Tistung Fm

Katmandu region (Tethyan sequence)

"The Phulchauki Gr commences with the Tistung Formation, which is comprised mainly of slates, phyllites, and meta-sandstones. Also noticeable is a distinct decrease in metamorphic grade from bottom to top of this formation. The Lower portion of the Tistung Formation consists of dark gray phyllites and fine biotite schists, but while moving stratigraphically upwards, biotite gradually disappears and sericite and chlorite remain as the constituent metamorphic minerals. Similarly, the dark green-gray colors, so characteristic of the schists and quartzites composing the underlying formations, give way in places to conspicuous pink, buff, and purple tints. These colors are more vivid, particularly in meta-sandstones. As a result, there is frequently red and green color banding owing to the alternation, respectively, of meta-sandstone and phyllite. There are also a few bands of pale yellow and white clean quartzite. Sun cracks, ripple marks, cross-lamination, and worm tracks are regularly observed in this formation. The fine-grained rocks commonly alternate with thin limestone beds, and the associated sandstones have a slightly calcareous matrix. The sandstones are generally slabby to flaggy, and as such, they can form a single slab of several meters in length and width. The rocks frequently exhibit deep pink, blue, violet, and purple colors in their weathered state. Normally, deep redpurple soil develops on this formation. The Tistung Formation reaches a thickness of about 3,000 m (Stöcklin and Bhattarai 1977, p. 30).