Upper Eocene tektite and impact ejecta layer on the continental slope off New Jersey

Abstract— During Leg 150 of the Ocean Drilling Project (ODP), two sites (903C and 904A) were cored that have sediments of the same biostratigraphic age as the upper Eocene tektite-bearing ejecta layer at Deep Sea Drilling Project (DSDP) Site 612. Core 45X from ODP Site 904A (～4 km north of Site 612) contains a 5 cm thick tektite-bearing ejecta layer, and Core 56 from Site 903C (～8 km north-northwest of Site 904) contains a 2 cm thick layer of impact ejecta without any tektite or impact glass. Shocked quartz and feldspar grains, with multiple sets of planar deformation features (PDFs), and abundant coesite-bearing grains are present at both sites. The major oxide contents, trace element compositions, and rare earth element (REE) patterns of the Site 904 tektites are similar to those of the Site 612 tektites and to North American tektites (especially bediasites). The ?_Sr and ?_Nd values for one composite tektite sample from Site 904 fall within the range previously obtained for the Site 612 tektites, which defines a linear trend that, if extrapolated, would intersect the values obtained for North American tektites. The water contents of eight tektite fragments from Site 904 range from 0.017 to 0.098 wt%, and, thus, are somewhat higher than is typical for tektites. The heavy mineral assemblages of the 63–125 μm size fractions from the ejecta layers at Sites 612, 903, and 904 are all similar. Therefore, we conclude that the ejecta layer at all three sites is from the same impact event and that the tektites at Sites 904 and 612 belong to the North American tektite strewn field. Clinopyroxene-bearing (cpx) spherules occur below, or in the lower part of, the main ejecta layer at all three sites. At all three sites, the cpx spherules have been partly or completely replaced with pyrite that preserved the original crystalline textures. Site 612, 903, and 904 cpx spherules are similar to those found in the Caribbean Sea, Gulf of Mexico, central equatorial Pacific, western equatorial Pacific, and eastern Indian Ocean. The cpx event appears to have preceded the North American tektite event by 10–15 ka or less. The fining-upward sequence at all three sites and concentration of the denser, unmelted impact ejecta at the top of the tektite layer at Sites 612 and 904 suggest that the tektite-bearing ejecta layers are not the result of downslope redeposition and that the unmelted ejecta landed after the glass. Geographic variations in thickness of the tektite-bearing ejecta layer, the lack of carbonate clasts in the ejecta layer, and the low CaO content of the tektite glass suggest that the ejecta (including the tektite glass) were derived from the Chesapeake Bay structure rather than from the Toms Canyon structure. A sharp decline in microfossil abundances suggests that local environmental changes caused by the impact may have had adverse effects on benthic foraminifera, radiolaria, sponges, and fish as well as the planktic foraminifera.     

Krypton and xenon fractionation in North American tektites

Abstract— Elemental and isotopic compositions of the noble gases have been determined in six North American tektites (4 bediasites and 2 georgiaites) and one Ivory Coast tektite. Radiogenically produced ⁴He may explain the large ⁴He/³⁶Ar ratios measured relative to air, despite significant diffusive losses. The Ne isotopic composition is enriched in ²⁰Ne consistent with a single stage mass fractionation process. The enormous ²⁰Ne/³⁶Ar enrichments observed in all tektite samples, similar to those reported from other tektites and impact glasses, are attributed to atmospheric diffusion into the samples following solidification. The North American tektites show a systematic increase in ⁸⁴Kr/³⁶Ar and ¹³²Xe/³⁶Ar relative to air, with enrichments greater than those determined for any other tektite group or terrestrial samples other than shales. These enrichments are inconsistent with existing models of dissolving Kr and Xe in tektite glass without elemental fractionation at atmospheric pressures equivalent to ∼40 km altitude. The Kr and Xe isotopic compositions are indistinguishable from atmospheric within experimental uncertainty.     

