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. The image demonstrates the extensive drainage in this part of the East Jordanian desert, with regional drainage cutting across the ring structure, and the outer rim acting as a watershed generating both inward and outward directed drainages. The central elevation (so-called inner ring) has seemingly not been breached by drainage trends around its outside. Source: Royal Geographic Jordanian Centre, Amman. d) Digital elevation model created from a combination of Landsat 7 ETM + and WGS 84 (15 m horizontal resolution) data by Olive Branch Information Technology of Jordan. The ring structure lies in a plain at the foot of elevated Tertiary strata. The upturned Cretaceous cherts of the outer rim form a prominent ring. Within the ring syncline surrounding the central uplifted area a shallow uplift ring is recognizable. It is also obvious that the outer ring is breached in several sectors, allowing the regional drainage to continue denuding and, thus, eroding the structure. View towards the east. Crater diameter is 5.5 km. 1684 E. Salameh et al.

Fig. 2. Geology of the Jebel Waqf as Suwwan structure, after Heimbach (1969). Also shown are ten locations where shatter coning has been observed. All these sites occur along the complexly deformed block zone with arenitic strata surrounding the innermost limestone/marl- dominated area.

(compare Salameh et al. 2006, Fig. 3), it is this strong radial total thickness of 300 m (compare Table 1 as well as Figs. 1b drainage around the outer crater rim and off the central uplift and 4a, 4b). area that emphasizes the presence of the near-circular Waqf as Annular faults dipping consistently towards the structure Suwwan structure. (i.e., inward) surround the outer ring at a distance of a few The oldest exposed rocks in the area are sandstones of tens of meters. These ring faults separate the steep flanks of Lower Cretaceous age that occur within the innermost part of the outer ring from the surrounding flat-lying Eocene the inner complex. The sandstone is varicolored with reddish, carbonates. The surrounding carbonate dips at 2–4° towards violet, brown and yellowish tones. Around the periphery of the structure. A number of apparently normal faults segment the innermost zone one finds blocks of quartzite, also locally the outer ring structure. They trend generally highly oblique incorporated into the sandstone. Overlying the sandstone is a to the strike trend of the outer chert ring, and some of them sequence of alternating marl, shale, chalk, sandstone, trend radially with respect to the center of the crater structure. dolomite, and limestone, with some phosphate lenses, of a Locally, prominent drag into the fault plane has been The first large meteorite impact structure discovered in the Middle East 1685

Fig. 3. a) Shatter cone in fine-grained sandstone of the outer zone of the central uplift structure. Coin for scale: 1.5 cm wide. b) Several striated surfaces on a typically wind-ablated sandstone boulder in the outer part of the central uplift zone. Note that striations vary from near-parallel to clearly divergent, and that striated surfaces are spoon-shaped to undulating—similar to such features described, for example, from the Vredefort impact structure (Wieland et al. 2005). For scale, pen is about 13 cm long. Some remnant striae have been emphasized by thin lines. c) Extensive brittle deformation ( jointing at the mm- to cm-scale) of marly limestone of the central uplift. Hammer is about 35 cm long. d) Cataclasis including local clast rotation in marly limestone (outer part of the central uplift). Visible part of the pen is about 8 cm long. e) Cataclasis of chert on top of the southern outer rim. Hammer, for scale, is 35 cm long. f) Windkanter on top of the southern outer rim. Extremely fine-grained chert which had been jointed tightly, with joint strike parallel to the rim strike, was then eroded by persistent wind. Pen, for scale, is 13 cm long. 1686 E. Salameh et al.

