Muwaqqar Chalk-Marl Formation

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Muwaqqar Chalk-Marl Formation (Jordan)

The Muwaqqar Chalk-Marl Formation, also called the Muwaqqar Formation, is a geological unit in Jordan dating from the latest Cretaceous (Maastrichtian) to the early Paleocene. It stretches across the Jordanian Highlands from north to south and contains Jordan’s famous oil shales, among the largest in the world. Some outcrops preserve fossils exceptionally well, making the site a lagerstätte.

Depositional setting: a pelagic subtropical environment on the outer continental shelf of the Afro-Arabian plate during a major transgression of the Tethys Ocean. The Harrana locality was deposited in water no deeper than about 100 meters. Cold upwelling from the Tethys likely boosted plankton production, helping form the oil shales as organic material fossilized. Excellent fossil preservation at some sites may come from low-oxygen conditions on the seafloor and rapid burial, though scavenging indicates oxygen levels were not completely absent.

Timing: overall sedimentation spans from the early Maastrichtian to the end of the Paleocene, but some localities show a gap at the Cretaceous-Paleogene boundary, possibly due to a sea-level drop, with deposition continuing after a later sea-level rise in the Paleocene. The most fossil-rich interval was laid down in a few hundred thousand years at the end of the Maastrichtian.

Harrana Lagerstätte: A Konservat-Lagerstätte at Harrana contains exceptionally well-preserved fossils from the latest Maastrichtian (about 66.5–66.1 million years ago), one of the last such deposits before the mass extinction at the K-Pg boundary. Fossils are found in concretions exposed by limestone mining that began around 1995. Notable finds include articulated fish and mosasaurs, mosasaur skin impressions, and evidence of carcasses scavenged by nurse sharks and other fishes. The fossil fauna of Harrana was documented by Hani Kaddumi in a 2009 book, and many fossils are housed in the Eternal River Museum of Natural History in Jordan.

The Harrana fossil list is based mainly on Kaddumi (2009), with contributions from Krewesh et al. (2014) and Jagt et al. (2017).