Carboniferous geology of Northern England

The British Geological Survey (BGS) has produced a wholesale rationalisation of Carboniferous lithostratigraphical nomenclature. This presentation describes the Carboniferous stratigraphy of northern England, illustrated with research carried out as part of recent BGS mapping projects. During the Tournaisian and Visean a phase of north–south rifting resulted in the development of grabens and half-grabens, separated by platforms and tilt-block highs. Visean marine transgressions resulted in the establishment of platform carbonates, which gradually onlapped raised horst and tilt-block highs. The evolution of one such tilt-block high, the Askrigg block, and associated Great Scar Limestone Group, is described in detail. During late Visean times a cyclic succession of fluvio-deltaic clastics, marine reworked sandstones and shallow-shelf marine carbonates (Yoredale Group) dominated across northern England, terminating deposition of the platform carbonates. To the south of the Craven fault system, which defines the southern margin of the Askrigg Block, the block and basin structures persisted, though generally the high subsidence rates created a province dominated by hemipelagic mudstones and carbonate/siliciclastic turbidites (Craven Group). Cessation of rifting during the late Visean in the area between the Southern Uplands and the Wales–Brabant High resulted in a period dominated by thermally induced regional subsidence during Namurian and Westphalian times, with formation of the Pennine Basin. During early Namurian times fluvio-deltaic systems started to feed siliciclastic sediment into the northern margin of the basin (Millstone Grit Group). Initial deposition in the basinal areas is marked by the formation of thick turbidity-fronted delta successions. By late Namurian times, the southern part of the basin began to be infilled by fluvio-deltaic systems entering the basin from the east and south-east, but ultimately still sourced from the north. Three case studies are described in detail: the Kinderscout Grit, Ashover Grit and Chatsworth Grit. The development of these sand bodies occurred within a regime of regular and marked sea level changes. Evidence will be provided for the duration of this cyclicity. From early in the Westphalian, a coal-forming delta-top environment, associated with formation of the Pennine Coal Measures Group became established across the Pennine Basin. There was gradual waning of the influence of marine flooding events in the basin. The sediment influx into the Pennine Basin progressively changed from a dominantly northern provenance, comparable to the Millstone Grit Group, to initially a western source and subsequently to a southern one, later in the Westphalian

Anthropocene

The world today is undergoing rapid environmental change, driven by human population growth and economic development. This change encompasses such diverse phenomena as the clearing of rainforests for agriculture, the eutrophication of lakes and shallow seas by fertilizer run-off, depletion of fish stocks, acid rain, and global warming. These changes are cause for concern—or alarm—among some, and are regrettable if unavoidable side effects of economic growth for others

Human bioturbation, and the subterranean landscape of the Anthropocene

Bioturbation by humans (‘anthroturbation’), comprising phenomena ranging from surface landscaping to boreholes that penetrate deep into the crust, is a phenomenon without precedent in Earth history, being orders of magnitude greater in scale than any preceding non-human type of bioturbation. These human phenomena range from simple individual structures to complex networks that range to several kilometres depth (compared with animal burrows that range from centimetres to a few metres in depth), while the extraction of material from underground can lead to topographic subsidence or collapse, with concomitant modification of the landscape. Geological transformations include selective removal of solid matter (e.g. solid hydrocarbons, metal ores), fluids (natural gas, liquid hydrocarbons, water), local replacement by other substances (solid waste, drilling mud), associated geochemical and mineralogical changes to redox conditions with perturbation of the water table and pH conditions and local shock-metamorphic envelopes with melt cores (in the case of underground nuclear tests). These transformations started in early/mid Holocene times, with the beginning of mining for flint and metals, but show notable inflections associated with the Industrial Revolution (ca 1800 CE) and with the ‘Great Acceleration’ at ∼1950 CE, the latter date being associated with the large-scale extension of this phenomenon from sub-land surface to sub-sea floor settings. Geometrically, these phenomena cross-cut earlier stratigraphy. Geologically, they can be regarded as a subsurface expression of the surface chronostratigraphic record of the Anthropocene. These subsurface phenomena have very considerable potential for long-term preservation

