Yak Kharka Fm
Type Locality and Naming
Uppermost formation in Thinigaon Gr. Defined by Garzanti, 1999: "The upper part of the Norian succession ("upper assemblage'' of Dolpo: Garzanti et al., 1992; "middle and upper members'' of Manang: Garzanti et al., 1994b), which can be easily recognized for its much more varied lithology (e.g. including patch reefs, nodular limestones and ironstone horizons), is here for the first time distinguished from the Tarap Fm. under the new name Yak Kharka Formation. … This new stratigraphic unit, with type section displaying both base and top and continuously exposed for nearly 150 m just south of the alpage named Yak Kharka in the Jarsgeng Valley of N.W. Manang (Fig. 3; section described in Garzanti et al., 1994b, Figs. 1, 8 and 10)."
Lithology and Thickness
Lower sandy coral limestone; Upper siltstone-limestone-ironstone. "includes an up to 30 m thick lower "coral limestone'' member, recognized by Fuchs et al. (1988; middle member of Garzanti et al., 1994b) and tentatively correlated with the mid-Norian reefs of Spiti ("coral limestone'' of Hayden, 1904; Bhargava and Bassi, 1985). The upper member ("upper member'' of Garzanti et al., 1994b; 106 m thick in the type-section), consisting of siltstones and quartzo-feldspathic sandstones intercalated with transgressive arenites, is undated, and may be either entirely mid to late Norian in age or reach into the Rhaetian."
Relationships and Distribution
Lower contact
Overlies the Tarap Fm siltstone.
Upper contact
Overlain by the Thini Fm (Zhamure Sandstone Fm)
Regional extent
In the Thakkhola Graben and Dolpo, the ``coral limestone " horizon has never been reported so far, and the base of the Yak Kharka Fm. (previously called informally ``upper assemblage "; Garzanti et al., 1992) is marked by a sharp-based coastal sandstone body (Fig. 4(B), (C)). In Dolpo the unit can also be subdivided into two members ("lower and upper intervals" of Garzanti et al., 1992), containing each a transgressive ironstone horizon at the base. The Yak Kharka Fm. compares with the ``coral limestone " and ``Monotis shales " of the Spiti-Zanskar Synclinorium (e.g. Hayden, 1904; Fuchs, 1982; Garzanti et al., 1995), and condensed horizons found within the unit may correlate with those identified in the "Monotis shales" of Spiti (i.e. I4 and I5 intervals of Garzanti et al., 1995, Figs. 7, 8, 12, 19). The Yak Kharka Fm. might represent a broad equivalent of the "Derirong Formation" recognized by Chinese Authors in S. Tibet (e.g. Liu, 1992), and may be traced as far as Kumaon, where "regular layers of grey limestone" are reported to occur in the upper part of the Kuti Shales (Heim and Gansser, 1939), a broad equivalent of the "Tarap Shales''.
GeoJSON
Fossils
Age
Depositional setting
Additional Information
" In the upper part of this otherwise monotonous succession a shoreface sand- stone body documenting a forced regression was recognized from Dolpo to Thakkhola, whereas in Manang regressive sandstones are overlain by lenticular coral patch reefs. These rocks, which may be equivalent to the mid-Norian "coral limestone'' of the N.W. Himalaya (Fuchs et al., 1988), along with the overlying quartzo-feldspathic silt- stones to sandstones and intercalated transgressive are- nites rich in ferruginous ooids, black grains and lithoclasts, are formally distinguished from the underlying Tarap Fm shale and assigned the name Yak Kharka Formation"