Eugene M. Shoemaker

Moenkopi Formation (Triassic? and Triassic) in Salt Anticline Region, Colorado and Utah

The Moenkopi formation of Triassic(?) and Triassic age is widely exposed in the salt anticline region in southeastern Utah and southwestern Colorado. The distribution of the Moenkopi is that of a blanket of irregular thickness with several large holes in it, due to non-deposition and pre-Chinle erosion. Four members of contrasting lithology have been mapped in the Moenkopi in the salt anticline region. In ascending order these members are: (1) the Tenderfoot member, composed dominantly of muddy or silty poorly sorted sandstone; (2) the Ali Baba member, composed of interstratified arkosic conglomeratic sandstone and fissile siltstone; (3) the Sewemup member, composed dominantly of fissile siltstone with minor beds of conglomeratic sandstone and gypsum; and (4) the Pariott member composed of interstratified sandstone and siltstone. Part of the Tenderfoot member of the Moenkopi formation is correlative with the Hoskinnini member of the Moenkopi formation of southeastern Utah, a unit which may be either Permian or Early Triassic in age or possibly both. If equivalents of the type Moenkopi of northeastern Arizona are present in the salt anticline region they may include the upper part of the Sewemup member and part or all of the Pariott member.

Uncompahgre Front and Salt Anticline Region of Paradox Basin, Colorado and Utah

Growth of the salt anticlines of the Paradox basin, Colorado and Utah, began in Middle Pennsylvanian time shortly after deposition of the salt of the Paradox Member of the Hermosa Formation. Several of the salt structures developed adjacent to structurally high areas in pre-salt rocks that apparently were in existence prior to and during salt deposition. The northeast margin of the salt basin was bordered by the front of the ancestral Uncompahgre uplift, and arkosic debris derived from the crystalline core of the uplift was shed into the margin of the basin. A pulse of uplift on the ancestral Uncompahgre range, marked by the spread of arkosic debris into the basin, resulted in termination of conditions requisite for evaporite deposition. Initial gentle folding of the salt structures probably occurred at this time. During the remainder of Middle and Late Pennsylvanian time the basin continued to sink while receiving a cover of dominantly marine sediments, and the major salt structures in the basin increased their amplitudes by an amount that generally matched the thickness of beds deposited on their flanks. Arkosic debris derived from the Uncompahgre was shed several miles into the basin. Strong uplift on the ancestral Uncompahgre range, which occurred near the end of Pennsylvanian time, resulted in withdrawal of the seas and in the spread of arkosic debris across the basin. Thick sections of continental sediments were deposited adjacent to and between the salt structures in the deep-trough part of the basin, and by the end of Permian time the salt structures had amplitudes ranging from about 5,000 to 9,000 feet. By the end of Permian time, most of the salt may have been transferred from beneath the flanks of the salt structures into their cores, and the growth of the salt structures slowed considerably or ceased. Renewed pulses of uplift in the Uncompahgre, occurring from latest Permian through Middle Triassic time, were marked by corresponding renewed active growth o the salt structures. Uplift of the Uncompahgre largely ceased by Late Triassic time and the crystalline core of the uplift near the Uncompahgre front was buried by a veneer of Upper Triassic and younger sediments. The salt structures grew slowly during Late Triassic and Early and Middle Jurassic time, and probably most were buried in Late Jurassic time.

