Tectono-stratigraphic evolution and crustal architecture of the Orphan Basin during North Atlantic rifting

The Orphan Basin is located in the deep offshore of the Newfoundland margin, and it is bounded by the continental shelf to the west, the Grand Banks to the south, and the continental blocks of Orphan Knoll and Flemish Cap to the east. The Orphan Basin formed in Mesozoic time during the opening of the North Atlantic Ocean between eastern Canada and western Iberia–Europe. This work, based on well data and regional seismic reflection profiles across the basin, indicates that the continental crust was affected by several extensional episodes between the Jurassic and the Early Cretaceous, separated by events of uplift and erosion. The preserved tectono-stratigraphic sequences in the basin reveal that deformation initiated in the eastern part of the Orphan Basin in the Jurassic and spread towards the west in the Early Cretaceous, resulting in numerous rift structures filled with a Jurassic–Lower Cretaceous syn-rift succession and overlain by thick Upper Cretaceous to Cenozoic post-rift sediments. The seismic data show an extremely thinned crust (4–16 km thick) underneath the eastern and western parts of the Orphan Basin, forming two sub-basins separated by a wide structural high with a relatively thick crust (17 km thick). Quantifying the crustal architecture in the basin highlights the large discrepancy between brittle extension localized in the upper crust and the overall crustal thinning. This suggests that continental deformation in the Orphan Basin involved, in addition to the documented Jurassic and Early Cretaceous rifting, an earlier brittle rift phase which is unidentifiable in seismic data and a depth-dependent thinning of the crust driven by localized lower crust ductile flow

Anxiety and Depression in Adults with Autism Spectrum Disorder: A Systematic Review and Meta-analysis

Adults with autism spectrum disorder (ASD) are thought to be at disproportionate risk of developing mental health comorbidities, with anxiety and depression being considered most prominent amongst these. Yet, no systematic review has been carried out to date to examine rates of both anxiety and depression focusing specifically on adults with ASD. This systematic review and meta-analysis examined the rates of anxiety and depression in adults with ASD and the impact of factors such as assessment methods and presence of comorbid intellectual disability (ID) diagnosis on estimated prevalence rates. Electronic database searches for studies published between January 2000 and September 2017 identified a total of 35 studies, including 30 studies measuring anxiety (n = 26 070; mean age = 30.9, s.d. = 6.2 years) and 29 studies measuring depression (n = 26 117; mean age = 31.1, s.d. = 6.8 years). The pooled estimation of current and lifetime prevalence for adults with ASD were 27% and 42% for any anxiety disorder, and 23% and 37% for depressive disorder. Further analyses revealed that the use of questionnaire measures and the presence of ID may significantly influence estimates of prevalence. The current literature suffers from a high degree of heterogeneity in study method and an overreliance on clinical samples. These results highlight the importance of community-based studies and the identification and inclusion of well-characterized samples to reduce heterogeneity and bias in estimates of prevalence for comorbidity in adults with ASD and other populations with complex psychiatric presentations

Localized quaternary uplift of south-central England

The Early Quaternary of south-central England is characterized by uplift, as is indicated by the river gravels that extend intermittently from Oxfordshire, through Northamptonshire, to Lincolnshire. The earliest of these gravels contain abundant quartz and quartzite clasts derived from Lower Triassic conglomerates in the West Midlands, but later deposits contain progressively larger amounts of locally derived Jurassic sediments. This compositional change is associated with the incision of the rivers that flowed eastwards from the West Midlands. Subsequently, the headwaters of some of these rivers were diverted towards the Bristol Channel and their suspended material was deposited on the outer parts of the UK continental shelf and slope. The area of incised drainage (Gloucestershire to Lincolnshire) did not extend to East Anglia (in the east) or to Somerset (in the west). Both these coastal regions contain several marine horizons showing that the area of uplift did not include the whole of southern England. The uplift cannot therefore be attributed to eustatic changes in sea level. The area of uplift is centred on the broad topographic depression of the English Midlands and corresponds approximately to the outcrop of thick (c. 1 km) Upper Triassic and Lower Jurassic mudrocks. We have used an Ordnance Survey 50 m × 50 m topographic 'grid' to estimate the amount of mudrocks that has been removed from the depression and 2D flexural unloading models to calculate the tectonic uplift that resulted, for various assumptions of the effective elastic thickness (which is determined by the flexural rigidity) of the lithosphere. The amount of material removed is in accord with what is known of the volume of Quaternary deposits offshore, and the uplift accounts for the incised plateau surfaces of the flanking Cotswold Hills and the high ground of Northamptonshire to the east, and the Forest of Dean and the hills of Herefordshire to the west

