Oman 2022 – GeoWorld Travel Diaries

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Day 4: Sohar to Nizwa, Friday 4^th March

We awoke in the city of Sohar for a second day and, leaving the city, drove south back down the coast until we reached a wonderful location where we could see a fossilised white smoker. Unlike the black smoker we’d seen the day before, this feature was on the ocean floor near the spreading ridge. It was formed by cooler temperatures than the black smoker (100°C rather than 300 °C). Fluids penetrated the crust and rose to the surface as they warmed. However, these fluids were cooler and therefore they precipitated fewer metal sulphides. Most of the deposits are opaline silicates. We spent a wonderful time examining tube-like structures where the fluids had been forcing their way through the rock and we also saw beautiful samples of opal and silicate rock.

Our next stop was a site nearby, only two minutes away, where archaeological remains can be found. People smelted copper and we could see the slag lying around. There was also a magnificent cliff, in which we saw many different types of the ocean crust rocks. We saw pillow basalts and numerous dykes cutting through the pillow basalts. At the top of the cliff there was a very interesting sill with columnar cooling structures.

Our journey continued, stopping for a comfort break at a location which also gave us a really good view of the surrounding area. We were standing on ophiolitic mantle rock, but just in front of us the rocks dramatically changed – the mountains were made from deeply folded sedimentary rocks. These were rocks of the Hawasina nappe. We also saw a very strange looking white-coloured, small mountain in front of us. This was a fossilised atoll; this atoll had been a submarine volcano with a coral reef growing on top of it. The coral reef later turned to marble and the entire atoll got jammed in a subduction zone when the Semail Ophiolite was thrusting over the Hawasina Ophiolite.

Heading down into the valley, we saw some extraordinary rocks: high-temperature metamorphic rocks. These are Hawasina sediments that had been heated by the hot Semail Opholite nappe as it passed over the top. The heat of this hot nappe, hot because it’s the mid ocean ridge, changed these rocks into metamorphic rocks. This is known as the “metamorphic sole” of the ophiolite.

Further still down the Wadi, we came across some beautifully folded Hawasina sediments. These sediments were deposited as turbidites and a fining-up sequence from sandstones into mudstones could be seen. These turbidites are very tightly folded and these folds were emplaced when the Hawasina nappe was thrust up onto the Arabian foreland.

A little further on, we stopped for lunch and had a picnic under a tree. Our lunch spot was another site where we saw beautiful folds and faults in the Hawasina sediments.

Carrying on, we drove along the boundary of the two nappes (Hawasina and Semail) where we saw volcanic rock of former submarine volcanoes. Then we reached an absolutely extraordinary viewpoint called Wadi Murri. There we saw the Jurassic rocks of the Arabian foreland, which were limestones, in a dramatic plunging anticline (a big, big fold) folding down. Stacked against it were sediments of the Hawasina nappe and against that was the Semail Ophiolite nappe. We saw the two nappes against each other and against the Arabian foreland. This means we saw the subduction zone and how the Arabian foreland would go underneath these two nappes and the two nappes were thrusting up above it. The scale of the scenery was just spectacular.

We then drove for an hour down the rough-surfaced mountain road through extraordinary scenery to finally reach the Aly Ayn beehives UNESCO World Heritage Site. At this site there are numerous Bronze-age tombs which look like beehives, and they are on a hilltop made up of Hawasina sediments. Behind them was a stunningly beautiful mountain called Jebel Misht. This was an atoll and another one of these so-called “Oman exotics”. It has a volcanic base, and the top portion of the mountain is all made from marble. The marble was once limestone, and the limestone was once the coral reef growing on top of the atoll. We then left the site and made our way into the city of Nizwa. For two nights we stayed in a beautifully restored hotel called The Antique Hotel right next to Nizwa fort. It was created by restoring old houses within the mud-walled area of the old part of Nizwa Town.

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Day 5: Nizwa to Nizwa, Saturday 5^th March

Our day started with a drive to the Al Hoota Caves. These caves are the largest show caves in Arabia. They are in Cretaceous-aged limestones and have been formed by water enriched with dissolved carbon, which makes carbonic acid, that has passed through the caves dissolving the caves. However, the caves are quite dry now and most of the cave formation would have happened in the last ice age when it was much wetter and the water would have filled to the roof of the cave. Inside the cave we were able to see beautiful stalagmites and stalactites, some resembling animals such as a lions – there were even real bats in the cave too! We had a very interesting guided tour of the caves and then enjoyed the excellent geological museum. The museum contains a brilliant computer animation on how the ophiolite has been emplaced on Oman as well as lots of different specimens of rocks and fossils that can be seen around the country.

