The formation appears to have been deposited in a pelagic subtropical environment on the outer continental shelf of the Afro-Arabian continent, with the Harrana locality being deposited no deeper than 100 metres (330 ft) below the surface, based on the occurrence of depth-limited fauna such as nurse sharks.[4] The formation of this habitat likely originates from a major marine transgression of the Tethys Ocean at the same time as this depositional event, turning it into an open water ecosystem. The oil shales may have formed from cold upwelling currents from the Tethys that increased the region's planktonic productivity, with these fossilized plankton eventually turning into oil.[2][3] The sites of excellent fossil preservation may have been formed by anoxic conditions on the seafloor hindering the decomposition of organic matter as well as rapid burial of fossils, although the presence of bottom-dwelling scavengers suggests that anoxic conditions must have been relatively moderate.[4]
While the formation as a whole lasts from the early Maastrichtian to the end of the Paleocene based on foraminifera-based dating, a significant uncomformity exists in some localities at the Cretaceous-Paleogene boundary, which may be due to a drop in sea levels at the time, with deposition continuing following a second sea level rise in the Paleocene.[1] In addition, the highly fossiliferous portion of the formation was only deposited in the span of a few hundred thousand years at the end of the Maastrichtian.[6]
A locality in Harrana is a Konservat-Lagerstätte with extremely well-preserved fossils that were deposited during the latest Maastrichtian, around 66.5 to 66.1 million years ago[6], making it one of the last lagerstatten to be deposited before the Cretaceous-Paleogene extinction event. The preservation is akin to that of the older, more well-known Sannine Formation from Lebanon. Fossils are contained in concretions exposed by limestone mining, which started in the Harrana region around 1995. Notable fossils from this locality include articulated fish and mosasaur skeletons, mosasaur skin impressions, and evidence of mosasaur carcasses scavenged by nurse sharks & other fishes.[4]
The fossil potential of the Harrana locality was documented by geologist Hani Kaddumi, who described most of the formation's taxa in a 2009 book. Many fossils from this locality are held in the Eternal River Museum of Natural History in Jordan.[4]
The following list of biota is based primarily on Kaddumi (2009). Unless stated otherwise, a majority are from the Harrana locality:[4]
An indeterminate marine reptile, initially described as a late-surviving polycotylidplesiosaur, but more recently found to possibly be a marine crocodylomorph.[8]
^ abcdefKaddumi, Hani Faig (2009). Fossils of the Harrana fauna : and the adjacent areas. Jordan: Eternal River Museum of Natural History. OCLC709582892.
Jordan
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