LAND MOLLUSK RECORDS FROM THE LUOCHUAN LOESS SEQUENCE AND THEIR PALEOENVIRONMENTAL SIGNIFICANCE

Terrestrial mollusk fossil assemblages of the Luochuan loess section h ave been investigated so as to improve the reconstruction of environme ntal changes in the last 110 ka. A total of 118 samples, taken at an i nterval of 10 cm in the S0-S1 portion, have been analyzed. Results sho w that mollusk fossil assemblages have recorded detailed paleoclimatic and paleoecological changes. The Luochuan area has experienced cold-d ry and warm-humid alternations in the lat 110 ka. However, even under the prevailing cold-dry condition, short-term or seasonal warm-humid c limates frequently occurred in this area, reflecting the impact of sum mer monsoons temporarily. Comparison of mollusk records from the Luoch uan loess sequence with those of grain-size and aridity index from RC 27-61 core in the Indian Ocean reveals obvious similarities in several time intervals, suggesting that climate variations in the Loess Plate au may have been also subjected to the influences of the Indian monsoo n to a certain extent in th geological past. The presence of some spec ific cold-humid and cold-dry species represents deteriorated climate c onditions, which might be the cooling events similar to the Heinrich e vents recorded in the Northern Atlantic. Six principal factors obtaine d by correspondence analysis and their related environmental significa nce have been discussed.