U-Pb dating of oil charge in superimposed basins: A case study from the Tarim Basin, NW China

Abstract

Abstract Direct dating of oil charge in superimposed basins is essential to understanding the evolutionary histories of petroleum systems, especially in sedimentary basins with complicated tectonic evolution and thermal histories. Based on analyses of different phases of calcite veins and primary oil inclusions, episodes of oil charge were determined by laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) in situ U-Pb dating of calcite veins from an Ordovician reservoir within the Tahe Oilfield of the Tarim Basin, NW China. This basin has been subjected to multiple uplifts and erosions and repeated oil charges. The U-Pb dating results indicate that the first phase of oil charge occurred from 329.7 ± 1.6 Ma to 308.1 ± 4.1 Ma, and the second phase occurred from 249.3 ± 2.6 Ma to 220.5 ± 7.3 Ma. The timing of oil charge determined by fluid inclusion analysis alone can lead to great uncertainties due to the existence of multiple phases of oil charge and complex thermal evolution in superimposed basins. Our study demonstrates that U-Pb dating of calcite veins originating from the reservoirs offers a unique solution to determining the oil charge history, which avoids the multi-solution uncertainties in the timing of oil charge inferred from fluid inclusion analysis in superimposed basins.