摘要:
从生物礁碳酸盐岩的沉积特征、孤立台地生物礁沉积模式2个方面对巴哈马滩与西沙群岛进行对比分析:巴哈马滩礁区主要沉积粒状灰岩、泥质灰岩、斜坡发育生物碎屑灰岩,海底文石和镁方解石胶结作用强烈,致大部分原始孔隙度阻塞,孔隙度降低;西沙礁滩海滩岩以生物碎屑灰岩为主,地层主要发育生物碎屑灰岩和白云岩,各种藻类格架的杂乱分布增大岩石的孔隙度。巴哈马滩以孤立碳酸盐岩台地生物礁为主,发育台地边缘斜坡及滩礁型孤立台地,西沙孤立台礁区主要发育永乐、宣德2类环礁沉积系统,以及台地边缘礁、塔礁、马趾礁、环礁、点礁等多种生物礁类型。大巴哈马滩具有侧向生长的潜力和周期性进积作用的特征,西沙陡坡高能带发育进积型与侵蚀型2种沉积类型,风暴潮与盛行风作用成为灰沙岛的主要成因机制。
Abstract:
Comparative study of the reef platforms is made in this paper for the Bahama banks and the Xisha Islands upon depositional characteristics and facies models. Clastic, argillaceous and slope bioclastic limestones are well distributed in the two areas. The deposition of the cements of aragonite and magnesium calcite on the seafloor has made most of the original pores blocked and thus porosity reduced. Bioclastic limestone dominates the beach rocks on the Xisha reefal flat. In the subsurface stratigraphy, however, bioclastic limestone and dolomite predominate. The existence of various algal clutter causes the increase in the porosity of rocks. The Bahama Bank is an isolated carbonate reef platform,consisting of platform margin deposits, slope deposits and reef flat deposits. The Xisha Islands is also an isolated carbonate platform reef in general,and the Yongle-Xuande atoll is the main reef complex in the region. Many types of reefs,including platform-edge reef,tower reef,horseshoe-like reef,atoll,patch reefs etc, are observed there.The Bahama Bankis characterized by cyclical progradation. Thereare two sedimentary types of sequences, however, progradational and erosional,in the steep slope of high energy in the Xisha Islands. The lime-sand island in the Xisha owes its origin to storm surge and prevailing wind.
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