Page 166 - Life & Land Use on the Bahrain Islands (Curtis E Larsen)

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Quaternary Environments
Quaternary sediments make up a varied array of both terrestrial and marine
deposits belonging to both the Pleistocene and Holocene epochs. Powers et al.
(1966) and al-Sayari and Zotl (1978) provide valuable reports of Quaternary
sediments in eastern Arabia, while Doornkamp, Brunsden, and Jones (1980) discuss
the surface deposits of Bahrain. In both areas, the Quaternary deposits are
characterized by fluvial sand and gravel deposits, calcareous or gypsiferous
duricrusts, lacustrine and playa deposits, shallow water and littoral marine
sediments, and evaporites. All are pertinent to Bahrain, but to a lesser extent than
on the mainland. Where the Arabian Peninsula has major Plio-Pleistocene wadi
systems draining large catchment areas, Bahrain's wadi systems are minor. Hence,
alluvial deposits are less extensive. More important are duricrusts, lake sediments,
marine sediments, and evaporites. Sabkhas underlain by evaporites, marine or lake
sediments, and eolian sands are also prevalent. As a group, these surface deposits
are useful in reconstructing the paleoenvironmental changes of the region.
Together with radiocarbon dating, the Quaternary sediments provide a context
linking the natural environment with the human past.
A clear understanding of Quaternary sedimentary processes for eastern
Arabia and Bahrain is not yet at hand. Changing patterns of past moisture and
aridity are more defined than when Powers et al. (1966), Willis (1967) and Tleel
(1973) published their work. TTie first concrete evidence for Pleistocene
paleoenviron mental changes in Saudi Arabia has been recently published by
McClure (1976, 1978) and McClure and Swain (1974). Al-Sayari and Zotl (1978) have
added still further insights. On the basis of numerous radiocarbon dates from
lacustrine deposits in the Rub al-Khali, McClure has defined two periods of
relatively greater moisture associated with the Late Pleistocene and Early
Holocene. The first of these occurred between 17,000 and 36,000 B.P., when lakes
were common on the southwestern margin of the "empty quarter." Aridity likened
to the present condition began by 17,000 B.P. and lasted until 9000 B.P. TOis
change is indicated by the deposition of eolian sands and the development of a seif
dune topography. A second period of greater moisture was attained between 9000