Geology Today最新文献

The beauty of an eclogite is something to behold: any petrologist marvels in the combination of red garnet and green omphacite that are the main mineral constituents of the rock. But besides their stunning appearance, there is much more to eclogites: fundamental concepts in metamorphic petrology and geodynamics were developed based on scientific investigations of eclogites. It is well established that they derive from precursor rocks of basaltic composition and form under high-pressure conditions at more than c. 45 km depth, but other aspects of their occurrences and geological significance remain debated. The relative scarcity of eclogites among crustal rocks renders them largely unknown to the layperson, so following the 200th anniversary of the term eclogite in 2022, there is an opportunity to take a closer look at this fascinating rock.

The Jurassic strata running through the county of Buckinghamshire, English south midlands, culminate in the marine to non-marine Upper Tithonian (formerly Portlandian) Portland and Purbeck formations. Despite poor exposure, this richly fossiliferous and strongly regressive carbonate-clastic succession allows reconstruction of shallow marine, coastal lagoonal and ultimately lacustrine environments, against the backdrop of a hot, greenhouse climate.

Although not a common feature of either group, solitary rugose corals and Palaeozoic crinoids may be anchored by unsegmented, rod-like root structures, referred to as ‘radiciform’ processes and ‘pseudoradices’, respectively. Crinoid pseudoradices likely penetrated the sediment radially from the column, like the roots of a tree. Radiciform processes may have fulfilled a similar function for a solitary rugose coral, but they were also encrusters.

The forthcoming energy transition driven by the need to reduce CO₂ emissions requires large amounts of critical elements to construct renewable energy devices such as car batteries, wind turbines and solar panels. For many elements such as Li, Co, REEs and Ti, the production sources are located in countries with poor social and environmental standards, prone to political destabilization such as military conflicts, or vulnerable to strained relationships with consumer countries. Lately, the volatile geopolitical context has further demonstrated the high dependency of Europe and other developed countries in terms of raw material supply. In addition, there is a debate about the Earth's potential to sustain the transition toward a green society by using conventional resources from mining of terrestrial rocks. As nature conservation and climate mitigation are now priorities for the majority of governments, and since conventional mining on Earth suffers from a growing social resistance, humankind may need to look toward new frontier resources for supplying the mineral needs of the coming decades. Here, we explore the use of extra-terrestrial resources as a potential source to feed the future supply of critical metals. Extra-terrestrial mining may be an opportunity for wealth creation and an option for critical metal resource supply when mining on Earth becomes increasingly untenable. We conclude that the potential impacts of extraction and exploitation of space resources, both good and bad, could be societally profound.

Large calcite-cemented sandstone concretions found in Middle Jurassic sandstones from the isles of Eigg and Skye are a striking feature of the Jurassic geology of the Inner Hebrides. Recent clumped isotope data unequivocally give concretionary calcite cementation temperatures above 50°C and up to 98°C. The high temperatures contrast with the mild thermal history of the enclosing less permeable Jurassic mudrocks. The clumped isotope data also enable calculation of the oxygen isotopic composition of the precipitating fluids: these included percolating rainwater that had interacted with Paleocene volcanics; then, later hot fluids of deeper, basinal origin, squeezed out of compacting mudrocks at depth as the Paleocene lava pile loaded the crust. There is thus direct connection between ‘Jurassic’ sedimentary features and the complex Paleocene volcanic history of the region.

The Bovey Basin in south Devon, UK, provides an instructive example of a Palaeogene pull-apart basin with a complex fluvial sedimentary fill. The basin, one of three that lie along the NW-SE-trending Sticklepath Fault Zone, is filled by about 1200 m of sediment, of which about the lower 700 m (mainly lower Bovey Formation) is concealed. The main Bovey Basin is separated from a smaller sub-basin (the Decoy Basin) south of Newton Abbot. Two main lithofacies are present in the Bovey Formation: lignite-clay; and clay-sand, with subordinate lithofacies of red-mottled clay and sand; and gravel and conglomerate. The upper 500 m or so of the sedimentary infill (middle and upper Bovey Formation) is divided into 10 members. Deposition in the basin was by a variety of fluvial processes, notably floodplain clays and sands deposited by meandering rivers; forest swamps with associated short-lived shallow lakes; and (mainly in the upper Bovey Formation) braided stream sands and gravels that formed mainly on alluvial fans. Lignites in the basin formed from plants that grew in place in forest swamps, a revision of the long-held view that the lignitic material was transported into the basin from forests of the conifer Sequoia couttsiae growing outside the basin on adjacent uplands. Newly discovered ichnofabrics occur in some lignitic sequences and probably represent root traces (rhizoliths).

Granites are coarse-grained igneous intrusive rocks, which, although present in most tectonic settings, are most characteristic of continental crust. While basalts are the most abundant volcanic rocks, granites are the most abundant intrusive rocks. On the scale of the Solar System, while basalts are ubiquitous, granites seem to be restricted to the Earth. The volcanic equivalent of granite is rhyolite, although rhyolites are of much lower abundance than granite, probably because such magmas are more viscous and less likely to reach the surface. In addition, many pyroclastic rocks have a granitic composition and are likely to have their origins in underlying granitic plutons. Granites may originate by differentiation of a basaltic magma, but the abundance of granites and the low abundance of intermediate rocks argues in general against this possibility and granite magmas are generally thought to have formed by melting of pre-existing rocks. Several distinct types of granite are recognized depending on their origin.

Following the end of the last ice age, decelerating global post-glacial sea level rises submerged the southern North Sea, and along this coast, 63 km of soft glacial deposits are still being rapidly washed away. The collapse of the massive ice sheets covering Britain, Ireland and Fennoscandia was a complex process, with warming after 14.7 ka. Limited glaciation then returned during the Loch Lomond Stadial at the end of the Pleistocene, Doggerland, connecting Britain with the continent, was slowly immersed, becoming a shrinking island which was rapidly submerged after 8 ka. This coincided with the Storegga tsunami which hit what remained of Doggerland’s shores and along the coasts of Scotland and Northumberland. Since then, the sea has risen by around 27.5 m. Now it is clear eustatic increases in global sea levels are starting to accelerate once again, we must start adjusting to this reality in the way we manage our coastal infrastructure and try to understand more about how this interacts with naturally dynamic shorelines.