Proceedings of the Geologists Association最新文献

We report on a new assemblage of coleoid arm hooks found in the Blue Lias (Lower Jurassic) succession near Lilstock (Somerset, UK). As there are no soft tissues or other materials (ink sac, phragmocone, etc.) preserved in the vicinity of the hooks, the genus and species cannot be accurately identified. Unlike the hooks of Clarkeiteuthis, which have distinctive inflated, bilobate bases, the hooks discussed herein are delicate, with a gently curved apex, which makes them quite similar to the arm hooks of Belemnotheutis or Acanthoteuthis. The assemblage of hooks shows a distinct organisation and, in some places, the hooks are clearly aligned as they would have been in life position. Comparable material of late Jurassic age from the Etches Collection (Kimmeridge, Dorset) is compared to the new arm hook assemblage.

The El Mers I and II formations (Middle Jurassic, Bathonian) are geological units outcropping in the folded Middle Atlas of Morocco rich in body and trace fossils of dinosaurs. The numerous tracksites of these units have been little studied and are severely affected by ongoing erosion (e.g., seasonal flooding) and, to a lesser degree, human activities (e.g., urbanisation). The aim of this project is to fully document and interpret the dinosaur tracks of two historic sites and four new sites discovered in the El Mers area using digital photogrammetry. The ichnofauna comprises abundant tracks and trackways of theropod and sauropod dinosaurs as well as of probable crocodylomorph tracks. The theropod tracks include several footprints of high anatomical fidelity, but the majority of the discovered tracks are identified to be penetrative tracks, with one site preserving abundant swim tracks. The sites preserve both small and enormous sauropod tracks. The enormous sauropod tracks are among the largest known worldwide, with a pes track length of up to 130 cm. The obtained 3D models are compared with site maps created by analogue mapping performed more than 15 years ago of the historical sites, revealing how erosion has both destructed surfaces and exposed new ones. The application of photogrammetry allows for the rapid collection of accurate high-resolution data with sustainable costs. The resulting 3D models can be used in research to digitally conserve threatened sites, and as a basis for knowledge transfer to the public. The present contribution encourages the intellectual, logistical, and social involvement of the local population to collaborate with scientists for the conservation of the rich geological heritage. Furthermore, scientific investigations in this area could shift from academic-only research to research focused on conservation and geotourism initiatives that involve local communities.

Fires have been shown to have been common in many Carboniferous ecosystems worldwide yet we still have little understanding of the detail of what, where and how such fires occur or indeed their effects both on the local ecosystem as well as on the Earth System as a whole. The Kingswood Limestone, of late Viséan (Mississippian age) found near Pettycur in Fife, Scotland, is interpreted as being deposited within a crater lake. The limestone contains a range of volcanic clasts together with charcoalified and uncharred plants. Two distinctive communities existed. One dominated by the small scrambling lycopsid Oxroadia that is permineralised and a second dominated by a range of pteridosperms and other gymnosperms preserved as charcoal. Fires surrounding a crater lake charred the plants that were then washed into the lake by post-fire erosion. All plant organs are found as charcoal including woody axes, leaves, pollen organs and ovules. Oxroadia that was living close to the lake was not affected by fire. Rising lake and sea levels allowed saline water to be introduced to the lake and connection to the sea was established. Many new charcoalified plants have still to be formally described. The Kingswood flora, together with the nearby Pettycur flora represents two of the most important Mississippian plant sites globally.

