Magnetic components contributing to the NRM of Middle Siwalik red beds

The components of the NRM in Middle Siwalik red beds are carried by two phases of hematite, a red pigment phase and a specular hematite phase. We present evidence in the form of a conglomerate test that the specularite phase carries a remanence acquired during or shortly after deposition. The red pigment, however, post-dates deposition, in many cases by at least one reversal boundary. This secondary component has a higher coercivity but a lower blocking temperature in these rocks and can therefore be selectively removed by thermal demagnetization to reveal a primary magnetization useful for magnetostratigraphic studies.     

The hydrothermal system of Nevado del Ruiz volcano,Colombia

Hot springs and steam vents on the slopes of Nevado del Ruiz volcano provide evidence regarding the nature of hydrothermal activity within the summit and flanks of the volcano. At elevations below 3000 m, alkali-chloride water is discharged from two groups of boiling springs and several isolated warm springs on the western slope of Nevado del Ruiz. Chemical and isotopic geothermometers suggest that the boiling springs are fed by an aquifer having a subsurface equilibration temperature of at least 175°C, and the sampled warm spring is fed by an aquifer having a subsurface equilibration temperature near 150°C. Similarities in conservative solute ratios (e.g., B/Cl) indicate that the alkali-chloride waters may be related to a single reservoir at depth. Isotopic ratios of hydrogen and oxygen indicate that recharge for the alkali-chloride aquifers comes mostly from higher elevations on the volcano. Steam vents and steam-heated bicarbonate-sulfate springs at higher elevations, along a linear structural trend with the alkali-chloride springs, may be derived partly from the alkali-chloride water at depth by boiling. Steam from the vents (84°C) yields a gas geothermometer temperature of 209°C. Acid-sulfate-chloride and acid-sulfate waters are discharged widely from warm springs above 3000 m on the northern and eastern slopes of Nevado del Ruiz. Similarities in B/Cl and SO₄/Cl ratios suggest that the acid waters are mixtures of water from an acid-sulfate-chloride reservoir with various proportions of shallow, dilute groundwater. The major source of sulfate, halogens, and acidity for the acid waters may be high-temperature magmatic gases. Available data on hot spring temperatures and compositions indicate that they have remained fairly stable since 1968. However, the eruption of November 13, 1985 apparently caused an increase in sulfate concentration in some of the acid springs that peaked about a year after the eruption. Long-term monitoring of hot spring compositions over many years will be required to better define the effects of volcanic activity on the Nevado del Ruiz hydrothermal system.     

Sulphide synthesis and ore genesis

This review of experimental work on the formation of sulphide ores shows how the development of geological thought on the genesis of these deposits influenced the direction of these investigations. The experimental work to date emphasises the necessity for the chemist and the physical chemist to work together with the geologist so that the complex processes that contribute to the formation of a metal sulphide deposit may be defined and their individual roles evaluated.

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Zusammenfassung Diese Zusammenfassung von Arbeiten über die Bildung sulfidischer Erze zeigt, wie die Entwicklung geologischen Denkens die Forschungen über die Genese der Vorkommen beeinflußte. Moderne Experimentalarbeiten lassen die Notwendigkeit erkennen, daß Chemiker und Physiko-Chemiker mit den Geologen zusammenarbeiten müssen, damit die komplizierten Prozesse, die zur Bildung sulfidischer Ablagerungen führten, geklärt und ihre Einzelheiten verstanden werden können.

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Published by permission of the Director, Bureau of Mineral Resources, Geology and Geophysics, Canberra, Australia.     

Beach erosion under rising sea‐level modulated by coastal geomorphology and sediment availability on carbonate reef‐fringed island coasts

This study addresses gaps in understanding the relative roles of sea‐level change, coastal geomorphology and sediment availability in driving beach erosion at the scale of individual beaches. Patterns of historical shoreline change are examined for spatial relationships to geomorphology and for temporal relationships to late‐Holocene and modern sea‐level change. The study area shoreline on the north‐east coast of Oahu, Hawaii, is characterized by a series of kilometre‐long beaches with repeated headland‐embayed morphology fronted by a carbonate fringing reef. The beaches are the seaward edge of a carbonate sand‐rich coastal strand plain, a common morphological setting in tectonically stable tropical island coasts. Multiple lines of geological evidence indicate that the strand plain prograded atop a fringing reef platform during a period of late‐Holocene sea‐level fall. Analysis of historical shoreline changes indicates an overall trend of erosion (shoreline recession) along headland sections of beach and an overall trend of stable to accreting beaches along adjoining embayed sections. Eighty‐eight per cent of headland beaches eroded over the past century at an average rate of ?0·12 ± 0·03 m yr^?1. In contrast, 56% of embayed beaches accreted at an average rate of 0·04 ± 0·03 m yr^?1. Given over a century of global (and local) sea‐level rise, the data indicate that embayed beaches are showing remarkable resiliency. The pattern of headland beach erosion and stable to accreting embayments suggests a shift from accretion to erosion particular to the headland beaches with the initiation of modern sea‐level rise. These results emphasize the need to account for localized variations in beach erosion related to geomorphology and alongshore sediment transport in attempting to forecast future shoreline change under increasing sea‐level rise.     

