Proceedings of the Geologists Association最新文献

Limestones of the Takche Formation (Spiti, Himalaya) are characterized by normal marine fauna and flora typical for the Late Ordovician. The flora is represented by algae, mostly by receptaculitids and dasyclad green algae. Various calcareous microorganisms such as calcitarchs, Rothpletzella and Girvanella are present. There are some differences in the microfossil content and abundance between different lithofacies of the Takche Formation. Two main biofacies types could be recognized on the basis of the abundance of algae and calcitarchs, namely algal rich and algal poor biofacies. The abundance of dasyclad green algae in limestones of the Takche Formation is characteristic of the warm climate. The Himalaya (Gondwana) has calcitarchs in common with Baltica.

Fluvio-lacustrine deposits are promising archives that afford to decipher climate and tectonic signatures, typically when evidence of changes in the depositional settings therein is remarkable. As such, the present work coveys a case study whose fluvio-lacustrine deposits may serve to provide insights into climate and tectonic controls on palaeoenvironmental settings. The study area lies in the northwestern portion of Ain Cheggag, southeastern the Sais foreland basin (northern Morocco). The lithostratigraphical analysis of Plio-Quaternary fluvio-lacustrine deposits in the area has enabled the identification of nine facies. The depositional systems are organized into three deposit units, each of which reflects a typical depositional environment. The first (lower) unit consists of detrital facies implying deposition in alluvial-dominated settings. The alternation of detrital and carbonate facies giving way to the second (middle) unit suggests sedimentation in a fluvio-lacustrine environment. Whilst being carbonate-rich, the third (upper) unit reflects a shift into lacustrine-dominated settings. Accordingly, the vertical succession of the sedimentary pile delivers remarkable insights into a general palaeo-environmental shift from alluvial settings, with enhanced pedogenesis processes, towards carbonate-dominated lacustrine conditions where early- and late-stage diagenesis processes would have prevailed. This broad shift in depositional systems is likely to be the response of palaeohydrological changes that are modulated both by the neotectonic subsidence background and, specifically, the general palaeoclimate evolution towards more humid conditions. Bioturbation, desiccation, and void-filling with internal sediments are key features of early-stage diagenesis processes, whereas cementation, micritization, recrystallization, dissolution, and iron and manganese oxidation are the main features of late-stage diagenesis altering the primary structures of the studied deposits. Finally, we highlight the significance of fluviolacustrine deposits in deciphering palaeoclimatic signatures and tectonic implications.

Theropods originated in the Late Triassic and their relations and early evolution are still topics of discussion. Within Neotheropoda, coelophysoids represent their earliest worldwide radiation and include most Triassic theropods, but their internal relations remain volatile. In this paper, we discuss the significance of a coelophysoid femur from the Rhaetian Tytherington fissures near Bristol, UK. The specimen belongs to a small-sized individual and is complete, but for the fourth trochanter blade. The most distinctive aspects of the femur are a sharply pointed lateral condyle and the pentagonal distal outline. The features that supposedly correlate with ontogenetic development, in addition to several well-developed scars, indicate it probably pertains to a mature individual. Its inclusion in a taxon-character matrix recovered the specimen within Coelophysoidea, but created a polytomy encompassing all members of the group. A definitive referral of the femur to the previously recorded coelophysoid Pendraig milnerae is precluded by the lack of overlap in diagnostic anatomical parts, the paucity of specimens from the Bristol Channel Triassic fissures, and the possible geological age difference between them.

The complexity of subglacial till sedimentology is discussed at the microscale to develop a revised model of microstructure evolution and development in subglacial tills. Mapped thin sections from the Northwest Territories and southern Ontario, Canada reveal a myriad of microstructures. Discussion of the relevance and meaning of these microstructures leads to a new revised model of subglacial soft sediment deformation to account for the development and evolution of these microstructures. The model is time-transgressive such that over time both pervasive and non-pervasive deformation conditions persist repetitively within the subglacial till environment under mixed rheologies. Microstructure types appear to be sequential in development and, during progression, are partially or wholly overprinted, destroyed, rotated, and suffer further subsequent deformation, or remain intact but intercalated with structures of other later or earlier deformation phases. This new revised model helps explain that the vagaries of till microsedimentology can be accounted for and, in most instances, predicted.

An almost complete ichthyosaur skeleton 10 m long was discovered in January 2021 at the Rutland Water Nature Reserve in the county of Rutland, UK. This was excavated by a small team of palaeontologists in the summer of the same year. Nicknamed ‘The Rutland Sea Dragon’, this almost fully articulated skeleton is an example of the large-bodied Early Jurassic ichthyosaur Temnodontosaurus. The specimen was analysed in situ, recorded (including a 3D scan using photogrammetry), excavated and removed from the site in a series of large plaster field jackets to preserve taphonomic information. Significantly, the specimen is the largest ichthyosaur skeleton to have been found in the UK and it may be the first recorded example of Temnodontosaurus trigonodon to be found in the country, extending its known geographic range significantly. It also represents the most complete skeleton of a large prehistoric reptile to have been found in the UK. We provide an account of the discovery and describe the methods used for excavating, recording and lifting the large skeleton which will aid palaeontologists facing similar challenges when collecting extensive remains of large and fragile fossil vertebrates. We also discuss the preliminary research findings and the global impact this discovery has had through public engagement.

A calculus is a solid mineral concretion such as a kidney stone, bladder stone, gall stone or stomach stone that forms naturally in a body under certain dietary or environmental conditions. Calculi that form in the gastrointestinal tract are enteroliths and these are often near-spherical objects, sometimes with a hollow centre, with a concentrically layered structure composed of radiating crystals oriented perpendicular to the surface. They are known in the archaeological record but are almost entirely absent from the fossil record, most likely due to them simply not being recognised for what they are. We describe a fossil calculus from the Upper Kimmeridge Clay (Upper Jurassic, c., 150 million years old) marine deposit at Kimmeridge in Dorset, UK. This is the oldest calculus known from the fossil record with previous confirmed records from the terrestrial Oligocene of Colorado and the marine Upper Cretaceous Chalk of Germany: it extends the temporal range of known calculi in the fossil record by at least 59 million years. Although there are a wide range of potential hosts, the Kimmeridge calculus may have been produced by a large marine reptile.

The Paleogene outlier at Collier's End, Hertfordshire lies on the northern rim of the London Basin. This small outlier has archaeological and geological significance. Silica-cemented concretions of Hertfordshire Puddingstone lie within a regionally mappable pebble bed. The first discovery of a Roman quarry to recover puddingstone for manufacture of querns was made in the outlier. A rare complete section from the Chalk Group up through the Paleogene was temporarily exposed in 2021 and is recorded here. The Paleogene shows features that may be associated with the Paleocene–Eocene Thermal Maximum (PETM). The chalk in the new exposure is Late Coniacian. This age provides further evidence of relatively deep erosion of the chalk in this area, as erosion of chalk at the crest of a regional dome preceded advances and retreats of the western shore of the Paleogene North Sea. These events may be linked to the early development of the Icelandic mantle plume.