Evolution of the Early Permian Haushi Sea of Oman and Comparison with Other Gondwanan Post-Glacial Marine Sequences

Michael H. Stephenson¹*, Lucia Angiolini², Melanie Leng³, Fabrizio Berra², Flavio Jadoul², Gabriele Gambacorta², Bader Al Beloushi⁴, and Vincenzo Verna^2
1British Geological Survey
²University of Milan, Italy
³NERC Isotope Geosciences Laboratory, UK
⁴PDO
*[email protected]

The Early Permian Haushi Sea covered most of northern Oman and parts of southeast Saudi Arabia. Its southern extent was controlled by high elevation and by prograding coastal sediments, and its eastern extent by the Huqf Arch. The Haushi Sea, being fully marine, must have been sourced from the Tethys but the position of ingress is unknown. The shallow Haushi Sea persisted through the Late Sakmarian, but a regressive trend halted limestone deposition and replaced it with fluvial and minor lacustrine palaeonvironments in a low accommodation space setting (Middle Gharif Member). Palynology indicates increasing hinterland aridity during deposition, while microfacies, stable isotopes and brachiopod diversity indicate a trend from eutrophic to oligotrophic conditions and progressive marine closure and isolation. d ¹⁸O values of –3.7 to –3.1‰ from brachiopods at the base probably relate to glacial melt water. Above this, increase in d¹⁸O may indicate either (1) ice accumulation elsewhere in Gondwana, or (2) a period of evaporation related to marine isolation, as suggested by the biota. After the Haushi limestone was deposited, possible subaerial exposure and downward penetration of meteoric water during Middle Gharif times precipitated porosity-destroying calcite cement turning the Haushi limestone into a regional seal. The interplay between Early Permian glacio-eustatic sea-level rise, local topography and tectonic subsidence controlled the distribution of post-glacial marine sediments in the Tethys margins. The earliest transgressions (e.g. in India), produced low-diversity, cold-water fauna and limestones. In Oman, the transgression did not occur until later Early Permian times. Later post-glacial limestones such as the Haushi and Callythara Formation (western Australia) are temperate with diverse fauna.

AAPG Search and Discovery Article #90077©2008 GEO 2008 Middle East Conference and Exhibition, Manama, Bahrain