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Smithsonian Contributions to the Earth Sciences

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Partially Melted Kyanite Eclogite from Roberts Victor Mine, South Africa
George Switzer and William G. Melson
9 pages, 5 figures, 6 tables
1969 (Date of Issue: 15 April 1969)
Number 1, Smithsonian Contributions to the Earth Sciences
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Abstract

Three specimens have been studied of the rare kyanite eclogite nodules in kimberlite from the Roberts Victor mine, South Africa. All are essentially the same with the primary assemblage: kyanite, omphacite, garnet, diamond (in one sample), chrome diopside, and rutile. There is also present a fine-grained secondary assemblage that appears in two forms: (1) primary omphacite altered to a mixture of plagioclase, clinopyroxene, and possibly glass; and (2) thin layers along omphacite, kyanite, and garnet grain boundaries. These layers have a clear-cut igneous texture and consist of plagioclase microlites with glass or devitrified glass, or plagioclase microlites and subhedral augite, with or without glass. Hornblende, spinel, and calcite are accessories, and analcite fills vesicles. Corundum and mullite occur at the margins of kyanite grains.

The glass in the secondary assemblage has a composition roughly equivalent to what one might expect if it was derived by incongruent melting of omphacite, followed by partial crystallization. Omphacite at one atmosphere pressure begins to melt at about 1030° C and melting is complete at about 1260° C. At 30 kilobars (O'Hara and Yoder, 1967) melting begins at about 1570° C and is complete at 1600° C. Thus, sudden pressure release of an eclogite at high temperature could cause partial melting of omphacite.

These kyanite eclogites clearly contained an interstitial melt that has been rapidly cooled. Evidence points to this melt having been generated mainly by partial melting of primary omphacite rather than by introduction of an externally derived melt. The partial melting may have occurred in response to one of the following three processes or some combination of them:

  • Increase in temperature at constant pressure.
  • Introduction of water into the eclogite at constant temperature and constant total pressure.
  • Release of pressure at constant temperature.

The third process seems to offer the most reasonable explanation for the partial melting.


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
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Abstract

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.


Minor and Trace Elements in Meteoritic Minerals
Brian Mason and A. L. Graham
17 pages, 1 figure, 17 tables
1970 (Date of Issue: 17 September 1970)
Number 3, Smithsonian Contributions to the Earth Sciences
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Abstract

Nickel-iron, troilite, olivine, pyroxenes, plagioclase, chromite, and phosphate minerals (chlorapatite and/or merrillite) have been separated from a number of meteorites (Modoc, St. Severin, Winona, Haraiya, Marjalahti, Springwater, Johnstown, Mt. Egerton, Soroti) and analyzed for minor and trace elements with the spark-source mass spectrometer. The elements Ni, Co, Ge, As, Ru, Rh, Pd, Sn, Sb, W, Re, Os, Ir, Pt, and Au are concentrated in nickel-iron: Se and Ag in troilite; Th, U, and the lanthanides in the phosphate minerals and in diopside; Eu, Sr, Ba, Rb, and Cs in plagioclase. Molybdenum and tellurium are concentrated in nickel-iron and troilite. The elements Ti, Sc, V, Cu, Zn, Mn, and Ga are distributed over several coexisting minerals.


Volcanic Eruption at Metis Shoal, Tonga, 1967-1968: Description and Petrology
William G. Melson, Eugene Jarosewich and Charles A. Lundquist
18 pages, 13 figures, 3 tables
1970 (Date of Issue: 16 October 1970)
Number 4, Smithsonian Contributions to the Earth Sciences
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Abstract

The 1967-1968 eruption of Metis Shoal, Tonga, was evidentially similar to the frequent shallow submarine eruptions of the inner island arc of Tonga. The eruption began about 10 December 1967, and an island eventually emerged; by 19 February 1968, the island had been eroded to beneath wave base. The eruptions were characterized by explosions of steam and ash which hurled bombs a few to several hundred feet into the air. The rocks ejected are pumiceous dacites which, for their silica content, have unusually low alkali contents and rare earth-element contents. The chemical characteristics of the dacite are hard to account for by partial melting of an ocean-ridge basalt parent. The peculiar properties of the dacite appear to characterize other Tongan lavas and support the idea that Tonga is part of a distinct petrographic province.


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
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Abstract

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-Jiminéz 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.


Distribution of Echinarachnius parma (Lamarck) and Associated Fauna on Sable Island Bank, Southeast Canada
Daniel J. Stanley and Noel P. James
24 pages, 8 figures, 6 plates, 1 table
1971 (Date of Issue: 27 April 1971)
Number 6, Smithsonian Contributions to the Earth Sciences
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Abstract

A combined bottom photographic and sampling survey of Sable Island Bank southeast of Nova Scotia, Canada, reveals locally high densities (to 180 individual/m2) of the northern sand dollar Echinarachnius parma. Populations of this form are closely related to texture of the sea floor and generally concentrated on moderately sorted fine to medium sand surfaces. Topography and current regime are also correlatable factors; depth, time, salinity, and temperature apparently are not. Sand dollars are second in importance, after current activity, in reworking surficial sediments, and these organisms modify at least a third of the total Bank surface in the study area. Bioturbation is particularly intense in the sector north of Sable Island. Associated epifauna and infauna populations occur in two east-west trending areas on the Bank north and south of Sable Island. Absence of conspicuous fauna, save E. parma, in an east-west zone along the crest of the Bank and near Sable Island results from extremely strong current activity concentrated in this region.


