Slabby pahoehoe from the western Deccan Volcanic Province: evidence for incipient pahoehoe–aa transitions

The pahoehoe–aa transition for a flow exposed near Bodshil village from the western part of the Deccan Volcanic Province (DVP) is reported for the first time. The 1-km-long Bodshil flow issued as a small sheet from a pre-existing lobe. Near the source, the crust is characterised by numerous squeeze-ups. A number of gaping fractures, parallel to sub-parallel to the flow direction, are exposed on the surface in the medial portion of the flow. About 800 m away, the flow completely transforms to slabby pahoehoe. The terminal portion of the flow is characterised by concentrations of slabs, blocks and lava balls. The size and concentrations of the slabs and lava balls appear to increase along the length of the flow. Petrographic studies reveal a dominant hypohyaline texture. The flow core is coarse and is characterised by plagioclase set in a glassy matrix. The presence of clinopyroxene in addition to plagioclase and glass distinguishes the crust and interslab crust from the core. On the basis of mineralogy, a temperature range of 1146±15°C to 1169±15°C is inferred for the Bodshil flow. Increased vesicle deformation across the transition is discernible and an average D-value of <0.4 indicates moderate strain rates during emplacement. In light of the morphology and petrography, the cooling history and the mode of emplacement of the Bodshil flow is discussed. The flow originated as a small toe at the leading edge of a pahoehoe flow, and grew into a sheet by the mechanism of inflation. Continuous inflation caused the brittle crust to uplift and produce a network of inflation clefts that were subsequently occupied by squeeze-ups. Temporary stagnation of the flow due to cessation of lava supply or storage allowed the crust to grow and thicken. Renewed movement of the stored and cooled lava to the flow front at a fairly high volumetric rate was responsible for the initial disruption of the crust. High rates of crustal disruption induced higher rates of degassing and cooling, which resulted in rapid crystallisation of the fluid core. Increase in crystallinity lead to the onset of yield strength, and it is envisaged that at least the terminal parts of the flow behaved as a Bingham fluid. The Bodshil flow is unique to the DVP because it is the first to record slabby pahoehoe and provide evidence for the incipient transformation of basaltic lava from pahoehoe to aa.     

20th Century Climate Change in the Tropical Andes: Observations and Model Results

Linear trend analysis of observational data combined with model diagnostics from an atmospheric general circulation model are employed to search for potential mechanisms related to the observed glacier retreat in the tropical Andes between 1950 and 1998. Observational evidence indicates that changes in precipitation amount or cloud cover over the last decades are minor in most regions and are therefore rather unlikely to have caused the observed retreat. The only exception is in southern Peru and western Bolivia where there is a general tendency toward slightly drier conditions. Near-surface temperature on the other hand has increased significantly throughout most of the tropical Andes. The temperature increase varies markedly between the eastern and western Andean slopes with a much larger temperature increase to the west. Simulations with the ECHAM-4 model, forced with observed global sea surface temperatures (SST) realistically reproduce the observed warming trend as well as the spatial trend pattern. Model results further suggest that a significant fraction of the observed warming can be traced to a concurrent rise in SST in the equatorial Pacific and that the markedly different trends in cloud cover to the east and west of the Andes contributed to the weaker warming east of the Andes in the model. The observed increase in relative humidity, derived from CRU 05 data, is also apparent in the model simulations, but on a regional scale the results between model and observations vary significantly. It is argued that changes in temperature and humidity are the primary cause for the observed glacier retreat during the 2nd half of the 20th century in the tropical Andes.     

Imaging and mechanical property measurements of kerogen via nanoindentation

Most analyses of kerogens rely on samples that have been isolated by dissolving the rock matrix. The properties of the kerogen before and after such isolation may be different and all sample orientation information is lost. We report a method of measuring kerogen mechanical properties in the rock matrix without isolation. An atomic force microscope (AFM) based nanoindenter is used to measure the hardness and reduced modulus of the kerogen within Woodford shale. The same instrument also provides useful images of polished rock sections on a submicrometer scale. Measurements were carried out both parallel and perpendicular to the bedding plane.     

