Abstract
Oil–source relationships in the Tarim Basin remain controversial because Paleozoic oils may record contributions from multiple marine source rock systems. We compiled 207 source rock trace element, 184 source rock rare earth element (REE), 44 crude oil trace element, and 33 crude oil REE records to evaluate elemental proxies in an overmature marine carbonate petroleum system. Lower Cambrian source rocks generally record more reducing conditions than the Saergan Formation, although both groups are compositionally variable. PERMANOVA shows significant separation in V/Ni–Ni/Co and Ni/Mo–Mo/Co spaces (R2 = 0.4675 and 0.6381; p < 0.001), but PERMDISP indicates unequal dispersion only for V/Ni–Ni/Co. Thus, Ni/Mo–Mo/Co provides the more robust source rock separation. Some Ordovician reservoir oils are compositionally compatible with the Lower Cambrian field, whereas others occupy intermediate or outlying positions. However, whole-rock and ashed oil analyses represent different elemental pools, precluding unique genetic assignment. REE parameters have limited discriminatory capacity because source rock fields overlap and oil data are incomplete and strongly study dependent. V–Ni–Mo–Co relationships should therefore be used as complementary evidence together with biomarkers, stable isotopes, and regional petroleum geology.