The Caledonian Orogeny redefined

Recent advances in our understanding of Palaeozoic tectonics, and in the precise dating of tectonic events require exact definitions of terminology. The Caledonian Orogeny is here redefined to include all the Cambrian, Ordovician, Silurian and Devonian tectonic events associated with the development and closure of those parts of the Iapetus Ocean, which were situated between Laurentia (to the NW) and Baltica and Avalonia (to the SE and east). We suggest that the term 'Caledonian Orogeny' be restricted in this geographic sense, but that (as in modern usage) it continues to encompass a series of tectonic, or orogenic, phase (related to arc-arc, arc-continent and continent-continent collisions as Iapetus was closing). Many of these phases have been named; these and many more unnamed events are defined as orogenic phases (local components) of the Caledonian Orogeny. Some of these phases were synchronous over long distances, whereas others were diachronous. The whole Caledonian Orogeny occupied a time interval of around 200 Ma. Thus the term Caledonian should not be used to indicate age

The Caledonian Orogeny redefined

Recent advances in our understanding of Palaeozoic tectonics, and in the precise dating of tectonic events require exact definitions of terminology. The Caledonian Orogeny is here redefined to include all the Cambrian, Ordovician, Silurian and Devonian tectonic events associated with the development and closure of those parts of the Iapetus Ocean, which were situated between Laurentia (to the NW) and Baltica and Avalonia (to the SE and east). We suggest that the term 'Caledonian Orogeny' be restricted in this geographic sense, but that (as in modern usage) it continues to encompass a series of tectonic, or orogenic, phase (related to arc-arc, arc-continent and continent-continent collisions as Iapetus was closing). Many of these phases have been named; these and many more unnamed events are defined as orogenic phases (local components) of the Caledonian Orogeny. Some of these phases were synchronous over long distances, whereas others were diachronous. The whole Caledonian Orogeny occupied a time interval of around 200 Ma. Thus the term Caledonian should not be used to indicate age

The Cambrian-Silurian tectonic evolution of the northern Appalachians and British Caledonides: history of a complex, west and southwest Pacific-type segment of Iapetus

This paper is included in the Special Publication entitled 'Lyell: the past is the key to the present', edited by D.J. Blundell and A.C. Scott. This paper presents new ideas on the Early Palaeozoic geography and tectonic history of the Iapetus Ocean involved in the formation of the northern Appalachian-British Caledonide Orogen. Based on an extensive compilation of data along the length of the orogen, particularly using well-preserved relationships in Newfoundland as a template, we show that this orogen may have experienced a very complicated tectonic evolution that resembles parts of the present west and southwest Pacific Ocean in its tectonic complexities. Closure of the west and southwest Pacific Ocean by forward modelling of the oblique collision between Australia and Asia shows that transpressional flattening and non-coaxial strain during terminal collision may impose a deceptively simple linearity and zonation to the resultant orogen and, hence, may produce a linear orogen like the Appalachian-Caledonian Belt. Oceanic elements may preserve along-strike coherency for up to several thousands of kilometres, but excision and strike-slip duplication, as a result of oblique convergence and terminal collisional processes, is expected to obscure elucidation of the intricacies of their accretion and collisional processes. Applying these lessons to the northern Appalachian-Caledonian belt, we rely principally on critical relationships preserved in different parts of the orogen to constrain tectonic models of kinematically-related rock assemblages. The rift-drift transition, and opening of the Iapetus Ocean took place between c.590-550 Ma. Opening of Iapetus was temporally and spatially related to final closure of the Brazilide Ocean and amalgamation of Gondwanaland. During the Early Ordovician, the Laurentian margin experienced obduction of young, supra-subduction-zone oceanic lithosphere along the length of the northern Appalachian-British Caledonian Belt. Remnants of this lithosphere are best preserved in western Newfoundland and are referred to as the Baie Verte Oceanic Tract. Convergence between Laurentia and the Baie Verte Oceanic Tract was probably dextrally oblique. Slab break-off and a subsequent subduction polarity reversal produced a continental magmatic arc, the Notre Dame Arc, on the edge of the composite Laurentian margin. The Notre Dame Arc was mainly active during the late Tremadoc-Caradoc interval and was flanked by a southeast- or south-facing accretionary complex, the Annieopsquotch Accretionary Tract. Southerly drift of Laurentia to intermediate latitudes of c.20-25°S was associated with the compressive (Andean) nature of the arc and the accompanying backthrusting of the already-accreted Baie Verte Oceanic Tract further onto the Laurentian foreland. Equivalents of the Notre Dame Arc and its forearc elements in the British Isles have been preserved as independent slices in the Midland Valley and possibly the Northern Belt of the Southern Uplands. During the late Tremadoc (c.485 Ma), the passive margin on the eastern side of Iapetus also experienced obduction of primitive oceanic arc lithosphere. This arc is referred to as the Penobscot Arc. The eastern passive margin was built upon a Gondwanan fragment (Ganderia) that rifted off Amazonia during the Early Ordovician and probably travelled together with the Avalonian terranes as one microcontinent. The departure of Ganderia and Avalonia from Gondwana opened the Rheic Ocean. Equivalents of the Penobscot Arc may be preserved in New Brunswick and Maine, Leinster in eastern Ireland, and Anglesey in Wales. An arc-polarity reversal along the Ganderian margin after the soft Penobscot collision produced a new arc: the west-facing Popelogan-Victoria Arc, which probably formed a continuous arc system with the Bronson Hill Arc in New England. The Popelogan-Victoria Arc transgressed from a continental to an oceanic substrate from southern to northeastern Newfoundland. Rapid roll-back rifted the Popelogan-Victoria Arc away from Ganderia during the late Arenig (c.473 Ma) and opened a wide back-arc basin; the Tetagouche-Exploits back-arc basin. The Popelogan-Victoria Arc was accreted sinistrally oblique to the Notre Dame Arc and, by implication, Laurentia during the Late Ordovician. After accretion, the northwestward-dipping subduction zone stepped eastwards into the Tetagouche-Exploits back-arc basin

