关键词: 地壳运动, 晚更新世, 古地震, 福建

Abstract: Crustal movement in Shenhuwan Bay area during the early and middle stages of late Pleistocene was dominated by subsidence, resulting in the deposition of alluvial and fluvial gravel-bearing sandy clays. Since the middle stage of late Pleistocene, crustal movement here has been characterized by uplift followed by subsidence. In the past 1 500 years, the crust was relatively stable. During the time period of 25.58± 2.49ka～15.46ka B.P., the crustal movement in Shenhuwan Bay was characterized by uplift simultaneous with the eustatic change of sea-level. The amplitude of uplift reached up to 8m, and the rate of uplift was about 0.78mm/yr. During that time, the coastal environment was relatively stable, and oysters were growing in Shenhuwan Bay. In 15.46～11.00ka B.P., however, the crust in Shenhuwan Bay was rapidly uplifted. The amplitude of uplift reached up to 10m or more, while the rate of uplift reached up to 2mm/yr. In that period, the Shenhuwan Bay had possibly experienced sudden uplift caused by strong earthquakes, resulting in the rapid escape of the ancient oyster bank from the tidal zone to avoid wave erosion. At that time, several low-lying depressions filled with late Pleistocene gravel-bearing sandy clays were formed in the Shenhuwan Bay, while the ancient oyster bank had become a tableland. Afterward, the crust tended to be stable, and forest was flourishing in the low-lying land of the Shenhuwan Bay. At 7 000yr B.P. a sudden crustal subsidence had occurred in the Shenhuwan Bay due to a strong earthquake, which caused the transformation of low-lying land into the lagoon environment, and hence the ancient oyster bank became closer to the sea level. Since 2,800yr B.P. the Shenhuwan Bay had been slightly uplifted again, and the lagoon had become land. A strong earthquake occurred at 2 000yr B.P. had given rise to the sudden crustal subsidence in Shenhuwan Bay, causing the submergence of the ancient forest into a deeper sea bottom, and the return of the ancient oyster bank to the tidal zone or offshore. It is concluded that in the past 45,000 years, the Shenhuwan Bay had experienced a complicated process including subsidence-uplift-sudden uplift-stable-sudden subsidence-stable-slight uplift-sudden subsidence-stable, and at least 3 strong paleoearthquakes. It seems that the Shenhuwan Bay had experienced 3 times of land-forming and 3 times of sea-forming processes.

Key words: Crustal movement, Late Pleistocene, Paleoearthquake, Fujian