Meteoritics & Planetary Science 43, Nr 10, 1681–1690 (2008) Abstract available online at http://meteoritics.org The first large meteorite impact structure discovered in the Middle East: Jebel Waqf as Suwwan, Jordan Elias SALAMEH1, Hani KHOURY1, W. Uwe REIMOLD2, and Werner SCHNEIDER3 1University of Jordan, Faculty of Science, Amman 11492, Jordan 2Museum for Natural History, Humboldt University, Invalidenstrasse 43, 10115 Berlin, Germany 3Im Ziegenförth 15, 38108 Braunschweig, Germany *Corresponding author. E-mail: [email protected] (Received 16 December 2007; revision accepted 30 April 2008) Abstract–Triggered by re-evaluation of a 1960s report on the regional geology of the northeastern border region of Jordan and following Landsat satellite image investigation, a 5.5 km diameter, complex, circular structure was discovered in the central eastern region of the Kingdom of Jordan. Initial ground truthing revealed complex geological structures involving Upper Cretaceous and Paleogene strata, and including a prominent outer rim rising up to 60 m above the surrounding plain, an intermediate ring of up to 20 m elevation within a ring syncline, and a central zone of stratigraphically uplifted sedimentary strata characterized by intense macroscopic (folding and faulting, widespread cataclasis) and locally mesoscopic (cataclasis) deformation. Ten sites with shatter cone development in fine-grained sandstone or limestone have been mapped to date, mostly in the outer parts of the central uplifted area. This finding confirms that the Jebel Waqf as Suwwan structure was formed as the result of the impact of an extraterrestrial projectile. Search for impact- diagnostic micro-deformation has been rather unsuccessful: only 1 quartz grain with both planar deformation features and planar fractures has been detected in a sandstone sample to date. The overall majority of the approximately 70 samples investigated by micropetrographic analysis consist of extremely fine-grained chert, siltstone, or marly limestone. Cataclasis is widespread in chert and limestone, also on the micro-scale. Considering the severely limited amount of characteristic impact microdeformation, and the stratigraphic situation within the central uplift, it is likely that a relatively deep level of the central uplift is currently exposed. The extensive drainage demonstrated for this region supports the conclusion that this impact structure could be quite deeply eroded—especially as its geology involves some relatively soft lithologies (marls, limestones). The age of this impact event is at present poorly constrained at post-Middle to Lower Eocene. INTRODUCTION complex,” the so-called “Jebel Waqf as Suwwan” (Arabic for “Mountain of Upright Chert”) structure (Figs. 1a and 2b), To date not a single sizable impact structure has been centered at 31°03′222′′N/36°48′230′′E in northeast Jordan, in identified in the entire region of the Middle East, west/ a remote area of the eastern Jordanian desert, close to the northwest of India, with the exception of the Wabar small- border with Saudi Arabia. While providing a detailed crater field in the Rubh al Khali desert of Saudi Arabia (e.g., stratigraphic description and some structural detail, Mittlefehldt et al. 1992; Wynn and Shoemaker 1998; Heimbach (1969) concluded that the structure was of “crypto- www.unb.ca/passc/ImpactDatabase/). This is even more volcanic” origin due to its alleged structural similarity to the astonishing, as much of this huge terrane is desert land, with Wells Creek and Jephta Knoll structures, examples for excellent possibilities for remote sensing investigations. Bucher’s (1936, 1963) “cryptovolcanic structures,” in the In the late 1960s, a detailed geological investigation of USA (note that Wells Creek has since been confirmed as an the territory of the Kingdom of Jordan was carried out by the impact structure—Earth Impact Database, accessed 22 April Bundesanstalt für Geowissenschaften and Rohstoffe (BGR; 2008, wheras Jephta Knoll is listed in some compilations of Federal Geological Survey of Germany; Bender 1968, 1975; impact structures, e.g., Kennedy and Coleman 2000, but is not Heimbach 1969). The latter author described a unique “ring recognized by the Earth Impact Database). Heimbach did 1681 © The Meteoritical Society, 2008. Printed in USA. 1682 E. Salameh et al. Table 1. Stratigraphy of the Jebel Waqf as Suwwan region. Formation symbols as applied in Fig. 2 (modified after Heimbach 1969). System Series Symbol Age (Ma) Description Middle to Lower Eocene tt2 56–37 Chalk and chalk-marl-chert sequence with grey or reddish chert, nodules and concretions. At the base, white massive marls (10 m thick). Paleogene Lower Eocene tt1 56–48 Whitish to light grey limestone, with some chert layers. Limestone, marly limestone, and chert sequence. Paleocene C4 65–56 Whitish, yellowish to green marl with limestone concretions at the base. Some chert beds. Maastrichtian C3 71–65 Layered brecciated chert, with some phosphatic limestone beds. Upper Cretaceous Campanian-Turonian C2 92–71 Yellowish, greenish, or whitish marls and marly