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Abstract

  1. Top of page
  2. Abstract
  3. Introduction
  4. The Kamil Impact Crater
  5. Samples and Methods
  6. Results
  7. Discussion
  8. Conclusions
  9. References

Abstract– The 45 m in diameter Kamil impact crater was formed <5000 yr ago in the eastern Sahara, close to the southern border of modern Egypt. The original features of this structure, including thousands of fragments of the meteorite impactor, are extremely well preserved. With the exception of a single 83 kg regmaglypted individual, all specimens of Gebel Kamil (the iron meteorite that formed the Kamil crater) are explosion fragments weighing from <1 g to 34 kg. Gebel Kamil is an ungrouped Ni-rich (about 20 wt% Ni) ataxite characterized by high Ge and Ga contents (approximately 120 μg g−1 and approximately 50 μg g−1, respectively) and by a very fine-grained duplex plessite metal matrix. Accessory mineral phases in Gebel Kamil are schreibersite, troilite, daubréelite, and native copper. Meteorite fragments are cross-cut by curvilinear shear bands formed during the explosive terrestrial impact. A systematic search around the crater revealed that meteorite fragments have a highly asymmetric distribution, with greater concentrations in the southeast sector and a broad maximum in meteorite concentration in the 125–160° N sector at about 200 m from the crater rim. The total mass of shrapnel specimens >10 g, inferred from the density map compiled in this study is 3400 kg. Field data indicate that the iron bolide approached the Earth’s crust from the northwest (305–340° N), travelling along a moderately oblique trajectory. Upon hypervelocity impact, the projectile was disrupted into thousands of fragments. Shattering was accompanied by some melting of the projectile and of the quartz-arenite target rocks, which also suffered shock metamorphism.


Introduction

  1. Top of page
  2. Abstract
  3. Introduction
  4. The Kamil Impact Crater
  5. Samples and Methods
  6. Results
  7. Discussion
  8. Conclusions
  9. References

Macroscopic meteorites genetically related to impact craters have rarely been found on Earth. During high-energy crater forming impacts, the meteoritic projectile is largely or completely melted and/or vaporized (e.g., Melosh 1989); any meteorite fragments that survive the impact are thereafter subjected to terrestrial weathering that rapidly degrades the fragments, eventually reducing them to mere geochemical anomalies within the impacted target rocks. Accordingly, it is not surprising that small-scale and geologically young impact craters are those in which macroscopic remnants of the meteoritic projectile have been more frequently found. Among the 178 impact craters so far identified on Earth (Earth Impact Database, http://www.passc.net/EarthImpactDatabase/index.html, accessed May 2011), only 27 (approximately 15%) are both Quaternary in age and <4 km in diameter (4 km is generally assumed as the transition diameter from simple to complex terrestrial craters; e.g., Grieve et al. 1981). Many (18 of 27) of these small, young craters are associated with certainty to iron or stony-iron meteorite impactors (e.g., Sikhote Alin, Barringer, Campo del Cielo, Whitecourt, Kaalijarv, Morasko, Dalgaranga, Wabar, etc.).

The understanding of how small impact craters form and assessment of the hazard that small-scale impacts pose to the human population have largely benefited from information obtained from the study of both the geology and morphology of craters (e.g., nature of the target rocks, crater diameter and depth, thickness of the brecciated crater filling, geometry of the ejecta blanket, etc.) and of meteorite fragments (e.g., their spatial and size distribution, shape and structure, and total mass; e.g., Bland and Artemieva 2006; Tancredi et al. 2009; Kofman et al. 2010). Until recently, the main limitation to such studies has been the incomplete preservation of the impact structure and meteorite fragments. The recent discovery of the 45 m-diameter Kamil crater in southwestern Egypt (Folco et al. 2010, 2011) has provided us with an exceptional example of a small impact structure that is still very close to its pristine state. Due to its very young age (probably <5000 yr) and the ideal dry climatic conditions in the Sahara Kamil crater preserves rayed ejecta, various types of shock-metamorphosed materials (including impact melt rocks) and a nearly intact assemblage of fragments of the iron meteorite impactor. This article focuses on the full petrographic, mineralogical, and geochemical characterization of the Gebel Kamil meteorite, its field distribution, and the impact dynamics, thus expanding upon the preliminary information reported in Folco et al. (2010, 2011) and in Meteoritical Bulletin No. 98 (Weisberg et al. 2010). Results have implications for the impactor mass, the incident direction of the impactor, the mechanism of shrapnel formation, and the impact scenario.

The Kamil Impact Crater

  1. Top of page
  2. Abstract
  3. Introduction
  4. The Kamil Impact Crater
  5. Samples and Methods
  6. Results
  7. Discussion
  8. Conclusions
  9. References

Kamil crater (Fig. 1) is located in a rocky desert plain approximately 600 m above sea level in the East Uweinat district of southwestern Egypt (22°01′06″ N, 26°05′15″ E). It was identified during a Google Earth survey in 2008. In February 2010, we undertook a geophysical survey to confirm the impact origin of the crater. A first report of this geophysical survey is given in Folco et al. (2010, 2011).

image

Figure 1.  Kamil crater, southwestern Egypt (enhanced true color QuickBird satellite image taken 22 October 2005; courtesy of Telespazio). Note the simple crater structure and prominent ejecta ray pattern. Inset: location map.

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Kamil crater is a 45 m-diameter simple crater with an ejecta ray structure (Fig. 1). It occurs on exposed pale sandstones (mainly quartz-arenites) belonging to the Gilf Kebir Formation (Lower Cretaceous). It is bowl-shaped, 16 m deep, and has an upraised rim approximately 3 m above the average pre-impact surface. The crater floor is overlain by an approximately 6 m-thick crater-fill material consisting of displaced blocks and fallback debris. An eolian sand deposit covers the northern wall of the crater. An ejecta blanket extends radially for approximately 50 m from the crater rim. The three longest ejecta rays extend as far as 350 m from the crater rim in northward, southeast, and southwest directions.

Thousands of iron meteorite specimens were found scattered within the crater and in the surrounding area up to 1.6 km east of the crater rim. With the exception of an 83 kg regmaglypted individual, meteorite specimens are shrapnel (explosion fragments). No buried masses greater than a few tens of kilograms were identified during a geomagnetic survey in and around Kamil crater. Centimeter-scale masses of impact glass occur in and around the crater.

