认识偏心率周期的地层古气候意义

介绍了偏心率周期在地层和古气候研究方面的新发展.现有地球轨道模式对250Ma以来的轨道运算误差能控制在0.2%之内, 使基于偏心率周期来划分地层年代成为可能.新的国际标准地层年代表以405ka长偏心率周期为基础来划分主要地层界线.新生代将包括E1-E162偏心率长周期, 底界年龄(65.5±0.3) Ma.这一地层年代表的建立, 标志着轨道地层学时代的到来.偏心率的100ka短周期和405ka长周期在诸多地质记录中都有反映, 特别是来自深海钻孔的物理化学古气候指标.很多古气候重大事件往往发生在偏心率周期的弱振幅时期, 表明弱振幅时期易受其他因素的干扰影响, 这些因素包括碳储库、冰盖和海平面变化、电磁场, 以及区域构造重组等等.越来越多的研究发现碳同位素在偏心率周期上与地球轨道驱动相关, 且常领先于氧同位素的变化, 表明热带碳循环过程是影响全球气候变化的关键因素之一. 

Recognizing the Stratigraphic and Paleoclimatic Significance of Eccentricity Cycles

This paper introduces some new developments concerning orbital eccentricity in stratigraphic and paleoclimatic studies. The less than 0.2% error in calculating the current orbital model for the last 250 Ma makes possible stratigraphic subdivisions based upon eccentricity cycles. The newly erected international standard chronostratigraphic timescale uses the 405 ka long eccentricity cycles for separating major stratigraphic boundaries, and the Cenozoic Era now comprises E1 to E162 long eccentricity cycles, with the base dated at (65.5±0.3) Ma. The 100 ka and 405 ka eccentricity cycles have been found in many geological records, especially those paleoclimate proxies based upon physiochemical records from deep-sea drilling cores. Many important paleoclimatic events appear to have concurred with weak amplitude periods over the eccentricity band, indicating these periods were likely prone to the influence of such factors as the global carbon reservoir, ice caps, sea level and electromagnetic field, as well as regional tectonic reconfigurations. More and more studies show that the δ13C record is mainly related to orbital forcing over the eccentricity cycles, and its changes often precede δ18O changes, supporting the hypothesis that the carbon cycle is one of the key factors influencing the earth's climate.