LOWER BOUNDARY OF THE MARINE PLEISTOCENE IN NORTHERN SHELF OF THE SOUTH CHINA SEA

A marine stratigraphic sequence across the Pliocene / Pleistocene boundary has been found in the northern continental shelf of the South China Sea. The marine Quaternary deposits in the Yinggehai Basin may exceed 2,000 m in thickness, probably providing the best section for studying the lower boundary of the marine Pleistocene in South China. The vertical succession with planktonic foraminifers and nannofossils revealed in boreholes in the basin has been well correlated with that in the international stratotype section of the Pliocene / Pleistocene boundary at Vrica, Italy, resulting in the acquirement of a biostratigraphic boundary at 1.64 Ma. This boundary, however, does not coincide with any prominent lithological palaeoenvironmental changes in the study area and can hardly be used in geological practice. There are, in contrast, significant changes at the level of LAD of Globorotalia multicamerata sensu lato located below the above-mentioned boundary. The percentage of planktonic foraminifers in the total population and preservation of foraminiferal tests display great changes at this level corresponding to a clear onlap on the seismic profiles and indicating a depositional hiatus at ca. 2.0-2.5 Ma. Since the level can be widely traced in the Pearl River Mouth Basin and the Beibu Gulf Basin and well corresponds with the marked depositional environmental changes recorded in the west Pacific and other regions, it is recommended that the Plio / Pleistocene boundary be drawn at the level of Gr. multicamerata sensu lato LAD, roughly concurrent with the Gauss / Matuyama turn.