Karst in northeastern Saudi Arabia

Abstract EN

Exposed carbonate strata of the Paleogene Umm er Radhuma Formation (UER) are karstificd in northeastern Saudi Arabia.

Detailed studies around Ma'aqala, 28(» km west of Dhahran, have been conducted by a joint team from King Fahd University of Petroleum and Minerals and the Austrian Academy of Sciences.

An area of 500 km2 containing 58 dahls or dolines has been mapped.

These are mostly vertical sinkholes, 10 to 30 m deep, leading to sub- horizontal cave systems.

In the subsurface, all caves examined in the UER limestones are dry and were developed long ago.

as the present ground water table is at depths of 130 to 210 m.

Karstification was possibly initiated during Middle to Late Eocene and Oligocene.

when the UER may have been exposed to weathering, although most karstification is Quaternary.

Miocene calcareous sandy sediments were disconformably deposited on the eroded UER limestones.

Later erosion removed these Neogene strata over the very gentle Ma'aqala Arch and UER limestones were predominantly karstified during Quaternary pluvial phases.

Well- developed karst features are unusual in hyperarid areas.

Here, they are primarily relict fea- tures.

Typical karst features found near Ma‘aqala include karren, sinkholes, dolines, uvalas, poljes.

blind valleys, vertical and horizontal caves, stalactites and stalagmites.

Caves are struc- turally controlled by major vertical joint trends of N30° E, N40° W.

a less well-developed trend of N75° E, and minor N-S and E-W joints, as shown very clearly by the UPM Cave and Dahl Abu Hashemi.

4 and 8 km NNE of Shawyah.

respectively.

Stratigraphic control of cave de- velopment is seen in the UPM Cave with three levels of galleries caused by more soluble cal- careous strata.

The longest cave mapped in the UER is 1.1 km.

Dolines are also found in adjacent Neogene calcareous sandy strata, e.g., Dahl Aba Jirfan.

Some of these dolines contain locally used perched water.