晋江龙湖湖盆古凹陷内古河流形成与消亡及与地震关系

根据野外调查及龙湖湖内和沿岸共78个钻孔岩心揭示的龙湖及沿岸混合花岗岩及其风化土、残坡积层和晚更新世以来的沉积层展布,分析了龙湖成湖前的凹陷和发育在凹陷内的古河流环境。研究发现龙湖湖盆内下游古河床相对邻近上游河床被大幅度抬升达3 m余。龙湖的最早湖相沉积年龄为2 430±90 aBP,其年龄落在导致古森林更深沉没于海的深沪湾晚全新世强古地震的时间范围内,认为龙湖的形成可能与2 430 aBP左右深沪湾大地震,导致控制深沪湾陆地地堑的衙口-氵丙州断裂西北侧地块翘起掀升,使得湖盆凹陷内下游古河床被快速抬升,古河流被堵塞有关。龙湖是地震断塞湖,不同于断陷湖,是向斜坳陷湖的又一种构造湖。研究得出龙湖成湖前的古河流约在7 000 aBP开始形成,这正是导致深沪湾古森林首次沉没于海的深沪湾早全新世强古地震大致年龄,结合古河床形成前的凹陷形态,认为龙湖湖盆内古河流的形成可能与7 000 aBP左右深沪湾大地震导致龙湖地区环境改变有关。

FORMATION AND ABANDONMENT OF A PALAEO-RIVER CHANNEL IN THE LONGHU LAKE DEPRESSION IN JINJIANG COUNTY, FUJIAN PROVINCE AND ITS RELATION TO PALAEO-EARTHQUAKE

Study of 78 boreholes,in addition to field investigation,have been carried out in the Lonhu Lake and its coast in Jinjiang County of Fujian Province.In the depression of Longhu lake palaeo-river channels were developed before the lake formed and the inlets and outlets of the channels were defined with the sediment records from the 78 boreholes.We found that the formation of palaeo-river channels and the lake were all resulted from palaeo-earthquakes in the Holocene.The uplifting of the block in the lower reaches of the channels caused the formation of the Longhu Lake.The earliest lacustrine deposits in the Longhu Lake appeared 2 430±90 aBP.It coincided with the great earthquake happened in the Shenhu Bay region in Late Holocene from 2 800±100 to 1 460±90 aBP.which resulted in the subsidence of the palaeo-forests in Shenhu Bay into the sea.The bottom of the lower reach of the river channel was about 3 meters higher than that of the upper reach.It suggests that the Longhu Lake was formed by the earthquake in（2 800±100）^{1 460±90}aBP.which blocked the river channel.In this regard,the Longhu Lake is a seismic fault blocked lake only formed in Late Holocene.The palaeo-river was formed 7 000 aBP in early Holocene as the result of another great earthquake which made the palaeo-forests of Shenhu Bay basin sunk for the first time into the sea.The earthquake brought about great environmental changes in the region of the Shenhuwan Bay.