Searle (2022) argues, based on data from Scotland alone, that the deformation and metamorphism of the Scottish Highlands is continuously diachronous from the early Ordovician (Grampian) in the Dalradian of the Grampian Highlands to the mid-Silurian (Scandian) in the Moine of the Northwest Highlands. Necessarily, he disputes substantial offset along the Great Glen Fault (GGF). He compares the Scottish Caledonides with the Himalayas. We take the different view, which also considers evidence from along-strike in Ireland and Newfoundland, that the Grampian and Scandian orogenies were discrete events. The Grampian Orogeny involved major deformation and metamorphism across the Grampian and Northwest Highlands to the Moine Thrust Zone, whereas the Scandian Orogeny affected only the Northwest Highlands. The early Ordovician Grampian Orogeny was generated by the collision and obduction of an oceanic arc-ophiolite with and onto the Laurentian continent. The mid-Silurian Scandian Orogeny was caused by continental collision between Laurentia and Baltica. Late Silurian – early Devonian sinistral slip along the GGF emplaced the the Moine of the Northwest Highlands from a distant location to the north in the Scandian collision zone, against the Dalradian, which had not been involved in the Scandian collision. We outline several (eight) arguments that we believe contradict evidence for progressive northwestward propagation of a Himalaya-style thrust wedge from the early Ordovician to the mid-Silurian.

Calcite veins are common in organic-rich mudrocks, but their genesis and ability to transmit fluids are debated. A combined microstructural and isotopic investigation of an array of calcite veins recovered in core from the Marcellus Formation reveals that the veins grew via a combination of continuous fibrous growth and punctuated fracture-opening increments. Continuous opening is the result of pressure-solution creep and involves no mechanical fracturing, but rather the growth of a pressure fringe around a pre-existing, sealed fracture. In contrast, incremental opening is accomplished by overpressured, mineral-saturated fluid, which repeatedly ruptures the rock at the cement / host-rock interface. Punctuated growth increments occurred repeatedly throughout an otherwise protracted, continuous growth history, indicating that the present structures preserve hybrid deformation conditions between brittle, fluid-assisted cracking and plastic strain. Stable isotopic signatures match those of a regional opening-mode fracture set that formed in response to catagenetic fluid overpressures amid a tectonically imposed (Alleghanian) stress field. It is concluded that calcite veins form as opening-mode hydraulic fractures and are susceptible to increments of brittle reactivation, even while inelastic growth processes widen and fill the veins with fibrous cement.

The Huangshaping deposit is unique in southern Hunan Province, China, as it hosts economic reserves of both W–Mo and Pb–Zn mineralization, which are usually associated with granite and granodiorite porphyry in this area, respectively. This study reports results of in situ LA-MC-ICP-MS sulphur isotopic composition analyses conducted on sulphides from both W–Mo and Pb–Zn mineralization from the Huangshaping deposit with the aim of constraining ore genesis for this deposit. All samples from the proximal W–Mo mineralization have relatively uniform and high δ34S values (8.7 ‰ to 16.0 ‰), close to the range for carbonate sediments in this deposit (13.8 ‰ to 18.1 ‰). These patterns suggest that the granite porphyry in this deposit was the sulphur source for W–Mo mineralization, and that the assimilation of evaporite from the carbonate sediments led to the high δ34S values of the granite porphyry. Sulphides from the Pb–Zn mineralization have δ34S values (2.2 ‰ to 10.3 ‰) lower than those of the W–Mo mineralization, and generally increase in this paragenetic order, with the lowest δ34S values being similar to those of the basement (3.8 ‰ to 7.7 ‰). These patterns indicate that the original sulphur for the Pb–Zn mineralization was most likely derived from the basement, with input of sulphur from the carbonate sediments increasing during the evolution of ore-forming fluids. On the basis of the measured sulphur isotopic compositions, it is suggested that the ore-forming materials for the W–Mo mineralization were derived from the granite porphyry, whereas ore-forming materials extracted from the basement dominated the Pb–Zn mineralization.

Ediacaran rangeomorphs were the first substantially macroscopic organisms to appear in the fossil record, but their underlying biology remains problematic. Although demonstrably heterotrophic, their current interpretation as osmotrophic consumers of dissolved organic carbon (DOC) is incompatible with the inertial (high Re) and advective (high Pe) fluid dynamics accompanying macroscopic length scales. The key to resolving rangeomorph feeding and physiology lies in their underlying construction. Taphonomic analysis of three-dimensionally preserved Charnia from the White Sea identifies the presence of large, originally water-filled compartments that served both as a hydrostatic exoskeleton and semi-isolated digestion chambers capable of processing recalcitrant substrates, most likely in conjunction with a resident microbiome. At the same time, the hydrodynamically exposed outer surface of macroscopic rangeomorphs would have dramatically enhanced both gas exchange and food delivery. A bag-like epithelium filled with transiently circulated seawater offers an exceptionally efficient means of constructing a simple, DOC-consuming, multicellular heterotroph. Such a body plan is broadly comparable to that of anthozoan cnidarians, minus such derived features as muscle, tentacles and a centralized mouth. Along with other early bag-like fossils, rangeomorphs can be reliably identified as total-group eumetazoans, potentially colonial stem-group cnidarians.

The Abu Kharif area in the Northern Eastern Desert consists of contrasting granitic magma suites: a Cryogenian granodiorite suite (850–635 Ma), an Ediacaran monzogranite suite (635–541 Ma) and a Cambrian alkali riebeckite granite suite (541–485 Ma). Tungsten mineralization occurs within W-bearing quartz veins and a disseminated type confined to the monzogranite.

