Page 172 - Life & Land Use on the Bahrain Islands (Curtis E Larsen)

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Near Abqaiq and adjacent to archeological site 208-76 (Adams et al.
1977), two further sections
were exposed. These were in a close association with
the river and lake system but were chiefly composed of eolian fine- to medium-
grained sands. Two strong paleosols, developed in these sands, indicate periods of
increased soil moisture thought to relate to higher levels in the adjacent lake. A
lower paleosol dated to 3315 + 245 B.P. (1565-1595 B.C.) was covered by eolian
sands upon which had developed a second paleosol dated to 2560 + 170 B.P. (750
B.C.). Together these paleosols reflect upon a long period of dessication (ca. 815
years). Overlying this entire geological section and covering several hectares of the
adjacent land surface were late first millennium B.C. ceramics related to the
Hellenistic collections from Thaj (Bibby 1973).
Other dated stratigraphic sections from al-Hasa come from the eastern
border of the Hofuf Oasis, where aerial photographs shows traces of abandoned
irrigation networks. Archeological survey of this same area shows the abandoned
canals to be related to late Early Islamic period cultivation. A black organic soil
associated with this Early Islamic cultivated area is underlain by a gypsiferous silty
sand pointing to salinization related to possible soil saturation from the irrigation
network. Regardless of the cause of evaporites, a lower paleosol has been dated to
2040 + 175 B.P. (20 A.D.). TTiis soil was developed on gray silty sand of uncertain
environmental history. Further evidence for greater moisture conditions during the
Early Islamic period was discussed above in connection with the Hotzl, Kramer, and
Maurin (1978) studies of the same area, where organic soils dated to A.D. 850-830
were covered by deep water marsh deposits. TTiis ponding of water may indicate a
change in total runoff, or may show a purposeful channeling of irrigation water to
this portion of the oasis.
To be sure, this runoff from Hofuf cannot be translated a priori into terms
of paleoclimatic changes. Even though the oasis collects surface water from the
surrounding Shedgum Plateau and the flanks of the Ghawar anticline, the major
artesian flows from the Khobar limestone near al-Hofuf complicate our
understanding of the water budget for the oasis. The lakes and rivers which drained
the oasis show a composite of rainfall, artesian flow, and cultural