Geology of the Lincoln Area, Lewis and Clark County, Montana
William G. Melson
29 pages, 13 figures, 8 tables
1971 (Date of Issue: 15 October 1971)
Number 7, Smithsonian Contributions to the Earth Sciences
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Abstract

The Lincoln area (townships 13 and 14 N, ranges 7 and 8 W, about thirty miles northwest of Helena, Montana) is underlain by Pre-Cambrian Belt sedimentary rocks intruded by late Cretaceous (?) granitic stocks with concomitant widespread contact metamorphism and mineralization. The granitic stocks are probably related to the Boulder batholith. The pre-intrusion structure is characterized by high angle faults and broad open folds of Cretaceous age (Laramide). Oligocene (?) volcanic rocks were extruded on an eroded surface of the Belt rocks and granitic stocks. A second period of mineralization followed extrusion of the volcanic rocks.

Fracture cleavage which dips consistently to the southwest as well as the overall structure show that a southeast plunging syncline which marks the north end of the Boulder batholith continues into the Lincoln area. The syncline extends at least twenty miles north of the batholith and dominates the structure over an area of about 350 square miles.

About forty square miles of middle Tertiary volcanic rocks are composed of a lower series of andesitic to latitic flows and an upper series of rhyolitic welded ash flows. The features of the welded ash flows suggest that they were deposited in part by a vesiculating mass of rhyolitic magma (pumice froth flows). The volcanic rocks are presumably about the same age as the Lowland Creek volcanics of the Butte area.

The area and the region several miles to the north are about the northern limit of Boulder batholith activity, Tertiary volcanism, and associated mineral deposits. The superposition of these two periods of igneous activity and their gross similarities imply that they are genetically related.

Gold and silver have been produced from epithermal fissure veins. The scant available data suggests that the veins are vertically zoned. There were probably at least two periods of epithermal mineralization: one during the late stage cooling of the stocks, and a second after extrusion of the lower volcanic series.

Remnants of Tertiary surfaces preserved under the volcanic rocks imply that there have been topographic inversions since the middle Tertiary.

Glacial deposits suggest at least one early period of valley glaciation and later, perhaps recent, periods of restricted mountain glaciation. Rich gold placer deposits, such as in McClellan Gulch, accumulated after the earliest period of valley glaciation.


Late Quaternary Progradation and Sand Spillover on the Outer Continental Margin Off Nova Scotia, Southeast Canada
Daniel J. Stanley, Donald J. P. Swift, Norman Silverberg, Noel P. James and Robert G. Sutton
88 pages, 83 figures, 6 tables
1972 (Date of Issue: 11 April 1972)
Number 8, Smithsonian Contributions to the Earth Sciences
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Abstract

Three distinct sediment types have prograded seaward from the outer shelf to the slope and rise in the vicinity of Sable Island Bank southeast of Nova Scotia during late Quaternary time. On the slope, the oldest facies recovered in cores is a brown to brick red, irregularly stratified, pebbly-sandy-clayey silt. Locally it is covered by an olive gray, clayey silt with a low sand and pebble content. This more homogenous gray facies displays abundant biogenic structures. A third facies, a thin layer of very fine, gray sand and muddy sand, locally covers brown and olive gray sediments on the slope and upper rise. All three facies contain similar light, heavy, and clay mineral suites.

The regional distribution of these facies has been determined by core traverses normal to the shelf edge, including one passing down the axis of The Gully (largest submarine canyon in the area), and another extending down the dissected slope off Sable Island Bank. The brown, late Pleistocene unit is exposed on the floor of The Gully and on its dissected deep-sea fan; postglacial bottom processes have kept younger sediments from accumulating in these areas. The brown beds also are exposed on the lower slope and rise off Sable Island in areas of slumping or nondeposition. The olive gray facies, late Pleistocene-Holocene in age, occurs primarily on the slope; it is thicker on flanks of slope valleys and thinner or absent on the divides. It is absent on part of the lower slope and upper rise. On the lower rise, tan mud with a coarse fraction rich in Foraminifera and shell debris may be the equivalent of the olive gray slope facies.

These sediments reflect changes in the sedimentary regimen during the post-Wisconsinan transgression. The observed sequence starts with the Wisconsin low stand of the sea when glacial drift, including reddish-brown, fluvioglacial sediments, were deposited over the Nova Scotian Shelf as far as Sable Island Bank. Periglacial outwash spread across the bank and flowed seaward around it. Deposition of the slope and rise brown facies is associated with this period; textural inhomogeneity suggests downslope transport by mass movement. Pebbly lenses resulted, in part, from ice-rafting prevalent during this phase. The contact between brown and the overlying olive gray, clayey silt facies is often abrupt, commonly occurring within several centimeters; this change is correlated with the rise of the late Quaternary sea above the margin of Sable Island Bank.

