Apr162009
Geological Breakdown
Written by Ava

What does a rock geologist know about the ocean? That's what we were wondering when we first encountered San Francisco Bay Area resident Brian, a sedimentary geologist and researcher who writes mostly about Earth Science and energy issues but who frequents the marine world (ocean topography, sea-floors, rocks located near the ocean) as part of his work. Like the climate scientists, marine biologist, and reef hobbyists that have come before, does Brian have what it takes to, in his own way, make the marine world a better place?   

In our first marine geology interview, answering a series of questions brought to him by the TRT crew, let Brian tell you himself...

Tell us about the work you are currently doing as a sedimentary geologist and research scientist.

I’ve been out of graduate school a little over a year and am currently working in the petroleum industry. I conduct research, collaborate with academics whose research we fund, and develop and teach internal training courses. Our research is focused on understanding deep-marine sedimentary systems, which I will explain a bit more below.  

In what ways does your work focus on marine geology, the ocean, etc.?

My primary research interest is to better understand the transfer of sediment from the land to the deep ocean, especially over geologic time scales. The sedimentary processes that deliver sediment to the deep sea are still not very well understood. The main reason for this is because it is extremely difficult to observe and measure the processes directly. To better understand how sediment is transferred and distributed in the deep sea, I study detailed maps of sea-floor topography (known as bathymetry) along with sediment and core samples. The geology and geomorphology of the ocean floor can be as rich and complex as on land, but we still have very little of it mapped in detail. As oceanographer Robert Ballard has noted, we have the surface of Mars mapped in more detail than we do our own ocean floor.  

Your PhD research focused on ancient and modern deep-marine depositional systems.  Explain.

One of the primary processes that move sediment from shallow water to deeper water is called a turbidity current. It is similar to an avalanche but, instead of snow, it is a mixture of sand, mud, and water. The turbidity current flows down the continental slope through submarine canyons and channels and when it finally comes to rest in the deep ocean the sediment is deposited. That deposit is called a ‘turbidite’. As mentioned above, direct observation and measurement of turbidity currents is extremely difficult. In addition, the occurrence of turbidity current events is quite rare on a human time scale – big ones may occur only once every hundred years (or even once every thousand years!).

One way to indirectly study these processes is to look at a record of the deposits – to look at the turbidites themselves. Over geologic time (millions of years) some deep-sea sedimentary systems are buried and then subsequently uplifted during a later mountain-building event. These ancient sediments, now lithified into sedimentary rock, are exposed at the surface of the Earth in what geologists call 'outcrops'. Some of the very best outcrops have hundreds or even thousands of feet of sedimentary section exposed. This preserved record is like a 'book' of Earth history -- and by describing, mapping, and characterizing the deposits in great detail, we are attempting to interpret the story in that book. A component of my Ph.D. research investigated Cretaceous (about 70 million years old) turbidite deposits now exposed in mountains in southern Chile. You can read more about these ancient deep-sea deposits and a paper I published about the study on my blog here.

Outcrops of ancient deep-sea sedimentary systems provides information about the turbidite deposits themselves, but it can be challenging to reconstruct what the geomorphology of the sea floor was like from preserved sedimentary rock. It is also very difficult to learn about what causes these avalanches of sediment in the first place. So, in order to learn more about these systems, another component of my Ph.D. involved investigating much younger deep-sea sedimentary deposits (from 7,000 years ago to present) offshore southern California.

What we found was that the changes in climate over the last few thousand years was a major control on the amount and timing of sediment delivered to the deep ocean. I have a peer-reviewed paper about that study coming out in a couple of months and will blog about it on Clastic Detritus once it is published. In the meantime, check out this older post about the project here.

What have been some of the best experiences in the various marine locations you have visited?

The bulk of my field experience is from investigating ancient deep-marine sediments now exposed in mountain belts. That work has taken me to locales in Canada, Chile, Argentina, South Africa, France, and areas in my home country, the United States. During graduate school in California I had the opportunity to go on a research cruise with Monterey Bay Aquarium Research Institute (MBARI) to collect sediment cores offshore the central California coast. We went out on a vessel called The Western Flyer and used their ROV (remotely operated vehicle) to collect samples of sediment from the sea floor in 1,000 meters water depth. The samples were brought up to the ship by the ROV and then we described and sampled them onboard while the ship moved to the next location. I hope to do more ship-based work in the future – I really enjoy integrating investigations of both ancient and modern deep-sea sediments and think it is the best way to gain a comprehensive understanding of these systems.

What have these marine locations/experiences taught you about what is happening to marine life, bodies of water, the ocean?

Although my research interests aren’t directly related to marine life, the geomorphology of continental margins has a profound impact on marine life. For example, the steep continental slopes of the California coast create a setting in which nutrient-rich waters from deeper depths come to shallower waters (known as upwelling). In addition, submarine canyons can be important habitats for deep-marine life. Because these canyons are sculpted by turbidity currents I discussed above these processes can have huge impacts on how these habitats might change with future environmental change. More generally, studying the larger-scale physiography of continental margins, which is related to plate tectonic processes, is important for the oceanography and marine biology community to understand. I feel that I can play a role in helping increase our knowledge of these dynamic environments.  

What kind of problems are we facing according to your marine geology research?