Fig. 4. a) View from the southwestern crater rim across the syncline (the car is parked just beyond the shallow elevated ring feature which is barely visible as a thin brownish band just to the left of the car) towards the central uplift. b) View from the eastern part of the arenitic outer zone of the central uplift area across variably oriented blocks (note the diverse bedding orientations) of the block-faulted innermost zone, dominated by sandstone and marl. The little outcrop of chert in the foreground right serves as a scale and is about 1.5 m high and 5 m long. c) Several apparent thor features of chert, similar to the foreground feature in (b), from the outer chert zone of the Waqf as Suwwan central uplift complex are strongly reminiscent of the chimney like features from the outer part of the Oasis structure described by Koeberl et al. (2005). These authors interpreted these columnar features as erosional remnants of the limbs of decametre, upright folds formed in the upturned (thus, space-depleted) parts of that impact structure. Area shown is about 80 m wide. d) Another example of shatter coning (in this case, a fine example of “horse-tailing”) in fine-grained limestone from the central uplift of Waqf as Suwwan. Scale bar: 1 cm intervals. Note the obliquely cut surfaces that also display striations (marked with the thin red lines). Sample from locality 31°02′52.2′′Ν, 36°48′32.6′′Ε. observed. Cataclasis is also severe in places within the brittle that Lower Eocene limestone-chert layers could have been chert layer. Generally, the chert is extensively fractured (with incorporated into this zone (we have, however, not yet fractures generally relatively widely spaced at a centimeter to observed any evidence supporting this notion). several millimeters scale). The centralmost part of the structure (Figs. 1b and 4b) is Towards the interior of the structure, the outer ring is some 650 to 750 m wide. The early regional mapping followed by a synclinal feature with a relatively flat-lying determined that this central zone was displaced by a few floor that, towards its middle part, is however gently warped hundred meters towards the northwest, off the geometric (Fig. 4a). It can at this stage not be excluded that a shallow (2–4°) center of the crater structure. This innermost zone has a inward-dipping fault exists in the area of the central warp, at maximum elevation of 60 m above the surrounding synclinal 1.4 km from the center of the ring structure, as proposed by zone. Its innermost part is somewhat topographically Salameh et al. (2006)—additional fieldwork is required to depressed. As mapped by Heimbach (1969) and confirmed by confirm this. The topographic elevation associated with this us, the central zone shows a stratigraphic succession, towards warp is up to 20 m. On this subdued ring feature black-brown its interior, from relatively younger (Campanian- and strongly jointed, locally brecciated (monomict breccia) Maastrichtian) to older (Cenomanian-Santonian, followed by chert is extensively exposed. Heimbach (1969) remarked that basal Cenomanian) strata. The zone has been strongly the “strong disturbance of this inner ring zone” could imply affected by differential erosion, with chert and sandstone The first large meteorite impact structure discovered in the Middle East 1687

Fig. 5. Backscattered electron images: a) Two ostracoda forms (smooth and spongy) within marl of the central uplift. The fossiliferous concretion, which consists of silica and Mg-Al phyllosilicates, is surrounded by typical, very fine-grained silica. Scale bar: 20 µm. b) Another example of the very fine-grained chert occurring in the outer parts of the central uplift zone. Note the bimodal grain size distribution comprising relatively larger, subrounded and sometimes with irregular outer forms, quartz clasts set into a fine-grained mosaic-textured silica groundmass. The darker subrounded feature in the lower left is a Mg-Al enriched concretion of finest grained phyllosilicate. Scale bar: 20 µm. c) Brecciated (cataclasis) and possibly slightly sheared calcareous chert, composed of a mixture of calcite, quartz, and rather amorphous appearing Mg-Al silicate. This sample originates from the outer ring. Scale bar: 1 mm. d) Sample 60 originates from the top of the outer rim and represents a well-crystallized, micro-brecciated chert. Note the well developed crystal shapes in this sample. Scale bar: 20 µm. having been more resistant than limestone and marl. Detailed Amman), for the region around Jebel Waqf as Suwwan is structural analysis of this central zone is required; in shown in Fig. 1e. The ring structure is shown to lie in a plain particular it must be established whether all valley features in at the foot of elevated Paleogene strata. The upturned this area correspond to fault zones. Our fieldwork of 2007 Cretaceous cherts of the outer rim form a prominent ring. indicated that at least in some cases drag on adjacent strata is Within the ring syncline surrounding the central uplifted area notable at such gully structures. However, it must also be the shallow uplift ring is indicated but not prominent. It is also checked whether the obvious local juxtaposition of different obvious that the outer ring has been breached in several stratigraphic horizons and of lithologies of contrasting sectors, allowing the regional drainage to continue denuding resistance to weathering is responsible for the highly complex and, thus, eroding also the interior of the structure. topography. Structurally the innermost zone is highly complex A digital elevation model, based