A prehistoric trail, approximately 100 m due north of the crater, is overlain by rock blocks ejected from the crater. There is no evidence of tools made from the iron meteorite in the ruins of prehistoric settlements a few hundred meters from the crater. Folco et al. (2011) thus concluded that the impact occurred sometime during the last approximately 5000 yr, after the onset of hyperarid conditions and the consequent human exodus toward the Nile River valley (Kuper and Kröpelin 2006). This inference is consistent with the high degree of preservation of the Kamil crater and its ejecta ray structure. Such well-preserved rayed structures are only observed elsewhere associated to the impact craters of atmosphere-free bodies within the solar system.

Samples and Methods

  1. Top of page
  2. Abstract
  3. Introduction
  4. The Kamil Impact Crater
  5. Samples and Methods
  6. Results
  7. Discussion
  8. Conclusions
  9. References

The systematic search for Gebel Kamil meteorites was first conducted by a team of seven people within a 450 × 450 m area centered on the crater (Fig. 2a), which was subdivided into 50 × 50 m cells to optimize operations. Due to the large number of meteorites, we focused on specimens greater than or equal to approximately 10 g. All specimens were collected and their position recorded. Note that, due to the limited cargo space, only half of this lot of specimens was transported to Cairo at the end of the 2010 field survey. The other half was left in the field.

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Figure 2.  The meteorite distribution around Kamil crater derived from a systematic search carried out during our geophysical survey in February 2010. a) Maps showing the 50 × 50 m gridded area (gray cells) around the crater, where the systematic search was conducted. The roughly radial and concentric traverses are also shown. b) Meteorite distribution map showing the location of shrapnel <5 kg (small white circles) and >5 kg (large gray circles) and that of the 83 kg regmaglypted individual (white star). Dashed line outlines the area featured in (c). c) Meteorite density map (g m−2) obtained through linear interpolation of average meteorite density values of 50 × 50 m cells positioned at their centers. Contour lines are shown at 5 g m−2 intervals.

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A systematic search was subsequently conducted along a number of concentric and radial traverses up to 1.7 km from the crater (Fig. 2a) by a team of five people spaced 7–10 m apart. With the exception of an 83 kg specimen (see below) which was collected and transported to the Egyptian Geological Museum in Cairo, meteorite specimens identified in this instance were weighed and left in the field after recording their general features and GPS position.

Long-range surveys up to 5 km from the crater were also conducted to check the limits of the strewn field. Field data indicate that the survey covered approximately 50% of the meteorite-bearing surface and allowed us to produce the meteorite distribution map shown in Fig. 2b, the meteorite density map shown in Fig. 2c, and the shrapnel weight versus distance from the crater plots shown in Fig. 3. The surface density contour lines in Fig. 2c were generated through linear interpolation of average meteorite density values for 50 × 50 m cells (values were assumed to be positioned at the center of cells).

image

Figure 3.  a) The meteorite distribution around Kamil crater, and the 132–135° N trending ejecta ray. Small white circles, shrapnel fragments <5 kg; large gray circles, shrapnel fragments >5 kg; white star, the 83 kg regmaglypted individual. b) Meteorite specimen mass (kg) versus distance from the crater (m) for the whole population of recovered shrapnel fragments. c) Meteorite specimen mass (kg) versus distance from the crater (m) for the shrapnel fragments recovered along the 132–135° N ejecta ray.

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The samples analyzed for this study were taken from the collections of specimens maintained at Siena University’s Museo Nazionale dell’Antartide (15 kg) and Pisa University’s Museo di Storia Naturale e del Territorio (5 kg). These specimens were allocated to these two Italian institutions as a permanent loan for research and public exhibition purposes within the framework of the “Egypt-Italy Science Year 2009 (EISY 2009).”

Mineral compositions were determined with a CAMECA SX50 electron microprobe fitted with four wavelength dispersive spectrometers at the CNR Istituto di Geoscienze e Georisorse in Padova. Running conditions were 20 kV accelerating voltage, 20 nA beam current, and 1 μm nominal beam spot. Counting times at peak and background wavelengths were, respectively, 10 s and 5 s for P, S, Cr, Fe, Ni, whereas they were both increased to 20 s for Si and Co. The manufacturer-supplied PAP procedure was employed for raw data reduction. Pure elements (Fe, Co, Ni, Cu, and Cr) and mineral (apatite for P, sphalerite for S, and diopside for Si) standards were used for instrumental calibration.

Bulk chemical analysis of Gebel Kamil meteorite samples was performed at Pisa University’s Dipartimento di Scienze della Terra by conventional inductively coupled plasma–mass spectrometry (Thermo PQII Plus), following a modified version of the procedure described in D’Orazio and Folco (2003); to obtain better accuracy, the sample solutions were measured using the method of standard addition instead of external calibration.

Backscattered electron (BSE) images of polished slices and semiquantitative chemical analyses were obtained at Pisa University’s Dipartimento di Scienze della Terra with a Philips XL30 Scanning Electron Microscope operating at 20 kV coupled with an X-ray energy dispersive spectrometer.

Results

  1. Top of page
  2. Abstract
  3. Introduction
  4. The Kamil Impact Crater
  5. Samples and Methods
  6. Results
  7. Discussion
  8. Conclusions
  9. References

Field Distribution of Meteorites

An 83 kg specimen, detached from the main mass of the Gebel Kamil meteorite before impact with the ground, was found during a reconnaissance traverse approximately 230 m due north of the Kamil crater (Figs. 2b and 4a; 22°01′13.5″ N 26°05′15.4″ E) prior to systematic search (see below). It was found sitting on the desert soil with no associated crater, and is the only individual found in the Kamil crater area.

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Figure 4.  Photos of the 83 kg Gebel Kamil meteorite individual. a) The specimen in its find position 230 m due north of the crater (the pen is 14 cm long). b) Close-up of the surface of the meteorite showing well-developed regmaglypts up to 3–4 cm wide and remnants of the fusion crust (white arrows). Millimeter-sized linear pits due to the selective melting of large schreibersite and troilite + daubréelite crystals (black arrows) are also shown.

