Geoscience

Stratigraphic Location of Paleomagnetic Polarity Boundary Identified

The boundary of the Matuyama-Brunhes paleomagnetic polarity reversal (MBB) is recorded in the marine isotope stage (MIS) 19 in the marine sediments, corresponding to an interglacial period. However, most of the previous loess reports about the MBB displayed that it is recorded in the eight loess horizon (L8, a glacial period). This discrepancy was interpreted as the large scale lock-in depth of the natural remanent magnetization in the Chinese loess; however, another point claimed that this phenomenon may be caused by the phase lag of the climate between loess and marine sediments. In this study, scientists have measured five sets of parallel samples from the L8+S8 of the Mangshan section in Henan province. The thickness of the MBB has been accurately determined using the previous analysis method (JGR paper, 2010). Their conclusion further demonstrates that L8 and S8 should be correlated to MIS 18 and 19. The research result was published in Palaeogeography, Palaeoclimatology, Palaeoecology (Jin, et al. 2011, 299: 309-317).

Fossil Evidence Proves Mass Extinction Event

In the past 540 million years of geological history, totally 5 mass extinctions occurred on the earth. The extinction at the end of the Permian which was 250 million years ago represented the most horrifying event in the development history of life, and killed nearly 90% marine species. Prof. Shen Yan’an conducted a detailed geochemical research on the Meishan profile in Zhejiang Province. It is the “GSSP” profile near the Permian-Triassic boundary. Prof. Shen Yan’an, Member of the “1000-Elite Program” from the School of Earth and Space Sciences of USTC/CAS and Key Laboratory of Crust-Mantle Materials and Environments, USTC and his colleagues precisely measured multiple sulphur isotopes of the Meishan profile and discovered the composition of sulphur isotopes became abnormal episodically with the gradually unfolding of the extinction. They believed the abnormality of sulphur isotopes was caused by the episodic shoaling of anoxic water. In terms of time, the episodic shoaling of sea water was in line with the significant reduction of species before the final catastrophe. Therefore, they came up with the idea that episodic shoaling of anoxic sea water contributed to the profound crisis of the decrease of species. This research result showed the prolonged deterioration of epigeosphere of the earth might lead to the mass extinction in Late Permian. This conclusion is of great enlightening significance for the contemporary global changes. On Feb. 22, the research thesis Multiple S-isotopic Evidence for Episodic Shoaling of Anoxic Water during Late Permian Mass Extinction by Prof. Shen Yan’an was published recently online in Nature Communications.