I have been a bit lax with the photo’s of the week lately. Sorry about that! Here is a nice one from last year’s field season showing a cute little marmot sitting on an erratic with a great vista behind him.
(Photo: Matt Herod)
The little guy stuck around long enough for me to get a close-up. (Photo: Matt Herod)
Cheers,
Matt
We all know that cement is a man-made substance and therefore cement is always synthetic right? Wrong!
In the unusual case of Maqarin, Jordan the stars aligned to produce natural cement and many of the “synthetic” minerals found therein. The Maqarin site has been the subject of an intense geological investigation by a consortium of over 100 researchers for years in an attempt to try and understand this system and its implications. A fairly good overview is available here. Maqarin is located in north-east Jordan, near the border with Syria, in the river valley of the Yarmouk River. The valley is deeply incised allowing a good view of the stratigraphy. There are also several springs coming out of the sides of the valley wall and it is these and their relationship to the unusual geology that make Maqarin so interesting.
A map of Jordan. The location of Maqarin is starred. (Source)
Geologic History
The geologic history of the Maqarin site is very interesting and in many ways unique. Indeed, it was a unique combination of geology and geological events that led to its formation.
1. During the Cretaceous bituminous marls are formed. Basically, rocks that are full of bitumen and calcium carbonate. This rock has up to 20% organic matter! Bitumen forms when organic matter is heated during lithification and is similar to oil. It will burn. The marl is a white, chalky mineral primarily made of CaCO3. There is also about 10% sulphate, which becomes important later on in the geologic history.
2. Overlying the bituminous marls are chalky limestones that were deposited in the Tertiary.
3. The upper unit is basalt, which was deposited during the Pleistocene.
4. The bituminous marl underwent “pyro-metamorphism”. Basically, the rocks were heated to a point where the carbonate rocks cooked and formed high temperature cement minerals such as portlandite, ettringite and thaumasite. The heating though was not due to burial but actually from spontaneous combustion of the bitumen (Khoury et. al., 1992). The presence of sulphate allowed these minerals to form and better simulated a modern cement environment. When the marl, which is CaCO3, is combusted CaO or lime is formed. Then the infiltrating groundwater allows portlandite to form, which then reacted with the suplhates and silicates present to form the other cement minerals.
5. The rocks in the area are all highly fractured allowing water to easily seep through the site. This has led to weathering of the cements. The water seeping through the sites discharges near by and has a pH of 13!!!! The water that seeps through the “cement zone” of the Maqarin site picks up all sorts of dissolved ions and minerals. Remember that heating carbonate + water gives Ca(OH)2. Therefore, there is a huge supply of hydroxide available to raise the pH.
These 5 steps created the Maqarin analogue site as we see it now. Everything had to be perfect for it’s formation to happen: the rocks had to have the right chemistry, pyro-metamorphism had to occur and, the hydrogeology had to allow water to infiltrate and react with the rocks to produce the hyperalkaline springs. See the references below for a more detailed description of the geology and mineralogy of Maqarin.
An image of the Yarmouk River Valley from the Jordan Times. Notice the bedded cliffs along the river. At Maqarin it is these cliffs that have the springs in them. In the distace you can also make out the sraker, overlying basalt. (Source)
Some Geochemistry
I mentioned the “hyper-alkaline springs” above. These springs are super interesting to geochemists, since there not very many places on Earth where we can find springs of highly elevated pH. Indeed, it is much more common to find acidic springs than alkaline ones. However, the springs of Maqarin have exceptionally high pH’s. Why?
The alkaline springs, which flow out of the hillsides at Maqarin, formed due to the unique combination of the hydrogeology, structural geology and mineralogy of the site. As the water infiltrates through fractures in the rock it intially dissolves NaOH and KOH followed by Ca(OH)2, which is the cement mineral portlandite. All of the OH ions that enter solution contribute to the raising of the pH to around 12.5. This now caustic water is then able to react with other minerals and pick up a lot of metals such as uranium, chromium, vanadium and other exotic elements that would usually be insoluble and hence difficult to transport (Khoury et. al, 1992).
The stable isotopes also tell and interesting story about the origins of the water and its pathways at Maqarin. In arid climates, such as Jordan, the groundwater often reflects evaporation that took place either before or during recharge. The waters of Maqarin plot below the local meteoric water line, which is indeed indicative of evaporation before or during recharge of the groundwater. However, there is more to these waters than just evaporation. In fact, the hydration of the cement minerals, such as portlandite, can cause an 18O enrichment, which can also be seen in the Maqarin groundwaters, although it is difficult to differentiate this effect from that of evaporation, which also produces the same trend (Khoury et. al. 1992).
