Electrostratigraphic Study of the Tainan Coastal Plain, Southwestern Taiwan

Abstract

In order to study the electrostratigraphy, the depositional environments and the change of shoreline, a geoelectric survey was carried out on the Tainan coastal plain. The DC resistivity method was used, and the sound ing data were interpreted by the 1-D inversion method.Based on the electric resistivities and the thicknesses of the layers de rived from the sounding data, three electrostratigraphic units are found and specified. They are designated as the T, R, and S fades corresponding to the strata from the surface to 200 meters in depth. The T-facies is char acterized by layers of resistivity ranging from 12 to 400 ohm-m at the top of the layer sequence. This unit is less than 100 meters thick and is widely distributed in the area studied. The S-facies is characterized by a thick layer or layers of resistivity less than 5 ohm-m, and is generally accompanied with thin layers of resistivity less than 12 ohm-m. The S-facies is 50 to 200 meters thick and is mostly overlain by the T -facies in the western and the central parts of the coastal plain, and is absent in the eastern part. The R facies is characterized by a thick layer or layers of resistivity ranging from 12 to 70 ohm-m. It is overlain by the T-facies in the east and by the S-facies in the west. The R-facies intertongues with the S-facies in the north-center and is absent in the south-center. The T-facies was deposited in terrestrial and estuarine environments during the Holocene. The S-facies was depos ited in marine environments in the late Pleistocene to Holocene. The upper part of the R-facies in the east was deposited in terrestrial and estuarine environments in the late Pleistocene. These three units are similar in lithol ogy being mainly composed of layers of clay, mud, silt, and fine sand.A marine transgression occurred when the strata between the depths of 200 and 40 meters were deposited in the area studied except for the Tainan tableland, and was then followed by a marine regression. At the peak pe riod of the marine transgression, the shoreline reached the line connecting Anding, Hsinhua, and the east of Gueizen. Since the beginning of the re-

Water and Sediment Discharge from Small Mountainous Rivers, Taiwan: The Roles of Lithology, Episodic Events, and Human Activities

“…While the impact of human activities-both increasing and decreasing sediment loads and yieldscannot be denied, we also should point out that post-Last Glacial Maximum (LGM) sedimentation rates in the coastal plain of western Taiwan (Cheng et al 2001;Hsieh et al 2006, unpublished manuscript) and in the Taiwan Strait submarine delta located off the Jhuoshuei River (Liu et al, unpublished manuscript) suggest that post-LGM sediment fluxes from western rivers have averaged at least 80 Mt yr À1 , a value not too different from the collective present-day discharge from these rivers, a point also made by Liu et al (unpublished manuscript). In other words, based on available data, present-day sediment fluxes from western rivers may not reflect the anthropogenically accelerated denudation noted in the eastern rivers.…”

Flux and fate of small mountainous rivers derived sediments into the Taiwan Strait

“…But another sink for western river sediment is the broad western coastal plain stretching from the Tsengwen northward to the Tanshui River (Fig. 12), which numerous shallow borings and 14 C dates reveal to have Holocene fluvial deposits locally thicker than 100 m (Cheng et al,1999;Chen and Liu, 2003;Hsieh et al, 2006). A preliminary isopach map of the Holocene sediment in coastal plain (Fig.…”

Spatiotemporal Dynamics of Ecological Variation Affect an Endangered Migratory Bird Black-faced Spoonbill (<i>Platalea minor</i>) in Southwestern Coast of Taiwan

“…It heaps along the coast to form series of sandbars and lagoons, and become a rich fishery habitat [11] [12]. The land rising and sediment accumulating along coasts are considered to enrich the seabed terrain and the organic matter, thus being suitable for a diverse fish to spawn and forming an abounding ecosystem.…”