Search

Heliolitines are a major tabulate coral group, which experienced their early diversification in the Katian (Late Ordovician). Fossils of this group are well represented in the Kuruktag area of northeastern Tarim Basin, Northwest China, but detailed studies of corals from this area are still lacking. Here, we systematically describe early Katian heliolitines of the Tarim Block based on new material from the lower Katian Yuanbaoshan Formation of southern Kuruktag, which include the plasmoporellids Plasmoporella xinjiangensis and Plasmoporella grandis, the sibiriolitids Mongoliolites obliterans and Mongoliolites sp., the protoheliolitid Wormsipora sp., the proporid Acdalopora sokolovi, the pseudoplasmoporid Navoites irregularis, and the heliolitid Apekinella zeravshanica. A faunal comparison indicates that the biogeographic connections of Tarim Block are closest to Chu-Ili and South Tienshan, but relatively weaker with Qilian and North China. [ABSTRACT FROM AUTHOR]

Linguliform brachiopods are a minor but distinctive component of the Palaeozoic Evolutionary Fauna. However, there is no formal research on Katian (Late Ordovician) linguliform microbrachiopods in South China. Fossils from the 'Pagoda', 'Linhsiang' and Daduhe formations, Wanhe section of Yunnan Province, South China, provide a unique opportunity to bridge the gap. Here, we report and systematically describe, for the first time, a deep‐water Katian linguliform microbrachiopod association, including 13 species assigned to nine genera, namely Paterula cf. numerosa Popov, Hisingerella tenuis Holmer, Scaphelasma sp., Torynelasma? sp., Biernatia holmi Holmer, ?Biernatia maruiaensis Percival et al., Biernatia pseudoplana Percival et al., Biernatia wrighti Percival et al., Opsiconidion praecursor Popov et al., Opsiconidion sp., Eoconulus puteus Percival et al., Acanthambonia sp. and Nushbiella lillianae Holmer. To explore the composition and distribution model of global deep‐water micromorphic linguliforms in the Katian, a dataset of occurrence of 40 genera from five superfamilies and 10 localities in Baltica, Avalonia, Australian Gondwana, Boshchekul Island Arc and South China is established. Compared with those of other localities, the Chinese association is dominated by Acrotretoidea with no taxon of Discinoidea or Paterinoidea. The global dataset is analysed using non‐metric multidimensional scaling. The results indicate an endemic biogeographical pattern for the Katian linguliform microbrachiopods, which can be explained by oceanic circulation or environmental differences. [ABSTRACT FROM AUTHOR]

Three‐dimensionally preserved pyritic internal moulds of the Late Ordovician graptolites Appendispinograptus leptothecalis and Styracograptus chiai from the Upper Ordovician Wufeng Formation of the Daheba section, Hunan Province, South China, were imaged by micro‐CT. The distinctive pea‐shaped pits/dimples aligned in a zigzag line arising from the second/third thecal pair on the tubarium in these species are interpreted as the surface expression of the junction between the lateral thecal walls and the thickened internal cross‐bars that support the nema. The relations between different internal structures such as the nema, median septum, aboral lists, interthecal septa and cross‐bars are summarized, and examples of these supporting systems in different taxa are illustrated. The presence of isolated cross‐bars in different diplograptid tubarium may suggest that they have evolved as a result of constructional restrictions. [ABSTRACT FROM AUTHOR]

The Katian (Upper Ordovician) Shiyanhe Formation at the Sigang section, Neixiang area, Henan Province, central China, has been investigated for carbon isotope (δ13Ccarb) chemostratigraphy. The carbon isotopic data document signal between the two major Ordovician positive shifts in δ13C, the early Katian Guttenberg and the Hirnantian excursions. The Kope (Ka1/2), Fairview (Ka2/3), Waynesville (Ka3/4), Whitewater (Ka4) excursions and a doubtful Elkhorn (Ka4) excursion are identified herein. The continuous and well-defined conodont zonal succession of the Sigang section provides a secure biostratigraphic framework for the mid-late Katian carbon isotope chemostratigraphy in China. Correlation between carbon-isotope data curve and the relative sea-level changes shows no clear correspondence, and hence the sea-level change is probably not the main driver of δ13C excursions during the Katian. Intercontinentally, the mid–late Katian carbon isotope excursions, identified mainly in the North American and Baltoscandian successions, are useful for improving long-distance stratigraphic correlations. This further suggests that these excursions represent global perturbations in the carbon cycle. [ABSTRACT FROM AUTHOR]

