[S-EM16] Geomagnetism, paleomagnetism, and rock magnetism

[SEM16-10] New paleomagnetic results revealing a large late Mesoproterozoic high-latitude carbonate platform in the North China craton

*Hanqing Zhao¹, Shihong Zhang¹ (1.China University of Geosciences Beijing)

Keywords:paleomagnetism, late Mesoproterozoic, North China craton, high-latitude carbonate platform, greenhouse climate

Recent paleomagnetic results indicate that the carbonate rocks in the lower part of the Nanfen, Xinxing, and Liulaobei formations (collectively referred to as the Nanfen Formation [Fm] and its correlative strata) in the Liaodong-Xuhuai regions in the eastern North China craton (NCC) were deposited in high-latitude areas. The Jingeryu Fm in the Yanliao region, northern NCC, has long been considered as a correlative stratum unit to the Nanfen Fm and its equivalents. However, systematic paleomagnetic studies on the Jingeryu Fm have been lacking. The Jingeryu Fm is well exposed on both banks of the Luanhe River in eastern Hebei Province, with a depositional environment characterized by tidal flats. The main lithologies are purple-red and bluish-gray thin to medium-thick layers of dolomitic micritic limestone. Paleomagnetic sampling was conducted on two sections with significantly different attitudes in the region, yielding a total of 102 core samples. Rock magnetic analyses reveal that the magnetic carriers in the Jingeryu Fm are magnetite and/or hematite. Systematic demagnetization experiments show that stable two-component remanent magnetization signals can be isolated from 94 samples. After tilt correction, the characteristic remanent magnetization exhibits steep magnetic inclination characteristics. The primary nature of the characteristic remanent magnetization is supported by reversal and fold tests. The paleolatitude of the sampling location in eastern Hebei Province is constrained at ~73.7°. The paleomagnetic pole obtained from the Jingeryu Fm overlaps, at the 95% confidence level, with that obtained from the lower part of the Nanfen Fm and its correlative strata, but it is different from all previously reported Precambrian paleomagnetic poles in the NCC. This result supports the regional stratigraphic correlation scheme proposed by earlier researchers based on lithological and stratigraphic sequence similarities, namely, that the Jingeryu Fm is correlative with the Nanfen, Xinxing, and Liulaobei formations. The Jingeryu, Nanfen, and other formations constitute a high-latitude carbonate platform widely distributed in the central and eastern parts of the NCC during the late Mesoproterozoic. The discovery of this high-latitude carbonate platform suggests a greenhouse climate during the mid-Proterozoic.