Oman's smashing Geology

From a geological perspective it may be said that Oman appeared on the horizon of the outside world with the discovery of oil.

Like its culture, Oman’s geological heritage has survived relatively intact. There is a lot of geology in Oman spanning a wide window in time, covering hundreds of millions of years of earth history, from the very beginning of life on earth. Its geology also covers an exceptional wide range of rocks, exposed in all their details by the desert climate. Like a book, quite often missing a few pages, torn out by the very geological processes that wrote the book, but still very readable to anybody that is willing to open it.

Being a geologist in Oman is great. There is the Pre-Cambrian, the time before life as we know it developed on earth, cropping-out in the core of the Oman Mountains, but also in the Huqf area in Central East Oman. Old glacial rocks tell a story of global glaciations that are known as ‘ice-ball’ earth. Overlying massive limestones erode with spectacular deep canyons that are great for ‘canyoning’ with a lot of swimming and climbing. Oman rocks feature the transition from the Pre-Cambrian to the Cambrian, with primitive life developing approximately 542 million years ago preserved in an exceptionally complete succession of limestone and rock-salt from which also oil is being produced in South Oman.


Qarat Kibrit, 2003, cave in Cambrian-Precambrian (± 540 million years old) rock salt, pushed from deep down all the way up to the surface.


Tracks left by Cambrian trilobites, some 400-500 million years ago (just picture something looking like big woodlice) in the Huqf of Central Oman (2003).

 

Massive earth movements left these early rocks tilted and overlain by much younger rocks. In the Huqf area there is a much younger (Permian) glaciation that left deep ice-carved groves in the older rocks. It is a weird feeling to see and feel these ‘ice’ rocks in the middle of a desert. There are rocks in which one can find primitive life, such as trilobites and crinoids. Fossil hunting in the desert is great! From rocks in an old oil well in central Oman come samples of the earliest plants found in the world. Deep wells in south Oman have recovered possibly the oldest volcanic glass in the world. Other rocks have released remains of some of the oldest fish in the world.


Deep grooves left in Precambrian rocks by Permian (300 million years ago) ice, Huqf area, 2003.

Yet younger limestones form the high peaks of the Oman Mountains, flanked by spectacular scarps. The limestones act as a large storage buffer for the sparse rainfall. That water feeds springs high up along the scarps of the mountains. That’s where people have carved terraced gardens fed by water through age-old water channels (falaj) sustaining a peaceful existence for many thousands of years.

 


The village of Al Ain on the edge of the Saiq Plateau in the Hajar Mountains. Notice the terraced gardens that are dependent on spring water from the limestone rocks just below the village (2005)


Rim walk along the vertical limestone cliffs of the Nakhr gorge near Jabal Shams in the Hajar Mountains.

The mountains are flanked by the black Ophiolites and deep sea sediments. These rocks originate from a now completely disappeared ocean called Tethys that closed some 90 million years ago in a titanic struggle for space between continental and oceanic plates. Oceanic crust, consisting of deep rocks from the earth’s mantle (originally some 6-7 km deep), together with overlying magmatic and volcanic rocks, were pushed on top of the eastern edge of the Arabian plate. These are the black rocks that form the backdrop of the Muscat area 9some call it a natural furnace in summer times), but also as far north as Sohar.


Pillow lavas in the Ophiolite rocks, wadi Jizzi (Sohar, 2003), originally lava flows like those flowing in the sea at Hawaii.

Copper that was found in these rocks has been mined already many thousands of years ago, with copper artifacts originating from Oman found in excavations of the ancient civilizations in Mesopotamia and India.

The Oman Mountains were only formed in relatively recent geological time, some 10 million years ago, related to the opening of the Red Sea and the Gulf of Aden and the collision of the Arabian plate against the Eurasian plate, with Iran in the crush zone. Oman’s northern tip, Musandam, at the straits of Hormuz, is slowly pushed down as a result of this collision and that explains Musandam’s magnificent drowned coastline (like fjords).