As the sea transgressed across Sable Island Bank in late glacial time, fines winnowed from fluvioglacial sediment were moved north of the Bank (into the Gully Trough) and seaward onto the slope. Coarse materials no longer reached the slope with former frequency, and the fines were supplied at a markedly lower rate. This decrease in sedimentation rate on the slope coincides with an increase in the organic fraction and bioturbation. Suspended fines were reduced to a gray hue as they passed through the sediment-water interface whose rate of upward growth was now an order of magnitude smaller. The Pleistocene-Holocene boundary of approximately 10,000 years B.P. occurs within the olive gray facies. As sea level attained its near-present position, and the present configuration of bottom currents was established, the lag (modified relict or palimpsest) sands on the Nova Scotian Shelf began a pattern of radial dispersal that may now be observed on Sable Island and associated banks. This bottom current activity has resulted in the development of spillover sands on the upper slope and deposition of thin discontinuous layers (including some turbidites) on the slope and rise and in The Gully Canyon.


Mineral Sciences Investigations, 1969-1971
William G. Melson, editor
94 pages, 34 figures, 34 tables
1972 (Date of Issue: 16 August 1972)
Number 9, Smithsonian Contributions to the Earth Sciences
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Abstract

Seventeen short contributions from the Smithsonian's Department of Mineral Sciences from 1969 to 1971 are gathered together in this volume. The scientific and technological subjects treated in these contributions include studies of lunar samples from Apollo 12, meteorites, petrology and volcanology, and descriptive mineralogy, as well as of the history and description of one of the Smithsonian Institution's most important recent acquisitions the Carl Bosch Collection of Minerals and Meteorites.


Mineralogy, Mineral-Chemistry, and Composition of the Murchison (C2) Meteorite
Louis H. Fuchs, Edward Olsen and Kenneth J. Jensen
39 pages, 19 figures, 9 tables
1973 (Date of Issue: 14 August 1973)
Number 10, Smithsonian Contributions to the Earth Sciences
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Abstract

The Murchison meteorite shower, September 28, 1969, occurred in and around Murchison, Victoria, Australia. Chemical and mineralogical analyses established it as a type II carbonaceous chondrite (C2). Murchison consists largely of fine-grained black matrix which has been identified as primarily a mixture of two iron-rich, low-aluminum chamosite polytypes. Contained in the matrix are four main types of inclusions: (1) single crystals and crystal fragments, (2) loosely aggregated clusters of crystals ("white inclusions"), (3) discrete true chondrules, (4) xenolithic fragments of two other meteorite types (mostly a unique kind of C3 chondrite).

The first type of inclusions consists of unzoned and highly zoned olivines, unzoned (disordered and ordered) orthopyroxenes, clinoenstatite, and rare diopside. Prominent minor phases are calcite, chromite, metal (with occasional traces of schreibersite), troilite, pentlandite, and two phases that could not be fully characterized.

The second type of inclusions consists primarily of grains of olivine (Fa 0 to Fa 40), lesser low-Ca pyroxenes, and minor spinel, calcite, whewellite, hibonite, perovskite, chromite, pentlandite, and rare Ca-pyroxene.

The true chondrules consist of olivine, Ca-poor pyroxene, occasional metal, and, in rare instances, one of the poorly characterized phases. The chondrules are not texturally typical of the ordinary chondrites, but resemble more closely those chondrules seen in C3 and C4 chondrites.

The fourth type of inclusion consists mainly of distinct xenolithic fragments of a light blue-gray chondrite type that resembles certain C3 chondrites (like Vigarano), though not in all aspects. These xenolithic fragments consist of disequilbrated olivines and pyroxenes, abundant pentlandite and troilite, and virtually no metal. In addition, a single xenolithic fragment was found of an unknown meteorite type.

Ca- and Al-rich glasses (of varying compositions) are found as blebs, with or without gas bubbles, contained within olivine crystals. The average Ca/Al ratio of these glasses approximates that for all meteoritic matter. They may represent early (nonequilibrium) subcooled condensates from the solar nebula. This nonequilibrium stage was apparently followed by equilibrium condensation through intermediate to low temperatures at which the layer-lattice phases condensed in abundance and incorporated crystals and fragments of the higher temperature phases.


Underwater Television Survey of the Atlantic Outer Continental Margin near Wilmington Canyon
Daniel J. Stanley and Peter Fenner
54 pages, 18 figures
1973 (Date of Issue: 2 August 1973)
Number 11, Smithsonian Contributions to the Earth Sciences
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Abstract

The study summarizes the results of an underwater television survey of the sea floor at the shelfbreak and at the head of Wilmington Canyon off the Middle Atlantic States. Distributions are shown for bottom currents and sedimentary structures, suspended matter, bottom firmness, bottom lithology, shell percentage, and fauna. A number of man-made objects on the sea floor in this area is documented. The Appendix is a listing of observations made at 26 stations. These data, based on direct visual observation of the sea floor, serve to complement earlier marine geological investigations made in this region. Mapping shows that surficial outer shelf and canyon head sediments at the shelfbreak are undergoing modification by both bottom current processes and bioturbation and that at the present time the Wilmington Canyon is receiving sediment mainly from the adjacent margin. Gravel, oyster banks, and near-vertical cavernous cliffs occurring at depths between 100 and 200 m are relict features related to eustatic changes of sea level that affected the outer continental margin during the Pleistocene.


