12 consecutive monthly sediment samples were collected from the tidal flat surface in Dafeng County, Jiangsu province. Palynological analysis of these samples indicates that seasonal palynological features of the tidal flat sediment are distinct and some palynological indices such as species percentages of Arboreal and Herbaceous pollen and spore are good indicators for discriminating the depositional seasonality of the tidal flat sediment. Sedimentary sequences formed between 1984 and 1994 were used to verify this method. The result proposes that this method can be applied to muddy flat and the species percentage of arboreal pollen is the best indicator for the seasonality study of the tidal flat sediment.The possible response of typhoon and storm surge frequency in response to global warming has aroused much interest among scientists. Simulated tests have illustrated that the intensity of typhoon or hurricane would increase as the climate warms [1,2] . Our previous result also showed that the increased frequency of typhoon occurring in the west Pacific Ocean and landing on China is related to global warming [3] . When the climate in the past (e.g. the middle Holocene) was warmer than the present, was the storm surge frequency greater than the present? In terms of ascertaining the ancient storm surge frequency, the key problem is how to confine the time interval between two storm surge events. Modern dating methods could not solve this problem. We have to rely on the sediment that has recorded the storm surge information. In order to discriminate the storm sediment formed by typhoon from that formed by cold snap or cold front, we have to discriminate the winter sediment from the summer one.
Research methodsUsing the ratio of spring pollen to summer and autumn pollen, Wu and Gray indicated that the thin beddings with alternative black and white colors found in the lascustrine sediment of the middle Pleistocene are a kind of seasonal laminae [4] . As for the successively deposited tidal flat sediment, its sporopollen assemblage should vary with the seasons. In order to understand the features of the tidal flat sediments deposited in different seasons and their discriminating indices, we had, from April 1993 to March 1994, observed and sampled on the tidal flat, which remained in accumulative condition and located in the vicinity of Doulonggong at Dafeng County in the middle of Jiangsu coast. Twelve mud samples were collected from the tidal flat surface during the monthly neap. In addition, three other mud samples were collected on the tidal flat surface at Maojiagong, Dongtai County in June, September and December of 1993. All of these samples were analyzed in the laboratory by sporopollen analysis. Based on the results, the seasonal features of the tidal flat sediment and their discriminating indices are discussed.
ResultsThe results of sporopollen analysis are: ⅰ) The total number of the sporopollen species is the highest in the spring, reaching 27 and the lowest in the autumn, only 4 (table 1); the second highe...