The Lower Cretaceous Chouf Sandstone of Lebanon: A Regional Reservoir Level in the Levant?

The lowermost unit of the Cretaceous succession onshore Lebanon is a widespread prominent sandstone formation traditionally known as the “Gres de Base”. The formation commonly consists of sandstones with some claystones, shales, lignites and locally volcanic rocks. Based on outcrop samples taken in the central and northern parts of Mount Lebanon the petrographical composition of the typical Chouf Sandstone is dominated by monocrystalline quartz (85–95%) indicating a well-sorted sandstone. Sedimentological observations suggest that the Chouf Formation deposited in fluvial, coastal plain and deltaic environments. The Barremian Chouf Sandstone is variable in thickness, ranging from a few metres to more than 700 m. Some abrupt lateral isopach variations are interpreted to be the result of deposition in individual extensional mini-basins located in a much larger overall basin extending into neighbouring Syria, Jordan and Israel/Palestine. Due to the lack of subsurface information, the isopach values were estimated from remote sensing observations of the Chouf outcrop geometries in NW Lebanon. Assuming a syn-rift origin for this formation, the thickness measurements were interpreted in the context of numerous half-grabens with the master normal faults trending WNW-ESE. The petrography of the Chouf Sandstone exposed at the surface suggests a potentially moderate to good reservoir in the subsurface as well. U–Pb detrital zircon geochronology of eight Chouf rock samples collected in NW Lebanon confirms this interpretation in agreement with earlier findings on age equivalent sandstones, some 400 km to the south. The good reservoir potential of these regional Neocomian to Barremian sandstones is mostly due to their recycled nature from quartz-rich Cambrian-Ordovician sandstones. Age-equivalent sandstones are proven reservoirs in the broader region, therefore the Chouf play could be a viable petroleum exploration target in both offshore and onshore Lebanon.