The Aouelloul crater, Mauritania: On the problem of confirming the impact origin of a small crater

Koeberl, Christian; Reimold, W. U.; Shirey, Steven B.

doi:10.1111/j.1945-5100.1998.tb01655.x

Cited by 27 publications

(13 citation statements)

References 27 publications

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“…Both data sets suggest upward turning of basalt fl ows along the crater wall similar to the impact deformation of target rocks at other simple craters (Shoemaker, 1960;Shoemaker and Eggleton 1961;Brandt and Reimold, 1995;Koeberl et al, 1998;Reimold et al, 1998b). Kumar (2005) also suggested that the major faulting and slumping present at the NNE sector of the crater (Fig.…”

Section: Discussionmentioning

confidence: 93%

Structural and anisotropy of magnetic susceptibility (AMS) evidence for oblique impact on terrestrial basalt flows: Lonar crater, India

Misra

Arif

Basavaiah

et al. 2009

Geological Society of America Bulletin

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The anisotropy of magnetic susceptibility (AMS) technique, combined with the analyses of satellite images and the geological structure, are examined on Lonar crater , a small, ~1.8-km-diameter impact crater in India, to evaluate the direction and obliquity of asteroid impact. The Advanced Spaceborne Thermal Emission and Refl ection Radiometer (ASTER) image (15-m resolution) of the ca. 52 ka Lonar crater in the subhorizontal Deccan basalt (ca. 65 Ma) shows that this simple, bowl-shaped impact crater has a near-circular rim with a circularity of ~0.95. Most of the highly refl ecting, continuous-ejecta blanket around the crater rim can be enveloped with an ellipse whose major E-W axis is coincident with the diameter of the crater rim and minor N-S axis is relatively displaced toward the west by ~200 m. The present ejecta distribution, which appears to be close to its pristine shape, extends to a distance of ~700 m in all the directions from the crater rim except to the west where it extends to a distance of a little more than 1 km. The circular shape of the crater rim, the E-W bilateral symmetry of the enveloping ellipse on the ejecta, and the greater extension of the ejecta toward the west appear to be the result of an oblique impact from the east with an angle of incidence of 30°-45° when compared with experiments. The AMS data suggest that the target basalts occurring at ~2 km west-southwest of the crater rim are highly shocked, as indicated by the random orientation of their K 3 susceptibility axes in comparison to the unshocked basalts at ~2 km east-southeast of the crater; the unshocked basalts show a bimodal distribution of susceptibility axes typical of lava fl ows. Moderate to strong westward shifts of the K 3 axes are seen for the majority of the shocked basalts on the crater rim and westsouthwest of the crater; the shocked basalts also indicate an oblique impact from the east when compared with modeling and experiments. A general lowering of degree of anisotropy of the Lonar shocked basalts (~1.01) compared to the surrounding unshocked basalts (~1.03) is found to be a characteristic feature of impact crater target rocks. Variation in attitudes of the basalt fl ows on the Lonar crater rim shows a bilaterally symmetrical distribution about an E-W axial plane, which includes quaquaversal dips of the fl ows all around the crater rim, except to the west where overturned dips of the basalt fl ows are seen. It appears that oblique impact and the symmetry in structural variations around the crater rim have a relationship for a small crater such as Lonar.

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Section: Discussionmentioning

confidence: 93%

Structural and anisotropy of magnetic susceptibility (AMS) evidence for oblique impact on terrestrial basalt flows: Lonar crater, India

Misra

Arif

Basavaiah

et al. 2009

Geological Society of America Bulletin

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“…(); (14) Taylor (); (15) Smith and Hodge (); (16) Hodge and Wright (); (17) Gurov and Gurova (); (18) Koeberl et al. (); (19) McHone et al. (); (20) Bunch and Cassidy (); (21) Reimold et al.…”

Section: Discussionmentioning

confidence: 99%

Shock metamorphism and impact melting in small impact craters on Earth: Evidence from Kamil crater, Egypt

