We have analyzed carbon and oxygen isotopes of two groups of planktonic foraminiferal shells from sediments near the Pliocene/ Pleistocene (P/P) and the Miocene/Pliocene (M/P) boundaries, in the Lower Gutingkeng Formation in southwestern Taiwan. The P/P shells display heavier isotopic compositions (δ18O = -1.5‰, δ13C = 1.5‰) over a narrow range, suggesting a pristine environmental signature. On the other hand, the M/P shells are much lighter (δ18O = -3 to -7‰, δ13C = 1 to -1.5‰), and more scattered, associated with secondary carbonate diagenesis. Our detailed SEM examination confirms this proposition. The P/P shells display a clean micro-texture and are free from carbonate recrystallization. However, there are abundant secondary calcite crystals in the M/P shells. Therefore, the extreme shift of δ18O and δ13C in foraminiferal shells provides a guideline for evaluation of diagenetic artifacts of deeply buried sediments that have been uplifted on land.
All Science Journal Classification (ASJC) codes
- Earth-Surface Processes