Clay mineral assemblages at IODP Site U1340 in the Bering Sea and their paleoclimatic significance
Résumé
Clay mineral assemblages and crystallinities in sediments from IODP Site 1340 in the Bering Sea were analyzed in order to trace sediment sources and reconstruct the paleoclimatic history of the Bering Sea since Pliocene (the last ∼4.3 Myr). The results show that clay minerals at Site U1340 are dominated by illite, with a moderate amount of smectite and chlorite, and minor kaolinite. Sediment source studies suggest that the clay mineral assemblages and their sources in the studied core are controlled primarily by the climate conditions. During the warm periods, clay minerals originated mainly from the adjacent Aleutian Islands, and smectite/(illite+chlorite) ratios increased. During the cold periods, clay minerals were derived primarily from the Alaskan region, and smectite/(illite+chlorite) ratios decreased. Based on smectite/(illite+chlorite) ratios and clay mineral crystallinities, the evolutionary history of the paleoclimate was revealed in the Bering Sea. In general, the Bering Sea was characterized by warm and wet climate condition from 4.3 to 3.94 Myr, and then cold and dry condition associated with the enhanced volcanism from 3.94 to 3.6 Myr. Thereafter, the climate gradually became cold and wet, and then was dominated by a cold and dry condition since 2.74 Myr, probably induced by the intensification of the Northern Hemisphere Glaciation. The interval from 1.95 to 1.07 Myr was a transitional period of the climate gradually becoming cold and wet. After the middle Pleistocene transition (1.07 to 0.8 Myr), the Bering Sea was governed mainly by cold and wet climate with several intervals of warm climate at ∼0.42 Ma (MIS 11), ∼0.33 Ma (MIS 9) and ∼0.12 Ma (MIS 5), respectively. During the last 9.21 kyr (the Holocene), the Bering Sea was characterized primarily by relatively warm and wet climatic conditions.