Burtsa Fm

Upper Shyok Valley: Type section is in Burtsa locality in the Racky Nala, Upper Shyok Valley, eastern Karakoram India. [Original Publication: Gergan, J. T. & Pant, P. C., 1983. Geology and stratigraphy of eastern Karakoram, Ladakh. In: Thakur, V. C. and Sharma, K. K., (eds), Geology of Indus Suture Zone of Ladakh, Wadia Institute of Himalaya Geology, Dehra Dun, India, 99-106; Juyal, K.P. 2018. Lithostratigraphy, biostratigraphy and palaeogeography of the Eastern Karakoram, India. WIHG Monograph series, No. 3. 1-126.]

Limestone. More than 1000 m of dark grey to pink limestone with shells of megalodontids. This limestone in the upper part is intercalated with 15 m light green/grey, very soft, friable calcareous shale which contains easily separable hydrozoans. Limestone, laterite and gypsum intercalations. Pink shale and massive limestone intercalations also occur in upper part.

Foraminifers (after Juyal, 2018).

(i) Aulotortus sinuosus – Auloconus permodiscoides Assembalge Zone (Zone-I): Aulotortus oscillens, Semiinvoluta sp., Ophthalmidium sp. Pseudonodosaria sp.; Quinqueloculina sp.; Thaumatoporella sp. and Megaladon spp. Ladinian to Norian age is assigned to the Assemblage Zone-I of the Burtsa Formation.

(ii) Heterastridium pachystylum –Triasina hantkeni Assemblage Zone (Zone-II): Heterastridium pachystylum, Triasina hantkeni, H. conglobatum, Heterastridium sp., Angulodiscus communis, Lituolipora termieri; Ammodiscus sp. Triasina hantkeni and Aeolisaccus sp.The fauna recorded from this part suggest Norian age to the Assemblage Zone-II of the Burtsa Formation.

(iii) Arinovidalina chialingchialingensis - Involutina liassica Assemblage Zone (Zone-III): Besides zonal fossils this assemblage zone has yielded Aulotortus (Paratrocholina) oscillens (=Trocholina (Paratrocholina) oscillens, Ophthalmidium sp., Miliopora cuvillieri, Pseudocucurbita sp., Auloconus sp., Aulotortus sp., Endothyranella sp., Ammobaculites sp., Ammodiscus sp., Angulodiscus sp., Semiinvota sp., Lenticulina sp., Megalodon spp., Palaeomiliolina montruosum, Nautiloculina oolithica, Amijiella sp., Amijiella amiji (Henson) ; Nodosaria sp., Dentalina sp., Vidalina sp., Thoumatoporella sp., Pseudopfenderina butterlina, Verneuilina sp., Brizalina sp, Bolivina sp., Lingulina sp., Textularia sp., Cornuloculina sp., Sigmoilina sp., Eggerella sp., Miliolid sp., echinoids, algae, ribbed gastropods, spong spicules and shell fragments. The fossils record shows that the sediments of Assemblage Zone- III of the Burtsa Formation were deposited during Upper Triassic (Rhaetian) to Middle Jurassic time.

(iv) Nautiloculina oolithica – Gaudryina sp. Assemblage Zone (Zone- IV) : Besides zonal fossils this assemblage zone has yielded Pseudocyclammina aff. liassica, Lenticulina sp., Nodosaria sp., ?Sigmoilina sp., Gsollbegella sp., Spiroloculina sp., Dentalina sp., ?Lingulina sp., ? Nezzazatinella sp.; Pseudocucurbita sp., ?Reophax sp., Mililoid sp., Meseteripora sp., Crissina sp., gastropod shell, echinoiderm urchin, crinoids, ostracod, oncoidal bioclast and invertebrates. The faunal record shows that in the present work large number of species suggests upper Late Jurassic age to the Assemblage Zone-IV of the Burtsa Formation of Eastern Karakoram.

(v) Trocholina valdensis - Dentalina sp. Assemblage Zone (Zone V): Besides zonal fossils, this assemblage zone has yielded Lagena sp., Textularia sp., Lenticulina sp., Gaudryina sp., Salpingoporella sp., bryozoans species Meseteripora sp., Crisisna sp. and indeterminate forams, ostracods, indeterminate algae, gastropods (sometimes ribbed) prigmatic wall and echinoids. Overall, fossils assemblage found in this zone strongly suggest Early Cretaceous (Valanginian) age for the uppermost part of the Burtsa Formation.

[Figure 1: Biostratigraphic section of Burtsa Formation (eastern Karakoram) showing the distribution of fauna (Juyal, 2018)]

Not available.