Major and trace element compositions of georgiaites: Clues to the source of North American tektites

Abstract— Electron microprobe and laser ablation, inductively‐coupled plasma mass spectrometer analyses of 24 georgiaites show that these tektites are all Si‐rich (79–83 wt% SiO₂) glasses with variable major and trace element abundances (e.g., FeO varies from 2.1 to 3.7 wt%). Glass compositions are similar to but not identical with average upper continental crust. For example, georgiaites are light rare earth element enriched with small negative Eu anomalies (Eu/Eu*=0.73‐0.86) and La‐Th‐Sc systematics are intermediate between that of Archean and post‐Archean continental crust. When the georgiaite data are placed in the context of data for all North American tektites, triangular arrays appear on some oxide‐oxide plots (e.g., FeO‐MgO). Large variations in refractory element abundances and ratios compared to the variation in SiO₂ favors mixing over volatilization as a cause of the compositional variation. If all the tektites formed as a result of a single impact, then triangular arrays in oxide‐oxide variation diagrams require at least three source components. These components include a Si‐rich material, probably a quartz‐rich sand that was predominant in the formation of georgiaites. Two relatively silica‐poor and Fe‐rich components have compositional characteristics similar to shales and greywackes. The La‐Th‐Sc systematics of the georgiaites and most other North American tektites are distinctive and could potentially be used to link the tektites to Eocene sediments at the Chesapeake Bay impact structure.     

North American tektite debris and impact ejecta from DSDP Site 612

Abstract— A layer of tektite glass and shock-metamorphosed grains found in an upper Eocene section of core 21 from DSDP Site 612 taken on the continental slope off New Jersey may belong to the North American tektite strewn field. However, the Site 612 glasses generally have higher K₂O and lower Na₂O contents for a given SiO₂ content and different Sr and Nd isotopic compositions. In order to better define the layer, a series of samples was taken continuously through the layer at 1 cm intervals. Tektite fragments are in an 8 cm thick layer; microtektites are concentrated in the upper 4 cm, while spherules with “crystalline” textures (microkrystites) are concentrated in the lower half of the layer. Millimeter-size splash forms are mostly in the lower part of the tektite-bearing layer. Rock and mineral grains showing evidence of shock metamorphism are abundant in the upper half of the tektite-bearing layer. Coesite is abundant, and stishovite was found in one rock fragment. The size and abundance of the tektite glass and the abundance of shocked debris indicate that Site 612 is relatively close to the source crater, which may be to the north of Site 612 on the coastal plain or adjacent continental shelf.     

Ocean Drilling Project Hole 689B spherules and upper Eocene microtektite and clinopyroxene-bearing spherule strewn fields

Abstract— Montanari et al. (1993) reported a positive Ir anomaly in the upper Eocene sediments from Ocean Drilling Program Hole 689B on the Maud Rise, Southern Ocean. Vonhof (1998) described microtektites and clinopyroxene-bearing (cpx) spherules associated with the Ir anomaly in Hole 689B and suggested that they belong to the North American and equatorial Pacific cpx strewn fields, respectively. We searched a suite of 27 samples taken through the spherule layer from Hole 689B, and we recovered 386 microtektites and 667 cpx spherules. We studied the petrography of the microtektites and cpx spherules and determined the major element compositions of 31 microtektites and 14 cpx spherules using energy dispersive x-ray analysis. We also determined the minor element compositions of eight microtektites using instrumental neutron activation analysis. We found that the peak abundance of cpx spherules is ～2 cm below the peak abundance of the microtektites (～128.7 m below sea floor), which suggests that the cpx spherule layer may be slightly older (～3–5 ka). The microtektites are mostly spherical and are generally transparent and colorless. They are similar to the North American microtektites in composition, the biggest differences being their generally lower Na₂O and generally higher Zr, Ba, and Ir (up to 0.3 ppb) contents. We agree with Vonhof (1998) that the Hole 689B microtektites probably belong to the North American tektite strewn field. We calculate that the number of microtektites (>125 μm)/cm² at Hole 689B is 52. This number is close to the concentration predicted by extrapolation of the trend of concentration vs. distance from the Chesapeake Bay structure, based on data from other North American microtektite-bearing sites. Thus, the North American strewn field may be at least four times larger than previously mapped. The Hole 689B cpx spherules range from translucent yellow to opaque black, but most are opaque tan to dark brown. They are generally spherical in shape and all are < 125 μm in diameter. Some contain Ni-rich spinels in addition to clinopyroxene microlites. The cpx spherules are petrographically and compositionally similar to cpx spherules previously found in the northwestern Atlantic Ocean, Caribbean Sea, Gulf of Mexico, equatorial Pacific, and eastern Indian Ocean. The abundance and widespread geographic occurrence of these spherules suggest that the strewn field may be global in geographic extent. Assuming a global extent, we estimate that there may be at least 25 billion metric tons of cpx spherules in the strewn field. Based on age, size, and geographic location, we speculate that the 100 km diameter Popigai crater in northern Siberia may be the source of the cpx spherule layer.     

