Abstract:

The source area of sub-lacustrine sandbody in the center of basin is generally multidirectionality，with uncertain position and horizon, and different scale and distribution.Determining the direction of provenance quickly and accurately is the foundation and the key in mastering sandbody scale and distribution.The authors took the Chengdian sub-lacustrine sandbody in Biyang Lake basin for example，studied the direction of provenance and sandstone distribution based on clastic zircon dating analysis of sandstone samples from well C1 and B365 in Chengdian sub-lacustrine and samples from well B155 and B296 in the Houzhuang delta.The result shows:zircons microareaapparent age of Chengdian sub-lacustrine and Houzhuang delta mainly similarly distributes between Early Cretaceous and Middle Jurassic with single age peak of 120-140 Ma.Zircons during this period of two areas can be divided into two types.The first type occupies the main  part.Zircons of the first type are euhedral in shape and show the typical oscillatory zoning，which indicates their magmatic origin.Their Th/U ratios ranging from 0.21 to 2.94 implies that they derived from crystallization of magma.The second type is metamorphic with relatively small number.Also，there are some zircons distributing in the age populations of 210-238 Ma，416-451 Ma，663-813 Ma and 1 702-2 442 Ma.In combination with regional geological settings，the authors come to the following preliminary conclusions: the sub-lacustrine sandbody derived from Houzhuang delta and the sub-lacustrine sandbody distributes from north to south.The main formation period of source rock is Early Cretaceous to Middle Jurassic，corresponding to Yanshan tectonic stage. Moreover，the source area is mainly Yanshanian granite in Funiushan region，including Yanshanian metamorphic rocks and the metamorphic rocks or magmatic rocks of Prejinningian period，Jinningian period，Caledonian period and Indosinian period may offer contributions at different degree.

Key words: Nanxiang basin, Biyang depression, sandstone, sediment transport, isotopes, zircon