After we left the caves, we drove, stopping next at a viewpoint called Wadi Ghul. There, we saw a beautiful, ruined village before ascending on hairpin bends to reach one of the highest roads in Oman, just below the country’s highest mountain. This is called Jebel Shams and stands just over 3,000 metres high. We looked over the side of a massive canyon called Wadi al Nakhr. It’s also known as the “Grand Canyon of Arabia” and is 1,500 meters deep. We looked through the entire, spectacular Cretaceous and Jurassic sequence of the Arabian foreland.

Since it’s much cooler up on the mountain than at lower altitude this was a very pleasant place for lunch, so we took a break and enjoyed another delicious lunch. We then descended to and stopped at an archaeological site called “Coleman’s Rock”. This is widely thought of as being the most important rock art monument anywhere in south-eastern Arabia. We stopped at two separate sites; one had rock engravings of people on horses or camels and there was even a great big leopard. The other site, the main “Coleman’s Rock” itself, is a big block of limestone and on it are carved out numerous figures. One of the best carvings on one of the faces shows a man, a woman, and a child and on another face, there was a large man. All the different faces of the block have carvings on them but depending on the direction of sun they can be difficult to see. This time it was much more visible than previous times we had visited the monument.

We then carried on to our last stop of the day which was on the outskirts of the city of Nizwa; the “Falaj Daris” UNESCO World Heritage Site. This is an irrigation system where people have dug boreholes or wells down to reach the water table, connecting between them to make a canal system, then allow the canal to flow out of the mountainsides and to the surrounding areas to irrigate them. These irrigation canals are thousands of years old. We were able to sit there, put our feet in the water and look at all the pretty fish that live in there – they even came and nibbled our feet! It was a very peaceful park and a very pleasant end to the day. After this, we returned to our hotel in the Old Town of Nizwa.

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Day 6: Nizwa to Wahiba Sands, Sunday 6^th March

For a second morning we awoke in the historic town of Nizwa. Nizwa was once Oman’s capital, and it is a beautiful old city in the mountains. We all had some free time this morning and didn’t set off in until 11:00 o’clock, which gave us free time to visit Nizwa’s fort, a museum and just to have a wander around the souk, with its huge variety of things on sale.

After this interlude, it was time to get back in the vehicles and get on with the geology! We drove for just over an hour and reached an interesting site where we could see a type of rock called plagiogranite. This rock is also known as tonalite or trondhjemite. It is a bright white granitic rock that makes you wonder: “Why is there granitic rock here amongst all the ultramafic gabbro and mantle rocks?!” This is because this plagiogranite, which is nearly all quartz and the plagioclase feldspar albite, is the result of extreme fractional crystallisation at the top of the gabbro magma chamber. In the classic ophiolite sequence, there are pillow basalts at the top, below these are the sheeted dykes, below this is the gabbro magma chamber, and it’s just at this junction of magma chamber and sheeted dykes that the plagiogranite forms. As mafic minerals escape to the sheeted dykes above, the remaining magma chamber becomes more and more concentrate in quartz; eventually a very concentrated melt can form, which is mostly quartz and plagioclase feldspar. This is the plagiogranite.

Our next stop was fairly close by, where we saw another of the “Oman exotics” – another one of these submarine volcanoes which had coral on top. We stopped next to an outcrop of this coral which had been weathered by wind erosion to resemble a skull. We set up our picnic there and while the picnic was being set up, we examined the limestone and saw that it contained coral and crinoid fossils. Around it were radiolarian cherts and volcanic rock, which is rhyolite, and that was the volcano that the limestone sat on.

Driving a short distance around this limestone outcrop, we came back into the ultramafic rocks – the peridotites of the mantle. We drove up a rough track to an abandoned chromite quarry. Here, a vein rich in chromite, which contains the element chromium, had been mined and we saw pieces of the chromium, sort of metallic flecks in darker areas. We also observed very serpentinized minerals, which have a fibrous texture, within the peridotite rocks.

Having left that site, we pulled in at the roadside just a few miles down the road to take in a wonderful view of a mountain. The lower 3/4 of the mountain are one colour but the top quarter of the mountain was another colour. That’s because the lower 3/4 of the mountain were made of peridotite but the top quarter of the mountain was made from gabbro. What we saw was the MOHO once more, the boundary between crustal rocks and mantle rocks. Here we could clearly see this defined line on the side of the mountain.

