July 2009 Geology and GSA Today Media Highlights

Variations in 238U/235U in uranium ore deposits: Isotopic signatures of the U reduction process?
Charles John Bopp IV et al., University of Illinois at Urbana-Champaign, Dept. of Geology, 245 Natural History Building, 1301 West Green St., Urbana, Illinois 61801, USA. Pages 611-614.

Variations in uranium isotope ratios have been both hinted at and refuted in the geological literature. Recent work has shown, however, that uranium isotope ratios do vary by geologic setting. Bopp et al. analyzed a subset of the samples first analyzed by Cowan and Adler in their 1976 paper on variations of 235U content in uranium ores. They confirm their results by modern multicollector-inductively coupled plasma-mass spectrometer and double isotope tracer methods, showing an approx. one part per mil difference between samples drawn from lower-temperature reduced (sandstone) uranium deposits and higher-temperature (magmatic) uranium deposits. They go further and hypothesize that this is due to an unorthodox isotope effect called the nuclear field shift. Finally, they propose that this effect could be used as a tracer to monitor the remediation of uranium contamination.

Plant-driven fungal weathering: Early stages of mineral alteration at the nanometer scale
Steeve Bonneville et al., Earth and Biosphere Institute, School of Earth and Environment, University of Leeds, Leeds LS2 9JT, UK. Pages 615-618.

For the first time, the boundary between fungi and rock has been imaged on a nanoscale --unraveling the fundamental processes by which fungi break down rocks into soil whilst extracting essential nutrients. Bonneville et al. show that fungi launch a dual attack to decompose rocks, first weakening them through mechanical strain and then by chemical alteration. This process is extremely common (occurring in 90% of trees in the Northern Hemisphere where roots are in symbiosis with fungi), but up to this point little understood. In exchange for the delivery of nutrients, the fungi receive carbon that has been fixed by the trees during photosynthesis, which effectively links the carbon cycle with the formation of soil from rocks. The implications of this work are therefore very broad, from soil fertility and agriculture to the chemistry of river water, the atmosphere, and Earth's climate.

Late Miocene onset of the Amazon River and the Amazon deep-sea fan: Evidence from the Foz do Amazonas Basin
J. Figueiredo et al., Dept. of Earth and Ocean Science, University of Liverpool, Liverpool, UK. Pages 619-622.

Oceanic margins provide a unique insight into paleoclimate and paleogeography on land. Although it seems contradictory, sediment aprons in the proximity of major rivers hold a continuous record, whereas evidence from land is mostly scattered. Until recently, the Amazon Fan kept its secrets on the history of the Amazon River tightly. A sediment column of over 10 kilometers in thickness proved a hard nut to crack, and scientific drilling expeditions such as the Ocean Drilling Program could only reach a fraction of it. However, recent exploration efforts by Petrobras -- the national oil company of Brazil -- lifted the veil and for the first time permitted an insight into the history of one of the mightiest rivers on Earth. Sedimentological and paleontological analysis showed that the Amazon River was initiated as transcontinental river around 11 million years ago and took its present shape around 2.4 million years ago. Prior to this time, a carbonate shelf characterized this part of the Atlantic coast. This research by Figueiredo et al. has huge implications for our understanding of South American paleogeography and the evolution of species in the Amazonian Region and the Atlantic coast of South America.