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The Allende Meteorite Reference Sample
Eugene Jarosewich, Roy S. Clarke, Jr. and Julie N. Barrows, editors
49 pages, 32 tables
1987 (Date of Issue: 24 February 1987)
Number 27, Smithsonian Contributions to the Earth Sciences
DOI: 10.5479/si.00810274.27.1
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Abstract

A reference material for comparative analytical studies and standardization was prepared from fresh, clean specimen material from the Allende, Mexico, Type CV3 carbonaceous chondrite fall of 8 February 1969. Fragments weighing 4 kg were powdered, homogenized, and split into 1 g and 5 g subsamples. Analytical results for a total of 74 elements were provided by 24 analysts or groups of analysts. A variety of techniques were used, and many elements were determined by more than one technique. Reports from contributors of data outline their procedures and give their results in detail. Sample homogeneity has been evaluated in terms of this body of data, and " recommended values" are suggested for 43 elements.


The Allende, Mexico, Meteorite Shower
Roy S. Clarke, Jr., Eugene Jarosewich, Brian Mason, Joseph Nelen, Manuel Gomez and Jack R. Hyde
53 pages, 36 figures, 6 tables
1971 (Date of Issue: 17 February 1971)
Number 5, Smithsonian Contributions to the Earth Sciences
DOI: 10.5479/si.00810274.5.1
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The Allende meteorite fell near Parral, Chihuahua, Mexico, between 0105 and 0110 Central Standard Time on Saturday, 8 February 1969. The fireball approached from the south-southwest (S37?W), and broke up in the atmosphere, producing thousands of fusion-crusted meteoritic stones. The smallest individuals were recovered 4 km east of Rancho Polanco (26?432 N, 105?282 W), and the largest near, Rancho El Cairo (27?062 N, 105?122 W), some 50 km to the north-northeast across the Parral-Jimin?z highway. Specimen size increases generally as one moves to the north-northeast within the field, and many large specimens (5-15 kg) were recovered in and around the area enclosed by Pueblito de Allende, San Juan, Rancho Blanco, and Santa Ana. At least two tons of meteoritic stones have been recovered, with crusted individuals ranging in weight from approximately 1 g to one individual of 110 kg. Specimen shapes are mainly fragmental, due to one major disruption of the parent body, followed by minor subsequent fragmentation. Individual stones have primary and secondary fusion crust, and some fresh fracture surfaces due to late-stage breaking. A small percentage of stones shows strong ablative shaping due to oriented flight. The elongate strewnfield possibly exceeds 300 km2 in area, making Allende the largest recorded stony meteorite fall both in its areal extent and in total weight of recovered meteorites. Allende fell near the sites of find of two major iron meteorites, Morito and Chupaderos.

Chemical and mineralogical compositions establish that Allende is a Type III carbonaceous chondrite. Three distinct components can be recognized: finegrained black matrix (<"60%), chondrules (<"30%), and irregular white aggregates (<"10%). The matrix consists almost entirely of iron-rich olivine (average 50% Fe2SiO4), with minor amounts of troilite, pentlandite, and taenite, rendered opaque by dispersed carbonaceous material. Most of the chondrules are magnesium-rich, and consist of olivine (average 9% Fe2SiO4) with minor amounts of clinoenstatite and some glass; a few chondrules are rich in calcium and aluminum, and are made up largely of anorthite, gehlenite, augite, and spinel. The irregular aggregates are also rich in calcium and aluminum, and contain anorthite, gehlenite, augite, spinel, nepheline, grossular, and sodalite (the last two minerals have not previously been recorded from meteorites). Complete chemical analyses have been made of the bulk meteorite, a dark inclusion, the matrix, a chondrule concentrate, two individual chondrules, and a single aggregate.


An Atlas of Volcanic Ash
Grant Heiken
101 pages, 15 figures, 33 plates, 3 tables
1974 (Date of Issue: 12 April 1974)
Number 12, Smithsonian Contributions to the Earth Sciences
DOI: 10.5479/si.00810274.12.1
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Volcanic ash samples collected from a variety of recent eruptions were studied, using petrography, chemical analyses, and scanning electron microscopy to characterize each ash type and to relate ash morphology to magma composition and eruption type.

