松辽盆地嫩江组一、二段氢同位素特征、古气候与有机质富集

Hydrogen isotope characteristics,paleoclimate and organic matter enrichment of Nen⁃1 and Nen⁃2 members of Nenjiang Formation in Songliao Basin

为明确松辽盆地白垩纪温室气候变化与有机质富集之间的关系,采用气相色谱、高温裂解、同位素比值质谱等方法,测定古龙凹陷A井、G井的正构烷烃组分和氢同位素值。结果表明:松辽盆地古龙凹陷A井、G井晚白垩世嫩一段上部各个链长的正构烷烃均存在显著的氢同位素负偏移现象,其中G井、A井短链正构烷烃氢同位素分别出现约40‰、90‰的负偏量;中链正构烷烃氢同位素分别出现约60‰、110‰的负偏移;长链正构烷烃氢同位素值呈现出不同的变化趋势,但是整体规律与短链、中链一致;嫩江组沉积时期大气降雨氢同位素值为-76‰~-20‰,这与现今华北地区大气降雨氢同位素值(-50‰)基本一致;A、G井的嫩一段上部的氢同位素偏移事件指示该时期强烈且持续的大气降水;晚白垩世的陆地水循环加强改变了源-汇体系,使陆源输入量增加、生产力增强,有机质富集,这是导致嫩江组二段烃源岩形成的重要原因。研究成果可为嫩江组烃源岩的形成提供理论依据。

In order to identify the relationship between greenhouse climate change and organic matter enrichment of Cretaceous in Songliao Basin,the composition of normal alkanes and hydrogen isotope values of Well A and Well G in Gulong Sag are measured by means of GC,rock pyrolysis and IRMS.The results show significant negative shifts of hydrogen isotopes in normal alkanes of various chain lengths in upper part of Nen-1 Member of Late Cretaceous in Well A and Well G in Gulong Sag of Songliao Basin,with negative shifts of hydrogen isotopes of short-chain nor⁃mal alkanes of about 40‰ and 90‰ respectively,and negative shifts of hydrogen isotopes of medium-chain normal alkanes of about 60‰and 110‰respectively.Hydrogen isotope values of long-chain normal alkanes shows differ⁃ent variation trend,but the overall law is consistent with that of short-chain and medium-chain.The meteoric water hydrogen isotope value of Nenjiang Formation during deposition period is−76‰~−20‰,which is basically consis⁃tent with meteoric water hydrogen isotope value(−50‰)in North China today.Hydrogen isotope migration event in upper part of Nen-1 Member in Well A and Well G indicates strong and continuous atmospheric precipitation.The strengthening of terrestrial water cycle in Late Cretaceous changed the source-sink system,with terrestrial input in⁃creased,hydrocarbon generation capacity enhanced and organic matter enriched,being important factor for the for⁃mation of hydrocarbon source rocks in Nen-2 Member of Nenjiang Formation.The research provides theoretical ba⁃sis for the formation of hydrocarbon source rocks in Nenjiang Formation.