9.Oligocene-Miocene Planktonic Foraminifer Biostratigraphy site 1148 Northern South China Sea.pdf

9.Oligocene-Miocene Planktonic Foraminifer Biostratigraphy site 1148 Northern South China Sea.pdf

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9.Oligocene-Miocene Planktonic Foraminifer Biostratigraphy site 1148 Northern South China Sea

Prell, W.L., Wang, P., Blum, P., Rea, D.K., and Clemens, S.C. (Eds.) Proceedings of the Ocean Drilling Program, Scientific Results Volume 184 9. OLIGOCENE–MIOCENE PLANKTONIC FORAMINIFER BIOSTRATIGRAPHY, SITE 1148, NORTHERN SOUTH CHINA SEA1 Qianyu Li,2,3 Zhimin Jian,3 and Baohua Li4 ABSTRACT Over 30 first and last occurrence (FO and LO, respectively) plank- tonic foraminifer datums were recognized from the Oligocene–Miocene section of Ocean Drilling Program (ODP) Site 1148. Most datum levels occur in similar order as, and are by correlation as probably synchro- nous with, their open-ocean records. Several datum levels represent lo- cal bioevents resulting from dissolution and Site 1148’s unique pale- oceanographic setting in the northern South China Sea. An age of 9.5– 9.8 Ma is estimated for the local LO of Globoquadrina dehiscens (257 meters composite depth [mcd]), whereas the local LO of Globorotalia fohsi s.l. (301 mcd) is projected to be at ~13.0 Ma and the local FO of Globigerinatella insueta (367 mcd) is projected to be at ~18.0 Ma. The combined planktonic foraminifer and nannofossil results indi- cate that the Oligocene–Miocene section at Site 1148 is not complete. Unconformities up to 2–3 m.y. in duration, occurring at and before the Oligocene/Miocene boundary (OHS1, OHS2, OHS3, and OHS4 = MHS1), are associated with slump deposits between 457 and 495 mcd that signal tectonic instability during the transition from rifting to spreading in the South China Sea. Shorter unconformities of 0.5 m.y. duration that truncate the Miocene section were more likely to have been caused by sea-bottom erosion as well as dissolution. A total of 12 Miocene unconformities, MHS1 through MHS12, are mainly affected by dissolution and an elevated carbonate compensation depth (CCD) during Miocene third-order glaciations recorded in deep-sea positive oxygen isotope Mi glaciation events. Respectively, they fall at ~457 mcd (MHS1 = Mi-1), 407 mcd (MHS2 = Mi-1a), 385 mcd (MHS3 = Mi-1a

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