Climate information associated with a glaciation, such as temperature or moisture source, is recorded by the oxygen isotope composition of its ice. Unfortunately, few glacial ices on Earth have survived for more than 1 million years. The oxygen isotope composition of older glacial ices must be found indirectly via oxygen-bearing minerals that formed in the glacial meltwater. This is difficult because of the scarcity of suitable minerals and deposits formed and preserved in meltwater environments. Yongbo Peng and colleagues show that sulfate minerals (barite and malachite) in the immediate vicinity of chalcocite clasts in a Neoproterozoic diamictite from South China bear extremely negative oxygen isotope values. The low oxygen isotope sulfate minerals are best explained by formation via chalcocite oxidation in glacial meltwater. The data suggest that the diamictite was deposited on land in Neoproterozoic glacial meltwater that had almost the same oxygen isotope value as modern glaciers in Antarctica. This study opens up a new possibility for retrieving glacial meltwater isotope signatures in deep Earth history.
Northeast African vegetation change over 12 m.y.
Sarah J. Feakins et al., Dept. of Earth Sciences, University of Southern California, 3651 Trousdale Parkway, Los Angeles, California 90089-0740, USA. Posted online 17 Jan. 2013; http://dx.doi.org/10.1130/G33845.1.
This study by Sarah J. Feakins and colleagues reports vegetation change over 12 million years i
|Contact: Kea Giles|
Geological Society of America