Fenestrida and Rhabdomesida (Bryozoa) of the Otter Formation (Viséan), central Montana

Four species of Fenestrida and two species of Rhabdomesida occur in the Otter Formation (Viséan) of the Little Belt Mountains, central Montana. Four species are new: Laxifenestella snyderi n. sp., Rectifenestella concava n. sp., Streblotrypa (Streblascopora) eastoni n. sp., and Nikiforovella beltensis n. sp. Several of these species are very similar to species described in Viséan rocks of central Mongolia, northeast Russia, Kazakhstan, and Japan. Fabifenestella cf. F. vulgaris compares closely with F. vulgaris Gorjunova and Morozova from the Lower Carboniferous of northern Mongolia. Most of the bryozoans in the Otter Formation occur in the normal marine, subtidal carbonate mud and calcareous shale microfacies.

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Late Cenozoic Uguumur and Bod-Uul Volcanic Centers in Northern Mongolia: Mineralogy, Geochemistry, and Magma Sources

Minerals ◽

10.3390/min10070612 ◽

2020 ◽

Vol 10 (7) ◽

pp. 612

Author(s):

Alexander Perepelov ◽

Mikhail Kuzmin ◽

Svetlana Tsypukova ◽

Yuri Shcherbakov ◽

Sergey Dril ◽

...

Keyword(s):

Basaltic Magma ◽

Magma Source ◽

Depth Range ◽

Late Cenozoic ◽

Central Mongolia ◽

Cenozoic Volcanism ◽

Northern Mongolia ◽

Magma Sources ◽

Response To Stress ◽

Isotope Systematics

The paper presents new data on mineralogy, geochemistry, and Sr-Nd-Pb isotope systematics of Late Cenozoic eruption products of Uguumur and Bod-Uul volcanoes in the Tesiingol field of Northern Mongolia, with implications for the magma generation conditions, magma sources, and geodynamic causes of volcanism. The lavas and pyroclastics of the two volcanic centers are composed of basanite, phonotephrite, basaltic trachyandesite, and trachyandesite, which enclose spinel and garnet peridotite and garnet-bearing pyroxenite xenoliths; megacrysts of Na-sanidine, Ca-Na pyroxene, ilmenite, and almandine-grossular-pyrope garnets; and carbonate phases. The rocks are enriched in LILE and HFSE, show strongly fractioned REE spectra, and are relatively depleted in U and Th. The low contents of U and Th in Late Cenozoic volcanics from Northern and Central Mongolia represent the composition of a magma source. The presence of carbonate phases in subliquidus minerals and mantle rocks indicates that carbon-bearing fluids were important agents in metasomatism of subcontinental lithospheric mantle. The silicate-carbonate melts were apparently released from eclogitizied slabs during the Paleo-Asian and Mongol-Okhotsk subduction. The parent alkali-basaltic magma may be derived as a result from partial melting of Grt-bearing pyroxenite or eclogite-like material or carobantized peridotite. The sources of alkali-basaltic magmas from the Northern and Central Mongolia plot different isotope trends corresponding to two different provinces. The isotope signatures of megacrysts are similar to those of studied volcanic centers rocks. The P-T conditions inferred for the crystallization of pyroxene and garnet megacrysts correspond to a depth range from the Grt-Sp phase transition to the lower crust. Late Cenozoic volcanism in Northern and Central Mongolia may be a response to stress propagation and gravity instability in the mantle associated with the India-Asia collision.

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The Biostratigraphy and Lithological Features of the Lower Carboniferous Urmugteyul Formation (Orkhon Trough, Northern Mongolia)

Russian Journal of Pacific Geology ◽

10.1134/s1819714021060063 ◽

2021 ◽

Vol 15 (6) ◽

pp. 538-554

Author(s):

O. R. Minina ◽

A. V. Kurilenko ◽

I. Ariunchimeg ◽

L. N. Nebericutina ◽

T. V. Stukova

Keyword(s):

Lower Carboniferous ◽

Northern Mongolia

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Lithostratigraphy of the Kweekvlei Formation (Witteberg Group), Cape Supergroup

South African Journal of Geology ◽

10.25131/gssajg.120.3.421 ◽

2017 ◽

Vol 120 (3) ◽

pp. 421-432 ◽

Cited By ~ 2

Author(s):

C. Browning ◽

M. Reid

Keyword(s):

South Africa ◽

Transition Zone ◽

Distal Part ◽

Vascular Plant ◽

Trace Fossil ◽

Plant Debris ◽

Lower Carboniferous ◽

Fossil Assemblage ◽

Low Diversity ◽

Storm Wave

AbstractThe Lower Carboniferous, probably Tournaisian, Kweekvlei Formation is part of the Witteberg Group (Cape Supergroup) of South Africa. Together with the overlying Floriskraal Formation, it forms an upward-coarsening succession within the Lake Mentz Subgroup. Sedimentary features of the Kweekvlei Formation suggest deposition in a storm-wave dominated marine setting, within the storm-influenced, distal part of an offshore transition zone environment. This predominantly argillaceous formation preserves a low diversity trace fossil assemblage. Reworked vascular plant debris (including the problematic genus Praeramunculus sp.) and a shark spine have been reported for the Kweekvlei Formation. There are no known stratigraphic equivalents in South Africa.

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