Robang Fm
Type Locality and Naming
Katmandu region (Lesser Himalayan succession)
Lithology and Thickness
The Robang Phyllites comprise primarily green-gray sericite– chlorite phyllites and some darker slates akin to those of the Benighat Slates Fm. There also occur bands of dark green chloritic phyllites and associated with them are metamorphosed basic tuffs, metadiabases, and metagabbros. The tuff-like bands sometimes alternate with light green, soapy, talcose phyllites. There are also sporadic intercalations of thin calcareous beds. A boulder-bed of about 2 m thickness and similar to those found in the Benighat Slates was observed in the Hugdi Khola (Stöcklin and Bhattarai 1977, p. 21). But, different from the Benighat Slates Fm, the Robang Formation frequently contains thin to thick alternations of light green to white quartzites. The more prominent quartzite bands are included in the Dunga Quartzite Beds. They are generally medium-grained, clean, white quartzites with minor phyllite intercalations, and they may attain a thickness of 500 m. But there also appear varieties that are thinly bedded and very fine-grained, almost like the bedded chert. The thickness of the Robang formation ranges from 200 m to more than 1,000 m.
Relationships and Distribution
Lower contact
The underlying Malekhu Limestone exhibits perfectly gradational contacts with the overlying slate bands of this Robang Fm. The transition is generally marked by an approximately 20–30 m thick alternation of calcareous and argillaceous rocks.
Upper contact
The Mahabharat Thrust or Main Central Thrust brings the Kathmandu Complex (of which the Raduwa Fm is the lowest formation of the Bhimphedi Gr) over the Upper Nawakot Gr (Robang Fm is the uppermost preserved unit). However, on some rare occasions, the thrust approaches the Siwaliks, concealing the whole Lesser Himalayan sequence. The Main Central Thrust is commonly associated with a sheared and mylonitized zone.
Regional extent
GeoJSON
Fossils
Age
Depositional setting
Additional Information