Oxygen and carbon isotope ratios in gastropod shells as indicators of paleoenvironments in the afar region of ethiopia

Abstract

The oxygen and carbon isotope ratios in the shells of ancient freshwater gastropods, coupled with geological, geographical and hydrological data from their area and time of origin, can yield information concerning general climatic conditions prevailing at the time the gastropod lived. In addition, sequential oxygen isotope analyses along the growth spiral of the shell provides indications of seasonal variability in the life span of the organisms. Such data were collected for some freshwater gastropods collected from two lakes and two springs in the Afar region of Ethiopia, spanning late Pleistocene to modern age. Episodes of high rainfall in the Ethiopian highlands were clearly evident in the depleted δ 18O values in some shells, whiel arid spells produced enriched levels in others. Hot springs introduced an added complication to the isotope record. This study, on a region of particularly complex hydrology and highly variable environmental history, indicates the utility of stable isotope analyses as proxies for past climates, but also emphasizes the problems involved.