Provenance of coarse-grained detritus in fan-delta systems, Miocene Pohang Basin, SE Korea: Implications for boundary fault movements

In fan-delta systems, contemporary activities of boundary faults can be effectively constrained by tracing coarse-grained detritus. In order to reveal provenance and tectonic activities in the western margin of the Pohang Basin (Miocene), a total of 6000 clasts were examined in four fandelta systems for composition and compared with probable source rocks in the drainage area. Clasts in the Doumsan, Maesan, and Duksung fan-delta systems are dominated by granite, granodiorite, gray mudstone, and sandstone with sub-ordinate amounts of rhyolite, dacite, and tuff. The Malgol fan-delta system comprises silicic volcanics (mainly dacite), red or light gray sandstone, and mudstone. These clasts are similar in composition to the rocks exposed in the drainage area (Cretaceous Banyawol and Kisadong formations and Eocene granite and dacite bodies). The results indicate that strike-slip movements along the basin margin were inactive during the deposition of these fan deltas and each system was self-sustained.