Sequence composition of the Izyayu Formation (Upper Devonian–Lower Carboniferous) in the type area – the south of Tchernyshev Uplift

Research subject. The article considers the Famennian‑Tournaisian sequence of the South-Eastern part of the Tchernyshev Uplift (North Cis-Uralian). The sequence corresponds to the Izyayu Formation.Materials and methods. The article is focused on the clarification of the stratigraphy, composition and depositional environment of this formation. Research data about the Izyayu Formation in the type area (Izyayu River) were used. The stratigraphic framework of this study included data on conodonts, foraminifers and carbonate carbon isotopic shifts.Results. In the type area under study, the Izyayu Formation corresponds to the interval from the upper part of the Famennian (upper part of the Palmatolepis marginifera utahensis conodont Zone) up to the middle part of the Tournaisian (Lower crenulata conodont Zone). The formation is 100– 120 m thick. The Izyayu Formation grades to the upper part of the deep-water Syvyu Formation in the east, and to the shallow-water Kamenka Formation and the lower part of the Ydzhid Formation. The areal of the Izyayu Formation comprises the South-Eastern part of the Tchernyshev Uplift. The Formation was deposited in the environment of a gentle prograding slope of a carbonate platform.Conclusions. The Izyayu Formation in the type area is composed of thin clayey-carbonate graded cycles. It covers the stratigraphic interval from the Zelenets Regional Stage through the Tcherepet Regional Stage. This formation is easily distinguishable by lithological features in outcrops and borehole cores.

Taxonomic revision of the snakes of the genera Palaeopython and Paleryx (Serpentes, Constrictores) from the Paleogene of Europe

Large constrictor snakes, referred to the genera Palaeopython and Paleryx, are an ecologically prominent part of the fauna of Europe during the Paleogene. Most species were named over a century ago and their taxonomy is largely based on isolated vertebrae. Furthermore, the majority of named taxa originate from imprecisely known localities within the Phosphorites du Quercy, in southern France, and thus their exact age is not known. We critically review and re-diagnose these genera based on personal examination of all existing type material, an array of new specimens, and a detailed literature review. We consider Palaeopython and Paleryx to be valid and propose vertebral characters to distinguish them. We recognize three valid species of Palaeopython, i.e. Palaeopythoncadurcensis (type species) from the Phosphorites du Quercy, Palaeopythonceciliensis from Geiseltal, and Palaeopythonhelveticus from Dielsdorf (Switzerland), and one valid species of Paleryx, i.e. Paleryxrhombifer (type species) from Hordle Cliff (England). Four other species, which were previously treated as members of Palaeopython and Paleryx, i.e. “Palaeopython” filholii and “Palaeopython” neglectus from the Phosphorites du Quercy, “Palaeopython” fischeri from Messel, and “Paleryx” spinifer from Geiseltal, are also considered as valid but pertain to other genera. Among these four taxa, “Palaeopython” fischeri has been recently assigned to its own genus, Eoconstrictor. A new genus, Phosphoroboa gen. nov. is established to accommodate “Palaeopython” filholii. We designate a lectotype for Palaeopythoncadurcensis and establish that the paralectotype maxilla and dentary are reasonably referred to this species. New material attributed to Palaeopythoncadurcensis is described from the old collections of the Phosphorites du Quercy. Paleryxcayluxi, another species established from the old collections of the Phosphorites du Quercy, is synonymized here with Palaeopythoncadurcensis. We further clarify important errors in the original description and figures of Paleryxcayluxi, identify the exact specimens that comprise the type series, and designate a lectotype. Much new material is described for Palaeopythonceciliensis from its type area in Geiseltal and intracolumnar variation is considered. We describe additional vertebral and cranial material of Paleryxrhombifer from its type area in Hordle Cliff. Based on this cranial material, we suggest non-booid affinities for Paleryxrhombifer. We designate a lectotype for Paleryxdepressus and agree with its previous suggested synonymy with Paleryxrhombifer. We re-describe the lectotype and paralectotypes of “Palaeopython” neglectus and refer and describe new material of this species from the Phosphorites du Quercy, paying special attention to intracolumnar variation; we also defer a decision on its generic relations until more abundant and complete material can be studied. We describe new vertebral material of the booid Eoconstrictor cf. fischeri from Geiseltal; similar material was previously known only from Messel and Dielsdorf. We determine that Eoconstrictorfischeri contains two distinct and unrelated species and describe intracolumnar variation in the nominotype. We clarify certain issues regarding the type series of Paleryxspinifer, designate a lectotype, and report previously unrecognized cranial material associated with the latter specimen; we transfer this species to Eoconstrictor based on cranial features and recombine it as Eoconstrictorspinifer comb. nov. We finally describe much new vertebral and cranial material of Phosphoroboafilholii comb. nov. from the Phosphorites du Quercy (both from the old collections but also from the late Eocene localities of Escamps A and C), paying special attention to intracolumnar variation. Based on this cranial material from Escamps, we identify Phosphoroboa gen. nov. as a booid. An analytical approach is undertaken in many isolated remains in order to quantify vertebral structures and assess intracolumnar variation, as well as associating isolated cranial elements to vertebral-based taxa. 3D models of the type material of the Geiseltal and Messel taxa are presented. The importance of vertebrae in the taxonomy of fossil Constrictores is addressed, although it is acknowledged that it is cranial material that can afford the most reliable phylogenetic conclusions. The diversity, distribution, biogeographic origins, and final demise and extinction of large Constrictores in the Paleogene of Europe are discussed.

