Proceedings of the Geologists Association最新文献

The age of the lower component of the Burtness Comb rock avalanche debris tongue, Lake District, northwest England, has been determined by in situ produced terrestrial cosmogenic (¹⁰Be) surface-exposure dating of quartz veins from three boulders. Uncertainty-weighted mean ages of 17.37 ± 0.94 ka (determined using the Loch Lomond calibration dataset) and 16.08 ± 1.25 ka (determined using the CRONUS-Earth default calibration dataset) indicate that this component of the rock avalanche occurred during deglaciation following the local Last Glacial Maximum. The surface morphology displayed by the debris indicates it likely accumulated on glacier-free terrain, suggesting that the Burtness Comb cirque glacier had decoupled from the Buttermere valley glacier at the time of debris emplacement. The debris may have travelled across the surface of a waning glacier in the upper part of the cirque. Although the upper component of the rock avalanche is as yet undated its position and configuration indicate it to be younger than the lower component and sourced from a different part of the comb headwall. The rock avalanche is only the third of 84 rock slope failures recognised in the Lake District and adjacent Howgill Fells to have been dated using ¹⁰Be. Whilst the rock avalanche is regarded as a paraglacial landform, additional ages on other members of this population are required in order to establish their temporal pattern and to propose the most probable underlying cause(s) of failure.

A temporary exposure of the nearshore marine Atherfield Clay (Lower Greensand Formation, Aptian, Early Cretaceous) in the Reigate area (Wonham Mill) of Surrey was sampled for microvertebrate remains in Autumn 2013. Samples amounting to 858 kg of sediment were washed, dried, and sieved to 0.325 mm and the residue searched for all fossil content. This is the first definitive study of the Atherfield Clay chondrichthyan fauna of Surrey. The samples yielded teeth of hybodont sharks (Planohybodus ensis, Lonchidion breve), neoselachian sharks (Heterodontus sulcatus, Cretascyllium hassei, Protospinax sp., Protolamna sokolovi, Lamnid indet., Scyliorhinus muelleri, Scyliorhinus gen. et sp. indet., Protoscyliorhinus sp.) and batoids (Belemnobatis picteti, Squatirhina sp.). The neoselachian sharks and rays all constitute the first confident records for the various genera in the Atherfield Clay of the United Kingdom. Dermal denticles and bony fish teeth are also present in the samples, which also yielded small numbers of invertebrates (ammonite and crustacean), microcoprolites (Tomaculopsis tomaculopsis) and plant remains (fern indusia). The state of preservation of the chondrichthyan material suggests that none of the specimens are derived from older strata; the fauna is indigenous. The Surrey Atherfield Clay fauna is distinct from that recorded from the Atherfield Bone Bed on the Isle of Wight and the roughly coeval boreal fauna of the Speeton Clay.

The terrestrial sediments of the Petrockstowe and Bovey basins in Devon, UK were examined. Their age is considered to be Eocene and Oligocene. The sediments (kaolinitic clays, silts, sands, gravels, and lignites) from both basins were analysed for carbon isotopes of organic material, in conjunction with total organic carbon and palynological analyses used to unravel the type of and provenance of organic matter present. Within the Petrockstowe Basin, the lowermost interval examined shows a palynological distribution dominated by phytoclasts, whilst the upper part of the core is dominated by higher concentrations of palynomorphs (up to 90 %) and an increase in amorphous organic matter consistent (up to 37 %) with a change from sand-filled fluvial channels followed by an ephemeral lake or lake margin setting. Our palynological data from the South John Acres Lane Quarry section, Bovey Basin, show that within the lignites palynomorphs are high again (up to 95 %) consistent with them representing more ephemeral lakes or lake margins periodically exposed with mires. Our palynological data set further allows us to determine that isotope trends are not overly determined by the source of carbon in the basins. Our study suggests that the observed patterns were primarily produced by variations of the isotope ratios of terrestrial atmospheric carbon reservoirs. Even with our less than well constrained biostratigraphical control, the data indicate that the carbon isotope excursions seen in the Eocene and Oligocene could be associated with several transient carbon isotopic shifts (associated with the Paleocene–Eocene Thermal Maximum). Our findings therefore appear to lend support to the surface ocean and atmosphere behaving as coupled reservoirs at this time.