Fazio

Folco

D’Orazio

et al. 2014

Meteorit & Planetary Scien

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Kamil is a 45 m diameter impact crater identified in 2008 in southern Egypt. It was generated by the hypervelocity impact of the Gebel Kamil iron meteorite on a sedimentary target, namely layered sandstones with subhorizontal bedding. We have carried out a petrographic study of samples from the crater wall and ejecta deposits collected during our first geophysical campaign (February 2010) in order to investigate shock effects recorded in these rocks. Ejecta samples reveal a wide range of shock features common in quartz‐rich target rocks. They have been divided into two categories, as a function of their abundance at thin section scale: (1) pervasive shock features (the most abundant), including fracturing, planar deformation features, and impact melt lapilli and bombs, and (2) localized shock features (the least abundant) including high‐pressure phases and localized impact melting in the form of intergranular melt, melt veins, and melt films in shatter cones. In particular, Kamil crater is the smallest impact crater where shatter cones, coesite, stishovite, diamond, and melt veins have been reported. Based on experimental calibrations reported in the literature, pervasive shock features suggest that the maximum shock pressure was between 30 and 60 GPa. Using the planar impact approximation, we calculate a vertical component of the impact velocity of at least 3.5 km s−1. The wide range of shock features and their freshness make Kamil a natural laboratory for studying impact cratering and shock deformation processes in small impact structures.

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“…The composition of the glass is similar to that of the sandstone in which the crater is exposed, but some siderophile elements are enriched in the glass (Koeberl and Auer 1991). Re-Os isotope studies of the target sandstone and the impact glass demonstrated the presence of a distinct extraterrestrial component in the glass (Koeberl et al 1998). …”

Section: Samplesmentioning

confidence: 96%

“…The fission track and K-Ar dating of the impact glass show that this crater was formed 3.1 ± 0.3 Ma ago (Fudali and Cressy 1976;Storzer and Wagner 1977). The 390-m-diameter crater is exposed in an area of Ordovician Oujeft quartzite and Zli sandstone (Koeberl et al 1998). Aouelloul impact glasses contain lechatelierite and baddeleyite (El Goresy 1965;El Goresy et al 1968), partly digested quartz and feldspar grains, low water content (Beran and Koeberl 1997), and abundant schlieren of different chemical composition (Koeberl 1994).…”

Section: Samplesmentioning

confidence: 99%

Infrared, Raman, and cathodoluminescence studies of impact glasses

Gucsik

Koeberl

Brandstätter

et al. 2004

Meteorit & Planetary Scien

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Abstract-We studied the infrared reflectance (IR), Raman, and cathodoluminescence (CL) spectroscopic signatures and scanning electron microscope-cathodoluminescence (SEM-CL) images of three different types of impact glasses: Aouelloul impact glass, a Muong Nong-type tektite, and Libyan desert glass. Both backscattered electron (BSE) and CL images of the Muong Nong-type tektite are featureless; the BSE image of the Libyan desert glass shows only weak brightness contrasts. For the Aouelloul glass, both BSE and CL images show distinct brightness contrast, and the CL images for the Libyan desert glass show spectacular flow textures that are not visible in any other microscopic method. Compositional data show that the SiO 2 composition is relatively higher and the Al 2 O 3 content is lower in the CL-bright areas than in the CL-dark regions. The different appearance of the three glass types in the CL images indicates different peak temperatures during glass formation: the tektite was subjected to the highest temperature, and the Aouelloul impact glass experienced a relatively low formation temperature, while the Libyan desert glass preserves a flow texture that is only visible in the CL images, indicating a medium temperature.All IR reflectance spectra show a major band at around 1040 to 1110 cm −1 (antisymmetric stretching of SiO 4 tetrahedra), with minor peaks between 745 and 769 cm −1 (Si-O-Si angle deformation). Broad bands at 491 and 821 cm −1 in the Raman spectra in all samples are most likely related to diaplectic glass remnants, indicating early shock amorphization followed by thermal amorphization. The combination of these spectroscopic methods allows us to deduce information about the peak formation temperature of the glass, and the CL images, in particular, show glass flow textures that are not preserved in other more conventional petrographic images.

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The Aouelloul crater, Mauritania: On the problem of confirming the impact origin of a small crater

Cited by 27 publications

References 27 publications

Structural and anisotropy of magnetic susceptibility (AMS) evidence for oblique impact on terrestrial basalt flows: Lonar crater, India

Structural and anisotropy of magnetic susceptibility (AMS) evidence for oblique impact on terrestrial basalt flows: Lonar crater, India

Shock metamorphism and impact melting in small impact craters on Earth: Evidence from Kamil crater, Egypt

Infrared, Raman, and cathodoluminescence studies of impact glasses

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