中沙、西沙群岛海区表层沉积物中微型腹足类、双壳类的分布

MICROGASTROPOD AND MICROBIVALVE DISTRIBUTION IN SURFACE SEDIMENTS OF XISHA AND ZHONGSHA ISLANDS, SOUTH CHINA SEA

中沙、西沙群岛海区表层沉积物中微型腹足类、双壳类主要由热带、亚热带种类和广温性种类组成，并以典型的热带珊瑚礁型种类为主，见有腹足类176种，双壳类48种。可划分出3个沉积组合类型。温度、水深、底质、海底地貌是控制本区腹足类、双壳类分布的主要环境因素。腹足类、双壳类遗壳埋藏群由原地埋藏类型和异地埋藏类型组成。在珊瑚礁深水处这两种类型呈明显混合分布。在水深22，90，115m处属原地埋藏的潮间带或浅水类型含量丰富，优势属种明显，这表明自晚更新世末次冰期以来，南海海平面上升过程出现3次间歇性停顿。随水深增大，异地埋藏类型增多，反映了群岛区陡峻的地势与海流在礁壁处形成的垂直分流对生物埋藏群分布的影响。

The whcromolluscs collected from the sea bottom samples in the waterdepth of 20-1150m in the Xisha and Zhongsha Islands of the South China Sea(15°24, -17°08'N 115, 10'-114°57'E) include 176 microgastropod species belongingto 39 hanilies and 113 genera, and 48 microbivalve species belonging to 21 familiesand 40 genera. Three assemblages have been divided in this region in the water depthof 20-1150m according to biotal distribuhon and environmental factors. Temperature,water depth, substrates and sea bottom topography can be regarded as the majorenvironmental factors controlling the deposihonal distribuhon of ndcrogastropods andmicrobivalves in this region. The biota in this region is composed of three types:thehdal zone or shallow water representatives of autochthonous deposit the deep waterrepresentatves of autochthonous deposit and the representahves of allochthonous deposit.In the deep water are the autochthonous deposit and the allochthonous deposit mixtogether, forming a biota with mixed ecological featUres. The hdal zone or shallowwater representahves are obviously rich in the water depth of 22m, 90m, 115m,indicahng that there were at least three pauses during sea level rise since Holocene.