Towards resolving the paleoposition of the North China Block at the Carboniferous-Permian boundary: preliminary paleomagnetic results of limestones from the ∼300 Ma Taiyuan Formation, North China.

Abstract

The North China Block (NCB), sandwiched between the Paleo-Tethys and Paleo-Asian Ocean realms, is crucial to the paleogeographic reconstruction of the East Asian blocks in the assembly of the Pangea supercontinent. However, paleoposition of the NCB remains poorly constrained during ∼330–290 Ma, due to difficulties in obtaining reliable paleomagnetic results from the pervasive coal-bearing strata. To solve this puzzle, we find the exclusive targets, several layers of limestones from the Taiyuan Formation in the Xiangning and Lingchuan areas, southern Shanxi Province, and conducted a combined petrographic, rock magnetic, and paleomagnetic study. The dominant magnetic carriers of the Xiangning limestones are magnetite and subordinate pigmentary hematite. The hematite is of secondary origin, while the unoxidized magnetite retains the ability to carry primary remanences. Magnetic carriers of the Lingchuan limestones are magnetite, subordinate hematite, and pyrite. Characteristic remanent magnetizations are isolated from 61 of 99 samples. The newly obtained Lingchuan pole is close to the 120 Ma pole of the NCB, possibly indicating a secondary remagnetization obtained in the Yanshanian Orogeny. The Xiangning pole is located at P_lat = 39.9°N, P_long = 340.7°E (A₉₅ = 5.0°, n = 6 samples). Although limited specimens are insufficient to reliably constrain the paleoposition of the NCB, we note the invaluable preliminary pole does not overlap with any younger poles, shedding light on finally resolving the paleoposition of the NCB at the Carboniferous-Permian boundary. Thus, we suggest the Xiangning limestones likely record primary remanences, indicating an equatorial paleolatitude of the NCB.