贵州紫云晚二叠世-早三叠世初火山作用与生物礁的沉积演化   总被引：1，自引：1，他引：0  

范广慧  王永标  孟峥  李国山 《沉积学报》2017,35(1):24-34

晚二叠世长兴期是华南地区重要的成礁期,也是火山事件频发的一个时期。生物礁是一种对海洋环境十分敏感的生态系,晚二叠世的火山作用势必影响到当时生物礁的生长和沉积相的演化。然而,前人有关晚二叠世火山事件的研究主要集中在二叠系与三叠系界线附近,而对整个长兴期生物礁的演化与火山事件关系的研究则较少。选择贵州紫云的台地边缘礁为研究对象,通过大量磁化率的测试,分析整个晚二叠世生物礁的沉积演化与火山作用的关系。分析结果显示,长兴早期和末期岩石的磁化率值明显偏高,反映较强的火山活动。在这两个时期,造架生物相对不发育。长兴中期,岩石的磁化率值相较于长兴早期和长兴晚期总体偏低,表明火山活动相对较弱,导致生物礁的快速生长。但长兴中期生物礁灰岩中夹有几层生物碎屑灰岩,其磁化率值有小幅度的升高,说明短时期小规模的火山作用虽然导致了生物礁生长的暂时中断,但礁相动荡的环境使得火山灰中细小的铁磁性物质难以沉积下来。研究发现,尽管早三叠世早期泥岩具有高的磁化率值,但泥质岩中多层火山黏土具有异常高的磁化率值,火山灰物质对磁化率大小的影响远远超过陆源物质的贡献。  相似文献   

The evolution of planets. Venus as the Earth’s probable future     

N.L. Dobretsov 《Russian Geology and Geophysics》2017,58(1):1-11

The general evolution of planets in the Solar System is discussed with a focus on the structure and history of Venus compared with the Earth. The history of the planets of the terrestrial group has been similar and included at least six correlated stages. Many common features the terrestrial planets shared in their early and late evolution have been due to their common origin from the protoplanetary gas-and-dust nebula and plume magmatism widespread on all the planets of the terrestrial group. The characteristic features of the structure and evolution of Venus are most brightly manifested in the specific composition of its atmosphere and of plume magmatism. Venus, with its surface as hot as 450 °C and the near-surface pressure of 92-93 bars, has a hot and dense atmosphere 93 times that of the Earth in mass. Most of its atmospheric mass (99%) belongs to the 65-km thick troposphere consisting of CO₂ (96.5%) and N₂ (3.5%). The upper troposphere includes a 25-30 km thick cloud layer composed mainly of sulfuric acid droplets, water vapor, and SO₂. At a height of 49.58 km, the clouds approach the conditions of the terrestrial surface and might be hospitable to bacterial life. Volcanism, the most active and widespread process of Venusian geology, maintains continuous SO₂ emission. There are diverse volcanic edifices on Venus, which are most often large and are similar to the Earth’s plume-related volcanoes. The evolution before 1 Ga, as well as the share and the role of alkaline rocks and carbonatites among its volcanics, are among the most debatable issues about Venus. Being located closer to the Sun, Venus cooled down more slowly and less intensely than the Earth after the primary accretion. In the Proterozoic, it began heating and reached its present state at ~ 1 or 2 Ga. In the future, as the Sun becomes a red giant, the Earth is predicted to begin heating up in 500-600 Myr to reach the temperature of present Venus in about 1.5 Gyr.  相似文献   

夏季陆地爆发性气旋的模拟与诊断分析     

郭丽霞  张婉莹  郑艳萍  高桂芹 《气象》2007,33(6):59-66

利用观测资料、FY-2C卫星云图和NCEP再分析资料,对2003年6月22—23日黄河下游的气旋爆发性发展过程进行天气学分析和中尺度数值模拟与诊断,研究这次爆发性气旋的发展特征。结果表明：河套高空槽东移与山东南部的切变线合并产生这次爆发性气旋。MM5数值模式可以很好地模拟夏季陆地爆发性气旋发展过程。夏季陆地爆发性气旋发生在与高度场气旋性弯曲相重合的高空急流出口区,气旋从急流出口区右侧向左侧行进的过程中爆发性发展。气旋爆发性发展需要高空有急流,低空有西南和东南风急流为其提供强的暖平流和水汽通道。气旋的爆发性发展伴随着上升运动强烈发展,上升运动区高层强辐散、低层强辐舍。气旋爆发性发展在高能场中,大气具有强对流性不稳定。  相似文献