New insights on the age of the Mengyejing Formation in the Simao Basin, SE Tethyan domain and its geological implications

Knowledge on the origin and mechanism of the large potash formation in the southeast Tethyan tectonic domain are still under debate, one of which mainly due to the controversial ages of the potash-bearing strata. Here we present a detailed detrital zircon U-Pb geochronologic-magnetostratigraphic study of the potash-bearing Mengyejing (MYJ) Formation (Fm) from the Simao Basin. 948 paleomagnetic cores and 4 detrital zircon U-Pb samples were collected from a 932-m thick Jiangcheng section. Thermal demagnetization isolated 857 primary characteristic remnant magnetization (ChRM) directions, indicated by positive reversals and fold tests and petrologic examinations. Seven normal and seven reversed polarity zones were identified and correlated well with chrons C27r to C34n of the geomagnetic polarity timescale (GPTS2012), yielding the first known age sequence of >112 to similar to 63 Ma for the MYJ Fm. The ages for the potash bearing strata in the Simao commenced similar to 20 Ma earlier than those in the adjacent Khorat basins, opposite to the traditional viewpoint that the former would rather correspond to the middle and lower parts of the latter. Given the paleogeographic reconstruction of likely a pan-Simao-Khorat basin during the Cretaceous, similar to 85 Ma would be another important potential period for future potash exploration in the Simao Basin.