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The systematic search in the 450 × 450 m gridded area centered on the crater (Figs. 2a and 2b) led to the recovery of 3673 shrapnel specimens greater than or equal to approximately 10 g for a total of approximately 1179 kg. During subsequent searches along concentric and radial traverses up to 1.7 km from the crater, 1544 meteorite specimens with a total mass of 531 kg were identified. The largest shrapnel weighs 34 kg and was found on the southern rim of the crater (Fig. 5d). Shrapnel specimens were found either on exposed bedrock or partially buried in soil (Fig. 5). All specimens were found with their exposed surface finely pitted due to wind erosion, and their surfaces in contact with the ground partially oxidized due to terrestrial weathering. No meteorite accumulations indicative of selective mass transport and redeposition were identified anywhere in the area. No meteorites were found during long-range (greater than approximately 1.7 km from the crater) surveys.

image

Figure 5.  Photos of Gebel Kamil meteorite shrapnel specimens in the field. a) A 2.5 kg specimen showing jagged margins and a twisted edge (ruler scale in cm). b) An 8.7 kg specimen showing a smooth, rounded shape (ruler scale in cm). c) Four small specimens found on a large quartz-arenite block (the largest meteorite on the right is 3.0 cm long). d) A 34 kg specimen (the second largest specimen after the 83 kg individual) found on the southern crater rim (photo not taken at the find location). e) A concentration of meteorite fragments lying on the southeastern wall of the crater (the large quartz-arenite boulder indicated by the arrow is 20 cm long).

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The meteorite distribution map in Fig. 2b shows that the distribution of shrapnel is not uniform. The 276 specimens recovered from within the crater were found scattered along its southeastern wall (Fig. 5e). Specimens around the crater are concentrated in the plains due southeast of the crater up to 1.3 km from the crater rim, with some isolated finds up to 1.6 km east of the crater. Only six specimens were found in the northwestern quadrant within 50 m of the northwestern crater rim. With the exception of two ENE-SSW trending ridges (mineralized faults) as high as 30 m above the average ground level and about 150 m from the crater rim, the area due northwest of the crater is morphologically similar to the desert plains due southeast of the crater. The highest concentration of meteorite specimens was found in the latter area, within a few hundred meters of the crater rim.

Figure 2b also shows that the large shrapnel specimens (>5 kg) are preferentially concentrated southeast of the crater and within approximately 500 m of its rim. Many clusters of specimens were found due northeast, east, and southeast of the crater up to 300 m from the crater rim. Each cluster consists of tens of specimens of variable size (total mass up to 7.5 kg) arranged in irregular circles up to 1.5 m in diameter (Figs. 6a and 6b). They probably represent ejected shrapnel specimens shattered upon impact with the ground.

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Figure 6.  Clusters of meteorites consisting of tens of shrapnel specimens of variable size arranged in irregular circles up to 1.5 m in diameter. These clusters probably represent large ejected meteorite fragments that shattered upon impact with the ground. The orange handle of the magnet stick in (a) is 13 cm long, whereas the handheld GPS in (b) is 11 cm long.

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Figure 2c shows that meteorite fragments are concentrated due southeast of the crater also in terms of mass. A peak density in excess of 80 g m−2 is found along the southeastern ejecta ray about 200 m from the crater rim in a 125–160° N direction. Little or no meteoritic material is found along the other two major ejecta rays due southwest and north, respectively. According to our density map, the total mass of the impactor in the form of shrapnel >10 g present at the surface around the Kamil crater amounts to approximately 3400 kg.

Figure 3 reveals another characteristic of the shrapnel field. The shrapnel mass (uncorrected for shattering; see above) tends to decrease with distance from the crater rim. In particular, large masses are frequently found within 500 m of the crater rim; many are in the approximately 5 kg to approximately 10 kg range, and some are as heavy as approximately 34 kg. At greater distances, masses larger than 5 kg are rare and most specimens are smaller than approximately 2.5 kg.

External Morphology

The overall dimensions of the individual specimen of the Gebel Kamil meteorite are approximately 73 × 24 × 20 cm. It has an elongated shape, with one pointed end, and is completely covered by large, well-developed regmaglypts up to 3–4 cm wide and generally less than 1 cm deep (Fig. 4a). Overall, the external surface is dark brown. Where the surface of the meteorite was better protected from the abrasive action of wind-driven sand, it preserves irregular portions of black fusion crust (Fig. 4b). The surface of the individual specimen typically shows many sharp linear pits about 1 mm wide and several millimeters long, which formed through selective melting of large schreibersite and troilite crystals (Fig. 4b).

The shrapnel fragments of the Gebel Kamil meteorite are covered by a dark-brown oxidation patina and vary in shape from flattened, sharp-edged, and jagged (Fig. 5a) to more rounded, smooth, and equidimensional (Fig. 5b). Samples with twisted edges, as well as with deep indentations, are quite common. The surface of many specimens shows slickensides resulting from shear deformation. The morphology of the Gebel Kamil shrapnel fragments is quite similar to that of other shrapnel irons associated with small impact craters, in particular the Sikhote Alin (Krinov 1966), Whitecourt (Herd et al. 2008; Kofman et al. 2010), and Henbury (Spencer and Hey 1933; Buchwald 1975) craters.

Preimpact Internal Structure and Mineral Chemistry

The examination of several polished and etched sections of Gebel Kamil individual and of shrapnel specimens allowed us to distinguish meteorite structures predating the terrestrial impact (occurring in both the shrapnel and the individual) from those originated during the hypervelocity collision of the meteorite projectile with the target (occurring only in the shrapnel). The deformational structures of the meteorite developed during crater formation will be described in the next section.

Specimens of the Gebel Kamil meteorite show an ataxitic texture with oriented sheen and speckled by numerous millimetric to centimetric crystals of schreibersite and troilite + daubréelite (Fig. 7). These crystals are systematically enveloped within a 50–300 μm-wide inner rim of polycrystalline kamacite (i.e., swathing kamacite), consisting of equant polygonal crystals, and a thinner (approximately 20–40 μm wide) outer rim of taenite (Figs. 8a and 9a). The examination of several slices, covering a total surface area of approximately 250 cm2, revealed that the abundance of large (>0.5 mm) schreibersite and troilite + daubréelite crystals is highly variable, with an average frequency of approximately 1.3 per cm2, and that schreibersite is approximately seven times more abundant than troilite + daubréelite.

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Figure 7.  Polished and etched slices of the Gebel Kamil individual (top) and of a large shrapnel (bottom). Note the curvilinear shear bands in the shrapnel (white arrows), which are totally lacking in the individual. Numerous millimetric crystals of schreibersite and subordinate troilite + daubréelite enveloped in swathing kamacite occur in both sections (black arrows). Also, note how some shear bands are subparallel to the external surface (gray arrow). The black area at the bottom of the shrapnel slice is a large natural hole.

