Geology Today最新文献

Titanosaurs were a globally distributed group of sauropod dinosaurs. They had diverse forms and a wide-gauge stance, with a few of their species reaching immense sizes, such as Argentinosaurus huinculensis and Patagotitan mayorum (reaching >35 m in length). There are about 100 valid titanosaur species known so far, but most of the originally described species are no longer valid, due to the incomplete nature of fossil materials. Our understanding of titanosaur skull morphology is based on very few incomplete fragmented cranial materials and findings of the complete skull are even rarer. Understanding the skull morphology of extinct animals helps palaeontologists make deductions of feeding mechanisms and also provide an idea about their appearance when they were alive. Diversity in titanosaur skull morphology is greater than that of any other sauropod clade, indicating diversity in feeding mechanism among these dinosaurs. Titanosaurs were the last surviving clade of sauropod dinosaurs, occupying nearly every ecological niche around the world during the Late Cretaceous, and resulting in a rich diversity in this group. This article highlights diversity in the basic structure of sauropods with special emphasis on titanosaur skull morphology.

Across Ireland there is a striking topographical contrast between predominantly limestone-floored lowlands and uplands developed on silicate-dominated rock types. This arises from the fundamentally different way in which limestone and other rocks are removed. Limestone is removed through dissolution, a low-energy process enhanced by vegetation. Other rock types are removed by erosion, a high energy process that is inhibited by vegetation. In Ireland countless ‘soft days’ over the last 60 Ma have been more effective at removing limestone than other rock types. Limestone uplands have survived only where they were protected by a cover of insoluble rock, such as sandstone or mudstone, which has been stripped away relatively recently by glacial erosion. The large-scale removal of considerable thicknesses of limestone across Ireland has increased the relief of non-limestone uplands through the effects of isostatic uplift. Denudation across the Irish landscape has led to changing outcrop patterns of limestone and other rocks, resulting in profound long-term changes in topography and drainage patterns.

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.