Provenance of the He 8 Member of the Upper Paleozoic Shihezi Formation, Ordos Basin, China: Insights from Heavy Minerals, Paleocurrents, Detrital Zircon Chronology, and Hf Isotopes

The Ordos Basin is located in the western part of the North China Craton. The Upper Paleozoic Shihezi Formation, particularly the He 8 Member, is one of the main gas-bearing strata. However, the source areas for the north and south sections have not been clearly distinguished, which has constrained oil and gas exploration to some extent. Therefore, understanding the source rock evolution of He 8 Member in both the south and north basins will provide a favorable theoretical basis for oil and gas exploration. The provenance of the He 8 Member of the Shihezi Formation in the Ordos Basin has not been well defined until now. Seven wellbore sandstone samples and three field outcrop sandstone samples from the He 8 Member in the Ordos Basin were analyzed. Based on zircon U–Pb dating and Lu–Hf isotope analyses, zircon assemblages of 520–386 Ma and 350–268 Ma in the southern Ordos Basin might have originated from the North Qinling Orogenic Belt (NQinOB) and the North Qilian Orogenic Belt (NQiOB); the 350–268 Ma age group of zircons from the NQinOB, and a large number of ~320–260 Ma detrital zircons supplied to the southern Ordos Basin by the NQinOB suggest that NQinOB magmatic and/or metamorphic events may have occurred in the NQinOB during the ~320–260 Ma period. From ~320–260 Ma, the NQinOB might have experienced significant tectonic activity that has not been fully revealed thus far. The zircons from 2600–2300 Ma, 2000–1600 Ma, and 450–300 Ma in the northern Ordos Basin might have been derived from the Trans-North China Orogenic Belt (TNCO), the Khondalite Belt, the Yinshan Belt, and the Alxa Belt. The paleocurrent and heavy mineral analyses determined that there are certain differences between the northern Ordos Basin and southern Ordos Basin, with unstable minerals such as barite and pyrite, as well as moderately stable minerals such as garnet, showing an increasing trend from south to north. There are also differences in the dominant paleocurrent directions between the south and north parts of the basin, and the Hf isotope data in the Ordos Basin show two-stage Hf model ages (TDM2) ranging from 918 Ma to 3574 Ma. As a result, the He 8 Member deposits in the southern Ordos Basin and northern Ordos Basin had different sources. The southern Ordos Basin might have derived from the NQinOB, the NQiOB, and the TNCO, and the northern Ordos Basin might have derived from the TNCO, the Khondalite Belt, the Yinshan Belt, and the Alxa Belt.