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image

Figure 8.  Optical microscope views (reflected light) of polished Gebel Kamil slices. a) Swathing kamacite enveloping a large schreibersite crystal (plane polarized light, PPL). b) Association of schreibersite, troilite, and daubréelite showing the polycrystalline nature and lamellar twinning of troilite. Shear deformation is highlighted by the displacement of the daubréelite crystal (partially crossed polarized light, XPL). c) Detail of polycrystalline troilite showing a finely recrystallized margin (partially XPL). d) Particle of metallic copper associated with troilite, daubréelite, and schreibersite (PPL). e) Homogeneous area of duplex plessite (PPL). f) Detail of kamacite spindles nucleated on schreibersite and arranged in a Widmannstätten pattern. The kamacite spindles are rimmed by taenite, and are set in a duplex plessite matrix (PPL). Abbreviations: Dau = daubréelite; Kam = kamacite; Sch = schreibersite; Tae = taenite; Tro = troilite. Black areas are polishing defects.

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Figure 9.  Scanning electron microscope images of Gebel Kamil polished sections. a) Composite X-ray map (P Kα, S Kα, Cr Kα, and Ni Kα) of an association of troilite, daubréelite, and schreibersite enveloped in swathing kamacite. b) Backscattered electron (BSE) image of the duplex plessite in a shrapnel specimen. c) BSE image of the duplex plessite in the individual specimen. d) BSE image of kamacite spindles in the duplex plessite matrix. Abbreviations as in Fig. 8.

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Schreibersite forms isolated skeletal and elongated crystals, which can occasionally be up to approximately 20 mm long and approximately 2 mm wide, or grows in association with troilite and daubréelite. Large schreibersite crystals are monocrystalline and fractured. Smaller schreibersite crystals (10–100 μm) are also scattered within the plessite matrix and are characterized by Ni/Fe atomic ratios that are more than twice those of the larger crystals (1.5–1.6 versus 0.5–0.7; Table 1). This marked compositional variation may be mainly related to the crystallization temperature that would have been lower for the small crystals occurring in the metal matrix with respect to the large skeletal crystals (Yoshikawa and Matsueda 1992).

Table 1.   Selected analyses (EPMA) of daubréelite, troilite, and schreibersite.
Analysis#123983955124396400794152023417419 
SampleSSIISSIISSISSII 
Mineraldaudaudaudautrotrotrotroschschschsch matrixsch matrixsch matrixsch matrixd.l.(wt%)
  1. S = shrapnel; I = individual; dau = daubréelite; tro = troilite; sch = schreibersite; <d.l. = below detection limit; n.d. = not determined.

Si (wt%)0.030.020.050.040.030.030.040.040.020.020.050.030.020.050.050.02
P<d.l.<d.l.<d.l.<d.l.<d.l.<d.l.<d.l.<d.l.14.714.714.814.714.415.615.30.02
S43.543.744.044.036.336.336.236.1<d.l.0.06<d.l.<d.l.<d.l.<d.l.<d.l.0.06
Cr36.035.635.836.10.190.250.060.24<d.l.<d.l.<d.l.<d.l.<d.l.<d.l.<d.l.0.06
Fe19.019.319.119.263.363.263.262.550.050.254.632.132.232.332.40.06
Co<d.l.<d.l.<d.l.<d.l.<d.l.<d.l.<d.l.<d.l.0.180.170.300.070.070.060.070.06
Ni<d.l.<d.l.<d.l.<d.l.<d.l.<d.l.<d.l.<d.l.34.134.830.651.852.353.252.20.06
Cun.d.n.d.<d.l.<d.l.n.d.n.d.<d.l.<d.l.n.d.n.d.<d.l.n.d.n.d.<d.l.<d.l.0.06
Total98.698.698.999.399.999.799.598.999.099.9100.498.899.0101.2100.1 
Cation formula (a.p.f.u.) based on 7, 2, 4 atoms for daubréelite, troilite and schreibersite, respectively
Si0.0030.0020.0050.0040.0010.0010.0010.0010.0020.0010.0030.0020.0020.0030.004 
P        0.9720.9640.9650.9810.9601.0131.003 
S3.9693.9823.9943.9780.9960.9980.9981.000 0.004      
Cr2.0282.0012.0072.0190.0030.0040.0010.004        
Fe0.9961.0090.9940.9970.9990.9971.0000.9941.8301.8221.9691.1881.1931.1621.181 
Co        0.0060.0060.0100.0020.0030.0020.002 
Ni        1.1881.2031.0511.8241.8401.8181.810 
Cu                

Troilite occurs as blebs and bars with a maximum length of approximately 10 mm. It is polycrystalline, and is very often found in association with schreibersite (always grown upon troilite) and daubréelite (Fig. 9a). The individual grains of troilite show lamellar twinning with 1–15 μm-wide lens-shaped lamellae (Figs. 8b and 8c). Some troilite grains show undulatory extinction and finely recrystallized margins (Fig. 8c). The composition of troilite is nearly stoichiometric FeS with some additional Cr (Table 1).

Daubréelite has been found exclusively within troilite. This mineral forms gray-colored euhedral platy crystals up to 1 mm long and 200 μm wide (Figs. 8b and 9a) or sets of parallel lamellae 2–5 μm wide. The composition of daubréelite is nearly stoichiometric FeCr2S4 (Table 1).

Shear dislocations offset daubréelite and troilite crystals by tens of micrometers (Fig. 8b). The occurrence of twinned, polycrystalline, and recrystallized troilite and of shear dislocations in daubréelite and troilite in both the shrapnel and individual specimens indicate that the Gebel Kamil meteoroid suffered preterrestrial-impact shock pressures of between 35 and 60 GPa (Schmitt et al. 1993).

Native copper completes the accessory mineral assemblage of Gebel Kamil. It is occasionally found as tiny (50–150 μm) anhedral particles nucleated at the troilite/kamacite or troilite/schreibersite interfaces (Fig. 8d). Copper is preferentially partitioned into sulfur-rich liquid metal with respect to both solid Fe-Ni metal and troilite (Fleet et al. 1993; Chabot et al. 2003); thus, it is expected that it could reach supersaturation levels after a protracted crystallization.

