泥盆纪海相碳酸盐岩碳同位素组成及演变

CARBON ISOTOPIC COMPOSITIONS AND EVOLUTION IN THE DEVONIAN MARINE CARBONATE ROCKS

关键词:  碳同位素组成  海相碳酸盐岩  泥盆纪  海平面变化  气候变化

Key words:  carbon isotopic composition  marine carbonate rock  Devonian  sea-level change  climatic change

摘要:

根据对六景泥盆系碳酸盐岩碳同位索组成的系统分析表明:从落霍柯夫期到布拉格期海洋中的δ¹³C是逐渐变重。埃姆斯期明显变轻,艾菲尔期又开始变重,特别是基维特期有较明显的正向偏移,并继续向上变重,至弗拉斯期与法门期之交达到最大,尔后逐渐变轻,反映了泥盆纪海洋碳同位索组成的演变趋势。这和泥盆纪(二级)海平面的变化趋势是基本一致的,反映海洋碳同位素组成与海平面变化及相关的气候和海洋、大气中CO₂含量的成因联系。弗拉斯阶-法门阶界线附近δ¹³C的变化型式表明其间发生的生物绝灭事件是海平面升降和缺氧环境的周期性扩展等因素的累积效应的结果。

Abstract:

The Devonian carbonate rocks in Liujing,Hengxian,Guangxi exhibit the following trend of carbon isotopic compositions:δ¹³C became progressively heavier from the Lochko-vian to Pragian;but obviously lighter during the Emsian;heavier once again during the Eifelian resulting in a remarkable positive excursion during the Givetian;the heaviest near the Frasnian-Famennian boundary,and subsequently lighter once again.This secular trend is positively correlated with (second-order) sea-level changes during the Devonian, implying the genetic affiliation with sea-level changes and relevant changes in climates and CO₂ contents in the atmosphere and oceans.The evolutionary patterns of carbon isotopic compositions near the Frasnian-Famennian boundary suggests that the mass extinction events near the boundary were probably caused by the accumulated effects of the eustatic fluctuations and periodic extension of anoxic environments.