoid trilobite Tsunyidiscus acutus from the Lower Cambrian of South China

Abstract: The morphology and ontogeny of the eodiscid trilobite Tsunyidiscus acutus Sun is described on the basis of numerous calcified specimens collected from the Lower Cambrian Shuijingtuo Formation in Yichang and Changyang, Hubei Province, South China. An ontogenetic series is established based on the articulated material including the previously unknown protaspides and meraspides (degrees 0 and 1). The material, revealing some prominent morphological changes such as the number of pygidial axial rings, genal spines retained throughout ontogeny and pygidial pleurae from furrowed to unfurrowed, enables a discussion on the trunk segmentation schedule, indicating that somitogenesis and tagmosis occurred independently during the ontogenetic development of T. acutus.

Early Cambrian metazoan fossil record of South China: Generic diversity and radiation patterns

South China with its rich fossil record is an important region for studying Early Cambrian metazoan diversity patterns. Compilation of a database of metazoan genera from the traditional Lower Cambrian (Cambrian Series 1–2) of South China allows a quantitative analysis of biodiversity changes. The dataset shows that about 876 genus names have been reported from the Lower Cambrian of South China. Of these only about 582 genera are now considered valid after taxonomic scrutiny. Plotting generic diversity shows a two-part, first-order trend: 1, diversity increase through the most of the Meishucunian and Qiongzhusian stages (South China usage), but punctuated by a modest decline during the upper Meishucunian; followed by 2, diversity decline in the Canglangpuan and Longwangmiaoan stages (South China usage). About 155 genera of small shelly fossils (SSFs) occur in Meishucunian rocks. The Meishucunian fauna is dominated by helcionellids, orthothecimorph hyoliths and other enigmatic fossils and is very consistent with the pretrilobitic ‘Tommotian Fauna’. Diversity increases in the Qiongzhusian stage, reaching 304 genera, the peak value known for the Cambrian. The Qiongzhusian fauna is characterized mainly by the occurrence of dominant pan-arthropods and crown-group brachiopods, representing an initial phase of the Cambrian Evolutionary Fauna. A substantial decline in generic diversity through the Canglangpuan (ca 153 genera) and Longwangmiaoan (ca 69 genera) stages is due partly to a eustatic regression, and it approximates the global pattern, reflecting an extinction event at the end of the Lower Cambrian. The observed regional biodiversity through this interval has both evolutionary and taphonomic influences: the decline in SSF diversity beginning in the upper Meishucunian was not only related to the decimation of SSFs, but also to a reduction in phosphogenesis. An apparent peak in diversity during the Qiongzhusian was somewhat exaggerated by the exceptional Chengjiang Biota.

Pediculate Brachiopod Diandongia pista from the Lower Cambrian of South China

Abstract The Chengjiang Lagerstätte has been celebrated for prolific soft‐bodied fossils. Based on specimens recently excavated in the Chengjiang Lagerstätte by the Early Life Institute, Northwest University, Diandongia pista Rong, 1974, is directly revealed to be a pediculate brachiopod, assigned to the Family Botsfordiidae, as is further confirmed by the exceptionally preserved vascular system including dorsal and ventral mantle canals. These specimens described herein exhibit some peculiarities, notably the extremely thin and long pedicles, which suggest that Diandongia is epifaunal rather than burrowing brachiopod. A study of this group of animals indicates that they may be vital to understand the relationship between the lingulids and the remaining brachiopods, and the character evolution of the early Cambrian brachiopods.

Reconsideration of the supposed naraoiid larva from the Early Cambrian Chengjiang Lagerstätte, South China

AbstractThe Chengjiang Lagerstätte in the Lower Cambrian of South China yields a small, larva‐like arthropod, which was considered to be a protaspis of naraoiids by many authors. The discovery of a large number of well‐preserved specimens from many new localities has allowed the original study to be revised. The relatively large size, stable morphology and unusual structure of the appendages indicate that these specimens represent adults of a new arthropod, Primicaris larvaformis. The larva‐like outline is considered to have arisen by the heterochronic process of progenesis. In addition, this animal displays primitive aspects of bodyplan and limb morphology that suggest a basal position within arachnomorphs, or perhaps even arthropods, and the similarities to the Vendian arthropod‐like animal Parvancorina probably provide an evolutionary link between Vendian forms and Cambrian arthropods.

