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. Bulletin of the Natural Histort Museum. Geology series. UPPER ORDOVICIAN BRACHIOPODS FROM KAZAKHSTAN 21 Quadrangle 73°22'30" to 73°30' E; 45° to 45°05' N). A summary of the Ordovician geology and lithostratigraphy of this locality is in Nikitin et al. (1980, text-figs 18, 20). The Anderken Formation consists mainly of siliciclastic rocks with a thick unit of polymict conglomerates at the base and a number of carbonate mud-mounds in the upper part (Fig. 3). The carbonate unit in the top of the sequence is a bed of nodular algal limestone about 6-10 m thick with numerous Girvanella sp., C

. Bulletin of the Natural Histort Museum. Geology series. UPPER ORDOVICIAN BRACHIOPODS FROM KAZAKHSTAN 21 Quadrangle 73°22'30" to 73°30' E; 45° to 45°05' N). A summary of the Ordovician geology and lithostratigraphy of this locality is in Nikitin et al. (1980, text-figs 18, 20). The Anderken Formation consists mainly of siliciclastic rocks with a thick unit of polymict conglomerates at the base and a number of carbonate mud-mounds in the upper part (Fig. 3). The carbonate unit in the top of the sequence is a bed of nodular algal limestone about 6-10 m thick with numerous Girvanella sp., C Stock Photo
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. Bulletin of the Natural Histort Museum. Geology series. UPPER ORDOVICIAN BRACHIOPODS FROM KAZAKHSTAN 21 Quadrangle 73°22'30" to 73°30' E; 45° to 45°05' N). A summary of the Ordovician geology and lithostratigraphy of this locality is in Nikitin et al. (1980, text-figs 18, 20). The Anderken Formation consists mainly of siliciclastic rocks with a thick unit of polymict conglomerates at the base and a number of carbonate mud-mounds in the upper part (Fig. 3). The carbonate unit in the top of the sequence is a bed of nodular algal limestone about 6-10 m thick with numerous Girvanella sp., Cyclocrinites nikitini and Mastopora reticulata and brachiopods of the Acculina—Dulankarella Associa- tion (Locality 1041a of Nikitin = Sample 390/76 of Kovalevskii). which underlies a lens of massive, micritic limestone up to 20 m thick which forming the mud-mound core. The unit thins about 200 m westward from Locality 1041 a, where it is represented by bedded and nodular limestone with the brachiopods Pionodema opima, Dulankarella larga and Mabella conferta (Sample 818). The upper- most 10 m of the underlying unit, of fine-grained sandstone intercalating with siltstone, contains a different brachiopod assem- blage with Tesikella necopina (Sample 818a), in association with abundant cystoid columnals. Locality 7. Sorbulak spring on the east side of the River Karatal In the south Betpak-Dala Desert, about 20 km west of Baigara Mountain, the Anderken Formation is well exposed on both sides of the River Karatal (Fig. 1, locality 7). Here it rests on the graded sandstones and siltstones of the Llandeilo to Lower Caradoc upper Baigara Formation (Fig. 2), or is in contact with intrusives. About 2 km south-east of the Karatal river, south of Sorbulak spring, it comprises (1) polymict conglomerates more than 50 m thick, (2) medium- to fine-grained sandstones 169-170 m thick with Ectenoglossa sorbulakensis about 10-15 m above the base of the unit (Fig. 3, Sample 1024); and (3) inte