Cyclostratigraphy of the Middle to Upper Ordovician successions of the Armorican Massif (western France) using portable X-ray fluorescence

To expand traditional cyclostratigraphic numerical methods beyond their common technical limitations and apply them to truly deep-time archives we need to reflect on the development of new approaches to sedimentary archives that traditionally are not targeted for cyclostratigraphic analysis, but that frequently occur in the impoverished deep-time record. Siliciclastic storm-dominated shelf environments are a good example of such records. Our case study focusses on the Middle to Upper Ordovician siliciclastic successions of the Armorican Massif (western France), which are well-studied in terms of sedimentology and sequence stratigraphy. In addition, these sections are protected geological heritage due to the extraordinary quality of the outcrops. We therefore tested the performance of non-destructive high-resolution (cm-scale) portable X-ray fluorescence and natural gamma-ray analyses on outcrop to obtain major and trace element compositions. Despite the challenging outcrop conditions in the tidal beach zone, our geochemical analyses provide useful information regarding general lithology and several specific sedimentary features such as the detection of paleoplacers, or the discrimination between different types of diagenetic concretions such as nodules. Secondly, these new high-resolution data are used to experiment the application of commonly used numerical cyclostratigraphic techniques on this siliciclastic storm-dominated shelf environment, a non-traditional sedimentological setting for cyclostratigraphic analysis. In the lithological relatively homogenous parts of the section spectral power analyses and bandpass filtering hint towards a potential astronomical imprint of some sedimentary cycles, but this needs further confirmation in the absence of more robust independent age constraints.

Study on the Formation Mechanism of Shale Roof, Floor Sealing, and Shale Self-Sealing: A Case of Member I of the Upper Ordovician Wufeng Formation–Lower Silurian Longmaxi Formation in the Yangtze Region

Similar to North America, China has abundant shale resources. Significant progress has been made in the exploration and exploitation of shale gas in China since 2009. As the geological theory of unconventional oil and gas was proposed, scientists have started researching conditions for shale gas preservation. The shale roof and floor sealing and the shale self-sealing are the critical objects of such research, which, however, are still in the initial stage. This article studies the formation mechanism of shale roof and floor sealing and shale self-sealing by taking marine shales from Member I of the upper Ordovician Wufeng Formation–lower Longmaxi Formation in the upper Yangtze region as the research object. Analyses were performed on the TOC content, mineral composition, and porosity, as well as the FIB-SEM, FIB-HIM, and gas permeability experiments on the core samples collected from the marine shales mentioned above. The conclusions are as follows: for the sealings of shale roof and floor, the regional cap rocks, roof, and floor provide sealing for shales due to physical property differences. For the self-sealing of shales, the second and third sub-members of Member I of the Wufeng Formation–Longmaxi Formation mainly develop clay mineral pores which are dominated by macropores with poor connectivity, while the first sub-member of Member I of the Wufeng Formation–Longmaxi Formation mainly develops organic-matter pores, which are dominated by micropores and mesopores with good connectivity. Owing to the connectivity difference, the second and third sub-members provide sealing for the first sub-member, while the methane adsorption effect of shales can inhibit large-scale shale gas migration as it decreases the gas permeability; thus, the organic-rich shales from the first sub-member of Member I of the Wufeng Formation–Longmaxi Formation provides sealing for itself.

Diverse labechiid stromatoporoids from the Upper Ordovician Xiazhen Formation of South China and their paleobiogeographic implications

A diverse labechiid stromatoporoid assemblage that includes 16 species in 8 genera was found in the Upper Ordovician Xiazhen Formation (mid–late Katian) at Zhuzhai, Jiangxi Province of South China. The assemblage is characterized by a combination of (1) North China provincial species succeeding from their origination in the Darriwilian, including Pseudostylodictyon poshanense Ozaki, 1938, Labechia shanhsiensis Yabe and Sugiyama, 1930, Labechia variabilis Yabe and Sugiyama, 1930, and Labechiella regularis (Yabe and Sugiyama, 1930) and (2) South China endemic species, including three new species (Labechia zhuzhainus Jeon n. sp., Labechiella beluatus Jeon n. sp., Sinabeatricea luteolus Jeon n. gen. n. sp.), and four species in open nomenclature (Rosenella sp., Cystostroma sp., Pseudostylodictyon sp., and Labechia sp.). The finding of Labechiella gondwanense Jeon n. sp., Stylostroma bubsense Webby, 1991, Stylostroma ugbrookense Webby, 1991, and Thamnobeatricea gouldi Webby, 1991 in the formation indicates that Tasmania was closely related to South China and had a closer paleobiogeographical relation with peri-Gondwanan terranes than with Laurentia. In addition, the occurrences of Labechia altunensis Dong and Wang, 1984 and Stylostroma species support a close biogeographic link between Tarim and South China through the Middle to Late Ordovician interval, corresponding with the results from other fossil groups such as brachiopods, conodonts and chitinozoans. The diverse labechiids from the Xiazhen Formation improve our understanding of the diversity of Ordovician stromatoporoids in peri-Gondwanan terranes and the biogeographic affinities among Australia (especially Tasmania), Tarim, and South China. UUID: http://zoobank.org/4f46c91b-fa4c-4fe5-bea9-e409f1785677

