(Editor's Note: The Al Ain chapter has made several trips to Jebel Shams and the Cliff Walk. Reports of two of these trips can be seen here (2004 trip) and here (2005 trip).)Geological background
Geologically this excursion offers the best place to examine the contact between the Arabian platform sequence of Ac and the overlying rocks of Supersequence B with the intervening sediments of the Aruma Group (Ar). The Hawasina is dominated by widespread exposures of Oman Exotics.Oman Exotics (Ex)
Oman Exotics are so called because their lithology can not be matched laterally to any of the adjacent rocks. They are not only most abundant here but include the largest Exotic ever documented from the Tethys Ocean. It is about 35km long, 2Okm at its maximum width and reaches a height of 2960m. It is known as Jabal Kawr. It forms mountains on the left hand side of the road as you drive up Wadi Ghul. These exotics consist of shallow marine limestone deposited in Mid-Permian to Triassic times and include coral, crinoids and stromatolites (algae) along with many other shallow marine fossils. They were possibly deposited above submarine volcanoes (vol) that formed a ridge separating the proximal basin of Hamrat Duru from the distal Umar basin in the Hawasina basin. They are often seen in the field underlain by volcanic rocks such as basalts and trachytes. They were over-ridden by hot ophiolite and most Exotics are metamorphosed to marble.Aruma Group
The syntectonic Aruma Group is best examined in this excursion. As described in the geological background (part 1) it includes a mélange unit, the Muti conglomerates (Mu) and Fiqa shales. The latter two are well represented here and combined as (Mu) in the map. The conglomerates are made up of rounded to sub rounded fragments derived from the top of the Hajar Super Group. They are found between the top of the autochthonous Supersequence (Ac) and the base of the allochthonous Supersequence (B).En route
Set the odometer to zero at the turn off to Wadi Ghul by the petrol station about 12km from the main Nizwa-Bahla road.
|0.0||The journey starts with numerous Exotic limestones (Ex) on the left side of the track.|
|2.5||On the left you will see a large block of the shelf sequence within a shale unit possibly
belonging to the Aruma Group (Mu). On the right the dip slope of the Jabal Akhdar flank has been
affected by well-developed fracture systems.
|5.0||On the left of the road you will see the Jabal Kawr Exotics.|
|At 5.7km cross and examine some of the volcanics (vol) underneath them. They are mainly basalts
and have been mapped recently as Misfa Formation. These belong to the Kawr Group. These basalts are also found as sills
between the limestone and dolomite of the Jabal Kawr and Misht Exotics.
They may in places occur as a volcanic breccia -- a rock made up of angular volcanic fragments cemented together. Such breccia can be seen on the left.
|6.0||Wadi Ghul Dam.|
|9.5||A fork to the right takes you to the new Ghul village.|
|10.5||Wadi Nakhr and Ghul villages. On the right of Wadi Nakhr stands the new village of Ghul while on the left are two old deserted villages. The houses were built on the dip slope of the Natih Formation (Nt) and it is difficult to see them from the road – particularly those up the slope to the left. Here, on the left you will see the shale of the syntectonic sediments (Mu). They do not react with 5% hydrochloric acid (HCI) and are therefore non-calcareous, indicating a relatively deep sea environment. Climbers or experienced hikers may be interested to know that they can follow the stream up Wadi Nakhr from Ghul village to reach the top of the Grand Canyon.|
|17.8||A view of the contact between the grey carbonate rocks representing the top of the Hajar Super Group of Supersequence Ac on your right and the Muti Formation (Mu) on the left. This can also be seen at 19km.|
|19.0||On the left is a blue road sign (18km). Here you can see what is known as a hardground, an iron-rich crust on top of the Natih (Nt). This can be examined at a village built on the contact at 19.3km. The hardground is a reddish zone formed at the sea bottom, usually a few cm thick which is lithified to form a hardened surface, often encrusted and bored by organisms. It implies a very slow rate of sedimentation (non-deposition) between the platform carbonates (Ac) and the syntectonic sediments (Mu). This is the period during which the supersequence B made the journey to Oman.|
|20.0||Muti Conglomerate (Mu) on your left. These are grey-colored conglomerates with fragments derived mainly from shelf sequence rocks. Individual fragments contain the prealveolina fossils (white elongated fossils with circular or ring-like structures described in Wadi Muaydin). This fossil is abundant in the Natih Formation near the Grand Canyon.|
|20.1||Large blocks of the Natih
are seen within the syntectonic Muti sediments indicating that
it was broken and re-deposited as blocks in the syntectonic
This stop is followed by a sharp double bend in the track with a village on your right. The odometer reading of 21km almost coincides with the blue road sign (20km).