A brief overview of the ACEP project: Ecosystem Processes in the KwaZulu-Natal Bight§

This introductory paper lays the basis for this supplementary issue by briefly presenting the state of knowledge on the KwaZulu-Natal (KZN) Bight at the start of this multi-disciplinary, multi-institutional, ship-based research project that ran from 2009 to 2013. The rationale and aims of the project are also described. The project was a major component of the South African Department of Science and Technology’s African Coelacanth Ecosystem Programme (ACEP), which has been prominent in supporting research on the east coast of South Africa and the wider South-West Indian Ocean. Pivotal to this was the RS Algoa, which was made available for two 30-day surveys (winter and summer) in the KZN Bight by the Department of Environmental Affairs. Although some aspects of the bight ecology are known, much of the research is dated and fragmented, and required refreshing and consolidation in order to produce a platform upon which the understanding of the region’s ecosystem functioning could be established. Much of the oceanographic knowledge is also dated, with no dedicated surveys and significant measurements undertaken since 1989. The overarching theme of the KZN Bight project was to examine the relative importance of sources of nutrients to the central KZN coast and how these are taken up and recycled in the ecosystem, and to describe aspects of the benthic biodiversity, which is poorly described in much of this region. An ambitious project, its accessibility to a ship-based research platform and the diverse scientific skills of the participating scientists allowed considerable success, as reflected in the papers that follow.     

Impact of predicted climate change on landslide reactivation: case study of Mam Tor, UK

Global change is expected to result in worldwide increases in temperature and alteration of rainfall patterns. Such changes have the potential to modify stability of slopes, both natural and constructed. This paper discusses the potential effect of global climate change on reactivation of landslides through examination of predicted changes in rainfall pattern on the active landslide at Mam Tor, Derbyshire, UK. This landslide is of Pleistocene origin and is crossed by a road that is now abandoned. Damaging winter movement is known to occur when precipitation reaches both 1-month triggering and 6-month antecedent thresholds. Return periods for threshold exceedence is modelled statistically, and the climate change data from the UKCIP 2002 report (Hulme et al. 2002) is applied to this model. For the predicted changes in precipitation, it is shown that the instability threshold could decrease from 4 to 3.5 years by the 2080s for the medium–high climate change scenario. However, predicted temperature changes could influence the response of the landslide through increased evapotranspiration leading to a change in the triggering precipitation thresholds, and this will help counter the impact of changes in precipitation. Analysis of sources of uncertainty in the model has been used to establish the factors that contribute to the predicted changes in stability. Assessment of these factors can provide an indication of the potential impact of climate change on landslides in other areas of the UK.     

Numerical modelling of deformation and fluid flow in the Shuikoushan district, Hunan Province, South China

The Shuikoushan district, in Hunan Province, South China, contains major Pb–Zn–Au–Ag polymetallic mineralisation. Two groups of numerical models have been constructed to study the interactions between deformation and fluid flow in the district during the Yanshanian compression event (180 to 90 Ma). The first group includes district-scale conceptual models of coupled deformation and fluid flow during folding. The models show that fluid flow patterns are controlled by deformation within the fold system inferred for the district. During regional shortening and folding, fluids are generally focused towards the fold hinge/core areas along higher permeability layers (in particular Permian limestone units), in preference to flowing across the low permeability seal units (Permian and Jurassic terrestrial sequences). The efficiency of this fluid focusing can only be significantly increased if these folded seal units are allowed to undergo permeability increase as a result of tensile failure. The modelling results show that permeability enhancement localises mostly at fold hinges, dominantly within the silicified zone on the top of the Permian limestone unit. This process results in increased flow velocities and facilitates fluid focusing towards fold hinge/core locations at this silicified rock horizon. The second group includes deposit scale models for the Kangjiawan deposit, which is one of the two major deposits in the Shuikoushan district. The models show patterns of tensile failure, permeability creation, fluid focusing and mixing, and fracture development along a selected exploration cross section through the deposit. These results are consistent with the observed brecciation and mineralisation features. Regions of maximum brecciation in the district are associated with: (1) a combination of fold hinge and fault intersection locations (structural); and (2) the silicified zone and Permian limestone unit (lithological). Such brecciation zones are associated with extensive fluid focusing and mixing, and therefore represent the most favourable locations for mineralisation in the district. On the basis of this work, ideas for future research work and mineral exploration in the district are proposed.     

