LAUSR

The strata exposed at Jal Az-Zor escarpment in northern Kuwait represent one of the best outcrops in the country, extending over 60 km in length with a cliff-face of around 36 m. The age assignment of these rock units was mostly done during the 1920s to 1960s and was largely based on taxonomy grouping of an oyster-rich bed present at the base of Jal Az-Zor correlated to what appeared to be a similar layer that belongs to the Lower Fars Formation in Iran. In the subsurface, the results of biostratigraphic analysis using different taxonomic groups have suggested ages that position this exposed lithological unit in the range of late Miocene to Pliocene (11.63–2.58 Ma). Due to the lack of radiometric numerical data, the strontium isotope ratio (87Sr/86Sr) age-dating method was applied on carefully selected surface and subsurface samples including an oyster shell, beds with abundant fossils, and calcite cemented specimens. Petrographic, XRD, and SEM-EDX analyses were utilized to determine the rock composition, assist in identifying the biomass, and carbonate content of the samples before performing age dating on selected areas of the sample. Numerical age determination based on (87Sr/86Sr) ratio revealed that an oyster shell taken from the cliff of Jal Az-Zor is 20.53 Ma in age (Aquitanian), the fossiliferous bed exposed at the foot of the escarpment is 24.39 Ma in age (Chattian), and the Sabriyah roadcut beds exhibit an age of 30.32 Ma (Rupelian). The subsurface extracted samples that are dominated by calcite cement uncovered an age range between 36 and 19.41 Ma (Burdigalian to Priabonian). This analysis introduces the late Eocene and Oligocene to Kuwait’s stratigraphy otherwise known to be eroded. The implications of such findings can revamp the Paleogene and Neogene tectonic evolution of Kuwait and potentially lead to the renaming of the undifferentiated Kuwait Group strata to a more representative name, such as the Kuwait Formation that combines the traditional tripartite subdivision of the group.