Land mollusk records from the Luochuan loess sequence and their paleoenvironmental significance

摘要

Terrestrial mollusk fossil assemblages of the Luochuan loess section have been investigated so as to improve the reconstruction of environmental changes in the last 110 ka. A total of 118 samples, taken at an interval of 10 cm in the S0-S1 portion, have been analyzed. Results show that mollusk fossil assemblages have recorded detailed paleodimatic and paleoecological changes. The Luochuan area bas experienced cold-dry and warm-humid alternations in the last 110 ka. However, even under the prevailing cold-dry condition, short-term or seasonal warm-humid climates frequently occurred in this area, reflecting the impact of summer monsoons temporarily. Comparison of mollusk records from the Luochuan 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 Plateau may have been also subjected to the influences of the Indian monsoon to a certain extent in the geological past. The presence of some specific cold-humid and cold-dry species represents deteriorated climate conditions, which might be the cooling events similar to the Heinrich events recorded in the Northern Atlantic. Six principal factors obtained by correspondence analysis and their related environmental significance have been discussed.