|24.4||Take the left fork. The right hand track will take you to the village of Sabayib which is again on the contact between the light grey Natih Formation of the carbonates and the syntectonic Aruma sediments.|
|24.7||More grey blocks of Natih within the Fiqa shales and at 24.9km and 26.4km are blocks of Muti Conglomerates within the shales.|
|Driving on the ocean floor|
|25.7||Fork. Take the right turn heading to Jabal Shams. The left hand track leads to Misfat Al Khawatir. Between 27.3km and 30.1km the road was constructed on the flat shelf carbonate itself. Now you are actually driving on what was a sea bottom almost 90 million years ago when the deposition of the Natih Formation ceased.|
|30.1||Here on the right there is a highly-cleaved clay bed within the Natih Formation in which the cleavage is steep and well-spaced.|
|Dar Al Ghubira view point|
|30.5||Fork. The left turn will take you to a small village with some green terraces called Dar Al Ghubira. Stop and walk around looking back towards the SW for a spectacular view. There in the far distance to the right is the Jabal Misht Exotic. It is a cuesta (an asymmetric ridge with a gentle slope on one side and steep slope on the other). On the left is the mountain of Jabal Kawr whilst in the foreground is Jabal Misfa. The Hawasina deep oceanic sediments of the Hamrat Duru Group form the intervening dark low hills. Wadi Al Ayn and the road leading to Ibri can be seen with the aid of binoculars. Go back to the track and continue up towards Jabal Shams.|
|31.0||In front of you is white Exotic limestone underlain by dark volcanic rocks. At 31.3km is the Natih formation on your right and you are now driving almost along its contact with the Aruma. Continue driving uphill ignoring a right junction at 34km leading to Dawarat Al Gheil. You should pass a blue road sign (34km) at odometer reading 35.9km.|
|35.9||Ignore a left junction to Dar Al Sawda.|
|36.4||On the right is multi-colored orange and green shale displaying tight folds.|
|36.6||Take the right junction leading to the Grand Canyon signposted 'Al Khateem 8km' and 'Heil 4km'.|
|The Grand Canyon of Oman|
|38.0||At 38km you will have the first glimpse of the cliffs of the Grand Canyon.|
|40.1||At 40.1km the track leads out onto a plateau and then touches the
edge of the Grand Canyon on the left at 40.9km. The Canyon is
undoubtedly one of the most impressive and beautiful land forms’
in the country. It is in some ways more impressive than the
famous Grand Canyon in the U.S.A. because here one feels the
1000m vertical drop to Wadi Nakhr below. The origin of the Canyon
has provoked intense speculation. Was it formed due to sudden
uplift or as a result of relatively slow rate of cutting down by
erosion or is it a collapsed cave?
At its deepest it offers a unique opportunity to see the top of the Jurassic and the whole Cretaceous sequence of rocks. They are from bottom to top as follows. The dark grey rocks at the base belong to the Jurassic Sahtan (Sa) followed by the base of the Cretaceous, a light color Rayda Formation (R) overlain by the Salil Formation (S). The remaining sequence belongs to the Kahmah Group with the Shams Formation (Sh) as a dark grey cliff-forming limestone.
You are standing on top of the Natih Formation (Nt) and the thin underlying beds belong to the Nahr Umr Formation (Nr). Walk around looking for the large oval foraminifera prealveolina, rudists, which are ubiquitous in this area, as well as corals, gastropods and many shells.
There is a very thin ridge in the middle of the Canyon. There are two wadis to the NE of this ridge. The further is called by the local people Wadi Masirat and the other is called Wadi Bimah. The third wadi close to you is called Al Wadi Al Sagheer which means the 'small wadi'. Half way down the sheer cliff to your left are terraces and a small village known as Saab Bani Khamsi. Local people call it Saab Al Khamamsah after the Khamamsah tribe. There are 11 houses, some of which are padlocked. A cave in the middle of the second dark limestone cliff can be seen. Local people believe that it could accommodate about a thousand people. You can walk down to the village and its terraces from Al Khateem village at the end of the drivable track and examine one of the most impressive of ancient engineering works. Some of the terraces were constructed on an overhang with a sheer drop of hundreds of meters.
Geological map of Wadi Ghul and Jabal Shams
Deserted village built on the dip-slope of the top shelf carbonates: western side of Wadi Nakhr (mouth of the Grand Canyon), Wadi Ghul
The contact between the Natih Formation (top of the Hajar Super Group) and the base of the Aruma (syntectonic sediments) as seen in numerous localities along the way to Jabal Shams
View from Dar Al Ghubira looking southwards. Note the characteristic cuesta of the Exotic limestone of Jabal Misht (top right)
The Kahmah Group as seen from Jabal Shams in the Grand Canyon
Rudist: a special type of bivalve found in Jabal Shams indicating that these rocks (now 3km high) were once covered by a shallow sea
Reproduced from Field Guide to the Geology of Oman by Dr. Samir Hanna and published by the Historical Association of Oman (1995).