Takhtabulak Fm

Includes in SE Murghab district (Mynkhadjr type), SE Murghab district (Istyk type (Dunkeldyk area), SE Murghab district (Gurdumdin type), SE Murghab district (Gurdumdin type Kastanatdjilga, Buryukurmes rivers), SE Murghab district (Gurdumdin type Shin and Igrymiyu rivers), SE Murghab district (Gurdumdin type Gurumd and Kattamardzhana rivers).

The Takhtabulak Formation was established by Dutkevich (1937) and later subdivided into three units by Grunt and Dmitriev (1973). [It is unclear in the publications, but either a lateral equivalent or the upper of the “three units” might be the Kastanatdjilgin Fm (кастанатджилrинская свита) of massive organogenic limestones with a thickness of 40-80 m, enclosing at the base and within themselves interlayers of limestone conglomerates?]

Synonym: Тахтабулакская толща , Taktabulak stratum, Takhtabulak Fm

Reference section:

It is composed of tuffs, tuffaceous shales, volcanic sandstones, and gravelites, containing lenses of spilite-diorites and dolerite porphyrites. Most of the formation is made of dark green volcaniclastic sandstones, shales and subordinate conglomerates, with sedimentary structures as parallel lamination and gradation; rare intercalations of sandy calcarenites occur. Sandstones are dominated by mafic volcanic detritus including abundant basalt grains and lathwork rock fragments.

At the base of the formation in the Kutal 2 section, meter-sized boulders of basaltic lavas and limestones are embedded in volcaniclastic sandstones. In the middle part of the formation in the Kuristyk section and at Mudzubulak, meter-sized boulders of stratified bioclastic limestones and algal, coral, and sponge biostromes occur. Microfacies of bioclastic limestones reveal coarse packstones with fusulinids, rugosa and tabulate corals, sphinctozoans, brachiopods, echinoderms, ostracods and carbonate and volcanic extraclasts. The upper part of the series is formed by interbedded marly shales, limestones, cherts, sandstones. Its thickness is 0-140 m.

“The intercalation of bioclastic limestones and the boulders of coral-sponge-bryozoan bioconstructions embedded in the formation contains a very rich biota of fusulinids (Reichelina pulchra), smaller foraminifers, algae, brachiopods (Anchorhynchia sarciniformis,

Costisteges sp. ind., Enteletella nikschitshi, Enteletes dzaghrensis, E. meridionalis, Heterelasmina lepton, Martinia bisinuata, M. aff. warthi, M. rupicola, M. sp. 1, M. sp. 2., Notothyrina pontica, Notothyris pseudodjoulfensis, Orthothichia avushensis, Parenteletes ruzhencevi, Paramarginifera sp. ind., Streptorhyncus aff. pelargonatus, and Stenoscisma armenica), bivalves, echinoderms, bryozoans, tabulate and rugosa corals and sponges (sphinctozoans)” (Angiolini et al., 2015) Here, representatives of foraminifera genera, unknown in deposits older than the Pamir horizon, have also been found: Palaeofusulina, Reichelina, Colaniella, Codonofusiella. In addition, representatives of older Neoschwagerina, Verbeekina, Sumatrina, Armenina, Cancellina, Pseudodoliolina have been encountered.

In the sections examined by Angiolini et al. (2015), the local facies of this formation is: “The pure volcaniclastic composition, recorded by the detrital modes of the Taktabulak Fm, attests to erosion of a mafic volcanic edifice. Sedimentary structures in the volcaniclastic sandstones and conglomerates are also indicative of resedimentation along a slope. Tectonic activity should have been intense, with slope instabilities causing resedimentation of meter-sized olistoliths of bioclastic limestones, biostromes and basaltic lavas. There are several features, which suggest that both the bioclastic limestone boulders and the bioconstructions are olistoliths transported along the slope. The limestone boulders are in fact stratified obliquely to the S0 of the formation. The build-ups are not growing on the sandstones of the slope as suggested by Grunt and Dmitriev (1973), as most reefal organisms are in life position but they are discordant to the stratigraphic polarity of the succession.” [However, one must be careful to generalize these local observations to the regional extent of this unit.]