Geology Today最新文献

The unique geological history which resulted in the evolution of the Chiltern Hills to the north of London, The United Kingdom, created the underlying foundations for everything that we see there on the surface today. The roots of the Chiltern Hills lie in their Chalk foundations. To understand the details of the way the chalk acts as an aquifer it is important to understand first the origins of the chalk sediment and how the subsequent geological history of the region has impacted on the rocks preserved today.

Unusual conjunctions of geological phenomena in the modern environment may alert us to their potential presence in the rock record. Two erratics of Carboniferous limestone from the beach at Cleveleys on the Irish Sea coast, Lancashire, northern England bored by sponges and polychaete worms, are suggestive of potential occurrences of borings in ancient conglomerates. Such distinctive patterns of boring, commoner in crystalline veins than in limestone, are certainly unfamiliar. But borers are well-known for invading crystalline organic substrates, such as belemnites and oysters.

Basalt is a fairly familiar word, although few laymen could define it. In fact, basalts are the commonest rocks of the Solar System. On Earth, they are found in all tectonic settings and of all ages throughout geological time. Basalts are volcanic rocks, rich in magnesium and poor in silica, consisting of plagioclase (with a composition in the labradorite range) and the mafic minerals: olivine, pyroxene, iron oxides and sometimes hornblende. They are dark-coloured, fine-grained (although larger crystals, known as ‘phenocrysts’ or ‘megacrysts’ may occur) and are typically found as lava flows. Basalt makes up enormous accumulations, often over 1 million square kilometres in size, known as ‘large igneous provinces’ or LIPs, which may be associated with mass extinctions. Other, more siliceous, rocks are hypothesized to be derived from basaltic magmas by the process of igneous differentiation.

The origin of volcanism in the Canary Islands has been a matter of controversy for decades. Discussions have hinged on whether the Canaries owe their origin to seafloor fractures associated with the Atlas Mountain range or to an underlying plume or hotspot of uprising hot material from the deep mantle. The debate has recently concluded, however, following the discovery of nannofossils preserved in the products of the 2011–2012 submarine eruption at El Hierro, which constrain the age and growth history of the westernmost island of the archipelago and so cement a clear East to West age progression within the archipelago. Light-coloured, quartz-bearing pumice-like ‘floating rocks’ (xeno-pumice) were found on the sea surface during the first days of the 2011 El Hierro eruption and proved to be fragments of pre-island, sedimentary strata that were picked up by ascending magma. Upper Cretaceous to Pliocene calcareous nannofossils such as coccolithophores were retrieved from the xeno-pumice fragments, and these marine micro-organism biostratigraphical markers now provide crucial evidence that island growth at El Hierro commenced in the Pliocene. Here we discuss how these essentially continental (quartz-bearing) sediments on the African continental shelf derive from dominantly wind-blown Sahara dust and marine (re)-deposition and describe present-day aeolian processes that are in operation in the region. We investigate the mineralogy of Sahara dust that is currently deposited in the Canary Islands and discuss source areas and intra-transport fractionation of mineral dust during trans-Atlantic transport. Finally, we explore how present-day dust deposition can be used as analogue to explain the deposition of pre-island continental material in the East-Atlantic Ocean basin beneath the Canary archipelago and we show how the dust-derived sedimentary deposits can be utilized as geological tool in the Canary Islands.

The hot springs of Ramsar, Iran are located at the northern zone of the Central Alborz Mountain Range along the Caspian Fault. Ramsar is a well-known area with amongst the world's highest levels of natural radiation. Due to the local geology, which includes high levels of radium in rocks, soils, and groundwater, Ramsar residents are also exposed to high levels of alpha activity in the form of ingested radium. Nine springs were selected from the hot springs of Ramsar for this research, and water samples were tested to find the amount of dissolved materials and elements. Analysis of the results suggests that the hot springs of Ramsar originated from the sea. The results indicate that coincident with subduction of the southern Caspian basin and obduction of the Central Iranian crust over the southern Caspian crust, saline seawater reaches fracture zones of the Caspian Fault where it is heated due to mixing with radioactive materials and release of radon as a result of activity of the faults and its decay into radium. Then it migrates along the Caspian thrust faults and forms hot springs originated from regional surface waters of Ramsar. Those hot springs located next to thrust faults were the result of collision, and the origin of neighbouring cold springs is karst.

Belemnites are extinct cephalopods that evolved in the early Late Triassic (~240 Ma) and became extinct at the Cretaceous/Palaeogene boundary (66 Ma), at the same time as the extinction of the dinosaurs. Their bullet-shaped internal skeleton, called a rostrum, are commonly found alongside the much more famous coiled ammonites. Whereas ammonites have gone on to become a universal symbol of palaeontology, belemnites are often overlooked by fossil hunters. The intention of this short introduction to belemnites is to furnish a greater appreciation for these fascinating creatures. Not only were they an incredibly important component of Mesozoic marine ecosystems and their exceptionally preserved fossils can tell us much about coleoid diversity throughout geological time, it is their applications that set belemnites apart from other macrofossils. Belemnite geochemistry can provide high-resolution data regarding past ocean chemistry and temperatures. Such information is vital in the reconstruction of Mesozoic climate systems.

The monographs of the New Naturalist book series have been a source of information for natural historians in the British Isles since the 1940s. Unlike the books dedicated to birds, insects, plants and other aspects of our natural environment, the only volume devoted specifically to Fossils was first published in 1960. Over 60 years later, is it still worthy of our attention?