Based on the compositions and distributions of biomarkers in thirty|five representative oil samples, oils from the Tarim Basin of northwestern China are mainly divided into two oil families. One oil family contains relatively low amounts of C-{15}|C-{20} isoprenoid hydrocarbons and shows pristane predominance with Pr/Ph ratios ranging from {1.50} to {3.00}. The GC/MS analytical data of these oils show the occurrence of abundant hopanes, and low concentrations of steranes and tricyclic terpanes with hopanes/steranes ratios from {6.25} to {12.24} and tricyclic terpanes/hopanes ratios from {0.03} to {0.24}. These oils contain low drimane relative to homodrimane (C-{15}/C-{16}{1.0}), low hopanes/steranes ratios ({0.65}-{2.50}), high tricyclic terpanes/hopanes ratios ({0.30}-{2.00}) and a dominant peak at C-{23} in tricyclic tepanes, suggesting a marine organic origin. Oil|source rock correlation indicates that these two oil families seem to have been derived from Mesozoic Jurassic|Triassic terrestrial source rocks (shales and coal seams) and Lower Paleozoic Ordovician|Cambrian marine source rocks, respectively.
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