Palaeoenvironmental Changes of the Ancient Nihewan Lake Area-Sr Isotope Evidence from Xiaodukou Foraminifera

By using the improved trace(50μg) Sr isotope analytical method the ^87Sr/^86Sr ratios of Xiaodukou foraminifera fossils were measured,giving a range of 0.71105-0.71274,apparently higher than the value of contemporaneous seawater(0.709087-0.709147)and also slightly higher than the average value of modern Yellow River(0.7111),demonstrating that the contemporaneous environment where Xiaodukou foraminifera inhabited was an inland lake.Detailed analyses of △ Sr values showed that there occurred an event responsible for environmental changes in the ancient Nihewan Lake area during the time(about 1.0Ma ago)when Xiaodukou foraminifera appeared.Because of strong evaporation the salinity of the lake would increase and a regional salt-water of brackish-water lacustrine environment would be produced,thus providing a suitable and inhabitable environment for foraminiferae.It is concluded that Xiaodukou foraminiferal fossil assemblaes belong to non-marine foraminiferal species.

By using the improved trace (50μg) Sr isotope analytical method the ~87Sr/~86Sr ratiosof Xiaodukou foraminifera fossils were measured, giving a range of 0. 71105 - 0. 71274, apparently higher than the value of contemporaneous seawater (0. 709087 - 0. 709147 ) and alsoslightly higher than the average value of modern Yellow River (0. 7111 ), demonstrating thatthe contemporanoous environment where Xiaodukou foraminifera inhabited was an inland lake.Detailed analyses of △Sr values showed that there occurred an event responsible for environmental changes in the ancient Nihewan Lake area during the time (about 1.0 Ma ago) whenXiaodukou foraminifera appeared. Because of strong evaporation the salinity of the lake wouldincrease and a regional sall-water or brackish-water lacustrine environment would be produced,thus providing a suitable and inhabitable environment for foraminiferae. It is concluded that Xiaodukou foraminiferal fossil assemblages belong to non-marine foraminiferal species.