Climatic and tectonic uplift evolution since ~7 Ma in Gyirong basin, southwestern Tibet plateau: clay mineral evidence

Abstract

Climate evolution associated with the uplift in Gyirong, southern margin of the Tibetan plateau, was investigated based on the clay mineralogy of the Gyirong sediments, using X-ray diffraction and scanning electron microscopy methods. The (chlorite ? illite)/(kaolinite ? smectite) ratio and the illite crystallinity index suggest the trend of paleoclimate evolution in Gyirong basin during *7-1.7 Ma BP, with a warm and humid climate in *7.0-5.8 Ma, a relative cool and dry climate in *5.8-5.5 Ma, a relative warm and humid climate in *5.5-2.5 Ma, and a much warmer climate in *2.5-1.7 Ma, respectively. The fluctuating kaolinite/smectite index and calcite content and the frequent occurrence of gypsum in the episode of *6.7-5.5 Ma suggest intense climatic fluctuations between humid and more seasonal humid conditions. Five peaks exhibit at 5.8, 4.9, 4.3, 3.6, and 2.5 Ma in the curves of illite and chlorite content and illite crystallinity. The intense uplift and tectonic-forced cooling at *5.8 and 4.3 Ma were indicated by the high-illite crystallinity index and illite and chlorite content. A remarkable increase in illite and chlorite content associated with only little increase in illite crystallinity at *3.6 Ma indicates a rapid uplift, but no significant climate change. And a sharp increase in illite crystallinity, while small change in illite and chlorite content at *2.5 Ma suggests that no remarkable relief was produced by the uplift, which may take place in the whole south Tibet plateau, while cooling at 4.9 Ma is probably a record of the global climate cooling.

Extended stratigraphy, palynology and depositional environments record the initiation of the Himalayan Gyirong Basin (Neogene China)

“…8). This is in agreement with the occurrence of Hipparion fauna (Huang and Ji, 1979) and two new rodents (Li and Chi, 1981), as well as clay minerals (Chen et al, 1977;Hong et al, 2010) in the Gyirong Basin, which all suggest a warm and humid subtropical paleoenvironments with local steppe development. This type of climate created suitable condition for the expansion of C 4 grasses which may be linked with the migration of the Hipparion fauna from North China into the Gyirong Basin.…”

“…8. Comparison of the paleoclimate phases marked by pollen and ostracods data records at the Woma section with (a) clay mineral index (Hong et al, 2010) and (b) stable isotope data (Wang et al, 1996) in the Gyirong Basin, mass accumulation rate and grain size of eolian dust (c) at Site 885/886 (Rea et al, 1998), the benthicforaminiferal carbon and oxygen isotope (d) from ODP Site 1088 (Billups, 2002). from 10.5 to 9.5 Ma (Nakayama and Ulak, 1999;Chirouze et al, 2012).…”

Clay Mineralogy of the Zhada Sediments: Evidence for Climatic and Tectonic Evolution Since ~9 Ma in Zhada, Southwestern Tibet

“…The presence of abundant ephedra and chenopodiaceae and the fluctuating but overall large chenopodiaceae/artemisia value also reflect an unusually warm and seasonal arid climate in the period ( Figure 5). These climate patterns are similar to those of the Gyirong area in the period 6.7À5.5 Ma BP (Hong et al, 2010), which was probably caused by intensity variations of the Asian monsoon Hu et al, 2005).…”

“…Chamley, 1989;Thiry, 2000). Study of the clay minerals of basin sediments can provide evidence of climatic and environmental changes and, in particular, of topographic changes related to uplift in the area (Thiry, 2000;Hong et al, 2007Hong et al, , 2010. Previous studies of the Zhada sediments, however, have focused mainly on chronology, sedimentology, and sporopollen assemblages; clay-mineral investigations of the sediments have not been undertaken.…”

Early middle Miocene tectonic uplift of the northwestern part of the Qinghai–Tibetan Plateau evidenced by geochemical and mineralogical records in the western Tarim Basin

“…These uplifts potentially caused regional aridification reducing chemical weathering. The dating is indirect via magnetostratigraphically dated ostracod biostratigraphy and detrital zircon chronology and currently not good enough to compare the shift accurately in time with the onset of the global middle Miocene Climate Plateau, such as the Qaidam, Xining, Linxia, Girong, and Zhada basins (Dettman et al 2003;Dupont-Nivet et al 2008;Graham et al 2005;Hong et al 2007Hong et al , 2010Hong et al , 2012Rieser et al 2009). The relationship between uplift of the QTP and climate change remains scarcely documented in the Tarim Basin.…”