# Microscopic impactor debris in the soil around Kamil crater (Egypt): Inventory, distribution, total mass, and implications for the impact scenario

Luigi Folco, Massimo d'Orazio, Agnese Fazio, Carole Cordier, Antonio Zeoli, Matthias van Ginneken, Ahmed El-Barkooky

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Luigi Folco, Massimo d'Orazio, Agnese Fazio, Carole Cordier, Antonio Zeoli, et al. Microscopic impactor debris in the soil around Kamil crater (Egypt): Inventory, distribution, total mass, and implications for the impact scenario. Meteoritics and Planetary Science, 2015, 50 (3), pp.382-400. 10.1111/maps.12427. hal-04933138

HAL Id: hal-04933138

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# Microscopic impactor debris in the soil around Kamil crater (Egypt): Inventory, distribution, total mass, and implications for the impact scenario

Luigi FOLCO<fnref n="1" />*, Massimo D'ORAZIO<fnref n="1" />, Agnese FAZIO<fnref n="1" />, Carole CORDIER<fnref n="2" />,<fnref n="3" />, Antonio ZEOLI<fnref n="4" />, Matthias VAN GINNEKEN<fnref n="5" />, and Ahmed EL-BARKOOKY<fnref n="6" />

*(Received 18 August 2014; revision accepted 11 December 2014)

**Abstract**–We report on the microscopic impactor debris around Kamil crater (45 m in diameter, Egypt) collected during our 2010 geophysical expedition. The hypervelocity impact of Gebel Kamil (Ni-rich ataxite) on a sandstone target produced a downrange ejecta curtain of microscopic impactor debris due SE–SW of the crater (extending ~300,000 m<fnref n="2" />, up to ~400 m from the crater), in agreement with previous determination of the impactor trajectory. The microscopic impactor debris include vesicular masses, spherules, and coatings of dark impact melt glass which is a mixture of impactor and target materials (Si-, Fe-, and Al-rich glass), plus Fe-Ni oxide spherules and mini shrapnel, documenting that these products can be found in craters as small as few tens of meters in diameter. The estimated mass of the microscopic impactor debris (<290 kg) derived from Ni concentrations in the soil is a small fraction of the total impactor mass (~10 t) in the form of macroscopic shrapnel. That Kamil crater was generated by a relatively small impactor is consistent with literature estimates of its pre-atmospheric mass (>20 t, likely 50–60 t).

## INTRODUCTION

The characterization of microscopic projectile debris occurring at small-scale meteorite craters (≤1500 m in diameter) can improve our understanding of the physical–chemical interaction between projectile and target, including impactor fragmentation and dispersion, impact melt (and vapor) production, ejecta, and plume evolution in small impact events (e.g., Hörz et al. 2002; Artemieva and Pierazzo 2009, 2011; Ebert et al. 2013; Hamann et al. 2013; Kenkmann et al. 2013; Shuvalov and Dypvik 2013).

Kamil crater (Egypt; Fig. 1) is a pristine (or nearly so) type structure for small impacts on Earth (Folco et al. 2010, 2011) and it thus offers the possibility to document the characteristics of the microscopic impactor debris, and its expansion and distribution in small-scale meteorite impacts. Kamil crater is a 45 m

diameter simple crater, produced by the hypervelocity impact of the Ni-rich (~20 wt%; D'Orazio et al. 2011) Gebel Kamil iron meteorite on layered sandstones with subhorizontal bedding, interbedded with minor siltstones and wacke (Urbini et al. 2012; Fazio et al. 2014). Due to its very young age (probably <5000 yr; Folco et al. 2011) and the dry climatic conditions in the Sahara (e.g., Kuper and Kröpelin 2006), it is exceptionally well-preserved with an unaltered crater structure, rayed pattern of bright ejecta, various types of shock-metamorphosed and impact melt rocks (from cm-sized bombs to microscopic impact spherules), and a nearly intact assemblage of fragments of the projectile that fragmented into thousands of shrapnel (i.e., unmolten projectile fragments; O'Keefe and Ahrens 1985) upon impact and were deposited in and around the crater (D'Orazio et al. 2011; Folco et al. 2011; Urbini et al. 2012; Fazio et al. 2014). The concentration

<footnote n="1">¹Dipartimento di Scienze della Terra, Università di Pisa, Via S. Maria 53, 56126 Pisa, Italy</footnote>

<footnote n="2">²Université de Grenoble Alpes, BP 53, 38041 Grenoble, CEDEX 9, France</footnote>

<footnote n="3">³CNRS, Istitut des Sciences de la Terre (ISTerre), BP 53, 38041 Grenoble, CEDEX 9, France</footnote>

<footnote n="4">⁴Museo Nazionale dell'Antartide, Università di Siena, Via Laterina 8, 53100 Siena, Italy</footnote>

<footnote n="5">⁵Department of Earth Science and Engineering, Imperial College, Prince Consort Road, London SW7 2BP, UK</footnote>

<footnote n="6">⁶Department of Geology, Faculty of Sciences, Cairo University, Giza, Egypt</footnote>

<footnote>*Corresponding author. E-mail: luigi.folco@unipi.it</footnote>
<figure><img src="image_2.png" /><figcaption>Fig. 1. Kamil crater, southwestern Egypt, and location map of the collected soil samples. Base map: enhanced true color QuickBird satellite image (22 October 2005; courtesy of Telespazio S.p.A.).</figcaption></figure>

of large shrapnel fragments (from ~10 g to ~30 kg) due SE of the crater indicates an oblique impact from the NW (D'Orazio et al. 2011). The mass of shrapnel found through visual search (D'Orazio et al. 2011) and geomagnetic survey (Urbini et al. 2012) indicates that the mass of the projectile was at least ~5000 kg. Both noble gases and radionuclides in Gebel Kamil point to a pre-atmospheric mass >20 t, with a preferred estimate of 50–60 t (Ott et al. 2014). Shock metamorphic and melting features in the target indicate peak pressure between 30 and 60 GPa, and impact velocities of 3.5–5.5 km s⁻¹ for vertical impact or 5.0–7.5 km s⁻¹ for an impact angle of 45° (Fazio et al. 2014).

In this paper, we investigate the microscopic impactor debris of Gebel Kamil. Soil samples around Kamil crater were collected during our 2010 geophysical expedition (Folco et al. 2010). Following similar studies, mainly conducted at Barringer crater (e.g., Nininger 1956; Rinehart 1958), this work provides an inventory of the various types of microscopic impactor material that can be produced in small-scale impact craters and constrains the trajectory of the Gebel Kamil iron

meteorite, providing an estimate of its total mass at the time of impact.

