Late Neogene environmental changes in the central Himalaya related to tectonic uplift and orbital forcing

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

“…The (chlorite + illite)/(kaolinite + smectite) ratio and the illite crystallinity index are indicative for warm and humid conditions between 7.0 Ma and 5.8 Ma. Moreover, this consistent with relatively high paleo-temperatures ($20°C) reported from the same stratigraphic intervals in the Gyirong Basin by Wang et al (2012). This apparent contradiction between warm and humid local conditions in the basin and high altitude cool and arid conditions from the pollen is best explained by a mixed record.…”

“…The Gyirong Basin (N28°30 0 -29°00 0 , E84°40 0 -85°30 0 ) is one of several south-north trending Neogene extensional troughs formed during the Himalayan uplift (Garzione et al, 2000;Zhang et al, 2007). The rich paleoenvironmental records of the basin have previously been documented by other researchers (Xu et al, 1973;Huang and Ji, 1979;Chen, 1982;Wang et al, 1996;Shi et al, 1998;Yue et al, 2004;Wang et al, 2006;Sun et al, 2007;Wang et al, 2009;Yang et al, 2009; see in particular, Wang et al, 2012). Recent advances in palynology and regional structural analysis were made during geologic mapping of the Saga county (Sangsang district) and Gyirong county sheets at a scale of 1:125,000 (Sun et al, 2007;Wang et al, 2009).…”

“…(CAS, 1989). Based on carbon isotopic analysis of this layer (Chen, 1982;Wang et al, 2006), these organisms required a rather hot and wet, subtropical environment, and the presence of significant amounts of C 4 grasses suggests that at 7 Ma the elevation might have been less than 3000 m. This is confirmed and quantified by more substantial isotopic results from Wang et al (2012).…”

“…A simple explanation may be activation of faulting and uplift in the NE of the basin as illustrated o Fig. 7 of Wang et al (2012) After 7.0 Ma, pollen data suggest high altitudes with subalpine shrub steppe in the uplands and drought-tolerant (Chenopodiaceae, Artemisia, Ephedra) as well as cold-tolerant pollen taxa (Abies and Picea) from the presumably higher altitude source area in the NE of the basin. Nevertheless, the presence of ostracods (Candona, Candoniella, Leucocytherella) suggests it was a period with locally prevailing warm and humid lacustrine condition (Fenning Chen, unpublished;Hong et al, 2010, this paper).…”

Edifice growth and collapse of the Pliocene Mt. Kenya: Evidence of large scale debris avalanches on a high altitude glaciated volcano

“…Only later during the Pliocene the Himalayas gained similar estimated altitudes (e.g. Garzione et al, 2000;Wang et al, 2012), while the Andes attained their higher altitudes only during the Quaternary (e.g. Coltorti and Ollier, 2000).…”