Uranium Mineralization in Hopi Buttes, Arizona: ABSTRACT

The Hopi Buttes dominate the landscape north of Holbrook, Arizona, rising to heights of ~1,000 ft (305 m) above the surrounding countryside. The buttes, erosional remnants of lava-filled diatremes and associated sediment-filled diatremes, are approximately 5 m.y. in age. The volcanic rocks of the diatremes are limburgite and monchiquite, which are distinguished from normal alkalic basalts of the Colorado Plateau in their extreme silica unsaturation, high water, TiO2, and P2O5. Many trace elements are also unusually abundant, most notably Zr, Ba, Nb, Ce, and U (average value of about 4 ppm U compared to an average of 1 ppm for continental basalts). Many of the diatremes are filled with local maar lake sediments believed to have been deposit d in part by rising thermal solutions. Limestone lake beds locally resemble travertine deposits and contain high concentrations of phosphate, sulfate, Ba, Sr, and As, as well as U and Se. Areas of high Se content are recognizable in the Hopi Buttes by the abundance of Astragalus patersoni (loco weed). Approximately 300 diatremes occur in the Hopi Buttes area. Of 79 studied during the past year, 35 contain lake-bed deposits with radioactivity exceeding background levels. Scintillometer traverses have shown 20 of these diatremes to have radioactivity exceeding 5 times background. An airborne gamma-ray survey shows sharp-peaked anomalies over all 20 of these diatremes. Hydrogeochemical sampling in the area also revealed anomalous concentrations of uranium in spring and well waters from the Hopi Buttes area. Uranium ore was mined during the 1950s from the Morale claim. Production records show the average grade for 186 tons of ore was 0.15% U3O8. Extensive drilling in this diatreme in October 1979 revealed intervals within limestone and siltstone maar lake sediment up to 20 ft (6 m) thick and 500 × 300 ft (152 × 91 m) in area containing an average of 0.015% U3O8. The potential for uranium in the Hopi Buttes is for low grade deposits within 50 ft (15 m) of the surface, some of which may contain on the order of 100 tens of U3O8 per diatreme. End_of_Article - Last_Page 802------------

Manned Spaceflight--A Challenge to Geologists and Geophysicists: ABSTRACT

The advent of man in space opens new opportunities in the disciplines traditionally concerned with the surface and interior of the Earth. The synoptic view of the Earths surface from an orbiting manned spacecraft affords a new avenue for investigation of regional geology. Considerable research and imagination are required to exploit it. The techniques developed may be expected to have important applications later in the exploration of Mars. Men landing on the Moon will be able to apply the methods and instruments of geophysics and classical geology that are already well developed in the study of the Earth. Constraints of weight and time in spaceflight operations, however, require that considerable effort be spent in adapting these methods and instruments for optimum use in manned lunar missions. The ultimate results of this effort will include not only new knowledge about the Moon, but also new ideas, new techniques, and light-weight sophisticated instruments that can be applied in the study of the Earth. End_of_Article - Last_Page 370------------

Interplanetary Correlation of Geologic Time: ABSTRACT

Asteroid impact has produced a significant number of medium and large craters on the earth in comparatively recent geologic time, and the rate of impact can be interpreted to have remained fairly steady for at least the last half-billion years. By extrapolation of this rate, the age of major stratigraphic units on the moon may be estimated from the number and distribution of superimposed primary impact craters. With appropriate modification, the same principle should be applicable to Mars when detailed photographs become available for photogeologic mapping. A second potential method of interplanetary correlation depends on the actual transport of impact debris from other planets to the earth, where the debris becomes incorporated in the terrestrial stratigraphic record. Some rock debris is ejected at escape velocity by asteroid impact on the Moon and probably also on Mars; part of the lunar ejecta must land on earth and a very small fraction of Martian ejecta is probably also swept up by Earth. Some tektites are probably formed by ablation of ejects thrown into orbit around the earth. It may be possible to identify the craters from which ejecta are derived at some advanced stage of lunar and planetary exploration and thus tie the age of these craters directly to the terrestrial time scale. A ray crater in the size range from Aristarchus o Tycho is the probable source of the ejecta from which the australites and associated Pleistocene tektites were formed. End_of_Article - Last_Page 130------------

Distribution of ore deposits and spectrographic analyses of some rocks and ores on the Colorado Plateau

The geographic pattern of known igneous rocks and ore deposits on the Colorado Plateau suggests a zonal arrangement of several types of ore d.e:pos:i.ts around centers of igneous activityo Spectrographic analyses of rocks and ores on the Plateau have bee!.l obtained in an effort to determine the distr:ibution of elements a:rd to examine the relationships between types of ore deposits and. between the ore deposits and igneous rockso Over 170 analyses of r ocks and ores are given in th:is reporto A preliminary study of these analyses suggests that the proportion of uranium, vanadium

Late Paleozoic and Early Mesozoic Structural History of the Uncompahgre Front

copper~ a:rrd silver in the uranium ores varies geograph:i.cally, and that the pattern of variation may be in part concentric about some of the matjor 1acco1ithic in.trusion.s. It is also suggested that the following rat:i.os of metals contained in the uranium ores are possible guides to largertha:2-average ore deposits: (l) lead/uranium greater than 1, (2) lead./ zinc greater than 10, and (3) zinc/geometric mean of cobalt and nickel