We explore the contribution of fractures (joints) in controlling the rate of weathering advance for a low-porosity rock by using methods of homogenization to create averaged weathering equations. The rate of advance of the weathering front can be expressed as the same rate observed in non-fractured media (or in an individual block) divided by the volume fraction of nonfractured blocks in the fr...

Plants affect the spatial distribution of soil microorganisms, but the influence of the local abiotic context is poorly documented. We investigated the effect of a single plant species, the cushion plant Silene acaulis, on habitat conditions, and microbial community. We collected soil from inside (In) and outside (Out) of the cushions on calcareous and siliceous cliffs in the French Alps along ...

Two data sets commonly used for geological resource assessment include bedrock geology and stream-sediment geochemistry. Traditional methods for determining relationships between these data include both qualitative and quantitative techniques. Qualitative interpretation and integration is generally based upon visual observations of spatial coincidence between the data. Quantitative results can ...

Digital elevation models of two “steady-state” mountain ranges, the Olympic Mountains (OM) and Oregon Coast Range (OCR), are used to examine relationships between slope distributions, the development of threshold hillslopes, and steady-state topography. Plots of drainage area versus slope for these mountain ranges exhibit substantial scatter that complicates comparison of range form to analytic...

Mass balance studies in forested catchments in the northeastern USA show that S losses via streamwater SO4 exceed measured atmospheric S inputs. Possible sources of the excess S loss include underestimated dry deposition, mineralization of organic S in soils, desorption of soil sulphate, oxidation of recently formed sulphides and mineral weathering. Evaluating the relative contribution of these...

The emission of methane and the higher hydrocarbons is observed in both mid-ocean ridge and subduction-related hydrothermal systems. It has been recently reported that methane emanating from an extensional ultramafichydrothermal system originates from the abiogenic reduction of (mantle) CO2 (1). The same process is also known to occur in subaerial subduction-related systems (2). These findings ...

Chromitites associated with strongly altered peridotite from six distinct localities in the Santa Elena ultramafic nappe (Costa Rica) have been investigated for the first time. Santa Elena chromitites commonly display a compositional variation from extremely chromiferous (Cr/(Cr+Al)=0.81) to intermediate and aluminous (Cr/(Cr+Al)=0.54). This composition varies along a continuous trend, correspo...

We apply a tool based on element distribution between orthopyroxene and clinopyroxene for quantifying rare earth element (REE) disequilibria in ultramafic rocks in the subsolidus state. We present case studies of the REE contents of mineral cores in mantle xenoliths and abyssal peridotites using in situ analytical tools. Even when only mineral cores are measured (to avoid enriched rims), equili...

Acanthomorphic acritarch fossils, including some interpreted to be the fossils of the earliest animal embryos, first appear in the lower Doushantuo Formation of the Yangtze Gorges area (YGA). Further, the complete paleontological and geochemical record for the YGA has played a central role in defining the global biological and geochemical backdrop that presaged and witnessed the dawn of diverse...

Fluids from the ultramafic-hosted Lost City hydrothermal field were analyzed for total dissolved organic carbon and dissolved organic acids. Formate (36–158 lmol/kg) and acetate (1–35 lmol/kg) concentrations are higher than in other fluids from unsedimented hydrothermal vents, and are a higher ratio of the total dissolved organic carbon than has been found in most marine geothermal systems. Iso...