This paper presents the results of a detailed macro- and microscale structural study of the glacitectonised sequence at Kilcummin Head on the western side of Killala Bay, County Mayo, northwest Ireland. The sequence comprises two laterally extensive, thrust-stacked rafts of Carboniferous limestone and mudstone emplaced upon the in situ bedrock of the Ballina Limestone Formation. Restored cross-sections reveal that the glacitectonised sequence has undergone extensive deformation and shortening of 61 %. This accompanied the formation of a prominent thrust-moraine associated with a northward ice advance across Killala Bay during the Midlandian (Devensian). A five-stage model is proposed to describe the deformation. Stage 1 comprises detachment of the rafts, and the majority of the sequence shortening. North-directed transport of the rafts occurred on a major décollement surface located at the base of the rafted sequence, marked by a mudstone-rich glacitectonite. Stage 2 accommodated further shortening via a series of imbricate thrusts leading to the stacking of the bedrock rafts (Stages 3 and 4). Stage 5 saw final stacking of rafts within a prominent thrust-block moraine, followed by the deposition of a sequence of coarse-grained, ice-marginal glacigenic deposits.

A recent revelation has come to our attention, revealing the remarkably well-preserved post-cranial remains belonging to Protosiren. These remains include vertebrae, ribs, and fragmentary bones, and were discovered from two different horizons located in the Mokattam Formation of El-Galala Plateau, North Eastern Desert of Egypt. The first specimen, GCU0101, is identified as Protosiren sp., whereas the GCU0201 specimen is recognised as Protosiren cf. P. fraasi due to certain distinguishing features. These include vertebrae with wide keyhole-shaped neural canals, reduced tuberculum on the ribs, lack of pachyostotic ribs, and the possession of rugose articular rib head. This discovery is remarkable, as it offers a unique opportunity to study the ancient marine mammal's morphology and osteology, shedding light on its evolutionary history and ecological niche. The study documents the first occurrence of Protosiren from an ornamental limestone of the Middle Eocene (Bartonian) Observatory Formation from El-Galala Plateau, Northeastern Desert, Egypt.

A pulsed mantle convection model has been proposed for regional third-order cyclic sea level changes during time intervals for which robust evidence of extensive polar ice caps is lacking. One such interval, the Late Jurassic–Early Cretaceous, is represented in southern England's Wessex Basin by the marine to non-marine Portland and Purbeck Limestone groups and Wealden Group and Supergroup. Third-order cyclicity in this succession is reviewed against the mantle convection model, involving pulsed growth of a regional uplift centred on the Cornubian Massif, bordering the Wessex Basin. Supporting evidence for the model is forthcoming from cyclicities in the Upper Tithonian marine Portland Group and Hauterivian–Lower Aptian alluvial–lacustrine–lagoonal Weald Clay Group. Third-order cycles in the Berriasian–Valanginian alluvial–lacustrine Hastings Group reflect fault reactivation along the Anglo-Brabant Massif, conventionally linked to North Atlantic opening. Credible cyclicities on comparable scales have not been identified in the Upper Tithonian–Lower Valanginian lagoonal–lacustrine Purbeck Limestone Group or the Valanginian–Barremian fluvial–alluvial Wessex Formation. Purbeck lithofacies are defined largely by climatic and local tectonic signals; cyclicities were potentially masked in the Wessex Formation by dynamic fluvial processes in proximity to the massif. Certain biotic events in the Purbeck Limestone Group and fluvial events in the Wessex Formation possibly reflect vertical movements of the Cornubian uplift.

Scelidosaurus is a herbivorous dinosaur belonging to the ornithischian clade Thyreophora. Until recently, its distribution was limited to the cliffs of Charmouth, on the south coast of Dorset, United Kingdom. In 2021, a fragmentary specimen from Lower Jurassic strata in Northern Ireland (BELUM K3998) was referred tentatively to Scelidosaurus. This bone, the proximal end of a femur, was suggested to be an ornithischian based on several characteristics, including gross morphology and osteohistology. This study reassesses these characteristics, and finds no evidence to support their use for identifying this specimen as either an ornithischian or Scelidosaurus. With the most comprehensive studies on Scelidosaurus finding no autapomorphies of the proximal femur, this study regards BELUM K3998 as Dinosauria indet. Additionally, this study highlights the importance of apomorphy-based approaches in taxonomy and the benefits of such methodologies.

