Drilling the Waqf as Suwwan impact structure

Abstract

The about 6-km diameter, near-circular Waqf as Suwwan structure located at E36°48′/N31°03′ in eastern Jordan was only recently recognized as a somewhat eroded, complex impact structure. Surface geological mapping, geophysical interpretation, remote sensing, and petrographic and mineralogical analyses have been carried out to understand the structure. In particular, the complex geology of the remnant of the central uplift has been scrutinized. A recent drilling project afforded an opportunity to expand the investigation of the structure to previously inaccessible strata of the ring syncline in the environs of the central uplift. Three boreholes were drilled, two to 140 and 110 m depth to the north and outside of the central uplift, and a further short hole to 5 m depth into the innermost part of the central uplift. Preliminary assessment of these cores has revealed the presence of around 11 m of fluvial breccias (wadi deposit) that are dominated by chert fragments at the top of the syncline fill. This is underlain by a normal succession of late Maastrichtian to Campanian strata. A variety of microstructures such as fracturing with vertical, as well as inclined at 45° and 30° fractures occurs throughout the cores. Some joints have slickensides along their walls. Limestone and marly limestone constitute the most abundant rocks in the boreholes. Distinct shock deformation effects are entirely lacking in the cores from the syncline. These observations are interpreted as a result of substantial erosion of the impact structure down to a level within the crater floor. The microstructures and the preliminary results of the analyses of sediment ages, textures, and compositions (nanofossils and sediment mineralogy) show that sediments as old as Campanian and as young as late Maastrichtian were affected by the impact. Unfortunately, the drilling did not expose any lithologies such as impact melt breccias that could lend themselves to absolute chronological analysis for a better constraint of the impact age.