Paleomagnetic ChRM directions of the Early Cretaceous sedimentary sequence in the southern Simao Basin, SE Tibetan Plateau

Precise stratigraphic chronology is the basis of many studies (e.g., tectonic, paleoclimate and mineralization) in geoscience. Here, we carried out a detailed youngest detrital zircon U-Pb age-constrained magnetostratigraphic study on the middle-lower parts of a 2309 m-thick Late Jurassic-Early Cretaceous sequence from west Jiangcheng in the southern Simao Basin, southeastern Tibetan Plateau. A total of 2262 paleomagnetic cores were collected for magnetostratigraphy, and 5 siltstone/sandstone samples were collected for detrital zircon U-Pb analyses. Progressive thermal and alternating field demagnetizations isolated 1575 robust primary characteristic remnant magnetization directions, which yielded twenty-five normal-polarity (N7-N31) and 25 reversed-polarity (R8-R32) intervals. The adopted maximum depositional ages calculated using the youngest detrital zircon U-Pb ages are 159.0 Ma, 154.0 Ma, 161.0 Ma, 149.3 Ma and 139.5 Ma for the stratigraphic horizons at 2303 m, 1986 m, 1600 m, 1350 m and 1110 m, respectively, in the section. Together with the previous magnetostratigraphic results of the upper part of the section, the observed polarity zones were best correlated with chrons C34n-M17r on the geomagnetic polarity timescale (GPTS2012), yielding magnetostratigraphic ages of ~143.5 to ~65.0 Ma for the whole stratigraphic sequence of the section. Paleogeographic analysis revealed that the Simao Basin was in a low-latitude offshore environment during the Late Jurassic-earliest Cretaceous (>142.3 Ma), a dominant fluvial environment at 20~24°N during the early-middle Early Cretaceous (142.3-111.5 Ma), with widespread desertification at the end of this period, a saline lake sedimentary environment during the late Early Cretaceous-early Late Cretaceous (111.5-88.7 Ma), and a fluvial environment during the late Late Cretaceous (88.7-65.0 Ma). This evolutionary process was concordant with regional/global tectonic and paleoclimate changes.