A NEW DATA ON UPPER ORDOVICIAN CONODONTS FROM THE GURYANOVKA FORMATION, NORTHEAST OF GORNY ALTAI

The detailed study of the Guryanovka Formation key sections at the northeast of Gorny Altai (Biya and Bura sections) for the first time revealed the representative collection of conodonts. The conodont fauna is composed of 12 species belong to 9 genera: Belodina compressa (Branson and Mehl, 1933), Phragmodus undatus Branson and Mehl, 1933, Panderodus gracilis (Branson and Mehl, 1933), Panderodus acostatus (Branson, Branson, 1947), Tasmanognatus careyi Burret, 1979, Aphelognathus sp., Panderodus sp., Drepanoistodus sp., Drepantodus sp., Colaptoconus sp., Paltodus sp., Scandodus sp. For the first time, the precise position of the P. undatus conodont Zone was defined in Gorny Altai (continuous Biya Section, base of unit 3).

THE UPPER ORDOVICIAN BIOSTRATIGRAPHY OF THE CHUNYA RIVER BASIN (RIGHT TRIBUTARY OF THE PODKAMENNAYA TUNGUSKA RIVER, SIBERIAN PLATFORM)

The article deals with presented results of studying Upper Ordovician sections of the Mangazeya Formation in the Chuya River basin (right tributary of the Podkamennaya Tunguska River) of the Siberian Platform. The given layer by layer section description and new data on leading groups of fauna (ostracods, trilobites, brachiopods, conodonts) allowed for significantly expanding paleontological characteristics of enclosing sediments. The description of the Baksan Horizon deposits is given for the first time, it updates the earlier description of underlying formations in the stratotypic section of the Dolbor Horizon 2 km above the mouth of the Upper Chunku R. (left bank). As a result of biostratigraphic analysis for different groups of fauna, both from published sources and newly obtained data, it has become possible to clarify the stratigraphic position of the section located 0.4 km below the mouth of the Amutkan River. The correlation of studied sections with the Gaindinskaya-3 test well was carried out.

On the enigma of Palaenigma wrangeli (Schmidt), a conulariid with a partly non-mineralized skeleton

Palaenigma wrangeli (Schmidt) is a finger-sized fossil with a tetraradiate conical skeleton; it occurs as a rare component in fossiliferous Upper Ordovician strata of the eastern Baltic Basin and is known exclusively from north Estonia. The systematic affinities and palaeoecology of P. wrangeli remained questionable. Here, the available specimens of P. wrangeli have been reexamined using scanning electron microscopy and x-ray computed tomography (microCT). Additionally, the elemental composition of the skeletal elements has been checked using energy dispersive X-ray spectroscopy. The resulting 2D-, and 3D-scans reveal that P. wrangeli consists of an alternation of distinct calcium phosphate (apatite) lamellae and originally organic-rich inter-layers. The lamellae form four semicircular marginal pillars, which are connected by irregularly spaced transverse diaphragms. Marginally, the diaphragms and pillar lamellae are not connected to each other and thus do not form a closed periderm structure. A non-mineralized or poorly mineralized external periderm existed originally in P. wrangeli but is only rarely and fragmentary preserved. P. wrangeli often co-occurs with conulariids in fossil-rich limestone with mudstone–wackestone lithologies. Based on the new data, P. wrangeli can be best interpreted as a poorly mineralized conulariinid from an original soft bottom habitat. Here the new conulariinid family Palaenigmaidae fam. nov. is proposed as the monotypic taxon for P. wrangeli.

Acritarch Elektoriskos? williereae (G. & M. Deflandre, 1965) Vanguestaine, 1979 emend. nov. from the Upper Ordovician of the Siberian Platform: New Morphological and Stratigraphic Data

The morphology of acritarch species Elektoriskos? williereae (G. & M. Deflandre, 1965) Vanguestaine, 1979, previously considered as a Silurian index of the Llandovery, has been clarified, the diagnosis emended, and the stratigraphic distribution expanded. According to new data, the first appearance of E.? williereae was confined to the upper part of the Baksan Horizon near the boundary of the Sandbian and Katian stages of the Upper Ordovician. Co-occurrence of E.? williereae with representatives of the genera Gordonirundum, Nirundella, Peteinosphaeridium, and Sacculidium is a distinct, well-recognizable palynological characteristic of the Katian deposits of the Siberian Platform which can serve for identification, dating, and correlation of the acritarch-bearing strata. Morphological variations in E.? williereae are a stable diagnostic feature of the species that distinguishes it from other taxa. It is possible that the species was sensitive to paleoenvironments and, probably, highly adaptive, which allowed it, remaining almost unchanged, to overcome the global Late Ordovician cooling, which became fatal for many other groups of organisms.