After enjoying, this fabulous view, we got back in the cars and carried on driving. Towards the end of the afternoon the road ended and that’s when we started to drive on sand…! We whizzed through the sand to keep up the speed, so we didn’t get stuck and we drove on for a good 10 km into sand dunes to reach the Bedouin Rustic Camp. This is a wonderful place where we stayed in tents. We let out the air from the tyres of one of the Land Cruisers and we gunned it right up on top of one of the sand dunes to watch the sunset. We had quite an adventure up there because the sand conditions were quite hard, as there had been a lot of wind in the last few days. The sand was very soft… and we got one of our Land Cruisers completely stuck and had to abandon it! The next morning before breakfast we went back and, using another Land Cruiser as an anchor, put straps around the wheels, which effectively turned the wheels into a winch. Then we were able to pull the stuck Land Cruiser out. But back to the previous evening! After we returned from our adventure in the sand dunes, before we had dinner, we had an opportunity to learn about Omani dancing. We put on Omani national dress and were taught how to do this dancing. Our host was clapping and singing Omani songs and banging a sword on his shoe. We then all had a chance to try to do these dances, which was a lot of fun! Then we had a lovely traditional Omani meal at the camp. After that, our host, who is a Bedouin, took us to a campfire just near the tents. We sat around the fire while he told us all about the cultural history of how the Bedouin would use camels to ferry goods across the deserts and how dangerous it was because there were different tribes who were always fighting each other. He also talked about the animals that live in the desert, like snakes and scorpions, and about the stars and about how the Bedouin life has changed in just one generation. Today, children go to school, live in the town and have iPads, so their Bedouin way of life is being lost very quickly.

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Day 7: Wahiba Sands to Sur, Monday 7^th March

After we freed the stuck Land Cruiser from the sand and pumped up the tyres again, we set off. We reached a site where we could see the crystalline basement of Arabia. Here we saw rocks which were between 1,000 to 800 million years old, the oldest rocks in Arabia. We saw granites that have formed when different continental fragments were accreting together, building the continent. Then later, this crust extended and huge gabbro dykes were intruded. Some time after this episode, both rocks were cut with granitic pegmatite dykes (dykes with very large crystals).

We then carried on our journey and reached the coast, parked at the beach and walked onto the beach where we saw a very unusual outcrop. It was an outcrop of volcanic rock called kimberlite. Kimberlite derives from a very deep mantle source and we’re not sure what the mechanism is, but it is sure that pressure is released in the mantle and gases are sent from very deep to the surface, making a small volcano. Kimberlites can bring very exotic minerals from very deep down. Kimberlite is named from the town of Kimberley in South Africa which has one of the most famous diamond mines in the world. Diamonds are often brought to the surface by kimberlites. This particular kimberlite doesn’t contain any diamonds, but it contains some very exotic, different pieces of rock that had been brought to the surface in this explosion.

Our lunch stop was a picnic at a nearby site, overlooking the coast. As we were eating, a German man arrived in his car with surfboards in the back looking for a place to surf – not what we were expecting! He was an environmental consultant who had been living in Oman for 16 years and we had an interesting chat with him about conservation.

After lunch, we carried on to reach one of Oman’s most famous geological stops which is nicknamed the “mother of all outcrops”. This is an incredible, beautiful rock sequence of interbedded red and white stripes which are folded and faulted. The red bands are radiolarian chert and form from Radiolaria, that have a silicon skeleton that fall to the sea floor. The white, pure, bands form from white porcellanite, some calcite and some sort of mud. These sediments were deposited in an ocean maybe 4,000-5,000 metres deep. Fascinatingly, these marine rocks are, like radiolarian cherts that we’ve seen earlier on in the trip, on the surface of Oman due to being emplaced by an ophiolite. However, they were emplaced by a different ophiolite, the Masirah Ophiolite, which occurred 15 to 20 million years after the Semail Ophiolite. That means it is a completely different nappe, called the Batain nappe. That was really an amazing sight to see.

Just a few miles from the site was another site with the same interbedded red and white layers of rock. But within these layers of red and white rock were black layers of rock. These black layers of rock were completely enriched in the manganese mineral “pyrolusite”. The whole site was a quarry where pyrolusite was being mined. We were able to look at that and collect some nice mineral specimens.

After our mineral finding stop, we moved on to a stop at another very interesting volcanic rock. It is a little roadside outcrop with exotic lava called carbonatite. This is an ultramafic lava very enriched in carbon. It was really interesting to see this unusual type of rock. Fascinatingly, it was cut with veins containing beautiful amethyst crystals, a purple variety of quartz.