The ashes are best placed into two broad genetic categories: magmatic and hydrovolcanic (phreatomagmatic). Ashes from magmatic eruptions are formed when expanding gases in the magma form a froth that loses its coherence as it approaches the ground surface. During hydrovolcanic eruptions, the magma is chilled on contact with ground or surface waters, resulting in violent steam eruptions. Within these two genetic categories, ashes from different magma types can be characterized. The "pigeon hole" classification used here is for convenience; there are eruptions which are driven by both phreatic and magmatic gases.

The morphology of ash particles from magmatic eruptions of high-viscosity magma is governed primarily by vesicle density and shape. The vitric ash particles are generally angular, vesicular pumiceous fragments, or thin vesicle wall fragments. The morphology of lithic fragments is dependent on the texture and mechanical properties of the rock units broken up during the eruption; most of the samples studied contain equant, angular to subrounded lithic fragments.

Ash particles from eruptions of low-viscosity magmas are mostly droplets; droplet shape is in part controlled by surface tension, acceleration of the droplets leaving the vent, and air friction. Shapes range from perfect spheres to a variety of twisted, elongate droplets, with smooth, fluidal surfaces.

The morphology of ash particles from hydrovolcanic eruptions is controlled by stresses within the chilled magma which result in fragmentation of the glass to form small blocky or pyramidal ash particles. Vesicle density and shape play only a minor role in determining the morphology of these ash particles.


Catalog of Antarctic Meteorites, 1977-1978
Ursula B. Marvin and Brian Mason, editors
50 pages, 39 figures, 2 tables
1980 (Date of Issue: 25 July 1980)
Number 23, Smithsonian Contributions to the Earth Sciences
DOI: 10.5479/si.00810274.23.1
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During two expeditions to Antarctica (1976-77 and 1977-78), more than 300 pieces of meteorites were collected from a small area adjacent to the Allan Hills (77?S, 159?E) in Victoria Land. The 1977-78 meteorites were collected with special care to avoid contamination, and were transported in frozen condition to the Johnson Space Center, Houston, where they were processed under similar conditions to those used for the lunar samples. Eighty-five specimens of the 1977-78 collection, including most of those weighing over 100 grams, have been characterized, and are described in this monograph. Appendices provide a listing of these in numerical sequence and with significant data, and a table of chemical analyses. A summary of the published data on the ten meteorites of the 1976-77 collection is also included.


Catalog of Chemical Analyses of Rocks from the Intersection of the African, Gulf of Aden, and Red Sea Rift Systems
Paul A. Mohr
7 pages, 392 plates
1970 (Date of Issue: 16 December 1970)
Number 2, Smithsonian Contributions to the Earth Sciences
DOI: 10.5479/si.00810274.2.1
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A compilation is presented of all published chemical analyses of rocks from the Red Sea, Gulf of Aden, and Ethiopian rift junction area. The chemical analyses are accompanied by further computations, in particular weight-norm and Niggli values, and by brief mineralogical descriptions. A full bibliography and indexes are included.


Catalog of Meteorites from Victoria Land, Antarctica, 1978-1980
Ursula B. Marvin and Brian Mason, editors
97 pages, 41 figures, 13 tables
1982 (Date of Issue: 29 July 1982)
Number 24, Smithsonian Contributions to the Earth Sciences
DOI: 10.5479/si.00810274.24.1
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This is the second catalog of meteorite specimens collected on expeditions to Victoria Land led by William A. Cassidy of the University of Pittsburgh. The first (Catalog of Antarctic Meteorites, 1977-1978, U. B. Marvin and B. Mason, editors, 1980) presented the results of the 1976-1977 and 1977-1978 field seasons and described the collection and curation procedures that were adopted under a three-agency agreement between the National Science Foundation, the National Aeronautics and Space Administration, and the Smithsonian Institution for the purpose of protecting the meteorites from terrestrial contamination and allocating them for research. This catalog reports the results of the subsequent two seasons: 309 specimens were collected in 1978-1979, and 73 in 1979-1980. Classifications are given for all specimens weighing more than about 100 grams and also for some smaller pieces from each of the four field seasons. The catalog describes the field camps, the geodetic measurements of ice motion and ablation at the Allan Hills site, and the search for new concentrations. Current information about the character of the collections and new types of meteorites represented in them is outlined in brief articles describing Antarctic achondrites, carbonaceous chondrites and irons, and meteorite weathering and terrestrial residence times on the polar icecap. There is a bibliography of major articles on Antarctic meteorites. An Appendix lists all of the Victoria Land specimens classified as of December 1980, by numerical order for each locality and by meteorite class.