## SAMPLES AND ANALYTICAL METHODS

To study the microscopic impactor debris at Kamil crater, we collected 44 soil samples around the crater (Fig. 1; Table 1). Samples were collected at incremental distances from the crater rim along eight radial traverses (45° apart, starting from the north) extending up to 1.6 km from the crater rim (i.e., at about the distance from the crater rim where the most distant macroscopic shrapnel was found; D'Orazio et al. 2011). Each sample consisted of a 30 × 30 × ~5 cm soil volume, i.e., we assumed that this volume contained all the microscopic impactor debris deposited on the considered surface. This assumption is based on the fact that the fine-grained ejecta deposit is typically less than some centimeters in thickness anywhere around the crater; even within the ejecta blanket, i.e., within ~50 m from the crater rim (Urbini et al. 2012), the bulk and the thickness of the deposit is given by boulders and
<table><caption>Table 1. Magnetic extract <5 mm of soil samples from Kamil crater: location and mass. Samples are listed according to the bearing of the profiles starting from the north, and to their increasing distance from crater rim.</caption><thead><tr><th>Label</th><th>Profile/ Location</th><th>Distance from crater rim (m)</th><th>Latitude S</th><th>Longitude E</th><th>Altitude (m a.s.l.)</th><th>Mass of magnetic extract (g)</th></tr></thead><tbody><tr><td>S12</td><td>N</td><td>15</td><td>26° 05' 18"</td><td>22° 01' 06"</td><td>599</td><td>4.5</td></tr><tr><td>S13</td><td>N</td><td>100</td><td>26° 05' 19"</td><td>22° 01' 05"</td><td>602</td><td>6.6</td></tr><tr><td>S14</td><td>N</td><td>200</td><td>26° 05' 23"</td><td>22° 01' 06"</td><td>602</td><td>7.8</td></tr><tr><td>S15</td><td>N</td><td>400</td><td>26° 05' 29"</td><td>22° 01' 07"</td><td>609</td><td>8.8</td></tr><tr><td>S16</td><td>N</td><td>800</td><td>26° 05' 42"</td><td>22° 01' 06"</td><td>615</td><td>13.3</td></tr><tr><td>S35</td><td>NE</td><td>15</td><td>26° 05' 59"</td><td>22° 01' 03"</td><td>597</td><td>2.8</td></tr><tr><td>S36</td><td>NE</td><td>100</td><td>26° 05' 14"</td><td>22° 01' 07"</td><td>596</td><td>10.5</td></tr><tr><td>S37</td><td>NE</td><td>200</td><td>26° 05' 11"</td><td>22° 01' 06"</td><td>608</td><td>18.4</td></tr><tr><td>S38</td><td>NE</td><td>400</td><td>26° 05' 07"</td><td>22° 01' 05"</td><td>604</td><td>11.0</td></tr><tr><td>S39</td><td>NE</td><td>800</td><td>26° 05' 00"</td><td>22° 01' 03"</td><td>605</td><td>9.0</td></tr><tr><td>S01</td><td>E</td><td>15</td><td>26° 04' 47"</td><td>22° 01' 07"</td><td>603</td><td>15.2</td></tr><tr><td>S02</td><td>E</td><td>100</td><td>26° 05' 15"</td><td>22° 01' 07"</td><td>601</td><td>11.7</td></tr><tr><td>S03</td><td>E</td><td>200</td><td>26° 05' 15"</td><td>22° 01' 10"</td><td>605</td><td>13.3</td></tr><tr><td>S04</td><td>E</td><td>400</td><td>26° 05' 16"</td><td>22° 01' 13"</td><td>604</td><td>4.0</td></tr><tr><td>S05</td><td>E</td><td>800</td><td>26° 05' 14"</td><td>22° 01' 19"</td><td>615</td><td>4.0</td></tr><tr><td>S06</td><td>E</td><td>1200</td><td>26° 05' 13"</td><td>22° 01' 33"</td><td>606</td><td>23.1</td></tr><tr><td>S23</td><td>SE</td><td>15</td><td>26° 05' 15"</td><td>22° 01' 04"</td><td>597</td><td>12.1</td></tr><tr><td>S24</td><td>SE</td><td>100</td><td>26° 05' 15"</td><td>22° 01' 02"</td><td>595</td><td>21.7</td></tr><tr><td>S25</td><td>SE</td><td>200</td><td>26° 05' 15"</td><td>22° 00' 58"</td><td>600</td><td>18.2</td></tr><tr><td>S26</td><td>SE</td><td>400</td><td>26° 05' 14"</td><td>22° 00' 58"</td><td>596</td><td>17.1</td></tr><tr><td>S27</td><td>SE</td><td>800</td><td>26° 05' 15"</td><td>22° 00' 36"</td><td>592</td><td>9.8</td></tr><tr><td>S28</td><td>SE</td><td>1220</td><td>26° 05' 22"</td><td>22° 00' 24"</td><td>588</td><td>10.1</td></tr><tr><td>S17</td><td>S</td><td>15</td><td>26° 05' 16"</td><td>22° 01' 04"</td><td>600</td><td>10.3</td></tr><tr><td>S18</td><td>S</td><td>100</td><td>26° 05' 17"</td><td>22° 01' 02"</td><td>594</td><td>25.3</td></tr><tr><td>S19</td><td>S</td><td>200</td><td>26° 05' 20"</td><td>22° 01' 00"</td><td>596</td><td>13.7</td></tr><tr><td>S20</td><td>S</td><td>400</td><td>26° 05' 25"</td><td>22° 00' 56"</td><td>595</td><td>15.6</td></tr><tr><td>S21</td><td>S</td><td>800</td><td>26° 05' 35"</td><td>22° 00' 47"</td><td>591</td><td>7.6</td></tr><tr><td>S22</td><td>S</td><td>1280</td><td>26° 05' 44"</td><td>22° 00' 36"</td><td>592</td><td>7.5</td></tr><tr><td>S29</td><td>SW</td><td>15</td><td>26° 05' 14"</td><td>22° 01' 05"</td><td>599</td><td>11.7</td></tr><tr><td>S30</td><td>SW</td><td>100</td><td>26° 05' 12"</td><td>22° 01' 03"</td><td>597</td><td>6.4</td></tr><tr><td>S31</td><td>SW</td><td>200</td><td>26° 05' 10"</td><td>22° 01' 01"</td><td>602</td><td>12.7</td></tr><tr><td>S32</td><td>SW</td><td>400</td><td>26° 05' 04"</td><td>22° 01' 01"</td><td>596</td><td>5.3</td></tr><tr><td>S33</td><td>SW</td><td>800</td><td>26° 04' 58"</td><td>22° 00' 46"</td><td>596</td><td>6.1</td></tr><tr><td>S34</td><td>SW</td><td>1160</td><td>26° 04' 46"</td><td>22° 00' 46"</td><td>592</td><td>13.7</td></tr><tr><td>S07</td><td>W</td><td>15</td><td>26° 05' 17"</td><td>22° 01' 07"</td><td>597</td><td>2.9</td></tr><tr><td>S08</td><td>W</td><td>100</td><td>26° 05' 18"</td><td>22° 01' 09"</td><td>593</td><td>5.9</td></tr><tr><td>S09</td><td>W</td><td>200</td><td>26° 05' 21"</td><td>22° 01' 11"</td><td>592</td><td>5.7</td></tr><tr><td>S10</td><td>W</td><td>400</td><td>26° 05' 24"</td><td>22° 01' 16"</td><td>596</td><td>7.9</td></tr><tr><td>S11</td><td>W</td><td>800</td><td>26° 05' 33"</td><td>22° 01' 25"</td><td>603</td><td>8.6</td></tr><tr><td>S41</td><td>NW</td><td>100</td><td>26° 05' 12"</td><td>22° 01' 09"</td><td>596</td><td>3.0</td></tr><tr><td>S43</td><td>NW</td><td>400</td><td>26° 05' 06"</td><td>22° 01' 11"</td><td>600</td><td>5.0</td></tr><tr><td>S44</td><td>NW</td><td>800</td><td>26° 04' 53"</td><td>22° 01' 27"</td><td>596</td><td>7.6</td></tr></tbody></table>

blocks with a thin layer of fine-grained ejecta in between. Samples were collected using shovel, paint brush, blade, and measuring tape (Fig. 2A). Samples were dry sieved in the field to obtain the <5 mm size fraction. Exploiting the contrasting magnetic properties of projectile and target rocks, the magnetic particles were subsequently extracted using a field extractor (Fig. 2B) and weighed. To complete magnetic separation, we used the Extractor S-E in-line magnetic separator,

with a stainless steel housing and three Nd magnet rods arranged in a triangular matrix producing a magnetic force of 0.6 T (S+S Separation and Sorting Technology GmbH, Schönberg, Germany). A separation efficiency >80% was derived through a number of random field tests at various locations.

The magnetic extracts from each soil sample were first observed under the stereomicroscope to identify the various types of magnetic particles, including impactor
<figure><img src="image_3.png" /></figure>

Fig. 2. Field photos of soil sample collection around Kamil crater (A, B) and stereomicrographs of representative samples of their magnetic components (C–E). A) A surface soil volume measuring 30 × 30 × ~5 cm (arrow) was collected at each site and sieved (<5 mm). Inset: a detail of the sampling surface. B) The sieved sample was then passed through a powerful field magnetic separator (arrowed) to obtain the magnetic extract studied in this work. The picture features one of the preliminary extraction tests. C) The magnetic extract of sample S23 (<5 mm; 15 m due SE of crater rim) showing abundant dark impact melt glass particles mainly in the shape of vesicular clastic masses, mini-to-microscopic individual or compound spheroids, and coatings of pale target rock particles (mainly shocked sandstone fragments and or lechatelierite, as revealed by electron microscopy and microanalyses). Subordinate mini-to-microscopic iron meteorite shrapnel and microscopic Fe-Ni oxide spherules also occur. D) Magnetic extract of sample S44 (<5 mm; 800 m due NW of crater rim) dominated by Precambrian crystalline basement rock fragments (mainly amphibolite gneiss). E) Close-up view of the magnetic extract of sample S27 (<400 µm; 800 m due SE crater rim) showing abundant Fe-Ti oxide plus garnet grains of terrestrial origin. Abbreviations: CS = cosmic spherule; DG = individual masses of dark impact melt glass; DGc = dark glass coatings; DG sph = dark glass spheroids; Fe-Ti ox = Fe-Ti oxides; GK = Gebel Kamil iron meteorite shrapnel; Grt = garnet; Fe-Ni sph = Fe-Ni oxide spherule; Qtz = quartz.

debris and terrestrial particles, and their overall distribution around the crater.

A selection of the magnetic particles from a representative number of samples was then studied under the scanning electron microscope (SEM). Particles were first observed as whole specimens to characterize their morphology and structure. They were then sectioned to define their texture and overall composition. Analyses were performed using a Philips XL30 SEM, operating at 20 kV coupled with an energy-dispersive X-ray fluorescence spectrometer (EDX), available at Pisa University's Dipartimento di Scienze

della Terra, and a field emission scanning electron microscope (FE-SEM) Jeol JSM 6500F (upgraded to 7000 series), available at the Istituto di Geofisica e Vulcanologia (INGV) of Rome.

