Abstract:

 A NS-striking thrust-nappe belt is developed in the western Ordos Basin, through the cross-section shortening amount calculated and the strain distribution of the strata exactly estimated, the deformation characteristics of the strata have been quantitatively revealed, therefore the dynamic mechanism of the thrust-nappe was recognized. Due to the development of small-scale folds and faults, a bigger error of the shortening amount may appear using traditional cross-section balancing. In this study, a nonlinear method called fractal theory has been adopted to calculate the cross-section shortening amount. Through this method, a bedded plane can be regarded as a complex curve in the two-dimension plane, and the fractal dimension D can be calculated, furthermore, the total amount of cross-section shortening can be obtained. A case study of geological profile AB across Zhuozishan which is located in the north of the western Ordos Basin indicates that the shortening amount and strain are 8 km and 22.2% respectively, and the shortening amount caused by the small-scale folds and faults is 1 km.

Key words: the western Ordos Basin, thrust-nappe belt, fractal theory, cross-section shortening amount