Page 179 - Life & Land Use on the Bahrain Islands (Curtis E Larsen)

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The southern playa is more extensive (ca. 65 km ) and contains not only
silts and aeolian sands, but also thick layers of gypsum or anhydrite deposited in a
former Pleistocene lake. This lake left behind sufficient organic remains for
radiocarbon dating, while the margins have yielded unidentified flint artifact
collections (A.S. Goudie, personal communication). This playa is discussed in
greater detail in the following section, where the available record of lake changes
points to a moisture record consistent with the record from the Late Pleistocene
and Early Holocene lakes of the Arabian Peninsula (McClure 1976, 1978).

Basins of Deposition
Lake deposits provide more helpful evidence for paleoenv iron mental changes than
do the various wadi fills. Several such basins were examined during the course of
this fieldwork. Four of the many stratigraphic sections were sampled and analyzed.
Depositional basins are located at the northern and southern ends of the island—
both inside and outside of the interior basin. The first basin studied is a structural
depression filled with lacustrine deposits and identified as a collapse feature by
Italconsult (1971). TTie second basin lies within and at the southern end of the
interior basin. This, too, received runoff from several sources and is now filled
with a variety of Quaternary lacustrine and eolian sediments. The stratigraphic
sections discussed here are: sections GAS1 and KSS1 from the northern basin and
sections TLW2 and TLW4 from the southern basin (fig. 30).
Sediment samples consisting of approximately 100 grams were collected
from each described stratigraphic layer, unless the sedimentary unit appeared to be
uniform. In this case, samples were taken at ca. 20-cm intervals throughout the
sequence. Each sample was air-dried in the laboratory and disaggregated using a
mortar and rubber-tipped pestle. A representative sediment sample was shaken for
10 minutes on an automatic Ro-Tap shaker through a nested series of wire mesh
sieves chosen to retain sediment grains at a one half phi-internal. After shaking,
each sieve was emptied and the retained sediment weighed to the nearest 0.01
gram. A visual inspection of each grain size increment was then made using a 10
power hand lens. Grain shape, texture, and mineralogy were recorded. Cumulative