on the combination of (examples are shown in Figs. 1c and 4b). Strata dip variably Landsat-7 ETM and WGS 84 (15 m) data (OBIT Co., (subhorizontal to vertical) either towards or away from the 1688 E. Salameh et al. center. In the former case, these strata are partially coesite, stishovite, or diamond) in upper crustal rocks, (3) overturned. While locally talus covers the outcrop, it is shock metamorphic evidence, such as planar deformation obvious that the terrain encompasses megablocks separated features (PDF) in quartz, or (4) shatter cones (e.g., Montanari by faults, and that many of these blocks involve strongly and Koeberl 2000; Koeberl 2002; Reimold 2007). folded strata. Clearly, some blocks have been rotated by The initial investigations by Salameh et al. (2006) and our folding (drag being prominent), whereas others have been 2007 work have lead to the identification of by now 10 rotated and seemingly are displaced. The fact that brittle chert locations (Fig. 2) that exhibit shatter cones (Figs. 3a and 3b, and jaspilitic iron formation have been folded on a ten meter 4d), all within the highly deformed rocks (sandstone as well as scale, without extensive brittle deformation accompanying limestone) of the central, uplifted zone. For example, at this, is indicative of the dynamic nature of the deformation 31°02′57′′Ν/36°48′42′′Ε a small limestone enclave occurs process. Locally gentle folding is observed which can be within chert, which contains shatter cones throughout its mass. correlated to a stage of compressional deformation tentatively Figure 3b shows examples of striated, variably plane or related to the collapse of the central uplift. curved, even curviplanar, fracture surfaces that are very much The overall impression that there is a distinct succession like the striated joint phenomena known extensively, for from older to younger strata in an outward direction is not example, from the central uplift of the Vredefort impact maintained when mapping at the ten to hundred meter scale, structure in South Africa (e.g., Manton 1962, 1965; which is the result of juxtaposition of blocks of such sizes and Nicolaysen and Reimold 1999; Wieland et al. 2006). Striated from different stratigraphic levels. Already Heimbach (1969) fracture surfaces at Jebel Waqf as Suwwan at some sites occur found that in the outer parts of this inner zone faulting had in multiple orientations. Surface alteration in the harsh desert resulted in juxtaposition of steep-standing Lower environment seemingly has widely obscured striations (a Maastrichtian and blocks of subhorizontally layered Eocene typical example of a sandstone surface with remnants of strata. Figures 3 and 4 give several impressions of the intense partially ablated shatter cone striae—emphasized with thin deformation of this innermost zone, at variable scales. lines—is shown in Fig. 3b), and care has to be taken to However, as mentioned, detailed structural analysis still distinguish remnants of shatter cones from also, but rarely, remains to be carried out. The innermost area is near-circular occurring ventifacts (compare Fig. 3f, which illustrates wind and surrounding rocks mostly dip inward. “Dike-like” bodies erosional features, so-called windkanter, from the outer rim of of both carbonate and silicious rock occur apparently the structure). The shatter cone in limestone shown in Fig. 4d squeezed between larger blocks, and being characterized by was revealed when the sampled hand specimen, collected extensive brittle deformation (jointing and fracture cleavage). because of a crude shatter cone remnant on its outside, split The lower areas within this central zone are widely covered open during handling, indicating that shatter cones occur by talus and debris fans off the higher hills. penetratively at Jebel Waqf as Suwwan. This sample is derived On the mesoscale, the quartz-rich strata of the inner from 31°02′49.7′′Ν/36°48′33.7E. The perfect horsetailing is, complex are extensively deformed (Figs. 3a–c, 4c). thus, preserved on both the positive and the negative sides of Fracturing (locally resembling fracture cleavage) is intense, the shatter cone sample. Note that the inner margins of the two and decimeter to meter wide areas of intense cataclasis photographs display striations on two different fracture-planes abound. Some of these cataclasites have been infilled with a (emphasized by thin lines marking the divergence of striae) groundmass of carbonate and/or barite, attesting to post- oriented nearly vertical to the prominent horsetailing. At deformational hydrothermal activity. Whether this can be 31°02′52.2′Ν′/36°48′32.6′′Ε intense jointing of the type called related to the immediate post-impact phase is, however, not “multipli-striated joint surfaces (MSJS)” by Nicolaysen and indicated. Reimold (1999) was observed. These authors linked the MSJS to the shatter cone phenomenon. EVIDENCE OF IMPACT DEFORMATION Monomict brecciation of sandstone and limestone is found widespread in the outer parts of the central uplift area Regarding the macrostructure, the make-up of Jebel (e.g., Figs. 3c and 3d), as well as locally along the outer rim Waqf as Suwwan (Fig. 1a) is generally consistent with a comprising chert (Fig. 3e). Figure 3f illustrates the extensive cross-section through a complex impact structure, comprising jointing found along much of the outer chert rim. This an upturned rim surrounding a gently deformed ring syncline deformation has also been strongly exploited by wind erosion, feature, in turn surrounding an intensely, at various scales, resulting in arrays of sharp windkanters formed parallel to the deformed central area with distinct stratigraphic uplift. major wind direction. However, in order to confirm the presence of an impact Figure 5 shows several microscopic to submicroscopic structure, one or more of impact-diagnostic recognition features of cherts from Jebel Waqf as Suwwan. This includes criteria need to be fulfilled. These include (1) identification of a fossiliferous (two types of ostracoda) and phyllosilicate-rich remnants of an extraterrestrial projectile, (2) impact (shock) concretion (Fig. 5a), and also shows that these cherts are diagnostic mineral transformations (such as formation of composed of two generations of deposited material (silica as The first large meteorite impact structure discovered in the Middle East 1689

