Proceedings of the Geologists Association最新文献

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 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 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.

Construction of the Holderness/Flamborough Head moraine belt on the East Yorkshire coast, England, records the oscillatory onshore flow of the North Sea Lobe of the British-Irish Ice Sheet from ~ 25.8 to ~ 19.7 ka BP, during which time a thick sequence of multiple diamictons and associated stratified sediments were emplaced. The sedimentology of a > 40 m thick stratigraphy through the moraine belt at Filey Bay, in combination with local borehole records, is used here to reconstruct the depositional processes associated with glacier ice moving ca., 12 km onshore and damming the mouth of the Vale of Pickering, which resulted in the accumulation of an unusually thick and complex sequence of deposits traditionally classified as the “Filey till”. The base of the sedimentary sequence comprises stratified diamictons, which are interpreted as glacilacustrine deposits emplaced predominantly by sediment gravity flows in an ice-contact ‘mud apron’ on the distal slope of a subaqueous push ridge constructed in the earliest proglacial lake in Filey Bay; a vertical increase in coarse-grained lithofacies records increasing glacier proximity. Glacier overriding of the mud apron is recorded by a stacked sequence of tills that interdigitate with lake sediments inland. A zone of till-lake sediment interdigitation migrated first westward during North Sea Lobe advance and then eastward during its retreat, into and out of Glacial Lake Pickering, respectively. Multiple tills and intra-till stratified beds and lenses at the top of the sequence at Filey represent alternating deforming bed-sliding bed facies (subglacial traction tills and subglacial canal fills) associated with the construction of inset push moraines, constructed by sub-marginal incremental thickening or punctuated aggradation. This depositional scenario addresses the problems arising from genetic classifications of substantial accumulations of glacigenic diamictons as ‘till’ when modern analogues indicate only modest thicknesses of subglacial traction till beneath glaciers. Onshore thickening of glacigenic deposits through subaqueous push moraine construction and mud apron progradation is compatible with glacier surging behaviour, but not necessarily solely diagnostic of a surging North Sea Lobe during the last glaciation.

The fossil remains of a pterodactyloid pterosaur from the Kimmeridge Clay Formation (Jurassic: Tithonian) of Abingdon, Oxfordshire, central England are identified as a partial left first wing finger phalanx. The elongation of the phalanx and distinctive morphology of the proximal articular region, in particular the square outline of the extensor tendon process, permit the specimen to be assigned to Ctenochasmatoidea. Although fragmentary, it is sufficiently well preserved to determine accurately its dimensions when complete. Morphometric analysis reveals the specimen to represent one of the largest known examples of a Jurassic pterosaur, with an estimated wingspan of at least 3 m, and is one of the first pterodactyloids to be reported from the Jurassic of the United Kingdom.

The cliff and foreshore sections at Lavernock, South Wales form the type section of the Penarth Group, representing the Rhaetian stage in the UK, the latest Triassic. The Rhaetian bonebeds here have been famous for over 150 years for their vertebrate fossils. Here, we show that, unusually, the Lavernock basal Westbury Formation bonebed is dominated by osteichthyan teeth, with sharks such as Lissodus relatively rare. The rounded teeth of the durophagous bony fish Sargodon are abundant, with teeth of Severnichthys next in abundance, and Gyrolepis the rarest, quite unlike most other Rhaetian bone beds. Also, small elements such as shark denticles have not been found, whilst larger bones of marine reptiles (ichthyosaurs, plesiosaurs) and dinosaurs do occur. The dinosaur bones are unusual, and Lavernock may have yielded more such bones than any other British Rhaetian bone bed. These terrestrial elements suggest that the lower bone bed accumulated close to shore, but underwent considerable transport, with clasts perhaps moving back and forwards, to explain the abrasion of specimens, the larger elements and absence of smaller specimens. Dinosaurs are more widely documented in the Late Triassic of the Penarth area, around Lavernock, than anywhere else in the UK.

A great range and number of journals exist to promote and disseminate local knowledge in the areas of natural history, geology, geography and ecology. Many are still active; others are lost. The journals act as mouthpieces for local societies and are a repository of local knowledge. Some are hard to locate but the websites of local societies provide information on topics covered and the regularity of publication of the journals. The loss of journals seems to be the result of the pressure on academics to publish in international outlets and the growth of highly informative websites.

A series of historical documents by the 19th-century amateur naturalist and palaeontologist Alfred Brown report the earliest discovery of bone-bearing cave breccia in the former Transvaal (South Africa). The oldest of these reports dates from 1890 and predates the first mention of the existence of bone-bearing breccia at the famous Sterkfontein-Kromdraai caves by five years. The breccia fragment was kept by Brown in his collection, where it was noted to come from the Monte Christo gold mine near Ventersdorp (North-West Province). Brown's specimen is lost, but we could relocate the mine and confirm the presence of breccia deposits. Alfred Brown's notes are the earliest scientific report about the bone-bearing nature of Plio-Pleistocene South African caves and the first to acknowledge them as a potential source of hominin fossils, some 30 years before the discovery of the Taung Child, Australopithecus africanus. The finding strengthens the chronology of the discovery of the South African fossil hominin sites. It also significantly shortens the gap between the gold rush and the first discovery of bone-bearing breccia in the Witwatersrand.