全新世长江三角洲地区的海进海退层序

现代三角洲地区海进海退是经常发生的,引起的原因是多方面的。本文根据500多个钻孔资料的分析对比,着重讨论全新世长江三角洲海进海退层序的特点,发育过程和控制因素。

HOLOCENE TRANSGRESSIVE-REGRESSIVE SEQUENCE IN YANGTZE DELTA AREA

Yangtze delta area has undergone a transgression caused by postglacial rapid rise in sea level and regression resulted from delta progradation. Consequently, the Holo-cene lithofacies relationship may be grouped into transgressive and regressive sequences. The transgressive-regressive sequence in delta plain of Yangtze consists of transgressive channel-fill sequence and overlying deltaic sequence. On the strandplain the transgressive sequence is composed mainly of barrier-lagoonal deposits; the regressive sequence consists of radiated bar sedimentary complex on the northern flank of Yangtze, and of progradation of tidal flat on the southern flank.Transgressive-regressive sequences in Yangtze delta area show a distinct cyclothem in ascending order: the variation in grain sire is coarse-fine-coarse; facies relationship: littoral-shallow marine-littoral; apparent resistivity pattern-high-low-high; climate referred by sporal-pollen assemblage is cold-temperate-cool. The changes of these features can be correlated fairly well with each other.With the alternation of transgression and regression the sand bodies are characterized by double beds in vertical distribution. The transgressive sand bodies are overlain by the regressive ones, and between them exists a wedge marine clay.