The Early Triassic Geomagnetic Timescale and Bio-Chemo-Magnetostratigraphic Global Correlation of the Lower Trias-Sic

The Early Triassic, the earliest epoch of the Mesozoic, was a critical time following the end-Permian mass extinction that had major biological and environmental changes during the prolonged recovery. A high-resolution temporal global framework is essential to understand the patterns of recovery after catastrophes. The Lower Triassic strata of South China have been intensively studied, and three Global boundary Stratotype Section and Point (GSSPs) have been defined or proposed in this region to delimit the Lower Triassic stages, including the Meishan D for base of the Induan Stage (Permian-Triassic Boundary), Chaohu for base of the Olenekian Stage (Induan-Olenekian Boundary), and Wantou/Guandao for base of the Anisian Stage (Olenekian-Anisian Boundary). Based on the review, updates and correlations of data from the reference sections of Xiejiacao, Chaohu, Xiakou, Guandao and Wantou in South China and correlations to reference sections in the Arctic and Europe, we propose a revised Geomagnetic Polarity Time Scale (GPTS) for the Early Triassic that includes magnetostratigraphy, conodont biostratigraphy, chemostratigraphy and cyclostratigraphy. The timescale for Early Triassic polarity magnetochrons is calibrated either by radioisotopic dating, or by identified 405-kyr long-eccentricity cycles from the Chaohu, Xiakou and Guandao sections in South China and similar cyclostratigraphic scaling of the magnetostratigraphy from the Germanic Basin. The revised GPTS provides a powerful tool for high-resolution correlation of marine global environment fluctuations in all settings, including shallow marine and non-marine strata. The beginning of chron LT1n (the first normal-polarity chron of the Early Triassic) corresponds to the first appearance datum (FAD) of Hindeodus changxingensis, within the narrow interval between the Latest Permian mass extinction (LPME), as recognized by the major biota loss and a rapid negative carbon isotopic excursion, and the Permian-Triassic boundary (PTB) as recognized by the FAD of Hindeodus parvus or other earliest Triassic taxa. The beginning of LT3n was slightly after the FAD of Novispathodus waageni eowaageni(potential index marker for the Induan-Olenekian Boundary) and the maximum of a positive carbon isotopic excursion, which was slightly prior to the beginning of LT3n. The middle point of carbon isotopic excursions associated with the FAD of Nv. pingdingshanensis (potential proxies for the Smithian-Spathian Boundary) is close to the end of the LT6n. The FAD of Chiosella timorensis (potential index marker for the Olenekian-Anisian Boundary) was between subchrons MT1n and MT2n, and close to the maximum of the positive carbon isotopic excursion. This updated Early Triassic geomagnetic polarity timescale provided a framework for better correlation and dating of successions in the Boreal and Tethyan marine realms and in non-marine terrestrial basins.