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Abstract A recent study of conodonts from the Wuxiahe Formation (lower to middle part) in the Ziyang-Langao region suggested its age of middle Telychian (Llandovery) to lower Sheinwoodian (Wenlock), contradicted by subsequent graptolite studies indicating an age of late Telychian for the same interval. New samples from the Qiaoxi section for conodonts to re-access the age of the Wuxiahe Formation collected in this study show that the lower to middle part of the formation belongs to the Pterospathodus amorphognathoides amorphognathoides Biozone, suggesting the age of late Telychian; thus, the Llandovery–Wenlock boundary in the section is most probably higher than previously estimated, but its precise position is not determined since the identification of the Wenlock graptolite Cyrtograptus cf. lundgreni in the section is to be further confirmed. Based on the conodont faunas recognized in the Qiaoxi and Tianwancun sections, the base of the Wuxiahe Formation in the Ziyang-Langao region is diachronous, i.e., not higher than the upper Telychian Pterospathodus amorphognathoides amorphognathoides Biozone at Qiaoxi, but not lower than the lower Sheinwoodian Kockelella ranuliformis Biozone at the Tianwancun setion.

Abstract Age of the Baiyaya Formation in the Ziyang-Langao region of Shaanxi Province remains debatable. Ten samples were taken for conodont biostratigraphical studies from the Tianwancun section. The first discovery of Astropentagnathus in China indicates that the genus has a wider geographical distribution than previously known. Conodont fauna from the Baiyaya Formation suggests that the lower part of the unit corresponds to the Pterospathodus eopennatus Superbiozone, and its upper part to the lower Wenlock (probably mainly to the Kockelella ranuliformis Superbiozone). Diachroneity of the Baiyaya Formation in the region is confirmed by conodont studies from the Tianwancun and Qiaoxi sections. Further studies are required to find out age-variation of the formation more precisely.

Abstract The Hungshihyen Formation represents the Lower to Middle Ordovician near-shore siliciclastic deposits on the western margin of the Yangtze Platform, South China. However, its age is still debated, largely because of insufficient studies. Here we documented the Bursachitina maotaiensis–B. qianbeiensis chitinozoan assemblage from the lower part of the Hungshihyen Formation at Songliang, Qiaojia County, eastern Yunnan Province. This assemblage is remarkably similar to an assemblage that roughly correlates to the middle part of the Corymobograptus deflexus graptolite Biozone in northern Guizhou Province, indicating that the Hungshihyen Formation at Songliang is probably of late Floian age and may extend into the early Dapingian. Additionally, a revision on the chitinozoans previously documented from the strata assigned to the same formation in the Wuding area was made according to the latest classification. The revision allows the recognition of the Euconochitina symmetrica–Eremochitina brevis assemblage, and therefore suggests a late Tremadocian age for this interval based on regional and global chitinozoan biostratigraphic correlations. Considering also its lithologic succession, we argue that the chitinozoan-bearing strata in the Wuding area previously assigned to the Hungshihyen Formation correspond most likely to the uppermost part of the underlying Tangchi Formation or the lowermost part of the Hungshihyen Formation. The base of the Hungshihyen Formation appears therefore to be diachronous in eastern Yunnan Province.

Abstract Trace fossils are common in the Ordovician and Silurian shallow marine carbonate succession of Estonia, with 45 ichnofossil genera and five bioclaustration structures identified, representing 31 categories of architectural designs and nine categories of ethological classification. Diverse soft sediment traces, bioerosional traces and bioclaustrations occur both in the Ordovician and Silurian. Diversity of trace fossils is similarly high in the Late Ordovician and Silurian, but markedly lower in the Middle Ordovician. This could be explained by the fact that during the Late Ordovician, Baltica drifted to the subtropical climatic zone where ichnofauna is usually more diverse than in temperate climatic settings. In addition, the Great Ordovician Biodiversification reached its peak in the Late Ordovician for many groups of organisms, which further contributed to the increase in ichnodiversity. Distribution of trace fossils is also controlled by the type of sedimentation, so that the mixed carbonate-siliciclastic systems prevailing in the Late Ordovician and Silurian have higher ichnodiversity than the pure carbonate settings of Middle Ordovician age. Feeding and locomotion traces are relatively rare in the Ordovician and Silurian of Estonia with the exception of the feeding structure Arachnostega, which is formed inside of protective shells and therefore has abundant occurrences. Bioerosional trace fossils may be extremely common in places, with a large number of different genera in the Upper Ordovician, supporting the idea of the Ordovician Bioerosion Revolution.

Abstract We review the enigmatic Leveilleites hartnageli , a noncalcified algal fossil tentatively assigned to red algae, which was first described from the Ordovician of southern Ontario, Canada, and more recently discovered as a significant part of the exceptionally preserved algal flora of the Kalana Lagerstatte from the Silurian (Aeronian, Llandovery) of Estonia. The morphology of L . hartnageli is described, including morphological changes during different growth phases of the thallus. The new collection from two quarries and several drill cores complements the material from North America and reveals the geographical extent of the species, showing that the species inhabited large areas in both sides of the Iapetus ocean — the epicontinental seas of Laurentia and Baltica. Because the original specimen on which the species was erected is lost and the paratypes are in poor condition, a neotype is designated here.

