Impact crater lakes potentially form valuable climatologic archives. The lacustrine succession of the 15-million-year-old Ries Crater Lake has previously been interpreted as climate-controlled development from a playa to a highly saline soda lake, which successively decreased in salinity to reach freshwater sedimentation with temporary coal swamps. New multidisciplinary investigations based on a partial section now question this view: The sediments of this new drill core reflect increasing, not decreasing salinities, with brown coals formed by plant debris swept into a hypersaline setting. In addition, the chemical composition of the inflowing waters changed due to the weathering of different ejecta layers in the catchment area. Interpolated to the whole succession, a new model for the Ries Crater Lake is developed: After the development of a brackish soda lake and erosion of the upper ejecta blanket (suevite), an increasing ion influx from the lower ejecta (Bunte Breccia) caused a change to a marine-like, and finally hypersaline salt lake. Therefore, intrinsic factors, such as weathering history in the catchment area, probably dominated over external, climatic factors with respect to the chemical and ecological evolution of this impact crater lake. Moreover, the initial suevite blanket might have been more widespread than previously assumed.
Oroclines: Thick and thin
S.T. Johnston et al., School of Earth & Ocean Sciences, University of Victoria, PO Box 3065 STN CSC, Victoria British Columbia, Canada V8P 4B2. Posted online 22 Feb. 2013; http://dx.doi.org/10.1130/B30765.1.
Folded rocks characterize young and old mountain bel
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Geological Society of America