The Seismic Project of the National Tsunami Hazard Mitigation Program

In 1997, the Federal Emergency Management Agency (FEMA), National Oceanic and Atmospheric Administration (NOAA), U.S. Geological Survey (USGS), and the five western States of Alaska, California, Hawaii, Oregon, and Washington joined in a partnership called the National Tsunami Hazard Mitigation Program (NTHMP) to enhance the quality and quantity of seismic data provided to the NOAA tsunami warning centers in Alaska and Hawaii. The NTHMP funded a seismic project that now provides the warning centers with real-time seismic data over dedicated communication links and the Internet from regional seismic networks monitoring earthquakes in the five western states, the U.S. National Seismic Network in Colorado, and from domestic and global seismic stations operated by other agencies. The goal of the project is to reduce the time needed to issue a tsunami warning by providing the warning centers with high-dynamic range, broadband waveforms in near real time. An additional goal is to reduce the likelihood of issuing false tsunami warnings by rapidly providing to the warning centers parametric information on earthquakes that could indicate their tsunamigenic potential, such as hypocenters, magnitudes, moment tensors, and shake distribution maps. New or upgraded field instrumentation was installed over a 5-year period at 53 seismic stations in the five western states. Data from these instruments has been integrated into the seismic network utilizing Earthworm software. This network has significantly reduced the time needed to respond to teleseismic and regional earthquakes. Notably, the West Coast/Alaska Tsunami Warning Center responded to the 28 February 2001 Mw 6.8 Nisqually earthquake beneath Olympia, Washington within 2 minutes compared to an average response time of over 10 minutes for the previous 18 years.     

Nouvelle interprétation tectonique de la montagne Sainte-Victoire (Provence,France)

The explanation normally given for the tectonics of Sainte-Victoire Mountain, a dozen kilometres east of Aix-en-Provence, to the north of the limestone Provence, is incorrect. To the east, the morphology of the Sainte-Victoire is subdued, whereas to the west, before the mountain breaks savagely, the morphology is that of a young mountain as appears in Alpine landscapes. This unusual aspect in the region and the large subvertical faults with vertically striated surfaces that mark the massif to the south and to the west, induce the idea of strong vertical uplifts and caste doubt on the tectonic interpretation given in 1962 by Corroy et al. According to those authors, the Sainte-Victoire is a unit of Jurassic and Cretaceous formations overthrusting 1800 m to the south conglomerates of the Late Cretaceous or Palaeocene. New observations about the conglomerate transgression over the Jurassic and Cretaceous beds, and about the faults around and on the massif do not give evidence of an overthrusting but, on the contrary, induce the idea of a uplift, perhaps still active, in the form of a ‘piano key’ inclined to the northeast. To cite this article: J. Ricour et al., C. R. Geoscience 337 (2005).     

A 300 year record of environmental change from Lake Tuborg, Ellesmere Island, Nunavut, Canada

Lamination thickness measurements in sediments from Lake Tuborg, northern Ellesmere Island, Canada document an increase in high-energy hydrologic discharge events from ∼1865 to 1962. The timing of these events corresponds with evidence for an increase in the amount of melt on the adjacent Agassiz Ice Cap, as recorded in ice cores. There appears to have been a non-linear change in depositional energy resulting from a dramatic increase in Agassiz meltwater discharge, particularly after ∼1908. A strong correlation between the Lake Tuborg varve thickness record, the amount of melting on the Agassiz Ice Cap and Eureka 900 mb air temperature records suggests that changes in the height of the freezing level in the atmosphere have affected the extent of summer melting on the Agassiz Ice Cap, leading to high volume discharge events and associated sediment flux to Lake Tuborg.     

Long-term trends in the macrobenthos and water quality of the lower Chesapeake Bay (1985–1991)

Long-term trends in macrobenthic communities of the lower Chesapeake Bay, USA, were examined using data collected quarterly (March, June, September and December) from 1985 to 1991 at 16 stations along a salinity gradient from tidal freshwater regions of the major tributaries (James, York and Rappahannock rivers) to the polyhaline region of the main-stem of Chesapeake Bay. A non-parametric trend analysis procedure was applied to five parameters characterizing macrobenthic community structure: community biomass, species richness, abundance of individuals, proportion of biomass composed of opportunistic species (opportunistic biomass composition) and proportion of biomass composed of equilibrium species (equilibrium biomass composition). For the parameters tested 36 trends were detected. For community biomass, five trends were significant; all had positive slopes and occurred in the James and York rivers. For species richness, six trends were significant; all had positive slopes with three trends in the James River, two trends in the York River and one trend in the main-stem of Chesapeake Bay. For abundance of individuals, 17 trends were detected; all abundance trends were seasonally dependent, had positive slopes and occurred at 12 of the 16 stations. For opportunistic biomass composition, four trends were significant; all had positive slopes with one trend in the lower Rappahannock River and three trends in the main-stem of Chesapeake Bay. For equilibrium biomass composition four trends were significant; two trends had positive slopes (one in the James River and one in the York River) and two trends had negative slopes (one in the Rappahannock River and one in the main-stem of Chesapeake Bay). Trends in the James and York rivers were considered to indicate improving conditions for the benthos, while trends in the lower Rappahannock River and the main-stem of the Chesapeake Bay were considered to indicate deteriorating conditions. Deteriorating conditions for the benthos were associated with regions exposed to summer, low dissolved oxygen events. The trends in the indicators of benthic biological community health were inferentially related to trends observed in water quality conditions in the tributaries and main-stem of Chesapeake Bay. All major water quality and biotic trends appeared to correspond in an ecologically meaningful manner.     