Australasian minitektites discovered in the Indian Ocean

Abstract— Large area sampling with a box core in the Indian Ocean has led to the discovery of minitektites (>1–3.75 mm long) and a tektite fragment (～1.25 mm) occurring with microtektites belonging to the Australasian tektite strewn field. Minitektites and the microtektites are found to have similar major element compositions conforming to the Australasian tektite/microtektite chemistry. Earlier studies based on isotopic evidence, dating, and chemistry had provided evidence of a single large tektite strewn field; however, the physical association of tektites occurring with microtektites has been lacking. The present study provides such an association.     

Fragmentation and hydration of tektites and microtektites

Abstract— An examination of data collected over the last 30 years indicates that the percent of glass fragments vs. whole splash forms in the Cenozoic microtektite strewn fields increases towards the source crater (or source region). We propose that this is due to thermal stress produced when tektites and larger microtektites fall into water near the source crater while still relatively hot (>1150 °C). We also find evidence (low major oxide totals, frothing when melted) for hydration of most of the North American tektite fragments and microtektites found in marine sediments. High-temperature mass spectrometry indicates that these tektite fragments and microtektites contain up to 3.8 wt% H₂O. The H₂O-release behavior during the high-temperature mass-spectrometric analysis, plus high CI abundances (0.05 wt%), indicate that the North American tektite fragments and microtektites were hydrated in the marine environment (i.e., the H₂O was not trapped solely on quenching from a melt). The younger Ivory Coast and Australasian microtektites do not exhibit much evidence of hydration (at least not in excess of 0.5 wt% H₂O); this suggests that the degree of hydration increases with age. In addition, we find that some glass spherules (with <65 wt% SiO₂) from the upper Eocene clinopyroxene-bearing spherule layer in the Indian Ocean have palagonitized rims. These spherules appear to have been altered in a similar fashion to the splash form K/T boundary spherules. Thus, our data indicate that tektites and microtektites that generally contain >65 wt% SiO₂ can undergo simple hydration in the marine environment, while impact glasses (with <65 wt% SiO₂) can also undergo palagonitization.     

Establishing the link between the Chesapeake Bay impact structure and the North American tektite strewn field: The Sr‐Nd isotopic evidence

