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Drag marks in the Upper Precambrian Winnall Beds of central Australia were made by semibuoyant flexible objects at least 15 centimeters long, which presumably were algae. This find extends the range of such marks into the Precambrian era and supplements the discovery of microflora in the same sedimentary sequence.
Categories: Publication; Types: Citation; Tags: Science
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The Apollo 16 landing site in the lunar central highlands encompassed terra plains and adjacent mountainous areas of hilly and furrowed terra. These morphologic units, representing important terrane types in the lunar highlands, had been interpreted as volcanic on most premission geologic maps. However, it became apparent during the mission that there are indeed few or no volcanic rocks or landforms at the site but rather that the area is underlain by a wide variety of impact-generated breccias.
Categories: Publication; Types: Citation
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At orbit insertion on 14 November 1971 the Martian surface was largely obscured by a dust haze with an extinction optical depth that ranged from near unity in the south polar region to probably greater than 2 over most of the planet. The only features clearly visible were the south polar cap, one dark spot in Nix Olympica, and three dark spots in the Tharsis region. During the third week the atmosphere began to clear and surface visibility improved, but contrasts remained a fraction of their normal value. Each of the dark spots that apparently protrude through most of the dust-filled atmosphere has a crater or crater complex in its center. The craters are rimless and have featureless floors that, in the crater complexes,...
Categories: Publication; Types: Citation; Tags: Science
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Lonar Crater is a young meteorite impact crater emplaced in Deccan basalt. Data from 5 drillholes, a gravity network, and field mapping are used to reconstruct its original dimensions, delineate the nature of the pre-impact target rocks, and interpret the emplacement mode of the ejecta. Our estimates of the pre-erosion dimensions are: average diameter of 1710 m; average rim height of 40 m (30-35 m of rim rock uplift, 5-10 m of ejected debris); depth of 230-245 m (from rim crest to crater floor). The crater's circularity index is 0.9 and is unlikely to have been lower in the past. There are minor irregularities in the original crater floor (present sediment-breccia boundary) possibly due to incipient rebound effects....
Categories: Publication; Types: Citation; Tags: The Moon and the Planets
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Discovery of shock-metamorphosed material establishes the impact origin of Lonar Crater. Coarse breccia with shatter coning and microbreccia with moderately shocked fragments containing maskelynite were found in drill holes through the crater floor. Trenches on the rim yield strongly shocked fragments in which plagioclase has melted and vesiculated, and bombs and spherules of homogeneous rock melt. As the only known terrestrial impact crater in basalt, Lonar Crater provides unique opportunities for comparison with lunar craters. In particular, microbreccias and glass spherules from Lonar Crater have close analogs among the Apollo specimens.
Categories: Publication; Types: Citation; Tags: Science
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E-4 is one of eight Geodynamics transects that cross the Atlantic margin of North America between Georgia and Newfoundland. Five of the transects are in the United States and three are in Canada. Transect E-4, which is 110 km wide and more than 1,100 km long, extends from the stable North American craton just west of the Grenville front near Lexington, Kentucky southeastward across Cape Fear, North Carolina, on the Atlantic coast to oceanic crust east of the Blake Spur magnetic anomaly. Like all of the other U.S. Atlantic coast transects, it crosses Cambrian and Jurassic continental margins of North America as well as the Appalachian orogen. The display, based upon published information, portrays the geology, tectonic...
Categories: Publication; Types: Citation
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The large Martian channels, especially Kasei, Ares, Tiu, Simud, and Mangala Valles, show morphologic features strikingly similar to those of the Channeled Scabland of eastern Washington, produced by the catastrophic breakout floods of Pleistocene Lake Missoula. Features in the overall pattern include the great size, regional anastomosis, and low sinuosity of the channels. Erosional features are streamlined hills, longitudinal grooves, inner channel cataracts, scour upstream of flow obstacles, and perhaps marginal cataracts and butte and basin topography. Depositional features are bar complexes in expanding reaches and perhaps pendant bars and alcove bars. Scabland erosion takes place in exceedingly deep, swift floodwater...
Categories: Publication; Types: Citation; Tags: Icarus
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Mariner 9 photographs of Phobos and Deimos have yielded new information about the orbits, rotation periods, sizes, shapes, and surface characteristics of the satellites. Both satellites appear to be in synchronous rotation. They are irregular, heavily cratered bodies whose shapes appear to have been determined largely by impact fragmentation and spalling. The surfaces of both satellites have crater densities close to saturation and nearly identical, very low albedos. Lower limits on the tensile and yield strengths are estimated, and it is concluded that both satellites may consist of well-consolidated, though possibly highly fractured material. ?? 1972.
Categories: Publication; Types: Citation; Tags: Icarus
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The first 4 months of Mariner 9 photography of the south polar region are discussed. Three major geological units have been recognized, separated by erosional unconformities. From oldest to youngest they are: cratered terrain, pitted plains, and laminated terrain. The latter unit is unique in occurrence to the polar region, volatiles are probably involved in its origin, and may still be present within the laminated terrain as layered ice. The residual south polar cap has been observed to survive the disappearance of the thin annual CO2 frost deposit and to last virtually unchanged in outline through the southern summer. That exposed deposit is inferred to be composed of water-ice. The residual cap appears to lie...
Categories: Publication; Types: Citation; Tags: Icarus
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[No abstract available]
Categories: Publication; Types: Citation; Tags: Science
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Small amounts of stishovite were separated from specimens of explosively shocked sandstones, novaculite, and single-crystal quartz. Estimated peak pressures for the syntheses ranged from 150 to 280 kilobars, and shock temperatures were from 150?? to 900??C. No coesite was detected in any sample. It is suggested that quartz can invert during shock to a short-range-order phase, with sixfold coordination. A small portion of this phase may develop the long-range order of stishovite, and, during the more protracted decrease of the pressure pulse through the stability field of coesite accompanying meteorite crater formation, a portion may invert to coesite.
Categories: Publication; Types: Citation; Tags: Science
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Field studies have thrown new light on a unique prehistoric encounter of a cosmic body with the earth.
Categories: Publication; Types: Citation; Tags: Science
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The purpose of the infrared (IR) and radar study of the Apollo data is to establish lunar surface conditions in the vicinity of the orbital tracks of the Apollo command modules during the J-series missions. Correlations and comparisons between the Earth-based radar observations, IR observations, and other data will be plotted on photomaps produced from the mapping and panoramic cameras. In addition, the Apollo photography will be used to improve the classifications of the anomalous IR and radar features. The three sets of Earth-based data have already been obtained. The IR (11 μm) data (ref. 29-112) were obtained during a total lunar eclipse. More than a thousand thermally anomalous regions with an unusually high...
Categories: Publication; Types: Citation
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This group of some 15 Late Quaternary explosion craters are typical maars, with rims of bedded pyroclastics. In all but the largest crater, the deposits consist entirely of clasts of country rock (granodiorite and Eocene volcanics). The maars were formed by phreatomagmatic explosions, possibly caused by groundwater originating from a major river. The deposits of the largest maar contain up to 20% juvenile fragments of two types. Tephrite clasts have phenocrysts of phlogopite, clinopyroxene, olivine and anorthoclase; the presence of hauyne as a groundmass phase is notable. Cumulate blocks of phlogopite-clinopyroxene rock also occur. The maar field is part of a distinct province of Quaternary alkaline volcanism, related...
Categories: Publication; Types: Citation; Tags: Bulletin Volcanologique