Tashkazyk 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).

Defined by Novikov (1976). Upper formation of the Bazardara Gr.

Synonym:

The Tashkazyk Fm, at least in the Kastenat Djilja area (Angolini et al., 2015) consists of sandstones, siltstones and black shales with fossiliferous calcareous sandstones at the top. Sandstones from the Tashkazyk Fm are characterized by quartz with K-feldspars and plagioclase. Plutonic grains are common. It is composed of several units – “a basal 40-60 m of claystone, bioclastic sandy limestones, calcareous sandstones with boulders of bioclastic sandy limestones (Bed 3 of Grunt and Novikov, 1994); 10 m of black claystones, siltstones and bioturbated sandstones (bed 4); 25–30 m of black claystones containing yellow marlstones and lenses of limestones (Bed 5); 40–50 m of claystones and siltstones with concretions of calcareous siltstones (Bed 6); 80–125 m of silty claystones and calcareous siltstones with rare bioturbated marly limestones and with carbonate, siliceous or clayey concretions (bed 7); 5–10 m of bioclastic calcareous sandstones (Bed 8); 20 m of black claystones and sandy siltstones with ferruginous crusts at the top suggesting emersion (bed 9). In general, the outcrops of the Bazardara Gr are poorly exposed and covered by talus or a thick soil cover, so that it is rather difficult to measure in detail stratigraphic sections and thicknesses. Tashkazyk Formation having a total thickness of 300–980 m. However, its thickness is very variable, being greater (700–980 m) in Karabeles and North Alichur, but reduced to 300–500 m in Kastenat Djilga and Kurteke areas.” (Angiolini et al. 2015)

“The Tashkazyk Formation comprises conulariids, crinoids, bryozoans, ammonoids (Metapronorites sp., Marathonites sp., Emilites sp.), bivalves (Pseudomyalina sp., Megadesmus sp.) (Leven, 1967; Pavlov, 1972) and very abundant brachiopods. According to Grunt and Dmitriev (1973) and to our own analysis, brachiopods from the Tashkazyk Formation comprise species of Costatumulus, Permochonetes, Reticulatia, Spirelytha, Tomiopsis, and Trigonotreta. We have found conodonts in a sample collected about 100mbelow the top of the Tashkazyk Formation at Mudzubulak. They comprise Mesogondolella monstra, Streptognathodus sp., Sweetognathus bucaramangus, S. cf. merrilli, S. cf. behnkeni, and S. whitei. Although S. whitei has normally been associated with an Artinskian age, it was determined that the holotype of S. whitei is older (Lucas, 2014; Henderson, 2014). Such older forms from Nevada (Ritter, 1987) and Bolivia (Suarez Riglos et al., 1987) are now ascribed to the late Asselian and early Sakmarian. According to Chernykh (2005) Mesogondolella monstra is typical of the Tastubian or early Sakmarian substage and the S. merrilli Zone.” (Angiolini et al., 2015)

“The abundance of quartz and feldspars grains associated to plutonic rock fragments in the Tashkazyk sandstones are all indicative of a granitoid source. The Tashkazyk Formation was considered a flysch by Novikov (1976, 1979) and Grunt and Novikov (1994). However, we could not find any sedimentary structure to suggest a flyschoid origin for these deposits. On the contrary, the formation shows a remarkable similarity to the Gircha Fm of Karakorum, Pakistan (Gaetani et al., 1995), which was deposited in neritic environments from nearshore to prodelta, storm dominated settings. Quantitative petrography of the two formations indicates that TJ77 is correlatable to the lower-middle Gircha Fm (Ashtigar section), whereas TJ83 is very close to the upper Gircha Fm (Ashtigar-Khudabad-Gircha). The taxonomic composition and diversity of the brachiopods are consistent with a cold water setting, particularly the assemblages from Bed 3. The limestone boulders resedimented in Bed 3 are the result of tectonic activity connected to the beginning of the detachment of the Cimmerian continents.