Plot of 18O vs 2H in the hyperalkaline springs of Maqarin, Jordan. The local meteoric water line (Irbid) and the eastern Mediterranean meteoric water line are both shown. Modified from Khoury et. al., 1992.
Why study Maqarin?
We need to understand how cement will behave over long time scales because in most nuclear waste storage or carbon sequestration designs one of the primary barriers between radionuclides/CO2 and the environment are the engineered barriers, many of which are made of cement. In fact, in a repository setting cement is everywhere. It will be used to contain the waste itself, plug up fractures, reinforce structures, and eventually to seal the whole place up. Sealing the place up water-tight (hopefully radio-nuclide tight also) is great, but what happens to the seals when they are subjected to a million years of groundwater flow? Well, the modelling suggests that…. Wait, did I just say modelling? You mean we rely on computer generated geochemical models to tell us what might happen in a number of scenarios? We don’t know exactly what will happen to all that cement that is plugging up a waste site?
An artists depiction of a deep geologic repository for low and intermediate level radioactive waste. (Source)
Enter Maqarin. Maqarin is such an interesting place because “cement” occurs naturally here and it provides a rare opportunity for researchers to actually see how cement and the minerals composing it behave over long time scales when subjected to weathering processes. Therefore, the site can be considered an analogue for the future behaviour of cement in the environment. Indeed, the hydration process that occurs in Maqarin when the groundwater reacts with NaOH, KOH and Ca(OH)2 is exactly what will happen when “man-made” cement is exposed to groundwater. Understanding the geochemistry and hydrogeology of a site like Maqarin gives real-world insights into the outcome of our modelling and we can take the data collected at places like Maqarin and compare them to our model results to verify its accuracy. Furthermore, using observations and empirical data to make conclusions about the future of waste repositories adds a whole new level of confidence in their design or identifies possible weaknesses.
In summary, since radioactive waste storage facilities, which are designed to have million year lifespans, are made of cement it is crucial that we know what will happen to them over long time periods. However, the problem is that modern cement is just that: modern. Therefore, we don’t really know how it will behave in certain environments or when conditions change, or during an ice age, etc, etc. In order to solve this problem we must turn to the next best thing, which is a natural site, such as Maqarin, that mimics the environmental conditions we are looking for and hopefully it can answer some of these questions. Hence, the beauty of the natural analogue.
Thanks for reading,
Matt
References
Khoury, H.N., Salameh, E., Abdul-Jaber, Q., 1985. Characteristics of an Unusual Highly Alkaline Water from the Maqarin Area, Northern Jordan. Journal of Hydrology 81, 79–91.
Khoury, H.N., Salameh, E., Clark, I.D., Fritz, P., Bajjali, W., Milodowski, a. E., Cave, M.R., Alexander, W.R., 1992. A natural analogue of high pH cement pore waters from the Maqarin area of northern Jordan. I: introduction to the site. Journal of Geochemical Exploration 46, 117–132.
This photo is a bit of a change of pace. This past weekend I was at the cottage (Garden Island, just outside of Kingston, Ontario) and was lucky enough to get pretty close to a Northern Water Snake that slithered over our swimming area. It later approached my girlfriend with a fish in his mouth as well…maybe it wanted to share? I dunno.
Of course, this wouldn’t be a photo of the week without geology so the rock that the snake is an Ordovician limestone that is part of the Black River Group. It is fairly fossiliferous and contains lots of large cephalopods and rugose corals.
A mature Northern Water Snake. They darken as they age. (Photo: Matt Herod)
This particular Nerodia sipedon is about 1m in length so a pretty large example. (Photo: Matt Herod)
We also had a massive Bullfrog move into the garden pond. Hope the snake doesn’t get him! (Photo: Matt Herod)
Today’s post is a special treat! An interview style post with one of the newest professors in the Department of Earth Science at the University of Ottawa: Dr. Pascal Audet.
What is your background? e.g. What was your undergrad in, PhD.
I graduated with a degree in physics from the Université de Montréal. By that time I knew I wanted to work in applied physics and I had always been curious about how the Earth works, so I enrolled in a Master’s program in Earth Sciences at the Université du Québec à Montréal, where I worked on gravity and topography modeling. I then decided that I wanted to do a career in geophysics, so I moved to Vancouver and started studying seismology at UBC. I graduated in 2008 and moved to California to do a postdoc at the University of California at Berkeley.
What was your PhD research about?
