Connally, Thomas C.1, Donald A. Rodgers2
(1) Landmark Graphics, Austin, TX
(2) Landmark Graphics, Houston, TX
ABSTRACT: Reactivated Forced Folds on the Arabian Peninsula
Producing fields and major structures of central Saudi Arabia and Kuwait are folds that
are generally asymmetric with one shallow dipping limb and one steeply dipping limb. These
structures were formed during the Carboniferous “Hercynian” orogeny and have
been reactivated in the early Triassic, late Cretaceous and early Miocene. The
“Hercynian” orogeny was a major structural event on the Arabian Peninsula and
removed over 3000 feet of section from Khurais, the Summan Platform and other structural
highs.
Present-day surface expression of Arabian structures is present at Ghawar, Dammam, and
Khurais, where early Miocene Zagros uplift reactivated Cretaceous and older faults. The
present structural forms in the subsurface and outcrop suggest that latest reactivation of
these structures was due to compressional stresses because the fold axes are inclined
toward the downthrown side of the faults. Published seismic, clay models, and comparison
to analogous structures in America indicate that the present shape of the folds was
produced by drape over high-angle reverse faults in the basement with the hanging wall
moving toward the basins.
Conventional models of the “Hercynian” orogeny on the Arabian Peninsula suggest
that the folding was produced by basement-involved high-angle normal faults. Clear
evidence of later compressional reactivation suggests that the original
“Hercynian” folding was also along high-angle reverse faults in the basement
because it would be mechanically difficult to change the dip of basement faulting in order
to produce the present structures. A compressional “Hercynian” origin for these
folds in Arabia also predicts the presence of upturned Devonian rocks on the downthrown
side of the fault, and an accumulation of eroded pre-Permian rocks in the early Permian
Unayzah Formation on both sides of the fold.
AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.