The texture and mineral composition of the metal matrix of Gebel Kamil vary between two extremes: the most abundant type consists of a very fine intergrowth of kamacite (approximately 60 vol%) and taenite (approximately 40 vol%) lamellae (1–5 μm), i.e., duplex plessite (Figs. 8e, 9b, and 9c); the other type consists of the same duplex plessite, plus kamacite spindles arranged in a Widmanstätten pattern (Figs. 8f and 9d). Within each section of the Gebel Kamil meteorite examined in this study, the plessite structure shows a constant orientation, indicating that, at least at the scale of the largest specimen, the metal in the meteorite is monocrystalline. The kamacite spindles are 15–25 μm wide, have an approximately 10 μm-thick rim of taenite, and are often nucleated upon small Ni-rich schreibersite crystals. The kamacite spindles frequently lie in straight lines corresponding to one of the octahedral directions (Figs. 8f and 9d). The composition of the Fe-Ni metal of Gebel Kamil varies between two extremes: the lowest Ni contents (approximately 3.8 wt%) were measured in the kamacite forming the spindles and the Ni-poor part of the duplex plessite, whereas the highest Ni contents (up to 44 wt%) were measured in the taenite forming the rims of the kamacite spindles and the Ni-rich part of the duplex plessite (Table 2). Swathing kamacite has an average Ni content of 5.75 ± 0.49 wt% (1 SD). The shrapnel and individual specimens show no significant differences in mineral chemistry (Tables 1 and 2).

Table 2.   Selected analyses (EPMA) of Fe-Ni metal phases.
Analysis#1113334084122128420422154072527421422 
 SSSIISSIISISSII 
Mineralkamkamkamkamkamkamkamkamkamtaetaetaetaetaetaed.l.(wt%)
 swaswaswaswaswaspinspinspinspinrim swarim swarim spinrim spinrim spinrim spin 
  1. S = shrapnel; I = individual; kam = kamacite; tae = taenite; swa = swathing kamacite; spin = spindle; <d.l. = below detection limit; n.d. = not determined.

Si (wt%)0.02<d.l.<d.l.0.050.060.030.030.050.020.020.050.040.020.060.050.02
P<d.l.<d.l.0.06<d.l.<d.l.<d.l.<d.l.<d.l.<d.l.<d.l.<d.l.<d.l.<d.l.<d.l.<d.l.0.02
S<d.l.<d.l.<d.l.<d.l.<d.l.<d.l.<d.l.<d.l.<d.l.<d.l.<d.l.<d.l.<d.l.<d.l.<d.l.0.06
Cr<d.l.<d.l.<d.l.<d.l.<d.l.<d.l.<d.l.<d.l.<d.l.<d.l.<d.l.<d.l.<d.l.<d.l.<d.l.0.06
Fe94.693.793.992.393.394.093.595.793.666.670.266.568.262.657.40.06
Co1.121.101.081.021.130.991.001.001.000.360.480.340.360.390.220.06
Ni5.235.795.046.706.323.884.763.815.4332.928.333.331.137.042.80.06
Cun.d.n.d.n.d.<d.l.<d.l.n.d.n.d.<d.l.<d.l.n.d.0.11n.d.n.d.0.130.12 
Total100.9100.6100.1100.0100.899.099.3100.6100.199.999.2100.299.8100.1100.6 
Cation formula (a.p.f.u.) based on a total of one atom
Si   0.0010.0010.0010.0010.0010.001 0.0010.001 0.0010.001 
P  0.001             
S                
Cr                
Fe0.9390.9340.9400.9250.9280.9520.9440.9530.9370.6780.7180.6740.6940.6370.583 
Co0.0100.0100.0100.0100.0110.0100.0100.0090.0090.0030.0050.0030.0030.0040.002 
Ni0.0490.0550.0480.0640.0600.0370.0460.0360.0520.3180.2760.3210.3010.3580.413 
Cu          0.001  0.0010.001 

The etched slices of the individual specimen show some textural features related to its atmospheric heating and ablation. Detection of the outermost part of the heat alteration zone is mainly based on the occurrence of melted schreibersite crystals with rounded shapes and dendritic texture (Fig. 10a). The innermost melted crystal, recording temperatures in excess of 1000 °C (Axon 1963), was found approximately 1 mm from the external surface. No obvious structural heat alteration was observed in the fine-grained duplex plessite matrix at the optical microscope scale.

image

Figure 10.  Scanning electron microscope BSE images of polished and etched sections of the Gebel Kamil individual specimen showing textures related to atmospheric heating and ablation. a) Completely molten schreibersite crystal showing Fe-Ni metal dendrites and very fine-grained eutectic texture of the residual melt. b) Multilayered fusion crust made of alternating layers of cellular (thickness, 15–25 μm, M1) and more homogeneous (thickness, 5–10 μm, M2) Ni-rich metallic melts. c) Enlarged view of the inset in Fig. 10b showing details of the texture of the metallic melt layers. Note the tiny spherical vesicles in the Ni-rich metallic veinlets within the cellular layers.

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The sample of the individual specimen available for this study preserves rare and partially eroded portions of the fusion crust. Figures 10b and 10c shows the best-preserved ablated surface of Gebel Kamil (elsewhere, the ablated surface was worn away or partially to completely replaced by limonitic products due to terrestrial weathering). Four microlayers of melted Ni-rich metal can be distinguished: two are 5–10 μm-thick and homogeneous, whereas the other two are thicker (15–25 μm), heterogeneous, and show a cellular texture made of 1–10 μm-wide cells surrounded by tiny (<1 μm-wide) veinlets of Ni-rich metal charged with rounded vesicles. A partially preserved approximately 8 μm-thick iron oxide layer, possibly of primary origin, overlies the four metallic layers. Schreibersite or troilite + daubréelite crystals cut by the external surface of the meteorite were lost due to selective melting during the ablative flight, so that only small pits remain (Fig. 4b).

