Tuesday, 11 July 2006 - 4:20 PM

Paleosols of the Southern Coastal Plain of Israel.

Moshe Wieder, Gdaliahu Gvirtzman, and Maoz Dassa. Bar-Ilan University, 52900 Ramat-Gan, Israel

Paleosols of the southern coastal plain were studied on a characteristic sequence situated in the Ruhama badland area. At the upper part of the sequence a Loessial Arid Brown Soil (Haploargids) appeared to be characteristic to the mildly arid area climate of the area. The soil has two calcic horizons and covers four clayey soil layers alternating with four calcareous layers beneath them. Each of this layers were considered by other researchers as distinct paleosol units. Physical, chemical, magnetic susceptibility data and micromorphological indications support the concept that each clayey layer together with the calcareous layer beneath it form a single pedogenic unit. These units are similar to modern Grumusolic soils ( Xeric Paleargids or Xerertic Calciargids) that occur in the semiarid belt of the southern coastal plain and developed on eolian dust parent material. The calcareous layers are in fact calcic horizons derived from the leaching of the carbonates from the clayey layers and accumulated in the form of "in situ" carbonate nodules. The leaching of the carbonates from the clayey layers is not complete. There are still 15-20 percent carbonates as microcalcites distributed homogenously in the clay and fine silt size fractions. This feature together with a typical brown color is characteristic of the modern soils that occur in the semiarid water regime of the area. The four superimposed paleosols are four cycles. It is suggested that they formed in two phases during the last glacial period. During a dry environment a short phase of rapid eolian dust accumulation prevailed followed by a long stable phase of soil development in somewhat wetter climate. The authors recorded a rapid accumulation of eolian dust during a short dry period, caused by the Younger Dryas event in the central coastal plain. In the present paleosol sequence it is assumed that the Younger Dryas period is expressed by the second distinct calcic horizon that occur in the upper Loessial Arid Brown soil. In all the soil materials formed on eolian dust parent material in the area the upper size limit of the grains is 0.1mm that represents the upper size capacity of the winds to carry eolian dust from the desert source at high elevations. Under the four cycles there occur two total leached paleosols that developed on sandy parent material. Both have a reversal magnetic polarity being older than 780Ka BP. The upper one has a brown color and the lower a strong red color. They developed during a humid climate showing intensive clay illuviation features. In the same time they are polygenetic soils including carbonates leached from the above calcareous material. The two paleosols formed in a different environment than the modern soils developed on sandy parent material that derives from sand dunes prvided by the delta of the Nile by the Mediterranean offshore currents. The distribution of the sand grains derived from the coastal sand dunes show that the largest grains are of medium size of 0.20-0.35mm. Quartz size that are larger than 0.5mm seldom can be found. In the reversal magnetic sandy paleosols many angular quartz sand grains larger than 0.5-1.0mm occur, that suggest a more terrestrial origin of the sandy material.

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