浙江天台-宁海晚中新世孢粉组合及其古植被和古气候

分析了浙江天台-宁海地区嵊县组第3沉积层的孢粉样品11个, 该层时代属晚中新世。其中, 在宁海县黄泥塘村和大路下村各采集4个, 天台县家湖村采集3个; 样品岩性主要为浅灰色至灰褐色湖相沉积的泥岩至泥质粉砂岩, 部分样品含较多硅藻土(采样地点分布范围 29°8'~29°10'N, 121°14'~121°16'E)。经化学处理, 除HNT-11, DLX-1和DLX-2以外, 在其余8个样品中发现了丰富且保存完好的孢粉化石, 共鉴定39个类群, 归属23科, 建立了以栎属(Quercus)—松属(Pinus)—禾本科(Poaceae)—菱属(Trapa)为主要特征的孢粉组合。结合同层位植物大化石记录, 推论晚中新世天台-宁海及其周边地区的植被类型丰富, 以具有一定垂直地带性的森林植被为主: 自山麓向上, 随海拔升高, 由常绿阔叶林逐渐向常绿、落叶阔叶混交林以及落叶阔叶林过渡; 研究区生长有松属(Pinus)及竹类植物, 草本植物生长茂盛, 并生长有一定量的蕨类植物; 研究区内湖泊、池塘及沼泽等平静的淡水水体普遍存在, 使得菱属等水生草本及盘星藻(Pediastrum)等淡水藻类广泛生长。该植被类型与现今浙江兼具一定垂直地带性的典型中亚热带常绿阔叶林较为相似。通过对当前孢粉组合应用共存分析法, 定量重建了晚中新世研究区的8个古气候参数, 即年平均气温(MAT)17.0~18.5℃, 年平均降水量(MAP)979.0~1722.0mm, 最热月平均气温(WMT)26.5~28.4℃, 最冷月平均气温(CMT)3.3~7.7℃, 平均最大月降水量(MMaP)176.2~265.0mm, 平均最小月降水量(MMiP)7.0~31.6mm, 平均最热月降水量(MWP)165.5~232.5mm以及气温年较差(DT)18.2~21.5℃, 表明晚中新世研究区的气候温暖湿润, 同该区现代气候相近。

PALYNOLOGICAL ASSEMBLAGE FROM THE LATE MIOCENE OF TIANTAI-NINGHAI AREA,ZHEJIANG, CHINA AND ITS PALEOVEGETATION AND PALEOCLIMATE

11 samples were collected from the 3rd sedimentary layer of the Shengxian Formation in Tiantai-Ninghai area, Zhejiang Province of China, including 4 samples from Huangnitang Village, Ninghai County, 4 samples from Daluxia Village, Ninghai County, and 3 samples from Jiahu Village, Tiantai County(the three sampling locations are within the range of 29°08'~29°10'N, 121°14'~121°16'E) .The geologic age of the layer of sampling belongs to the Late Miocene.All the samples are mainly greyish or greyish brown mudstone or pelitic siltstone of lacustrine facies, while some samples contain much diatomites.Through chemical treatment, except sample HNT-11, DLX-1 and DLX-2, abundant and well-preserved fossil spore-pollen were found in the rest of 8 samples.Then 39 palynomorphs were identified which belong to 23 families, and the palynological assemblage which is featured by Quercus-Pinus-Poaceae-Trapa was determined.By combining the macrofossil records from the same layer, the forest with a certain vertical zonality was recovered: with the elevation increasing, from the piedmont, evergreen broad-leaved forest into a mixed evergreen and deciduous broad-leaved forest, further into a deciduous broad-leaved forest, there were also pine trees and bamboos, while herbs flourished and a certain amount of ferns grew there.Placid freshwater bodies were likely widespread in the area, in which Trapa and Pediastrum as well as other aquatic herbs and freshwater algae flourished.From the above, this type of vegetation is similar to the typical mid-subtropical evergreen broad-leaved forest concurrently with a certain vertical zonality which exists in Zhejiang Province nowadays.The palaeoclimatic parameters of the research area were obtained by applying the Coexistence Approach: mean annual temperature(MAT)from 17.0℃ to 18.5℃, mean temperature of the warmest month(WMT)from 26.5℃ to 28.4℃, mean temperature of the coldest month(CMT)from 3.3℃ to 7.7℃, mean annual precipitation(MAP)from 979.0mm to 1722.0mm, mean maximum monthly precipitation(MMaP)from 176.2mm to 265.0mm, mean minimum monthly precipitation(MMiP)from 7.0mm to 31.6mm, mean precipitation of the warmest month(MWP)from 165.5mm to 232.5mm, difference in temperature between the coldest and warmest month(DT)from 18.2℃ to 21.5℃, indicating that in the Late Miocene, the climate in Tiantai-Ninghai area was warm and humid, similar to its modern climate.