Application of Strontium Isotope to the Study of Paleokarst——An Case from Ordovician in the Tahe Oilfield,Tarim Basin
Application of Strontium Isotope to the Study of Paleokarst——An Case from Ordovician in the Tahe Oilfield,Tarim Basin
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发表时间：
2007
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通讯作者：
Liu Cun-ge
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作者：
Liu Cun-ge
为了将锶同位素应用于古岩溶研究，本文对塔里木盆地塔河油田奥陶系碳酸盐岩缝洞充填方解石进行了系统分析，研究结果表明，低的87 Sr/86 Sr比值是加里东中期岩溶形成的方解石的一个特征，方解石的87 Sr/86 Sr比值受控于容矿岩石的87 Sr/86 Sr比值。早海西期古岩溶中的方解石具有较高的87 Sr/86 Sr比值，这主要受陆源锶和围岩溶解锶的控制，不同产状方解石的87 Sr/86 Sr比值存在差异;包气带产物比潜水带产物富集87 Sr，这主要是岩溶系统的渗流机制和水-岩相互作用的结果，O3 s组覆盖区的87 Sr/86 Sr比值高于北区，主要是由于赋矿岩石锶同位素比例的增加，锶同位素的区域变化和地质背景可能表明早海西期古岩溶对北区和O3 s组覆盖区奥陶系碳酸盐岩有重要影响，此外，极低的87 Sr/86 Sr比值可能是幔源的指示，早二叠世火山作用是提供地幔的主要时期，对塔河油田奥陶系古岩溶的研究表明，锶同位素具有较好的指示流体物源的能力，在古岩溶阶段划分上具有明显的优势。
For application of strontium isotope to study of paleokarst,the paper has systematically analyzed the calcites filled in fissure-cave of the Ordovician carbonate rocks in the Tahe oilfield,Tarim Basin.The research results indicated that lower 87Sr/86Sr ratios are a character of calcites formed in the karst during the Middle Caledonian,and the 87Sr/86Sr ratios of calcites are controlled by those of host rocks.However,the calcites of Early Herlynian paleokarst have higher 87Sr/86Sr ratios,which are controlled by the terrestrial strontium and the dissolved strontium from the wall rocks.The 87Sr/86Sr ratios of different attitude calcites differ;the products of vadose zone are enriched in 87Sr than phreatic zone,which mainly result from the seepage mechanism of the karstic system and water-rock interaction.Furthermore,the area covered with O3s Formation has higher 87Sr/86Sr ratios than the north area,and mainly contributes to an increased proportion of strontium isotope of the host rocks.Regional variations of strontium isotope and geologic backgrounds may indicate that the Early Hercynian paleokarst has important influences on the Ordovician carbonate rocks in the north area and the areas comprising the O3s Formation,and it is the main formation episode of karstic fissure-cave reservoir in the Tahe oilfield.In addition,the extremely low 87Sr/86Sr ratios may be an indicator of mantle source,and the volcanism of Early Permian is a main period of providing mantle-derived strontium.The study on the Ordovician paleokarst in the Tahe oilfield suggests that strontium isotope is of a better ability in indicating fluid's provenance,and therefore,it has distinct advantages in the division of paleokarst stages.