Whole-rock geochemical data classify the granodiorite as a late-orogenic I-type with calc-alkaline affinity, while the monzogranite and alkali riebeckite granite represent respectively a post-orogenic highly fractionated I-type with calc-alkaline affinity and an anorogenic A1-subtype with alkaline affinity. Geochemical modelling indicates that the three intrusions represent separate magmatic pulses where the granodiorite was generated by ∼75 % batch partial melting of an amphibolitic source followed by fractional crystallization of hornblende, biotite, apatite and titanite. The monzogranite was formed by 62 % batch partial melting of the normal ‘non-metasomatized’ Pan-African crust of calc-alkaline granite composition followed by fractional crystallization of plagioclase, biotite, K-feldspar, magnetite, ilmenite, with minor apatite and titanite. The alkali riebeckite granite was generated by 65 % batch partial melting of metasomatized Pan-African granite source followed by fractional crystallization of plagioclase, K-feldspar, amphibole and biotite with minor magnetite, apatite and titanite. In general, the parent magmas of the three intrusions were originally enriched in W, but with different concentrations. This W-enrichment would be caused by magmatic-related hydrothermal volatile-rich fluids and concentrated within the monzogranite.

In this study, we present a new granular rock-analogue material (GRAM) with a dynamic scaling suitable for the simulation of fault and fracture processes in analogue experiments. Dynamically scaled experiments allow the direct comparison of geometrical, kinematical and mechanical processes between model and nature. The geometrical scaling factor defines the model resolution, which depends on the density and cohesive strength ratios of model material and natural rocks. Granular materials such as quartz sands are ideal for the simulation of upper crustal deformation processes as a result of similar nonlinear deformation behaviour of granular flow and brittle rock deformation. We compared the geometrical scaling factor of common analogue materials applied in tectonic models, and identified a gap in model resolution corresponding to the outcrop and structural scale (1–100 m). The proposed GRAM is composed of quartz sand and hemihydrate powder and is suitable to form cohesive aggregates capable of deforming by tensile and shear failure under variable stress conditions. Based on dynamical shear tests, GRAM is characterized by a similar stress–strain curve as dry quartz sand, has a cohesive strength of 7.88 kPa and an average density of 1.36 g cm−3. The derived geometrical scaling factor is 1 cm in model = 10.65 m in nature. For a large-scale test, GRAM material was applied in strike-slip analogue experiments. Early results demonstrate the potential of GRAM to simulate fault and fracture processes, and their interaction in fault zones and damage zones during different stages of fault evolution in dynamically scaled analogue experiments.

Beothukis mistakensis from the Ediacaran System of Newfoundland, Canada demonstrates complex fractal-like morphology through the development of primary-, secondary- and tertiary-order Rangea-like units. The primary-order rangeomorph units observed in B. mistakensis are tightly juxtaposed, show no evidence of being independent of one another and are made up of chamber-like secondary-order – probably mesoglea-filled – units. The growth of these rangeomorph units demonstrates that the frond developed from the tip towards the basal region through ontogeny. The tertiary-order units of Beothukis are considered to represent surface morphology on the secondary-order units. This is in contrast to palaeobiological reconstructions of Beothukis that invoke three-dimensional fractal-like branches with independent units, which has been used to infer an osmotrophic mode of life. It is considered here that the fractal-like morphology of the lower surface of B. mistakensis was an adaptation to increase surface area to volume ratio. The quilted morphology of Beothukis proposed here is consistent with a sessile, reclining, phagocytotic and/or chemosymbiotic mode of life similar to that invoked for the reclining rangeomorph Fractofusus.

I welcome the comment from Dewey and Ryan on my paper (Searle, 2021), and the chance to clarify some conflicting Caledonian tectonic models and new ideas. As outlined in the paper, my review was based on the geology of Scotland, not Ireland, Newfoundland or the rest of the Caledonian orogeny beyond, mainly because of length constraints, and the fact that my personal field experience lies mainly in Scotland. The Great Glen fault and the Moine Supergroup are not exposed at all in Ireland, so critical parts, and half of the Caledonian orogeny are missing in Ireland. I argue that the Caledonian geology of Scotland can be explained by a Laurentia – Midland valley arc-microcontinent collision, progressing from NW-directed ophiolite obduction in the Late Cambrian to crustal thickening and regional metamorphism during the Ordovician and Silurian, across the Dalradian and Moine metamorphic rocks. Caledonian structures do continue north into Greenland, as summarized by Leslie et al. (2008), but the geological evolution of the Scottish Caledonides does not require any collision with Baltica. The Dewey and Ryan comment raises major tectonic questions, which this reply addresses.

Palaeopascichnida is a problematic group of extinct organisms that is globally distributed in Ediacaran sequences of Avalonia, Baltica, Siberia, South China and Australia. The fossils related to Palaeopascichnida consist of serially or cluster-like arranged, millimetre- to centimetre-scale globular or allantoid chambers, which are characterized by substantial differences in preservation, leading to no consistent diagnosis for these organisms. Here we integrate morphometric variation, stratigraphic distribution and habitat settings of more than 1200 specimens from all known fossil localities. The results of the morphological analysis demonstrate variation in chamber shape and size, and allow us to recognize six valid species within the group. Statistical analysis of the specimen distribution with respect to sedimentary environments indicates a significant difference in palaeoecological settings between species, making a significant contribution to the evolution and systematic palaeontology of these problematic organisms and perspective on their use in Neoproterozoic biostratigraphy. Our revision and systematic study sheds new light on one of the least studied groups of the late Ediacaran biota.