韩江三角洲地貌发育的新认识

韩江三角洲从晚更新世中期开始沉积,经历了Q_3~(2-1)的古冲积扇、Q_3~(2-2)的占三角洲、Q_3~3的风化和新冲积扇、Q_4~1—Q_4~(2-1)的新三角洲、Q_4~(2-2)的贝壳堤和沼泽以及Q_4~3的沙堤-泻湖等六个发育阶段。发育模式为河流冲积扇与三角洲的交替发展。重新划分了三角洲的界线,面积为915.08km~2。划分出二类十亚类地貌类型。

NEW VIEWS ON GEOMORPHOLOGICAL DEVELOPMENT OF THE HANJIANG RIVER DELTA

It is considered that geomorphological develoment of the Hanjiang River Delta is deeply affected by fault-block tectonics based on the analysis of sedimentology and chronology including the analysis of diatom, foraminfera, ostracoda, spore-pollen, shell, grain-size, trace element and heavy mineral, and datings of 14C and TL, from 40 borehole sections of the delta. The Hanjiang River Delta began developing during trie middle stage of Late Pleistocene beause the TL age of the bottom sediment is 51 130 +2606 ys. B. P. and has undertaken six deposi-tional phases such as the ancient alluvial fan development in Q32-1, the ancient delta development in Q32-2, the weathering action and alluvial fan development in Q33, the new delta development in Q41-Q42-1 the shell ridge and swamp development in Q42-2, and the sand-ridge and lagoon development in Q43 On the lower branch plain of the delta there are four chains of big sand ridges which show the shorelines of the delta in the Han (about 2 000 ys. B. P.), the early Tang (about 1 400 ys. B. P.), the end of Song (about 700 ys. B. P.), and the Qing (about 150 ys. B. P.) respectively. The development model of the Hanjiang River Delta is considered as alternate changes from alluvial fan to delta. The dominant factors controlling the alternate changes arc sea level changes and topographic-tectonic condition there. Boundary and Surrounding landform of the delta have been discussed. Landforms of the delta and the surroundings are divied into two ypes such as deltaic plain platform-hill, and into ten subtypes such as flood highland, flood lowland, swamp lowland, store-water depression, sand-ridge, highland lagoon lowland, braided stream lowland, plalorm, isolated hill, and hill. Modern landform of the delta shows four characteristics as follows: (1) horn-like shape of the delta plain on the plane; (2) four chains of island hills on the plain: (3) strong relief of the plain; and (4) obvious regional deversity.