Page 184 - Life & Land Use on the Bahrain Islands (Curtis E Larsen)

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dessication of the lake bed is indicated by evaporite-rich surface sediments
containing well-developed gypsum crystals. The sequence shows the development of
a playa lake of sufficient depth to allow the deposition of thick silt beds. Periodic
drying is indicated by the presence of four distinct root zones and from the deposit
of two thin anhydrite bands. Root development implies moist, subaerial conditions,
while anhydrite shows periods of aridity. The length of these arid periods at GAS1
was noticeably brief as indicated by the thinness of anhydrite layers. Sample 4
contained various root fragments collected and submitted for radiocarbon dating, i
but the small sample size did not provide meaningful results. Therefore, the
temporal placement of this lake cannot be discussed with certainty.
Approximately one kilometer east of this location is a possibly related
lacustrine sequence. TTiis is site KSS1, which is also capped by light brown, silty
fine sand with abundant gypsum crystals and is underlain by a shallow water
lacustrine sequence. TTiis section (fig. 33) shows the development of prominent
organic soils on the surface of sands deposited in a shallow lacustrine environment.
These paleosols are separated by a negatively skewed, fine sand of probable eolian
origin. The lower soil developed on a fine sand showing well-preserved oscillation
ripple marks. An upper paleosol developed on the eolian, slightly silty, fine sand.
Additional lacustrine fine sands overlie the upper paleosol. Aridity is signaled by
eolian sands which cover the second lacustrine phase and precede the deposit of the
evaporites at the surface (S-3 and S-l).
A radiocarbon date of 22,800 + 1035 B.P. was obtained on the lower of the
two paleosols. TTie interpretation of this sequence parallels the observed features
of GAS1. For example, a moisture peak bifurcated by a period of aridity is
indicated and finally superseded by conditions of hyperaridity. Thus, both sequences
relate to a late Pleistocene moist phase in agreement with McClure^s (1978)
evidence for late Pleistocene lake development in the Rub al-Khali. Section KSS1
appears to have been a lake margin environment at this time, while section GAS1
represents the deeper portion of the same lake.

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