The mineral chemistry of the various phases in a selection of the above particles was obtained by electron probe microanalyses (EPMA) using a Cameca SX50 electron microprobe at IGG-CNR, Padua (Table 2). Running conditions were 15 kV accelerating voltage, 15 nA beam current, and 1 µm nominal beam spot. The manufacturer-supplied PAP procedure was employed for raw data reduction. Standards used for instrumental
<table><caption>Table 2. Average major element bulk composition by EPMA of dark glass impact melt (in the form of vesicular particles, spherules, and coatings), Fe-Ni oxide blebs in dark glass. Fe-oxide spherules, lechatelierite in dark glass, and Fe-Ni metal blebs in dark glass (distinguished in high-Ni and very high-Ni compositional types). Limits of detections (LOD) for the analyses of silicates and oxides are: Mg = 0.03 wt%, Al = 0.04 wt%, Si = 0.04 wt%, P = 0.05 wt%, S = 0.04 wt%, K = 0.04 wt%, Ca = 0.04 wt%, Ti = 0.04 wt%, Cr = 0.06 wt%, Mn = 0.07 wt%, Fe = 0.04 wt%, Co = 0.08 wt%, Ni = 0.04 wt%. LOD for the analyses of the metal phases are: Si = 0.03 wt%, P = 0.04 wt%, S = 0.04 wt%, Cr = 0.05 wt%, Fe = 0.04 wt%, Co = 0.06 wt%, Ni = 0.04 wt%.</caption><thead><tr><th></th><th>Vesicular<br>glass</th><th>Glass<br>spherules</th><th>Glass<br>coatings</th><th>Fe-oxide<br>blebs</th><th>Fe-Ni oxide<br>spherules</th><th>L<sup>a</sup></th><th>Fe-Ni metal<br>blebs</th><th></th></tr></thead><tbody><tr><td>n. part.<sup>b</sup></td><td>1</td><td>6</td><td>3</td><td>2</td><td>11</td><td></td><td>H-Ni<sup>d</sup></td><td>VH-Ni<sup>e</sup></td></tr><tr><td>n. an.<sup>c</sup></td><td>9</td><td>9</td><td>48</td><td>5</td><td>29</td><td></td><td>9</td><td>2</td></tr><tr><td></td><td>ox wt%</td><td>σ</td><td>ox wt%</td><td>σ</td><td>ox wt%</td><td>σ</td><td>el wt%</td><td>σ</td></tr><tr><td>MgO</td><td>0.18</td><td>0.07</td><td>0.23</td><td>0.04</td><td>0.30</td><td>0.04</td><td>0.14</td><td>0.01</td><td>bdl</td></tr><tr><td>Al<sub>2</sub>O<sub>3</sub></td><td>10.4</td><td>2.8</td><td>12.3</td><td>1.9</td><td>16.1</td><td>1.4</td><td>4.79</td><td>2.48</td><td>0.04</td></tr><tr><td>SiO<sub>2</sub></td><td>57.0</td><td>10.1</td><td>49.2</td><td>4.0</td><td>47.3</td><td>3.2</td><td>4.81</td><td>1.65</td><td>0.77</td></tr><tr><td>P<sub>2</sub>O<sub>5</sub></td><td>bdl</td><td></td><td>0.09</td><td>0.05</td><td>0.13</td><td>0.03</td><td>0.57</td><td>0.62</td><td>0.10</td></tr><tr><td>SO<sub>3</sub></td><td>0.20</td><td>0.05</td><td>0.12</td><td>0.07</td><td>0.08</td><td>0.10</td><td>0.02</td><td>0.02</td><td>bdl</td></tr><tr><td>K<sub>2</sub>O</td><td>0.13</td><td>0.03</td><td>0.23</td><td>0.07</td><td>0.38</td><td>0.06</td><td>na</td><td>na</td><td>bdl</td></tr><tr><td>CaO</td><td>0.57</td><td>0.14</td><td>0.49</td><td>0.09</td><td>0.50</td><td>0.28</td><td>0.27</td><td>0.03</td><td>bdl</td></tr><tr><td>TiO<sub>2</sub></td><td>1.06</td><td>0.31</td><td>0.76</td><td>0.05</td><td>0.81</td><td>0.05</td><td>0.44</td><td>0.15</td><td>bdl</td></tr><tr><td>Cr<sub>2</sub>O<sub>3</sub></td><td>0.10</td><td>0.05</td><td>bdl</td><td></td><td>bdl</td><td></td><td>0.07</td><td>0.05</td><td>bdl</td></tr><tr><td>MnO</td><td>bdl</td><td></td><td>0.79</td><td>0.30</td><td>1.16</td><td>0.09</td><td>0.08</td><td>0.04</td><td>bdl</td></tr><tr><td>FeO<sup>τ</sup></td><td>27.6</td><td>7.5</td><td>30.9</td><td>3.7</td><td>29.2</td><td>3.0</td><td>79.6</td><td>4.32</td><td>71.6</td></tr><tr><td>CoO</td><td>bdl</td><td></td><td>0.10</td><td>0.05</td><td>bdl</td><td></td><td>bdl</td><td>0.82</td><td>0.09</td></tr><tr><td>NiO</td><td>0.16</td><td>0.10</td><td>2.71</td><td>1.08</td><td>1.54</td><td>0.63</td><td>0.08</td><td>20.9</td><td>1.90</td></tr><tr><td>Total</td><td>97.4</td><td></td><td>97.9</td><td></td><td>97.5</td><td>90.9</td><td>94.3</td><td>99.9</td><td></td></tr></tbody></table>

FeO<sup>τ</sup> = total iron as FeO; na = not analyzed; bdl = below detection limit.

<sup>a</sup>Lechatelierite.

<sup>b</sup>Number of analyzed particles.

<sup>c</sup>Number of total analyses in the average.

<sup>d</sup>High-Ni blebs.

<sup>e</sup>Very high-Ni blebs.
<table><caption>Table 3. Chemical composition of Kamil crater target rocks (X-ray fluorescence analyses, except where otherwise specified). Samples M26 and M27 were collected from the crater walls; sample M25 was collected from a stone fragment in the ejecta 740 m SSW of crater rim (Urbini et al. 2012; Fazio et al. 2014). Target rocks consist of layered sandstones with subhorizontal bedding belonging to the Gilf Gebir Formation. A 70 cm thick, pale quartzarenite layer (sample M26) is at the top of the impacted sedimentary sequence. The underlying rocks consist mainly of reddish, ferruginous quartzarenite layers up to some tens of cm in thickness (sample M27). The pale quartzarenite sporadically contains intercalations of pale wacke with siltstone levels (sample M25). A kaolinite-rich matrix (sample L13-L14) is an important component (20-40 vol.%) of the pale wacke siltstone levels.</caption><thead><tr><th></th><th>Pale<br>quartzarenite</th><th>Pale wacke with<br>siltstone levels</th><th>Reddish<br>quartzarenite, ~ 5<br>vol.% matrix</th><th>Kaolinite-rich<br>matrix (n = 18)<sup>a</sup></th></tr></thead><tbody><tr><td>Sample</td><td>M26</td><td>M25</td><td>M27</td><td>L13-L14</td></tr><tr><td>Oxide wt%</td><td></td><td></td><td></td><td></td></tr><tr><td>SiO<sub>2</sub></td><td>99.8</td><td>87.8</td><td>95.7</td><td>43.9</td></tr><tr><td>TiO<sub>2</sub></td><td>0.07</td><td>1.15</td><td>0.09</td><td>0.55</td></tr><tr><td>Al<sub>2</sub>O<sub>3</sub></td><td>0.25</td><td>10.1</td><td>1.98</td><td>34.7</td></tr><tr><td>Fe<sub>2</sub>O<sub>3</sub> T</td><td>0.11</td><td>0.74</td><td>1.71</td><td>1.31</td></tr><tr><td>MnO</td><td>&lt;0.01</td><td>0.02</td><td>0.06</td><td>&lt;0.01</td></tr><tr><td>MgO</td><td>0.18</td><td>0.14</td><td>0.25</td><td>0.22</td></tr><tr><td>CaO</td><td>0.05</td><td>0.11</td><td>0.31</td><td>0.05</td></tr><tr><td>Na<sub>2</sub>O</td><td>0.05</td><td>0.13</td><td>0.08</td><td>0.12</td></tr><tr><td>K<sub>2</sub>O</td><td>&lt;0.01</td><td>0.04</td><td>&lt;0.01</td><td>0.04</td></tr><tr><td>P<sub>2</sub>O<sub>5</sub></td><td>&lt;0.01</td><td>0.06</td><td>0.04</td><td>0.09</td></tr><tr><td>Sum</td><td>100.5</td><td>100.3</td><td>100.2</td><td>81.0</td></tr><tr><td>L.O.I.</td><td>0.65</td><td>3.91</td><td>1.19</td><td></td></tr><tr><td>Element µg g<sup>-1</sup></td><td></td><td></td><td></td><td></td></tr><tr><td>Ni<sup>b</sup></td><td>7</td><td></td><td>15</td><td></td></tr><tr><td>Co<sup>b</sup></td><td>&lt;1</td><td></td><td>12</td><td></td></tr></tbody></table>

$Fe_2O_3 T$ = total iron as $Fe_2O_3$; L.O.I. = loss on ignition.

<sup>a</sup>Average of EPMA analyses.

<sup>b</sup>Analyses by ICP-MS.

calibration were natural minerals (quartz, diopside, apatite, and sphalerite) and pure elements (Fe, Ni, and Co).

Whole-rock major elements of unshocked target material of Kamil area (namely, sandstones ranging from very coarse quartzarenite to coarse siltstone with intercalated levels of very fine wacke; Table 3) were determined for geochemical comparison with impact glass. Major elements were determined on glass beads by X-ray fluorescence (XRF, ARL 9400 XP spectrometer) at Pisa University's Dipartimento di Scienze della Terra (Italy), using the procedure described by Tamponi et al. (2003). Nickel and Co were determined by inductively coupled plasma-mass spectrometry (ICP-MS; Perkin Elmer NexION 300× spectrometer) available at the Dipartimento di Scienze della Terra of the University of Pisa.

