Mode and timing of kurkar and hamra formation, central coastal plain, Israel

Kurkar ridges along the coastal plain of Israel are composed of alternating calcareous aeolianite (kurkar) and paleosol (hamra) units. Precise infrared-stimulated luminescence dating on alkali feldspars from both types of sediment confirms that all the units comprising the most westerly kurkar ridge in the central coastal plain were deposited during the last 65 ka. Calculated rates of accumulation for the kurkar give 1-7 m/1000 years, with thick beds being deposited over periods as short as 2000-3000 years. On the other hand, accumulation rates for the hamra are at least one order of magnitude lower, about 0.1 m/1000 years, implying long periods of relative environmental stability. When these results are combined with measurements of the carbonate content of each unit, it appears that high carbonate content alone is not sufficient for kurkar formation, but a high accumulation rate is essential. Thus the governing factor that controls the fate of a deposited aeolianite, whether it will cement into kurkar or undergo pedogenesis, is the rate of accumulation.