Abstract— The Chesapeake Bay impact structure, which is about 35 Ma old, has previously been proposed as the possible source crater of the North American tektites (NAT). Here we report major and trace element data as well as the first Sr‐Nd isotope data for drill core and outcrop samples of target lithologies, crater fill breccias, and post‐impact sediments of the Chesapeake Bay impact structure. The unconsolidated sediments, Cretaceous to middle Eocene in age, have ?_Sr^{t = 35.7 Ma} of +54 to +272, and ?_Nd^{t = 35.7 Ma} ranging from ?6.5 to ?10.8; one sample from the granitic basement with a T^Nd_CHUR model age of 1.36 Ga yielded an ?_Sr^{t = 35.7 Ma} of +188 and an ?_Nd^{t = 35.7 Ma} of ?5.7. The Exmore breccia (crater fill) can be explained as a mix of the measured target sediments and the granite, plus an as‐yet undetermined component. The post‐impact sediments of the Chickahominy formation have slightly higher T^Nd_CHUR model ages of about 1.55 Ga, indicating a contribution of some older materials. Newly analyzed bediasites have the following isotope parameters: +104 to +119 (?_Sr^{t = 35.7 Ma}), ?5.7 (?_Nd^{t = 35.7 Ma}), 0.47 Ga (T^Sr_UR), and 1.15 Ga (T^Nd_CHUR), which is in excellent agreement with previously published data for samples of the NAT strewn field. Target rocks with highly radiogenic Sr isotopic composition, as required for explaining the isotopic characteristics of Deep Sea Drilling Project (DSDP) site 612 tektites, were not among the analyzed sample suite. Based on the new isotope data, we exclude any relation between the NA tektites and the Popigai impact crater, although they have identical ages within 2s? errors. The Chesapeake Bay structure, however, is now clearly constrained as the source crater for the North American tektites, although the present data set obviously does not include all target lithologies that have contributed to the composition of the tektites.     

Late Eocene microkrystites and microtektites at Maud Rise (Ocean Drilling Project Hole 689B; Southern Ocean) suggest a global extension of the approximately 35.5 Ma Pacific impact ejecta strewn field

Abstract— Late Eocene microtektites and microkrystites recovered from Ocean Drilling Project Hole 689B at Maud Rise (Southern Ocean) are stratigraphically and geochemically compared to spherules from the North American and Pacific strewn fields, and to devitrified spherules from the Eocene-Oligocene global stratotype section and point section in Massignano, Italy. The ODP 689B microkrystites compare well to the Pacific strewn field microkrystites, which suggests that the geographic extent of the Pacific strewn field was much larger than previously documented. The elemental composition of microtektites of ODP Hole 689B is comparable to tektites of the North American strewn field. Their ⁸⁷Sr/⁸⁶Sr ratio, however, is different. We tentatively interpret this to reflect geochemical heterogeneity within the North American strewn field but can not exclude the option that the chemical discrepancies result from the existence of a third late Eocene impact site.     

Sr and Nd analyses of upper Eocene spherules and their implications for target rocks

Abstract— Upper Eocene impact ejecta has been discovered all over the world. The number of upper Eocene impact layers and the geographic distribution of each layer, based on major chemical composition and biostratigraphic data, are not agreed upon. We have performed four Sr‐Nd isotopic analyses of clinopyroxene‐bearing spherules (cpx spherules) and three Sr‐Nd analyses of microtektites from five Deep Sea Drilling Project/Ocean Drilling Program (DSDP/ODP) sites in the South Atlantic and Indian Oceans. Our data support the hypothesis that there is only one cpx spherule layer in upper Eocene sediments. We also find that the microtektites associated with the cpx spherule layer in the South Atlantic and Indian Oceans are not part of the North American tektite strewn field, but belong to the same event that produced the cpx spherules. The microtektites, together with cpx spherules, are more heterogeneous than microtektites/tektites from other strewn fields. No direct link has been established between the microtektites from this study and possible target rock at the Popigai crater.     

Chemical variation within fragments of Australasian tektites

Abstract— In previous studies, intersample variation between compositions of different tektites from one particular group were studied and, in a few cases, major element variations within single tektites. No data for intra‐sample trace element variations existed. Thus, we sectioned a Muong Nong‐type tektite fragment from Vietnam and a splash‐form tektite fragment from the Philippines into eleven and six pieces, respectively, and analyzed the individual fragments for major and trace element contents. The compositions obtained agree well with those found in previous studies, supporting argument that tektites have been derived from terrestrial upper crustal sediments. Chemical variations within the tektite fragments are present, but do not show any systematic trends, probably reflecting incomplete mixing of parent rocks. The intra‐sample heterogeneity of the Muong Nong‐type tektite is more pronounced than that in the philippinite. For the Muong Nong‐type tektite, the intra‐sample variation in the trace element contents is higher than that for the major elements, again reflecting target rock properties. For the philippinite the intra‐sample variations mostly do not exceed the limits imposed by the precision of the analytical data, confirming that the splash form tektites are indeed well homogenized.     

