海南岛东部陆架海底地貌

SUBMARINE GEOMORPHOLOGY OF THE EASTERN CONTINENTAL SHELF OF THE HAINAN ISLAND

通过二十多条测线的测深、旁测声纳和浅地层连续测量的调查以及底质等资料，概述了海南岛东部陆架海底堆积平原地貌及其上的地貌类型，其中海底沟、坎、岗阜等地貌类型的线性排列和分布与古海岸线的位置相应。

a Data from more than 20 survey-lines of sidescan sonar,subbottom profile andsounding were used to outline the geomorphic feature and type of the east-northeasterncontinental shelf of the Hainan Island. 1)The aast-northeastern continental shelf of the Hainan Island,is broad in its east-ern part and narrow in its southwestern part.Its landform runs in NE-Sw direction,breaking into the continental slope at the depth of 130-150m.2)The eastern continental shelf of the Hainan Island can be divided into the innerand outer shelf accumulational plains. Data from subbottom profiles and sediments andtectonism show that the greater part of the outer shelf accmulational plain is mainlyrelict accumulation and many places were subjected to erosion. On the entire shelf floor,there are many kinds of geomorphologic features.Off the eastern Hainan coast in thenorth,there is a submarine shoal off the Tonggu spit and undersea delta off the Wan-quan River mouth,and along its southeastern coast,there is a submerged coastal terrace.In the northeast of the outer continental shelf,are wavy relief features,and at its south-western part are erosional depressions,Subbottom profile data show that there areburied ancient river courses and paleodepressions,and along the northeast part of theouter edge of the continental shelf,are pockmarked sands of diagonal bedding andmounds extending in NE-SW direction along the 100m,125m and 150m isobaths. Themounds are outcrops of buried strata or bulges,some exposed On the sea floor and somecovered by sediments.3)From data of subbottom profiles,it can be seen that buried ancient river coursesand paleodepressions are well developed.Gullies and scarps developed in the epicontinen-tal shelf correspond to buried ones,They are distributed separately at the locations of 100m,125m and 50m isobaths and arrange in a linear way.The exposed diagonal beddingof the foreset bed of the ancient delta is continuous with the buried bedding.The 20m,100m,125m and 150m isobaths of the present East China Sea may possibly correspondto the locations of the paleoshore lines,This shows that the linear distribution of geo-morphic features such as gullies, scarps and mounds on the continental shelf which con-tinuously appear at the same depths is one mark of the paleoshore lines.