This field study records that the Tortonian phosphatic hardground at S'Algar, Menorca has a diverse fossil macrobenthic fauna dominated by bivalves. These faunal elements occur in four preservational forms (A–D). Each taphonomic form within the hardground is characterised by different concentrations of Entobia isp. (clionaid sponge boring) and encrustation. The preservational forms have specific fossil macrofaunas associated with them, and the hardground represents a melange of bioclasts derived from different environments on the Menorcan Miocene shelf. These habitats are influenced by the upwelling event that provides the conditions for hardground mineralisation.

A Glycymeris-Crassatella-Clypeaster association (A) records part of a fauna that lived on the upper ramp slope that was periodically affected by high energy and low oxygen conditions due to upwelling waters. The smaller sized fauna (B), characterised by an arcid-carditid-venerid association is derived from the middle ramp that was affected by storms and a more persistent westward flowing current that intermittently drove upwelling. The fragmentary and disarticulated nature of both faunas indicates that they were mixed within the hardground via reworking processes driven by these seafloor energy regimes.

Some of the large gastropod taxa, dentition-up Glycymeris and Gastrochaena suggest that the hardground had its own fauna. Preservation A fauna and other opportunistic taxa inhabited an environment where the hardground was exposed on the Miocene seafloor as ‘islands’ surrounded by thin layers of looser sediment. Phosphatic bioclasts in the underlying limestone indicate that similar mineralised beds were formed elsewhere on the shelf prior to the formation of the studied outcrop.

A glacial origin for cirque-like hollows cut into the western escarpment of the Usk valley near Abergavenny, South Wales has become widely accepted. Associated supposed extensive moraine ‘festoons’ have been depicted merging and contemporaneous with Last Glacial Maximum (LGM) deposits formed by ice occupying the adjacent Usk valley. We re-interpret these festoons as the product mainly of rock slope failures (RSFs) emanating from the hollows. A cirque glacier origin is preferred to account for a compact double-ridge feature in one of the hollows. The equilibrium-line altitude (ELA) of the reconstructed glacier (357 m) is > 60 m lower than all similarly small, presumed Younger Dryas Stadial (YDS; c., 12.9–11.7 ka) glaciers elsewhere in South Wales. To test whether this glacier nevertheless might date from the YDS, we apply three approaches to reconstruct annual palaeo-precipitation amounts at the ELA, two based on relationships between accumulation and ablation for modern glaciers and the third on a simple degree-day model (DDM) using likely climatic characteristics for this event. The DDM can be tailored to represent the recognised large-amplitude YDS annual temperature range rather than the much smaller one experienced by modern glaciers, making it our preferred approach. Although conditions along the Usk valley escarpment during the LGM would have been well suited to cirque glacier formation, the DDM approach, using the large-amplitude annual temperature ranges, suggests that a YDS age might also be possible. The results have implications for re-assessing the likely ages of some former small glaciers in South Wales.

Scratch circles, previously defined as ‘bedding plane parallel sedimentary structures formed by the passive rotation of a tethered organism into the surrounding sediment’, have hitherto been identified in the geological record from the Ediacaran to the Paleocene, as well as in modern settings. They have not met the definition of trace fossils, being passively registered by a part of a plant. Several variations of scratch circle morphology have been identified in or on Pliocene and Pleistocene deposits on the Cape south coast of South Africa, allowing for an expansion of the scratch circle temporal range. Furthermore, these novel forms require a redefinition of the term ‘scratch circle’. Anthropogenic origins need to be considered for occurrences in the Pleistocene; guidelines to assist in distinguishing such causes from typical scratch circles are presented. Scratch circles may conceivably have inspired the creation of circular patterns (palaeo-art) in sand by Middle Stone Age hominins. Evaluation of scratch circles in snow allows for subtle features to be determined. A re-evaluation of what the term ‘trace fossil’ constitutes could be considered, in order to include the term palaeo-ichnobotany.