济阳坳陷古近纪的古气候区分析

古气候分区是古湖泊学研究的一个重要方面,对古湖泊生产力和有机质的保存有重要影响.本文尝试利用孢粉、沉积地球化学、沉积学等手段,根据不同气候带冷热干湿组合和碳酸盐矿物δ18O与古气候干湿对应关系,结合古风向,来恢复济阳坳陷古近纪的古气候分区.分析结果表明济阳坳陷在沙河街组沉积时孢粉组合表现出温暖与湿润、寒冷与干燥同步,碳酸盐矿物δ18O增高与古气候干旱同步的规律,东营组孢粉组合则表现为寒冷与湿润同步,碳酸盐矿物δ18O增高与古气候湿润同步的规律.这些特征揭示出,在沙河街组沉积时期,济阳坳陷主要处于东亚季风气候区；在东营组沉积期,济阳坳陷则更多地处于西风带的控制下.此外,古近系碳酸盐礁滩、碎屑浅滩的沉积规律也表明,济阳坳陷在沙四上-沙一段沉积时期盛行东亚季风.湖相优质烃源岩主要发育于季风气候带中由干冷向暖湿过渡的时期.

Eogene Paleoclimate Zone Study in the Jiyang Depression

Paleoclimate zoning is an important aspect of the palaeo-lake study;it influences paleoproductivity and preservation of organic metamorphism in palaeo-lakes.Based on the data of historical weather,palaeowind directions,and correspondence between carbonate mineral δ18O values and paleoclimate,we attempt to restore the Eogene paleoclimate zone in the Jiyang depression by means of spore powder,sedimentary geochemistry and sedimentology.The sporo-pollen assemblage in the Shahejie Formation shows the synchronization characteristics of warm while humid,of cold while dry,and of carbonate mineral δ18O values increasing when dry palaeoclimate.But the sporo-pollen assemblage in the Dongying Formation shows synchronization characteristics of cold while wet and of carbonate mineral δ18O values increasing when humid palaeoclimate.These results reveal the Jiyang depression was in the East Asian Monsoon climate zone during the Shahejie Formation depositional stage,and was typically controlled by the westerlies during the Dongying Formation depositional stage.Furthermore,the sedimentary rule of carbonate reef flat and clastic shoal in the Shahejie Formation show that the East Asia Monsoon was prevalent during the sedimentary period from the upper fourth member to the first member of the Shahejie Formation.Lacustrine high-quality source rocks mainly deposited in the stage of when the paleoclimate was changed from dry and cold to wet and warm in the East Asian Monsoon climate zone.