Rb sr dating
Illitic clay is ubiquitous in clastic hydrocarbon reservoirs, and the host for several radiometric isotopes such as the potassium-argon (K-Ar) and rubidium-strontium (Rb-Sr) systems.This study applied the isotope-dilution thermal ionization mass spectrometry technique for small samples (3–4 mg) to conduct illite Rb-Sr isotope dating of five illitic clay samples from the Silurian bituminous sandstone (SBS) intersected by five drillholes in the Tarim Basin, NW China.The black line in each diagram is the isochron regressed from data of all subsamples.The red dash line is the isochron regressed through selected data. The red dashed line is regressed without subsample A-3; (B) H6.The outcomes of this study show the robust potential of Rb-Sr clay subsample geochronology for cross-checking isotopic ages yielded by other systems (e.g.
Such a small degree of Rb/Sr fractionation may be a response to the microscale chemical variation in the precipitation environment, and each analyzed subsample may contain I/S particles of slightly variable degrees of illitization. IR is the percentage of smectite layers in I/S; (B) potassium (K) content vs IR of I/S; (C) Rb content vs K content; (D) Rb content vs IR of I/S; (E) Sr content vs IR of I/S. The consistency between Rb-Sr and K-Ar ages suggest that Sr isotopic homogeneity was attained during the illitization.The regression of the remaining four subsamples yields an isochron age of 111 ± 36 Ma (2σ, Fig. There is no obvious relation between H6: Regression of the isotope data yields an isochron age of 148 ± 68 Ma (2σ, Fig. One subsample (B-4) slightly deviates from the isochron, and the regression without this point yields an identical age within uncertainty (141 ± 61 Ma, 2σ, Fig. Initial , as the negative relation between IR values and K contents shows in Fig. Because Rb has a geochemical behavior similar to K (Fig.8C), Rb is also introduced to I/S during the illitization process (Fig. The broad positive correlation between the Sr contents and IR values of I/S indicates that the variation in Sr contents by illitization may be insignificant (Fig. Therefore, the Rb/Sr fractionation of clay samples is mainly controlled by the addition of Rb during the illitization of I/S.The red dashed line is regressed without subsamples D-2 and D-3; (E) TZ67.Sr higher than the other subsamples (Table 2), and is not included in the calculations.