impact origin. The following conclusions can be made from the preliminary studies completed to date:

1. Ample occurrence of shatter cones confirms the origin by impact. 2. Microdeformation evidence in favor of impact has so far remained extremely limited. This is interpreted as the result of significant erosion of the structure, in particular of those strata in the upper part of the central uplift structure where one would expect to find significant levels of shock metamorphism. 3. To date, extensive macro- and mesoscopic deformation has been recorded; however, the detailed structural analysis of this remains to be done and has the potential to make a significant contribution to the understanding of the deformation processes active in the central uplifts and rims Fig. 6. Photomicrograph of a shock-metamorphosed quartz grain of complex impact structures formed in sedimentary targets from a sandstone sample from the central uplift structure. Note the (e.g., in comparison with the structural studies of Upheaval multiple sets of planar deformation features (labelled 1–3) and planar Dome—Scherler et al. 2006, or the Haughton impact fractures (4, 5). Modified after Fig. 9 of Salameh et al. (2006). The structure—various papers in Meteoritics & Planetary photograph shows two sets of planar deformation features (PDF) Science 40, no. 12, 2005). marked 1 and 4, and two sets (2, 3) of planar fractures (where it is obvious that they are open features) or fluid inclusion trails (where 4. The rarity of shock metamorphic effects in the rocks of tiny vesicles can be recognized). Jebel Waqf as Suwwan could well be related to the fact that this impact took place into soft, porous, and strongly well as Mg, Al-rich clasts in silica dominated groundmass, stratified sedimentary target strata, with the structure now Fig. 5b). Brecciated and slightly sheared chert is shown in being deeply eroded. This situation can, for example, be Fig. 5c at the micro-scale, whereby the indicated ductile compared to the findings at Upheaval Dome, where deformation is suggestive of pre-impact tectonic overprint. similarly only very limited shock metamorphic evidence Typical mosaic and well-crystalline chert texture is shown in could be recorded (Kenkmann 2003; Buchner and Fig. 5d. In general, both crystallized and seemingly amorphous Kenkmann 2008). Further detailed analysis of this (i.e., likely deposited as colloidal matter) silica is observed in situation, in comparison with shock experimental work and these cherts. deformation studies at similar structures are vital to further Extensive search for planar microdeformation features elucidate the role that target composition and respective (PDFs or planar fractures [PFs]) has been carried out by us on rheology, porosity, and water content play with regard to some 70 specimens of chert and sandstone. However, only 1 the deformation levels attained. grain with well developed shock microdeformation has been 5. The age of the Jebel Waqf as Suwwan impact is currently discovered to date (Fig. 6) and was originally presented by only stratigraphically constrained at post-Paleogene Salameh et al. (2006, their fig. 9). Two sets of narrow spaced (about 30 Ma or younger). As discussed by Heimbach planar deformation features and two sets of comparatively (1969), the structure encompasses Middle Eocene strata, much wider spaced planar fractures (where identifiable as the deposition of which provides only an upper age limit open features) or planar fluid inclusion trails are clearly (Miocene or Pleistocene) for this impact event. recognizable. In addition, a number of thin sections of both fine-grained quartz-rich rocks (chert, sandstone) and Acknowledgments–The University of Jordan and the Higher limestone/marl frequently display micro-cataclasis, even Council of Science and Technology of Jordan are thanked for where the hand specimens did not indicate its existence. Thus, financial support. The BGR (Bundesanstalt für Geologie und cataclasis has been observed in the Jebel Waqf as Suwwan Rohstoffe) assisted with analyses of samples and scientific context at all scales from macroscopic to submicroscopic. Our advise. WUR’s research is supported by Humboldt University search for further shock-induced, impact-characteristic in Berlin and the German Science Foundation. R. Knöfler of microdeformation is ongoing. the Museum for Natural History, Humboldt University, provided excellent thin sections. Nils Hoff and Claudia CONCLUSIONS Crasselt assisted with graphics. The EBIT Co. of Amman processed and provided Fig. 1e. Reviews by Lucy Thompson The discovery of a number of sites with shatter cones and Jens Ormö, as well as editorial suggestions by John leaves no doubt that the Jebel Waqf as Suwwan structure is of Spray, improved the original manuscript. 1690 E. Salameh et al.

