Nourpui Fm

Katmandu region (Lesser Himalayan succession)

The Nourpul Formation represents an assorted succession, comprising quartzites, phyllites, and calcareous rocks. It is further subdivided into the following three members. The Purebesi Quartzite Member follows the predominantly phyllitic Dandagaon Phyllites Fm and forms the basal portion of the Nourpul Formation. It is represented by fine- to coarse-grained arkosic quartzites, displaying colors ranging from pure white to pink, pale yellow, and green. Infrequently rounded quartz grains of up to 2 mm in diameter occur in its lowermost horizons. Oftentimes, the quartzites display cross-lamination and ripple marks. The Purebesi Quartzite is about 300 m thick at its type locality. The Purebesi Quartzite is succeeded by the prominently phyllitic Middle Member, with a variable proportion of quartzitic and calcareous intercalations. The phyllites commonly display gray-green to blue-gray coloration in fresh outcrops, but they show vivid red tints in weathered conditions. The regularly alternating impure micaceous quartzites are frequently dark green or green-gray and sporadically pink. Similarly, there are regularly intercalated carbonate beds composed of dense and microcrystalline siliceous dolomite. Some of these beds are composed of fine quartz grains, whereas some others range from siliceous dolomite to dolomitic quartzite. The variegated carbonate beds show light gray, yellow, and pale green colors in fresh conditions but intense buff, orange, pink, carmine, and violet colors when weathered. The phyllite–quartzite and phyllite–dolomite alternations range in thickness from tens of meters to about 100 m between the thicker intervals of pure phyllite (Stöcklin and Bhattarai 1977, pp. 16–17). The dolomite and dolomitic quartzite intercalations become more abundant in the Upper Member of the Nourpul Formation. A regular alternation of decimetric green phyllite and buff or orange siliceous dolomite frequently results in beautiful color banding. The Nourpul Formation is about 800 m thick in its type locality, but its thickness varies widely in other places due mainly to tectonic causes (Stöcklin and Bhattarai 1977, p. 17).