The present study focuses on the temporal distribution of clay mineral in a new, complete type core ZX-1, recovered from the south-central Yangtze delta plain. Result demonstrates that the variation of clay mineral distribution in different Holocene stages is determined by several major physical factors, i.e. sea level fluctuation, climate change, and sediment sources.
Four diagnostic clay mineral suites are recognized from core bottom upward:
- Zone I - kaolinite and illite (late Pleistocene);
- Zone II - kaolinite and chlorite (early Holocene);
- Zone III - illite, smectite, and chlorite (early to mid-Holocene); and
- Zone IV - illite and smectite (late Holocene).
Smectite distribution in core sediment of early Holocene was linked to the rapid sea-level rise, which induced inundation of the current delta plain. Increase in kaolinite content as decrease in smectite, chlorite and illite in late Pleistocene stiff muds reflects a temporary climate warm stage in a general temperate to cold setting. As verified by pollen assemblages, chlorite high in Zone III of early Holocene can correlate to colder temperature and kaolinite high in Zone III of mid-Holocene was possibly associated with a climate warm. Clay mineral distribution also shed light on the late Quaternary sediment provenance of the study area. The terrigenous sediment sources of late Pleistocene and early Holocene were primarily derived from the provincial highlands, west of the study area, and the sediments of late Holocene were proved from the Yangtze basin. The mid-Holocene clay mineral suite indicates sediment input from both the western highlands and the Yangtze sources. This clay mineral study evidences potential usefulness in tracing sediment sources through time, and particularly is of significant value for better understanding the paleoenvironmental implication of the Yangtze delta, where sediment sources is being greatly altered by 3-Gorges dam.