Later sediments of the desert basins of central Mongolia. American Museum novitates ; no.77
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Date
1923
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New York City : The American Museum of Natural History
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Abstract
"It appears from this listing of the formational units distinguished by locality and structural features that there are at least four formations of locality significance of late Mesozoic age, presumably Upper and Lower Cretaceous, and four formations belonging to the Upper Tertiary, including beds of Miocene and Pliocene age. The early Tertiary is much less fully represented, or else is represented by formations not yet furnishing adequate fossil criteria. Only the Irdin Manha formation, in the Iren Dabasu region, and the beds of Shara Murun, one of the basins on the Uliasutai Trail, may have been placed earlier than the Miocene on fossil evidence. It may be, of course, that the lower barren beds of the Hsanda Gol are pre-Miocene also; but for this there is no direct evidence. This is an additional reason for grouping these scattered formational units into definite series. There are no used or published terms that have suitable limitations for this purpose. Obruchev's 'Gobi Series' was used by him to include all sorts of later sedimentary beds, without age distinction. Von Richthofen's term 'Khan-Khai Beds' has been used in the same way for all of the later sediments, without more intimate discrimination... the following terms are proposed for the smaller groups: 1. The Tsagan Nor Series (Upper Tertiary). 2. An unnamed series (Lower Tertiary). 3. The Shamo Series (Upper Mesozoic). The Tsagan Nor Series is intended to include formations of Pliocene and Miocene age, or the Upper Tertiary. To it belong the units already described as the Hung Kureh, Hsanda Gol, Ardyn Obo and Houldjin formations. Another series ought to include the Lower Tertiary, or the pre-Miocene Tertiary. Thus far, the only formations classified in this series are the Irdin Manha and the beds of another basin, the Shara Murun, farther west... The Shamo Series is pre-Tertiary. It is intended to include the Cretaceous beds overlying the great unconformity above the folded and eroded Jurassic. The units distinguished in the field are the Iren Dabasu, Ondai Sair, Ashile, and Dja-doch-ta formations... it appears that no less than 6000 to 8000 feet of later sedimentary strata are accounted for in the complex series of later sediments lying above the great post-Jurassic unconformity in the Gobi region of Mongolia. All of the formations named are distinguished by characteristic fossil content... All are of strictly continental type. No evidence of marine invasion was found anywhere..."--P. 13-16.
Description
16 p. : map ; 24 cm.
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