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This study is a part of the joint project of environmental changes on the coastal plain in the southwestern Taiwan. Two cores drilled at I-Chu and Tieh-Sien-Chiao were analyzed to decipher the characteristics of the sediments, the relative abundance of marine fossils and the organic geochemistry of the sediments in order to understand the paleo-environmental change of the coastal plain.
The analytical results in the I-Chu well indicate that the iintervals between 200 and 198.5 meter in depth and between 163.7 and 140 meter in depth are of a lagoon environment, the strata betwwen 198.5 and 163.7 meter in depth is of non-marine facies or a coastal environment, the strata between 140 and 117.2 meter in depth and betwwen 95.6 and 84.5 meter in depth are of non-marine facies, the stratum between 84.5 and 5.2 meter in depth is of a marine environment, and the stratum above 5.2 meter in depth is of non-marine facies. The last and obvious transgression occurred at the 84.4 meter in depth, which was approximately 1100 years ago. In the Tieh Sien-Chiao well, most of the sediments below 7.3 m is of marine depositional environment, indicating that most of this area was overlaid under sea water at 7800 yrBP. The change of the coastal ine in the southwestern coastal plain is consistent with the global sea level changes. The sedimentation rate is as high as 8 mm/yr. on an average in the last 11,000 years.
Organic geochemistry analysis reveals alkylcyclohexanes(C17~C22) in most of the sediments in the coastal plain in the southwestern Taiwan. The alkylcyclohexanes includes two groups, one of these two groups, i.e. C17~C22, is from primary sediments at the time of sedimentation; the othr, i.e. C29~C32, is from recycled sediments, and can be used as a useful indicator of sediment source.
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