limestone, with some phosphatic bands at the top. At the bottom, 10 m thick yellowish limestone with intercalated thin marls. Cenomanian C1 100–92 Red-brown, fine-grained sandstone, and partly silicified limestone. remark, however, on the lack of evidence for the existence of up to 0.8 m thick chert horizons, occurs. A detailed a magmatic body in the subsurface, but proceeded to infer an stratigraphic column for the Waqf as Suwwan region was allegedly hidden basalt plug underneath the centralmost part provided by Heimbach (1969). Paleontological findings of the structure. assisted to define the detailed stratigraphy (compare Some of us (WS, ES) reconsidered this interpretation and stratigraphic summary in Table 1). in 2005 began a ground-based investigation of Jebel Waqf as Aerial and satellite imagery (Figs. 1c and 1d) clearly Suwwan. Initial findings of shatter cones resulted in a depicts the extensive drainage patterns both in the entire preliminary publication that proposed an impact origin for environs and extending through the Jebel Waqf as Suwwan this structure but that also contained several speculative structure (see also next section). This illustrates that erosion is thoughts that are yet to be confirmed (Salameh et al. 2006). highly active in this area. Here we present a comprehensive description of Jebel Waqf as Suwwan and review all currently available evidence for an JEBEL WAQF AS SUWWAN: GEOLOGY impact origin of this conspicuous geographic and geological feature. We also present results from a field visit in April 2007 Heimbach (1969) determined that the ~5.5 km wide as well as results from a petrographic investigation of structure comprised an outer, near circular although faulted specimens from the central part of the structure as well as the ring anticline of extremely fine-grained brownish chert outer crater rim, with particular attention to the possible belonging to the Neogene period (Figs. 1a and 2). The outer presence of shock metamorphic evidence. ring structure is prominent, rising up to 800 m above sea level, up to 60 m above the surrounding plains, and up to 50 m REGIONAL GEOLOGY above the interior synclinal structure. The outer slope is generally steep, and steeper than the inner slope. According to Jebel Waqf as Suwwan is located in a remote part of Heimbach (1969) and our own observations, dips of the chert the eastern Jordanian desert (geological map, sheet Azraq, of the outer rim are varied from about 40 to 90° and are scale 1:250,000). The regional geology of northeastern mostly outward directed (Fig. 2a). However, local Jordan, in the area around Waqf as Suwwan, is dominated overturning is noted with high inward dips of the chert (up to by plains and occasional inselberge of table mountain >70°). The 20–30 m thick Upper Cretaceous chert on top of geometry representing a succession from Lower the anticline represents an excellent stratigraphic marker bed. Cretaceous to Paleogene strata (Cenomanian to Middle Drainage (Fig. 1c) is extensive in the form of wide wadis Eocene; compare stratigraphic chart of Table 1; also cf. in the generally flat region around Waqf as Suwwan, with Figs. 1a and 2). Dips of these stratigraphic formations are northerly, northeasterly, and southeasterly directed systems generally subhorizontal (generally less than 5°), generally being particularly prominent. Intense drainage emerges from directed towards the north or east. To the east of Jebel but also transgresses in a strong radial pattern the outer crater Waqf as Suwwan a prominent escarpment of generally flat- rim (Fig. 1c). Several drainage paths cut across the entire lying Middle Eocene strata occurs, and to the northwest the crater structure and funnel into a strong northward system. regional Middle Eocene cover thins to eventually reveal Notably, these drainage branches flow around the prominent, Paleocene strata. In summary, in the Jebel Waqf as somewhat triangular central uplift area, from which thin Suwwan area a >300 m thick pile of Upper Cretaceous and drainage lines emerge particularly towards the south and east/ Paleogene carbonate rocks, intercalated with extensive and northeast. On a regional aerial photograph or satellite image The first large meteorite impact structure discovered in the Middle East 1683 Fig. 1. a) Schematic geological cross section through the Jebel Waqf as Suwwan structure, as provided by Heimbach (1969). Considering this structure the result of “cryptovolcanism,” Heimbach envisaged a basalt plug underneath the central part of the structure. b) Photograph of the view from the southern outer rim (comprising dark colored and strongly jointed/brecciated and wind-eroded chert) across the here not visible syncline and across the extensively deformed strata of the inner ring. Note the centralmost, slightly depressed area surrounded by upturned, folded, and displaced blocks of arenitic and limestone/marl strata. Width of the area shown ~600 m. Photograph by W. Schneider. c) Aerial photograph (taken on 5 January 1961; image no. 1144 11 1085) of the near-circular Jebel Waqf as Suwwan structure and environs.