A story told by calcareous nannofossils—the timing and course of an Eocene meteorite impact in central Jordan

Abstract

A circular structure, 5.5 km in diameter, in central eastern Jordan has been interpreted as a large meteorite impact structure. The age of the Waqf As Suwwan impact is poorly constrained. By examining calcareous nannofossils from the sediments exposed in this structure, an age model of the timing of the event has been obtained. A total of 81 smear slides from two cores (BH-1, BH-2) penetrating the sediments of the central structure were prepared in order to obtain a biostratigraphic age for the post-impact sediments. The calcareous nannofossils assign sediments below the breccias of the core BH-1 an age of late Campanian to late Maastrichtian and a mixture of late Maastrichtian to early Eocene ages in the breccia horizon, while core BH-2 is of early Maastrichtian to late Maastrichtian age. The upper part of the sediments, removed in from adjacent area, consists of breccia components. The presences of calcareous nannofossil marker assemblages suggest that these components were derived from two different sources: a Cretaceous and a Paleocene-Early Eocene one. The deposition of the breccia resulted from gravitational collapse of water-saturated sediments in two stages; the earlier of these was more intensive than the latter. The stratigraphic framework and the presence of reworked Cretaceous and Paleocene calcareous nannofossils within Paleogene nannofossil Zone NP12/NP13 suggests an early Eocene age for the impact. The upper part of the Cretaceous sediments was thermally altered by the impact causing partial or complete dissolution of the calcareous nannofossils. This caused overgrowth for the more resistant species, while others were dissolved.