Guzhangian (late Middle Cambrian) agnostoids and trilobites are described from the Belvoir Road area, western Tasmania. The fauna comprises seven agnostoid species and six trilobite species. The specimen described here as Lisogoragnostus sp. may represent a new species. The trilobites include Conocoryphidae gen. et sp. indet., which probably represents a new genus. The age of the fauna is suggested to be within the Lejopyge laevigata Zone and possibly within the Lejopyge laevigata II Zone. This indicates that the fauna is the youngest known within the economically significant Mount Read Volcanics. James B. Jago* [jim.jago@adelaide.edu.au], Adelaide University, Mawson Lakes, South Australia 5095, Australia; Christopher J. Bentley [bigfossil@bigpond.com], 30 Albert Street, Clare, South Australia 5453, Australia; Keith D. Corbett [keith.corbett@bigpond.com], 35 Pillinger Drive, Fern Tree, Tasmania 7054, Australia.

Orbitally paced sea level changes and carbon isotope fluctuations in the middle-late Cambrian Xixiangchi Formation, Sichuan Basin, South China

Guzhangian (late middle Cambrian) agnostoids and trilobites are described from near Riana, northwestern Tasmania. Five agnostoid and five trilobite species are documented. The agnostoids include a new species, which is the oldest known representative of the genus Aspidagnostus. The trilobites include Monkaspidae indet, which probably represents a new genus. The librigena of the species described as cf. Penarosa sp. appears to be unique in that it has a segmented genal spine and possesses closely spaced small, stout spines on its margins. The age of the fauna is probably within the range of Lejopyge laevigata II Zone to lower Acmarhachis quasivespa Zone, which makes it the youngest known Cambrian fauna in the Dial Range Trough. Christopher J. Bentley [bigfossil@bigpond.com]; James B. Jago* [jim.jago@unisa.edu.au], University of South Australia-STEM, Mawson Lakes, South Australia 5095, Australia.

Abstract Archaeocyaths are biocalcified sponges largely restricted to the early Cambrian Period. Their perforated cup-shaped body facilitated filter feeding. Many of them were clonal modular animals that formed the earliest metazoan skeletal reefs. In Siberia, archaeocyaths extend from late Age 2 to Age 4 of the early Cambrian, representing an ~15 m.y. range (ca. 525–510 Ma). Elsewhere, archaeocyaths emerged later than in Siberia and, in places, survived to the middle-late Cambrian. The existing fossil record thus indicates an out-of-Siberia scenario and delayed biomineralization in archaeocyaths relative to many other animals, which acquired biomineralization in the Fortunian Age of the early Cambrian. Here we report two microscopic archaeocyath species—Primocyathus uniseriatus Wang and Xiao, gen. et sp. nov. and Sinocyathus biseriatus Wang and Xiao, gen. et sp. nov.—from the Fortunian Kuanchuanpu Formation (ca. 533 Ma) in South China. Preserved as phosphatized internal molds, they are interpreted to have had a biomineralized, two-walled, perforated, cup-shaped skeleton. They were likely filter feeders, but their solitary habit and millimetric body size indicate that they were unlikely reef framework builders. They substantially extend the stratigraphic range of archaeocyaths, challenge the out-of-Siberia hypothesis, support archaeocyath biomineralization in the beginning of the Cambrian explosion, and imply a Precambrian divergence of sponge classes.

The Shunbei 5 (SB5) strike-slip fault, situated in the central Tarim basin, is distinguished by its considerable length, significant variations in planar orientation, and intricate multi-stage tectonic evolution. This study delves into the geometric, kinematic, and dynamic features of both the southern and northern parts of the SB5 fault, utilizing the latest seismic data from the Fuman Oilfield, and examines the factors influencing the fault’s planar deflection. The fault can be categorized into three structural deformation layers based on lithological features and fault features: the deep structural deformation layer (below TЄ3), characterized by basement rifting and limited strike-slip activity; the middle structural deformation layer (TЄ3-TO3), marked by vigorous strike-slip movements and the dominance of flower structures; and the shallow structural deformation layer (TO3-TP), featuring echelon-type normal faults and boundary graben faults, specifically in the southern SB5 fault. The fault activity is more pronounced in its southern SB5 fault compared to the northern, with the weakest activity at the TЄ3 interface and the peak at the TO3 interface. The southern SB5 fault transitions to sinistral slip at the TO3 interface, while the northern SB5 fault shifts from dextral to sinistral slip at the TC interface, highlighting variable slip directions across different interfaces. Rifts are extensively distributed within the Precambrian basement along the SB5 fault. The initial strike-slip fault rupture, which is primarily localized in these areas, exerts a significant influence on the formation of the S-shaped fault plane. This process involves four distinct evolution stages: the embryonic stage of strike-slip activity during the Middle-Late Cambrian; the intense strike-slip fault activity stage during the Middle-Late Ordovician; the reactivation stage of deep strike-slip fault in the Silurian; and the connection and reactivation stage during the Devonian-Carboniferous.

