Characteristics of the Sahara as a meteorite recovery surface

Abstract

We describe the geological, geomorphological, and paleoclimatic setting of the Sahara of North Africa in particular, focused on the main meteorite dense collection areas (DCA; Morocco, Algeria, Tunisia, and Libya). We report on the outcome of several meteorite recovery field expeditions in Morocco and Tunisia since 2008, by car and by foot, that applied systematic search methods. The number of meteorites collected is 41 ordinary chondrites and one brachinite. The statistics of unpaired ordinary chondrites indicates that H chondrites are more abundant (21) than L chondrites (12), while LL chondrites are rare (2). Our meteorite density estimates for Tunisia and Morocco are in the order of magnitude of 1 met km−2. An estimate of the total maximum number of meteorites that could be recovered from the Sahara is 780,000 meteorites. We selected 23 meteorites from Aridal, Bou Kra, Bir Zar, and Tieret DCAs for 14C dating. The results show a wide range of terrestrial ages from 0.4 to more than 40 kyr with a majority of meteorites showing ages between 0.4 and 20 kyr. The weathering degree of these meteorites is ranges from minor (W1) to strong (W4). The highest weathering grades result from repeated oscillations between high and low humidity in the Sahara. However, there appears to be no correlation between weathering grade and terrestrial age of meteorites.

The distribution of the desert meteorites in China and their classification

“…The mass of desert meteorites from China is mainly concentrated between 10 and 1000 g with a peak between 100 and 1000 g, which is consistent with that from Africa (peak between 100 and 1000 g), but inconsistent with that from both Australia (peak between 10 and 100 g) and Antarctica (peak at <10 g) (Ouknine et al, 2019). The mass distribution of collected meteorites from Loulan Yizhi and Lop Nur shows a maximum within 10–100 g, while those from Kumtag and Hami are mainly distributed in the range 100–1000 g. The mass distributions of these DCAs correspond to those of DCAs from other deserts such as Tieret, Bir Zar, UAE, San Juan, Dhofar, and Acfer (Aboulahris et al, 2019). The difference in the mass distribution of collected meteorites from China, Africa, Australia, and Antarctica is mainly explained by the differences in surface features and collection methods (Ouknine et al, 2019).…”

“…In some typical DCAs of the Kumtag Desert, the numbers of ordinary chondrites of each type are as follows: Kumtag (7H/33L/2LL), Alatage Mountain (2H/3L), Loulan Yizhi (15H/24L/4LL), Hami (8H/11L/1LL), and Lop Nur (6H/8L). These ordinary chondrites type ratios are all characterized by a dominance of L chondrites, followed by H, and then LL chondrites, which is the opposite of DCAs from Sahara, Algeria, and Libya (Aboulahris et al., 2019; Ouknine et al, 2019). The dominance of L chondrites in the deserts of China may result from the lack of a systematic recovery method for the ordinary chondrite collection or might be caused by an insufficient pairing due to the lack of accurate information about the ordinary chondrites other than our samples studied in this paper.…”

“…6c), the accumulation time is ~10 kyr, which is estimated considering a meteorite flux of 0.24 meteorites km −2 Myr −1 (˃90 kg) from Halliday et al (1989); note that the meteorite flux was also corrected for the latitude effect according to the latitude model proposed by Evatt et al (2020) (Table 6). Previous studies suggest that small meteorites could be collected effectively by systematic search by foot; however, searching randomly by foot or vehicle favors bigger finds (Aboulahris et al, 2019). Considering the lack of systematic search in these areas (A, B, and C), we suggest that the error on the meteorite accumulation time estimated from area C should be lower than that from areas A and B.…”

“…In addition, the advantages of meteorites collected from hot deserts relative to Antarctica include that (1) hot deserts are easier to reach (Muñoz et al, 2007); (2) meteorite searching and collection in hot deserts costs less; (3) unlike Antarctic meteorites, hot desert meteorites are most often found where they fell and can provide statistics about meteorite shower distribution, and the bolide fragmentation processes during the atmospheric entry (e.g., Gnos et al, 2009; Kring et al, 2001; Pourkhorsandi et al, 2019). Therefore, an increasing number of hot deserts have been investigated and sampled; meteorites have been collected and studied from arid areas such as the Australian deserts (Benedix et al, 1999; Bevan & Binns, 1989), the Atacama (Drouard et al, 2019; Gattacceca et al, 2011; Hutzler et al., 2016; Muñoz et al, 2007), the Sahara (Aboulahris et al, 2019; Bischoff & Geiger, 1995; Ouazaa et al, 2009; Schlüter et al., 2002), the central and southwestern United States (Hutson et al, 2013; Kring et al, 2001; Rubin & Read, 1984; Rubin et al, 2000; Zolensky et al, 1990), the Arabian Peninsula (Al‐Kathiri et al, 2005; Gnos et al, 2009; Hezel et al, 2011; Hofmann et al, 2018; Zurfluh et al., 2016), and the Lut Desert (Pourkhorsandi et al, 2019).…”

Determination of olivine fayalite–forsterite composition in ordinary chondrites by X‐ray diffraction

“…Since increased humidity increases chemical weathering, especially in ordinary chondrites (Aboulahris et al, 2019; Velbel, 2014), the room temperature and humidity were recorded during this experiment. To measure the repeatability of the XRD analyses, as well as the potential for changes in results caused by exposure to room temperature and humidity, one ordinary chondrite sample prepared in the same manner and mixed with SRM 640a was analyzed four times over four successive days with no changes or adjustment to the sample between measurements.…”