A vermetid etching trace, Renichnus arcuatus, has been described from the outer surface of a single right valve of Hyotissa hyotis from the Lower Chelif Basin, Algeria. This is the first record of vermetid etchings from the Pliocene of the Mediterranean Sea's southern coast. The vermetids responsible for the etchings used bivalve shells as a hard substrate for attachment. The vermetids used mucus nets to feed and they may have benefitted from the feeding currents of the host if they colonized a living bivalve. The palaeogeography of similar etching records indicates that vermetids were common in the Mediterranean region in the Pliocene.

The Carnian Pluvial Episode (CPE), a 1–2 Ma interval of enhanced humidity midway through the Triassic Period, has been implicated in high levels of biotic turnover in marine environments. The Carnian stage on land also saw major faunal and floral reorganisation, including the extinction of rhynchosaurs, the diversification of dinosaurs and the origin of crocodylomorphs and mammaliaforms. An imperfect fossil record and dating uncertainties, however, make establishing a firm link to the CPE much more difficult, but the picture is gradually improving as new evidence accumulates. We review observed terrestrial biotic changes and suggest that in most cases the effects of the CPE in isolation remain ambiguous or were relatively minor or reversible. Rather, the Carnian biotic change was probably a staggered response to a number of factors, including climatic, set against the backdrop of long-term rebuilding of ecosystems following the end-Permian mass extinction.

The Kula–Salihli UNESCO Geopark, western Turkey, is a tectonically and volcanically active region in which the most recent eruptions of basaltic lava, associated with scoria cone formation, were during the latest Pleistocene and the Holocene. Much older volcanism within the same volcanic province is also in evidence, with some of the older lavas capping mesa-style uplands, such that they have preserved underlying poorly consolidated sediments that would otherwise have been lost to erosion. Beneath these hill-capping lavas, above the Neogene sediments representing endorheic basin-fill, are the early gravels of the River Gediz system, forming narrowly separated terraces (separation by a few metres) thought to have been formed in response to the ~ 41 kyrs obliquity-driven climate cycles of the Early Pleistocene. The rarity of terrace preservation from this early part of the Quaternary makes this a very valuable part of the geopark, in which there is also evidence for the progressive incision into the landscape, and for periodic damming of the river system by lava eruptions, bringing about lacustrine phases that can be recognized from lake sediments and deltas that were built into the former lakes. The combination of volcanic and drainage evolutionary evidence has few if any parallels elsewhere. The geopark, which also contains sites of archaeological and historical importance, is managed sustainably in order to maximize its educational, economic, touristic and heritage value.

Lower and Middle Paleolithic archaeological sites in England risk falling through the cracks between different types of heritage conservation, since they lack recognisable structures; these sites have often benefitted from protection under geoconservation, particularly through selection as Geological Conservation Review sites, and subsequent designation as Sites of Special Scientific Interest (SSSIs). The geoconservation of key sites, particularly in the formative years of British geoconservation, has allowed combined geological and archaeological reinvestigation. This is of particular benefit to understanding Lower and Middle Paleolithic artefact assemblages, which were often collected in the later 19th–earlier 20th century and consequently lacked both detailed spatial or stratigraphic provenance and contextual geological information. As such, the ‘fine grained’ data which could be gleaned from such artefact collections was limited. Here we review the benefit of geoconservation in allowing the contextualisation of historical archaeological collections, focussing on six key English sites where geological and archaeological reinvestigation has led to important archaeological findings. In particular, the emerging evidence of chronological patterning in Lower and Middle Paleolithic artefacts makes the preservation of such deposits valuable to Quaternary science in general.