Karasu 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).

This is the upper formation in Gan Gr

Synonym: Карасинckая толща, Karasin Fm, Karasinskaya stratum,

Reference section:

The upper part of the Gan Gr consists of very thick polymict conglomerates and breccias, which are clast-supported, immature, poorly sorted, with both spherical and elongate, rounded and angular 3–40 cm-wide clasts of cherts, limestones, and volcaniclastic rocks. In the lower part of the unit, the conglomerates form lenticular bodies with erosive bases, which cannibalize each other; in the upper part, they are better organized in meter-thick beds. Sporadic intercalations of volcaniclastic ashes, thin-bedded limestones (wackestones with radiolarians, sponge spicules and pelagic bivalves) and slumpings are also present. In the Kutal 2 section, the conglomerates are less thick and the Gan Gr ends with [the Kutal Fm of] about 30 m of cherty bioclastic limestones (calcarenites and calcirudites; subordinate calcilutites) and volcaniclastic ashes.” (Angiolini et al., 2015). The regional thickness of the stratum is 5-50 m.

Numerous remains of foraminifera are found in it, many of which are redeposited. Stratigraphic importance is represented by the first appearance of species of the following genera, characteristic of the Pamir horizon: Palaeofusulina, Colaniella, Codonofusiella, Dunbarula, Kahlerina, Yabeina, and the species Neoschwagerina cf. katoi Oz. Together with them, redeposited fusulinids, typical for the Murghab horizon, are present: Neoschwagerina haydeni Dutk., N. craticulifera (Schw.), N. simplex Oz., and representatives of Verbeekina, Sumatrina, Praesumatrina, Armenina, Cancellina, and others (Gushchin, 1973; Leven, 1967). [See Gan Gr for synthesis of later biostratigraphic work.]

The thick conglomerate bodies [Karasu Fm; uppermost formation in the Gan Gr] indicate a marked reprisal of tectonic activity possibly related to syn-depositional block faulting and formation of debris flow along steep fault scarps, during a major regression, which occurred at the end of the Capitanian. They are thus correlatable to similar debris flows, which occur in the late Middle Permian Kundil Fm of Karakorum, Pakistan (Gaetani et al., 1995). This suggests that this tectonic activity coupled with regression is a global event recognizable in the most of the Cimmerian blocks.