Deformational Structures Related to the Terrestrial Impact

All the examined sections of the Gebel Kamil shrapnel specimens show macroscopic deformation structures that are lacking in the individual specimen and are therefore definitely related to the crater forming impact event (Fig. 7). Plastic deformation is well developed in the plessite matrix that shows marked “necking” and bending (Figs. 11a and 11b). Very sharp and curvilinear shear bands occur in almost every specimen (Figs. 7, 11a, and 11b); along these bands the crystals of schreibersite and troilite + daubréelite, and the duplex plessite pattern are displaced up to several centimeters. They consist of mylonitised material (Figs. 11c and 11d), as observed in the Henbury meteorite shrapnel specimens (Axon and Steele-Perkins 1975). In the shear bands, kamacite, plessite, and schreibersite show different styles of deformation determined by their extremely different mechanical properties. For instance, Fig. 11c shows a shear band in kamacite exhibiting a ductile mylonitic fabric that envelops a schreibersite crystal undergoing brittle deformation, namely rigid-body faulting and rotation according to the “bookshelf” sliding model. Shear bands are superimposed on the deformational bending as a result of extreme strain in the context of progressive deformation. In some cases, the internal curvilinear displacements are parallel to the external surface of the shrapnel (Fig. 7). It is therefore likely that the meteorite fragments with rounded morphology (e.g., Figs. 5b and 7) formed by separation along these curved surfaces of shear dislocation.

image

Figure 11.  Optical microscope images of polished and etched sections of Gebel Kamil shrapnel specimens showing deformation structures. a) Plastic deformation of the plessite matrix. b) Detail of the previous image showing the rigid displacement of a schreibersite crystal. c) Detail of a large schreibersite crystal enveloped in swathing kamacite showing brittle and ductile deformation, respectively. d) Intensely sheared and comminuted material along a shear band.

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Shocked Target Material, Impact Melts, and Gebel Kamil Meteorites

Some shrapnel specimens had a peculiar lithic material stuck to the surfaces protected from eolian erosion. This material has a dark gray to greenish color, and is dotted with white millimetric particles that may occasionally reach 1 cm in size (Figs. 12a and 12b). Examination under optical and scanning electron microscopes revealed that it is composed of an aggregate of quartz-arenite clasts, loose quartz crystals, and Fe-Ni metal spherules set in a heterogeneous matrix of very fine-grained quartz, vesicular brown to colorless glass, and secondary iron hydroxides. The quartz crystals show widely varying degrees of shock metamorphism, from negligible to very high (>60 GPa). The observed shock deformation textures in quartz vary from planar fractures to strong mosaicism (Fig. 12c) and, possibly, planar deformation features (Fig. 12d). Semiquantitative SEM-EDS analyses indicate that the impact melt silicate glass varies between two endmember compositions: the optically brown type (Fig. 12e) is dominated by SiO2 (approximately 55 wt%), FeOtot (approximately 29 wt%), Al2O3 (approximately 14 wt%), and minor TiO2 and CaO, whereas the colorless type mainly consists of SiO2 (approximately 74 wt%), Al2O3 (approximately 20 wt%), CaO (approximately 4 wt%), and minor TiO2 and FeOtot. The spherules of Fe-Ni metal range from 150 μm to <<1 μm in diameter (Fig. 12f); the larger ones show dendritic textures attesting to their origin as quenched metallic melt droplets. Semiquantitative SEM-EDX analyses indicate higher Ni/Fe ratios than the bulk metal in the Gebel Kamil iron.

image

Figure 12.  Images of the target rock material stuck onto the surfaces of some shrapnel specimens. a, b) Two specimens showing abundant shocked and melted target rock material (black arrows). c) Quartz crystals showing strong mosaicism (transmitted XPL). d) Quartz crystal showing three sets of planar features (possibly planar deformation features; transmitted PPL). e) Brown vesicular iron-rich impact glass (transmitted PPL). f) Tiny subspherical droplets of Fe-Ni metal dispersed in the iron-rich, vesicular, impact glass (SEM BSE image). Images c), d), e), and f) refer to features found in the material sampled from the shrapnel of image (a).

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To our knowledge, this peculiar association of impact melts and shocked minerals with iron meteorite fragments has never been observed before.

Bulk Chemistry and Classification

Subsamples for bulk chemical analysis of the metal in Gebel Kamil were taken from a 535 g shrapnel specimen and from the 83 kg specimen.

With the exception of Sb, the concentrations of the determined elements in the two samples (Table 3) vary within 6% (mostly within 4%). Taking into account analytical uncertainties and the slight heterogeneity of the analyzed materials, this variability is not meaningful. The higher variability of Sb (approximately 11%) is due to the lower analytical precision for this element at the concentration level in Gebel Kamil.

Table 3.   Inductively coupled plasma–mass spectrometry analyses of bulk metal of Gebel Kamil.
SampleShrapnelIndividual
  1. Ni and Co are in wt%, the other elements are in μg g−1. At the concentration levels of Gebel Kamil, the analytical uncertainties (RSD%) are comprised between 2% and 5% for all elements excluding Sb and Re (RSD% ≈ 10–20%; D’Orazio and Folco 2003).

Ni20.620.9
Co0.760.77
Cu436426
Ga49.748.0
Ge121116
As15.615.7
Mo9.910.0
Ru2.302.29
Rh0.730.72
Pd4.84.9
Sb0.280.25
W0.420.42
Re0.040.04
Ir0.550.54
Pt3.73.5
Au1.571.53

The Gebel Kamil meteorite is characterized by high Ni, Co, and Cu contents (approximately 20 wt%, approximately 0.75 wt%, and approximately 450 μg g−1, respectively). The high Ge and Ga contents (approximately 120 μg g−1 and approximately 50 μg g−1, respectively) and low Ir content (0.55 μg g−1) set Gebel Kamil apart from the members of the IVB iron meteorite group, which have relatively high Ni concentrations (from 15.5 wt% to 18.5 wt%), but have Ge and Ga contents more than two orders of magnitude lower and Ir content more than one order of magnitude higher (Walker et al. 2008; Fig. 13). Other irons with Ni concentrations similar to Gebel Kamil belong to the IAB complex (Wasson and Kallemeyn 2002) or are ungrouped irons. As a whole, the bulk chemistry of Gebel Kamil does not fall within any of the known chemical groups; Gebel Kamil is therefore classified as an ungrouped Ni-rich ataxite.

image

Figure 13.  Plots of (a) Ga versus Ni, (b) Ge versus Ni, and (c) Ir versus Ni of bulk metal composition of iron meteorites characterized by Ni contents ranging from 15 to 24 wt%. Note that the Y-axis is in logarithmic scale. Gebel Kamil is an ungrouped iron close in composition to the ungrouped iron Morradal (Norway). Literature data mainly from Wasson and Kallemeyn (2002) and Walker et al. (2008). S, shrapnel specimen; I, individual specimen.

