Characteristics of Pyrolitic Gaseous Hydrocarbons ofCambri an-Ordovician Carbonate Rocks of Tarim Basin and TangshanDistrict, Determined by Differential Thermal-Gas Chromatography

The Differential Thermal-Gas Chromatography is a kind of pyrolitic analytic equipments which can obtain a lot of usefull in-formation on maturity, types of source materials and potential of gas and petroleum generation from different kinds of geologicalsamples by means of changes of pyrolitic gas compositions and total gas amounts produced during heating processes at different tem-perature points. In Cambrian-Ordovician carbonate rocks of Tarim Basin and Tangshan district, ethanes are the major peaks in pyroliticgaseous hydrocarbons from 550℃ or so to 700,0 temperature point range, whereas in Palaeozoic mudstones of Tarim Basin, ter-restrial kerogens of different periods (Permian, Jurrassic and Tertiary) of Zhungeer Basin, and two terrestrial coals with differentranks ( Ro = 0. 36 %，2.32% respectively), urethanes are the major peaks from 500℃ to 600℃ range. The difference in the py-rolytic gaseous hydrocarbon compositions betweennn carbonate rocks and other geological samples mentioned above is mainly causedby contributions of enclosed organic matter to pyrolitic gaseous h州rocarbons of carbonate rocks. By means of comparison with total gas amounts at different temperature points of the terrestrial kerogens of Zhungeer Basin,and coals, it is found that the Cambrian-Ordovician carbonate source rocks still have certain hydrocarbon generation potential at700℃ high temperature point, again showing contributions of enclosed organic matter in carbonate rocks to hydrocarbon generationat late stage. By means of comparison between transformation ratios (S₁/(S₁+S₂))from Rock-Eval and total gas amounts produced fromper gram organic carbon during eleven temperature points from 1000C to 7000C，thd Cambrian-C!rdovician carbonate rocks ofTarim Basin have higher maturity than those of Tangshan district, which is consistent with geological history of the two districtsduring Early Palaeozoic Era.