Page 144 - Life & Land Use on the Bahrain Islands (Curtis E Larsen)

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Dammam and Bahrain, which indicates a mid-Tertiary formation of these domes.
Subaerial erosion during the Oligocene was followed by a marine transgression.
This is shown by a prominent angular unconformity.

Neogene Complex

Where there is good definition, the Miocene and Pliocene sedimentary sequence can
be subdivided into the Hadrukh, Dam, and Hofuf formations. Only an
undifferentiated sequence of clay, marl, and sandy limestone is present on Bahrain.
While these may tentatively be identified as the Dam and Hadrukh formations, they
are generally referred to as the "Neogene complex.” Like the Dammam formation,
these rocks increase in thickness away from the flanks of the Bahrain dome.
The basal unit of the Neogene complex is a thin sandy limestone generally
considered to be a hydraulic part of the Alat limestone (Willis 1967). Theoretically,
it is separated from the Alat member by an erosion surface. This basal unit is
overlain by as much as 21 m of soft, gray clay and shale and by light colored,
porous, sandy limestones and marls of the Dam formation. The terrestrial Hofuf
formation of the Arabian coast is absent on Bahrain. Tleel (1973) believes the clays
and marls of the Dam Formation recognized at the Dammam dome are
representative of a middle Miocene marine transgression which covered the dome
and produced tidal flats around a central island. A similar interpretation can be
suggested for Bahrain.

Geologic Structure
The sedimentary formations of eastern Arabia lie upon the Interior Platform of the
Arabian Peninsula. This structural province is characterized by nearly horizontal,
near-surface, sedimentary beds which contrast with the more steeply dipping strata
of the Interior Homocline to the west. Both the homocline and platform have been
relatively stable tectonically, Surface irregularities are limited to gentle
structural folds that often lack a well defined orientation. Examples of such folds
are a variety of north-south trending anticlines, best known as the significant oil
fields of Arabia—the Ghawar anticline and the related folds at Abqaiq and Qatif.