Geochemical diversity of shergottite basalts: Mixing and fractionation,and their relation to Mars surface basalts

The chemical compositions of shergottite meteorites, basaltic rocks from Mars, provide a broad view of the origins and differentiation of these Martian magmas. The shergottite basalts are subdivided based on their Al contents: high‐Al basalts (Al > 5% wt) are distinct from low‐Al basalts and olivine‐phyric basalts (both with Al < 4.5% wt). Abundance ratios of highly incompatible elements (e.g., Th, La) are comparable in all the shergottites. Abundances of less incompatible elements (e.g., Ti, Lu, Hf) in olivine‐phyric and low‐Al basalts correlate well with each other, but the element abundance ratios are not constant; this suggests mixing between components, both depleted and enriched. High‐Al shergottites deviate from these trends consistent with silicate mineral fractionation. The “depleted” component is similar to the Yamato‐980459 magma; approximately, 67% crystal fractionation of this magma would yield a melt with trace element abundances like QUE 94201. The “enriched” component is like the parent magma for NWA 1068; approximately, 30% crystal fractionation from it would yield a melt with trace element abundances like the Los Angeles shergottite. This component mixing is consistent with radiogenic isotope and oxygen fugacity data. These mixing relations are consistent with the compositions of many of the Gusev crater basalts analyzed on Mars by the Spirit rover (although with only a few elements to compare). Other Mars basalts fall off the mixing relations (e.g., Wishstone at Gusev, Gale crater rocks). Their compositions imply that basalt source areas in Mars include significant complexities that are not present in the source areas for the shergottite basalts.     

Small melt inclusions can record bulk magma compositions: A planetary example from the Martian basalt (shergottite) Tissint

Melt inclusions in igneous minerals can provide constraints on magma compositions, especially for planetary samples where mass is severely limited. Small inclusions (<15 μm diameter) are more abundant than large ones, but have been used little from concern that they did not entrap average magma, but are rich in melt of a diffusional layer against the host mineral. We compared bulk compositions and calculated original compositions of small and large melt inclusions in the Martian basalt meteorite (shergottite) Tissint. Small and large melt inclusions are consistent with the same line of igneous differentiation, have the same abundance ratios for incompatible elements (P, Ti, Al, K, Na), and are consistent with derivation from the bulk composition of Tissint (inferred to represent its parent melt composition). For Tissint, then, small melt inclusions show no evidence of entrapping diffusional boundary layers, and appear to have entrapped bulk magma. Thus, its small inclusions can be as useful as larger ones; this may be so for other planetary samples, and thus provides an additional tool for investigating planetary magmas.     

Spreadsheet Modeling of Slug Tests Using the van der Kamp Method

Slug testing is frequently employed to calculate aquifer transmissivity and hydraulic conductivity. The van der Kamp technique for interpreting slug test data which experience force-free water level oscillations is not routinely employed because it requires adjusting equations to match the observed well response data. This adjustment can be rapid and convenient when a commercial spreadsheet is employed.     

The quaternary travertine deposits of Europe and Asia Minor

A summary is provided of the published information relating to all aspects of Quaternary travertine formation in Europe west of the Ural Mountains. The deposits have been divided into two broad groups, the meteogene travertines, which result primarily from the degassing of soil-borne aqueous CO₂, and thermogene deposits resulting from the degassing of thermally generated CO₂. Meteogene deposits are rare above latitude 58°N, and in regions where the mean annual air temperature is below 5°C. A significant positive correlation exists between mean air temperature and travertine deposit thickness. The combined effects of temperature and rainfall are used to provide a zoned map showing the travertine-forming potential of limestones within the region. Information from ¹⁴C dating indicates that deposition reached a maximum in the period 5–10 ka BP) and is currently limited by land and water management practices in the populated areas. Thermogene deposits occur in regions of high CO₂ discharge resulting from tectonic activity, such as Italy and Turkey where there is much vulcanism. These travertines are frequently more massive and less readily weathered than meteogene deposits. Fully referenced information is provided for 320 important, mostly well studied sites (227 meteogene, 93 thermogene), of which 156 are currently active.     

Suspended sediment load in the Amazon basin: An overview

In this report the state of knowledge of sediment transport by rivers of the Amazon drainage basin is reviewed. On an annual basis the Amazon river transports about 1200×10⁶ tons of sediment from the South American continent to the ocean, which puts it among the world's largest rivers in this respect. The main source of sediment is erosion in the Andes mountains and this material is progressively diluted with sediment poor runoff from lowland draining tributaries. Almost half of the Amazon river transport is attributable to one tributary, the Rio Madeira (488×10⁶ t/y). The Rio Negro, which drains the N crystalline shield, has a comparable water discharge to the Rio Madeira, but only contributes 7×10⁶ t/y. In general the sediments in transport are about 1% organic carbon by weight and this results in an annual particulate carbon to the oceans of 13×10⁶ t/y. Total carbon transport, particulate plus dissolved, is about twice this amount.     

Mountain environments: An assessment

The celebrated 1972 Stockholm environmental conference focused attention on the condition of the world's environment. A twenty year retrospective summary is provided by the introduction and specialty papers on all facets of mountain society and habitat relationships. Theories, models and paradigms that guided mountain research are critically examined. Specific attention is given to the application of the ecology paradigm. Contemporary discoveries and developments about resource management in mountains are elucidated. Assessments of the mountain environment, including wildlife habitat, tourism and recreation, forests, hazards, deforestation, food plant biodiversity, risk and hazard, are provided by the specialty articles. These papers were prepared for the 1992 Earth Summit in Rio de Janeiro.     

A microscopic study of the combustion residues of subbituminous and bituminous coals from Alberta, Canada

Chars produced by the combustion of a set of three coals from Alberta, Canada, were classified morphologically using reflected light microscopy. Produced chars are different in morphological features, pore thickness, anisotropy and degree of reactivity, because of differences in the vitrinite and inertinite contents.The subbituminous A coal produced the highest percentage of unreactive or slightly reactive components due to its high inertinite content (20.0%), followed by isotropic cenospheres. Isotropic cenospheres, both thin- and thick-walled, and exploded cenospheres are the characteristic chars produced by the high-voltile bituminous B coal, whereas the low-volatile bituminous coking coal produced cenospheres with granular anisotropy (mosaic) on the walls and abundant coke fragmentsOptical microscopy is useful in differentiating the performance of a series of coals during combustion based on petrographic composition and rank and can aid in understanding the relationship between ‘reactive’ and ‘non-reactive’ coal macerals to burnout performance.     

The weathering rates of some sandstone cliffs central Weald,England

Short-term (1-30 months) weathering rates were obtained for steep cliffs of Cretaceous Ardingly Sandstone in southern England, using a new photographic method. Mean rates for an exposed and a sheltered outcrop were 0.11 and 0.033 mm a^?1 respectively. Significant (p < 0.1) positive correlations were obtained with illumination and algal biomass and a significant negative correlation (p < 0.05) with slope angle. There was no correlation with grain size, porosity, or mean surface temperature. Highest weathering rates were observed on south- and west-facing exposed cliffs. The results are discussed with reference to algal growth, climate, and wind direction.