New UK in-situ stress orientation for northern England and controls on borehole wall deformation identified using borehole imaging

The nascent development of a UK shale gas industry has highlighted the inadequacies of previous in-situ stress mapping which is fundamental to the efficacy and safety of potential fracturing operations. The limited number of stress inversions from earthquake focal plane mechanisms and overcoring measurements of in-situ stress in prospective areas increases the need for an up-to-date stress map. Borehole breakout results from 36 wells with newly interpreted borehole imaging data are presented. Across northern England these demonstrate a consistent maximum horizontal stress orientation (SHmax) orientation of 150.9° and circular standard deviation of 13.1°. These form a new and quality assured evidence base for both industry and its regulators. Widespread use of high-resolution borehole imaging tools has facilitated investigation of micro-scale relationships between stress and lithology, facilitating identification of breakouts as short as 25 cm. This is significantly shorter than those identified by older dual-caliper logging (typically 1-10+ m). Higher wall coverage (90%+ using the highest resolution tools) and decreasing pixel size (down to 4mm vertically by 2° of circumference) also facilitates identification of otherwise undetectable sub-centimetre width Drilling Induced Tensile Fractures (DIFs). Examination of borehole imaging from wells in North Yorkshire within the Carboniferous Pennine Coal Measures Group has showed that even though the stress field is uniform, complex micro-stress relationships exist. Different stress field indicators (SFI) are significantly affected by geology with differing failure responses from adjacent lithologies, highlighted by borehole imaging on sub-metre scales. Core-log-borehole imaging integration over intervals where both breakouts and DIFs have been identified allows accurate depth matching and thus allows a synthesis of failure for differing lithology and micro-structures under common in-situ conditions. Understanding these relationships requires detailed knowledge of the rock properties and how these affect deformation. Strength and brittleness of the facies are indicative of their likely failure-modes which are in turn controlled by their lithology, diagenesis and clay mineralisation, often highlighting dm-scale stress rotations around lithological boundaries. Breakouts are seen to concentrate within “seatearths” (palaeosol intervals directly under the coals), whereas intervals immediately above coals are marked disproportionately by DIFs. In-situ stress magnitude data information is not yet available for these wells, further work is required to quantify the geomechanical properties

Geology and the Anthropocene

It is useful to have Todd Braje's perspective on the Anthropocene. As he states, it is a concept that has spread widely and that has had various interpretations (within not just the sciences, but the arts and humanities too) in the 15 years since Paul Crutzen and Eugene Stoermer proposed the term (Crutzen & Stoermer 2000). Various suggestions are made in Braje's paper: perhaps foremost is that the Anthropocene should be retained as a loosely defined term to focus on the nature and effect of human activities, to be a ‘rallying cry’ for better planetary stewardship. He suggests, indeed, that precise characterisation and formalisation as a stratigraphic unit may hinder such use, causing (for instance) all humans—rather than specific socio-economic groups—to be held equally responsible for the degradation of planetary systems

Summary of the new stratigraphic guide to the Chalk Group in the UK and Norwegian sectors of the North Sea

This brief guide summarizes the updated and unified stratigraphy of the Chalk Group for the UK and Norwegian sectors in the North Sea. The information was presented at the ‘Chalk of the Northern Province’ symposium held in Hull on 12 September 2015. The update rationalizes Chalk Group lithostratigraphy across the North Sea, reducing the need to use unique names for reservoir units, without proper documentation or lack of biostratigraphic and correlative insight

Stratigraphic Guide to the Cromer Knoll, Shetland and Chalk Groups, North Sea and Norwegian Sea

