CORRELATION OF MODERN DELTAIC SEDIMENTARY SYSTEMS IN NORTH AND SOUTH CHINA

The mid-seventies is the period of full bloom in delta sedimentation researches on large rivers abroad, but the papers on delta sedimentation were published in the late seventies and the early-eighties in China. Recently delta studies are concentrating on fan-deltas and transgressive channel-filling sequence. The deltaic sedimentation studies contribute a favourable condition for comparison between deltaic sedim-etary systems in North and South China, which includes their general and distinct charactereristics. The pattern of main facies, the vertical sequence and the transgressive channel-filling sequence belong to the former, and the distribution model of deltaic sand bodies, the vertical superimposition, the facies criteria, the development and the reworking belong to the later (Table 1). This paper deals with the transgressive channel-filling sequence, the progradational rate and the reworking of Table 1 Correlation of the delta systems in Soth and North China deltaic systems. The transgressive channel-filling sequence overlain by deltaic sequence is a fining-upward one with an erasional base surface and gravelly sand or sand in its lower part. It usually contains foraminifera with an upward increase in marineness and also contains marine authigenic minerals such as glauconite in subtropic zone of South China. The transgressive channel-filling sequences in delta areas of the Yangtse, Luanhe, Nanliujiang Rivers can be put in order of marineness. The marineness of transgressive channel-filling sequence in the coastal area is higher than that in the apical area of the Yangtse delta. That in the coastal area of the Luanhe delta is similar to the later, but the transgressive channel-filling sequence in its apical area absents marine microfossil. According to simulating tests, field observations and our recent measurements in the Yangtse, Nanliujiang and Qiantangjiang Rivers, there are the intrusion of sea water, flood tidal current, the backwater caused by datum rising and the retrogressive aggradation in lower reaches of river. Data from modern tidal estuaries show that the distances of retrogressive aggradation, backwater, flood tidal current and intrusion of sea water decrease in proper order. The retrogressive aggradation caused by postglacial sea-level rising formed the transgressive channel-filling sequence, whose characteristics were controlled by flood tidal current and intrusion of sea water. During the maximum transgression, transgressive channel-filling sequence without marine criteria could develop where retrogressive aggradation occured but no flood tidal current, such as the Luanhe fandelta area. This would also develop in the subtropic Nanliujiang delta area, but it was rewoked into a single normal river sequence by the river.