Lake Elji and a geological perspective on the evolution of Petra, Jordan

Abstract

The draining of the herein introduced ancient Lake Elji, and the subsequent erosion of its lacustrine sediments, were necessary precursors to the Late Epipalaeolithic (Natufian) and later settlement of Petra. This study investigates this geological history and relates it to human occupation of the broader region. Widespread carbonates consisting of algal mat deposits, beach rocks, and rhizoliths are consistently present at the 1060 m contour line of what is believed to be the shoreline of Lake Elji in the Petra basin. Well sorted siliciclastic fluvio-lacustrine sediments at lower elevations and human settlement patterns all indicate that a standing body of water once existed in the area. Stable isotopes of carbon and oxygen, as well as the fossil assemblages and the textures of the carbonate deposits, suggest that the body of water was an open lake with regular outflows. A sill has been identified at Ras Btahi, indicating a southward outflow direction, as opposed to the current drainage pattern towards the west. The lack of a basin closure towards the west at the time, as evidenced by thick, low energy sediment accumulations, suggest that tectonic movements were responsible for breaching the lake and establishing the current hydrological pattern. Results obtained from the optical stimulated luminiscence (OSL) in the palaeolake sediments indicate that the basin was closed from at least 100 Ka up to approximately 9 Ky. This timeline is also supported by the distribution of archaeological sites in the area and a previously documented massive erosional event at the end of this period. Subsequent gradual denudation of the basin sediments allowed for the settlement in the center of Petra during the Early Nabatean period.