Petroleum accumulations in the tarim basin during various tectonic stages as revealed by U–Pb dating of multi-phase calcite veins in deeply buried carbonate reservoirs

Orbitally-Paced Carbon-Isotope Fluctuations and Carbonate Sedimentary Process During the Middle-Late Cambrian, Sichuan Basin

Distribution, evolution and structural properties of Wushenqi paleo-uplift in Ordos Basin, NW China

The Steptoean Positive Carbon Isotope Excursion (SPICE) event at ca. 497−494 Ma was a major carbon-cycle perturbation of the late Cambrian that coincided with rapid diversity changes among trilobites. Several scenarios (e.g., climatic/oceanic cooling and seawater anoxia) have been proposed to account for an extinction of trilobites at the onset of SPICE, but the exact mechanism remains unclear. Here, we present a chemostratigraphic study of carbonate carbon and carbonate-associated sulfate sulfur isotopes (δ13Ccarb and δ34SCAS) and elemental redox proxies (UEF, MoEF, and Corg/P), augmented by secular trilobite diversity data, from both upper slope (Wangcun) and lower slope (Duibian) successions from the Jiangnan Slope, South China, spanning the Drumian to lower Jiangshanian. Redox data indicate locally/regionally well-oxygenated conditions throughout the SPICE event in both study sections except for low-oxygen (hypoxic) conditions within the rising limb of the SPICE (early-middle Paibian) at Duibian. As in coeval sections globally, the reported δ13Ccarb and δ34SCAS profiles exhibit first-order coupling throughout the SPICE event, reflecting co-burial of organic matter and pyrite controlled by globally integrated marine productivity, organic preservation rates, and shelf hypoxia. Increasing δ34SCAS in the “Early SPICE” interval (late Guzhangian) suggests that significant environmental change (e.g., global-oceanic hypoxia) was under way before the global carbon cycle was markedly affected. Assessment of trilobite range data within a high-resolution biostratigraphic framework for the middle-late Cambrian facilitated re-evaluation of the relationship of the SPICE to contemporaneous biodiversity changes. Trilobite diversity in South China declined during the Early SPICE (corresponding to the End-Marjuman Biomere Extinction, or EMBE, of Laurentia) and at the termination of the SPICE (corresponding to the End-Steptoean Biomere Extinction, or ESBE, of Laurentia), consistent with biotic patterns from other cratons. We infer that oxygen minimum zone and/or shelf hypoxia expanded as a result of locally enhanced productivity due to intensified upwelling following climatic cooling, and that expanded hypoxia played a major role in the EMBE at the onset of SPICE. During the SPICE event, global-ocean ventilation promoted marine biotic recovery, but termination of SPICE-related cooling in the late Paibian may have reduced global-ocean circulation, triggering further redox changes that precipitated the ESBE. Major changes in both marine environmental conditions and trilobite diversity during the late Guzhangian demonstrate that the SPICE event began earlier than the Guzhangian-Paibian boundary, as previously proposed.

Mixed carbonate-siliciclastic rocks were particularly widespread during the Furongian (late Cambrian), a critical time interval marked by biotic turnovers, extinction events and carbon cycle perturbations. In this context, the Zagros Basin (SW Iran) is a key area for the study of this time interval due to the well-exposed mixed carbonate-siliciclastic successions. Nevertheless, these are still poorly constrained from a sedimentological point of view. The current study aims to contribute to the palaeoenvironmental reconstruction of the Zagros Basin during the Furongian through high-resolution facies and microfacies analysis of the Tang-e-Ilbeyk section. The latter includes, in ascending order, the upper Mila C Member and Ilbeyk Formation. The facies and microfacies analysis recognized six facies associations, representing different settings of a mixed carbonate-siliciclastic ramp at the north-eastern Gondwanan margin. The vertical stacking pattern of these facies associations revealed five medium-scale Transgressive-Regressive cycles, superimposed by larger-scale sequences. In particular, during the latest Miaolingian (formerly late middle Cambrian) to early Furongian, a climate change from arid to humid conditions caused a major regressive event with the progradation of clastic shorelines and the following pollution and drowning of the Mila C Member's carbonate factory. The latter was replaced by a storm-dominated siliciclastic shelf (Ilbeyk Formation) that, throughout middle/late Furongian, experienced a large-scale transgressive event, culminating with a maximum flooding interval. A significant forced regression occurred in the latest Furongian when shallow water conditions were re-established (uppermost Ilbeyk Formation). The palaeoenvironmental reconstruction of this study allowed correlation with other coeval depositional events at regional (Arabian plate) and global (Laurentia and Baltica) scales, contributing to new constraints for the lower Palaeozoic evolution of north-eastern Gondwana.

