论文部分内容阅读
吉隆盆地为高喜马拉雅中新世晚期约10Ma时期形成的一个南北向断陷盆地,其东侧为同沉积正断层,沃马剖面位于盆地沉降中心的东南部.在该剖面下部新发现一套中新世巨厚砾岩层(旦增竹康组).通过锆石和磷灰石裂变径迹年代学研究得出吉隆盆地控盆断裂早期活动时间为13.4±1.9Ma,源区12～11Ma发生构造热事件,据此推算出吉隆盆地初始裂陷后开始沉积的底界年龄约为10Ma.综合前人在吉隆盆地得出的7.20～1.67Ma古地磁测年值,可得出吉隆盆地旦增竹康组年龄为10.0～7.4Ma,沃马组年龄为7.40～1.67Ma.根据孢粉组合带和孢粉组合反映的植物类型和古环境变化,沿剖面自下而上划分为3个孢粉组合带和9个孢粉组合及其对应的植被类型.吉隆地区古气候变化可划分为3个阶段:(1)组合带Ⅰ和孢粉组合1～2,为温暖偏干环境的常绿与落叶针阔叶混交林,地层对比时代为晚中新世(10.0～7.0Ma);(2)组合带Ⅱ和孢粉组合3～7,为寒冷干旱环境的落叶针叶林,期间存在一次暖湿气候的波动,地层对比时代为晚中新世晚期-早上新世(7.0～3.3Ma);(3)组合带Ⅲ和孢粉组合8～9,为温凉偏干的气候下生长暗针叶林和落叶阔叶林构成的针阔叶混交林,地层对比时代为晚上新世(3.30～1.67Ma).
The Geelong Basin is a north-south trending faulted basin formed at about 10 Ma in the late Himalayas, with a synsedimentary normal fault on the east side and the Wauma section in the southeast of the subsidence center of the basin. Pliocene thick conglomerate (Danzengzukang Formation) .Through the zircon and apatite fission track chronology study, it was found that the early activity time of the basin-controlled fracture in the Geelong Basin was 13.4 ± 1.9Ma and the tectonic activity occurred in 12 ~ 11Ma in the source area According to the above, we can deduce that the bottom boundary age of the initial sedimentary rupture in the Geelong Basin is about 10 Ma.According to the previous geomagnetic dating data of 7.20-1.67 Ma dating from the Geelong Basin, According to the plant types and paleoenvironmental changes reflected by the combination of sporopollen assemblages and sporopollen assemblages, three sporopollen assemblages And nine sporopollen assemblages and their corresponding vegetation types.The paleoclimatic change in the Geluon area can be divided into three stages: (1) the combination of I and sporopollen 1 ~ 2, the evergreen and deciduous needle Broad-leaved mixed forest, stratum contrast to the late Miocene (10.0 ~ 7.0M (2) The deciduous coniferous forest with combination of Ⅱ and sporopollen assemblages 3-7 is a deciduous coniferous forest in cold and arid environment with a fluctuation of warm and humid climate, and the stratigraphic contrast period is Late Late Pliocene-Early Pliocene 7.0 ~ 3.3Ma). (3) Combination belt Ⅲ and sporopollen assemblages 8 ~ 9 are coniferous and broad-leaved mixed forests composed of dark coniferous forest and deciduous broad-leaved forest in warm and dry climate. The stratigraphic contrast time is Night Pliocene (3.30 ~ 1.67Ma).