 


Khor Najd, Musandam; a drowned coastline with massive limestone cliffs rising from the azure sea. The northeastern flank of Musandam is gradually subsiding, pushed down at the edge of the Arabian plate in a gigantic struggle with the Iranian edge of the Eurasian plate (2005).
Most people associate deserts with sand, but most deserts are actually rocky. Oman is no exception, but there are also the classical deserts, the well known Wahiba Sands (Al Sharqiya Sands) just south of the Mountains, and the huge Sea of Sand flanking the western border of Oman with Saudi Arabia; the Rub Al Khali, or Empty Quarter. Perhaps surprising are the huge sabkha’s, large flat areas where water evaporates leaving salt, anhydrite and mud, not only along the coast but also in the interior. The large wadi’s draining the Oman mountains end in the desert, with the lowest area forming the huge Umm As Samim sabkha, literally translated as the ‘mother of poison’, a name that does not leave a lot to the imagination.
The enormous sabkha of the Umm As Samim


Rub Al Khali, near the border with Saudi Arabia (2007)

 


The Rub Al Khali, massive sand dunes as far as the eye ca see (2007)
Oman must be one of those places in the world where the direct link between geology and the world we live in is most clear.
Sunset over Jabal Khawr, Hajar Mountains, 2006

Further Reading

For the Professional

  • Glennie, K.W, M.G.A. Boeuf, M.W. Hughes Clarke, M. Moody-Stuart, W.F.H. Pilaar and B.M. Reinhardt, 1974, Geology of the Oman Mountains, Verhandelingen van het Koninklijk Nederlands Geologisch Mijnbouwkundig Genootschap, deel 31 (NE ISSM 0075-6741).
  • Lees, G.M. 1928, The geology and Tectonics of Oman and parts of south-eastern Arabia. Quarterly Journal of the Geological Society of London, 84, 585-670.
  • Wilson, H.H., 1969, Late Cretaceous eugeosynclinal sedimentation, gravity tectonics and ophiolite emplacement in the Oman Mountains, southeastern Arabia, American Association of Petroleum Geologists Bulletin 53, 626-671.
  • The surface geology of Oman was mapped from 1982-1984 by the French Bureau de Récherches Géologiques et Minières (BRGM).

For the professional and lay-man:

  • Blanford , W.T., 1872, Note on MASKAT AND MASSANDIM ON THE EAST COAST OF ARABIA, by W.T. Blanford, A.R.S.M., F.G.S., Deputy Superintendent, Geological Survey of India. RECORDS OF THE GEOLOGICAL SURVEY OF INDIA Vol. 5 ,Part 3 {August 1872} Page 75-77.
  • Glennie, K.W. (ed), 2006, Oman's Geological Heritage, 2nd edition (check-out www.pdo.co.om)
  • Glennie, K.W., 2005, The Desert of Southeast Arabia, ISBN 99901-04-89-1
  • Hanna, S. S., 1995, Field-Guide to the Geology of Oman, Published by the Historical Association of Oman.
  • Hanna, S. and Mohamed Al Belushi, 1996, Caves of Oman, published by Sultan Qaboos University (published by International Printing Press, Ruwi Oman)

  • Hughes Clarke, M., 1990, Oman’s Geological Heritage. Published by Petroleum Development Oman.
  • Robertson, A.H.F, M.P. Searle and A.C. Ries, 1990, The Geology and Tectonics of the Oman Region. Geological Society Special Publication No. 49.
  • Thomson, A., 2000, Origins of Arabia, Stacey International, ISBN 1 900988 04 6

Symposia and Conferences

  • Symposium on Ophiolite Genesis and evolution of ocenanic lithosphere. Ministry of Petroleum and Minerals, Unesco, Sultan Qaboos University Muscat, January 7-18 1990.
  • International Conference Geology of Oman. Ministry of Commerce and Industry, Unesco and Sultan Qaboos Univeristy. January 12-18 2001.

General

In the September issue of the PDO magazine "Al Mahal" two contributions on two important bits of Oman's outstanding geological beauty (Files in Adobe Acrobat PDF Format)

Also check-out the website of the Geological Society of Oman (GSO).

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          Number of visits since 12 October 2006

@ J. Schreurs 03/11/09