Fluvial-shallow marine-glacio¯uvial depositional environments of the Ordovician System in Jordan

The Ordovician System, cropping out in southern and west-central Jordan, consists entirely of a 750 m thick clastic sequence that can be subdivided into six formations. The lower Disi Formation starts conformably above the Late Cambrian Umm Ishrin Formation. According to Cruziana furcifera occurring in the upper third of the Disi Formation, an Early Ordovician age is con®rmed. The Disi Formation, consisting mainly of downstream accretion (DA) ¯uvial architectural element, was deposited in a proximal braidplain ¯owing N±NE from the southerly-located Arabian±Nubian Shield towards the Tethys Seaway. The braidplain depositional environment evolved into a braid-plain-dominated delta through the middle and upper parts of the Disi Formation and the lower part of the overlying Um Saham Formation. The delta was replaced by siliciclastic tidal ¯ats, that in turn evolved into an upper to lower shoreface environment through the upper part of the Um Saham Formation. The depositional environment attained the maximum bathymetric depth during the deposition of the lower and central parts of the third unit, the Hiswa Formation, where offshore graptolite-rich mudstone with intercalated hummocky cross-strati®ed tempestites were deposited. The Tethys Seaway regressed back through the upper part of the Hiswa Formation promoting a resumption of the lower±upper shoreface sedimentation. Oscillation between the lower to upper shoreface depositional environment characterized the entire fourth unit, the Dubaydib Formation, as well as the Tubeiylliat Sandstone Member of the ®fth unit, the Mudawwara Formation. The depositional history of the Ordovician sequence was terminated by a glacio¯uvial regime that ®nally was gradually replaced by a shorefac