Our final stop of the day was just on the outskirts of the city of Sur where we saw Eocene-aged limestone. In this Eocene limestone was a notch cut into the outcrop which contained a lot of pitted holes. The holes were caused by marine molluscs that were boring holes into the rock, which demonstrates that this notch must have been created by the highest sea level at the time. The notch has been dated to around 120,000 years old which is the same age as the Eemian interglacial. The Eemian interglacial was a period in the last ice age, and at this site in Oman we can see that the sea level was 3.7m higher than the present day. What is concerning is that we already have a higher CO₂ concentration today than in the Eemian, which is well known for being several degrees warmer in temperature. There were hippos, for example, living in the River Thames in England during this interglacial. Because our CO₂ is already higher than it was then, this is a warning of the type of temperature and sea level rises that we may expect to have in the not-too-distant future.

With the geological sites done for the day, we got back in the cars, crossed over Sur’s famous bridge and drove past its wonderful dhow making sites where they make the traditional wooden dhows at the side of the beach. We drove through the middle of the city to reach our hotel, the Sur Plaza Hotel.

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Day 8: Sur to Muscat, Tuesday 8^th March

We started today in the city of Sur and headed back towards Muscat. Our first stop was a site where we saw a fossilized Quaternary coral reef near Tiwi. What is very interesting about this site is the way it is structured in terraces. There is the modern shore at the base, then one step up there is a wave-cut platform of Eocene limestone, and another step up are the Quaternary coral fossils, and again another step up is a recent conglomerate from rocks that were deposited in fluvial conditions. This stepped shoreline shows us the different sea levels of the past. The terraces presumably formed due to the uplift of the area after the emplacement of the Semail Ophiolite (which caused the land to rise) and there were lots of interesting fossils to be seen.

After this we proceeded up the coast and arrived at the site of Wadi Shab, a site for mainstream tourists and geological tourists alike. It’s thought by many to be the most beautiful canyon in Oman. We parked our cars and took a little ferry, or rather, a little motorboat, across the river. Then we walked up the gorge for about almost an hour and arrived at a lovely pool. We swam in the pool up the gorge to reach the other side. There, we climbed up the rocks, walked across and reached another pool. We did this with four or five other pools. At the final pool there’s a little space following the line of the fault just high enough for your head. It looks like the wall just ends, but you can swim through there. Then you enter a large cave where part of the ceiling has collapsed and the light is flooding in. There’s a beautiful waterfall and, even though it’s very slippery and difficult, it’s possible to climb up the waterfall. You could jump in from a height, which is what some of us did, but it’s not really something suitable for everyone! It was a wonderful swim, which also enabled us to take in the geological story that as the land has been rising, the river has cut down and cut out this beautiful gorge.

The next stop was very close to Wadi Shab on the coastline just a few kilometres north. Here we could see something extraordinary; there were 40-ton blocks of limestone sitting on top of the cliff and around them there was a clear washed surface. Then started a whole train of boulders, big boulders, all stacked up against each other in a pattern that one could describe as “imbrication”. The boulders got smaller further away from the shore until they finally ended in a debris apron. What on earth could have caused rocks to behave like this? The theory is that there was a giant tsunami wave that came in, broke off the lip of the cliff and chucked the big boulders on top of the cliff. The wave was so powerful it was able to wash the slightly smaller blocks inland and stack them on each other. What we witnessed was a deposit from a tsunami – a very cool site indeed!

Continuing up the coast, we stopped at another site which is of interest to geologists and mainstream tourists alike; the Bimmah Sinkhole. A sinkhole forms when a cave collapses into an open hole. This hole here actually has brackish water because the water via submarine caves is connected with the open sea. However, the Bimmah Sinkhole is not actually a sinkhole, but a doline, which is a feature that occurs when there is a hole in soluble rock (like limestone) and the overlain insoluble rock layers sink into the hole in the soluble rock. In this case there is the Eocene limestone beneath, and on top of it is a thick conglomerate. A cave in the limestone collapsed and pulled the whole overlying conglomerate through. This sink hole is very large and has some steps going down to it – it was another site where we were able to have a refreshing swim!

