Nodular and massive calcretes, from alluvial terraces in the Sorbas area of southeast Spain, have been dated by the U/Th isochron method to between 8- > 350 ka. Alternative approaches have been used to generate the multiple samples for the isochron method for several of the calcretes. Dates agreed closely when obtained by total dissolution of a number of nodules or by the sequential dissolution in different acids of a single nodule. However, fractional dissolution of a single nodule in the same acid revealed two stages of precipitation of different age. It is considered that the calcretes may not be strictly pedogenic in origin and that groundwater processes linked to the alluvial environment may have been involved also. Nevertheless, their dates provide minimum ages for a chronostratigraphic framework for terrace evolution. (C) 2000 Elsevier Science Ltd.
ASJC Scopus subject areas
- Global and Planetary Change
- Ecology, Evolution, Behavior and Systematics