Page 149 - Life & Land Use on the Bahrain Islands (Curtis E Larsen)

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associated with chert deposits. Because of differential resistance to erosion, this
joint set may be recognized by topographic expression. Two prominent examples
on the southern slope of the Bahrain Dome are plainly visible as dark linear trends
on Landsat images of the islands (fig. 24). These same structural features are
identified as shallow synclines by Doornkamp, Brunsden, and Jones (1980:26), who
clearly recognize their underlying structural control—subsidence along deep-seated
normal faults of similar orientation. The remaining joint sets are more subdued,
but significant nonetheless. The N40°E and N60°E joint sets are located
approximately perpendicular to Zagros folds. Thus, these appear to be extension
joints related to the Zagros orogeny. Also potentially related to Zagros mountain­
building is a N40°W joint set which can be interpreted as stress release fractures
parallel to fold axes. The remaining joint sets may also be connected with Zagros
or earlier folding. Certain specialized jointing was doubtless connected with the
vertical uplift and lateral compression of the Bahrain dome.
Joint analyses are a superficial attempt to understand the complexity of
the underlying geologic structure. While the equal area net shown in Figure 23 is a
useful tool for identifying the orientation of joint sets, it is not easily applied to
land use analyses. The interface between the underlying structural fabric and land
use can be found in Figure 6 by comparing the linear arrangement of cultivated
areas with the identified joint sets.
Studies by Italconsult (1971) led to the recognition of normal faulting
below Bahrain's northern coastal plain. Interviews with BAPCO geologists yielded
further indication for complex faulting below some of the cultivated areas. As an
aid, additional subsurface data were collected to investigate the orientation of
prominent faults. This was done by examining water-well boring logs on file with
Bapco and the Bahrain Department of Water Resources. The latter information was
compiled by Ercon (1973) for the northwestern and western coastal plains.
Additional northern and northeastern coastal plain borings were obtained from
Bapco.