To quantify the amount of the iron impactor debris and to define its distribution around the crater, we determined the concentration of a number of elements in aliquots of the magnetic extracts (obtained using a small stainless steel splitter), including the

expected tracers of the iron impactor Fe, Ni, Co, and P (Table 4). Elemental concentrations were determined through the total dissolution method (HF + HNO₃ + HClO₄ + HCl) followed by inductively coupled plasma-atomic emission spectroscopy (ICP-AES) analyses at ACTLABS (Ancaster, Ontario, Canada). Due to the high concentration of Ni (>10,000 µg g⁻¹) in samples S23 and S24, they were re-run for siderophile elements at an appropriate dilution using ICPS-MS, at the Dipartimento di Scienze della Terra of the University of Pisa. Note that prior to grinding and powdering of the magnetic extract for geochemical analyses, we separated, counted, and weighed Gebel Kamil shrapnel down to 1 mm in size from each magnetic sample under the stereomicroscope (the two fractions are denominated “shrapnel fraction” and “soil fraction” in Table 4). This procedure was adopted to avoid problems in powdering and dissolving relatively large metal particles, and we discuss the distribution and mass of the impactor debris in the soil with and without mini shrapnel.
<table><caption>Table 4. Magnetic extract (<5 mm) of soil samples from Kamil crater: geochemical composition by ICP-AES except for Ni in samples S23 and S24 which was determined by ICP-MS (see text for details), and contents of impactor equivalent mass. ICP-AES LOD for Fe, Ni, Co, P, Mg, Ca, Ti, and V are: Fe = 0.01 wt%, Ni = 1 µg g⁻¹, Co = 1 µg g⁻¹, P = 0.001 wt%, Mg = 0.01 wt%, Ca = 0.01 wt%, Ti = 0.01 wt%, and V = 2 µg g⁻¹. Samples are listed according to the bearing of the profiles starting from the north, and to their increasing distance from crater rim as in Table 1. The bulk chemical composition of Gebel Kamil by handheld X-ray fluorescence (HH-XRF; Gemelli et al. 2014) is reported for comparison. Element concentrations for Gebel Kamil are averages and standard deviations from 22 spot analyses given in el%.</caption><thead><tr><th>Label</th><th>Shrapnel fraction mass (g)<sup>a</sup></th><th>Soil fraction mass (g)<sup>b</sup></th><th>Fe wt% (soil)</th><th>Ni µg g<sup>-1</sup> (soil)</th><th>Co µg g<sup>-1</sup> (soil)</th><th>P wt% (soil)</th><th>Mg wt% (soil)</th><th>Ca wt% (soil)</th><th>Ti wt% (soil)</th><th>V µg g<sup>-1</sup> (soil)</th><th>Impactor equivalent mass (g) (soil)<sup>c</sup></th><th>Total Ni µg g<sup>-1</sup> (soil plus shrapnel)<sup>d</sup></th><th>Impactor equivalent mass (g)<sup>e</sup></th></tr></thead><tbody><tr><td colspan="14"><strong>N profile</strong></td></tr><tr><td>S12</td><td>–</td><td>4.53</td><td>18.5</td><td>293</td><td>65</td><td>0.023</td><td>1.85</td><td>1.34</td><td>0.36</td><td>118</td><td>0.007</td><td>293</td><td>0.007</td></tr><tr><td>S13</td><td>–</td><td>6.62</td><td>10.8</td><td>115</td><td>39</td><td>0.030</td><td>1.26</td><td>2.01</td><td>0.17</td><td>41</td><td>0.004</td><td>115</td><td>0.004</td></tr><tr><td>S14</td><td>–</td><td>7.77</td><td>9.99</td><td>85</td><td>32</td><td>0.030</td><td>1.08</td><td>2.01</td><td>0.20</td><td>53</td><td>0.003</td><td>85</td><td>0.003</td></tr><tr><td>S15</td><td>–</td><td>8.77</td><td>9.03</td><td>70</td><td>26</td><td>0.029</td><td>1.09</td><td>2.26</td><td>0.15</td><td>48</td><td>0.003</td><td>70</td><td>0.003</td></tr><tr><td>S16</td><td>–</td><td>13.27</td><td>8.53</td><td>86</td><td>29</td><td>0.035</td><td>1.28</td><td>2.30</td><td>0.15</td><td>50</td><td>0.006</td><td>86</td><td>0.006</td></tr><tr><td colspan="14"><strong>NE profile</strong></td></tr><tr><td>S35</td><td>–</td><td>2.77</td><td>10.9</td><td>227</td><td>39</td><td>0.041</td><td>1.39</td><td>2.74</td><td>0.17</td><td>56</td><td>0.003</td><td>227</td><td>0.003</td></tr><tr><td>S36</td><td>–</td><td>10.49</td><td>7.75</td><td>69</td><td>25</td><td>0.031</td><td>1.04</td><td>1.87</td><td>0.26</td><td>118</td><td>0.004</td><td>69</td><td>0.004</td></tr><tr><td>S37</td><td>–</td><td>18.37</td><td>10.9</td><td>102</td><td>53</td><td>0.041</td><td>1.67</td><td>2.76</td><td>0.19</td><td>98</td><td>0.009</td><td>102</td><td>0.009</td></tr><tr><td>S38</td><td>–</td><td>10.97</td><td>9.86</td><td>96</td><td>34</td><td>0.030</td><td>1.60</td><td>2.25</td><td>0.13</td><td>57</td><td>0.005</td><td>96</td><td>0.005</td></tr><tr><td>S39</td><td>–</td><td>9.10</td><td>20.7</td><td>118</td><td>33</td><td>0.012</td><td>1.05</td><td>0.48</td><td>0.20</td><td>148</td><td>0.005</td><td>118</td><td>0.005</td></tr><tr><td colspan="14"><strong>E profile</strong></td></tr><tr><td>S01</td><td>0.359</td><td>14.87</td><td>8.15</td><td>4830</td><td>200</td><td>0.032</td><td>0.59</td><td>1.21</td><td>0.27</td><td>65</td><td>0.359</td><td>9430</td><td>0.718</td></tr><tr><td>S02</td><td>–</td><td>11.75</td><td>9.14</td><td>355</td><td>48</td><td>0.036</td><td>1.04</td><td>1.87</td><td>0.21</td><td>91</td><td>0.021</td><td>355</td><td>0.021</td></tr><tr><td>S03</td><td>–</td><td>13.27</td><td>10.6</td><td>136</td><td>34</td><td>0.032</td><td>1.19</td><td>1.87</td><td>0.13</td><td>65</td><td>0.009</td><td>136</td><td>0.009</td></tr><tr><td>S04</td><td>–</td><td>3.97</td><td>12.6</td><td>112</td><td>40</td><td>0.030</td><td>1.35</td><td>1.86</td><td>0.19</td><td>66</td><td>0.002</td><td>112</td><td>0.002</td></tr><tr><td>S05</td><td>–</td><td>3.97</td><td>10.4</td><td>113</td><td>34</td><td>0.022</td><td>1.47</td><td>1.62</td><td>0.19</td><td>61</td><td>0.002</td><td>113</td><td>0.002</td></tr><tr><td>S06</td><td>–</td><td>23.07</td><td>11.1</td><td>105</td><td>27</td><td>0.017</td><td>0.89</td><td>1.54</td><td>0.21</td><td>106</td><td>0.012</td><td>105</td><td>0.012</td></tr><tr><td colspan="14"><strong>SE profile</strong></td></tr><tr><td>S23</td><td>1.388</td><td>10.68</td><td>12.4</td><td>15871</td><td>624</td><td>0.060</td><td>0.21</td><td>0.35</td><td>0.44</td><td>116</td><td>1.032</td><td>37058</td><td>2.236</td></tr><tr><td>S24</td><td>0.838</td><td>20.83</td><td>9.28</td><td>10927</td><td>428</td><td>0.050</td><td>0.50</td><td>1.17</td><td>0.37</td><td>82</td><td>1.149</td><td>18238</td><td>1.976</td></tr><tr><td>S25</td><td>0.864</td><td>17.30</td><td>17.7</td><td>1290</td><td>68</td><td>0.025</td><td>0.71</td><td>0.77</td><td>0.22</td><td>154</td><td>0.112</td><td>10743</td><td>0.976</td></tr><tr><td>S26</td><td>–</td><td>17.10</td><td>15.1</td><td>218</td><td>48</td><td>0.028</td><td>1.28</td><td>1.33</td><td>0.21</td><td>126</td><td>0.019</td><td>218</td><td>0.019</td></tr><tr><td>S27</td><td>–</td><td>9.77</td><td>16.4</td><td>179</td><td>50</td><td>0.016</td><td>1.87</td><td>0.83</td><td>0.23</td><td>140</td><td>0.009</td><td>179</td><td>0.009</td></tr><tr><td>S28</td><td>–</td><td>10.09</td><td>11.4</td><td>121</td><td>33</td><td>0.027</td><td>1.26</td><td>1.82</td><td>0.15</td><td>97</td><td>0.006</td><td>121</td><td>0.006</td></tr><tr><td colspan="14"><strong>S profile</strong></td></tr><tr><td>S17</td><td>0.036</td><td>10.23</td><td>22</td><td>6200</td><td>305</td><td>0.078</td><td>0.33</td><td>0.33</td><td>0.49</td><td>256</td><td>0.317</td><td>6877</td><td>0.353</td></tr><tr><td>S18</td><td>2.749</td><td>22.55</td><td>9.36</td><td>4870</td><td>205</td><td>0.046</td><td>0.98</td><td>1.96</td><td>0.19</td><td>73</td><td>0.549</td><td>26071</td><td>3.298</td></tr><tr><td>S19</td><td>1.775</td><td>11.89</td><td>16.4</td><td>8840</td><td>367</td><td>0.070</td><td>1.04</td><td>1.04</td><td>0.42</td><td>205</td><td>0.526</td><td>33668</td><td>2.301</td></tr><tr><td>S20</td><td>0.142</td><td>15.42</td><td>14.4</td><td>3000</td><td>161</td><td>0.037</td><td>0.60</td><td>0.34</td><td>1.49</td><td>352</td><td>0.231</td><td>4802</td><td>0.374</td></tr><tr><td>S21</td><td>0.113</td><td>7.45</td><td>12</td><td>342</td><td>47</td><td>0.058</td><td>1.16</td><td>2.29</td><td>1.74</td><td>373</td><td>0.013</td><td>3328</td><td>0.126</td></tr><tr><td>S22</td><td>–</td><td>7.47</td><td>12.9</td><td>344</td><td>44</td><td>0.019</td><td>1.12</td><td>0.55</td><td>0.20</td><td>134</td><td>0.013</td><td>344</td><td>0.013</td></tr><tr><td colspan="14"><strong>SW profile</strong></td></tr><tr><td>S29</td><td>–</td><td>11.67</td><td>15.5</td><td>898</td><td>73</td><td>0.046</td><td>1.06</td><td>1.89</td><td>0.15</td><td>67</td><td>0.052</td><td>898</td><td>0.052</td></tr><tr><td>S30</td><td>–</td><td>6.40</td><td>10.9</td><td>2030</td><td>109</td><td>0.033</td><td>1.06</td><td>1.59</td><td>0.22</td><td>74</td><td>0.065</td><td>2030</td><td>0.065</td></tr><tr><td>S31</td><td>0.414</td><td>12.25</td><td>9.45</td><td>586</td><td>46</td><td>0.037</td><td>1.14</td><td>2.63</td><td>0.12</td><td>69</td><td>0.036</td><td>7096</td><td>0.449</td></tr><tr><td>S32</td><td>0.005</td><td>5.26</td><td>11.3</td><td>184</td><td>48</td><td>0.039</td><td>1.79</td><td>1.73</td><td>0.19</td><td>80</td><td>0.005</td><td>382</td><td>0.010</td></tr><tr><td>S33</td><td>–</td><td>6.07</td><td>11.2</td><td>247</td><td>39</td><td>0.034</td><td>1.20</td><td>2.29</td><td>0.14</td><td>53</td><td>0.007</td><td>247</td><td>0.007</td></tr><tr><td>S34</td><td>–</td><td>13.67</td><td>11.5</td><td>145</td><td>42</td><td>0.046</td><td>0.96</td><td>0.67</td><td>2.41</td><td>403</td><td>0.010</td><td>145</td><td>0.010</td></tr><tr><td colspan="14"><strong>W profile</strong></td></tr><tr><td>S07</td><td>–</td><td>2.87</td><td>20.1</td><td>980</td><td>76</td><td>0.048</td><td>0.50</td><td>0.76</td><td>0.51</td><td>256</td><td>0.014</td><td>980</td><td>0.014</td></tr><tr><td>S08</td><td>–</td><td>5.93</td><td>16.4</td><td>241</td><td>61</td><td>0.029</td><td>1.08</td><td>1.38</td><td>0.18</td><td>65</td><td>0.007</td><td>241</td><td>0.007</td></tr></tbody></table>
<table><caption>Table 4. Continued. Magnetic extract (<5 mm) of soil samples from Kamil crater: geochemical composition by ICP-AES except for Ni in samples S23 and S24 which was determined by ICP-MS (see text for details), and contents of impactor equivalent mass. ICP-AES LOD for Fe, Ni, Co, P, Mg, Ca, Ti, and V are: Fe = 0.01 wt%, Ni = 1 µg g⁻¹, Co = 1 µg g⁻¹, P = 0.001 wt%, Mg = 0.01 wt%, Ca = 0.01 wt%, Ti = 0.01 wt%, and V = 2 µg g⁻¹. Samples are listed according to the bearing of the profiles starting from the north, and to their increasing distance from crater rim as in Table 1. The bulk chemical composition of Gebel Kamil by handheld X-ray fluorescence (HH-XRF; Gemelli et al. 2014) is reported for comparison. Element concentrations for Gebel Kamil are averages and standard deviations from 22 spot analyses given in el%.</caption><thead><tr><th>Label</th><th>Shrapnel fraction mass (g)<sup>a</sup></th><th>Soil fraction mass (g)<sup>b</sup></th><th>Fe wt% (soil)</th><th>Ni µg g<sup>-1</sup> (soil)</th><th>Co µg g<sup>-1</sup> (soil)</th><th>P wt% (soil)</th><th>Mg wt% (soil)</th><th>Ca wt% (soil)</th><th>Ti wt% (soil)</th><th>V µg g<sup>-1</sup> (soil)</th><th>Impactor equivalent mass (g) (soil)<sup>c</sup></th><th>Total Ni µg g<sup>-1</sup> (soil plus shrapnel)<sup>d</sup></th><th>Impactor equivalent mass (g)<sup>e</sup></th></tr></thead><tbody><tr><td>S09</td><td>–</td><td>5.67</td><td>10.8</td><td>227</td><td>37</td><td>0.021</td><td>0.94</td><td>1.49</td><td>0.16</td><td>41</td><td>0.006</td><td>227</td><td>0.006</td></tr><tr><td>S10</td><td>–</td><td>7.87</td><td>7.57</td><td>65</td><td>30</td><td>0.061</td><td>1.03</td><td>2.41</td><td>1.79</td><td>266</td><td>0.003</td><td>65</td><td>0.003</td></tr><tr><td>S11</td><td>–</td><td>8.57</td><td>12.2</td><td>113</td><td>37</td><td>0.030</td><td>1.49</td><td>2.09</td><td>0.12</td><td>87</td><td>0.005</td><td>113</td><td>0.005</td></tr><tr><td colspan="14">NW profile</td></tr><tr><td>S41</td><td>–</td><td>3.20</td><td>17.1</td><td>121</td><td>51</td><td>0.031</td><td>1.39</td><td>2.05</td><td>0.14</td><td>45</td><td>0.002</td><td>121</td><td>0.002</td></tr><tr><td>S43</td><td>–</td><td>5.20</td><td>10.7</td><td>88</td><td>30</td><td>0.031</td><td>1.23</td><td>2.72</td><td>0.18</td><td>74</td><td>0.002</td><td>88</td><td>0.002</td></tr><tr><td>S44</td><td>–</td><td>7.60</td><td>10.4</td><td>128</td><td>38</td><td>0.034</td><td>1.97</td><td>2.50</td><td>0.19</td><td>56</td><td>0.005</td><td>128</td><td>0.005</td></tr><tr><td colspan="14">Gebel Kamil</td></tr><tr><td></td><td></td><td></td><td>Fe</td><td>σ</td><td>Ni</td><td>σ</td><td>Co</td><td>σ</td><td>P</td><td>σ</td><td>S</td><td>σ</td><td></td></tr><tr><td></td><td></td><td></td><td>78.5</td><td>0.2</td><td>20.6</td><td>0.2</td><td>0.69</td><td>0.05</td><td>0.04</td><td>0.01</td><td>0.02</td><td>0.07</td><td></td></tr></tbody></table>

