Proceedings of the Geologists Association最新文献

During the Oxfordian, sea-level rise created widespread carbonate platform deposition on the margins of Neotethys, although some areas remain poorly described. One such area is the Saharan Atlas of Algeria. Accordingly, the middle Oxfordian Theniet Et-Temar Formation at a new locality, Kef El Meleh, is described for the first time. Formed of marl/limestone cycles, 6 broad microfacies are present within the limestones, representing deposition in lagoon, shoal and nearshore environments. Whilst overall shallowing-up is evident, it is unclear if the smaller scale marl–carbonate cycles represent higher frequency shallowing-up, or allocyclic depositional patterns.

The Theniet Et-Temar Formation contains an important archive of macrofossils and microfossils. Of note at Kef El Meleh is the presence of a microfacies rich in dasycladalean algae, notably Salpingoporella annulata Carozzi, 1953. The specimens conform well to the type and subsequent descriptions. The assemblage is effectively monospecific in terms of algae, although the larger foraminifera Alveosepta jaccardi (Schrodt, 1894) is present. This record extends the knowledge of the distribution of S. annulata within Neotethys, especially within the Oxfordian, for which previous records are limited in comparison to those for the later Jurassic and Early Cretaceous.

A small collection of coprolites (fossilised faeces) is described from the Upper Couche III Bone Bed (latest Maastrichtian) phosphate horizon, approximately 2 m below the K/Pg boundary of Sidi Chennane Quarry in the Ouled Abdoun phosphate basin, Khouribga Province, Morocco. The coprolites have a distinctive morphology that identifies them as belonging in the ichnogenus Alococopros. This is the first record of the ichnogenus from the Late Cretaceous of Morocco. The coprolites are assigned to A. milnei isp. nov. Inclusions of triturated and polished phosphate debris in some specimens suggest that crocodilians or chelonians may have been the possible producer.

In bedrock-dominated upland terrains, local heterogeneity in the erodibility of rock masses is a critical but under-explored factor constraining sediment erosion, mobilisation and transport. Here we examine how fault-related fracturing controls variations in the erodibility and grain-size of bedrock source material at the hillslope-scale. We then assess how this influences the evolution of slope sediment systems using a case-study from the Southern Uplands, Scotland, UK. Faults are associated with fracture densities that are an order of magnitude greater than background joint- and bedding-related fractures in weakly metamorphosed sedimentary rocks. Thus, fault zones are enhanced source areas yielding more abundant, smaller clasts. They are associated with enhanced erosion, gullying and debris flows, and the development of blanket colluvium on steep open hillsides. The orientation at which faults intersect the hillslope constrains the evolution of the sediment system. Faults with trends closely aligned to the direction of slope are associated with higher erosion via confined-channel debris flow activity in strongly coupled gullies. Faults that are oblique to slope direction disrupt and segment gully systems developed on minor transfer faults. Overall, faults that are oblique to slope direction are associated with lower erosion and give rise to decoupling within debris flow systems. Inclusion of geological weighting parameters in the formulation of a sediment connectivity index to characterise the effect of faulting on the erodibility and mobility of source material improves correspondence of the model with observations and provides a simple approach that could be adapted for other sources of geological heterogeneity.

The first plate loboliths of scyphocrinitid crinoids to be found in Thailand are present in abundance near the top of a formation of Siluro-Devonian limestone in the Ban Tha Kradan area of Kanchanaburi province, western Thailand. Associated conodonts include the upper Ludlow–Pridoli Zieglerodina remsheidensis s.l. and confirm the near cosmopolitan occurrence of loboliths close to the Siluro-Devonian boundary.

In this study, we integrated cores and wireline logs to evaluate the petrographical and petrophysical properties of the Late Miocene Abu Madi sandstone reservoir from the onshore WAK gas field. Thin section petrographic analyses indicate that the reservoir consists of coarse to fine-grained, poorly sorted, subangular to subrounded glauconitic quartz arenites exhibiting high mineralogical maturity, poor textural maturity, and good volume of intergranular porosity. Based on the downhole pressure data, we estimated that the gas gradient was somewhere between 0.24 and 0.26 psi/m. The SEM images suggest the pore filling authigenic chlorite and kaolinite cementation to be the dominant diagenetic process reducing the reservoir quality. The presence of concavo-convex grain contacts in the reservoir samples is indicative of a moderate degree of mechanical compaction by burial load. The massive sandstone reservoir facies represents stacked braided fluvial channels deposited during a lowstand system tract unconformably above the Qawasim Formation. Based on well log-based petrophysical analyses, the Abu Madi reservoir has a total porosity of 17–20 % with 14.6–18.3 % effective porosity and 39.4 to 47.9 % water saturation. Gross reservoir thickness varies between 28.3 and 51.1 m, whilst the net pay thickness ranges between 18.4 and 43.7 m, which translates to a high net-to-gross (N/G) ratio of 0.65–0.84. Lateral distribution of the petrophysical parameters infers a superior reservoir quality towards the central part of the studied field which should be targeted for future infill development well drilling. The reservoir heterogeneity was mapped to substantially decrease the uncertainty of future drilling.

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.