Figure and table captions
Fig. 1. Simplified tectonic map of the southern Tibet (modified from Pan et al., 2004). Location of the study area is indicated by a red star.
Fig. 2. Photos are showing: (a) bioclastic grainstone, (b) bioclastic wackestone, (c) coral framestones, (d) shell bed mainly composed of Lithiotis , (e) mudstone and grainstone, (f) sand lens and erosive base. The contact between mudstones and grianstones is erosive.
Fig. 3. Correlation of stratigraphic distribution of carbonate carbon isotopes of the Menqu section and distribution of organic carbon isotopes of the Nianduo section (Han, Hu, Kemp, & Li, 2018). The blue dashed line means the boundary between the Pupuga Formation and the Nieniexiongla Formation.
Fig. 4. Photo of oolitic grainstones from Nieniexiongla Formation (plane polarized light microscopy image).
Fig. 5. EPMA points of ooilitic grainstones (polished thin section, EPMA backscattered electron image, results of green points with numbers could be seen in Table 1). (a) 17MQ56-03:1 and 17MQ56-03:2 are ferruginous mineral, 17MQ56-03:3 is quartz; (b) 17MQ66-02:1, 17MQ66-02:2, 17MQ66-02:3 and 17MQ66-02:4 are all ferruginous mineral.
Fig. 6. (a) ooid with euhedral ferruginous minerals in nuclei and ferruginous spheroids in cortex (polished thin section, SEM backscattered electron image), (b) ooid with euhedral ferruginous (polished thin section, SEM backscattered electron image), (c) euhedral ferruginous particles (fresh fragment, SEM image), (d) regular six-sided euhedral ferruginous particles (polished thin section, SEM backscattered electron image), (e, f) euhedral ferruginous minerals show concentric structure (polished thin section, SEM backscattered electron image).
Fig. 7. (a) ferruginous particles make up of a concentric layer around the cortex (polished thin section, SEM backscattered electron image), (b) ooids contain ferruginous particles with quartz nuclei (polished thin section, SEM backscattered electron image), (c) ferruginous aggregated spheroids (fresh fragment, SEM backscattered electron image), (d) ooids contain ferruginous particles with different nuclei (polished thin section, SEM backscattered electron image).
Fig. 8. Linear scan of sulfur and iron distribution of a ferruginous particle by SEM-EDS. Polished thin section, SEM backscattered electron image.
Table 1. Results of EPMA analysis of different minerals in red ooid grainstones (oxide values are given in molar).