台灣南部中上中新統層序地層學研究(II)

In southern Taiwan from Pingung to
Hengchung, middle-upper Miocene strata are
widely outcropped in the Western Foothills and
Central Range and extend westward in the
subsurface of the Coastal Plain and Taiwan
Strait. These silisiclastic strata are mainly coastal
to shallow marine deposits.
Based on the results of the second-year
research in 3 outcrop sections in the Pingtung
area, the lower part of the studied strata is
dominated by outer shelf and shelf edge facies,
while the upper part is composed of coastal
and inner shelf facies. The depositional
environment drastically deepen southwards,
whereas the thickness decrease. Four
depositional sequences are identified in these
marine successions. The sequences can be
compared with the upper 4 of the 5 sequences
identified in the Chia-I and Kaohsiung area in
the last-year study.The chronostratigraphic
framework can be delineated by nannofossil and
planktic foraminiferal biozonations.
Summarizing the results of the last 2
years, the middle-upper Miocene in southern
Taiwan appears as a siliciclastic wedge that
deepens and thickens toward the east and south.
During its accumulation, the wedge displays at
least 4 depositional cycles shifting from the shelf
edge, shelf, shoreline to terrestrial environments.
Owing to the significant environmental changes,
vast area in the present-day Taiwan Strait and
Coastal Plain had occasionally been subaerial
exposed. The depositional cycles are believed to
be related to the global sea-level fluctuations,
while the distinct thickness variations dominated
by the extensional tectonics of the continental
margin.