The genome of the obligate intracellular parasite Trachipleistophora hominis : new insights into microsporidian genome dynamics and reductive evolution

The dynamics of reductive genome evolution for eukaryotes living inside other eukaryotic cells are poorly understood compared to well-studied model systems involving obligate intracellular bacteria. Here we present 8.5 Mb of sequence from the genome of the microsporidian Trachipleistophora hominis, isolated from an HIV/AIDS patient, which is an outgroup to the smaller compacted-genome species that primarily inform ideas of evolutionary mode for these enormously successful obligate intracellular parasites. Our data provide detailed information on the gene content, genome architecture and intergenic regions of a larger microsporidian genome, while comparative analyses allowed us to infer genomic features and metabolism of the common ancestor of the species investigated. Gene length reduction and massive loss of metabolic capacity in the common ancestor was accompanied by the evolution of novel microsporidian-specific protein families, whose conservation among microsporidians, against a background of reductive evolution, suggests they may have important functions in their parasitic lifestyle. The ancestor had already lost many metabolic pathways but retained glycolysis and the pentose phosphate pathway to provide cytosolic ATP and reduced coenzymes, and it had a minimal mitochondrion (mitosome) making Fe-S clusters but not ATP. It possessed bacterial-like nucleotide transport proteins as a key innovation for stealing host-generated ATP, the machinery for RNAi, key elements of the early secretory pathway, canonical eukaryotic as well as microsporidian-specific regulatory elements, a diversity of repetitive and transposable elements, and relatively low average gene density. Microsporidian genome evolution thus appears to have proceeded in at least two major steps: an ancestral remodelling of the proteome upon transition to intracellular parasitism that involved reduction but also selective expansion, followed by a secondary compaction of genome architecture in some, but not all, lineages.Publisher PDFPeer reviewe

The late Palaeozoic relations between Gondwana and Laurussia

Reconstructions based on biogeography, palaeomagnetism and facies distributions indicate that, in later Palaeozoic time, there were no wide oceans separating the major continents. During the Silurian and Early Devonian time, many oceans became narrower so that only the less mobile animals and plants remained distinct. There were several continental collisions: the Tornquist Sea (between Baltica and Avalonia) closed in Late Ordovician time, the Iapetus Ocean (between Laurentia and the newly merged continents of Baltica and Avalonia) closed in Silurian time, and the Rheic Ocean (between Avalonia and Gondwana and the separate parts of the Armorican Terrane Assemblage) closed (at least partially) towards the end of Early Devonian time. Each of these closures was reflected by migrations of non-marine plants and animals as well as by contemporary deformation. New maps, based on palaeomagnetic and faunal data, indicate that Gondwana was close to Laurussia during the Devonian and Carboniferous periods, with fragments of Bohemia and other parts of the Armorican Terrane Assemblage interspersed between. It follows that, after Early Devonian time, the Variscan oceans of central Europe can never have been very wide. The tectonic evolution of Europe during Devonian and Carboniferous time was thus more comparable with the present-day Mediterranean Sea than with the Pacific Ocean