ORGANIC GEOCHEMICAL CHARACTERISTICS OF THE LOWER PALAEOZOIC CARBONATE ROCKS IN THE HUANGHUA DEPRESSION, THE BOHAI BAY BASIN
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摘要: 对渤海湾盆地黄骅坳陷下古生界碳酸盐岩样品开展了有机地球化学研究,研究揭示氯仿沥青A中正构烷烃的碳数分布以单峰型为主(主峰碳为nC16或nC18),奇偶优势值接近于1.0,升藿烷成熟度参数为0.58~0.63,显示其处于高成熟演化状态;Pr/Ph值普遍接近于1或略大于1,反映了一种弱还原─弱氧化的沉积环境.氯仿沥青C中正构烷烃碳数分布主要为双峰型,反映其成熟度低于氯仿沥青A;Pr/Ph值均接近于1,反映了弱还原─弱氧化的沉积环境.多数样品的氯仿沥青A和氯仿沥青C具有相似的碳同位素组成分布模式,反映氯仿沥青C中正构烷烃碳同位素组成并没有受到成岩后地质作用的强烈影响,保存了早期有机质的特征,因而可用于恢复古沉积环境,为环渤海地区下古生界潜在原生油气藏的判识提供依据.Abstract: A study has been conducted on the organic geochemical characteristics of the Lower Palaeozoic carbonate rock samples from the Huanghua Depression,the Bohai Bay Basin.The results show that the distribution of n-alkanes in chloroform bitumen A is characterized by a single peak type,with the main peak carbon at nC16 or nC18;the OEP is approximately equal to 1 and the ratio of C3122S/(22R+22S) homohopanes is between 0.58～0.63,indicating that the organic matter has evolved into a high maturity stage.The Pr/Ph ratio is commonly close to or slightly greater than 1.0,reflecting a depositional environment under a week reducing or week oxidizing condition.In contrast,the distribution of n-alkanes in chloroform bitumen C is characterized by a double peak type,suggesting that the maturity of the organic matter in chloroform bitumen C is lower than that in chloroform bitumen A.The Pr/Ph ratio approaches 1.0,similar to that of chloroform bitumen A,also reflecting a week reducing or week oxidizing depositional environment.The results also show that the carbon isotope pattern of the individual n-alkanes in chloroform bitumen C is similar to that in chloroform bitumen A in most samples,indicating that the carbon isotope of the individual n-alkanes in chloroform bitumen C had not been significantly affected by the post-diagenetic geological processes,and the main characteristics of the organic matter in the early stage has been kept.Therefore,it can be used in paleoenvironmental restoration,and can provide the basis for identifying the potential Lower Palaeozoic primary oil-/gas-reservoirs in the Bohai Bay area.
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Key words:
- biomarker /
- carbon isotope /
- chloroform bitumen /
- carbonate rock /
- Lower Palaeozoic /
- the Huanghua Depression /
- the Bohai Bay Basin
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