Australasian microtektites from Antarctica: XAS determination of the Fe oxidation state

The Fe oxidation state and coordination number of 29 impact glass spherules recently recovered from the Transantarctic Mountains (Antarctica) have been determined by X‐ray absorption near edge structure (XANES) spectroscopy. Based on geochemical, isotopic, and fission track data, these spherules are considered as microtektites from the Australasian tektite/microtektite strewn field. Their find location is the farthest so far discovered from the possible source crater region, and their alkali content is the lowest compared with other published data on Australasian microtektite glasses. The Fe³⁺/(Fe²⁺+Fe³⁺) ratio, determined from the analysis of the pre‐edge peak energy position and integrated intensity, is below 0.1 (±0.04) for all the samples, and is comparable to that of most tektites and microtektites from the Australasian strewn field. Also, the pre‐edge peak integrated intensity, which is sensitive to the average Fe coordination geometry, is comparable to that of other Australasian microtektites reported in the literature. The agreement of the Fe oxidation state and coordination number, between the Transantarctic Mountain microtektites (TAM) and the Australasian tektites and microtektites, further confirms the impact origin of these glass spherules and provides an independent suggestion that they represent a major extension southeastward of the Australasian strewn field. The fact that similar redox conditions are observed in tektites and microtektites within the Australasian strewn field regardless of the distance from the source crater area (up to approximately 11000 km) could be an important constraint for better understanding the different processes affecting microtektite formation and transport. The fact that the Fe oxidation state of microtektites does not increase with distance, as in the case of North American microtektites, means that thermal and redox histories of Australasian and TAM microtektites could differ significantly from those of North American microtektites.     

Weathering and polymerization of tektites: An x-ray photoelectron spectroscopy (XPS) investigation

Abstract— Tektites are natural glasses formed from terrestrial material that was melted and displaced by the impact of an extraterrestrial body. The surface and near-surface compositions of tektite glass results from fractionation during impact and ejection, and/or postsolidification weathering. The first goal of this study was to characterise the surface and near-surface (in the order of tens of angstroms) chemical composition of two tektites by x-ray photoelectron spectroscopy (XPS), and to estimate the importance of weathering vs. fractionation during flying. In order to separate the chemical modification due to weathering from that due to fractionation during ballistic flight, we studied two samples from the Australasian tektite strewn field. One of them was collected in a hot desert area (Nullarbor Plain, Australia) and the other, in a humid climate (Thailand). Our study reveals the presence of well-developed leached layers in both tektites. In the Australian tektite, Si is depleted in the topmost layers (a few tens of angstroms). A more complex chemical zoning is defined in the tektite from Thailand. These leached layers are comparable to those observed in weathered glasses, and therefore we conclude that weathering is responsible for the chemical composition of the surface and near-surface compositions. The second goal was to investigate the chemical environment of O, N and C in the glass. The O peak was resolved into two bridging O components (Si-O-Si and Al-O-Si) that are comparable to O environments in artificial glasses. The binding energy of the C_1s electron is typical for C-C and C-H bonds in hydrocarbons; minor organic acid components are also present. Nitrogen is only observed on the surface of the Thailand tektite. The binding energy of N_1s is comparable to that of ammonia, and the surface enrichment in N is interpreted as due to sorption related to interactions between glass and fluid buffered by the organic material in the soil.     

