Permian fusulinid biostratigraphy of the Baoshan Block in western Yunnan, China with constraints on paleogeography and paleoclimate

Abstract

Newly obtained fossil materials together with published data enable a review on the Permian fusulinids of the Gondwana-derived Baoshan Block in western Yunnan, China. The Baoshan Block yields rather impoverish Sakmarian–Yakhtashian fusulinids with just Eoparafusulina and Pseudofusulina in its northern and southern parts. These fusulinids biogeographically demonstrate the feature of peri-Gondwana province and signify a temperate-water condition. Further comparison suggests the Baoshan Block was located distant from the tropical region and even with higher latitude than Central Iran and Central Pamir during the Sakmarian–Yakhtashian. In contrast, Murgabian–Midian fusulinids are more diversified. In the southern Baoshan Block, the Schwagerina assemblage, the Eopolydiexodina assemblage, the Sumatrina assemblage and the Verbeekina assemblage could be recognized in the Xiaoxinzhai area, and the Yangchienia–Nankinella assemblage and the Chusenella–Rugosofusulina assemblage in the Bawei area, in ascending order. Contemporaneously, the Neofusulinella assemblage occurs in the northern and the Eopolydiexodina assemblage in the southwestern Baoshan Block respectively. These Murgabian–Midian fusulinids show affinity of western Tethyan province and suggest a warm-water environment. Interestingly, the Midian Verbeekina assemblage is characterized by relatively low diversity and rather abundance of just one genus. Such compositional feature most likely signifies warm but still not optimal sea-surface water for the diversification of fusulinids. Also taking into account of the presence of Verbeekinids and Neoschwagerinids and the moderate total diversity, the Middle Permian fusulinids indicate that the Baoshan Block, during the Murgabian–Midian, was probably located between equatorial region with warm water to the north and the majority of Sibumasu areas lacking Verbeekinids and Neoschwagerinids with temperate water to the south.