Thini Chu Gr

Disconformably overlying the Tilcho Lake Fm

Unconformity below Puchenpra Fm. "at the top of the Thini Chu Gr. a major regional unconformity correlatable with the unconformity separating in the N.W. Himalaya the Po Series [Po Gr] and Fenestella Shales [Fenestella Shales Fm] from the overlying Kuling Gr.

"The Group is much more complete in the Thakkhola Graben and Manang, where it comprises the Marsyandi Fm (including at the top the mid- Carboniferous "Syringothyris Beds" [Syringothyris Beds Fm), the Col Noir Shale [Col Noir Shale Fm], the Bangba Fm and the Braga Fm. All of these units were introduced and defined in Garzanti et al. (1994a). The Thini Chu Group as herein defined is missing altogether in western Dolpo (Fuchs, 1977), whereas in central Dolpo it is represented only by a less than 100 m thick quartzarenite unit, which has been corre- lated petrographically with the Bangba Fm. of the Manang region (Atali Quartzarenite Fm of Sciunnach and Garzanti, 1996). Sediment thickness, which progressively increases eastward reaching about 500 m in wes- tern Manang and about 800 m in eastern Manang, is still around 800 m at Nar Ma (Fig. 2; Le Fort, 1975). Sharp variations in thickness are reported in the Nar Tö-Pangre area (Bordet et al., 1975), where diamictites are found as in the Burhi Gandaki to Shiar Valleys (Colchen et al., 1986); in the latter area the unit is more pelitic and is over 1000 m thick (Fuchs and Paudel, 1998). Further to the east in the Bhote Kosi Valley of western S. Tibet, the rift sequence – represented by the Naxing Gr and Jilong Gr – reaches a thickness of about 1500 m, more than anywhere else in the central and N.W. Himalaya (Garzanti et al., 1998a)."

"The rift sequence, beginning with a major disconfor- mity (``rift unconformity'') and represented by black mudrocks with several intercalated intervals of white quartzose sandstones (Thini Chu Group), is missing altogether in western Dolpo, where Middle to Late Permian clastics directly overlie Devonian dolostones (Fuchs, 1977). Sediment thickness progressively increases eastward, but in central Dolpo the succession is still highly lacunose, including only the less than 100 m thick Atali Quartzarenite, overlying a few metres of marine mudrocks probably correlatable with the "Fenestella shales'' [Fenestella Shale Fm] of the N.W. Himalaya. Thickness reaches about 500 m in the Thakkhola Graben, and 800 m in eastern Manang, where the complete succession is spectacularly exposed (Fig. 2; Bordet et al., 1975; Colchen et al., 1986). Dark mudrocks with a few sandstone intercalations (Marsyandi Fm), containing fossiliferous intervals intercalated in the upper part (``Syringothyris beds''), are followed by dominant black mudrocks with com- mon ochre-weathering carbonate concretions (Col Noir Shale Fm), by interbedded mudrocks and quartzose sandstones with locally intercalated diamictites (Bangba Fm) and finally by siliciclastics including diamictites and containing sedimentary, granitoid and subordinate bimodal volcaniclastic detritus (Braga Fm.). Diamictites characterize the Upper Carboniferous to lowermost Permian section of eastern Manang (Bordet et al., 1975), whereas in S. Tibet glacial deposits – indicating that Gondwana had begun to drift towards higher southern latitudes – occur already in the Lower Carboniferous (Garzanti and Sciunnach, 1997). In spite of major lateral variations in thickness, the rift sequence displays remarkably similar characters all along the Tethys Himalaya, from N. India to S. Tibet (for further details see Garzanti et al., 1994a; 1996a; 1998a)."