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Gebel Kamil is closely related to the Morradal iron meteorite. Morradal is an ungrouped Ni-rich ataxite found as a single 2.75 kg mass in Norway in 1892 (Buchwald 1975). Like Gebel Kamil, Morradal has a duplex plessite metal matrix with sparse kamacite spindles, crystals of schreibersite (also occurring as smaller-sized crystals in the matrix), and troilite + daubréelite. In terms of Ni (18.7 wt%), Co (0.91 wt%), Cu (580 μg g−1), Ga (48 μg g−1), Ge (106 μg g−1), and Ir (0.61 μg g−1) Morradal is similar to Gebel Kamil. However, Morradal is characterized by a higher degree of terrestrial weathering and, unlike the Egyptian meteorite, it contains shock-melted troilite, but no native copper. Lavielle et al. (1999) estimated a terrestrial age of 12 ± 22 ka for the Morradal iron.

Discussion

  1. Top of page
  2. Abstract
  3. Introduction
  4. The Kamil Impact Crater
  5. Samples and Methods
  6. Results
  7. Discussion
  8. Conclusions
  9. References

Minimum Impactor Mass

The impactor mass is an important parameter for defining the impact scenario and cratering models. Upon hypervelocity impact, the projectile can undergo fragmentation, melting, and vaporization. In general, melting and vaporization become progressively more important than fragmentation with increasing impact velocities. These processes give rise to projectile debris that is found within the ejecta deposit in the form of meteorite fragments and microscopic quench and/or condensation droplets. For instance, meteorite explosion fragments and metallic spheroids occur at the 1.2 km-diameter Barringer crater, Arizona, USA, where they were produced by the Canyon Diablo iron meteorite (e.g., Buchwald 1975; Kring 2007), and at the 36 m-diameter Whitecourt Crater, Alberta, Canada (Kofman et al. 2010).

In this section, we provide an estimate of the mass of the meteorite that produced Kamil crater based on the total amount of meteorite specimens identified during the systematic search carried out in February 2010. Evidence suggests that the observed meteorite distribution was pristine, or nearly so. The fact that all specimens were found with their exposed surface finely pitted due to wind erosion and their surfaces in contact with the ground partially oxidized due to minor terrestrial weathering indicates that these meteorites had never been touched by humans. The overall freshness of the meteorite specimens, the lack of meteorite accumulations, and the pristine status of the ejecta blanket and ejecta rays (Folco et al. 2011) rule out important reworking of the meteorite distribution by geomorphic agents.

The total mass of shrapnel specimens >10 g identified during our systematic search amounts to 1700 kg. Their total mass inferred from the density map in Fig. 2c is 3400 kg. This mass value corresponds to a sphere slightly less than 1 m in diameter (measured density of Gebel Kamil = 7880 ± 30 kg m−3), and constrains the minimum size of the projectile that struck the ground and produced Kamil crater (note that this mass value does not include the 83 kg individual that detached from the main mass of the projectile prior to impact). Unfortunately, this estimate can no longer be verified because, after our February 2010 field survey, the crater site was visited by unknown people who illicitly removed hundreds of meteorite fragments without documenting their position or mass, and subsequently sold them on the international market (Margottini 2010).

The geomagnetic survey carried out in February 2010 in the gridded area around the crater (Fig. 2a) after systematic search for shrapnel greater than or equal to approximately 10 g revealed that there are no buried meteorite specimens larger than some tens of kilograms up to a distance of 450 m from the crater center (Folco et al. 2011). The quantity of meteorite fragments buried in the ejecta deposit in the form of shrapnel weighing much less than some tens of kilograms would have to be assessed to better estimate the projectile mass. Note that the minimum mass of the projectile inferred from the distribution of macroscopic shrapnel specimens around Kamil crater (3400 kg) is of the order of magnitude of the approximately 9100 kg calculated by Folco et al. (2011) by applying cratering models from the literature (i.e., Collins et al. 2005) to Kamil crater, assuming an impactor entry velocity of 18 km s−1, and entry angle of 45°. Higher impactor masses up to approximately 30,000 kg could be obtained assuming extreme input parameters, like very low entry velocities (approximately 13 km s−1) and low entry angles (approximately 30°).

Incident Direction of Impact

The asymmetric distribution of shrapnel specimens around Kamil crater (Fig. 2c) also provides insight into the incident direction of the meteorite impactor. The fact that shrapnel fragments are concentrated in terms of number of specimens and mass due southeast of the crater indicates that Kamil crater formed due to the oblique impact of a projectile that approached the Earth’s surface from the northwest. Numerical studies by O’Keefe and Ahrens (1985) predict that in an oblique hypervelocity impact, the projectile is deformed into a downrange jet of impactor debris. During the early phases of the contact and compression, the projectile material is compressed by shock that originates at the projectile-target interface and then propagates into the projectile. The projectile’s vertical component is significantly decreased by shock, whereas the horizontal component remains large. Rarefactions from the projectile’s free surface unload the projectile’s front (i.e., its free surface), and a downrange jet of projectile debris plus some target material is formed. Note that most fragments of the ordinary chondrite that generated the Carancas meteorite impact in Peru were found due southwest of the crater, i.e., downrange the incident direction of the witnessed fireball (e.g., Tancredi et al. 2009). Similarly, the shrapnel field of the iron meteorite that generated the Whitecourt impact crater extends downrange, northeast of the crater (e.g., Kofman et al. 2010). Microscopic meteoritic debris of the Canyon Diablo iron meteorite was also found concentrated due northeast of the Barringer crater, i.e., downrange the direction of the impacting body (Rinehart 1958).

A northwest direction of incidence is consistent with the find location of the regmaglypted individual, 230 m north of the crater (Fig. 2b). This meteorite fragment probably detached from the main impacting mass prior to or during ablative flight and, because it was smaller, decelerated more quickly. The fact that the peak in meteorite density (Fig. 2c) is in a sector area due southeast of the crater comprised between 125° and 160° N suggests that the incident direction of the projectile was 305–340° N.

An interesting feature of the shrapnel density distribution map (Fig. 2c) is that there is a broad maximum approximately 200 m from the southeast crater rim. One possible reason for this position is that part of the shrapnel close to the crater rim is buried in the ejecta deposit. Another possible explanation that should be investigated is that the maximum density area represents the site where most of the downrange plume actually landed, thereby defining the core of the downrange jet that follows reflection trajectories in moderately oblique impacts, i.e., approximately 45° (O’Keefe and Ahrens 1985).

