Triassic palynostratigraphy and palynofloral provinces: evidence from southern Xizang (Tibet), China

Abstract

Palynological analysis was carried out on Middle to Upper Triassic strata from Tulong, Nyalam County, southern Xizang (Tibet), China. Well-preserved miospore (pollen and spore) assemblages and sparse acritarch occurrences were identified. We recognized four formal and one informal biozones based on stratigraphically important taxa and compositional changes through the succession, in ascending order: the Triplexisporites Interval Zone (Anisian), the Staurosaccites quadrifidus Taxon-range Zone (upper Anisian to lower Norian), the Striatella Interval Zone (lower Norian), the Craterisporites rotundus Taxon-range Zone (middle to upper Norian) and the informal 'Dictyophyllidites harrisii zone' (Rhaetian). The zonation was supported by marine fossils (e.g., ammonoids and conodonts), and compositional similarity between the zones was examined using non-metric multidimensional scaling (NMDS). Correlation with other representative palynological sequences across Gondwana was also conducted. The presence of miospore taxa not previously recovered from the Late Triassic North and South China palynofloral provinces (e.g., Ashmoripollis reducta, Craterisporites rotundus, Enzonalasporites vigens, Minutosaccus crenulatus, Samaropollenites speciosus and Staurosaccites quadrifidus) calls for a new province in southwestern China, i.e., the Southern Xizang Province. It is proposed here that the modern expression of the northern boundary runs along the Yarlung Zangbo Suture, the remnant of the Tethys that separated the Indian Plate (southern Xizang) and the Lhasa Block during the Late Triassic. This new palynofloral province comprises typical elements of the Onslow Microflora, indicating the need for an extension of this microflora in southern Xizang, China.

Triassic vegetation and climate evolution on the northern margin of Gondwana: a palynological study from Tulong, southern Xizang (Tibet), China

“…3). For Middle to Upper Triassic sampling levels, see Peng et al (2018b). Rock samples were cleaned, crushed, weighed (∼60 g per sample) and processed using standard hydrochloric and hydrofluoric acid palynological processing techniques (Traverse, 2007).…”

“…2). The upper five zones of the Middle to Upper Triassic were described by Peng et al (2018b); here we introduce the new miospore zones for the Lower Triassic (the Endosporites-Densoisporites Abundance Zone and the Bisaccates-Aratrisporites Abundance Zone).…”

“…Southern Xizang (Tibet), located in the southwestern part of China, hosts continuous and extensive successions of well-exposed near-shore marine Triassic sedimentary deposits that include, among other fossil groups, rich pollen and spore assemblages (Rao et al, 1987;Schneebeli-Hermann et al, 2012;Peng et al, 2018b). This area was situated on the northern margin of Gondwana during the Triassic (Ogg and von Rad, 1994), and represents an important region to further understand the development of terrestrial ecosystems and vegetation of northern Gondwana during a key developmental phase of the evolution of the Tethys Ocean (e.g., Pan et al, 2012).…”

A review of the Triassic pollen Staurosaccites: systematic and phytogeographical implications

“…These samples originate from the Middle to Upper Triassic Laibuxi, Zhamure and Dashalong formations of the Tulong Section, located close to the Tulong village, Nyalam County, southern Xizang (Tibet), China. Details regarding the geological setting, sample horizons and palynological processing methods are provided by Peng et al (2018a). Material is housed in the collections of the Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences (NIGPAS).…”

A new Late Triassic palynological assemblage from western Gondwana (Carrizal Formation, Marayes Basin, Argentina)

“…However, Smith et al (2018 considered this result with caution because the dated grains may be detrital in origin and thereby provide only a maximum age for the Brisbane Tuff. Peng et al (2018) defined the middle to upper Norian Craterisporites rotundus Taxon-range Zone in the Southern Xizang Province (Tibet) which was situated in the southern mid-latitudes at the northern margin of the Indian Plate China, as a part of Gondwana. This important biostratigraphic species probably is also present in the Lower Carnian deposits of the Dolomites (van der Eem 1983); however, it was described as Bocciaspora blackstonensis (de Jersey) Van der Eem.…”