| 北部湾全新世海侵演进及其与气候、冰川关系分析 |
| 点此下载全文 |
| 引用本文：黄向青,梁开,习龙,夏真,张顺枝.2022.北部湾全新世海侵演进及其与气候、冰川关系分析[J].地球学报,43(1):49-64. |
| DOI：10.3975/cagsb.2021.070101 |
| 摘要点击次数: 2231 |
| 全文下载次数: 2433 |
|
| 基金项目:中国地质调查局地质调查项目“海南岛东北部沿海地区综合地质调查”(编号: DD20190308);地质科研项目“南海北部湾全新世环境演变及人类活动影响研究”(编号: 1212010914027) |
|
| 中文摘要:北部湾是我国热带和亚热带大型海湾且资源丰富, 了解其演进变化过程是环境保护、利用和预测的基础; 在接近湾口的南部海盆进行了岩芯钻取, 并对样品进行较高分辨率地球化学元素Sr、Ba和微体古生物化石测试、鉴定和14C测年。分析对比结果表明, 微体古生物化石丰富, 有孔虫共有42属67种, 主要为表层暖水种和近岸浅海种, 硅藻有19属29种, 主要为浅海广温广盐种。海侵进程可分为古河口湾、古海湾、近现代和现代海湾三个基本阶段。有孔虫和硅藻优势种以及Sr/Ba变化呈连续性和波动性, Sr/Ba为0.64~1.11, 与有孔虫丰度总体呈下降趋势, 但硅藻丰度则相反。浮游有孔虫优势种Globigerinoides quadrilobatus和G.ruber两者在上述各阶段平均为69.62%~93.50%, 硅藻优势种Cyclotella striata则为39.39%~100.00%, 次优势种有C.stylorum等, 余下围绕其波动变化并具有分散性。模拟古水深序列线性增加斜率为3.091 m/ka, 沉积速率亦同为增加, 但前者截距、斜率远高于后者。Sr/Ba和有孔虫丰度于 6.0~5.0 ka出现短暂峰值, 相对增幅依次为16.11%~344.74%, 显示冷暖天气系统进退交互和海平面波动剧烈, 对比同期北部近岸所取全新统岩芯岩性和微体古生物、Sr/Ba分析结果, 显示中全新世以来接受明显海侵。晚全新世4.0 ka尤其是3.0 ka以来上述海盆岩芯Sr/Ba总体处于最低值区间且小幅波动, 其后期海退特征与近岸Sr/Ba分析结果可对应, 对比可见近岸高海面遗迹集中出现于6.0~3.0 ka。以上全新世以来Sr/Ba阶段变化与全球和区域气候变化和冰期旋回相对应, 并与印—太海域海平面变化模式相似。北部湾约自 1.0 ka进入现代模式以全面进行岸线修整巩固, 对应全球和区域出现阶段性降温和冰进, 可再划分前小冰期至现代暖期三个亚阶段, 对比可见喜马拉雅—西藏高原造山带1.0 ka前后、小冰期冰进活跃, 冰进事件时间分布最为密集。综合认为: 北部湾对气候变化响应敏感, 应存在中全新世高海面以及古大北部湾等, 属于印—太海平面变化体系, 一级低地体系主导了海侵主体行径, 海侵通过水平传播以及垂向冲刷动力地貌的双重效应维持海盆主体, 早中全新世海侵由热带气候系统所推动, 中全新世由于其缩退而使得高海面势能向近岸次级低地传播侵没, 依次属于主动(聚集)、被动(释放)两种不同机制而奠定了现代北部湾的基础, 可知地质构造背景条件和气候因素起着关键作用, 现代北部湾的形成与代表西风环流和极涡扩张的喜马拉雅—青藏高原造山带冰进等存在遥相关。 |
| 中文关键词:北部湾 海侵 演化 气候 冰川 |
| |
| The Evolution of Beibu Gulf since Holocene Marine Progression and Its Relationship with Climatic and Glacial Change |
|
|
| Abstract:The understanding of the evolution of Beibu Gulf since Holocene is necessary in protection, utilization and forecasting of Beibu Gulf’s environmental progress because it is an important large-scale continent shelf gulf and continent-marine transition zone which owns abundant marine resources under the background of global change. In this paper, the authors carried out laboratory analysis of geo-chemical elements, micro-paleontology and 14C age for samples from sediments core STAT22 in the southern basin of Beibu Gulf. Comprehensive data analysis shows that there were relatively abundant foraminifera and diatom fossils with dominant surface species Globigerinoides quadrilobatus, G.ruber, broad-temperature species Cyclotella striata and sub-dominant C.stylorum respectively and non-dominant species which fluctuate discontinuously. Sr/Ba ratio varies from 0.64 to 1.11, indicating quick sea level rise and marine progression from slope and then shelf of northern South China Sea during early Holocene and generally turned down together with foraminifera afterwards, but diatom increased instead for a growth of land input. Based on Sr/Ba ratio and the continuous variation features of main foraminifera and diatom species, 3 primary phrases of Beibu Gulf evolution corresponded to inter-glacial and glacial cycles with mean G.quadrilobatus and G.ruber 69.62%~93.50% and C.striata 39.39%~100.00% respectively. Molded palaeo-water depth’s linear slope was 3.091 m/ka and sedimentation rate also relatively rather slowly increased, revealing scouring and relatively stable hydro-dynamic equilibrium to maintain the gulf basin. Sr/Ba ratio and foraminifera abundance appeared maximally during 6.0~5.0 ka with amplitude 16.11%~344.74% but became lowered quickly from Late Holocene, i.e., from 5.0 ka to minimum in 4.0 ka, and regression started along near-shore and also exhibited high stands along near-shore which varied from 6.0~3.0 ka. The evolution of sea level could be comparable with Indo-Pacific fit output modes. The palaeo-Beibu Gulf stepped into new pattern from ~1.0 ka through general regression which could be further classified into 3 sub-phrases corresponding to pre-LIA, LIA, and warming period of modern time, and there were also active glacier advances from ~ 1.0 ka in Himalaya-Tibet orogenic belt, as shown by comparison with other study results. It could be concluded that Beibu Gulf was sensitive to global and regional climatic change, and there might had been mid-Holocene high sea level, mid-Holocene progression to near-shore and then palaeo-Mega Gulf; in addition, the main body of transgression was guided by the first-grade lowland system formed under tectonic background such as Red River Fault, meanwhile there was bottom scouring through palaeo-tide to keep the dynamically geomorphic balance, and transgression and high sea level in mid-Holocene were driven and maintained before mid-Holocene by tropical climatic system but its potential energy converted into second progressive energy to near-shore’s low-land complex for above climatic system’s southward shift from mid-Holocene. The above two ways of active and non-active marine progression constituted the foundation of of Beibu Gulf, and ~1.0 ka as an important new climatic phase from 2.0 ka was probably the modern Beibu Gulf’s starting time, and there was a tele-connection between Beibu Gulf and glacier advances in the Himalaya–Tibet orogenic belt. The combination effects of climatically driving and tectonically sunken stress-induced geomorphic lowland complex played fundamental role in the formation of Beibu Gulf. |
| keywords:Beibu Gulf transgression evolution climate glacier |
| 查看全文 查看/发表评论 下载PDF阅读器 |
|
|
|
|
|