# RESULTS

## Petrography of Magnetic Particles

A first survey of the magnetic extracts under the stereomicroscope and the microanalytical SEM-EDS revealed a systematic difference in the distribution around the crater of the various types of magnetic particles. The magnetic extracts from samples collected in the E to SW sector are dominated by dark Fe-Ni glass in a variety of structures and occurrences, plus minor Fe-Ni oxide spherules and Gebel Kamil shrapnel (Fig. 2C). Magnetic extracts from the NW sector are dominated by amphibolite gneiss particles (Fig. 2D) belonging to the Precambrian Basement that crops out 100–150 m due NW of the crater rim (Urbini et al. 2012). In the other sectors, the magnetic extracts are dominated by crystals or crystal fragments of terrestrial Fe- and Fe-Ti oxides, garnet, and minor cosmic spherules mainly belonging to the barred olivine type (Fig. 2E). Although eolian quartz grains and sandstone particles are ubiquitous, they are more abundant in the samples collected due W of the crater. Although we cannot rule out that these particles could result from inefficient magnetic extraction, note that they often contain tiny inclusions of ferro-magnetic

minerals or they are coated by ferruginous deposits. Furthermore, we shall see that the external surfaces of the eolian quartz grains and sandstone particles from the East-to-the-South sector are speckled with tiny impactor splashes of dark Fe-Ni dark impact melt.

In the following two sections, we will focus on Fe-Ni particles, i.e., dark Fe-Ni impact melt glass and Fe-Ni oxide spherules. Due to their Ni-rich composition, we shall see that they are the only microscopic tracers of the Ni-rich impactor debris. For details on Gebel Kamil shrapnel, the reader should refer to D'Orazio et al. (2011).

## Dark Fe-Ni Impact Glass

Dark Fe-Ni glass occurs in the form of highly vesicular particles (Fig. 3), spherules (Fig. 4), and coatings (Fig. 5).

Dark glass vesicular particles are irregular masses characterized by delicate reticulite to pumiceous microstructures (Figs. 2 and 3). Under the stereomicroscope, they are brown to dark green. The composition of the glass (Table 2) is slightly variable and dominated by SiO₂ (57.0 ± 10.1 wt%), FeO (27.6 ± 7.5 wt%), and Al₂O₃ (10.4 ± 2.8 wt%), with subordinate TiO₂ (1.06 ± 0.31 wt%) and NiO (0.16 ±

<footnote><sup>a</sup>Total mass in grams of shrapnel (1–5 mm in size) separated from the magnetic extract under the stereomicroscope.</footnote>

<footnote><sup>b</sup>Total mass in grams of the soil fraction of the magnetic extract without shrapnel found under the stereomicroscope.</footnote>

<footnote><sup>c</sup>Total equivalent mass in grams of the impactor in the soil from the magnetic extract, i.e., it does not account for the contribution of shrapnel.</footnote>

<footnote><sup>d</sup>Total Ni concentration in µg g⁻¹ in the bulk sample, calculated from the contributions of shrapnel and the soil fractions of the magnetic extract. For the former, we assumed a concentration of Ni = 20 wt% (Gemelli et al. 2014) in the impactor.</footnote>

<footnote><sup>e</sup>Total equivalent mass in grams of the impactor in the bulk sample calculated from the footnote d, assuming a concentration of Ni = 20 wt% in the impactor (Gemelli et al. 2014).</footnote>
<figure><img src="image_4.png" /><figcaption>Fig. 3. Backscattered electron images of dark impact melt glass in the form of vesicular masses from sample S23. A) A highly vesicular particle consisting of a tenuous reticular network of glass. Oxide blebs up to tens of microns in size enriched in Fe, Ni, ± P, ± S float within the host glass (inset). They consist mainly of micron-sized oxides and are here referred as “Fe-oxide blebs.” Less frequently, Ni-rich metal blebs occur and are here referred as “Fe-Ni metal blebs.” A target rock clast (shocked sandstone) embedded in glass is indicated. B) Detail of another pumiceous particle showing abundant Fe-oxide and Fe-Ni metal blebs. CL = target rock clast; DG = dark glass, Fe-Ni bl = Fe-oxide and Fe-Ni metal blebs.</figcaption></figure>

