| Knowledge of Quaternary sedimentary environment. Quaternary lithology and its controlling factors in the Changjiang delta is urgently needed owing to the fast-developing urbanization and associated large engineering. The late Quaternary lithology is especially concerned, as most projects require the character of the sediment within -100 m in depth. This study utilizes several Quaternary and late Quaternary cores obtained during the recent geological survey, tending to study the evolution of the depositional environment, in associated with the neotectonics, and the oscillations of the paleoclimate and sea level in the present Changjiang delta plain.A Quaternary core (J25) of Pudong airport and three late Quaternary cores (J10, FX, and A5) were drilled for this study. Lithology was described in field. Measurement of paleomagnetism and Electronic Spin Resonance (ESR) were done for the dating of core J25. Carbon-14 and Optical Simulated Luminescence (OSL) were made for the dating of core MFC, FX, and A5. Grain size, microfossils, pollen and spore were analyzed for the all cores. Clay mineral was additionally measured for core J25. Besides, numerous cores recovered by previous work are combined into the present study. Some opinions were obtained as following:1. The neotectonics controls the evolution of the sediment basin, paleo- depositional environment and pattern of the present Changjiang delta plain.Two major faults (Taichuang-Fengxian and Luodian-Xinchang) oriented NW-SE divides the basin floor of Changjiang delta plain into three steps, resulting the thickness of the Quaternary sediments increases from SW to NE significantly. Tectonic subsidence also keeps throughout the Quaternary. The southwest area of Songjiang, Jinshan and Fengxian that is the first step was base rock exposed and was the highland for erosion during early Pleistocene. Filled gullies and valleys with some isolated hills dominated the second step that is sited between the two faults. Meandering river started to develop in the third step that is east to the Luodian-Xinchang fault. During mid Pleistocene, braided river developed in the first step owing to erosion and tectonic subsidence. The eastern part of second and third steps was meandering river-flood plain dominant and a major river named as ancient Liunan run through the area. Sediment composition and characteristicsof grain size obtained from core J25 evidenced such tectonic-controlled evolution of paleogeographic environment in the study area.2. Criteria including pollen and spore assemblage, clay mineral assemblage, crystallinity of clay mineral were obtained to reconstruct the climate change through Quaternary, showing pattern of cool in early Pleistocene, warm in mid Pleistocene, and warm and wet in late Quaternary. Also, some mid and short scale climate events occurred during different periods.Warm and dry climate prevailed during Pliocene, supported by the pollen and spore assemblage, clay mineral assemblage, and the high crystallinity of smectite of sediments from core J25. The smectite-dominant clay mineral assemblage also reveals the sediment source was primarily igneous rock.Abundant highly crystallinity illite and some kaolinite and chlorite of the early Pleistocene sediments show abrupt climate change from Pliocene to early Pleistocene, indicating cool and wet climate.During mid Pleistocene, pollen and spore assemblage demonstrate warm and wet climate, which is also evidenced by higher contents of kaolinite and smectite. Violent climate oscillation occurred during this period, supported by the intense change of clay mineral contents.Pollen and spore abundant increased significantly since late Pleistocene, indicating warm and wet environment. The fluctuation of pollen and spore keeps good agreement with the crystallinity of smectite during this period. Besides, very few pollen and spore and low content of kaolinite revealed the last glaciation maximum during late Pleistocene.3. The depositional environment and lithology of late Quater...
|
PDF Full Text Request