Marpha Fm
Type Locality and Naming
Thakkhola-Mustang graben fill succession. Described from the vicinity of Marpha and the Syang Khola, where it very gently (5–7°) dips due northeast.
Lithology and Thickness
Glacio-lacustrine sandstone-siltstone with some coarse clastics. It is a more than 200 m thick sequence of mudstone and siltstone interbedded with sandstone and conglomerate. These glacio-lacustrine deposits are also sporadically affected by penecontemporaneous deformation and slumping. The intercalated conglomerate beds contain imbricated pebbles and cobbles of quartzite, carbonates, granites, and slates. The coarse-grained sandstones generally pass upwards to laminated medium-grained sandstone, which, in turn, give way to muddy conglomerate beds. The lower part of the Marpha Formation could be equivalent to the upper part of the coarser-grained Sammargaon Fm.
Relationships and Distribution
Lower contact
Overlies Sammargaon Fm
Upper contact
Overlain by Holocene fluvial and debris flow deposits
Regional extent
Thakkhola-Mustang graben fill succession. This Cenozoic east–west extensional phase of Tibet has created many small and some large grabens dated about 14 or 8 Ma (Coleman and Hodges 1995; Harrison et al. 1995; Blisniuk et al. 2001). Some of the important ones are the Thakkhola–Mustang Graben, Gyirong Graben, and Yadong Graben. The Thakkhola–Mustang Graben is about 90 km long and 20–30 km wide.
GeoJSON
Fossils
Age
Depositional setting
The sediments in the Thakkhola–Mustang graben were deposited in alluvial fan, braided river, glacio-fluvial, and lacustrine environments. The paleocurrent directions measured on imbricated pebbles from all formations of the basin show a generally southwards flow, whereas limestone microfacies analysis indicates a flat and shallow lacustrine environment of carbonate deposition (Adhikari 2009).
Additional Information