A new Changhsingian brachiopod fauna from the Xiala Formation at Tsochen in the central Lhasa Block and its paleogeographical implications

Abstract

Permian faunal affinity in the Lhasa Block plays a critical role in reconstructing its paleogeographic evolution. Cisuralian and Guadalupian faunas have been described from the Lhasa Block, but very few Lopingian (late Permian) brachiopods have been reported so far. In this paper, a new diverse brachiopod fauna consisting of 17 species of 17 genera and an unidentifiable Orthotetoidea is described from the uppermost part of the Xiala Formation at the Aduogabu section in the central part of the Lhasa Block. The age of this fauna can be assigned to the Changhsingian (late Lopingian) as indicated by the associated foraminifers Colaniella parva (Colani, 1924) and Reichelina pulchra Miklukho-Maklay, 1954. Characteristic brachiopods include Spinomarginifera chengyaoyenensis Huang, 1932, Haydenella wenganensis (Huang, 1932), and Araxathyris cf. dilatatus Shen, He, and Zhu, 1992. They also generally suggest a Changhsingian age. Paleobiogeographically, this fauna is uniformly composed of typical Tethyan elements represented by Spinomarginifera Huang, 1932 and Haydenella Reed, 1944, and some cosmopolitan elements, but no typical cold-water taxa of Gondwanan affinity. This is in contrast to the contemporaneous brachiopod faunas from the Tethys Himalayan region that are characterized by typical cold-water taxa of Gondwanan affinity, e.g., Costiferina indica (Waagen, 1884), Retimarginifera xizangensis Shen et al., 2000, Neospirifer (Quadrospina) tibetensis Ding, 1962. Thus, it is strongly indicative that the Lhasa Block had drifted into a relatively warm-water regime during the Changhsingian. An analysis of the paleobiogeographic change of brachiopods in the Lhasa Block throughout the entire Permian further suggests that the Lhasa Block probably had rifted away from the northern peri-Gondwanan margin between the latest Cisuralian and middle Guadalupian, that is, the Neotethys Ocean had opened before middle Guadalupian.

A late Cisuralian (early Permian) brachiopod fauna from the Taungnyo Group in the Zwekabin Range, eastern Myanmar and its biostratigraphic, paleobiogeographic, and tectonic implications

“…There is potential to apply the above interpretation more broadly across the Cimmerian continents in South and Southeast Asia. For example, the Lhasa Block, like the Irrawaddy Block, is characterized by mixed conodonts and relatively cool-water brachiopods (Yuan et al, 2016(Yuan et al, , 2020Xu et al, 2019), whereas the South Qiangtang Block is dominated by brachiopod and fusuline faunas with typical Cathaysian affinities (Zhang et al, 2012;Shen et al, 2016), like those of the Sibuma Block. If the aforementioned interpretative model accounting for the late Cisuralian biogeographic difference between the Irrawaddy and Sibuma blocks is followed here, the Mesotethys (also known as the Bangong-Nujiang Ocean in some literature) separating the South Qiangtang Block in the north from the Lhasa Block in the south would have opened up before the Guadalupian (middle Permian), and this is certainly consistent with known stratigraphic and paleontologic evidence (Zhang et al, 2019(Zhang et al, , 2020.…”

“…It has been widely recognized that the Cisuralian deposits of the Sibumasu Block are characterized by glacial-marine diamictites containing typical cold-water biotas (Shi and Archbold, 1995;Metcalfe, 2002Metcalfe, , 2011Ueno and Charoentitirat, 2011;Ridd, 2016). Above the glacial-marine diamictites, marine faunas and their paleobiogeographic affinities progressively changed in the Permian during the northward drifting of the Cimmerian continents (Shi and Archbold, 1998;Jin, 2002;Ji et al, 2004;Shi et al, 2011;Shen et al, 2013;Zhang et al, 2013Zhang et al, , 2014Ueno et al, 2015;Yuan et al, 2016;Xu et al, 2019), as well as paleoclimatic amelioration from an icehouse to a greenhouse regime (Chen et al, 2013;Zhang et al, 2013;Haig et al, 2017;Liu et al, 2017). Thus, it can be assumed that the faunas and sedimentary sequences are different if the Irrawaddy Block and Sibuma Block had different tectonic and paleogeographic evolutionary histories.…”

First discovery of Wuchiapingian (Late Permian) foraminiferal fauna from the Zhari Namco area, central Lhasa Block, Tibet, and their palaeogeographic implications

“…The foraminifers Reichelina changhsingensis, Colaniella parva, C. nana, C. cylindrica and brachiopods Spinomarginifera chengyaoyenensis Huang, Haydenella wenganensis (Huang), Chonetinella sp., and Acosarina minuta (Abich) were found from the top of the Xiala Formation in this section. Those fossils suggest a Changhsingian age (Qiao et al, 2019;Xu et al, 2019).…”

“…cylindrica and brachiopods Spinomarginifera chengyaoyenensis Huang, Haydenella wenganensis (Huang), Chonetinella sp., and Acosarina minuta (Abich) were found from the top of the Xiala Formation in this section. Those fossils suggest a Changhsingian age (Qiao et al, 2019; Xu et al, 2019). In the current study, as previously noted, foraminifers from the upper part of the Xiala Formation in the southern Zhari Namco Lake indicate a Wuchiapingian age.…”

“…In the central Lhasa Block, the Wenbudangsang Formation was documented in the Wenbudangsang section, Geji County, which contains conodonts Neogondolella changxingensis, N. deflecta, N. yini, N. postwangi, and Hindeodus julfensis, in total suggesting a Changhsingian age (G. C. Wu, Ji, Trotter, Yao, & Zhou, 2014). In the Xiadong area in northwestern Tsochen County, the Aduogabu section was studied by Qiao et al (2019) and Xu, Zhang, Qiao, and Shen (2019). The foraminifers Reichelina changhsingensis, Colaniella parva, C. nana, C. cylindrica and brachiopods Spinomarginifera chengyaoyenensis Huang, Haydenella wenganensis (Huang), Chonetinella sp., and Acosarina minuta (Abich) were found from the top of the Xiala Formation in this section.…”