The Late Ordovician mass extinction (LOME) has long been known for its association with the Hirnantian glaciations. Two extinction pulses seem to reflect global cooling and warming, respectively. The effects climate change had on Ordovician life are well documented through palaeontological evidence, several geochemical proxies and further simulated in modelling scenarios. Preceding the Hirnantian extinction interval was a phase of prolific faunal migrations in notably the later parts of the Katian. Well-documented evidence shows that low-latitude faunas dispersed to high latitudes, and taxa that had previously been endemic to particularly Baltica and South China, suddenly began to appear in Laurentia. These events, referred to as the Boda warming event and the Richmondian invasion, have been suggested to reflect a biotic response to warmer climate indicating that the onset of the subsequent Hirnantian icehouse marked a considerable environmental shift from the latest Katian warming phase. Whereas a lot of focus has been on untangling the selective effects of the two Hirnantian extinction pulses on different clades, less focus has been on what led to the transition from the Middle Ordovician biodiversity rise to the dispersal phase seen during the Katian. It appears that most clades did not – during any point of time in the Ordovician – surpass the richness levels they had achieved by the earliest Katian. Rather, a plateau was established when all metazoan clades are compiled together. This could suggest that extinction rates began to increase relative to originations. Either a threshold was reached by the early Katian prohibiting ecosystems to expand, or an extinction pulse occurred that decimated overall biodiversity accumulation. Two lines of evidence suggest the latter to be the case. Firstly, several new clades became hugely diverse by the Katian. These include bryozoans, crinoids, rugose and tabulate corals, as well as molluscs such as bivalves and gastropods, and show that obviously increased ecosystem complexity with, for instance, more epifauna and tiering occurred. Secondly, large richness datasets compiled from all metazoan clades differ from biodiversity curves based on individual clades in that they show a drop in richness already by the earliest Katian (as opposed to the classic two-pulsed Hirnantian scenario). This discrepancy has long been an overlooked conundrum that arguably has been ascribed to the larger datasets having been temporally less well-resolved. However, these new multiclade Ordovician biodiversity curves are – in some cases – resolved down to the scale of millennia, and they still depict this large fall in richness levels during the early Katian. As this pattern is observed across vastly dispersed regions, it is arguably a true signal depicting a global extinction pulse that precedes the two classic Hirnantian extinction waves by several million years. If such a three-phased ‘extended-LOME’ interval is to be corroborated, it would imply a con­siderably different extinction scenario from the classic Hirnantian one. For instance, most of the Katian would then have to be viewed as being part of a protracted survival phase. In such a scenario, the global dispersal of faunas during the Boda and Richmnondian events could reflect faunas adapting to changing climatic and environmental conditions during not just the classic Hirnantian icehouse–greenhouse scenario but as part of a prolonged phase culminating with the Hirnantian extinctions. It would further entail a new perspective on the possible mechanisms driving this long extinction phase. Several extinction determinants, both intrinsic and extrinsic may be culprits, but it is hard to overlook the apparent correlation between the start of this ‘extended-LOME’ phase and some of the largest volcanic eruptions known in Earth’s history. Future better temporally resolved research into both the interplay between life and the environment during the earlier parts of the Late Ordovician hopefully will shed more light on this fascinating mass extinction event. [ABSTRACT FROM AUTHOR]

Understanding ancient climate changes is hampered by the inability to disentangle trends in continental ice volume from records of relative sea-level change. As a unique coastal deposit in tropical and subtropical regions, beachrock has been proved to be reliable for constraining the glacial meltwater signal and thus the total volume of land-based ice in Quaternary. However, beachrock is rarely recognized in the fossil record due to (a) the two-dimensional distribution of beach deposits, as opposed, for example, to extended platform sediments, and (b) the fact that specific environmental conditions are required in order to lithify sediments directly on the beach. By combining the stratigraphic architecture with petrography of characteristic carbonate cements, we demonstrate the first known occurrence of Ordovician beachrock in the Tarim Block, northwestern China. According to biostratigraphic data, a middle Katian (Upper Ordovician) palaeokarst surface is capped by carbonate conglomerate beachrock and this is suggesting a significant relative sea-level rise in late Katian. The beachrock can be correlated with widespread subaerial exposure surfaces and a pronounced stratigraphic gap within the Katian in northwestern Tarim. We suggest that the beachrock ‘fingerprinted’ a strong melt-water pulse in high latitudes after a short-lived Katian glaciation, which has not received much attention in scientific papers so far. [ABSTRACT FROM AUTHOR]

