חורש אלון מצוי מפותח על חבורת יהודה בעיקר על גבי מערכות קרסטיות בסלעי דולומיט CaMg(CO3)2. נבחנה השאלה מה יתרונה של סביבה זו. בסביבת אבן גיר מיקריטית של חבורת יהודה באזור הים תיכוני קיימת המסה רבה סמוך לפני השטח ונוצר חתך קרקע עבה יחסית. המים המחלחלים קרובים לרוויה בפחמות ואפשרותם להמיס סלע נוסף מעטה. בסביבה דולומיטית המים נשארים תוקפניים ונוטים לגרום להרחבת סדקים וליצירת כיסי קרקע מעמיקים. באבן גיר עשירת Mg נוצרים כיסי קרקע מפותחים יותר מאשר באבן גיר דלת Mg, ואילו באבן גיר אאוקנית מיקריטית של תצורת תמרת ביחס Mg/Ca=1:250 נוצרת קרקע עליונה רבה וכמעט ללא כיסי קרקע. עומק כיסי הקרקע בסלעים הקרבונטים הקשים מכתיב את עושר החורש המתפתח במקום. על קירטון של האאוקן קיים בית גידול אחר של חורש שנדון במאמרים אחרים
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Mg in carbonate rocks as a major factor controlling rock-soil relationship and Q. calliprinos maquies in Judea and Avedat Groups, Mediterranean zone, Israel. In Judea Group micritic limestone, intensive dissolution close to the surface renders the water almost saturated with carbonates, and little aggressiveness is left for deeper dissolution. The lower dissolution rate of dolomites allow the infiltrating water to remain aggressive, enlarge fractures and create deeper soil pockets. High-Mg limestones are thus associated with deeper soil-pockets compared with low-Mg limestones. Mg content is even lower in the Eocene Timrat Formation micritic limestone, whose Mg/Ca ratio is 1:250, supporting deep soil development with almost no pockets. The depth of soil pockets and their water capacity potential control local forest and maquis richness.
3. Mg in carbonate rocks as a major factor controlling
rock-soil relationship in Judea and Avedat Groups,
Mediterranean zone, Israel
Herr, N.,1
Frumkin, A.,2
Azaize, H.3
1. Soil and Water Department, The Hebrew University of Jerusalem,
76100 Rehovot
2. Geography Department, The Hebrew University of Jerusalem,
91905, Jerusalem
3. Research and Development Center the Galilee Society, 20200
Shefa’amr
Geomorphic and pedologic observations in the Mediterranean climatic
zone of Israel show that limestone and dolomite display a different soil-
rock interaction. The difference is reflected in karren-field structure, soil
pockets-rock-karren interaction, and the relationship between shallow and
deeper karst features. Dolomites apparently develop larger karren
formations, deeper soil pockets, and intensive karstification. Micritic
limestone of Avdat Group tends to support thicker homogenic soil cover,
almost without soil pockets. The rock-soil interaction apparently dictates
the floral ecosystem and species distribution.
Limestone and dolomite Mg content of Bina and Sakhnin Formations
seems to control the forest structure of the Upper Galilee. Additional
observations of forest and maquis in lower Galilee, Karmel and Samaria
indicate similar behavior in these regions too within Judea and Avedat
Groups. Comparison of rock-soil systems and meteoric water composition
along the route from surface to groundwater, indicate that the Mg influence
is not direct but rather involves variable dissolution processes associated
with variations of Mg content.
We compared Ca and Mg concentrations of meteoric water on bare rocks,
runoff, soil, karst shafts, caves and springs. Dissolution on bare rocks and
in the soil is more intensive on limestones compared with dolomites. Most
dissolution occurs at the soil-rock interface. On limestones, dissolution
capacity seems to be exosted in this interface, and solute concentration
does not increase much further down. On dolomites, dissolution is less
intensive at the upper unsaturated zone, and solute concentrations increase
significantly downwards through the shallow karst towards caves and
springs.
Suggested hypothesis: In Judea Group micritic limestone, intensive
dissolution close to the surface renders the water almost saturated with
carbonates, and little aggressiveness is left for deeper dissolution. The
lower dissolution rate of dolomites allow the infiltrating water to remain
aggressive, enlarge fractures and create deeper soil pockets. High-Mg
limestones are thus associated with deeper soil-pockets compared with
low-Mg limestones. Mg content is even lower in the Eocene Timrat
Formation micritic limestone, whose Mg/Ca ratio is 1:250, supporting deep
soil development with almost no pockets. The depth of soil pockets and
their water capacity potential control local forest and maquis richness.