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At least 541 records · Page 30
All sourcesNASA NTRSDOE OSTI
NASA NTRS1969

An investigation of volcanic depressions. Part 1: Airfall and intrusive pyroclastic deposits. Part 2: Subaerial pyroclastic flows and their deposits

Pyroclastic ejecta and the deposits they form were classified in many ways, and many interpretations were given to individual terms. Some classifications are based on the modes of orgin and deposition of the ejecta; others emphasized the chemical and physical composition of the ejecta. Particle-size was used as the prime basis of subdivision, and the same size-limits were used as those employed in the classification of sediments and sedimentary rocks.

Williams, H.↗
NASA NTRS1972

Structural aspects of Imbrium sculpture, part G

Apollo 16 metric photographs taken at low to high sun angles provided the first stereographic coverage of the distinctive landforms collectively referred to as Imbrium sculpture. The sculpture consists of a series of nearly linear ridges and troughs extending radially outward for more than 1000 km from the rim of the Imbrium Basin. The origin of the ridges and troughs, whether by deposition and impact scoring by fluidized clouds of ejecta from the Imbrium Basin or by faulting and volcanism during and subsequent to basin formation, is controversial. Evidence indicative of the mode of origin of Imbrium sculpture is summarized as follows. Evidence of volcano-tectonic mode of origin is favored by: (1) wide variation in relative age of parts of the sculpture; (2) furrows without rims; (3) absence of ballistic shielding; (4) asymmetry of sculpture; (5) absence of randomly oriented clusters; and (6) association with other features of structural origin. An origin by ejecta scoring and deposition is favored by the gradational ejecta with a Fra Mauro-type texture. Features that are ambiguous as to mode or origin are furrows made of coalesced crater chains and prominent rims on furrows.

Scott, D. H.↗
NASA NTRS1973

Emplacement of the Cayley formation

Analysis of the effects of ejection of materials from large lunar craters, photogeologic evidence, remote measurements of surface chemistry and petrology of lunar samples are synthesized. Previous theories for emplacement of the Cayley are volcanic ash emplacement and emplacement as ejecta from multiringed basins. Calculations show that materials ejected beyond the continuous deposits of large lunar craters produce secondary impact craters that excavate and deposit masses of local material equal to multiples of the crater ejecta deposited at the same place. It is shown that the main influence of a large cratering event on terrain at distances greater than 50 km from large lunar craters is one of cratering and deposition of local material by secondary craters rather than deposition of ejecta from the large crater.

Oberbeck, V. R.↗
NASA NTRS1972

Provenance of Apollo 12 KREEP.

Possible origins of KREEP in Apollo 12 lunar samples are evaluated in terms of their probabilities. Preference is given to the assumption that the KREEP may be a mixture of roughly equal proportions of (1) ejecta from Copernicus, (2) ejecta from Reinhold, (3) ejecta from local highlands, and (4) material excavated from Fra Mauro deposits buried below the landing site.

Wasson, J. T.↗
NASA NTRS1974

Seismic effects from major basin formation on the Moon and Mercury

Grooved and hilly terrains are reported which occur at the antipode of major basins on the Moon (Imbrium, Orientale) and Mercury (Caloris). Order-of-magnitude calculations, for an Imbrium-size impact on the Moon, indicate P-wave-induced surface displacements of 10 m at the basin antipode that would arrive prior to secondary ejecta. Comparable surface waves are reported which would arrive subsequent to secondary ejecta impacts and would increase in magnitude as they converge at the antipode. Other seismically induced surface features include: subdued, furrowed crater walls produced by landslides and concomitant secondary impacts; emplacement and leveling of light plains units owing to seismically induced "fluidization" of slide material; knobby, pitted terrain around old basins from enhancement of seismic waves in ancient ejecta blankets; and the production and enhancement of deep-seated fractures that led to the concentration of farside lunar maria in the Apollo-Ingenii region.

Schultz, P. H.↗
NASA NTRS1975

The role of ballistic erosion and sedimentation in lunar stratigraphy

Aspects of base surge transport are considered along with questions regarding the applicability of base surge transport to lunar sedimentation, the ballistic transport of crater and basin ejecta, Copernicus crater ballistics, and the effects of ejecta impact on preexisting lunar ground. An ejecta emplacement model is discussed and attention is given to the structure of the surface of continuous deposits of craters and basins, the thickness of crater and basin deposits, and the characteristics of impact melts.

Oberbeck, V. R.↗
NASA NTRS1975

Geologic setting of Boulder 1, Station 2, Apollo 17 landing site

Boulder 1 at Station 2 is one of three boulders sampled by Apollo 17 at the base of the South Massif, which rises 2.3 km above the floor of a linear valley interpreted as a graben formed by deformation related to the southern Serenitatis impact. The boulders probably rolled from the upper part of the massif after emplacement of the light mantle. The massif exposures are suggested to represent the upper part of thick ejecta deposited by the southern Serenitatis impact near the rim of the transient cavity. The ring structure of the southern Serenitatis basin and the radial grabens that give the massifs definition were imposed on this ejecta at a slightly later stage in the basin-forming process. There is no clear-cut compositional, textural, or photogeological evidence that Imbrium ejecta was collected at the Apollo 17 site.

