Permian oolitic carbonates from the Baoshan Block in western Yunnan, China, and their paleoclimatic and paleogeographic significance

Abstract

Marine carbonate ooids are environment-sensitive and hence valuable for paleoclimatic and paleogeographic reconstructions. This paper describes Permian ooids from the Baoshan Block in western Yunnan, China, in order to offer a new means to refine the uncertain paleogeographic details of this Gondwana-derived block. Four major types of ooids (micritic ooids, compound ooids, leached ooids and half-moon ooids) are documented from the Hewanjie Formation in the northern and the Shazipo Formation in the southern Baoshan Block. These ooids are dated via biostratigraphic analysis to be Wordian–early Wuchiapingian and signify an ameliorated shallow-marine temperature for the Guadalupian strata of the Baoshan Block. Results of this study, coupled with literature data, reveal diachronous debut of Permian ooids among the Gondwana-derived blocks: mostly Sakmarian in Central Taurides of Turkey, Central Iran, Central Pamir and Karakorum Block versus Wordian–Capitanian in Baoshan Block, Peninsular Thailand and South Qiangtang. In contrast, Asselian–Sakmarian strata of Baoshan Block as well as Peninsular Thailand and South Qiangtang are characterized by glaciomarine diamictites. These observations suggest that the Baoshan Block was probably situated at a considerably higher paleolatitude under distinct influence of Gondwana glaciation during the Asselian–Sakmarian than those blocks yielding Sakmarian ooids. Moreover, marine ooids are virtually absent nearby the equator within the Permian Tethys, similar to the modern situation. The Baoshan Block is accordingly interpreted to drift to warm-water southern mid-latitudes during the Wordian–Capitanian and remain to the south of Central Iran, Karakorum Block and South China, which were equatorially located in the Capitanian.