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
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Abstract

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.


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
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Abstract

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.


Mineral Sciences Investigations, 1972-1973
George S. Switzer, editor
88 pages, 29 figures, 28 tables
1975 (Date of Issue: 2 July 1975)
Number 14, Smithsonian Contributions to the Earth Sciences
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Abstract

Thirteen short contributions from the Smithsonian's Department of Mineral Sciences for 1972 and 1973 are gathered together in this volume. Scientific contributions include new data on some mercury minerals from Terlingua, Texas; a description of dashkesanite from St. Paul's Rocks; a note on high-alumina basalt from the Aleutian Trench; descriptions of samples from the Apollo 15 and 16 lunar missions; chondrule composition of the Allende meteorite; the Pulsora meteorite and metamorphic equilibration in chondrites; the possible survival of very large meteorites that encounter the earth's surface; data on eight observed-fall chondritic meteorites; chemical analyses of two microprobe standards; and a technological note on the preparation of multiple microprobe samples. A history of mineral sciences in the Smithsonian Institution and a list of meteorites in the Smithsonian collections complete the volume.


Sands in the Alboran Sea: A Model of Input in a Deep Marine Basin
Daniel Jean Stanley, Gilbert Kelling, Juan-Antonio Vera and Harrison Sheng
51 pages, 23 figures, 8 tables
1975 (Date of Issue: 16 June 1975)
Number 15, Smithsonian Contributions to the Earth Sciences
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Abstract

The Alboran Sea, an almost totally land-enclosed, mountain-bounded (Rif, Betic ranges) basin, lies east of Gilbraltar in the westernmost Mediterranean. A petrologic study of the sand fraction in river, river mouth, and beach samples collected on the coast of the Alboran Sea defines the composition and distribution of the principal light and heavy mineral groups along its margins. The investigation details 20 mineralogical provinces on the southern Iberian and northern Moroccan margins and the Strait of Gibraltar sector and identifies the major source terrains and fluvial and marine point sources of terrigenous sediment entering the basin.

Significant sample-to-sample changes in the proportion of mineralogical components are attributed to marine processes, particularly nearshore currents, which move sands laterally along the coast and, while so doing, modify the proportions of light and heavy mineral components. Lateral trends observed within Moroccan and Spanish mineralogical provinces provide evidence on the actual sense of nearshore sediment dispersal. Marine transport agents have a more pronounced effect on the light mineral fraction, while even unstable heavy mineral species appear to suffer less modification as a result of the transport in the marine environment. The paths followed by the sands between source terrain and final depositional site in deepwater environments are complex ones. A comparison of mineral assemblages in coastal sands and in sands in deep-sea cores shows a provenance from the Serranía de Ronda complex in the Betic range west of Málaga. After initial deposition on the coast, these river-borne sediments are transported in a southwestward direction toward Gibraltar and then eventually are funneled downslope in a southeastward direction toward the Western Alboran Basin through the Gibraltar Canyon and submarine valley.

In geological terms, the Alboran. Sea study can serve as a model for sedimentation in one type of elongate enclosed basin bounded by regions of high relief. Although the geographic and geologic configuration of the Alboran Sea and contiguous land conforms to a multisource basin model, the transport paths of sediment since the late Quaternary have been essentially longitudinal. This longitudinal input, with filling as a result of currents primarily from the Strait of Gibraltar sector, is independent of a major delta source and is thus unlike many elongate, deep-sea basins examined in present oceans and troughs (including flysch) mapped in the ancient rock record.


Late Quaternary Sedimentation and Stratigraphy in the Strait of Sicily
Andres Maldonado and Daniel Jean Stanley
73 pages, 39 figures, 5 tables
1976 (Date of Issue: 3 August 1976)
Number 16, Smithsonian Contributions to the Earth Sciences
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Abstract

The Strait of Sicily, a broad, elongate, topographically complex platform in the central Mediterranean, separates the deep Ionian Basin from the Algéro-Balearic and Tyrrhenian basins to the west. A detailed core analysis shows that the late Quaternary sections in the different sectors of the Strait are distinct from those in the deep Mediterranean basins. Strait lithofacies are characteristically uniform, highly bioturbated, and contain significant amounts of coarse calcareous sediment. Five major sediment types (coarse calcareous sand, sand- to silt-size sediment, ash, mud, and sapropel) are grouped into natural vertical successions termed sequences. The three major sequences defined in the Strait are upward-coarsening and upward-fining, uniform, and turbiditic (including both mud and sand-silt turbidites); sapropel sequences are recovered in cores on the Ionian slope east of the Strait.