Wolfe, E. W.↗
NASA NTRS1976

Candidate areas for in situ ancient lunar materials

Results of high-speed impact cratering in quartz sand targets are reported. Dissection of the ejecta plumes of the craters revealed that they are relatively thin conical sheets. Further dissection showed the relationship between individual particle trajectories and the ejecta plume. A model of cratering, based on the experiments, was used to explain the inverted stratigraphy previously described in laboratory impact craters and in meteorite craters. Mantling of secondary craters in peripheral parts of the continuous deposits of Tycho Crater and in the downrange parts of certain Tycho secondary crater clusters is accounted for by the model. Model results indicate extensive mixing by secondary cratering when basin ejecta is emplaced. The study reveals certain areas on the lunar uplands that have been relatively uncratered by basin secondaries and unmantled by secondary crater debris surges and that may represent in situ ancient lunar materials.

Oberbeck, V. R.↗
NASA NTRS1977

Pre-Imbrian history of the Fra Mauro region and Apollo 14 sample provenance

Pre-Imbrian impact structures in a large area surrounding the Apollo 14 site were identified in a study of the pre-Imbrian history of the Fra Mauro region. Calculations suggest that a total ejecta thickness of over 1700 m could have accumulated during Phase I (time prior to the Imbrium event) in the area of the ridge on which the Cone crater later formed. The majority (53%) of the ejecta at the site just prior to the Imbrium event was contributed by the numerous large Phase IB and IC craters in the vicinity and not by the lunar basins. Evidence exists for extensive pre-Imbrian volcanic activity in the Fra Mauro region. Early KREEP volcanic deposits may have existed in the target sites of many Phase IB and IC craters and would have been incorporated into their ejecta.

Hawke, B. R.↗
NASA NTRS1977

Geology of the Imbrium Basin Apennine Mountains and relation to the Apollo 15 landing site

Detailed mapping of the Imbrium Basin Apennine Mountains has emphasized several important factors in the geologic evolution of this region. Pre-Imbrian topography was composed of two types of landforms: (1) the nearby Serenitatis, South Imbrium, Aestuum, and Vaporum basins which produced widely spaced regional lows and a sequence of basin deposits; (2) pre-Imbrian craters that reworked existing basin deposits and produced local topographic lows. The sequence of events during the Imbrium impact can be summarized as follows: intensive structural uplift along the Apennine Front occurred prior to the emplacement of ballistic ejecta. Ejecta became more discontinuous toward the backslope and produced radial texture by sedimentary erosional and depositional processes. Post-ejecta-emplacement downfaulting exposed pre-Imbrian deposits along the front and caused severe seismic disturbances that reworked many of the previous units and accentuated pre-basin structures. Tectonic mapping and orbital geophysical data support the idea that little structural modification has occurred in the Apennines since their formation 3.9 b.y. ago.

Spudis, P.↗
NASA NTRS1977

Apollo 17 ropy glasses

Ropy glasses are a major soil component in the Apollo 17 gray soils 74240 and 74260. These particles form a distinct morphological type characterized by a wide range of dynamic shapes with a diagnostic sorted and welded fine-grained debris coating. Apollo 17 ropy glasses show abundant evidence for shock. Shocked lithic and mineral inclusions, lack of any igneous textures, and lechatelierite, all indicate an impact origin. A striking similarity is observed between the lunar ropy glasses and the glass impact bombs (Flaedle) of the Ries Crater in Germany. A highland basaltic composition was observed for the Apollo 17 ropy glasses in contrast to the KREEP composition of ropy glasses from the Apollo 12 and Apollo 14 landing sites. Other workers have presented convincing evidence that ejecta from Tycho reached the Taurus-Littrow Valley, and these ropy glasses may represent Tycho ejecta. However, the close stratigraphic association of the ropy glasses with the greater than 3.5 b.y. old orange glass suggests the ropy glasses may be too old to be Tycho ejecta, which should be only about 100 m.y. old. If this is the case, the ropy glasses represent impact glasses from a very old impact in an unknown highlands source area.

Fruland, R. M.↗
NASA NTRS1975

Exposure histories of Bench Crater rocks

A description is presented of the results of mass spectrometric analyses of the noble gases krypton and xenon, in eight Apollo 12 basaltic rocks. The significance of the results is evaluated. It is concluded that the Bench Crater rocks are not what they appear to be in their field relationships. They are not fragments ejected from bedrock by the Bench impact. Most, if not all, have had a previous history of regolith residence prior to the Bench impact. In retrospect, sampling of fresh ejecta from lunar craters during the Apollo missions turned out to be surprisingly difficult. Sampling was successful for Cone and North Ray craters where large boulders were available, but fresh South Ray ejecta was surprisingly elusive. The reported investigation shows that fresh ejecta was not obtained from Bench, and moreover, that the concept of 'radial sampling', in which the rocks sampled from a crater rim are supposed to represent the deepest material excavated, fails very badly for Bench.

