Preliminary studies on the core sediments of Ulaan Lake in Mongolia

Abstract

Ulaan Lake, which is located in Umungobi Province, the southern part of Mongolia, was a large lake with 25 km in length and 15 km in width when the lake level was the highest. But the lake has been dried-up since 1980s, and only the vestige of this lake remains now. This phenomenon seems to be related to global warming of the Earth, especially reflecting desertification of East Asia. We collected three sets of (668 cm, 830 cm, 1069 cm long) core sediment from three sites of Ulaan Lake, and the Quaternary paleoclimatic variations will be reconstructed by integration of sedimentological, mineralogical and geochemical analyses with pollen data. Core sediments were split into two halves and sedimentary facies were defined by macroscopic visual description including color, sedimentary structures and content of fossil and plant debris. Additionally, core images were obtained by using X-radiography, and magnetic susceptibility was measured. In the 830 cm long core, collected in the southern part of lake, sediment from the top to 10 cm includes sheet crack sand clay seam, and calcareous layer is developed at 13 cm from the top. Sediment from the top to 170 cm is almost homogeneous in color (10YR-5YR), whereas sediment below 170 cm horizon contains mottled features and several discrete cm-thick grayish layer (near 360 cm). This observation indicates that this area has been well-drained above ground water level with possible some faunal and floral activities. Plant debris are included ubiquitously and abundantly in the core interval from top to 150 cm, suggestive of root activity due to low groundwater level. Magnetic susceptibility value is almost constant down to 120 cm from the top, sharply drops down at near 120 cm and then increases gradually downcore. The sediment will be dated using 14C and OSL(optically stimulated luminescence). This multi-proxy study of sediment cores from Ulaan Lake will provide the continuous record of the paleoclimatic conditions in the southern M