A Catalog of the Type Specimens in the Mineral Collection, National Museum of Natural History
Arthur Roe and John S. White, Jr.
43 pages
1976 (Date of Issue: 22 November 1976)
Number 18, Smithsonian Contributions to the Earth Sciences
DOI: 10.5479/si.00810274.18.1
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A complete list, arranged alphabetically by mineral name, of the type specimens in the mineral collection of the National Museum of Natural History. These are the actual specimens that were used in defining new mineral species. For each species the catalog number, locality, literature citation for the original description, source of specimens, and date of ccession are given.


Catalonian, Eastern Betic, and Balearic Margins: Structural Types and Geologically Recent Foundering of the Western Mediterranean Basin
Daniel Jean Stanley, Henri Got, Neil H. Kenyon, Andre; Monaco and Yehezkiel Weiler
67 pages, 33 figures
1976 (Date of Issue: 20 September 1976)
Number 20, Smithsonian Contributions to the Earth Sciences
DOI: 10.5479/si.00810274.20.1
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A high-resolution seismic study of the Catalonian, eastern Betic, and Balearic regions in the western Mediterranean emphasizes the importance of large-scale post-Miocene vertical displacement of upper Miocene and overlying unconsolidated sediment sequences. The structural configuration of the Pliocene and Quaternary series observed on subbottom profiles indicates that the geologically recent margins in these sectors have subsided along preexisting (Oligocene or older) as well as more recent (post-Miocene) tectonic trends. The post-Miocene movements are not necessarily synchronous and marked differences of structural styles are identified. The origin of the three major types of margins - abrupt, intermediate (or steplike), and progressive - is closely related to tectonic trends on land. Subsidence of the sub-Pliocene seafloor on the order of 1500 m is estimated on the basis of seismic profiles presented here.

The abrupt margin type, exemplified by the Emile Baudot and Mazzaron escarpments, occurs in areas where the edge of the basin parallels the major structures on land and where vertical displacement has developed in a relatively restricted structural zone. Intermediate margins, such as the sector southeast of the Betic chain, are localized in areas where two major structural trends converge (NE-SW and NW-SE fractures predominate), and show a steplike (growth fault) displacement landward. Progressive margins, such as off Catalonia, display a flexing of the Pliocene and Quaternary cover and are related to Pliocene foundering followed by more gentle subsidence from the upper Pliocene to the present. This type of margin occurs seaward of Tertiary basins where older (Hercynian to Miocene) tectonic trends have been reactivated. Seismic evidence indicates that submarine canyon development on these different margins is associated with the post-Miocene tectonics as well as with Quaternary eustatic events.

The Balearic Rise, a large continental block detached from the southern part of the Balearic Platform, foundered largely in post-Miocene time, but this feature has not yet completely subsided to the level of the Alg?ro-Balearic Basin plain. It is possible that large continental blocks beyond the base of slopes that are presently buried by a thick Pliocene-Quaternary cover may have a structural origin analogous to that of the Rise. Margin formation and the evolution of the western Mediterranean Basin bear some similarities to the structural development of rift zones.


