南海北部海域柱状沉积的孢粉、藻类及其古环境意义

Sporopollen and algae in Core C4 of northern South China Sea and its paleoenvironment

对南海北部C4站柱状剖面进行了高分辨率孢粉、藻类研究,部分样品作了AMS14C年代测定。根据孢粉成分的变化将南海C4站从下至上划分了3个孢粉组合带,依次为:1带(258—194cm)为以Pinus-Quercus(常绿)-Polypodiaceae-Pteridium-Pteris-Dicranopteris-Adiantum为主的孢粉带;2带(194—94cm)为以Pinus-Quercus(常绿)-Pteridium-Polypodiaceae-Microlepia-Dicranopteris为主的孢粉带;3带(94—4cm)为以Pinus-Pteridium-Polypodiaceae-Quercus(常绿)-Microlepia-Dicranopteris为主的孢粉带。并相应恢复了南海北部9 800a BP以来3个植被、气候、古环境演替阶段,结合AMS14C测年资料,对C4站柱状地层时代划分作了讨论,为南海古气候、古环境演变研究提供了科学依据。

Based on the high-resolution sporopollen and algae research of the sediments at Core C4 in the northern South China Sea, three sporopollen zones have been distinguished in ascending order. Zone 1 （258-194cm） ： Pinu-Quercus （evergreen）-Polypodiaceae-Pteridium-Pteri-Dicranopteris-Adiantum; Zone 2 （194-94cm） ： Pinu-Quercus （ evergreen）-Pteridium Polypodiaceae-Microlepia-Dicranopteris ; Zone 3 （ 94-4cm ）： Pinus-Pteridium-Polypodiaceae-Quercus （ evergreen ） Microlepia-Dicranopteris. The sporopollen zones reflected three stages of vegetation, climate and paleoenviornment evolution of the northern South China Sea over the past 9 800 years. Stage 1： Shown by palynological Zone 1 in Core C4 and the Core 9 on the shelf of the South China Sea, the vegetation on the continental margin and the Hainan Island were evergreen and deciduous broadleaved mixed forest with conifers. The tree layers were dominated by evergreen Quercus, Castanopsis, deciduous Quercus, Pinus, Altingia, Myrica, Euphorbiaceae and so on. The vegetation layer under canopy included Gramineae, Polypodiaceae, Pteridium, Cyathea and Dicranopteris. During this period, the evergreen broadleaved elements in the southern subtropical group southward migrated, and those deciduous broadleaved elements adapting to the warm and humid environment developed well. The climate at that time became warmer. The AMS ^14C age at the depth of 258-260cm in Core C4 is 9 800 ± 40 a BP. Stage 2. This stage is indicated by the palynological Zone 2 in Core C4 and the Core 9 on the shelf of the South China Sea. The elements from the southern subtropical and tropical zone increased in the vegetation on the continental margin and the Hainan Island, where the trees were luxuriant. The main components were evergreen Quercus, Castanopsis, Altingia, Elaeocarpus, Euphorbiaceae, and others including Podocarpus, Dacrydium and Pinus. Mangrove plants grown along the coastal areas. The vegetation layer under the canopy consisted of Gramineae, Cyperaceae, Ranunculaceae, Polypodiaceae, Pteridiurn, Cyarhea and Pteris. The vegetation, characterized by the northern tropical semi-evergreen monsoon rain forest, reflected a hot climate with obvious dry and wet seasons at that time. The AMS ^14C age at the depth of 200-202cm is 4 910 ±35a BP in Core C4 and 4 700 ±110a BP in Core 10 near Core 9 on the shelf of the South China Sea, when the sea level rised. Stage 3. Indicated by palynological zone 3 in Core C4 Pinus, evergreen Quercus, Altingia, Castanopsis, Camel so on. The vegetation layers under canopy were dominated and Core 9, the vegetation mainly consisted of lia, Euphorbia, Podocarpus, Dacrydium and by ferns, including Microlepia, Polypodiaceae, Pteris, Adiantum, Dicranopteris, Diplopterygium, Cyathea and Lygodium. The herb layers were characterized by Gramineae, Cyperaceae, Chenopodiaceae and Artemisia. Mangrove occupied the tidal zones, which showed a warm and humid environment. The AMS ^14C age at the depth of 50 52cm in Core C4 is 2 870 ±30 a BP. Among the three palynological zones in Core C4, Zone 1 is in the Early Holocene. The Zones 2 and 3 show the situations in the periods of the Mid Holocene and the Late Holocene, respectively. The compositions of the palynological zones were well corresponding to the changes of vegetation and climate in the surroundings of the cores. Combined with AMS^14C dating, the sporopollen and algae data could be as one of science evidences for stratigraphic division and reconstruction of paleoclimate and paleoenvironment in the South China Sea.