桦甸盆地始新统桦甸组黏土矿物和无机地球化学特征及其古环境意义

摘要

Clay mineral and inorganic geochemical characteristics of Eocene Huadian formation in Huadian basin have been found through X-ray diffraction,scanning electron microscopy and inorganic geochemical element tests.Clay minerals of Huadian formation of the study area contain montmorillonite,kaolinite and illite.The content of montmorillonite is the highest,and illite/smectite mixed layer is rare.Mn,Sr,P,Cd,Sr/Cu,B/Ga,Sr/Ba and Ca/（Ca＋Fe）change with an exactly similar trend vertically,and Cu,Cs,Rb/Sr,V/（V＋Ni） and δCe change with another similar trend.Clay minerals and inorganic geochemical evidence reveal the characteristics of paleoclimate and paleolimnology：the upper section containing coal and the lower section containing pyrite of Huadian formation belong to terrestrial sedimentary environment under the condition of warm and humid climate and low salinity;the middle section containing oil shale belongs to frequently alternating freshwater and saltwater environment,alternating humid and drought climate.The largest expansion phase of lacustrine basin which was under reduction condition with alternating humid and drought climate and salinity stratification developed semi-deep lake and deep lake facies which formed oil shale;the shrinkage phase of lacustrine basin with warm and humid climate developed delta plain with peat swamp which formed coal.%根据119个油页岩和泥岩样品的X射线衍射、扫描电镜和微量元素测试结果,查明了桦甸盆地始新世桦甸组黏土矿物组合特征和无机地球化学特征。研究区桦甸组的黏土矿物组合为蒙脱石、高岭石和伊利石,蒙脱石占据优势,偶见伊蒙混层;垂向上Mn,Sr,P,Cd,Sr/Cu,B/Ga,Sr/Ba,Ca/（Ca＋Fe）等具有相似的曲线变化趋势,Cu,Cs,Rb/Sr,V/（V＋Ni）,δCe等具有相似的曲线变化趋势。黏土矿物和无机地球化学两方面证据揭示了桦甸组下部含黄铁矿段和上部含煤段为温暖潮湿气候下的低盐度陆相沉积环境,偶有湖水咸化;中部含油页岩段为气候湿润-干旱频繁交替的淡水-咸水交替的沉积环境。研究区湖盆最大扩张阶段,气候湿润-干旱频繁交替变化、盐度分层的还原环境条件下,半深湖-深湖形成油页岩;湖盆萎缩阶段,气候温暖潮湿,扇三角洲平原泥炭沼泽化聚煤。