Sedimentary features and ages of fluvial terraces and their implications for geomorphic evolution of the Taomi River catchment: A case study in the Puli Basin, central Taiwan

Fluvial terraces play an important role for research on previous geomorphic processes as their sediments can record various sedimentation stages. In the mountains of central Taiwan, however, the formation time of sediments in the Puli Basin is still unclear. In this study, we investigate the fluvial sediments of a fluvial terrace in the Taomi River catchment in the Puli Basin in terms of sedimentology and geochronology and consider their implications for geomorphic evolution in the Puli Basin. Optically stimulated luminescence (OSL) dating shows that fine-grained and homogeneous sediment in the studied fluvial terrace was deposited at 12.3 +/- 1.7 ka and 12.0 +/- 2.1 ka. These dating results are consistent with the age of 14.5 +/- 0.4 ka cal B.P. from the radiocarbon dating of a charcoal fragment. A third OSL age of 8.7 +/- 1.4 ka suggests that the overlying fluvial gravels started to form in the early Holocene. Based on the dating results and the sedimentological and geomorphic characteristics of the fluvial terrace under study, a preliminary model of the geomorphic evolution of the Taomi River catchment is proposed: I. The fine-grained sediment had been deposited at the end of the Late Pleistocene. II. In the early Holocene, fluvial gravel deposits were formed, probably caused by a climatic shift (from dry to wet). III. Huge-scaled incision of the Taomi River took place possibly associated with rapid Holocene river incision. IV. Incision stopped, and the studied fluvial terrace was formed. Later, young fluvial terraces, as derived from the analysis of a high resolution DTM, related to episodic incision of the river were formed. The modern river channel is 20 m below the studied outcrop.(C) 2012 Elsevier Ltd. All rights reserved.