(1) Dordt College, Sioux Center, IA
ABSTRACT: Extensional Tectonics and Salt Structures, Marib-Shabwa Basin, Yemen
The purpose of this study was to decipher the combined effect of extensional tectonics
and halokinesis on formation of structural features in the Marib-Shabwa basin of Yemen.
The basin formed by rifting in the Upper Jurassic, subsequently separated from the sea and
became an evaporating environment in Tithonian time. Differential loading of the
overburden and fault activity initiated salt mobilization and formation of salt pillows in
the early Cretaceous and later diapiric growth was maintained by passive downbuilding. A
major tectonic reactivation occurred in the Paleogene in association with the opening of
the Gulf of Aden when the extensional field slightly rotated anti-clockwise. The intense
Paleogene faulting induced reactive diapirism that in places evolved into active growth.
Following the extensional activity, the entire area underwent a regional emergence with
considerable erosion during the Neogene.
Based on seismic interpretations, a close relationship has been found between the tectonic position in half-grabens and full-grabens and the developed salt structures in these sub-basins. The hinge margin and hanging wall of half-grabens are characterized by salt rollers and salt pillow zones. Diapir zones, tilted basinward by uplift, dominate the footwall sides. Elongated diapirs formed in the axial zone of full-grabens that display changing structural character along strike: they are reverse fault-bounded at their middle portions in response to local contractional effects in the overburden; while towards their ends, the diapirs become normal fault-flanked indicating local extensional stresses. Accommodation zones among small-scale half-grabens are associated with normal faulted asymmetric or non-faulted symmetric diapirs.
AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.