The direct relation between sediment type, lateral lithofacies distribution, water depth, and structural displacement is demonstrated. For example, the proportion of turbiditic mud increases while that of hemipelagic mud and bioturbated strata decreases with depth. The effects of regional Quaternary events, particularly climatic changes and eustatic sea level oscillations, are well recorded in cores collected in shallow platform and neritic-bathyal environments; here the upper sediment sequences are truncated and fining- and coarsening-upward sequences, which include coarse calcareous sand layers interbedded with mud and sandy lutite, prevail. In contrast, well stratified units comprising sand (including gravity flow units and volcanic ash) alternating with hemipelagic and turbiditic mud form the surficial deposits in the deep (>1000 m) elongate Linosa, Pantelleria, and Malta basins. Homogeneous bioturbated light olive gray to dusty yellow muddy sequences predominate in the intermediate depth neritic-bathyal environments.

Stratigraphic correlation of cores based on carbon-14 analyses shows that individual units or sequences are not correlatable across the Strait or even within small basins, although it is possible to recognize a general vertical succession of depositional patterns. Sedimentation rates generally decrease with increasing depth. Rates in the deep basins have been relatively uniform from the late Quaternary to the present, while upper (Holocene) sequences in the shallow platform and neritic-bathyal environments have been truncated. Correlation of reflectors on high-resolution subbottom profiles indicates that faulting in many sectors of the Strait is of recent or subrecent origin and that the vertical displacement rate is locally in excess of the average sedimentation rate (i.e., greater than 20 cm per 1000 years).

The absence of sapropel layers in the Strait basins indicates that these depressions remained ventilated during periods when anaerobic conditions prevailed in the deep basins in the eastern and central Mediterranean. An early Holocene paleooceanographic model depicting a possible reversal of currents in the Strait of Sicily region is postulated.


Occurrence, Distribution, and Age of Australian Tektites
R. O. Chalmers, E. P. Henderson and Brian Mason
46 pages, 17 figures, 10 tables
1976 (Date of Issue: 9 September 1976)
Number 17, Smithsonian Contributions to the Earth Sciences
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Abstract

Extensive field work has shown that the Australian strewnfield is less extensive than previously thought, being essentially restricted to the region south of latitudes 24° to 25°S. The few australites found north of this region probably represent specimens transported by man. Throughout much of the desert interior australites are weathering out of a late Pleistocene or early Recent horizon in a well-consolidated calcareous red sandy aeolianite; field evidence indicates that in most places they are found essentially where they fell, or stream erosion and sheet wash has transported them short distances and concentrated them in claypans and playas. Distribution within the strewnfield is irregular and can be ascribed to: (1) original nonuniform fall; (2) burial by recent deposition; (3) removal by erosion. Australites (excluding the doubtful HNa/K type) show a continuous range of composition from 80% to 66% SiO2 with related variations in other major constituents, which is reflected in the range of specific gravities (2.36-2.52) and refractive indices (1.493-1.529). The composition range is not uniform over the strewnfield, the high-silica australites being concentrated along a northwest trending band extending from western Victoria to the Lake Eyre region. Other noteworthy features are: (1) a variation in the average size of australites from place to place, those on the Nullarbor Plain being notably smaller (average < 1 gram) than those of other regions (average 3-5 grams); (2) the occurrence of many large australites (> 100 grams) in the southwestern part of Western Australia.

Unsolved problems include: (1) the inconsistency between geological age (7000-20,000 years BP) and K-Ar and fission track ages (700,000-860,000 years); (2) the relationship, if any, between australites and the  microtektites in Indian Ocean sediments; and (3) the source region of the australite material.


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
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Abstract

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.


Mineral Sciences Investigations 1974-1975
Brian Mason, editor
125 pages, 48 figures, 37 tables
1977 (Date of Issue: 9 March 1977)
Number 19, Smithsonian Contributions to the Earth Sciences
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Abstract

Nine short contributions from the Smithsonian's Department of Mineral Sciences for 1974 and 1975 are gathered together in this volume. These contributions comprise an account of the composition of garnet xenocrysts from three kimberlite pipes in Arizona and New Mexico; a catalog of major element chemistry of abyssal volcanic glasses, and the application of these data to determine magma compositions; descriptions of the Harleton (Texas), St. Mary's County (Maryland), and Ras Tanura (Saudi Arabia) chondritic meteorites; a comparative study of eight chondrite meteorites from India and Pakistan; geochemical data on separated components of the Allende carbonaceous chondrite; and a mineralogical and chemical study of silicate inclusions in the El Taco mass of the Campo del Cielo iron meteorite.


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
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Abstract

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 Algéro-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.


Schreibersite Growth and Its Influence on the Metallography of Coarse-Structured Iron Meteorites
Roy S. Clarke, Jr. and Joseph I. Goldstein
80 pages, 28 figures, 20 tables
1978 (Date of Issue: 14 April 1978)
Number 21, Smithsonian Contributions to the Earth Sciences
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Abstract

The role that schreibersite growth played in the structural development process in coarse-structured iron meteorites has been examined. The availability of many large meteorite surfaces and an extensive collection of metallographic sections made it possible to undertake a comprehensive survey of schreibersite petrography. This study was the basis for the selection of samples for detailed electron microprobe analysis. Samples containing representative structures from eight chemical Groups I and IIAB meteorites were selected.