Metamorphism of the Buchan type-area, NE Scotland, and its relation to the adjacent Barrovian domain

The metamorphism of the Buchan block in northeast Scotland, and its relation to the Barrovian domain to its west, have been reassessed from consideration of mineral assemblages, microstructures, phase equilibrium modelling and monazite U-Pb geochronology. Zones of increasing metamorphic grade surround a central low grade domain (biotite zone) and define a northward-opening, U-shaped metamorphic map pattern ascribed to post-metamorphic folding. The eastern and southern Buchan domain show the classic Buchan-type prograde sequence cordierite – andalusite – sillimanite – migmatite/gneiss, representing a metamorphic field gradient of gently increasing pressure between 2.5-3.0 kbar, ∼550 °C and 3.5-4.0 kbar, ∼750 °C. A lower pressure metamorphic field gradient (by less than ∼0.5 kbar) is interpreted for the northeastern Buchan domain. The west Buchan domain shows a prograde sequence of staurolite+andalusite – sillimanite – gneiss/migmatite, representing a metamorphic field gradient higher by ∼1 kbar or less than the classic sequence. Uniquely in the northwestern Buchan domain is a staurolite-cordierite-andalusite domain in which staurolite-bearing schists are interpreted to have been overprinted by cordierite+andalusite assemblages. Monazite U-Pb geochronology of schists and gneisses from the Buchan block, including the Cowhythe and Ellon gneisses, yields ages in the range 470 ±5 Ma, supporting geological evidence that the gneisses are metamorphosed Dalradian strata rather than older basement gneisses. The metamorphic ages are similar to the ages of mafic igneous intrusions in the Buchan block, even though many of the exposed intrusions post-date the regional metamorphic zones. The Buchan metamorphic zones are truncated to the west by the Portsoy-Duchray Hill lineament (PDHL), a ductile shear zone that juxtaposes the Buchan rocks against higher-pressure, lower-temperature (kyanite-bearing) Barrovian schists to the west. A 2-15 km wide corridor of andalusite pseudomorphed by kyanite occurs between the PDHL and the Keith shear zone to its west. Monazite geochronology of the Barrovian rocks west of Portsoy shows little evidence of the c. 470 Ma signature of the Buchan block, instead yielding a dominant cluster of ages at c. 450 Ma and a more poorly defined grouping at c. 490 Ma.Supplementary materials: Analytical methods, thermodynamic modelling; tables S1-S13; figures S1-S5 are available at https://doi.org/10.6084/m9.figshare.c.5536745

A new lithostratigraphic framework and unified nomenclature for the Nsuze Group of the Nkandla sub-basin, southern Kaapvaal Craton, South Africa

