British Geological Survey

About: British Geological Survey is a government organization based out in Nottingham, United Kingdom. It is known for research contribution in the topics: Groundwater & Aquifer. The organization has 2561 authors who have published 7326 publications receiving 241944 citations.

The Dalradian rocks of Scotland: an introduction

Abstract: The Dalradian Supergroup and its basement rocks, together with younger plutons, underpin most of the Grampian Highlands and the islands of the Inner Hebrides between the Highland Boundary and Great Glen faults. The Dalradian is a mid-Neoproterozoic to early-Ordovician sequence of largely clastic metasedimentary rocks, with some volcanic units, which were deformed and metamorphosed to varying degrees during the Early Palaeozoic Caledonian Orogeny. Sedimentation of the lower parts of the Dalradian Supergroup, possibly commencing about 730 million years ago, took place initially in fault-bounded rift basins, within the supercontinent of Rodinia and adjacent to sectors of continental crust that were later to become the foundations of North America, Greenland and Scandinavia. Later sedimentation reflected increased instability, culminating between 600 and 570 million years ago in continental rupture, volcanicity and the development of the Iapetus Ocean. This left the crustal foundations of Scotland, together with those of North America and Greenland, on a laterally extensive passive margin to the new continent of Laurentia, where turbiditic sedimentation continued for about 85 million years. Later plate movements led to closure of the Iapetus Ocean and the multi-event Caledonian Orogeny. Most of the deformation and metamorphism of the Dalradian strata peaked at about 470 million years ago, during the mid-Ordovician Grampian Event, which has been attributed to the collision of an oceanic arc with Laurentia. The later, mid-Silurian Scandian Event, attributed to the collision of the continent of Baltica with Laurentia and the final closure of the Iapetus Ocean, apparently had little effect on the Dalradian rocks but marked the start of late-orogenic uplift and extensive magmatism in the Grampian Highlands that continued until Early Devonian times. The Dalradian rocks thus record a wide range of sedimentary environments (alluvial, tidal, deltaic, shallow marine, turbiditic, debris flow) and a complex structural and metamorphic history. In areas of low strain, original sedimentary and volcanic structures are well preserved, even at relatively high metamorphic grades. There is convincing evidence for glacial episodes of worldwide importance and economic deposits of stratiform barium minerals are unique. The Grampian Highlands include two of the World's type-areas for metamorphic zonation, Barrovian and Buchan, with spectacular examples of the key metamorphic minerals, and various stages of migmatite development. Polyphase folding is widespread on all scales and gives rise to a range of associated cleavages and lineations. Regional dislocations, both ductile and brittle, are associated with a range of shear fabrics, breccias, clay gouges and veining.

On the identification of a Pliocene time slice for data–model comparison

Abstract: The characteristics of the mid-Pliocene warm period (mPWP: 3.264–3.025 Ma BP) have been examined using geological proxies and climate models. While there is agreement between models and data, details of regional climate differ. Uncertainties in prescribed forcings and in proxy data limit the utility of the interval to understand the dynamics of a warmer than present climate or evaluate models. This uncertainty comes, in part, from the reconstruction of a time slab rather than a time slice, where forcings required by climate models can be more adequately constrained. Here, we describe the rationale and approach for identifying a time slice(s) for Pliocene environmental reconstruction. A time slice centred on 3.205 Ma BP (3.204–3.207 Ma BP) has been identified as a priority for investigation. It is a warm interval characterized by a negative benthic oxygen isotope excursion (0.21–0.23‰) centred on marine isotope stage KM5c (KM5.3). It occurred during a period of orbital forcing that was very similar to present day. Climate model simulations indicate that proxy temperature estimates are unlikely to be significantly affected by orbital forcing for at least a precession cycle centred on the time slice, with the North Atlantic potentially being an important exception.

Timing and duration of Palaeoproterozoic events producing ore-bearing layered intrusions of the Baltic Shield: metallogenic, petrological and geodynamic implications

Abstract: There are two 300-500-km long belts of Palaeoproterozoic layered intrusions: the Northern (Kola) Belt and the Southern (Fenno-Karelian) Belt in the Baltic (Fennoscandian) Shield. New U-Pb (TIMS) ages and radiogenic isotopic (Nd-Sr-He) data have been determined for mafic-ultramafic Cu-Ni-Ti-Cr and PGEbearing layered intrusions of the Kola Belt. U-Pb ages on zircon and baddeleyite for gabbronorite and anorthosite from the Fedorovo-Pansky, Monchepluton and Main Ridge (Monchetundra and Chunatundra), Mt. Generalskaya intrusions and gabbronorite and dykes from the Imandra lopolith of the Kola Belt define a time interval of more than 130 million years, from ca. 2.52 Ga to 2.39 Ga. At least four intrusive phases have been distinguished: three PGE-bearing, and one barren. This spread of ages is wider than that for intrusions of the Fenno-Karelian Belt which clusters at 2.44 Ga. Nd isotopic values for the Northern Belt range from - 1.1 to -2.4, implying an enriched mantle “EM-1 type” reservoir for these layered intrusions. Initial Sr isotopic data for the rocks of the intrusions are radiogenic relative to bulk mantle, with ISr values from 0.703 to 0.704. Geochemical data and 4He /3He isotopic ratios of the minerals reflect a significant contribution from a mantle source rather than the influence of crustal processes during emplacement. The geological and geochronological data indicate that in the eastern part of the Baltic Shield, mafic – ultramafic intrusive magmatism was active over a protracted period and was related to plume magmatism associated with continental breakup that also involved the Superior and Wyoming provinces.