0.10 wt%). Abundant oxide blebs up to tens of micrometers in size float within the glass (Fig. 3). They consist mainly of micrometer-sized Fe-oxides and are here referred to as “Fe-oxide blebs.” Their bulk composition (Table 2) is dominated by FeO (79.6 ± 4.32 wt%), SiO₂ (4.81 ± 1.65 wt%), and Al₂O₃ (4.79 ± 2.48 wt%), with traces of NiO (0.08 ± 0.02 wt%) and P₂O₅ (0.57 ± 0.62 wt%). Fe-Ni metal blebs, here referred to as “Fe-Ni metal blebs,” are sometimes also observed in the dark glass. They contain abundant Ni (26.3–94.2 wt%; Table 2); 4.45–69.1 wt% Fe; minor S (~2 wt%); and traces of P (~0.6 wt%), Co (<1.0 wt%), and Si (<0.2 wt%), suggesting that there was some mixing with the target material. Both types of blebs show nanometer-sized cellular intergrowths of—as yet—unidentified phases indicative of eutectic melts (Fig. 3A, inset). Submillimeter-sized, bedrock clasts (mainly sandstones) may also be found embedded in the dark glass (Fig. 3A).

The dark glass spherules (Fig. 4) are shiny and black under the stereomicroscope and show a number of splash form morphologies similar to those observed at Barringer crater (e.g., Hörz et al. 2002): from ovoids and irregular dumbbell to nearly perfect spherules, in the order of abundance. Some are delicately attached to each other and form compound spherules (Fig. 4B). Others are partially covered by splashes of other spherules (Fig. 4C). The vesicularity of the dark glass varies from moderate to negligible (compare Figs. 4A

and 4C). The external surfaces of the most vesicular particles are characterized by the occurrence of boiling and degassing microstructures including quenched bubbles and glass filaments (Fig. 4D). The filaments originate from the vesicles and are hollow. The external surfaces of the spherules are also finely decorated by dendrites of unidentified Fe-rich oxides <1 µm in size embedded in glass, often arranged in schlieren (Figs. 4A, 4D, and 4E). Sectioned spherules (Fig. 4E) show the characteristic vesicularity of the dark glass, its compositional heterogeneity, and the occurrence of several mineral and lithic inclusions. Inclusions mainly consist of bedrock fragments (quartzarenite), high-temperature (T > 1700 °C) silica glass or lechatelierite, and oxide and metal blebs (as described above). The heterogeneity of the glass is highlighted by schlieren and haloes with variable Si/Fe ratios around the inclusions. The composition of the glass (Table 2) is slightly variable, dominated by SiO₂ (49.2 ± 4.0 wt%), FeO (30.9 ± 3.7 wt%), and Al₂O₃ (12.3 ± 1.9 wt%), with subordinate NiO (2.71 ± 1.08 wt%) and TiO₂ (0.76 ± 0.01 wt%).

Dark glass coatings (Fig. 5) consist of mantles of shiny black glass continuously (or nearly so) enveloping small target lithic fragments (mainly quartzarenite) and lechatelierite. They are up to some 100 µm in thickness. The morphological, textural, microstructural, and compositional characteristics of their external surfaces are similar to those observed in dark glass spherules (see
<figure><img src="image_5.png" /><figcaption>Fig. 4. Backscattered electron images of dark glass spherules from sample S23. A) An ovoid spheroid showing abundant vesicles and a large glass bubble. B) Three spheroids stuck together to form a compound particle. C) A Fe-rich liquid splashed onto a glass spherule. D) Detail of the typical glass spheroid surface showing trails (schlieren) of Fe-rich oxides, glass bubbles, and glass filaments. The insets show that the filaments originate from the vesicles and are hollow. E) A sectioned spherule showing the characteristic abundant vesicularity of the dark glass, its compositional heterogeneity and the occurrence of several mineral and lithic inclusions. Inclusions mainly consist of fragments of quartzite, lechatelierite (vesicular), and Fe-oxide and Fe-Ni metal blebs. The heterogeneity of the glass is highlighted by schlieren and haloes around the inclusions. B = glass bubble; F = hollow glass filament; Fe-Ni B = Fe-oxide and Fe-Ni metal blebs; L = lechatelierite; Ox = oxides; Qtz = quartz; Sch = schlieren.</figcaption></figure>

above). Sectioned particles show that the glass coating is vesicular and envelops lithic fragments made by variably shocked and melted target quartzarenite, i.e., lechatelierite (Fig. 5D). The composition of the glass (Table 2) is slightly variable and dominated by $SiO_2$ (47.3 ± 3.2 wt%), $FeO$ (29.2 ± 3.0 wt%), and $Al_2O_3$ (16.1 ± 1.4 wt%), with subordinate $NiO$ (1.54 ± 0.63 wt%) and $TiO_2$ (0.81 ± 0.05 wt%). Similar microscopic glass coatings have been reported from Wabar (e.g., Mittlefehldt et al. 1992) and lunar samples (e.g., Apollo 16 lunar samples; Grieve and Plant 1973) and, at a cm-scale, also in impact melt lapilli and bombs at Barringer crater (e.g., Nininger 1954) and Kamil crater (Fazio et al. 2014).

## Fe-Ni Oxide Spherules

Fe-Ni oxide spherules (Fig. 6) are nearly perfect spheres typically ranging from 70 to 150 µm in diameter. Under the stereomicroscope, they are black with metallic luster and characteristic polygonal ridges on the external surface (Fig. 6A). Sectioned particles reveal that Fe-Ni oxide spherules consist mainly of interlocking crystals of at least two Fe-Ni-rich oxides yet to be determined. The less Ni-rich oxide, which

appears darker in backscattered electron images (Fig. 6B), is more abundant; it is most likely Ni-rich magnetite hosting very fine dendritic intergrowths of a more Ni-rich phase. The more Ni-rich oxide, which appears brighter in backscattered electron images (Fig. 6B), is more abundant toward the cores of the spheres. Relatively large voids are ubiquitous at the core of the spherules. They resemble contraction voids commonly observed in I-type cosmic spherules (i.e., molten micrometeorites consisting mainly of Fe-oxides; Genge et al. 2008) likely resulting from the rapid crystallization of the melt from the surface inwards (Feng et al. 2005), rather than vesicles. The bulk composition of the Fe-Ni oxide spherules (Table 2) is dominated by $FeO$ (71.6 ± 1.92 wt%) and $NiO$ (20.9 ± 1.90 wt%).

## Soil Particles Speckled with Dark Glass Splashes and Fe-Ni Oxide Spherules

An important fraction of the magnetic extract consists of soil particles (including quartzarenite and wacke fragments, eolian sand, etc.) whose external surfaces are speckled with tiny droplets and splashes of dark glass, Fe-oxide blebs, Fe-Ni metal blebs, and
<figure><img src="image_6.png" /><figcaption>Fig. 5. Stereomicrographs (A, B) and backscattered electron images (C, D) of dark impact melt coatings from sample S23. A) A whole particle coated with a shiny dark bubbly glass. B) A broken particle showing their typical structure: a dark glass coating a few tens of microns in thickness continuously envelops a target rock particle (in this case an aggregate dominated by quartz and colorless glass). C) A similar broken particle characterized by abundant glass bubbles at the surface. Inset: a detailed view of the contact between the glass coating and the internal target rock particle (in this case, a quartz grain). D) A sectioned particle showing that the glass coating is highly vesicular and envelops a particle made by a highly shocked quartzarenite. Inset: a close-up view of a quartz grain bearing three sets of PDF (at least one partially melted) and interstitial lechatelierite. B = glass bubbles; DG = Dark impact melt glass; PDF = planar deformation features; L = lechatelierite; Qtz = quartz.</figcaption></figure>

<figure><img src="image_7.png" /><figcaption>Fig. 6. Backscattered electron images of Fe-Ni oxide spherules from sample S23. A) A whole sphere showing the characteristic polygonal ridges on its outer surface. B) A section of the same sphere showing intergrowth of more Ni-rich and less Ni-rich oxides (pale and dark gray, respectively). Note the high vesicularity. Inset: fine intergrowth textures within the less Ni-rich oxide. Fe-Ni Ox = Fe-Ni oxides; I = fine intergrowth; V = voids.</figcaption></figure>

Fe-Ni oxide spherules (Fig. 7). These magnetic particles are abundant in the proximity of the crater and farther away in the E-to-SSW sectors.

## Main Geochemical Features of the Dark Glass

Although a detailed geochemical analysis of the impact melt glasses at Kamil crater will be reported in a separate paper, we briefly focus here on three main geochemical results.

The composition of the dark glass is heterogeneous at the submicrometer scale, but its bulk composition is similar in the three occurrences (Table 2). It is essentially a mixture of three components: SiO₂ (from
<figure><img src="image_8.png" /><figcaption>Fig. 7. Backscattered electron images of a soil fragment from sample S24. A) The soil fragment is speckled with tiny droplets of dark glass and Fe-Ni oxide spherules (plus splashes). The dashed area is the surface detailed in B). B) A close-up view of the same particle. CM = mostly clay material; DG sph = dark glass spheres; DG spl = dark glass splashes; Fe-Ni bl = Fe-Ni blebs; Fe-Ni sph = Fe-Ni oxide spherules.</figcaption></figure>

~47 to ~57 wt%), FeO (from ~28 to ~31 wt%), and Al₂O₃ (from ~10 to ~16 wt%). The Fe content, which is a minor component in the target, derives mostly from the iron impactor. The Si and Al contents, elements which are absent in the impactor, derive from the target. Bedrock quartzarenite and wacke may contain cm-thick levels of siltstones enriched in Al and kaolinite-rich matrix (Table 3). Figure 8A shows that the bulk compositions of the dark glass in the various occurrences lie on a mixing/mingling line joining the compositions of the two source materials: the target (Si-rich, plus Al) and the projectile (Fe-rich).