No Furongian Biodiversity Gap: Evidence from South China

A Cambrian Series 3 (Guzhangian, Boomerangian) fauna is described from Core 12 of the Gidgealpa 1 drillhole from the Warburton Basin, northeastern South Australia. There are four agnostoid taxa: Ammagnostus laiwuensis, Lejopyge calva, L. armata and an unassigned pygidium, and six polymerid trilobite taxa: Fuchouia sp., Dorypyge sp., Solenoparia changi sp. nov., Pianaspis sp., an unassigned cranidium and an unassigned pygidium. This fauna suggests a correlation with the Goniagnostus nathorsti Zone or the lower part of the Lejopyge laevigata Zone (Boomerangian on the northern Australian biostratigraphic scheme), with the latter preferred. These are the first published descriptions of fossils of this age from the Warburton Basin. Xiaowen Sun [Xiaowen_s@yahoo.com.au], Sun Petroleum Geoservices, 4 Jolie Grove, Box Hill, Victoria 3128, Australia; Christopher J. Bentley [ bigfossil@bigpond.com], 30 Albert Street, Clare, South Australia, 5453, Australia; James B. Jago [jim.jago@unisa.edu.au], University of South Australia–STEM, Mawson Lakes, South Australia 5095, Australia.

Quantifying the middle–late Cambrian trilobite diversity pattern in South China

A new species of late middle Cambrian (Guzhangian: Miaolingian) ptychoparioid trilobite is described from the Devoncourt Limestone just west of the Burke River crossing on the Duchess to Cloncurry Road. This is an addition to the extensive study of the fossil fauna of that district in the Burke River Structural Belt and provides another link to the Georgina Basin fauna, albeit younger by one zone, about 200 km west on Mungerebar Station. Generic assignment of the new species is discussed in relation to a worldwide complex of similar solenopleurid genera with small eyes situated well forward on the cephalon. Some comments are made in relation to family placement of the species, but the question of family concepts relies heavily on revision of an extensive northern hemisphere literature on these standard trilobites; so, although placement in the Solenopleuridae is favoured, no formal family assignment is made until family groups in this large complex of genera are better defined.

The Tasmanian species Asthenopsis conandersoni Bentley

Система комплексной поддержки и сопровождения научного журнала Elpub позволяет запустить двуязычный сайт журнала со встроенной системой электронной редакции в соответствии с лучшими издательскими практиками, а так же предусматривает техническую и методическую поддержку со стороны специалистов НЭИКОН.

Abstract Postel Nunatak in the Patuxent Range has been previously mapped as Nelson Limestone but there was no biostratigraphic support for that interpretation until now. We confirm that limestone exposures at Postel Nunatak are at least partly correlated with the Nelson Limestone of the Neptune Range, 160 km north-east, and are not correlative with the lower Cambrian Schneider Hills Limestone of the Argentina Range. Upper beds have yielded the trilobitesSuludella? davniiPalmer & Gatehouse, 1972 andSolenopleura pruinaPalmer & Gatehouse, 1972, which provide a basis for assignment to Cambrian Series 3 (late middle Cambrian), within the Drumian or lower Guzhangian stages. Limestone beds were deposited in a shallow marine setting, ranging from supratidal to lagoonal facies with rare subtidal intervals. These settings contrast with deeper water facies of the Neptune Range. Despite limitations in sampling density, isotopic analysis indicates that a greater than +2.5‰ shift in δ13C is consistent with δ13C trends documented for the Drumian Stage. Because the upper and lower contacts at Postel Nunatak are covered by snow and ice, the relationship with rocks mapped as the Patuxent Formation in the Patuxent Range remains uncertain, but part of it may belong to the Precambrian Hannah Ridge Formation.

Fingerprinting Gondwana versus Baltica provenance: Nd and Sr isotopes in Lower Paleozoic clastic rocks of the Małopolska and Łysogóry terranes, southern Poland

The sedimentary facies characteristics and lithofacies palaeogeography during Middle-Late Cambrian, Sichuan Basin and adjacent area

ABSTRACTThe ages of diabase outcropping on the southern Alxa Block and in related tectonic setting are not well constrained, but are important for exploring the tectonic evolution of the southern Alxa Block. The ages of the zircons from the diabase intruding the Middle–Late Cambrian Xiangshan Group were measured using sensitive high-resolution ion microprobe II (SHRIMPII) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), and the weighted mean ages of 276.8 ± 7.9 Ma and 276.2 ± 9.7 Ma were obtained, respectively. The major elements in the diabase indicate that it may belong to the tholeiitic series. With specific features of the rare earth elements (REEs) and trace elements, potentially affected by the continental crust based on the observed strong positive Pb anomaly, the diabase was produced in an intra-plate extension environment. Similar diabase/basalts were also found along the southern margin of the Alxa Block. Combined with sedimentary, palaeo-current, mafic, and felsic rocks in the southern Alxa Block, a back-arc extension environment potentially occurred in the southern Alxa Block during the Early–Middle Permian that resulted from the convergence between the North China Block (NCB) and the Yangtze Block.