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The complex of felsic to intermediate volcanic rocks intruded by plagiogranitic bodies is first revealed in the western part of the Tekturmas ophiolite zone of Central Kazakhstan. The U–Pb (SIMS) geochronological study of one of the plagiogranitic bodies dated back to the Early Cambrian (537 ± 5 Ma) is conducted for the first time. The peculiarities of the volcanic rocks and the composition of plagiogranites indicate their formation in a suprasubduction setting within the Early Cambrian primitive volcanic island arc. The formation of this arc was not related to the evolution of the Ordovician oceanic structures, the complexes of which participate in the structure of the Tekturmas zone. [ABSTRACT FROM AUTHOR]

A fragment of the ophiolite sequence composed of dunites, wherlites, pyroxenites, gabbro, gabbro-dolerites, and plagiogranites was described within the structure of the North Balkhash Zone of Paleozoides of Central Kazakhstan. This fragment represents a large block enclosed in the serpentinite mélange (Tesiktas massif). The Early Cambrian date (206Pb/238U; 531 ± 1 Ma) was obtained for the first time for plagiogranites of this massif. The age estimate is thought to indicate the termination time of the formation of the plutonic part of the ophiolite sequence. [ABSTRACT FROM AUTHOR]

The Ediacaran–Cambrian transition records distinct evolutionary changes of metazoans. The Ediacaran fossils ( i.e. , Ediacara-type biota and tubular fossils) are contrasting with the diverse small skeletal fossils (SSFs) from the early Cambrian. The apparent dissimilarities hindered studies deciphering their evolutionary relationships. This also led to a popular assumption that there exists a mass extinction of the Ediacara biota and cloudinids at the Precambrian–Cambrian (Pc–C) boundary. Here we report for the first time a transitional fauna which consists of typical elements of Ediacaran, i.e. cloudinids and related tubicolous organisms, together with Cambrian SSFs including protoconodonts, anabaritids and siphogonuchitids from South China and Maly Karatau (Kazakhstan). The sediments yielding the transitional fauna are characterized by siliceous rocks in both regions and were previously considered to be unfossiliferous. Their chronostratigraphic assignment in South China has been debated for years. Based on the new fossil assemblage, the siliceous strata of the Daibu Member (Northeast Yunnan, South China) and the basal Kuanchuanpu Formation (South Shaanxi, South China) can be assigned to the earliest Cambrian SSF biozone ( Anabarites trisulcatus – Protohertzina anabarica Assemblage Zone) and thus can be considered of early Cambrian in age. A new subzone of the earliest SSF zone in eastern Yunnan (South China) is proposed herein defined as Ganloudina symmetrica – Rugatotheca typica Interval Subzone. The new fauna demonstrates that the cloudinids, originally confined to the late Ediacaran, persisted into the Cambrian Fortunian, and no major extinction event occurred at the Pc–C transition. [ABSTRACT FROM AUTHOR]

A low diversity fossil assemblage dominated by Mongolitubulus spines, from the Early Cambrian Geres Member of the Shabakhty Formation at Koksu, Malyi Karatau, Kazakhstan, enables identification of its sclerite variability within the scleritome. No other sclerotised structures could be matched with the spines, indicating that these were the only sclerotised part of the body and were periodically shed. The prominent spines of Mongolitubulus have a scale–like external ornamentation and fibrous internal structure. Possibly they armed the body of a lobopodian similar to Xenusion. The Mongolitubulus spines belong to a series of Cambrian phosphatic fossils, the other end members of which are sclerites of Microdictyon, the second most abundant component of the Koksu assemblage. The latter superficially resemble schizochroal trilobite eyes, but in life covered the dorso–lateral sides of the body segments, as is evident from complete specimens from the Chinese Chengjiang locality. A pair of sclerites of Microdictyon, representing uncompleted exuviation, from Koksu show that each hole originally contained a non–phosphatised lenticular body. This makes a compound eye nature of the Microdictyon sclerites likely, and even their homology with arthropod eyes cannot be excluded. [ABSTRACT FROM AUTHOR]