Figure 8B shows that the Ni/Fe ratio in the dark glass is lower than that of Gebel Kamil, whereas the Ni/Fe ratio tends to be higher in coexisting Fe-Ni metal blebs. We explain this trend through selective fractionation of Fe and Ni into the dark glass and coexisting Fe-Ni metal blebs, respectively, as a result of preferential Fe oxidation of a melt containing a Fe-Ni projectile fraction. Iron is preferentially oxidized relative to Ni as $\Delta G^{0}_{Fe/FeO} < \Delta G^{0}_{Ni/NiO}$, where $\Delta G^{0}_{Fe/FeO}$ and $\Delta G^{0}_{Ni/NiO}$ are the Gibbs free energy variations in the reactions $Fe + 0.5 O_2 = FeO$ and $Ni + 0.5 O_2 = NiO$; furthermore, regardless of P, T, and $fO_2$, their partition coefficients between a metallic and a silicate melt are $D^{Ni}_{met/sil} >> D^{Fe}_{met/sil}$ (e.g., Righter et al. 1997). Similar geochemical trends were observed in impact melt glass at Barringer and Wabar (Mittlefehldt et al. 1992; Hörz et al. 2002; Hamann et al. 2013), emphasizing the importance of this chemical process during hypervelocity impacts. Figure 8B also shows that the very high-Ni metal blebs have distinctly higher Ni/Fe ratios relative to the coexisting high-Ni oxide blebs, indicating extreme Ni fractionation into the metallic phases. More systematic EPMA work is required to verify a possible compositional continuum between the two bleb populations. The lack of Ni in Fe-oxide blebs suggests that they formed through the melting of accessory

minerals like Fe-oxides, described by Fazio et al. (2014) in the target rocks.

The Fe-Ni oxide spherules are the product of the melting of the iron projectile, as they have similar Ni/Fe and Ni/Co ratios to that of Gebel Kamil (Figs. 8B and 8C). Their high Ni concentrations ($NiO = 20.9 \pm 1.9$ wt%; Table 2) are different from those typically observed in I-type micrometeorites ($NiO = 2.75 \pm 0.54$ wt%; Folco and Cordier 2015) and are thus not related to the sporadic flux of micrometeorites. Fe-Ni oxide spherules from Kamil crater are similar to Fe-Ni oxide spherules found at the Sikhote Alin (Russia) crater field and interpreted as ablation spherules (Badyukov and Rajtala 2012). According to Badyukov and Rajtala (2012), the spherules formed late during the flight of the Sikhote Alin iron meteorite through the melting of debris produced during its disintegration. Further investigation is required to establish whether the Fe-Ni oxide spherules from Kamil crater are impact melts of the projectile or ablation debris formed during low-altitude atmospheric flight (i.e., shortly before the impact). In any case, they are impactor debris.

## Bulk Chemistry of the Magnetic Extract

The concentrations of Fe, Ni, Co, P, Mg, Ca, Ti, and V in the magnetic extracts (without shrapnel) are reported in Table 4.

Figure 9A shows the excellent correlation between Ni and Co with a Ni/Co ratio that matches that of the Gebel Kamil iron impactor (Ni/Co in Gebel Kamil = $29.8 \pm 2.5$; average Ni/Co in magnetic extracts 25.8; Table 4). This indicates that the source of Ni and Co in the magnetic extracts is Gebel Kamil (D'Orazio et al. 2011) and that Ni and Co contents can be satisfactorily used as tracers of the microscopic impactor debris around Kamil crater. There is no correlation between Ni and other major elements
<figure><img src="image_9.png" /><figcaption>Fig. 8. Compositional diagrams of the dark glass and Fe-Ni spheres. A) Aluminum-Si-Fe (wt%) triangular plot. Dark glass is essentially a mixture of target material (mainly sandstones dominated by quartz) and the iron projectile Gebel Kamil. The vesicular glass tends to be enriched in target material. B) Ni versus Fe showing Fe-Ni fractionation trends between dark glass and coexisting Fe-oxide and Fe-Ni metal blebs (see text for details). Fe-Ni oxide spheres plot close to the Gebel Kamil Ni/Fe ratio, documenting their parentage with the impactor. Their high Ni contents rules out an origin as I-type micrometeorites (data from Folco and Cordier 2015). C) Ni versus Co. The Ni/Co ratios of the Fe-Ni spheres is distinct from those of I-type micrometeorites and similar to that of Gebel Kamil confirming their parentage.</figcaption></figure>
<figure><img src="image_10.png" /><figcaption>Fig. 9. Major, minor, and trace element variation diagrams of the magnetic extract (<5 mm) of soil samples (aliquots without mini shrapnel) from Kamil crater. A–D) Ni versus Co, Fe, P, Mg, respectively. The dashed line in A–C is the Gebel Kamil ratio. The composition of the target rock (mainly sandstones) is shown for comparison. Note the very good correlation between Ni and Co with a Ni/Co ratio that is similar to that of the iron impactor Gebel Kamil, thereby indicating that the source of Ni and Co in the magnetic extracts is Gebel Kamil.</figcaption></figure>

present in Gebel Kamil, like Fe and P, even if the samples with higher Ni concentrations have higher Fe and P contents (Figs. 9B and 9C). The lack of correlation indicates that Fe and P have an additional source other than Gebel Kamil, most likely the terrestrial magnetic minerals and target rock fragments mentioned above (Fe-Ti oxides, garnet, etc.). The lack of correlation between Ni and Mg (Fig. 9D) rules out a contribution of Ni from either magnetic minerals in the crystalline basement (which crops out due NW of the crater; Urbini et al. 2012) or Mg-rich olivine and glass in micrometeorites (e.g., Cordier et al. 2011).

## Ni Distribution in the Soil Around Kamil Crater and Mass of the Impactor Debris

We shall present here the Ni distribution in the soil around Kamil crater distinguishing the fractions with and without mini shrapnel (Table 4). The separation of mini shrapnel resulting from the analytical issues discussed

above enabled us to study possible differences in the two types of fractions. The Ni content of the fraction with mini shrapnel was calculated by summing the Ni contribution of the mini shrapnel, assuming a Ni content of ~20 wt% in Gebel Kamil (D’Orazio et al. 2011).

The Ni contents in the fractions without mini shrapnel range from 65 to 19,322 µg g⁻¹ (Table 4). Figure 10A shows that Ni concentrations >1000 µg g⁻¹ occur in the samples from the E, SE, S, and SW profiles with concentrations decreasing with distance from the crater rim. Samples from the other profiles have Ni concentrations <200 µg g⁻¹. Given that the typical Ni concentration in the continental crust is <105 µg g⁻¹ (Rudnick and Gao 2004), we conservatively assume that the background Ni content in the target rocks at Kamil crater is likely <200 µg g⁻¹, whereas higher concentrations are the signature of the impactor debris. Note that this background threshold implies a negligible loss of <1% of the total Ni content in the studied samples. The maximum Ni contents were observed in
<figure><img src="image_11.png" /><figcaption>Fig. 10. Concentrations of the magnetic extracts versus distance from crater rim along the different sampling profiles. A) Trend lines for aliquot without mini shrapnel. B) Trend lines for the same samples including mini shrapnel. The highest Ni concentrations are observed in the SE and S profiles.</figcaption></figure>

samples S23 and S24 (Table 4) collected within 100 m of the crater rim along the SE profile. Other high Ni concentrations are observed in the S profile with a maximum 200 m from the crater rim (sample S19; Table 4) and extending up to ~800 m from the crater rim (sample S20; Table 4).

By adding the Ni contribution of the separated mini shrapnel (Fig. 10B; Table 4), the distribution does not change substantially, but important Ni concentrations are observed due S and SW of the crater with a maximum ~200 m from the crater rim.

Concentration maps (impactor mass per unit soil surface) of the microscopic impactor debris are shown in Fig. 11. Impactor debris is mainly dispersed due SW-SE of the crater in an area of ~300,000 m² that tails off southwestwards, reaching ~400 m from the crater rim. The integrated mass of Gebel Kamil debris

in the form of dark glass and Fe-Ni oxide spherules is ~120 kg (with a relative error of 20% due to extraction efficiency). The addition of the mini shrapnel yields a total of ~290 kg. Note that due to extraction efficiency discussed above, these mass estimates should be considered as a first-order approximation. Comparison between Figs. 11A and 11B highlights a significant shift from SE to SW in the location of the maximum concentration of the microscopic impactor debris around Kamil crater with the addition of mini shrapnel in the count. This difference may be explained assuming a more heterogeneous distribution of mini shrapnel relative to that of the dark glass due to their different origins, i.e., solid-state fragmentation at the rear of the projectile versus impact melting at the front of the projectile during contact and excavation, respectively.

## DISCUSSION AND CONCLUSIONS

### Ejecta Curtain

The hypervelocity impact of the Gebel Kamil iron meteorite produced an ejecta curtain containing microscopic impactor debris due SE-SW of the crater. Such dispersion is consistent with a downrange expansion as it extends along almost the same direction as the macroscopic shrapnel scatter field, which is considered the strongest indicator of a moderately oblique impact from the NW (D'Orazio et al. 2011; Urbini et al. 2012).