Three positive carbon isotope excursions are reported from Middle-Upper Ordovician in Tahe oil-gas field, northern Tarim Basin. Based on conodont biostratigraphy, the Middle Darriwilian Isotope Carbon Excursion (MDICE) and the Guttenberg Carbon Isotope Excursion (GICE) are identified from Darriwilian to Early Katian by the aid of whole-rock carbon isotope data from two well cores. Positive excursion within conodont Pygodus anserinus zone is developed in Early Sandbian, and the fluctuation range is no less than MDICE. Because the range of this excursion in the generalized global carbon isotope curve is short, previous studies paid little attention to it, and named Early Sandbian Isotope Carbon Excursion (ESICE) in this paper. Furthermore, these positive excursions are not directly related to sea level fluctuations and the MDICE and GICE identified in northern Tarim can be globally correlated to that in southern China, North America, South America, and Europe. The Saergan Fm. source rocks of Middle-Upper Ordovician in Kalpin Dawangou outcrop are in accord with the geologic time of MDICE and ESICE, and GICE have strong ties to the source rock of Lianglitag Fm. in basin. Abundant organic carbon burial is an important factor in genesis of positive isotope carbon excursions. Positive oxygen isotope excursion, conodont fauna turnover, decreased conodont total diversity, and the change of sedimentary facies indicated that dramatic changes of paleoceanographic environment of Early-Middle Ordovician in Tarim Basin started from the end of Darriwillian, and an obvious icehouse climate of Late Ordovician occurred in ESICE. [ABSTRACT FROM AUTHOR]

Reefs in the Late Ordovician are usually built up by metazoans, whereas in the Early and Middle Ordovician microbial reefs are dominating. In the Late Ordovician (Katian) Lianglitag Formation, at Bachu, Tarim, NW China, however, three distinct stages of thrombolithic microbial reefs are exposed. The lower and upper reef intervals are characterized by widespread microbial carbonates with almost constant thicknesses (biostromes). The middle reef interval exposes dome-like mounds, and shows a higher diversity of reef-building and reef-dwelling organisms. Calcareous algae such as Vermiporella are abundant, but also other components such as fragments of Halysis, brachiopods, molluscs, echinoderms, bryozoans, and trilobites have been found in the microbial reef units. The purpose of this study is to describe for the first time the composition and microfacies of the reefs in this remote area. Especially the question of whether or not these Late Ordovician reefs represent remnants of the Early/Middle Ordovician microbial-dominated reef type just lacking Calathium and lithistid sponge is addressed. The results indicate that the local conditions on the leeward side of the carbonate platform, where waters are less well agitated and thus less well oxygenated, and probably also characterized by temporarily elevated water temperatures hampering the growth of metazoan reefs, were responsible for the proliferation of the Late Ordovician microbial reefs in the Bachu area. [ABSTRACT FROM AUTHOR]

Abstract: Late Sandbian–Early Katian marine carbonates from two sections in North America and one in south China were analyzed for paired δ 13Ccarb and δ 13Corg, and revealed similar δ 13Ccarb but varying trends in δ 13Corg stratigraphy while all sections recorded a well-known positive δ 13Ccarb shift. These δ 13Corg records are the first through the Guttenberg δ 13Ccarb excursion (GICE) in China, Oklahoma, and West Virginia. In south China a positive excursion in δ 13Corg is associated with the latter part of the positive δ 13Ccarb excursion and closely resembles trends from Iowa and Pennsylvania that have been interpreted to reflect a lowering of atmospheric pCO2 levels. The δ 13Corg trends from Oklahoma and West Virginia differ significantly from what is observed in China. This likely indicates that local changes in nutrient cycling and phytoplankton growth rates were the dominant control on 12C fractionation in Oklahoma and West Virginia, masking a possible global signal of lowered atmospheric pCO2 levels observed in China. [Copyright &y& Elsevier]