Editorial Handling—Dr. John Spray tectonics, edited by Koeberl C. and Henkel H. Impact Studies Series, vol. 6. Heidelberg: Springer-Verlag. pp.161–190. Manton W. I. 1962. The orientation and implication of shatter cones REFERENCES in the Vredefort Ring structure. Masters thesis, University of the Witwatersrand, Johannesburg, South Africa. 167 p. Bender F. 1968. Geologie von Jordanien. Beitrag zur regionalen Manton W. I. 1965. The orientation and origin of shatter cones in the Geologie der Erde, vol. 7, Berlin: Bornträger Publ. 280 p. Vredefort Ring. Geological Problems in Lunar Research. Annals Bender F. 1975. Geology of the Arabian Peninsula, Jordan. United of the New York Academy of Sciences 123:1017–1049. States Geological Survey Professional Paper 560. pp. 101–106. Mittlefehldt D. W., See T. H., and Hörz F. 1992. Dissemination and Bucher W. H. 1936. Cryptovolcanic structures in the United States. fractionation of projectile materials in the impact melts from 16th International Geological Congress. Washington, D. C., Wabar Crater, Saudi Arabia. Meteoritics 27:361–370. vol. 2. pp. 1055–1084. Montanari A. and Koeberl C. 2000. Impact stratigraphy: The Italian Bucher W. H. 1963. Cryptoexplosion structures caused from without record. Heidelberg: Springer-Verlag. 364 p. or from within the earth? (“Astroblemes” or “Geoblemes”?). Nicolaysen L. O. and Reimold W. U. 1999. Vredefort shatter cones American Journal of Science 261:597–649. revisited. Journal of Geophysical Research 104(B3):4911–4930. Buchner E. and Kenkmann T. 2008. Upheaval Dome, Utah, USA: Reimold W. U. 2007. The 29th De Beers Alex L. Du Toit Memorial Impact origin confirmed. Geology 36:227–230. Lecture: Revolutions in the Earth Sciences—Continental Drift, Earth Impact Database. http://www.unb.ca/passc/ImpactDatabase. Impact and Other Catastrophes. South African Journal of Accessed 15 April 2008. Geology 110:1–46. Heimbach W. 1969. Vulkanogene Erscheinungen in der Kalktafel Salameh E., Khoury H., and Schneider W. 2006. Jebel Waqf as Zentraljordaniens. Beiheft zum Geologischen Jahrbuch 81:149– Suwwan, Jordan: a possible impact crater—A first approach. 160. In German. Zeitschrift der deutschen Gesellschaft für Geowissenschaften Kenkmann T. 2003. Dike formation, cataclastic flow, and rock 157:319–325. fluidization during impact cratering: An example from the Scherler, D., Kenkmann T., Jahn A. 2006. Structural record of an Upheaval Dome structure, Utah. Earth and Planetary Science oblique impact. Earth and Planetary Science Letters 248:43–53. Letters 214:43–58. Wieland F., Reimold W. U., and Gibson R. L. 2006. New Kennedy S. and Coleman D. L. 2000. Maps of meteorite/asteroid observations on shatter cones in the Vredefort impact structure, impact craters on earth. Dubuque, USA: Jensan Scientifics. South Africa, and an evaluation of current models for shatter Koeberl C. 2002. Mineralogical and geochemical aspects of impact cone formation. Meteoritics & Planetary Science 41:1737– craters. Mineralogical Magazine 66:745–768. 1759. Koeberl C., Reimold W. U., and Plescia J. 2005. BP and Oasis impact Wynn J. C. and Shoemaker E. M. 1998. The day the sands caught fire. structures, Libya: Remote sensing and field studies. In Impact Scientific American, November 1998. pp. 1–10.