Geology of Ayn Al Majdoub Karstic Lake, Benghazi, NE Libya

Abstract

The major karstic area in Libya known as Ayn Zayanah system is a unique phenomenon of concentrated karstic surface and subsurface dolines and channels. By focusing on Al Majdoub Lake, as a case study, we can better understand how lithology, structure and hydrology contribute to the regional formation of the Karstic system. Geologically, the limestones of the middle Miocene, Benghazi Formation is forming the northern side of Benghazi region, which is characterized by well-developed surficial, interface, surface and subsurface karstic features that are open or filled with sediment. The formation of Ayn Majdoub doline is filled with saline water, which is attributed to the dissolution of a buried carbonate layer by fresh groundwater due to the drop of the Sea level and the associated groundwater levels. This is combined with epeirogenesis movements, which have caused the development of karstification to reach a depth of 130-150 m below present sea level in the Benghazi plain. Through this Karstic system, groundwater seeps from Benghazi Basin towards the Ayn Zayanah (The Spring) and then to the Blue Lagoon (The Lake) finally to the sea.