LAKE SEDIMENTS OF THE GADOT FORMATION IN THE HULA VALLEY, ISRAEL-A SOURCE OF BUILDING STONES

The Gadot Formation is exposed in the southern part of the Hula Valley (north of Lake Kinneret), covering an area of about 10 km². The sediments were deposited in a lake extending south of the present day Hula Valley; they overlie the Ruman Basalt unit in angular unconformity and are covered by the Yarda Basalt unit. The age of the Gadot formation ranges between 1.6-0.9 Ma based on K-Ar radiometric dating of the Ruman and the Yarda basalt units (Pleistocene). The Gadot Formation is composed of white to gray, massive, dense lacustrine limestone weathered into “nari” (caliche) in which only rare Melanopsis shells are found. The thickness of the Gadot Formation is about 25 to 30 m, but the exposed formation does not exceed 5 m. Eighteen representative samples were collected in the field from outcrops of the Gadot Formation and were studied for their ostracode assemblages. The assemblage of the ostracode species from the Gadot Pleistocene Lake includes: Cyprideis torosa, Candona neglecta, Ilyocypris gibba, Ilyocypris bradyi and Darwinula Stevensoni. C. torosa and C. neglecta are the most common ostracodes found. All ostracode species indicate that the environment of deposition was a rather shallow lake of fresh to oligohaline water (slightly brackish). The narization process of the upper 1-2 m of the Gadot formation gives the original soft lacustrine chalks additional strength and durability. Yet, it is still soft enough for working, very porous and relatively light (~1.75 gr/cm3) which makes an excellent insulator for building especially in the heat of the Hula Valley. The use of this rock type as a building stone was limited to few periods that cover more than 3,500 years of history (Middle Bronze to Recent).