Quaternary sandstones, northeast Jordan: Age, depositional environments and climatic implications

摘要

OSL dating of weakly consolidated, root-bound, non-calcareous quartz arenites in northeast Jordan, currently assigned to the Plio-Pleistocene Azraq Formation, suggests a Middle Pleistocene (652 +/- 47 ka) age. The sandstones are up to 15.5 m thick and overlain by a 2.5 m thick Holocene gypcrete caprock. Facies and textural analyses suggest that the sandstones are predominantly aeolian in origin, mainly derived from Tertiary sediments exposed close to the depositional site. The sands were transported by the prevailing NW winds and deposited in a broad, relatively flat sand sheet environment. Rhizoliths occur throughout the sandstones, mainly as long, downward tapering, vertical tap roots, rarely branched and with few laterals. Microscopic examination of root cores replaced by carbonate reveals the presence of alveolar fabrics, possible needle fibre calcite, calcified organic filaments of fungal, root vessel and root hair origins, characteristic of low magnesium beta calcretes, typical of humid climates.