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Facies changes along the Jurassic-Cretaceous boundary in Jordan
Issa Makhlouf, Basem K. Moh'd

Building: Muséum d'Histoire Naturelle de Genève
Room: Amphithéâtre
Date: 2018-12-06 03:50 PM – 04:10 PM
Last modified: 2018-12-01

Abstract


The Jurassic-Cretaceous boundary in Jordan is defined at the base of the overlying Lower Cretaceous, i.e., the Kurnub Sandstone Group, which is marked by the regional 'Lower Cretaceous Unconformity' (LCU). The upper part of the Jurassic strata is comprised of carbonate dominated facies, i.e., the Mughanniyya Formation, beneath the sandstones of the overlying Kurnub Sandstone Group. The topmost of the Jurassic succession is marked by a thin argillaceous sandy paleosol horizon containing plant remains, and are underlain by fossiliferous strata (limestones, marlstone, clay and dolomite) assigned a latest Bathonian to Callovian age. The peritidal setting of the uppermost Jurassic is evidenced by the variable lithofacies including dolomitic limestone, mudcracked mudstones with burrow mottling, and shallow scours with granular and pebbly sandstone infillings. A regressive event during the deposition of the Kurnub Group, when progressive shoaling of the sea floor and further retreat of the shoreline.

The lowermost Cretaceous Kurnub sequence consists of sandstone with shale and mudstone interbeds that formed under braided and meandering fluvial systems. These terrestrial facies passes upward into tidal and shallow marine carbonate facies. The boundary separating the Cretaceous strata from the underlying Jurassic strata is marked by the LCU that truncates all of rock formations below, when the land emerged and the Neotethys Sea retreated northwards due to a major eustatic sea-level fall, and the northward flowing streams accompanied a regional uplift of the Arabian-Nubian Shield.