Geological Field Work in Saudi Arabia in June

Everyone that went on the Neoproterozoic field trip has agreed that we now have some serious bragging rights--doing field work in Saudi Arabia in June is not for the faint of heart. It was 44C by noon every day. We left the hotel 5am but were chased back by 2pm. It was simply too hot to move, much less think by that time of day.

Because geological field trips are all about thinking. And looking. And talking. And arguing. As I am fond of saying, get a group of 10 geologists together and you'll end up with 12 explanations for something. And none or all of them may be right. Being able to create and defend multiple, even mutually exclusive, hypotheses is a skill unique to geologists that many other natural scientists don't share.

We spent almost 45 minutes at this one outcrop in town discussing whether the middle, darker bed was fluvial or eolian.

I've got several posts planned around all of the things we saw and did. After all, I managed to take more than 300 photos in about four days. This post is about the big picture.

Where did we go? We went to look at outcrops within the Arabian Shield, the mass of metasediments that forms the core of the Arabian Plate. Somewhat younger sediments are preserved within and on top of the shield and it was those sediments that we were studying. These sediments were deposited in the Neoproterozoic and earliest Cambrian...before there was any life more complicated than algae. One of the classic lines spoken on this trip was by Kent, one of Aramco's top sedimentologists: "Hmm, no plants, no animals. I am not sure how to deal with these rocks"! Biological processes have a profound effect on geological processes. That was made abundantly clear on this trip as we studied thousands of feet of sediment untouched and unaltered by biology.

Medinah is the second holiest city in the Islamic religion. More on that in another post. The flight across KSA only took about two hours. The dark rocks along the west coast are the Arabian Shield.

We flew from Dammam to Medinah, then got on a bus and drove five hours north to the town of Al Ula. Al Ula is an extremely old settlement located in a fault-controlled wadi in the shield. It has been occupied for centuries because there are reliable sources of water there. I took this next picture of Al Ula from an overlook with a bunch of cell phone towers. As an aside, we were in MOFN for most of this trip...and had cell phone reception for nearly all of it. I get better cell reception in KSA than in the US.

Looking south along the wadi, the town of Al Ula is stretched out below us. We can see clastics of the Saq Formation to the east on the other side.

Here is another picture showing Al Ula, the location of our hotel, and some of our field stops.

As you might expect, the landscape is quite surreal. The topography is very young, perhaps 25 million years or less, so it is rough and jagged. There are few plants than can survive out there and the ones that do scratch out a living are mostly brown. There is little green to relieve the eye.

Near the middle of the Robutain Formation looking south. Channels in the modern alluvial fans are picked out by the light colored grasses that grow in them. Those are sand dunes in the middle distance.

The first thing you do when you arrive at a field stop is get out and look at the big picture. And of course take lots of pictures. And start talking about what you see.

Our group was small, only 10 people total including Paul and Dominique, the trip leaders. We also had two young Saudi geologists with us.

Once you get the lay of the land, it is time to look at the rocks in more detail. That requires hiking. Sometimes you get nice easy outcrops like the one in town in the earlier photo. On this trip, that was an exception. Most of our outcrop work involved serious scrambling up steep slopes with lots of loose material.

Everyone in our group was fit and more or less prepared for the rigors of the trip. It was pretty hard to get ahead of them once we were on the outcrop so I could take pictures.

Here we are examining the contact between Muraykah unit 1 and the underlying Badayi volcanic formation. That day we proceeded to climb a couple of thousand feet up a really rough slope, mostly scree, to examine the entire Muraykah formation.

I took this picture from near the top of the Muraykah jebel looking southwest.

See that grungy whitish slope below? We climbed up that. We started on the valley floor. I certainly put my knee brace through its paces on this trip!

Field geology is an awkward activity. The best outcrops, the rarely seen but critical contacts, are usually in some nearly inaccessible spot.

The group is making its way to the contact between Muraykah unit 2 and the overlying lower Kurayshah. The contact is angular and unconformable. One of the guys is already standing on it, silhouetted on the slope.

I toss this last photo in for my Utah friends. Look familiar? The weathering pattern of these sandstones is very similar to that in Bryce and Zion although these rocks are about 400 million years older and not eolian in origin. Still, you take well cemented sandstones, break them up with some big joints and fractures, uplift and expose them in an arid environment, and voila! Easy! Same but different!


It was an interesting trip and I hope that besides learning more about KSA geology, I managed to make some new friends.