Climate and Moisture Variability in a Tropical Forest: Long-term Records from Barro Colorado Island, Panamá
Donald M. Windsor
145 pages, 35 figures, 51 tables
1990 (Date of Issue: 18 December 1990)
Number 29, Smithsonian Contributions to the Earth Sciences
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Long-term environmental monitoring results are presented documenting the seasonality experienced by the lowland tropical forest on Barro Colorado Island, Panam?. A dry season has developed during each of the past 62 years, typically starting in late December or early January and ending with the first heavy rains in late April or early May. Solar radiation totals climb during dry seasons to monthly levels 50% higher than normal in the wet season. Average daily maximum temperatures increase by two degrees C while average daily minimum temperatures increase by roughly one degree C. Development of the dry season is accompanied by a doubling in average daily windspeed and a drop of ten percent in average midday relative humidity.

Annual rainfall on Barro Colorado Island averages 2612 mm (1925-1989), 90% of which falls in the months of May through November. Rainfall on Barro Colorado Island and seven other sites in the middle of the isthmus has decreased significantly over time. The only long-term rainfall records without decreasing trend come from coastal sites, suggesting that convective, but not orographic, rainfall, has diminished during the last sixty years. Further, annual rainfall appears to be influenced by factors associated with El Ni?o events. Higher than normal rainfall tends to occur the year before and lower than normal rainfall tends to occur the year of such events. Dry-season forest and clearing temperatures on Barro Colorado Island were elevated during each of the three El Ni?o events occurring in the past 16 years.

Storms that drop most of their moisture in a minute or two are common during the wet season on Barro Colorado Island. The soils of Lutz catchment are steep and clay rich. Most moisture in storage resides in the upper 10 cm. Available soil moisture is largely depleted by mid- to late dry season.

Actual evapotranspiration, calculated as the difference between rainfall and runoff and changes in storage for each of 14 years averaged 64 percent of annual rainfall. Eighty-five percent (1534 mm) of annual rainfall was returned directly to the atmosphere as vapor in the dryest of the past 16 years (1976) while only 47% (1953 mm) was returned in the wettest year (1983). Comparison of average evapotranspiration and rainfall characteristics from 18 temperate and tropical hydrological studies suggests a loose positive relationship exists between these two quantities in forested ecosystems.


Distinctive Properties of Turbiditic and Hemipelagic Mud Layers in the Algéro-Balearic Basin, Western Mediterranean Sea
Nicolaas A. Rupke and Daniel Jean Stanley
40 pages, 21 figures, 8 tables
1974 (Date of Issue: 10 September 1974)
Number 13, Smithsonian Contributions to the Earth Sciences
DOI: 10.5479/si.00810274.13.1
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Two types of mud layers alternate in dominantly muddy cores of the southern Balearic Basin. Type A muds (a few cm to over 50 cm thick), macroscopically homogeneous, occur above turbidite sands or silt laminae. Type B muds (imperceptible to about 50 cm thick), comparatively coarse due to interspersed microskeletons, occur below turbidite sands or silt laminae, and lie above type A muds. The two types are distinguished in X-radiographs on the basis of texture and sedimentary structures. Type A and B mud layers in six cores were sampled at 1 to 8 cm intervals.

Type A muds are distribution graded (upward shift of the entire size distribution to finer sizes), continuing the upward grading of the underlying sand turbidites. A granulometric change occurs at the boundary with type B muds which contain sand (to 16 percent), largely tests of forams and pteropod shells. The sand fraction of type A muds (d" 1 percent) differs from that of type B in the proportion of terrigenous constituents and in remains of pelagic forams and of pteropods. Type B muds are not graded; their grain-size distribution is uniform. They have a higher (26 to 46 percent) carbonate content than type A (16 to 39 percent). In some instances, peak-height ratios of clay minerals change across the boundary between type A and type B mud layers. It is concluded that type A muds are turbiditic (deposited instantaneously), while B muds are hemipelagic deposits.

Carbon-14 ages were determined on the carbonate sand fraction of type B layers. The ages were plotted against the total sediment thickness above the dated samples in each core. A statistically significant correlation exists. However, when the turbiditic sand and mud layers are omitted and the ages are plotted only against the combined thicknesses of the hemipelagic type B layers, an even stronger correlation is obtained. The hemipelagic rate of sedimentation during the past 16,000 years approximates 10 cm/1000 years. The frequency of turbidity current incursions at a particular core location averages 3 per 2000 years.


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