LATE EOCENE IMPACT MICROSPHERULES: STRATIGRAPHY,AGE AND GEOCHEMISTRY

Recent discoveries of microtektite and related crystal bearing microspherule layers in deep-sea sediments of the west equatorial Pacific DSDP Sites 292, 315A and 462, off-shore New Jersey in Site 612 and in southern Spain have confirmed the presence of at least three microspherule layers in Late Eocene sediments. Moreover, these discoveries have extended the North American strewn field from the Caribbean and Gulf of Mexico region to the northwest Atlantic, and have established a third strewn field in western equatorial Pacific and Indian Ocean which may extend to the Mediterranean. Stratigraphically the oldest microspherule layer occurs in the planktonic foraminifer Globigerapsis semiinvoluta Zone about 0.5 m.y. prior to the closely spaced crystal bearing microspherule layer and North American microtektite layer in the Globorotalia cerroazulensis Zone. Major element composition of the G. semiinvoluta Zone layer and the crystal bearing microspherule layer overlap, but there is a clear trend towards higher Al₂O₃ and FeO values in SiO₂ equivalent microspherules of the latter layer. The G. semiinvoluta Zone microspherules also contain a higher percentage of non-crystalline spherules (microtektites) than the crystal bearing microspherule layer, but lower than the North American microtektite layer. Excess iridium due to an abrupt increase in supply is associated with the middle crystal bearing microspherule layer and to a lesser extent with the other two layers. But, Ir excess due to concentration as a result of carbonate loss was also observed at two sites (462, 612). The three late Eocene microspherule layers do not precisely coincide with planktonic foraminiferal species extinctions, but a major faunal assemblage change is associated with the G. semiinvoluta Zone layer. Abundant pyrite is present in the North American microtektite layer of DSDP Site 612 suggesting reducing conditions possibly due to a sudden influx of biologic matter (dead bodies) to the ocean floor, and the crystal bearing microspherule layer coincides with five radiolarian extinctions. All three microspherule layers are associated with decreased carbonate possibly due to sudden productivity changes, increased dissolution as a result of sea-level and climate fluctuations, or the impact events.     

Ablated tektite from the central Indian Ocean

Abstract A well-preserved ablated (button-shaped) tektite recovered from the surface sediments of the central Indian Ocean lacks flow ridges and has apparently undergone ablation of 6.9 to 7.9 mm. The lack of flow ridges and amount of ablation indicate that, if it originated in Southeast Asia, it must have had a very shallow trajectory (only a few degrees) and a velocity on the order of 7 km/s as it re-entered the atmosphere. The central Indian Ocean tektite is compositionally similar to high-magnesium (HMg) australites found at Serpentine Lakes and Lake Wilson, Australia, and to some HMg microtektites found in deep-sea sediments from the central Indian Ocean. This discovery supports a previous conclusion that the Australasian tektite strewn field covers most of the Indian Ocean.     

Exploration of tektite formation processes through water and metal content measurements

Abstract– Impact events are a significant surface‐modifying process on solar system objects lacking frequent resurfacing by atmospheric or igneous processes. To better explore the effects of impacts on surface materials, we measured the water and trace element compositions of tektites from Da Lat, Vietnam. Fourier transform infrared spectroscopy was used for water measurements and laser ablation inductively coupled plasma mass spectrometry was used for trace element measurements. Consistent with previous investigations of tektites, we found that the samples are depleted in volatile metals (e.g., Zn, Pb) as well as in water compared with the average continental crust, although water contents are still extremely high for rocks melted at atmospheric pressure. While Zn and Pb concentrations are linearly correlated with each other, there is no correlation between H₂O and Zn or Pb contents. Combined with water contents of other tektites in the Australasian strewn field, our results demonstrate that the source impact occurred at a wet site in or off the coast of the Indochina peninsula.     

