Pleistocene-Holocene sedimentation and diagenesis along the King Fahd causeway between Saudi Arabia and Bahrain

Abstract EN

TWO mineralogical units have been identified.

(1) a lower dolomite interval, as much as 40 m thick, and (2) an upper non-dolomite interval, three to nine m thick, comprising, in stratigraphic succession, quartz sandstone, calcitic skeletal grainstone.

quartz sand, and aragonitic skeletal/oolitic sand.

The dolomite interval includes several depositional cycle.

Each cycle comprises, from base to top.

skeletal packstone, wackestone/mudstone, pellctal grainstone, and green mudstone with thin horizons of white mudstone fragments.

Deposition began in a shallow marine envi- ronment, shallowing progressively to a restricted lagoonal environment with brief periods of subaerial exposure that produced desiccation fragments.

The dolomitic lithofacics were prob- ably deposited at sea level slightly lower than today.

The dolomitic lithofacics are though to have been deposited in mid-Pleistocene before the first major lowering of Pleistocene sea level (110.000-90.000 y.b.p.).

During lowstand the sed- iments were leached, cemented, and dolomitized.

Then, a thin, discontinuous quartz sand layer accumulated.

Skeletal grainstone was deposited during subsequent transgression (90,000-75.000 y.b.p.).

Next, the entire Gulf was emptied during the major late Pleistocene re- gression.

Rainfall during late Pleistocene pluvial periods supplied fresh water, causing solution of aragonitic constituents, precipitation of calcite cement, and calcitizing of deeper dolomite horizons.

As aridity increased, a blanket of dune sand accumnulated in the region.

Aragonitic oolitic and skeletal sand were deposited during the Flandrian Transgression after the Gulf was flooded (6,000 y.b.p.).

Lithostratigraphy and diagenesis of the non-dolomitic layers match the profile of sea level changes of F airbridge (1%1).