The microscopic impactor debris (i.e., the <5 mm-sized magnetic fraction of the ejecta curtain) consist mainly of shock melt particles. The shock melt is a mixture of a Si- and Al-rich target and Fe-Ni-rich projectile materials. The shock melt consists mainly of dark glass and occurs in the form of vesicular masses, spherules, and coatings enfolding variably shocked fragments of the target rocks. Subordinately, the microscopic impactor debris in the ejecta curtain contains Fe-Ni oxide spherules. Whether the latter are impact melt products or ablation spherules is yet to be determined. The microscopic particles formed a hot (as the melting of silica glass and iron meteorite requires temperatures higher than ~1700 °C), dense and turbulent spray in the ejecta curtain, as testified by the abundant dark glass particles found stuck to soil particles (Fig. 7), and by the abundant compound glass spherules (Fig. 4). The ejecta curtain containing microscopic shock melt particles was mainly dispersed due SW-SE of the crater in an area of ~300,000 m² extending up to ~400 m from the crater rim (Figs. 10 and 11).

Although the ejecta has an asymmetric, downrange distribution, we can generalize that the microscopic impactor debris in the ejecta of small-scale impact
<figure><img src="image_12.png" /><figcaption>Fig. 11. Concentration maps of the microscopic impactor debris around Kamil crater. A) Calculated mass distribution of the microscopic impactor debris of the soil without mini shrapnel. The total equivalent mass of the impactor equivalent is ~120 kg. B) Calculated mass distribution of the microscopic impactor debris of the soil with mini shrapnel. The total equivalent mass of the impactor is ~290 kg.</figcaption></figure>
<table><caption>Table 5. Impactor mass.</caption><thead><tr><th>Mass source</th><th>Method</th><th>Mass (kg)</th><th>Reference</th></tr></thead><tbody><tr><td>Regmaglypted specimens (individual)<sup>a</sup></td><td>Visual search</td><td>83</td><td>D'Orazio et al. (2011)</td></tr><tr><td>Shrapnel mass recovered on surface (&gt;10 g)</td><td>Visual search</td><td>700</td><td>D'Orazio et al. (2011)</td></tr><tr><td>Shrapnel mass weighed on surface (&gt;10 g)</td><td>Visual search</td><td>1500</td><td>D'Orazio et al. (2011)</td></tr><tr><td>Shrapnel mass on surface (&gt;10 g)<sup>a</sup></td><td>Estimate from density maps</td><td>3400</td><td>D'Orazio et al. (2011)</td></tr><tr><td>Shrapnel mass buried in ejecta (&gt;100 g)<sup>a</sup></td><td>Magnetic survey</td><td>1700<sup>b</sup></td><td>Urbini et al. (2012)</td></tr><tr><td>Impactor mass in impact melt debris in soil (&lt;5 mm)<sup>a</sup></td><td>Geochemistry</td><td>120</td><td>This work</td></tr><tr><td>Impactor mass in impact melt masses (&gt;5 mm)</td><td></td><td>n.d.</td><td></td></tr><tr><td>Shrapnel mass on surface (&lt;10 g)<sup>a</sup></td><td>Estimate from mass distribution</td><td>2250</td><td>This work</td></tr><tr><td>Shrapnel mass buried in ejecta (&lt;100 g)<sup>a</sup></td><td>Estimate from mass distribution</td><td>730</td><td>This work</td></tr><tr><td>Total</td><td></td><td>8283</td><td></td></tr></tbody></table>

n.d. = not determined.

ªMasses in the total.

ᵇThis is the maximum value of the 1100–1700 kg mass range estimated by Urbini et al. (2012).

craters such as Kamil crater is dispersed for only some crater diameters, and that the distribution is one order of magnitude smaller than that of the macroscopic shrapnel (i.e., masses >10 g), which at Kamil were found up to 1.6 km E of the crater rim (D'Orazio et al. 2011). The latter difference could be explained on considering that atmospheric drag decelerates small masses more efficiently than large masses, in agreement with recent models (Shuvalov and Dypvik 2013).

The impact melt products observed at Kamil crater are similar to those observed at Wabar (e.g., Mittlefehldt et al. 1992) and Barringer crater (e.g., Nininger 1956; Rinehart 1958) which were also generated by the hypervelocity impacts of iron projectiles on sedimentary targets including sandstone, dolostone, and loose sand. This documents that these impact cratering products can be found around small terrestrial craters with diameters ranging from several kilometers down to tens of meters.

Our estimate for the mass of the microscopic impactor debris at Kamil crater (~120–290 kg, without and with mini shrapnel, respectively) is a small fraction (~1.5–3.5%) of the estimated impactor mass in the form of macroscopic shrapnel (~8000 kg; see below: Table 5). Numerical models for the larger Barringer crater (~1.2 km diameter; iron impactor; sedimentary target; oblique impact; Artemieva and Pierazzo 2011) indicate much higher fractions (45%). We thus infer that molten microscopic impactor debris decreases significantly with decreasing crater diameter, whereas the production of macroscopic shrapnel increases. This is likely a consequence of projectile deceleration in the atmosphere. While in large craters, impact velocities are the same as pre-atmospheric velocities, in small craters, impact velocities are defined mainly by atmospheric entry (e.g., Melosh 1989).

## Impactor Trajectory

The distribution of the microscopic impactor debris around Kamil crater is concentrated due SW–SE of the crater. Overall, this asymmetric distribution is consistent with other findings, most notably the distribution of the macroscopic shrapnel (D'Orazio et al. 2011) indicating that the iron bolide approached the Earth’s crust from the northwest (305–340 °N), traveling along a moderately oblique trajectory. However, the distribution of the microscopic impactor debris is shifted south–southwestwards relative to that of macroscopic shrapnel. This deviation suggests that the microscopic impactor debris in the ejecta curtain was somewhat wind-blown by dominant north–northeasterly winds during deposition. In other words, after initial ballistic ejection from the launch point, air drag decelerated the microscopic impactor debris in the ejecta curtain until its motion was controlled by air flow.

Alternatively, the microscopic impactor debris distribution is, at least in part, secondary, possibly due to some south–southwestward eolian transport after deposition or occasional water runoff (see wadis in Fig. 11) after deposition. The lack of erosion features in the delicate microscopic dark glass particles (e.g., Figs. 3–5) favors the former hypothesis.

In any case, evidence from Kamil crater documents that, compared to the distribution of macroscopic shrapnel, the distribution of microscopic impactor debris is a weaker criterion for establishing the direction of impact.

## Impactor Mass in Microscopic Impact Melt Debris and Total Impactor Mass

The present study allows us to further constrain the impactor mass at the time of impact (Table 5). The
<figure><img src="image_13.png" /><figcaption>Fig. 12. Shrapnel mass distribution used in this work for an estimate of the total shrapnel mass <10 g on the surface and <100 g buried in the ejecta. The distribution is based on counts of specimens >10 g found in the field by visual search.</figcaption></figure>

mass of the impactor in the form of <5 mm impact melt debris (impact melt particles without mini shrapnel) estimated through concentration maps is ~120 kg. The total mass of the impactor in the form of <5 mm debris (impact melt particles plus mini shrapnel) estimated through concentration maps is ~290 kg. The total mass of macroscopic shrapnel >10 g inferred from concentration maps of specimens found on the surface around the crater during systematic search is 3400 kg (D'Orazio et al. 2011). The total mass of shrapnel >100 g buried in the ejecta blanket inferred through a geomagnetic survey is in the 1100–1700 kg range (Urbini et al. 2012).

Two size fractions of shrapnel must be now included in the count: shrapnel <10 g on the surface and those <100 g buried in the ejecta. To provide an estimate of the contributions of the first two shrapnel fractions above, we determined the shrapnel mass distribution (Fig. 12). The distribution is based on counts of specimens >10 g found in the field by visual search. Assuming that the logarithmic distribution applies to the two missing mass fractions, they should total ~2250 kg and ~730 kg, respectively (Table 5). In addition, the count should include the total mass of the impact melt bombs and lapilli of dark glass (impactor-rich glass) scattered in and around the crater (Folco et al. 2011; Fazio et al. 2014). Field observations indicate that this fraction should amount to a total mass comparable to that of microscopic impact melt impactor debris.

We thus speculate that the total mass of Gebel Kamil on impact with the target was close to 10 t. This is consistent with estimates of its pre-atmospheric mass, namely >20 t, most likely 50–60 t (Ott et al. 2014). The

estimated mass of the projectile at the contact is also consistent with calculations by Folco et al. (2011) and Urbini et al. (2012) by applying cratering models from literature (i.e., Collins et al. 2005) to Kamil crater. Scaling relations predict that a crater approximately 45 m in diameter can be generated in a sedimentary target by iron projectiles ranging from approximately 7 to 20 t in mass, assuming meteoroid entry velocities ranging from 12 to 18 km s⁻¹ and entry angles ranging from 30° to 45°.

*Acknowledgments*—This work was supported by the Italian Ministero degli Affari Esteri—Progetti di Grande Rilevanza, Protocollo Esecutivo ITALIA-EGITTO. The 2010 geophysical expedition work was carried out within the framework of the 2009 Italian-Egyptian Year of Science and Technology. We thank Prof. M. Alsherbiny (former President of the Egyptian National Academy for Scientific Research and Technology) and Prof. F. Porcelli (Scientific Attaché, Italian Embassy, Egypt) for diplomatic and institutional support; the Egyptian Army for logistical support. Luigi Folco and Massimo D’Orazio are also supported by the University of Pisa Fondi di Ateneo, and Agnese Fazio by the Barringer Family Fund for Meteorite Impact Research 2014. I Sterre is part of Labex OSUG@2020 (ANR10 LABX56). We thank F. Hörz and M. Ebert for constructive reviews, and N. Artemieva for editorial handling.

*Editorial Handling*—Dr. Natalia Artemieva

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