Variation of chemical composition in Australasian tektites from different localities in Vietnam

Abstract— One hundred and thirteen Australasian tektites from Vietnam (Hanoi, Vinh, Dalat, and Saigon areas) were analyzed for their major and trace element contents. The tektites are either of splash form or Muong Nong‐type. The splash‐form tektites have SiO₂ contents ranging from 69.7 to 76.8 wt%, whereas Muong Nong‐type tektites, which are considerably larger than splash‐form tektites and have a blocky and chunky appearance, have slightly higher silica contents in the range of 74–81 wt%. Major‐element relationships, such as FeO versus major oxides, Na₂O versus K₂O, and oxide ratio plots, were used to distinguish the different groups of the tektites. In addition, correlation coefficients have been calculated for each tektite group of this study. Many chemical similarities are noted between Hanoi and Vinh tektites from the north of Vietnam, except that the Hanoi tektites contain higher contents of CaO than Vinh; the higher content of CaO might be due to some carbonate parent material. Both Dalat and Saigon tektites have nearly similar composition, whereas the bulk chemistries of the tektites from Hanoi and Vinh appear different from those of Saigon and Dalat. There are differences, especially in the lower CaO and Na₂O and higher MgO, FeO, for the tektites of Dalat and Saigon in comparison to that of Hanoi tektites. Furthermore, the Dalat and Saigon tektites show enrichments by factors of 3 and 2 for the Ni and Cr contents, respectively, compared to those of Hanoi and Vinh. The difference in chemistry between the North Vietnam tektites (Hanoi, Vinh) to that of South Vietnam tektites (Saigon, Dalat) of this study indicate that the parent material was heterogeneous and possibly mixing between different source rocks took place. Muong Nong‐type tektites are enriched in the volatile elements such as Br, Zn, As, and Sb compared to the average splash‐form tektites of this study. The chemical compositions of the average splash‐form and Muong Nong‐type tektites of this study closely resemble published data for average splash‐form and Muong Nong‐type indochinites, indicating that they have the same source. The trace element ratios Ba/Rb (2.7), Th/U (5.2), Th/Sc (1.3), Th/Sm (2.2), and the rare earth element (REE) abundances of this study show close similarities to those of average upper continental crust.     

A review of volatile compounds in tektites,and carbon content and isotopic composition of moldavite glass

Abstract– Tektites, natural silica‐rich glasses produced during impact events, commonly contain bubbles. The paper reviews published data on pressure and composition of a gas phase contained in the tektite bubbles and data on other volatile compounds which can be released from tektites by either high‐temperature melting or by crushing or milling under vacuum. Gas extraction from tektites using high‐temperature melting generally produced higher gas yield and different gas composition than the low‐temperature extraction using crushing or milling under vacuum. The high‐temperature extraction obviously releases volatiles not only from the bubbles, but also volatile compounds contained directly in the glass. Moreover, the gas composition can be modified by reactions between the released gases and the glass melt. Published data indicate that besides CO₂ and/or CO in the bubbles, another carbon reservoir is present directly in the tektite glass. To clarify the problem of carbon content and carbon isotopic composition of the tektite glass, three samples from the Central European tektite strewn field—moldavites—were analyzed. The samples contained only 35–41 ppm C with δ¹³C values in the range from ?28.5 to ?29.9‰ VPDB. This indicates that terrestrial organic matter was a dominant carbon source during moldavite formation.     

New occurrences of Australasian microtektites in the Central Indian Basin

Abstract— Thirty-three microtektites have been recovered from four different sites in the Central Indian Basin. Based on their physical properties, geographical occurrence and chemical composition, they are identified as belonging to the Australasian tektite strewn field. Microtektites from three of the sites under study are from surficial samples implying bioturbation and/or erosion or non-deposition.     

Moldavites from Austria

Abstract— Several moldavites have been discovered in the northern part of Lower Austria. Tektites from two new locations (Altenburg and Radessen) have been analyzed. These new finds lend credibility to old reports about tektites from Lower Austria, some of which are associated with artefacts of prehistoric cultures. The new locations are situated between the Bohemian and Moravian parts of the moldavite strewn field, which is thus shown to extend further south than previously known. Most of the samples show clear indications of surface alterations by water and/or humic substances, and one sample shows signs of fluviatile transport. The geological setting of the moldavite-bearing sediments is similar to the Czechoslovakian occurrences but is probably less disturbed. Chemically the samples show considerable variations even within one location. No unambiguous association with either the Bohemian or the Moravian group is evident either for the major or trace element abundances.