Gan Gr

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).

Gan Gr (Ганскую свиту) was distinguished by E.Ya. Leven (1958), combining under this name the previously established upward succession of the Dhzamantal Fm, Deire Fm, Karasu Fm, and Kutal Fm (using spellings of Angiolini et al., 2015) (= Jamantalskaya, Dayrinskaya, Karasinskaya, and Kutalskaya suites; = джамантальакую, дейринскую, карасинскую и кутачьскую свиты нли толщи.) by G.A. Dutkevich (1936, 1937). The reasons for the combination were the small thickness and facies variability of the listed formations.

Synonym: Ганскую свиту, Gana Gr, Gansky suite

Reference section:

The Gan Gr is composed of various limestones and siliceous shales. Its thickness varies from 25 to 150 m. Since the Gansky suite combines formations that are stratotypes for a number of zones and horizons (or stages), a detailed description is given below.

The Lower part of the formation [Dhzamantal Fm, Deire Fm] consists of cherty bioclastic limestones (mostly fine calcarenites), cherts and greenish shales with a greater amount of volcaniclastic ashes with respect to the underlying formation; intercalation of conglomerates, channelized beds and slumpings occur.

The Middle part of the formation [Kutal Fm] is dominated by colored volcaniclastic ashes interbedded with thin-bedded nodular limestones and cherts. This unit is more evident in the Kubergandy section than in the Kutal 2 section. Two distinct microfacies were recognized in the limestones: (1) a microfacies of bioclastic packstones, finer than those of the Kubergand Fm, containing foraminifers, peloids, thin-shelled bivalves, and echinoderms; (2) a microfacies of wackestones/packstones with radiolarians, sponge spicules and thin-shelled bivalves.

The Upper part of the formation [Karasu Fm] 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.

“The Gan Formation is characterized by the occurrence of fusulinids, foraminifers, algae (Permocalculus sp.), pelagic bivalves, ostracods, echinoderms and Tubiphytes ex gr. obscurus. … According to our data … , fusulinids and foraminifers at the base of the Gan Formation in the Kutal 2 section comprise Climacammina sp., Endothyra sp., Eotuberitina reitlingerae, Geinitzina aff. spandeli, Globivalvulina sp., Hemigordiellina sp., Pachyphloia ovata, Polytaxis sp., Postendothyra sp., Pseudodoliolina? sp., and Schubertetella ex gr. melonica; at the top they include Bidagmarita sp., Codonofusiella sp., Globivalvulina sp., Midiella sp., Multidiscus? sp., Neogeinitzina sp., Pachyphloia ovata, Rectostipulina quadrata, and Reichelina pulchra. We also found conodonts …. In the Kubergandy section, conodonts at the base … comprise Mesogondolella pingxiangensis, M. siciliensis, and transitional forms Sweeetognathus guizhouensis-S. subsymmetricus; at the top Hindeodus wordensis and M. altudaensis. In the Kutal 2 section conodonts at the base … comprise M. lamberti, M. siciliensis, and transitional forms S. guizhouensis – S. subsymmetricus; at the top … : H. wordensis, M. altudaensis, M. omanensis, M. cf. postserrata, and Pseudohindeodus ramovsi.” (Angiolini et al., 2015)

The facies of the Gan Gr indicate deposition and resedimentation along a slope, but in a more distal setting than that recorded by the underlying Kubergandin Fm, and a remarkable increase in volcanic activity. As in the Kubergandin Fm, the metazoan fragments, the fusulinids and the conodonts are highly abraded and fragmented, indicating considerable transport. Also the ostracods are mainly deep-water species (S. Crasquin, pers. comm.). The maximum depth is recorded by the radiolarian and sponge wackestones intercalated to cherts and colored volcaniclastic ashes, just below the conglomerates. 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.