| dc.description.abstract | This study investigated the facies characteristics of the upper Nanchuang to Yangmei formations by examing San-Ying section, Dahan River section, and San-Ying borehole in northwestern Taiwan.
I recognized 21 lithofacies, including 5 mudstone facies, 2 mudstone & sandstone interbedded facies, 13 sandstone facies, and 1 mudclast facies. On the basis of different combination of lithofacies, I recognized 14 lithofacies associations, including offshore, lower shoreface, upper shoreface, tidal inlets/barrier islands, tidal flood delta, sandy & muddy central basin, tidal channel, tidal flat, marsh, channel sand bar, levee, crevasse splay, flood plain and sandy braided river. These lithofacies associations occurred in 3 major sedimentary environments: (1) wave- and tidal-inflenced open marine, (2) wave-dominated estuaries, and (3) meandering and sandy braided rivers.
In late Miocene, the sedimentary environments were fluvial and wave-dominated estuaries for the Nanchuang Formation, pertaining to a passive-margin setting. During the initiation of foreland basin, the basin started to subside and the environments became deeper to wave-dominated estuaries and wave- and tidal-inflenced open marine system when sediments of the Kueichulin Formation accumulated. During Chinshui Shale stage, the environments deepened into offshore, which was the deepest environment for the studied sequence. The foreland basin was filled up by subsequent deposits and the environments became shallower as wave-dominated estuaries during Cholan Formation stage and later became meandering and sandy braided rivers during Yangmei Formation stage. In summary, the trend of the sedimentary evolution for the studied sequence shows a deepening then shallowing upward trend.
Sediment thickness thicken toward the east as revealed from stratigraphic correlation. The Yangmei Formation along the Dahan River section can be correlated southwardly to the Chaochin Member of Yangmei Formation in the Hsinchu-Kuanhsi area and northwardly to the Paotoutso Member of the Tananwan Formation in the Linkou area. In addition, the Tamaopu Conglomerates of TY-07 borehole can be correlated to the Tamaopu Conglomerate in Hsinchu-Kuanhsi area and Linkou Formation in the north.
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