Comparison of grain-size distributions between nearshore sections and a deep-water sediment core from Dali Lake, North China, and inferred Holocene lake-level changes

摘要

The grain-size distribution of the sediments of closed lake basins is sensitive to lake-level changes and thus to changes in regional climate. Deep-water areas of lakes potentially yield high resolution, continuous records of sedimentation and lake-level changes. In contrast, the marginal areas of lake basins accumulate sediment in a wave-dominated, highenergy environment and may be more sensitive to lake-level changes than deep-water environments, but they might also be more affected by sedimentary hiatuses. Here, we present grain-size data from two sections of exposed nearshore sediments of Dali Lake, North China, and compare them with previously published results from a sediment core from the lake center. We used the grain size-standard deviation method to distinguish various grains-size components of the nearshore sediments, and compared the results with those from surface sediments from various depths in order to investigate past lake-level changes. Combining the grain-size results with a radiocarbon chronology, we defined four lake-level stages during the Holocene: (1) An intermediate lake level from early Holocene to 10.0 cal ka BP. (2) A high lake level from 10.0 to 6.6 cal ka BP. (3) A decline to an intermediate lake level from 6.6 to 1.0 cal ka BP. (4) An abrupt fall to a low lake level from 1.0 cal ka BP to the present when the marginal section was covered with eolian sand. Our results indicate that the total amplitude of lake-level variation during the Holocene was greater than 45 m. This record of lake-level change is in good agreement with previous results obtained from the lake center, and it indicates that the grain-size standard deviation method may be well suited for lake-level reconstruction from nearshore sediments. Moreover, the marginal sections provide evidence of an abrupt short-lived lake-level decline more clearly than the deep-water core.