Electron microprobe traverses were made across structures representative of the observed range of schreibersite associations. Particular emphasis was placed on schreibersite-kamacite interface compositions. An analysis of these data has led to a comprehensive description of the structural development process.

Massive schreibersite, one of the four major types of schreibersite encountered, may be accounted for by equilibrium considerations. Subsolidus nucleation and growth with slow cooling from temperatures at least as high as 850° C, and probably much higher, explain the phase relationships that one sees in meteorite specimens. The retention of taenite in the octahedrites establishes that bulk equilibrium did not extend as low as 550° C. Schreibersite undoubtedly continued in equilibrium with its enclosing kamacite to lower temperatures.

A second type of schreibersite to form is homogeneously nucleated rhabdite. It nucleated in kamacite in the 600° C temperature range, either as a consequence of low initial P level or after local P supersaturation developed following massive schreibersite growth.

A third type of schreibersite is grain boundary and taenite border schreibersite. It formed at kamacite-taenite interfaces, absorbing residual taenite. Nucleation took place successively along grain boundaries over a range of temperatures starting as high as 500° C or perhaps slightly higher. Grain boundary diffusion probably became an increasingly important factor in the growth of these schreibersites with decreasing temperature.

The fourth type of schreibersite is microrhabdite. These schreibersites nucleated homogeneously in supersatuated kamacite at temperatures in the 400° C range or below.

P diffusion controlled the growth rate of schreibersite. The Ni flux to a growing interface had to produce a growth rate equal to that established by the P flux. This was accomplished by tie line shifts that permitted a broad range of Ni growth rates, and these shifts account for the observed range of Ni concentrations in schreibersite. Equilibrium conditions pertained at growth interfaces to temperatures far below those available experimentally. Kinetic factors, however, restricted mass transfer to increasingly small volumes of material with decreasing temperature.


Mineral Sciences Investigations 1976-1977
Robert F. Fudali, editor
73 pages, 22 figures, 20 tables
1979 (Date of Issue: 11 September 1979)
Number 22, Smithsonian Contributions to the Earth Sciences
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Abstract

This volume is comprised of six short contributions reporting the results of some of the research carried out by the Department of Mineral Sciences, Smithsonian Institution, during the period 1976-1977. Included are: a comparison of impact breccias and glasses from Lonar Crater (India) with very similar specimens from the moon; petrographic descriptions and chemical analyses of virtually all the known pyroxene-plagioclase achondrite meteorites and a discussion of the relationships within this class; a comparative chemical study of sixty Australian tektites from widely separated localities; a description of a new, rapid technique of sample preparation for whole-rock analyses using the electron microprobe; an interlaboratory comparison of the precision and accuracy of electron microprobe analyses; and a tabulation of the chemical compositions of some electron microprobe reference samples.


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
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Abstract

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 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
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Abstract

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.


Inclusions in the Allende Meteorite
Brian Mason and S. R. Taylor
30 pages, 25 figures, 5 tables
1982 (Date of Issue: 5 October 1982)
Number 25, Smithsonian Contributions to the Earth Sciences
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Abstract

Six discrete groups of inclusions have been distinguished in the Allende meteorite. Groups I, V, and VI are mostly melilite-rich chondrules, although some have been extensively altered to fine-grained aggregates; Groups II and III are mostly fine-grained aggregates made up largely of spinel and fassaite; Group IV are olivine-rich aggregates and chondrules. Each group has a distinctive trace-element pattern, most clearly shown by the rare-earth (RE) distribution pattern. Group I has an unfractionated pattern (except for a small positive Eu anomaly) at about 10-15 times chondrites; Group II has a highly fractionated pattern with depletion of the heavier lanthanides (Gd-Er) and negative Eu and positive Tm and Yb anomalies; Group III has an unfractionated pattern at about 20 times chondrites, except for negative Eu and Yb anomalies; Group IV has a relatively unfractionated pattern at 2-4 times chondrites; Group V has an unfractionated pattern at 10-20 times chondrites; Group VI has an unfractionated pattern at 10-20 times chondrites, except for positive Eu and Yb anomalies (i.e., complementary to Group III). The complex patterns of trace element distribution in these Allende inclusions indicate a complex history of formation of this meteorite from the solar nebula.


Field and Laboratory Investigations of Meteorites from Victoria Land, Antarctica
Ursula B. Marvin and Brian Mason, editors
134 pages, 79 figures, 11 tables
1984 (Date of Issue: 8 June 1984)
Number 26, Smithsonian Contributions to the Earth Sciences
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Abstract

This monograph describes the meteorite collecting activities in Victoria Land during the 1980-1981 and 1981-1982 field seasons, and the geodetic measurements of ice motion and ablation at the Allan Hills site. Descriptions and classifications are given for all specimens collected during the 1980-1981 season and for most of those collected during the 1981-1982 season. Review articles are included on the petrology and classification of 145 small meteorites collected in the 1977-1978 season, on Antarctic Type 3 chondrites, and on cosmic-ray-produced nuclides in the Victoria Land meteorites. The first lunar meteorite is described. Chemical analyses of 25 Victoria Land meteorites are published, with a discussion of Antarctic weathering effects. The Appendix lists all of the Victoria Land meteorites classified as of June 1983, by numerical order for each locality and by meteorite class.


