Jianxin Yu

Volcanic perturbations of the marine environment in South China preceding the latest Permian mass extinction and their biotic effects

The Dongpan section in southern Guangxi Province records the influence of local volcanic activity on marine sedimentation at intermediate water depths (~200-500 m) in the Nanpanjiang Basin (South China) during the late Permian crisis. We analyzed ~100 samples over a 12-m-thick interval, generating palynological, paleobiological, and geochemical datasets to investigate the nature and causes of environmental changes. The section records at least two major volcanic episodes that culminated in deposition of approximately 25- to 35-cm-thick ash layers (bentonites) and that had profound effects on conditions in both the Dongpan marine environment and adjacent land areas. Intensification of eruptive activity during each volcanic cycle resulted in a shift toward conifer forests, increased wildfire intensity, and elevated subaerial weathering fluxes. The resulting increase in nutrient fluxes stimulated marine productivity in the short term but led to a negative feedback on productivity in the longer term as the OMZ of the Nanpanjiang Basin expanded, putting both phytoplankton and zooplankton communities under severe stress. Radiolarians exhibit large declines in diversity and abundance well before the global mass extinction horizon, demonstrating the diachroneity of the marine biotic crisis. The latest Permian crisis, which was probably triggered by the Siberian Traps flood basalts, intensified the destructive effects of the earlier local eruptions on terrestrial and marine ecosystems of the South China craton.

Environmental evolution of the south margin of Qaidam Basin reconstructed from the Holocene loess deposit by n-alkane and pollen records

This study provides the n-alkane and pollen records of the Holocene loess at Balong (巴隆) Town, Dulan (都兰) County, Qinghai (青海) Province, and the environmental changes reconstructed from both records agreed well. Three stages of past climate change were deciphered by variations of the n-alkane and pollen proxies. Before 5 370 a BP, the climate was warm-dry but slightly humid, corresponding to the Mid-Holocene climatic optimum; 5 370–3 830 a BP, the climate changed alternatively between warm-dry slightly humid and warm-dry, indicating the transition from the Mid-Holocene climatic optimum to the Late Holocene cold period; after 3 830 a BP, the climate was mainly warm-dry. The warm cool and extremely dry climate during 3 040–2 600 a BP was recorded by both the n-alkane and pollen proxies, suggesting the environment evolved into desert or salt lake, in accordance with the cold and highly frequent natural disaster period in the Western Zhou Dynasty (ca. 2 996–2 721 a BP) in China.

Permineralized Calamitean Axes from the Upper Permian of Xinjiang, Northwest China and Its Paleoecological Implication

Two anatomically preserved calamitean axes are reported for the first time from the Late Permian Wutonggou Formation in the southern Bogda Mountains, Xinjiang Uygur Autonomous Region, Northwest China. Based on the anatomical features, these axes are assigned to Arthropitys. A new species Arthropitys taoshuyuanensis sp. nov. is established. A. taoshuyuanensis sp. nov. possesses a large pith and comprises large pith cavity and a narrow perimedullary zone at the nodes and diaphragms at the internodes. Carinal canals are circular and surrounded by a single layer of metaxylem tracheids. Secondary xylem is divided into interfascicular rays and fascicular wedges. Interfascicular rays are initially four to five cells wide and taper abruptly centrifugally. Fascicular wedge consists of thick-walled tracheids and thin-walled fascicular ray cells. Radial tracheid walls have uniseriate or biseriate circular pits, or scalariform pits. The absence of growth rings in the Arthropitys specimens indicates that they probably lived in the wetland area under stable annual temperature and water sufficient conditions.