The Palaeogeography of the Pleshet and Ahuzam formations (Pliocene-Pleistone) in the Western Shomeron Foothills,Israel

Abstract

Loose sands and calcareous sandstones of the Pleshet Formation (Pliocene-Pleistocene) are found mostly in erosive sinkholes and cavities, probably of karstic origin, in the western Shomeron foothills. The cavities occur in limestones of the Bina Formation (Turonian) and chalks of the Menuha Formation (Santonian-Campanian). These sediments also overlie chalks of the Bet Guvrin Formation (Late Eocene). The sands and the calcareous sandstones are overlain by a polymictic conglomerate Ahuzam Formation (Pliocene-Pleistocene). The sediments of the Pleshet and Ahuzam formations lie on a truncation plane dipping 1–2° westward, reaching in the east a morphological step. The sands are composed of well-sorted fine quartz grains (0.1–0.2 mm). In the eastern occurrences close to the morphological step, the heavy mineral composition is somewhat different from that found in the western occurrences. It is proposed that the truncation plane and the morphological step were formed by the ingression of the sea which deposited the Pleshet Formation. The sediments were supplied through the longshore currents of the Mediterranean from the Nile Delta. These sediments are characteized by heavy mineral composition similar to that of the Proto-Nile, which is considered to be of pre-Middle Pleistocene age. With the regression of that sea, large stream valleys, up to 2 km in width, flowed westward from the mountainous are in the east. These streams dissected the morphological step and deposited large alluvial fans on this plane, covering the pockets of the sandy deposits of the Pleshet Formation.