Thini Fm

Named after village of Thini, Thakkola valley north of Annapurna, south of Tibet

Synonym: Zhamure Sandstone, Zhamure Sandstone Fm (proposed by Garzanti, 1999); Quartzite Fm (regional facies through Tethyan Himalaya). "All along the Tethys Himalaya, the Triassic succession is capped by quartzose sandstones and intercalated oolitic-bioclastic hybrid arenites, originally designated in Spiti as "Quartzite Series'' (Hayden, 1904). Although unsuitable for a number of reasons (e.g. the name does not fulfill the requirements of the stratigraphic code; the unit contains quartzo-feldspathic sandstones and not metamorphic quartzites), this term has been subsequently adopted not only in N. India but in Nepal as well from Dolpo to the Burhi

Gandaki area (Bassoullet and Mouterde, 1977; "Quartzite Beds'' of Fuchs, 1977; Fuchs et al., 1988)

to emphasize the similarity of facies along the Tethys Himalaya. However, significant diachroneities and facies differences have recently been documented between the Spiti-Zanskar Synclinorium and S. Tibet (Jadoul et al., 1998). Because the Nepal stratigraphy compares closely with S. Tibet and only loosely with the N.W. Himalaya, the term Zhamure – widely

adopted in the Chinese literature (Liu, 1992, and references cited therein) – is proposed herein [Garzanti, 1999] for Nepal also. Terms such as "lower lumachelle'' (Bodenhausen et al., 1964) or "Thini Fm.'' (Gradstein et al., 1989) should be avoided (see discussion in Garzanti and Pagni Frette, 1991, p. 12)." (from Garzanti, 1999). [Note: The Nepal-type section definition for a Thini Fm is retained in this Lexicon, because projecting the southern Tibet nomenclature may require further verification of continuity of the facies.]

Shallow-marine quartzo-feldspathic to quartzose sandstones and oolite-bioclastic hybrid arenites with subordinate mudrocks and limestones. Capped by an ironstone horizon in Manang (lithozone 6 of Garzanti et al., 1994b). In Dolpo, Thakkhola and Manang several lithozones can be distinguished but due to lack of biostratigraphic control their age cannot be easily assessed; the unit is generally capped by a 19 to 27 m thick, resistant interval of up to medium-grained quartzarenites

(Thakkhola; "white quartzite marker bed'' of Gradstein et al., 1989) to oolite-bioclastic quartzarenites (central Dolpo) displaying spectacular high-angle cross-lamination, which is replaced by more distal shoreface sediments in Manang."

"Finding of age-diagnostic fossils in the shallow-marine successions straddling the Triassic/Jurassic boundary is badly needed to establish former stratigraphic correlations between the N.W. Himalaya – where the "Quartzite Series'' are largely early Rhaetian in age (e.g. Jadoul et al., 1990; Garzanti et al., 1995) – and the central Himalaya – where hybrid siliciclastic deposits with all likelihood extend into the Liassic at least in proximal settings (Jadoul et al., 1998). On the other hand, the ironstone horizon capping the unit in Manang ("lithozone 6'' of Garzanti et al., 1994b) may correlate with the ironstone of Rhaetian age capping the Alaror Gr in Spiti (I6 interval of Garzanti et al., 1995)."