Pb, Sr, and Nd isotopic features in organic matter from China and their implications for petroleum generation and migration

To better understand processes and sources of crude oil and bitumen generat ion from kerogen rocks, a comprehensive study of Plp, Sr, and Nd isotopic s ystematics was undertaken for bitumen, crude oil, and kerogen from two larg e oil fields (Karamay and Liaohe) and two paleo-oil deposits (Tarim and Gui zhou) in China. The bitumen samples from the Karamay oil field have present -day Nd-143/Nd-144 ratios pointing to a depleted mantle origin (0.5126-0.51 30). They define a Rb-Sr isochron age of 286 +/- 12 Ma. Pb isotopic composi tions for bitumen and crude oil from Karamay, Liaohe, and Tarim all show fe atures of crust-mantle mixing. They are evidently different from Pb isotopi c compositions of kerogen that occurred in the same strata of the various o il fields, which mostly show crustal signatures. Sr isotopic compositions i n crude oil from Liaohe are consistent with those of carbonate sediments an d volcanic rocks in island arc environments (0.7065-0.7100). Radiometric is otope systems can be preserved in the bitumen with low vitrinite reflectanc e R-O (<0.5%) and therefore allow us to date petroleum generation. Both iso topic data and the geologic setting of the oil fields indicate that petrole um generation was associated with fluid action from deep sources, including the mantle, lower crust, and buried strata in rift basins and buried forel and basins at craton margins or subduction zones. Copyright (C) 2001 Elsevi er Science Ltd.