Burnett, D. S.↗
NASA NTRS1975

Seismically induced modification of lunar surface features

The formation of large impact craters and basins produced not only large volumes of ejecta but also catastrophic seismic waves. Theoretical models, extrapolation of terrestrial explosion data, and extrapolation of lunar impact data suggest surface displacements of 1-10 m at four crater radii from a Copernicus-size impact (4 x 10 to the 30th power ergs). Independent estimates of impact-generated stresses indicate that regions within 4 crater radii of an impact will receive shock waves with pressures exceeding 1 kbar. Greater areas also may receive shock effects as elastic waves following deep ray paths transform into shock waves near the surface. Additional seismic energy will be generated by impacts from secondary ejecta. The resulting large and long-lasting surface movement may contribute to the subdued appearance of the continuous ejecta blanket and secondary craters around large impact craters and to the degradation of small craters outside these zones.

Schultz, P. H.↗
NASA NTRS1981

Solar radio bursts of spectral type II, coronal shocks, and optical coronal transients

An examination is presented of the association of solar radio bursts of spectral type II and coronal shocks with solar flare ejecta observed in H-alpha, the green coronal line, and white-light coronagraphs. It is suggested that fast-moving optical coronal transients should for the most part be identified with piston-type phenomena well behind the outward-traveling shock waves that generate type II radio bursts. A general model is presented which relates type II radio bursts and coronal shocks to optically observed ejecta and consists of three main velocity regimes: (1) a quasi-hemispherical shock wave moving outward from the flare at speeds of 1000-2000 km/sec and Alfven Mach number of about 1.5; (2) the velocity of the piston driving the shock, on the order of 0.8 that of the shock; and (3) the regime of the slower-moving H-alpha ejecta, with velocities of 300-500 km/sec.

Maxwell, A.↗
NASA NTRS1980

Possible rim crest deposits in cores 12027 and 15008 - Some interpretations and problems for future research

Light colored coarse grained soils in the upper parts of cores 12027 and 15008 have a chaotic fabric and abundant bedrock-derived rock fragments. They overlie dark colored, fine grained soils with horizontal fabric and abundant regolith-derived rock fragments. The light colored soils are interpreted to be rim crest deposits associated with the craters seen in the lunar surface sampling photographs. The coarse size, poor sorting and chaotic fabric are believed to have originated by the violent mixing processes which are expected with ejecta deposition. The increase in bedrock-derived particles within the light colored soil can be explained by ejecta from craters that penetrated through or deep into the regolith. The dark soils are believed to predate the craters. Distribution of rock fragments in the material interpreted as rim crest ejecta does not fit a simple model of overturned stratigraphy.

Nagle, J. S.↗
NASA NTRS1981

The evolution of the lunar Nectaris multiring basin

The paper begins by discussing the pre-Nectaris crust, the formation of the basin, its age and its geophysics. The pre-mare basalt deposits are categorized into smooth plains deposits, cratered and patterned plains, knobby terrain, and massifs, and the structure, chemical composition, and probable origin of these are discussed. Alternative scenarios for the formation of the plains are that they consist of impact melt ejecta, ejecta overlying smoothed-out preexisting topographic material, or ejecta overlying extrusive deposits. The mare deposits are assessed in terms of their composition, basalt ages and thickness, and eruption styles. A probable age of 3.6 billion years for the basalts is given. The tectonics of mare ridges and fractures and floor-fractured craters are gone into. Post-mare cratering is also discussed. It is concluded that the morphology of multiring basins is strongly dependent on lithosphere thickness.

Whitford-Stark, J. L.↗
NASA NTRS1982

Depositional history of core 15008/7 - Some implications regarding slope processes

Structures and associated vertical changes in lithology of core 15008/7 are discussed with a view to providing data for interpretation of regolith-forming and accumulation processes that can take place on a continuous slope upon an impact-dominated surface. The light-colored soil between 49.1 and 55.6 cm in core 15007 is rich in clasts which contain abundant green glass and appears to be ejecta from downslope. The dark massive soils between 17.5 and 49.1 cm contain many crater bottom structures and crater fill, but apparently no rim-crest or proximal ejecta. The higher parts of the crater deposits appear to be removed by erosion, whereas the crater fill is preferentially preserved. Such material may be typical of slope deposits. The light-colored soil with contorted, friable clasts, between 0 and 17.5, appears to be ejecta from the crater seen in the sampling photographs.

Nagle, J. S.↗
NASA NTRS1981

Apollo 17 impact melts and their relation to the Serenitatis basin

Regional geologic relations are seen as suggesting that the distribution of highland landforms is not consistent with their derivation from a single impact event but is consistent with multiple events involving both distant basins and smaller, local craters. Thus the highland samples collected at the Apollo 17 landing site may not consist solely of Serenitatis basin ejecta but probably include both exotic ejecta and reworked local material. On the basis of these observations, it is suggested that the Apollo 17 highland melt breccias are not all derived from the Serenitatis basin impact; that is, the aphanitic melt rocks may be either other basin or local crater ejecta. It is thought that if the melt rocks collected at Apollo 17 are all derived from the same impact, the significant chemical and petrographic differences between the rocks may require modification of current models for impact melt petrogenesis.

Spudis, P. D.↗