The biggest challenge my particular discipline of deep-marine sedimentary systems faces is how to directly observe and measure these elusive submarine processes. Several academic and research institutions are working to develop better monitoring equipment that is deployed in the deep sea with the hopes of catching these processes in the act. Understanding the magnitude, frequency, and controls of these processes is important because they not only can impact marine habitats, but can also damage sea-floor infrastructure (e.g., communication cables). And, in case you are wondering why a petroleum company hired me, ancient turbidite deposits buried deep in the subsurface can be reservoirs for hydrocarbons. Although we will move away from hydrocarbon resources over the coming years, as we should, they will remain a significant part of the equation for a world demanding more and more energy for at least a few more decades. I think we need to be smart about how we explore and produce this energy – a strong scientific understanding of turbidite systems reduces the uncertainty, and thus impact, of these operations.

Does your marine geology research help you to understand issues such as marine conservation, ocean acidification and climate change? If yes, how?

That’s a great question. As mentioned above, my research involves geologic time scales (from thousands to millions of years). The research I did looking at the active systems offshore southern California showed that the deep-sea sedimentary processes correlated well with paleoclimate reconstructions. In that case, fluctuations in precipitation directly influenced how much sediment was eroded from land and subsequently delivered to the deep sea. A line of research I would love to pursue further is if we can use the characterization of these deposits to better constrain paleoclimate reconstructions in other areas of the Earth. Understanding how climate has changed in the recent geologic past is critical for understanding what the current and future climate changes have in store.      

Tell us one or two interesting facts about how the world’s current sedimentary record (rock research) has been used to reconstruct ancient environments, specifically referring to oceanic conditions and/or sea level fluctuations.

A popular conceptual model that has been developed from looking at the sedimentary rock record states that sea level is a major controlling factor regarding the timing of sediment delivery to the deep sea. Very simply, when sea level is very low the continental shelf is exposed and rivers deliver sand and mud directly to the continental slope. When sea level is high, the continental shelf is submerged and rivers can’t reach the shelf edge. For example, during the last ice age, sea levels were 130 m (425 ft) lower than they are today. In this map below of eastern North America (created in the free Java-based application called GeoMapApp) the continental shelf is the vast light-colored area between onshore (green) and the deep sea (blue). About 20,000 years ago, this entire area was land.


This conceptual model of sea-level control on where and when sediment is delivered over geologic time scales has been applied to ancient rocks to infer changes in sea level over Earth history. It some cases it works great, in other cases there are other factors that complicate the story. I was co-author on a paper in 2007 in the journal ‘Geology’ that discusses this model in more detail. You can read a blog post I wrote about it here.

How (if at all) does your marine geology research tell you about the damage the world population is doing to their marine environments?

Thus far, my own research has dealt primarily with pre-anthropogenic geologic processes and products – that is, older than impact from human civilization. However, a close colleague from MBARI that I’ve worked with has been collecting mud samples from the deep sea off the coast of California and sampling for the pesticide DDT. He is using it as a way to date the sediments. DDT was used as an agricultural pesticide from the 1940s-1970s in California and was incorporated into the rivers and streams, which eventually led to the ocean. This is just one of many examples of how human activity, even if it is on land, affects the health of the oceans.

How can we protect our marine geology?

I guess I would put it a different way. Instead of ‘protecting’ geology, I would encourage everyone interested in marine science and conservation to learn about the geology of our ocean basins. The location, distribution, and types of biological habitats are directly influenced by their geologic setting. The chemistry of our oceans is also strongly influenced by the types of rocks and sediments that are found on the sea floor. Although the time scales in which many geologic processes operate (e.g., plate tectonics) are much longer compared to the human experience, I think it is important that we recognize that our current snapshot in geologic history is a consequence of how the planet has evolved over billions of years.

Explain Clastic Detritus and tell us about your blog.


The word ‘clastic’ means ‘broken’ and the word ‘detritus’ essentially refers to ‘pieces of stuff’. So in the simplest sense, sediments are broken pieces of other things. When you go to the beach and look at those sand grains in your hand, remember that each of those grains was once part of a rock. And those pieces of rock have a story to tell. Sediments and sedimentary rocks are what I spend a lot of my waking hours thinking about and my blog is meant to communicate that. I started it in late 2006 while I was still in graduate school. To be perfectly honest, writing the blog during grad school was a great way to procrastinate writing my dissertation! The best part of blogging that I didn’t really anticipate when I started was building the network of other geoscience bloggers that I now consider friends (even though I haven’t met most of them in person). Being part of an online community of people with similar passions and interests from around the world is pretty exciting. It looks like The Reef Tank has also been successful in that regard.

The frequency of my blogging has decreased a little bit since finishing graduate school about a year ago. Now that I have a “real job” it gets increasingly difficult to find the time. But, I still post about once or twice a week and plan to keep blogging about sedimentary and marine geology for years to come.

For those that want to see a collection of posts about marine geology, I think the best place to start is a series I call “Sea-Floor Sunday”. On most (but not every) Sunday I post a sea-floor topographic (or bathymetric) image and discuss it. I have found a lot of fantastic online resources while searching for images, which I link to in these posts.

You will also find links on my site to the ever-growing community of geoscience bloggers.

If you'd like to ask Brian a question about his work or what was discussed in this Q&A, please go here.


Keep up with Brian's geological adventures on his blog: Clastic Detritus

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