A pipiscid-like fossil from the Lower Cambrian of south China

Exceptional fossil preservation is critical to our understanding of early metazoan evolution. A key source of information is the Burgess Shale-type faunas1,2,3,4,5. Fossils from these deposits provide important insights into metazoan phylogeny, notably that of stem-group protostomes2,3,6, and related topics such as trophic specialization7. Metazoan relationships are also being significantly reappraised in terms of molecular-based phylogenies8,9, but integration of these data with palaeontological systematics is not straightforward10,11. Moreover, molecular phylogenies are silent concerning the anatomies of stem-groups and the functional transitions that underpin the origin of different body plans2,6. Some hitherto enigmatic fossils possess unique character–state combinations that, although they can be shoe-horned into extinct phyla12, may be more profitably interpreted as defining major stem-groups2,3. Here we describe a possible pipiscid, a metazoan previously known only from the Upper Carboniferous13,14, from the Lower Cambrian of south China. Pipiscids are currently interpreted as being agnathan chordates13,14,15, but this discovery from the Chengjiang fossil-Lagerstatte indicates that the assignment of pipiscids to the Agnatha deserves to be reconsidered.

Carinachitiids, hexangulaconulariids, andPunctatus: problematic metazoans from the Early Cambrian of South China

Carinachitiids, hexangulaconulariids, andPunctatusare distinctive and abundant components of early skeletal faunas from the Lower Cambrian of South China. Carinachitiids are redescribed on the basis ofCarinachites spinatusfromKuanchuanpu, Shaanxi, andC. tetrasulcatusandC. curvatornatusfrom Emei, Sichuan. Tubes of all species are characterized by pronounced quadriradial symmetry, but whereasC. spinatusandC. curvatornatusgenerally have prominent ornamentation consisting of transverse ribbing, that ofC. tetrasulcatusis much more subdued. Neither apex nor well-defined aperture is evident in any of the carinachitiids. Hexangulaconulariids are redescribed on the basis ofArthrochites emeishanensisfrom Emei andHexaconularia sichuanensisfrom Kuanchuanpu. In common with the carinachitiids, the former species shows wide morphological variability. The tubes expand rapidly from a blunt apex, bear prominent ribbing, and possess variably developed lateral grooves that impose a quasi-hexaradial symmetry.Hexaconularia sichuanensisis described from fragmentary material with prominent ribbing and well-defined lateral grooves.Punctatus emeiensishas a tapering ribbed cone, with a stellate ornamentation adapically that is replaced by longitudinal ribbing towards the aperture. Carinachitiids and hexangulaconulariids are widely regarded as related to conularids, and this proposal receives additional support here. An external abortive ?borehole in a specimen ofCarinachitesalso supports the tubicolous interpretation of these fossils. An alternative suggestion that carinachitiids and hexangulaconulariids represent the internal rachis of a sea-pen is also considered. The affinities ofPunctatusare more speculative, but the genus may be related to the other two groups. The ecology ofPunctatus, however, remains problematic.

Tommotiids from the Lower Cambrian of South China

Tommotiids are a geologically short-lived group of early skeletal fossils, most abundant in the Lower Cambrian. Redescriptions of a lapworthellid (Lapworthella rete Yue, 1987) and a tannuolinid (Tannuolina zhangwentangi Qian and Bengtson, 1989) from the Jiulaodong Formation, Maidiping, Sichuan, augment previous accounts. Lapworthella rete approaches the L. dentata–L. schodackensis complex, but has a prominent external pattern of polygons that probably represent imprints of epithelial cells. Description of Tannuolina zhangwentangi emphasises ultrastructural features, including the mode of growth, development of canals, and possible epithelial imprints on the interior surfaces. Data on size variation of epithelial imprints in tommotiids are reviewed to try to infer possible variations in genome content of the cells. In addition, poorly preserved lapworthellids (Lapworthella sp.) are described from the Qiongzhusi Formation, Meishucun, Yunnan.