| dc.description.abstract | Taiwan had been a passive continental margin from the middle Oligocene to late Miocene. There were two local extensional events, leading to the formation of small rifted basins during the passive-margin stage. In order to establish a comprehensive sequence stratigraphic framework, we use well-log data of 11 boreholes near the B Fault and Yichu Fault in SW Taiwan for paleo-environmental and sequence stratigraphic analyses. The well data was provided by CPC Corporation.
Eight sedimentary facies and 8 types of parasequences are identified. Our results shows that Pachangchi Sandstone was accumulated in the shoreface environment. The overlying formations (i.e., Piling Shale to Talu Shale) exhibit offshore to shoreface environments. During the deposition of the Kuanyinshan Sandstone and the Nanchuang Formation, the environment changed into a tide-and-wave-dominated environment, consisting of tidal deposits, barrier complexes and shoreface deposits. For the sequence stratigraphic analysis, the Miocene strata is divided into 14 sequences, namely, K0, M0, M2, M4, M6, M8, M10, M12+M14, M16, M18, M20, M22, M24 and M26, in an ascending order.
According to borehole stratigraphic correlations and sequence stratigraphic analyses, we found that the thickness of the Pachangchi Sandstone and its equivalents at KTL-3 well is quite thick, up to around 400 m. While the thickness of the Pachangchi Sandstone in the rest of studied borehole is only 60 m to 100 m. Similarly, the thickness of Nanchuang Formation attains up to about 1200 m at HSY-1 well. Base on this observation and previous study, we divided the tectonic activity in this region into 3 stages. (1) K0, M0, M2 sequences (early post break up, 30~21 Ma): Yichu Fault became active and created a half graben as observed at KTL-3 well. Sequences of K0, M0 and M2 were deposited. (2) M4~M18 sequence (21~12.5 Ma, thermal subsidence): Thickness of each formation and sequence remains consistent, no major tectonic activities in this period. Sequences of M4~M18 were accumulated during this period (3) M20~M26 sequences (12.5~6.5 Ma, renewed extension): Yichu Fault and B Fault became active, leading to the formation of a graben as seen at the JY-1 well, while the area near northern B Fault became an uplifted platform. Sequences of M20~M26 were deposited. | en_US |