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
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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.


Field and Laboratory Investigations of Meteorites from Victoria Land and the Thiel Mountains Region, Antarctica, 1982-1983 and 1983-1984
Ursula B. Marvin and Glenn J. MacPherson, editors
146 pages, 86 figures, 14 tables
1989 (Date of Issue: 16 February 1989)
Number 28, Smithsonian Contributions to the Earth Sciences
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Abstract

This monograph describes the meteorite collecting activities of the United States Antarctic Search for Meteorites (ANSMET) expeditions of the 1982-1983 and 1983-1984 field seasons. Descriptions and classifications are given of most specimens collected during the 1982-1983 season and some of those collected in the 1983-1984 season. Articles are included reviewing topics such as Antarctic achondrites, carbonaceous chondrites, meteorite weathering under polar conditions, trace element contents of Antarctic meteorites in comparison with those found elsewhere, and the meteorite pairing problem. One chapter describes the crystalline fabric of the ice surrounding a meteorite discovered emerging at the surface. The Appendix lists all ANSMET specimens classified as of June 1984, in numerical order for each locality and by meteorite class. The Appendix also includes a tentative list of paired specimens.


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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Abstract

Long-term environmental monitoring results are presented documenting the seasonality experienced by the lowland tropical forest on Barro Colorado Island, Panamá. 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 Niño 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 Niño 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.


Field and Laboratory Investigations of Antarctic Meteorites Collected by United States Expeditions, 1985-1987
Ursula B. Marvin and Glenn J. MacPherson, editors
116 pages, 38 figures, 9 tables
1992 (Date of Issue: 18 December 1992)
Number 30, Smithsonian Contributions to the Earth Sciences
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Abstract

This monograph describes the meteorite collecting activities of the United States Antarctic Search for Meteorites (ANSMET) expeditions during the 1984-1985, 1985-1986, and 1986-1987 field seasons. Descriptions and classifications are given of most specimens collected during those expeditions with the exceptions of the types 4, 5, and 6 ordinary chondrites, whose properties are tabulated. Two articles are included that summarize data on the terrestrial ages and thermoluminescence properties of Antarctic meteorites. The Appendix lists all ANSMET specimens classified as of June 1987, in numerical order for each locality and by meteorite class.


The Port Orford, Oregon, Meteorite Mystery
Roy S. Clarke, Jr., editor
43 pages, 19 figures, 7 tables
1993 (Date of Issue: 4 January 1993)
Number 31, Smithsonian Contributions to the Earth Sciences
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Abstract

The Port Orford meteorite was allegedly discovered by John Evans, a contract explorer for the United States Government, on a mountain in southwestern Oregon in 1856. Efforts to organize the recovery of the alleged 10-ton body for placement in the Smithsonian Institution in Washington, D.C., began in late 1859, but were abandoned as a consequence of the simultaneous onset of the Civil War and Evans' death.

Early in this century journalistic reports revived the story and stimulated numerous unsuccessful amateur meteorite hunting expeditions into the inaccessible Siskiyou National Forest. Smithsonian investigators visited the vaguely defined site without success in 1929 and 1939. As time passed, it became increasingly obvious to some involved officials that there was something wrong with the original accounts. Nevertheless, most persons persisted in their belief that Evans' story was true.

This monograph combines an historical study by Howard Plotkin ("John Evans and the Port Orford Meteorite Hoax," pages 1-24), and a technical study by V.F. Buchwald and Roy S. Clarke, Jr. ("A Mystery Solved: The Port Orford Meteorite is an Imilac Specimen," pages 25-43).

In the first paper, Plotkin details the history of the mysterious lost Port Orford meteorite, and presents previously unreported evidence that indicates Evans was ill-trained for his scientific field work, which was superfically and unprofessionally executed, and that he had amassed a staggering personal debt by consistently overspending his budget. Most startling of all, Plotkin's research led him to the inescapable conclusion that Evans had acquired a small but very rare piece of meteorite, and had hatched a clever scheme whereby he could use it to turn around his financial affairs. Plotkin reconstructs in detail how Evans planned to carry out this hoax.

Finally, Plotkin endeavors to establish the true identity of the meteoritic sample. On the basis of its overall physical appearance, degree of weathering, and chemical composition, Plotkin argues that the Port Orford specimen is a fragment of Imilac, a Chilean pallasite discovered in 1820-1822. He further contends that Evans acquired it from someone else while crossing the Isthmus of Panama on his final return trip from Oregon during the fall of 1858.

In the second paper, Buchwald and Clarke describe the involvement of the National Museum of Natural History in attempts during this century to recover the meteorite, and they report on their detailed technical studies of the Port Orford specimen and other possibly related meteorites.

