Proceedings of the Geologists Association最新文献

Sphenodontids are a group of reptiles that were diverse and global for much of the Mesozoic but today they are only represented by the New Zealand tuatara. Here we describe new sphenodontid remains coming from the Cretaceous (Maastrichtian) Los Alamitos Formation, at Río Negro province, Argentina. Previous reports in the stratigraphical unit included an indeterminate sphenodontid and the enigmatic Kawasphenodon. The new material here reported includes an isolated and incomplete dentary and a palatine bone. The dentary belongs to a small taxon having quadrangular teeth and an interlocked mandibular symphysis. The palatine shows compressed teeth and a fang-like canine. These specimens probably belong to two new taxa. These, together with Kawasphenodon, suggest that Maastrichtian sphenodontians from northern Patagonia were at least as diverse as those reported from Cenomanian beds. This contrasts with the poorer record of lizards in the same beds. However, the record of Maastrichtian sphenodonts in southern Patagonia is restricted to a single finding of a Sphenodontine sphenodontid. In Australasia the sphenodont record is also restricted to Cenozoic sphenodontines, very similar to extant Sphenodon species. The currently available fossil record suggests that northern Patagonian rhynchocephalians were more morphologically diverse than those of southern Patagonia and Australasia during the Cretaceous, probably reflecting another faunistic particularity of the 'Weddelian Bioprovince'.

During the Late Triassic and Early Jurassic, the area around Bristol and South Wales was an archipelago of islands occupied by diverse small-sized tetrapods. The largest of these palaeo-islands was Mendip Island, now forming the Mendip Hills, and the location of some famous fossiliferous sites. These sites have not been described in detail before, and we present new data on three of them. Highcroft has yielded only sparse remains of rhynchocephalians, and Batscombe famously the gliding reptile Kuehneosuchus latissimus. Emborough yielded the richest fauna of the three, abundant pseudosuchians including crocodylomorphs as well as the gliding reptile Kuehneosaurus latus, rare trilophosaurs, a probable thalattosaur, rhynchocephalians, and the mammal Kuehneotherium. These include some of the last known taxa of clades that died out in the end-Triassic mass extinction. We report a new taxon of sphenosuchid crocodylomorph similar to Saltoposuchus and a find of Pachystropheus, an aquatic reptile shared with Holwell and the bedded Rhaetian at Blue Anchor Point, Aust and Westbury Garden Cliff. The discovery of a fish vertebra strengthens the model of Emborough fissure filling in a marginal marine location. The Emborough fauna differs from coeval assemblages from Cromhall, Tytherington and Ruthin in the scarcity of sphenodontians and the absence or great rarity of procolophonids as well as the abundance of kuehneosaurids and crocodylomorphs.

The Pridoli (upper Silurian) of Saaremaa Island, Estonia contains crinoid holdfasts and pluricolumnals that are colonized by many epibionts (encrusters). They comprise Palaeoconchus tenuis, Cornulites sp., Anticalyptraea calyptrata, Favosites sp., as well as hederelloids, cystoporate and trepostome bryozoans, and stromatoporoids. The taxonomic composition of encrusters of crinoid pluricolumnals differs from that of crinoid holdfasts. The encrusters on pluricolumnals were numerically dominated by trepostome bryozoans and microconchids; the other taxa formed just a minor part of the sclerobiont association. The trepostomes dominate by the area of encrustation on pluricolumnals. The encrusters on holdfasts were numerically dominated by microconchids, followed by cystoporate and trepostome bryozoans; the other taxa formed a minor part of the sclerobiont association. The bryozoans dominated by the encrustation area on holdfasts. There is likely a negative correlation between potential substrate mobility and abundance of microconchids. The cystoporates colonized only relatively stable substrates such as crinoid holdfasts whilst trepostomes colonized also mobile substrates.

The mixed siliciclastic–carbonate Teniet El Klakh Formation (Middle Jurassic, Bajocian) mainly consists of a monotonous, clay and fine-grained sandstone alternation with some intercalated carbonate beds. The trace fossil record displays moderate to high ichnological diversity with different behaviours, consisting of 28 ichnotaxa belonging to 23 ichnogenera: Arenicolites isp., Bolonia lata, Chondrites targionii, Chondrites isp., Circulichnis montanus, Curvolithus simplex, Diplocraterion paralellum, Glockerichnus isp., Gyrochorte comosa, Helminthopsis abeli, Lockeia isp., Megagrapton cf. irregulare, M. submontanum, Monomorphichnus cf. multilineatus, Neonereites cf. biserialis, Nereites isp., Ophiomorpha isp., Palaeophycus cf. striatus, P. tubularis, Palaeophycus isp., Planolites isp., Protovirgularia dichotoma, Protovirgularia isp., Rhizocorallium commune var. irregulare, Rutichnus irregularis, Skolithos linearis, Taenidium cf. serpentinum, and Thalassinoides suevicus. The distribution of these trace fossils in space and time is controlled by various environmental features, mostly referred to the accumulation of organic matter in softground substrate during short phases of low hydrodynamics in well-oxygenated environments, thus allowing the occurrence of abundant and diverse invertebrates frequently dominated by deposit-feeders. The integrated sedimentological and ichnological features suggest that the Teniet El Klakh Formation had been deposited in a storm-influenced continental shelf setting ranging from the lower offshore to the lower shoreface zones with fluctuating energy regime, corresponding to the archetypal and proximal Cruziana ichnofacies transitional to the Skolithos ichnofacies. The ichnological assemblage described herein is original and rather unique, since most of trace fossils are reported herein for the first time from the Ksour Mountains.

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.