Lastly, the meteorite distribution shown in Fig. 2c reveals that shrapnel is concentrated along the southeastern ejecta ray, whereas little or no macroscopic meteoritic material occurs along the northern and southwestern ejecta rays. This decoupling between projectile and bedrock debris appears to highlight the different stress fields imparted to the projectile and to the target upon impact (Melosh 1989). Despite the obliquity of the impact, a roughly hemispherical shock wave propagates in the target, producing a radial (or nearly so) distribution of ejecta; projectile debris preserves part of its pre-impact kinetic energy and linear momentum, and is preferentially projected forward with respect to the incident direction. Constraints to the ejection velocities of shrapnel fragments have been obtained through calculations of their ballistic trajectories (Mastin 2001). The minimum ejection velocities for the three meteorite fragments that were found at the greatest distance from the crater (1600 m, 1470 m, 1340 m) are 195 m s−1, 160 m s−1, and 140 m s−1, respectively. Landing (final) velocities in the order of 80 m s−1 and should be sufficient to cause the secondary shattering observed in several points of the meteorite field (Fig. 6).

Traces of a Small Catastrophe

Due to the excellent state of preservation, Kamil crater provides tangible evidence of the geological effects generated by the impact of meter-sized iron meteorites on the Earth’s crust and the hazard they pose to the human population. In particular, this study of the Gebel Kamil meteorite alone provides us with a vivid picture of the explosion of a meter-sized iron meteorite impacting the Earth’s crust and subsequent jetting of the impactor debris.

The fact that the bulk of the Gebel Kamil meteorite consists of thousands of shrapnel specimens (1700 kg of shrapnel and only one individual weighing 83 kg), along with the lack of secondary impact craters and of large buried portions of the impactor (Folco et al. 2011), suggests that the projectile penetrated the Earth’s atmosphere without significant fragmentation and separation, and that it struck the Earth’s surface, generating an explosion crater. Upon contact with the target, the projectile was catastrophically disrupted into thousands of fragments up to some tens of kg in mass, which were projected forward in a southeastern direction, giving rise to a down-range jet (Fig. 2c). Shattering was accompanied by some melting of the projectile and the target. The frequent occurrence of centimeter-sized glass masses stuck to the shrapnel specimens (Fig. 12b) provides us with a clear picture of the nature of the meteorite debris ejected during the earliest stage of impact cratering (namely when the projectile first contacts the target): a swarm of thousands of iron meteorite fragments was associated with a dense, hot spray of molten projectile and target material. Shrapnel as heavy as approximately 400 g was found downrange approximately 1.6 km due east of the crater, testifying to the force of the explosive jet.

Conclusions

  1. Top of page
  2. Abstract
  3. Introduction
  4. The Kamil Impact Crater
  5. Samples and Methods
  6. Results
  7. Discussion
  8. Conclusions
  9. References

The following conclusions can be drawn based on our mineralogic, petrographic, and geochemical study of Gebel Kamil––the meteorite that formed the 45 m-diameter Kamil crater in Egypt––and its field distribution:

  • 1
     The Gebel Kamil iron meteorite can be classified as an ungrouped Ni-rich (Ni approximately 20 wt%) ataxite characterized by high Ge and Ga contents (approximately 120 and approximately 50 μg g−1, respectively) and low Ir content (0.55 μg g−1). Although structurally and chemically similar to the ungrouped iron Morradal, Gebel Kamil expands the inventory of known solar system material.
  • 2
     With the exception of one 83 kg regmaglypted individual, meteorite specimens identified in the field consist of thousands of shrapnel pieces weighing up to approximately 34 kg. This indicates that the incoming impactor experienced minor fragmentation and separation during atmospheric flight, and that it was catastrophically disrupted upon impact with the sedimentary (namely quartz-arenite) target.
  • 3
     Pervasive mylonitic shear bands occur in every shrapnel specimen; sometimes they are sub-parallel to the external surfaces of specimens and indicate that fragmentation of the Gebel Kamil meteorite occurred through pervasive shearing and subsequent shock pressure unloading, as also observed in the Henbury iron meteorite (Axon and Steele-Perkins 1975).
  • 4
     Impact melt found stuck to some shrapnel specimens and consisting of a mixture of target and projectile melts indicates shock pressures in excess of 60 GPa (e.g., Melosh 1989), thereby suggesting that the Kamil crater formed through a hypervelocity impact. Note that this is the first report of the widespread finding of impact melt stuck to the surface of iron-shrapnel specimens. We think that such occurrence is most probably the norm in the context of small-scale hypervelocity impact craters on Earth. This feature is probably unique of Gebel Kamil due to its exceptionally good preservation conditions.
  • 5
     The occurrence of extreme shock metamorphism coupled with the catastrophic disruption of the impactor indicates that the Kamil crater is an explosively excavated crater.
  • 6
     Patches of fusion crust observed in the regmaglypted individual specimen are evidence of the short terrestrial residence time of the Gebel Kamil meteorite, in accordance with the excellent preservation of the Kamil crater impact structure.
  • 7
     The total mass of shrapnel specimens >10 g identified during our systematic search amounts to 1700 kg. The total mass inferred from the density map in Fig. 2c is 3400 kg. This mass value constrains the minimum size of the projectile that struck the ground and produced Kamil crater.
  • 8
     Shrapnel fragments are concentrated due southeast of the crater, defining the forward projection of the impactor debris. In particular, the peak in shrapnel density (Fig. 2c) occurs in an area due southeast of the crater located between 125° and 160° N, suggesting that the incident direction of the projectile was approximately 305–340° N.

Acknowledgments— This work was carried out within the framework of the “Egypt-Italy Science Year 2009 (EISY 2009).” We are grateful to T. Hussein (former President of the Egyptian National Academy of Science and Technology) and F. Porcelli (Scientific Attaché, Italian Embassy, Egypt) for diplomatic support. We are indebted to all the participants in the 2010 Egyptian-Italian geophysical expedition to the Kamil crater. Thanks are due to D. L. Schrader, R. S. Kofman, and G. Tancredi for their constructive reviews, and to N. L. Chabot for editorial assistance. We thank Università di Pisa (“Fondi di Ateneo per la Ricerca”), the European Commission (through the Marie Curie Actions–Research Training Networks ORIGINS project, ID: 35519), Banca Monte dei Paschi di Siena S.p.A, Fondazione Monte dei Paschi di Siena, and Fondazione Cassa di Risparmio di Torino for financial support.

Editorial Handling— Dr. Nancy Chabot

References

  1. Top of page
  2. Abstract
  3. Introduction
  4. The Kamil Impact Crater
  5. Samples and Methods
  6. Results
  7. Discussion
  8. Conclusions
  9. References
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