Buchwald and Clarke point out that only three distinct pallasite falls were known in the late 1850s: (1) the single Krasnojarsk, Siberia, mass, (2) the two large masses of the Brahin, Belorussiya, meteorite, and (3) the Imilac, Chile, shower. Both Krasnojarsk and Brahin were ruled out of a possible hoax scenario on the basis of physical properties and state of corrosion, which left Imilac as the only possibility short of invoking an otherwise completely unknown fall. They therefore undertook detailed metallographic and mineralogical examinations of the Port Orford specimen and several Imilac specimens in an attempt to resolve the matter.

They find that the Port Orford specimen is a main group pallasite that is chemically, structurally, and morphologically indistinguishable from Imilac. The steep thermal gradient of its heat-altered zone shows it to be an individual from a shower-producing fall and that it could not have been a specimen removed from a large mass. Its weathering history suggests the arid conditions of the high desert of Chile, not the humid Oregon coast forests. Port Orford's kamacite composition and hardness, olivine composition, trace element levels in metal, and shock levels in kamacite and troilite are all within observed ranges for the Imilac shower or within reasonable extensions thereof. These many congruencies led Buchwald and Clarke to conclude that the Port Orford meteorite is an Imilac specimen, and that Evans perpetrated a deliberate hoax using a small Imilac individual as bait.


The Guadalupian Symposium
Bruce R. Wardlaw, Richard E. Grant and David M. Rohr, editors
415 pages, 191 figures, 43 plates, 45 tables
2000 (Date of Issue: 21 August 2000)
Number 32, Smithsonian Contributions to the Earth Sciences
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Abstract

The internal stratigraphy of the Cutoff Formation in the Guadalupe Mountains is clarified, and the unit is divided into three members: the Shumard Canyon, the El Centro, and the Williams Ranch members. The Shumard Canyon Member of the Cutoff Formation in the Guadalupe Mountains correlates to the upper part of the Cathedral Mountain Formation in the Glass Mountains. The El Centro and Williams Ranch members of the Cutoff Formation and the lower part of the Brushy Canyon Formation, including the Pipeline Shale in the Guadalupe Mountains, correlate to the Road Canyon Formation. The changeover in conodonts from transitional forms to Mesogondolella nankingensis) provides a basal definition for the Guadalupian and occurs within correlation unit 3 in the El Centro Member of the Cutoff Formation and cycle 2 of the Road Canyon Formation.

The geology, stratigraphy, and depositional setting of the Permian in the Del Norte Mountains and of the Word Formation in the Glass Mountains are discussed in detail, and this data suggest deposition in a foreland basin or backbay between the Marathon Fold Belt and the Delaware basin. The internal stratigraphy of the Road Canyon, Word, Vidrio, Altuda, Capitan, and Tessey formations reveal the following: (1) the Road Canyon was deposited in four cycles and the Word in six cycles; (2) the Altuda can be divided into five informal members and the Tessey into three members; (3) the Vidrio is an unconformity-bounded unit; and (4) the Capitan displays characteristic platform margin to slope foresets.

Biozonation of the Guadalupian is discussed, and details are provided on the fusulinid and conodont zonations. Changes in conodont fauna, based on the succession of Mesogondolella species from M. nankingensis to M. altudaensis, divide the Guadalupian into five zones.

Five new species of conodonts (Sweetina crofti Wardlaw, Mesogondolella shannoni Wardlaw, Hindeodus wordensis Wardlaw, Iranognathus punctatus Wardlaw, and Sweetognathus bicarinum Wardlaw) and two new species of fusulinids (Codonofusiella (Lantschichites) altudaensis Wilde and Rudine and Rauserella bengeensis Wilde and Rudine) are described.


Great Basin Aquatic Systems History
Robert Hershler, David Madsen, and Donald R. Currey, eds.
405 pages, 190 figures, 21 tables
2002 (Date of Issue: 11 December 2002)
Number 33, Smithsonian Contributions to the Earth Sciences
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Abstract
The 14 papers collected herein treat diverse aspects of the aquatic history of the Great Basin of the western United States and collectively attempt to summarize and integrate portions of the vast body of new information on this subject that has been acquired since the last such compilation was published in 1948. In the first section, four papers (Lowenstein, Negrini, Reheis et al., Sack) focus on the physical aspects of the Great Basin paleolake histories, whereas a fifth paper (Oviatt) summarizes the contributions to the study of Bonneville Basin lacustrine history made by two early giants of the field, Grove Karl Gilbert and Ernst Antevs. In the second section, four papers synthesize perspectives on Great Basin aquatic history provide by diatoms and ostracods (Bradbury and Forester), fishes (Smith et al.), aquatic insects (Polhemus and Polhemus), and aquatic snails (Hershler and Sada), whereas a fifth (Sada and Vinyard) summarizes the conservation status of the diverse aquatic biota that is endemic to the region. In the final section, three papers integrate terrestrial biotic evidence pertaining to Great Basin aquatic history derived from pollen from cores (Davis), floristics (Wigand and Rhode), and the mammal record (Grayson), whereas a fourth (Madsen) examines the relationship between Great Basin lakes and human inhabitants of the region. Although diverse in scope and topic, the papers in this volume are nonetheless linked by an appreciation that integration of geological, biological, and anthropological evidence is a necessary and fundamental key to a mature understanding of Great Basin aquatic systems history.

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