The latest discovery of microfossils from the lower Cambrian (Fortunian Stage) Zhangjiagou Lagerstätte in South China are presented. This lagerstätte is rich in exceptionally preserved microfossils, including embryos of Olivooides multisulcatus, Olivooides mirabilis, and Pseudooides prima; hatched stages of O. multisulcatus, O. mirabilis, Hexaconularia sichuanensis, and Quadrapyrgites quadratacris; and cycloneuralians represented by Eopriapulites sphinx. The largest known fragment of O. mirabilis implies that its adult length can be more than 9.0 mm with at least 50 annuli, and the longest known specimen of Q. quadratacris has at least 18 annuli. These unusually large specimens refute the non-feeding larvae hypothesis for Olivooides and Quadrapyrgites.Based on the current material, it is inferred that (1) early cnidarians have a high diversity in the Fortunian Stage; (2) P. prima might represent the embryonic stages of H. sichuanensis; (3) adults of Olivooides and Quadrapyrgites may have reached centimeter-scale dimensions with more than 50 annuli; (4) Olivooides and Quadrapyrgites may be better interpreted as coronate scyphozoans; (5) cycloneuralians also had a high diversity in the Zhangjiagou Lagerstätte; and (6) cycloneuralians might have originally been part of the early Cambrian meiofauna rather than belonging to the macrobenthos. Such ancestral cycloneuralians might have been Eopriapulites-like, possessing pentaradially symmetric, backward pointing, and internally hollow introvert scalids used as locomotory devices.
Maikhanellids are a distinct group of Cambrian Fortunian small shelly fossils by the cap‐shaped profiles and scaly shell ornamentation. According to the individual shell shape and ornamentation feature types of SO maikhanellids fossils which were collected from Xixiang botia, we confirmed the family Maikhanellidae content of six genera, which are Maikhanella, Ramenta, Purella, Ramentoides, Yunnannopleura and Mediata. Unlike the halkieriid animals whose shells and spicules are articulated on different body parts, maikhanellids were presumably yielded by siphogonuchitid spicules penetrating the intermediate matrix (the “spicule shell” hypothesis), and this is the reason that some researchers treated maikhanellids and co‐occurring siphogonuchitids as synonyms. The affinities of Maikhanellids and siphogonuchitids remain debatable. Here, we report three dimensionally phosphatized maikhanellid shells and siphogonuchitid spicule bundles from the Cambrian Fortunian small shell faunas of South China. They differ from all the previously reported maikhanellids and siphogonuchitids, and may represent new types. The intact and smooth surface underneath the partially preserved scales of the shells challenges the “spicule‐shell” hypothesis. The present siphogonuchitid spicules differ from the maikhanellid scales in size, morphology, and arrangement pattern, thus the spicules might not be derived from the shells. Whether the shells and spicule bundles were articulated on different body parts of the same animals remains unknown.
Fine pyroclastic materials form bentonites through subsidence, hydrolysis, and argillation in alkaline marine environments, which can further transform to K‐bentonite. Bentonites or K‐bentonites are quite popular with geologists because their formation often reflects geologic events. However, studies mainly focus on K‐bentonite, and research on ordinary bentonites in China is almost nonexistent. Recent research shows that the Wangpo shale consists of ordinary bentonites. Through thorough field investigations, indoor experimentation and analysis, and comparison of petrologic and geochemical characteristics of the Wangpo shale with K‐bentonites, this paper explores the nature and genesis of source rocks and provides a basis for the study of ordinary bentonites. The petrological study shows that the Wangpo shale is a montmorillonite vitric tuff, which is mainly composed of montmorillonite and small amounts of quartz, opal, and heulandite. These indicate that it is a typical bentonite. In addition, the rock contains an abundance of fossils reflecting a coastal–shallow sea depositional environment. We chose the elements with stable chemical characteristics for obtaining source rock characteristics, and the results showed that the Wangpo shale has a genetic relationship with neutral alkaline magma. As a boundary between the Upper Permian and the Middle Permian, the Wangpo shale has an internal connection with eruption of the Emeishan basalt in Southwest China. In combination with previous work, it can be inferred that studying the volcanic activity represented by the Wangpo shale plays an important role in studying Emeishan large igneous provinces and the end‐Guadalupian mass extinction.
The Palaeoproterozoic Dakendaba Group and the Cambrian–Ordovician Tanjianshan Group occur on the northern margin of the Qaidam Basin. Their fracture structure is well developed, and intermediate‐acid rocks are widely distributed, providing an ideal setting for pegmatite mineralization. Field investigation has identified 200 pegmatite veins, of which more than 40 have various degrees of Nb and Ta mineralization. These pegmatites can be classified into four types, based on distribution, mineral assemblages, and a genesis sequence of ① microcline, ② microcline–albite, ③ albite, and ④ muscovite–albite. Pegmatite types ③ and ④ are typically mineralized, with Nb and Ta occurring as niobite and columbite–tantalite. These pegmatites have high silica and alkali content and are Al‐rich. The aluminium saturation index (A/CNK) is 1.36–1.60, and (A/NK) is 1.45–1.93. Their ∑REE values are 2.61–23.95 × 10−6. Other REE ratios have values of (La/Yb)N = 2.02–8.04, (La/Sm)N = 0.47–3.20, and (Gd/Yb)N = 1.34–4.93. Their REE distribution pattern is right‐inclined, with slight LREE enrichment. Negative Eu anomalies are apparent in types ① and ④ but not in types ② and ③. High field strength elements, such as Nb, Ta, Zr, and Hf, have low contents, with Y depletion. Concentrations of REE are generally low, although Sr and Ba are slightly enriched. Thus, pegmatites of this area have low Ca, K, and Al but high Na and Si and are rich in rare metal elements and poor in REEs. This suggests liquid immiscibility was involved in their metallogenic evolution process.
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