Abstract Stable carbon isotope chemostratigraphy has been applied for correlation of Ordovician marine sedimentary successions of many continents, but not yet for those located on the Siberian Craton. In this study we present the first δ13C data from the Middle and Upper Ordovician successions of the Tungus Basin, the extensive Palaeozoic intracratonic basin on the Palaeocontinent Siberia. Carbon isotope curves from two separate areas of the craton, from the Kulyumbe River and Podkamennaya Tunguska River regions, demonstrate a great similarity. Three global carbon isotope events can be recognized in the Tungus Basin: the Mid-Darriwilian Excursion (MDICE), the Upper Kukruse Low, and the lower rising interval of the Guttenberg Excursion (GICE). These data partly support the previous inter-continental stratigraphic correlations but also suggest that the base of the Upper Ordovician in the Siberian succession lies at a lower level than previously thought. Although the conodont fauna in Siberia differs almost completely from that in Baltoscandia, the distribution of selected Upper Ordovician conodont taxa do not contradict the isotope chemostratographic conclusions.

Abstract Soft-sediment deformation structures (SSDS) are documented in several horizons within silt- and sandstones of the Cambrian Series 2 (Dominopolian Stage) Tiskre Formation, and some in the underlying argillaceous deposits of the Lukati Formation in NW Estonia, northern part of the Baltoscandian Palaeobasin. The aim of this study was to map, describe, and analyze these deformation features, and discuss their deformation mechanism and possible triggers. Load structures (simple load casts, pillows, flame structures, and convoluted lamination) with varying shapes and sizes occur in the Tiskre Formation in sedimentary interfaces within medium-bedded peritidal rhythmites (siltstone-argillaceous material) as well as within up to 3 m thick slightly seaward inclined stacked sandstone sequences. Homogenized beds, dish-and-pillar structures, and severely deformed bedding are also found within these stacked silt- and sandstone units and within a large tidal runoff channel infill. Autoclastic breccias and water-escape channels are rare and occur only in small-scale — always related to thin, horizontal tidal laminae. Profound sedimentary dykes, sand volcanoes, and thrust faults, which are often related to earthquake-triggered soft sediment deformation, were not observed within the studied intervals. Deformation horizon or horizons with large flat-topped pillows often with elongated morphologies occur at or near the boundary between the Tiskre and Lukati formations. Deformation mechanisms identified in this study for the various deformation types are gravitationally unstable reversed density gradient (especially in case of load features that are related to profound sedimentary interfaces) and lateral shear stress due to sediment current drag (in case of deformation structures that are not related to loading at any apparent sedimentary interface). Synsedimentary liquefaction was identified as the primary driving force in most of the observed deformation horizons. Clay thixotropy may have contributed to the formation of large sandstone pillows within the Tiskre–Lukati boundary interval at some localities. It is discussed here that the formation of the observed SSDS is genetically related to the restless dynamics of the storm-influenced open marine tidal depositional environment. The most obvious causes of deformation were storm-wave loading, rapid-deposition and shear and slumping caused by tidal surges.

A Silurian (Llandovery, Aeronian) Lagerstatte in Kalana, Estonia, has revealed exceptionally preserved noncalcified flora of algal fossils. A new dasycladacean algal species Kalania pusilla has been described. The paper describes the fossil specimens, which demonstrate well preserved fine internal anatomy of these siphonous unicellular algae, specifically anatomy of fertile specimens. K. pusilla is characterized by cylindrical uniaxial thallus, two orders of lateral segments — perpendicularly arranged whorls of short bulbous primary laterals, which bear clusters of gametophores in their mature stage and fine hairy secondary laterals.

The province of Jamtland, central Sweden, records a well-preserved but very thin suite of the Lower-Middle Ordovician cool-water carbonates. In this study we present the first carbon isotope profile for these strata on the basis of whole-rock samples from the Brunflo 2 core. The studied succession is 41.55 m thick and includes, in ascending order, the Bjorkasholmen Formation, Latorp Limestone, Toyen Shale, and the Lanna, Holen, and Segerstad limestones. We identify two distinct positive delta C-13 excursions that can be used for intra-as well as inter-continental correlations. A positive excursion in the Toyen Shale probably correlates to the mid-late Floian and the Oepikodus evae Zone in Baltica and Precordillera, and the Reutterodus andinus Zone in North America. A continuous increase in delta C-13 values through the upper Holen Limestone and the preserved part of the overlying Segerstad Limestone is interpreted as the rising limb of the Middle Darriwilian Isotope Carbon Excursion (MDICE), an important tie-point for the global correlation of the Jamtland strata. Negative delta C-13 values associated with the Latorp Limestone may correlate with similar low values in the late Tremadocian and early Floian of the Argentine Precordillera and the Shingle Pass and Ibex sections in North America. (C) 2015 Elsevier B.V. and Nanjing Institute of Geology and Palaeontology, CAS. All rights reserved. (Less)