This guide provides a major revision and update of the stratigraphy of the Cromer Knoll, Shetland and Chalk Groups for the UK and Norwegian sectors in the North Sea, and of the Cromer Knoll and Shetland Groups in the Norwegian Sea. The first chapters deal with the paleoceanographic and geologic settings and updated biostratigraphy, followed by the chapters with the new and improved lithostratigraphy. The Cretaceous biostratigraphy calculated for the microfossil record in 37 Norwegian wells integrates over 100 foraminifer, dinoflagellate cyst, diatom and miscellaneous events in nineteen zones, numbered from NCF 1 through NCF 19 (North Sea Cretaceous Micro Fossil Zones 1–19). A literature based Dinoflagellate Cyst Zonation (DCZ), linked to the NCF zones, is also presented with eleven zones and thirty-nine subzones for Cretaceous marine strata in the North Sea. Both zonations are optimized for industrial applications with ditch cuttings samples. The lithostratigraphy of the North Sea, unified for the UK and Norwegian sectors describes 3 groups, 30 formation units and one member. The Cretaceous lithostratigraphy for the Norwegian Sea describes 2 groups, 17 formations and 14 members. This (long overdue) update alleviates misnaming and incidental use of unique names for reservoir units, without documentation and lack of biostratigraphic and correlative insight. The internet site www.nhm2.uio.no/norlex and the CD inserted with this publication provide core archives for the lithostratigraphic units

Extraordinary human energy consumption and resultant geological impacts beginning around 1950CE initiated the proposed Anthropocene Epoch

Growth in fundamental drivers—energy use, economic productivity and population—can provide quantitative indications of the proposed boundary between the Holocene Epoch and the Anthropocene. Human energy expenditure in the Anthropocene, ~22 zetajoules (ZJ),exceeds that across the prior 11,700 years of the Holocene (~14.6 ZJ), largely through combustion of fossil fuels. The global warming effect during the Anthropocene is more thanan order of magnitude greater still. Global human population, their productivity and energy consumption, and most changes impacting the global environment, are highly correlated. This extraordinary outburst of consumption and productivity demonstrates how the Earth System has departed from its Holocene state since ~1950 CE, forcing abrupt physical, chemical and biological changes to the Earth’s stratigraphic record that can be used to justify the proposal for naming a new epoch—the Anthropocene

A stratigraphical basis for the Anthropocene?

Recognition of intimate feedback mechanisms linking changes across the atmosphere, biosphere, geosphere and hydrosphere demonstrates the pervasive nature of humankind's influence, perhaps to the point that we have fashioned a new geological epoch, the Anthropocene. To what extent will these changes be evident as long-lasting signatures in the geological record? To establish the Anthropocene as a formal chronostratigraphical unit it is necessary to consider a spectrum of indicators of anthropogenically induced environmental change, and to determine how these show as stratigraphic signals that can be used to characterize an Anthropocene unit and to recognize its base. It is important to consider these signals against a context of Holocene and earlier stratigraphic patterns. Here we review the parameters used by stratigraphers to identify chronostratigraphical units and how these could apply to the definition of the Anthropocene. The onset of the range of signatures is diachronous, although many show maximum signatures which post-date1945, leading to the suggestion that this date may be a suitable age for the start of the Anthropocene

Evidence for a stratigraphic basis for the Anthropocene

The Anthropocene was proposed as a term (Crutzen and Stoermer 2000) before consideration was given to the nature of the key signatures, contrasting with standard procedures for defining such units. The term is being widely used in both popular and scientific publications before a decision is made as to whether it warrants formalisation and definition of a Global Stratigraphic Section and Point (GSSP). The deliberate human modification of the landscape and its subsurface, and the creation of human-generated novel sedimentary deposits, minerals, and landforms, are characteristic features of the development of Earth’s surface and near surface, which has accelerated in the past two centuries. The large-scale intentional excavation, transportation, and deposition of mixtures of rock and soil to form anthropogenic deposits and landforms represent a new geological process that could be used as a diagnostic signature of the Anthropocene