Abstract Avalonia, defined by its distinctive uppermost Ediacaran–Ordovician overstep sequence, extends from New England through Atlantic Canada to Wales. It unconformably overlies: (1) parts of one cratonic Neoproterozoic arc that which records several pulses at: 760–730 Ma, 680–600 Ma and 580–540 Ma; (2) an 800–760 Ma passive margin sequence; and (3) c. 976 Ma isolated plutons, possibly basement. Comparisons with modern arc dimensions suggest the dip of the Benioff Zone ranged from c. 22° W in Newfoundland to c. 52–67° elsewhere. A 600–580 Ma hiatus in arc magmatism in Cape Breton Island is attributed to overriding an oceanic plateau, leading to a 15° decrease in the dip of the Benioff Zone. The Collector magnetic anomaly along the Grand Banks and the Minas Fault is inferred to mark the Neoproterozoic southern margin of the Avalon Plate consisting of leaky transform faults and trench segments characterized by magnetite serpentinite mantle wedge beneath forearcs. The Minas Fault/Collector Anomaly connects similar arc units in Cape Breton Island and southern New Brunswick, suggesting that they were already offset by the Minas transform fault in the late Neoproterozoic. Similar tectonic, palaeomagnetic and isotopic data in the Timan Orogen of Baltica suggest that Avalonia may correlate with the Kipchak arc.

Abstract Although the Rheic Ocean was the widest to be closed during the assembly of Pangaea, its suture zone is dominated by a younger (Rhenohercynian) Wilson Cycle. The present paper briefly summarizes the Rhenohercynian and reviews the relicts of the Rheic. The absence of a Rheic orogen is mainly due to bipolar subduction of the Rheic Ocean, which created two magmatic arcs and largely destroyed the passive margin prisms, thus depriving the collision zone of building material. Also, displacement of Variscan zones in England, France and Germany along a curvature of the dextral Bristol/Bray/Bohemia shear zone has effected their anticlockwise rotation. Younger, ENE-trending reverse faults have truncated the NE-trending structural boundaries and excised pre-Devonian, Rheic-related rocks west of the River Rhine, while the northern Rheic Arc and Cambrian–Silurian deposits of the Rheic Ocean have been preserved further east. Opening of the Rhenohercynian successor ocean to the Rheic put a brake on plate convergence and hindered formation of a large collisional belt. Scarce relicts of the southern Rheic Arc and rocks with Silurian deformation exist in the (largely eroded) upper plate of the Rhenohercynian collisional belt, mostly in the form of clasts and detrital zircons in Upper Devonian/lower Carboniferous flysch and in tectonic mélange at the base of the allochthon.

Abstract The Chalk is an unusual karst aquifer with limited cave development, but extensive networks of smaller solutional conduits and fissures enabling rapid groundwater flow. Small-scale karst features (stream sinks, dolines, dissolution pipes, and springs) are common, with hundreds of stream sinks recorded. Tracer velocities from 27 connections between stream sinks and springs have median and mean velocities of 4700 and 4600 m d −1 . Tests to abstraction boreholes also demonstrate very rapid velocities of thousands of metres per day. Natural gradient tests from observation boreholes have rapid velocities of hundreds of metres per day. There is strong geological control on karst with dissolution focused on stratigraphical inception horizons. Surface karst features are concentrated near the Paleogene boundary, or where thin superficial cover occurs, but rapid groundwater flow is also common in other areas. The Chalk has higher storage and contaminant attenuation than classical karst, but recharge, storage and flow are influenced by karst. Point recharge through stream sinks, dolines, losing rivers, vertical solutional fissures, and soakaways enables rapid unsaturated zone flow. Saturated zone networks of solutional fissures and conduits create vulnerability to subsurface activities, and enable long distance transport of point source and diffuse pollutants, which may be derived from outside modelled catchment areas and source protection zones.

Abstract The Chalk is a strategically important aquifer in the UK, but it is at risk of contamination, with impacts on abstractions, because of extensive outcrop. Assessments of the risk of contamination impacting water supply are commonly based on bulk aquifer parameters, usually reported for abstraction wells, and do not consider the macro- and micro-scale variation at the site and within the Chalk succession. The presence of less permeable layers is significant in restricting contaminant entry into the aquifer, pushing the contaminants into fractures and voids, where their flow is limited by density differences that cause hydrocarbons to smear into micro-fractures. Dense solvents flowing to depth are further impacted by the presence of lower permeability layers within the Chalk, while horizontal flow is affected by fractures and faults. Porewater concentrations of contaminants are limited, by pore throat size and limited connectivity, to low concentrations of the most soluble compounds, but are characterized by electron acceptors that are observed as reduced and oxidized species. The combination of macro- and micro-scale physical structures, combined with natural attenuation, means that initial risk assessments for hydrocarbons and solvents in Chalk can be highly conservative and should be supported by further targeted investigation.

Abstract This chapter describes Lower Jurassic second-order sequences J00 and J10, and their component third-order sequences J1–J6 and J12–J18. Two sequences (J1 and J3) are new, four sequences (J2, J4, J12 and J16) are amended and one sequence (J17) is renamed. A significant unconformity at the base of the J12 sequence (Upper Sinemurian) is present near the base of the Dunlin Group in the North Viking Graben–East Shetland Platform and in the Danish Central Graben, and correlates with an equivalent unconformity around the margins of the London Platform, onshore UK. A marked unconformity at the base of the J16 sequence is recognized in the North Viking Graben and onshore UK, where it is related to structural movements on the Market Weighton High, eastern England. Several levels of carbon enrichment (carbon isotope excursions (CIEs)) and associated geochemical changes tie to J sequences defining maximum flooding surfaces: the Upper Sinemurian CIE equates to the base J6 maximum flooding surface (MFS), the basal Pliensbachian CIE ties to the base J13 MFS, the basal Toarcian CIE relates to the base J17 MFS and the Toarcian Ocean Anoxic Event corresponds with the base J18 MFS.

ABSTRACT Relationships between the weather and earthquakes have been suspected for over 2400 yr. However, scientific evidence to support such relationships has grown only since the 1980s. Because faults in Earth’s crust are generally regarded as critically stressed, small changes in stress and pore-fluid pressure brought about by rainfall, snow, and atmospheric pressure and temperature variations have all been proposed to modulate seismicity at local and regional scales. Elastic static stress changes as low as 0.07 kPa and pore-fluid pressure changes as low as 0.5 kPa have been proposed to naturally trigger earthquakes. In the UK, the spatial distributions of onshore earthquakes and rainfall are highly nonuniform and may be related; the wetter and most naturally seismically active areas occur on the west side of the country. We found significant spatial and temporal relationships between rainfall amount and the number of earthquakes for 1980–2012, suggesting larger volumes of rainfall promote earthquake nucleation. Such relationships occur when human-induced seismicity is included or excluded, indicating that meteorological conditions can also modulate seismicity induced by subsurface anthropogenic activities such as coal mining. No significant relationships were observed for monthly time lags, suggesting that the triggering effect of rainfall in the UK is near-instantaneous or occurs within 1 mo. With global climate changing rapidly and extreme weather events occurring more frequently, it is possible that some global regions may also experience changes in the spatial and temporal occurrence of earthquakes in response to changes in meteorologically induced stress perturbations.