海平面变化定量研究

THE SECOND-ORDER SEQUENCE DIVISION AND SEA LEVEL FLUCTUATION IN CAMBRIAN ON THE BORDER OF SICHUAN, GUIZHOU AND HUNAN

海平面变化规律是层序地层学研究的核心内容之一，全球海平面变化比相对海平面变化更具对比意义．用求构造沉降的方法，结合沉积物负载、压实、水深、水载等校正，通过数学计算定量地求出Ｒ１曲线（经压实、水深和水载荷校正，只含热影响，全球海平面变化及潜在的局部构造事件等因素引起的沉降）．用最小二乘法去除热引起的构造沉降，获Ｒ２海平面变化曲线，近似地反映了全球海平面变化．再经最佳多项式拟合，去掉长期波动的海平面变化效应，获Ｒ３曲线，可识别三级层序可容空间的变化．为了比较，绘制Ｆｉｓｃｈｅｒ点图（略称Ｆ．Ｐ．）及校正的Ｆ．Ｐ．（Ｆ．Ｐ．′）等曲线．进一步证明，沉降分析法在鄂尔多斯盆地南缘寒武纪应用效果良好．

Cambrian can be divided into three second-order sequences in the area based on time limit, orogenic episode and water depth changes. They are mesosequence Ⅱ 1 of Lower Cambrian, orthosequence set Ⅱ 2 and Ⅱ 3 of Middle-Upper Cambrian. They all possess basal plane SB 1. Second-order sequences correspond to second-order sea level fluctuation. Second-order sea level fluctuation, by comparing different masses, reflects that Yangtze plate is extremely different from North China plate and North American plate and is very similar to Tarim massif. These similarities and differences coincide with biogeographic areas of trilobita.