Estimating the inundation area of a massive,hypothetical jökulhlaup from northwest Vatnajökull,Iceland

Jökulhlaups are the consequence of a sudden and significant release of meltwater from the edge of a glacier. Such floods are sourced commonly from ice-dammed lakes, but occasional volcanic eruptions beneath ice can produce intense jökulhlaups due to prodigious rates of meltwater release. Globally, volcanogenic jökulhlaups have caused fatalities and damage to infrastructure within effected catchments. Here, we present the results of one-dimensional hydraulic modelling of the inundation area of a massive, hypothetical jökulhlaup on the Jökulsá á Fjöllum River in northeast Iceland; the floodwater source for this simulation is an eruption within the ice-filled caldera of Bárðarbunga: an active volcano beneath the Vatnajökull ice cap. Remotely sensed data were used to derive a digital elevation model and to assign surface-roughness parameters. We used a HEC-RAS/HEC-GeoRAS system to host the hydraulic model; to calculate the steady water-surface elevation; to visualise the flooded area; and to assess flood hazards. Maximum discharge was set notionally at 180,000 m³ s^?1 and the duration and volume of the jökulhlaup were placed at 39 h and 14 km³, respectively. During the simulated rise to maximum discharge, the mean velocity of the jökulhlaup was 2.8 m s^?1 over a distance of 120 km. At the height of the jökulhlaup an area of 460 km² was inundated. Modelling results showed that, along short reaches, stream-power values exceeded 11,000 W m^?2; such energy conditions would have allowed boulders up to 10-m in diameter to be mobilised by the jökulhlaup. Unsteady flow was simulated along a 22-km reach of the flood tract and it revealed strong spatial and temporal variations in flood power. Besides providing insight into the erosional and depositional effects of a volcanogenic jökulhlaup, the modelling results enable estimates of the relative timing and location of likely flooding hazards.     

Progress in optical dating of guano-rich sediments associated with the Deep Skull, West Mouth of the Great Cave of Niah, Sarawak, Borneo

The West Mouth of the Great Cave of Niah is one of the major archaeological sites in Southeast Asia; the radiocarbon chronology of this site currently places the earliest presence of Homo sapiens (a Deep Skull find) in Southeast Asia at about 45 ka BP. An optical dating programme using sand-sized quartz was initiated in the West Mouth to complement the radiocarbon chronology. This paper reports on the progress in dating a key sample (sample 376r) that was taken from deposits containing the Deep Skull. A somewhat novel procedure was developed to separate and clean quartz grains from the unusual guano-rich deposits. From this, only a small quantity of quartz grains could be recovered and 36 aliquots (1 mm in diameter) were prepared, each consisting of 80 grains. This sample was dated by means of the single-aliquot regenerative-dose (SAR) method using the protocols of Murray and Wintle [2000. Luminescence dating of quartz using an improved single-aliquot regenerative-dose protocol. Radiation Measurements 32, 57–73], and of Choi et al. [2003. Luminescence dating of well-sorted marine terrace sediments on the southeastern coast of Korea. Quaternary Science Reviews 22, 407–421]. The results showed a wide distribution of equivalent doses; this distribution is inferred to be due to bioturbation, variable bleaching at deposition, and to local variations in the dose rate within the sample site. Dose rates were measured using both field (in-situ γ-ray spectrometry, IGRS) and laboratory (inductively coupled plasma mass spectrometry/atomic emission spectrometry, ICP-MS/AES; and isotope dilution, ID) methods. There was significant disagreement between the concentrations of radioisotopes found using laboratory and field measurements, indicating sediment heterogeneity and also possible disequilibrium in the ²³⁸U decay chain. Future work in the West Mouth should therefore concentrate on taking sediment samples of at least 500–600 cm³, improving the dose rate estimates (e.g. by high-resolution γ-ray spectrometry) and investigating other luminescence signals (e.g. red thermoluminescence) as potential geochronometers.