The effect of water surface temperature on lake breezes and thermal internal boundary layers

A two-dimensional prognostic numerical model has been used to study a lake breeze event reported by Keen and Lyons (1978). Model predictions showed fair to good agreement with the observations. For the mature lake breeze, the model predicted inflow at the coast within about 1.5 m s^–1 of the observed value, lake breeze depth within 50–90 m of the observed, and inland penetration within about 6 km of the observed. The top of the thermal internal boundary layer (TIBL) was associated with a minimum in the predicted turbulent kinetic energy profile. This may be of consequence for attempts to evaluate pollutant dispersion using numerical models.Predicted lake breeze characteristics showed little sensitivity to temperature of the water surface, except when the water surface temperature was increased to a value exceeding the inland maximum temperature. The most sensitive lake breeze characteristic was the TIBL, which grew more slowly with inland distance and persisted for a greater distance inland as the lake surface became colder.     

Current research at CSIRO Australia on multi-element laterite geochemistry for detecting concealed mineral deposits

Currently a group of five scientists within CSIRO is collaborating with a group of exploration geoscientists (managed by Greenbushes Tin Ltd.) under an industry supported research/application thrust on multi-element laterite geochemistry. The broad aim of the study is to take findings on laterite geochemistry from the stage of individual orientation studies into effective operation.     

Some conceptual models for geochemistry in areas of preglacial deep weathering

In some glaciated regions, weathered mantles, formed under previous climatic regimes, were not always eroded bare by glacial activity, but instead lie buried beneath the glacial overburden. It is obviously important that geochemical exploration programs in such terrain should take into account some of the known regolith features seen in deeply weathered regions. The effects of glacial action upon deeply weathered terrain are considered in three conceptual models. The critical factor in each is the depth of truncation of the preglacial weathering profile. All three proposed models are dynamic systems and a wide range of intermediate situations must be expected.In Model 1 a complete, largely undisturbed, weathering profile is preserved beneath till. The key characteristic is preservation of a lateritic duricrust which may contain areally large (up to 200 km²) geochemical anomalies. It would be critical, firstly, that the duricrust be sufficiently continuous to allow a reasonable success rate in its being sampled, and secondly that the duricrust be recognizable in drill spoil. The most efficient geochemical exploration could be based upon wide-spaced overburden drilling directed at sampling the duricrust. For reconnaissance, holes could be based upon a 1-km grid where stratabound massive polymetallic sulphide or stratabound gold deposits are sought. Even wider spacing could be tried where larger-sized ore deposits are expected.Model 2 is characterized by a weathered profile that was partly stripped prior to glaciation. The essential feature is a vertically zoned weathering profile in the basement rock in which the upper levels of the weathering profile have undergone leaching of certain elements and lower levels contain enrichments of these elements. Any gossans present would show strong vertical zonation. Relatively strong sources for dispersion in till are likely to be enriched gossans where erosion has cut deep into the profile, zones of supergene enrichment of ore deposits, and supergene ore deposits themselves. In many situations, saprolite under glacial drift would be too soft to provide boulders so important in conventional till prospecting.The essential ingredient in hypothetical Model 3 involves progressive planing away of the weathering profile by glacial action. Thus any halo in duricrust is initially dispersed, followed by dispersion of progressively deeper levels of saprolite. If taken deep enough the supergene enriched zone of a mineral deposit could add to the glacial dispersion. A broadly zoned anomaly would be expected; a till anomaly would be characterized distally by elements from the former duricrust anomaly, with elements more characteristic of supergene zones closer to the source.