江苏洋口港地区埋藏古潮成砂脊年代学特征及古环境意义

Geochronological features of the buried ancient sand ridge in Yangkou port,Jiangsu,and their paleoenvironmental significance

江苏如东县洋口港地区普遍发育末次冰盛期(MIS 2)"第一硬粘土层"。全新世早期,该区暴露侵蚀,仅局部地区发育潮汐水道。全新世中期(7 000 a B.P.)以来,在最大海侵作用影响下,研究区大部分地区以潮坪沉积为主;高海平面时期(5 220 a B.P.),研究区大部分地区处于水下沉积环境;随着海平面下降,北部地区发育古潮成砂体,属于滨海潮坪—潮成砂脊沉积体系。根据地层沉积特征,识别出4期埋藏古潮成砂脊。地层AMS14C年龄表明,4期砂脊是依次在5 220～1 000 a B.P.沉积形成的,反映了潮汐动力作用下古潮成砂脊的动态演化过程。

During the last glaciation(MISⅡstage),the Yangkou port area in Rudong County,Jiangsu Province was developed with the Upper Most Hard Clay.This area,since the early Hologence,had been subjected to erosion,with tidal channels developed locally in this area.Since the middle Holocene,the study area was dominated by tidal-and-flat deposits under the effect of the maximum transgression(around 7 000 a B.P.).At the high sea level period(5 220 a B.P.),most of the study area was submerged in the sea.With the sea level falling,north of the Yangkou port developed a series of ancient radial sand ridges,which belongs to a sedimentary system of coastal tidal flat-tidal sand ridges.Based on the sedimentary features,four-period buried tidal sand ridges have been recognized.Stratigraphic AMS 14 C ages indicate that these ancient tidal sand ridges formed separately from 5 200 a B.P.to 1 000 a B.P.,reflecting the active evolution process of the ancient tidal sand ridges under the effect of tidal dynamics.