CARBON-NITROGEN RECORD IN SEDIMENTS OF CORE PD IN THE PEARL RIVER DELTA AND THE ENVIRONMENTAL SIGNIFICANCE

Organic carbon, allochthonous organic carbon and C/N ratio, together with microfaunal and radio carbon dating results of the delta sediments in core PD in the Pearl River delta area are investigated to determine environmental changes. Four stages can be recognized since late Pleistocene. The first stage(about 23.88~21.71 kaBP) is characterized by gradually increasing organic carbon and allochthonous organic carbon, with plenty of foraminifers and ostracods, which indicates the weakening of sea-level rising. The second stage(about 21.71~3.79 kaBP) is represented by a layer of multi-color clay with extraordinary low organic matter, which implies strong weathering. In the third stage(about 3.79~2.88 kaBP), C/N ratio, allochthonous and autochthonous organic carbon ratio fluctuate according to the balance state, which means a marine-terrestrial transitional environment. In the fourth stage(about 2.88 kaBP-present), higher allochthonous organic carbon proportion and C/N ratio reflect terrigenous facies mainly controlled by fluvial effect,and the warm and humid climate brings rich allochthonous clastic matter.