My PhD research was focused on the structure of subduction zones, especially the Cascadia subduction zone that is threatening the coastal cities of the Pacific Northwest (Vancouver, Victoria, Seattle, Portland). During my PhD I installed a few dozen seismic stations to record the ground motions caused by earthquakes from around the world. I used the information contained in the seismic records to study the structures deep below the stations. My results showed that the oceanic plate subducting beneath North America contains trapped pore-water at very high pressures, which could help explain some odd slip behavior of the subduction zone thrust fault.
Pascal had to chop all those trees down just to put in his seismic station. (Just kidding)
What field of geoscience do you study?
I consider myself a geophysicist, in that I use physical principles and techniques to investigate interesting questions about the Earth. My specialties are in seismology (the study of earthquakes and the waves they generate) and in gravimetry (study of the gravitational field of the Earth and other planets). I mostly deal with geophysical signals – seismic waves of gravity fields – and I develop processing techniques to obtain important information on Earth structures and dynamics.
How did you end up becoming interested in seismology and subduction zones?
At the time I started my PhD, I thought that studying seismology was the coolest job in the world, and subduction zones were the most interesting objects to study. Indeed, this is where a vast oceanic plate grinds past another tectonic plate on its way down to the Earth’s deep interior, producing the Earth’s most energetic events (e.g., the magnitude 9 Japan earthquake in 2011) in the process. I also had the good fortune to work with Michael Bostock at UBC, one of the best subduction zone seismologists. My interest never faded and here I am, doing research, teaching and training the next generation of geophysicists. I have the best job in the world!
What sort of techniques do you use to study seismology?
As I said, I use information contained in seismic records to obtain information on Earth structures. In a nutshell, earthquakes generate waves that propagate through the interior of the planet, and are recorded by very sensitive seismic instruments all around the globe. The signals contain information on the earthquake itself, but also on all the structures that the waves propagated through (via various wave effects that are well known in physics, such as refraction, reflection, diffraction, etc.). If we can remove the signature of the source from the seismic records, we are left with signals that contain information on structure alone. These signals then give us information on the seismic velocity of the medium, which is interpreted in terms of the geometry, temperature, composition and fluid content.
What sort of field work is involved in the study of seismology?
During my PhD I installed a few dozen seismic instruments in the northern part of Vancouver Island. Each station consists of the sensor, the data logger (recording device), and the power system. The sensor is typically buried about 2 meters in the ground and the power system is provided by solar panels that recharge a couple of car batteries. Carrying all this equipment and digging holes in clear cuts was quite challenging!
Join Pascal in the Yukon! He is looking for grad students. The field work is great.
What do you do with the data once you have gotten it from the field?
The data are recorded continuously on a disk. After collecting the disks at the end of the experiment, the data are archived at one of the data archiving centers and is available immediately to any researcher on the planet. With the right software, anybody can download seismic data from any seismic station. Some stations even provide real-time data, where a satellite connection is used to send the data seamlessly to the archiving center.
You are also interested in planetary tectonics. How do we study this field?
I am also very interested in the structure of planets and satellites within our solar system (e.g., the Moon, Mars, Venus). Since it is quite difficult and expensive to land on other planets and install seismometers (the Apollo Missions did install a few seismometers in the 1970s, but they only worked for a very brief period of time), one of the best tools to study their internal structure is to use the attraction from their gravitational field. Even though the gravity field appears to be uniform across the surface of the Earth (and other planets), there are minute variations that arise from small changes in the density structure of the deep interior. By studying these small variations in gravity, we can therefore obtain information on the internal structure of the planet. On remote planetary bodies, the gravity field is known by tracking satellites that orbit the planet. My current works is aimed at developing the tools to study the lateral variations in the gravity field.
What are your plans for future research?
This summer I am going back in the field to install 7 seismic stations in the Yukon and Northwest Territories, across the MacKenzie Mountains. These stations will use the satellite connection to send the data in real-time. The stations will be in the ground for 5 years, and the data collected will be used to study the structure and seismicity of the northern Canadian Cordillera – an area where we know very little about tectonic processes. This experiment is timed perfectly with the installation of stations in Alaska as part of the US Earthscope experiment (http://www.earthscope.org/). I will be spending a lot of time processing the data and will hopefully make interesting discoveries about the tectonics of this spectacular area.
Thanks so much Pascal!
By the way! Pascal is actively seeking graduate students interested in joining him in this exciting work in the Yukon or on planetary gravitational fields. If you would like to hear more about the MSc. and PhD. opportunities that Pascal has available post in the comments and I can put you in touch with him directly! He is also fully bilingual and a top notch hockey player.