We then carried on up towards Muscat and quite near the edge of the city we reached the final stop of the day, which is the Wadi al Mayh, a sheath fold. This is the largest sheath fold in the world. What is a sheath fold? A sheath fold is something quite complicated. Imagine taking a tablecloth, pinching the middle and pulling it up so it forms a fold in three dimensions. Here it occurs because the Arabian foreland was being dragged down the subduction zone as the ophiolite went over it. Normally, sheath folds are only centimetres to a metre in length, but this sheath fold is 15 km long! If you were to cut a sheath in half, it would look like concentric rings or ovals. Here, where it has been cut in section by the erosion of the Wadi, this phenomenon is visible. It was amazing to see the scale of this folding.

After this, we arrived in Muscat where we stayed for the final two nights of our tour.

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Day 9: Muscat to Muscat, Wednesday 9^th March

Today was the last day of our “Geology of Oman Tour”. We started the day in the modern area of the capital city Muscat, getting into the cars and driving down to the historic part of the city. Interestingly, the historic part of Muscat used to be two separate very small towns: Mutrah and Muscat. They were both hemmed in by the tall mountains which are all made of peridotite mantle rocks. The modern city, which sprawls for 40 km along the coast, is on the other side of these ophiolitic mantle mountains.

We started with a walk up quite a steep path on a historic trackway that used to link the old parts of the city and from this trackway we were able to see good details of the peridotite rock. We saw that when the rock was in darker bands it was harzburgite and when it was in the lighter bands it was dunite, which is nearly 100 % olivine. The harzburgite part has pyroxene as well. We saw lots of holes in the rock which exist because pods of 100 % olivine have weathered out of the dunite. We also saw another type of mineral called magnesite which forms from the breaking down of peridotite as it reacts with water. As well as getting a good look at these types of rock, the path also offered fabulous views over the old part of Muscat.

We then drove on through the old part of Muscat past the National Museum and the Sultan’s palace and then left the city. We came to within 10km of where we had been the previous night where we saw the Wadi Al Mayh sheath fold and today we saw a big anticline fold which is in fact part of the whole sheath fold complex. Even though we didn’t see any eyes, we saw a very large syncline fold.

After this, we moved on and came to a site where we had to climb up very steep slope. We reached a hilltop where we looked down on drowned valleys. Even though most of the Omani mountains are uplifting due to differential faulting, some areas are subsiding. We saw that the sea had come in and flooded a former river valley. Mangrove trees were now growing up in these river valleys.

Next, we continued on down the coast, passing through Permian aged sediments, the same aged sediments that were in the giant anticline fold. As we drove down, they progressively got higher-grade metamorphosed, because we were driving down the subduction zone in the continental rocks that were in the subduction zone. In a road cut near the town of As Sifah we stopped to observe how the sediments had changed to blueschist facies rocks, which is a high-pressure and low-temperature rock and typical for subduction zones.

Following this, we drove on, reaching the beautiful beach of As Sifah. We observed rocks at the beach which were turning to eclogite facies rocks – these are rocks that had once been basalt. These were the leading edge of the oceanic crust, part of the Arabian plate that had subducted the furthest underneath the ophiolite. The very best examples of these rocks required a difficult walk and scramble, so half of the group stayed on the main beach where we were setting up for lunch. and enjoyed the beach and had a swim, while the other half of the group scrambled over the rocks for around 1km to reach another beach where we saw spectacular outcrops of this eclogite. The eclogite contained a green mineral called omphacite, which is a type of green pyroxene, and some really well-formed brown-red coloured garnet crystals. This is a really important site for understanding the whole mechanism of emplacement of the Semail Ophiolite.

We then made our way back to the main As Sifah beach in time for our picnic lunch. The rest of the group then had a chance to swim and enjoy this wonderful beach before heading back towards Muscat for one final stop.

The final stop was at a place called Wadi al Kabir. We drove up a rough track to a hilltop looking down on parts of Muscat that were infilling a valley. We stood on Permian-aged limestones of the Arabian foreland and looked across a narrow valley – it was a superb view. The rocks on the far side of the valley were peridotite mantle rocks and in the valley was the plate boundary where these mantle rocks had been coming up over the Arabian foreland and over parts of Muscat city, which was completely jammed in this narrow valley. The Omanis have been smashing away some of the peridotite mountains to expand the city. There was Eocene marl rock in a very dramatic unconformity sitting on top of the Cretaceous-aged Semail Ophiolite which was deposited on top when the whole emplacement of the ophiolite had finished.

It was a wonderful place to end the trip: looking down on the city, seeing where the subduction zone was on the foreland and where the ophiolite came over the top, as well as the spectacular unconformity on the mountain.

After this great final stop, we all returned to the hotel in Muscat for a second and last night. We enjoyed a final group dinner and discussed our trip highlights and favourite sites.