Bulletin 64—Some Ordovician corals from New Mexico, Arizona, and Texas
By D. Hill, 1959, 25 pp, 2 plates, 1 index.
The Montoya group of southern NM contains three units of deposition of different ages: (1) remnants of Winnipeg-Harding equivalents; (2) a series of strata of Red River age, the Second Value Formation, commonly divisible into the Cable Canyon Sandstone and the Upham Dolomite; and (3) two formations of Richmond age, the dark, cherty Aleman Dolomite and the lighter, largely chert-free Cutter Dolomite.
Faunas are all but nonexistent in the first of these units. The Red River and Richmond Formations contain abundant faunas, but where dolomitization is advanced, original lithic differences between the formations are reduced and sometimes obliterated, and the contact between them may be so obscured that its position can be determined only with great difficulty.
Collections made prior to the recognition of the distinction between Red River and Richmond faunas in the limestones and dolomites are all but useless; except where the lithology of the associated matrix serves as a criterion, it is impossible to determine from which division the specimens were derived. New collections are being assembled which will ultimately serve as a basis of the restudy of these faunas. This work was in its very early stages when a discovery was made which precipitated the present paper. In NM, the early Paleozoic consists of the Bliss Sandstone, of Cambrian and early Canadian age, the El Paso Limestone, which contains a series of beds extending from very early to latest Canadian time, and the Montoya Dolomite, containing the three groups of deposits noted above. Erosion has truncated both the El Paso and the Montoya Groups; the patterns vary somewhat, but in general, the El Paso shows beveling to progressively greater depths as it is traced north and west from the Franklin Mountains in western Texas. In AZ, the calcareous beds beneath the Devonian have been called the Logfellow Limestone. They crop out only in two regions, near Dos Cabezas and in the Clifton-Morenci district. It has been evident that they represent the thinning erosion remnants of the El Paso Limestone, and that in the Clifton-Morenci region the only fauna known is that of the first endoceroid zone, whereas at Dos Cabezas this fauna occurs with that of the first piloceroid zone above it.
Poorly preserved corals of the genera Palaeophyllum, Streptelasma, Nyctopora, Calapoecia, Paleofavosites, and Reuschia are described from Ordovician formations in NM, AZ, and TX. Figures of thin sections of the holotype of Columnaria thomi Hall are given. Four small collections of corals from the western US were transmitted to the author for study, in 1953, through the courtesy and interest of Drs. R. H. Flower and C. Teichert. Unfortunately, the preservation leaves much to be desired, making safe determinations difficult.
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