Search

• Palynological investigation of late Paleoproterozoic Chuanlinggou Formation from North China is performed. • The iconic spinose eukaryote Tappania plana is first reported here in Yanliao Basin. • Diverse prokaryotic filaments dominated the Tappania -containing microfossil assemblage. The first radiation of eukaryotic life in Earth history began at least by the late Paleoproterozoic as evidenced by complex organic-walled microfossils from North China, India and Australia. However, among these oldest eukaryotic fossils, the spinose Tappania plana Yin, 1997 , which has been reported from the late Paleoproterozoic to early Mesoproterozoic sediments worldwide, is strangely absent in the well-known microfossil assemblages from the coeval strata in the Yanliao Basin, North China. Here we report the new finding of T. plana and associated microfossils from ∼ 1.64 Ga Chuanlinggou Formation in the eastern Yanliao Basin. T. plana occurs in the assemblage from the upper Chuanlinggou Formation and exhibits typical irregularly distributed tubular processes and neck-like extensions. The assemblage is dominated by a wide variety of filamentous microfossils likely representing cyanobacterial or other bacterial sheaths and trichomes, and includes 21 species (belonging to 10 genera) and 3 unnamed forms. In contrast, the assemblage from the lower Chuanlinggou Formation is composed of only simple spheroidal (Leiosphaeridia) and fusiform (Schizofusa) morphotypes, distinct from those of the upper assemblage. This taxonomic discrepancy likely resulted from different paleoenvironments. Overall, the occurrence of T. plana in the Yanliao Basin expands its paleographic distribution and further reinforces its stratigraphic potential as an index fossil for the late Paleoproterozoic and early Mesoproterozoic strata. Furthermore, the microfossil assemblages reported here document a microbiota overwhelmingly dominated by prokaryotic organisms, which is consistent with the hypothesis that eukaryotes likely constituted as marginal groups in ancient ecosystems during mid-Proterozoic. [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]

Abstract: The DOUNCE (Doushantuo negative carbon isotope excursion), characterized by a large shift in δ13Ccarb from +5‰ down to −12‰ in the upper part of the Ediacaran Doushantuo Formation, was previously known only from a few sections mainly in the Yangtze Gorges area, western Hubei, South China. As a consequence, it remains uncertain whether the DOUNCE is of diagenetic origin, of local significance only, or corresponds to the worldwide mid-Ediacaran Shuram–Wonoka anomaly. Here we report the widespread occurrence of the DOUNCE in nine sections from various depositional settings ranging from coastal shallow basin, offshore intra-shelf basin to deepwater slope on the Yangtze platform. The results indicate that the DOUNCE starts in the upper part of Doushantuo Sequence 2 and ends at the base of the Dengying Formation. The variable appearance of the DOUNCE is facies dependent and any absence of the DOUNCE is shown to be the result of stratigraphic hiatus. The fall and recovery of δ13Ccarb values that bracket the DOUNCE occur over a relatively short stratigraphic interval and were possibly of shorter duration than the nadir of δ13Ccarb values which remain stable for a much longer interval from the transgressive systems tract to the condensed portion of the sedimentary sequence. Both the fall and the recovery of δ13Ccarb values are gradual and independent of lithology, suggesting a non-diagenetic origin for the DOUNCE which is further supported by the lack of any systematic diagenetic positive covariation between δ13Ccarb and δ18Ocarb data, and systematic differences in absolute isotope values between dolostone and limestone units. Field investigations and sedimentary analysis suggests the occurrence of a major sequence boundary at the basal part of the DOUNCE and reveals that previous reports of an interval of positive δ13C values within the DOUNCE resulted from either post-depositional sliding or faulting. Similarities between the evolutionary pattern and stratigraphic occurrence of the DOUNCE and global Shuram–Wonoka anomalies demonstrate that the DOUNCE represents a global change in seawater chemistry during the mid-Ediacaran which was closely related to the evolution of macroscopic metazoans. [Copyright &y& Elsevier]

Abstract: The Doushantuo Formation of South China, consisting of intercalated siliciclastic and carbonate rocks which exhibit considerable variation in thickness and sedimentary facies, is one of the key sedimentary units in the world for understanding Ediacaran geobiological processes. However, stratigraphic correlation and sedimentary facies evolution of the Doushantuo Formation remain controversial. Sedimentary facies analysis of the well-known sections of the Yangtze Gorges area and new sections in northern Yichang, western Hubei indicate that the Doushantuo succession in the Yangtze Gorges area was deposited in an offshore intra-shelf basin within the Yangtze platform. In contrast, the Doushantuo Formation in the northern Yichang area which is characterized by one or a few phosphate-rich horizons represents deposition on the subtidal or intertidal shelf, and so is similar to the succession in the Weng’an area (central Guizhou Province). The carbon isotope profiles of the different sections exhibit significant variation, which is interpreted to result from facies differences. Sequence and high-resolution carbon isotope stratigraphy have clarified problematic correlations and the temporal relationship between fossil assemblages of the Doushantuo Formation on the Yangtze platform. The results confirm that a prominent negative δ 13Ccarb excursion (BAINCE, nadir down to −5‰) in the middle portion of the second sequence of the Doushantuo Formation is a widely traceable event. BAINCE together with three other δ 13Ccarb excursions, namely CANCE at the base, WANCE near the first sequence boundary near the middle, and DOUNCE at the top of the Doushantuo Formation, constitute a complete carbon isotope profile for the Doushantuo Formation that reflects contemporaneous seawater and so serves as a reference chemostratigraphic profile for global stratigraphic correlation and for evaluating the chemical evolution of seawater during the Ediacaran Period. [Copyright &y& Elsevier]

The Neoproterozoic Quruqtagh Group in eastern Chinese Tianshan consists of, in ascending order, the Bayisi, Zhaobishan, Altungol, Tereeken, Zhamoketi, Yukkengol, Shuiquan, and Hankalchough Formations. Diamictite units occur in the Bayisi–Altungol, Tereeken, and Hankalchough Formations. Our field observations confirm the glacial origin of the Tereeken and Hankalchough diamictites, but the glacial origin of diamictites in the Bayisi and Altungol Formations remain ambiguous. While siliciclastic strata dominate the succession, carbonate units are recognized between the diamictites and immediately atop the Tereeken and Hankalchough diamictites. Carbonates in the Altungol Formation are characterized by highly positive δ13C values (up to +10.4‰ versus PDB), comparable to those of pre-Marinoan but post-Sturtian carbonates. High-resolution sampling of the pinkish cap dolostone (ca. 10 m-thick) overlying the Tereeken diamictite shows a consistent δ13C chemostratigraphic pattern (ca. −5‰ at the base and slightly decreasing upsection) similar to that of Marinoan cap carbonates. This cap dolostone is also characterized by macropeloids similar to those in the Marinoan-age Raventhroat cap carbonate, Mackenzie Mountains. Chemostratigraphic and sedimentary features are suggestive of a Marinoan age for the Tereeken glaciation. Thus, the younger Hankalchough diamictite may represent a post-Marinoan glaciation. This interpretation is consistent with the occurrence of vendotaenid fossils in the Shuiquan Formation. The alternative interpretation—the Tereeken and Hankalchough diamictites are, respectively, Sturtian and Marinoan in age—is not consistent with the above evidence or the chemostratigraphic features of the Shuiquan Formation and the Hankalchough cap carbonate. A post-Marinoan age for the Hankalchough and other glaciogenic deposits indicates that the disappearance of Doushantuo-type acritarchs and the subsequent radiation of macroscopic animals are closely linked, in geochronological terms, with a Neoproterozoic glaciation. [Copyright &y& Elsevier]