Encountering desert deposits in Oman

Oman is a geologically fascinating country, where the bedrock beautifully exposes a one-billion-year history. I had the opportunity to explore this country in a group expedition, during which we pursued our own scientific studies from January to March 2014. My geological observations during the expedition were opportunistic and involved a variety of sights, having traversed from east to west from Muscat, across the dusty plains of the Empty Quarter (Rub’ Al Khali) desert to the Dhofar Mountains of Qamar.

Fig. 1. Geode in the Empty Quarter desert.

Rub’ Al Khali: The Empty Quarter Desert

The Empty Quarter desert is the largest sand desert expanse in the world (Peter Vincent, 2008) and is considered to have great oil prosperity under the dunes. The desert may lack bedrock exposure, but it is home to some unexpected sedimentary deposits. We found the light golden sand to be littered with brown bubbly balls – geodes (Fig. 1). When broken open, the insides are glazed with white calcite crystals sparkling in the desert sun. These had formed when rock cavities filled with crystallised calcite. In time, these balls of calcite weathered out from the host rock, before being transported by water and deposited here on the desert plains.

Fig. 2. Miscellaneous deposits showing evidence of human shaping, found in the Empty Quarter desert.

These were not the only interesting deposits found. Strangely shaped pebbles of flint and dark metallic-like forms also lay here (in an area previously documented to have archaeological interest). One can see how these appear to have been hand carved by humans thousands of years ago, to form mechanical cutting tools (Fig. 2). Furthermore, what initially looked like a carved archaeological object, transpired to be our first taste of the fossil rich landscape that is Oman (Fig. 3).

Fig. 3. Mollusc fossil found in the Empty Quarter desert.

Location: Qamar terrain, Dhofar

The Dhofar Mountains are a relic of the Dhofar uplift event (Martin Pickford et al, 2014), when dominantly shallow marine environments became increasingly terrestrial (Oligocene-Miocene). They are made up of folded strata, steep slippery slopes, winding wadis (Fig. 4), giant boulders, and floors of crumbling rock deposits. Gypsum can be found in lumps, exposed against the slopes of the high ground.

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