During the early 20th century the term Insuzi Series, later reclassified as the Nsuze Group of the Pongola Supergroup, was proposed for a volcano-sedimentary succession exposed in the upper Nsuze River valley in central KwaZulu-Natal, South Africa. Subsequently, however, there has been little consensus on lithostratigraphic frameworks within the type area, and limited correlation with the exceptionally well-defined stratigraphy within the main Pongola basin. Recent mapping, combined with newly acquired high-resolution aeromagnetic data, satellite imagery, and available published geochronological data suggest that previously published schemes within the Nkandla sub-basin require revision. Utilising important regional marker units, as well as the stratigraphic positions of distinct sedimentary facies within the otherwise volcanic Nsuze Group, a working model is proposed. Lithostratigraphic units are well represented in the Mhlatuze and Nkandla inliers with examples from these areas given prominence. Where exposed, potential correlates within the Nsuze nappe complex are discussed. Within the proposed scheme the siliciclastic Mantonga Formation forms the base of the Nsuze Group, nonconformably overlying basement granitoids of the Kaapvaal Craton within the Mhaltuze Inlier. Mafic volcanics of the Nhlebela Formation overlie the Mantonga Formation in the inlier. These two lower units are, however, not exposed elsewhere in the sub-basin. The sedimentary White Mfolozi Formation forms the base of the succession in the Nkandla Inlier. Diamictites and stromatolite-bearing carbonate lithologies unique to this unit are utilised for regional third-order correlations with the type-area in the White Mfolozi Inlier. Mafic volcanics of the Agatha Formation overlie the White Mfolozi Formation in all exposures, but are most extensively developed within the Mdlelanga syncline of the Nkandla Inlier. Sedimentary and volcaniclastic lithologies of the Mkuzane Formation cap the Nsuze Group in the Mhlatuze and Nkandla inliers. Thickness of this formation is, however, highly variable having been subjected to pre-Vutshini Formation erosion. Through detailed reinterpretation of the stratigraphy of the Nkandla sub-basin we present a third order, (formation) scale, lithostratigraphic scheme encompassing all the formational units of the currently accepted stratigraphy within the main Pongola basin. This working model has the potential for lower-ranking units to be identified and be placed at their appropriate stratigraphic levels in future.

Prognathodon (Squamata, Mosasauridae) from the Maastrichtian chalk of Denmark

Two mosasaur tooth crowns collected from the Maastrichtian chalk sequences of Stevns Klint and Møns Klint are here assigned to Prognathodon, a mosasaur genus hitherto unknown from Denmark. Together with previous records of the mosasaurs Plioplatecarpus, Mosasaurus and Carinodens, these new finds of Prognathodon document the coexistence of four mosasaurid genera in the Danish chalk and underscore simi-larities to coeval assemblages from the Maastrichtian type area in the Netherlands and Belgium.

Carbon isotope trends in north-west European mosasaurs (Squamata; Late Cretaceous)

The carbon stable isotope composition (δ13C) of tooth enamel in mosasaurid squa-mates reflects aspects of their diet and diving behaviour. Here we present new δ13C data for such marine squamates from the Maastrichtian of Denmark and compare these with results obtained in previous studies from the lower-latitude type area of the Maastrichtian Stage (latest Cretaceous; 72.1–66.0 Ma) in the south-east Nether-lands and north-east Belgium. For the Danish samples, there is a weak correlation between mosasaur body size and δ13C values, with larger-sized taxa having lower δ13C values, comparable to what has previously been observed for mosasaurs from the Maastrichtian type area.

The stratigraphy of the Kimmeridge Clay Formation (Jurassic) of the Vale of Pickering, Yorkshire, UK

The Upper Jurassic Kimmeridge Clay Formation (KCF) underlies much of the Vale of Pickering where it is almost wholly concealed by the Cretaceous Speeton Clay and Quaternary deposits. There are few KCF inland or coastal exposures in Yorkshire with the result that the succession was stratigraphically poorly known until the 1970s oil crisis when the British Geological Survey (BGS) drilled continuously-cored boreholes at Marton and Reighton to examine the formation as a possible source of hydrocarbons. These were supplemented in 1987 by continuously-cored boreholes drilled at Marton, Reighton, Ebberston and Flixborough by the Institut Français du Pétrole (IFP) for hydrocarbons research. Taken together, the boreholes have enabled the lithological, palaeontological, geochemical and geophysical characters of the full thickness of the formation to be examined. Comparison of the KCF successions proved in Yorkshire with those in the adjacent North Sea, the East Midlands and the Dorset coast type area, shows marked variations in thickness related to penecontemporaneous faulting. However, there are only minor variations in the lithologies and faunas at any particular stratigraphical level. This appears to be due to a combination of Milankovitch-driven climatic fluctuations and pulsed variations in sea level which combined to produce similar depositional conditions throughout the English KCF at any one time. The chronostratigraphical classification of the KCF developed in southern England has therefore been shown to be applicable to the Yorkshire outcrop and the southern North Sea. The changes in sea level may be eustatic rather than regional events, but there is insufficient paleontological evidence to enable them to be correlated with confidence with those of the standard Jurassic sea-level curve.