黔北坳陷小草坝泥盆系古油藏储层沥青充填于生物碎屑白云岩的溶蚀孔洞、晶间孔及裂缝中，储层沥青为固态，沥青等效镜质体反射率在4．08％～4．14％之间，在有机溶剂中基本不溶解。沥青正构烷烃轻重比较高，一般介于1．5～9．0之间，前峰优势显著；多数沥青样品的萜烷中三环萜丰度相对于霍烷具有明显优势，这些样品甾烷中C21孕甾烷和C22升孕甾烷丰度相对于C27－C29甾烷同样具有明显优势。沥青及沥青包裹体不发荧光，红外光谱中无脂族基团和含氧基团吸收峰。沥青的物理、光学性质及地球化学特征表明其经历了高温热演化，为热裂解成因。沥青的甾萜烷参数和碳同位素组成与筇竹寺组、龙马溪组烃源岩区别明显，而沥青碳同位素与上古生界烃源岩有很好的可比性，表明沥青的油源来自上古生界烃源岩。成藏史恢复表明，古油藏于三叠纪中晚期形成，白垩纪早期深埋裂解形成固体沥青，燕山－喜马拉雅期抬升暴露至地表。%The solid bitumen in the Xiaocaoba paleo⁃oil reservoir of Devonian in the Qianbei Depression fills so⁃lution caves, intracrystalline pores and fractures of dolomites containing biodetritus. The solid bitumen, with an equivalent Ro of 4.08%-4.14%, hardly dissolves in organic solvent. The n⁃alkanes have a high n⁃C21-/n⁃C22+value at the range of 1. 5-9. 0. Most bitumen samples have a higher abundance of cheilanthanes relative to ho⁃panes, and also a relatively higher abundance of C21⁃pregnane and C22⁃pregnane relative to C27-29⁃sterane. The bitumen and bitumen inclusions do not fluoresce, and the bitumen has no absorption peaks of aliphatic series⁃containing groups or oxygen⁃containing groups in the infrared spectrum. The physical, optical and geochemical characteristics of bitumen indicate that it formed in the process of thermal cracking under high temperature. The sterane and terpane parameters and theδ13 C of the bitumen are obviously different from those of sources rocks in the Cambrian Qiongzhusi Formation and Silurian Longmaxi Formation. But theδ13 C of the bitumen are very close to that of the Upper Paleozoic sources rocks, indicating that the bitumen derived from these source rocks. Ancient oil reservoirs are interpreted to have been trapped in the Middle-Late Triassic period. The bitumen formed in the Early Cretaceous period while oil reservoirs were deeply buried and then uplifted to ground level in the Yan⁃shanian and Himalayan periods.
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