Patagonia field work — Update #5
An update from down south. Field work is going well, the weather has actually been quite wonderful. We’ve had multiple days in a row of near-perfect field weather. Weather can make this type of work glorious or full of misery, and we’re getting lucky the past couple weeks.
I figured I’d take the time to explain in a bit more detail about the work we are doing down here. The overarching goal of our research is to understand the stratigraphic patterns and evolution of deep-marine sedimentation. The deep-sea environment is inherently difficult to study — it costs a lot to deploy ROVs and other instrumentation on the seafloor to make basic observations and measurements of physical processes. One of the dominant processes that transfer sediment from continents to the deep sea, called a turbidity current (picture a submarine avalanche of mud, silt, and sand), can end up destroying any instrumentation. Additionally, these events occur infrequently at the timescale of human observation — once every few hundred to thousands of years — which makes it impossible to directly study a sequence of events.
So, we look to the evidence left in the geologic record. The transfer of sediment from land to the deep sea can, under certain circumstances, get preserved in the stratigraphic record. We are investigating such deep-sea deposits that were buried and then at some later point uplifted into a mountain belt. Weathering and erosion of those mountains reveals exposures of the sedimentary rock that we can study in detail.
But, why do we travel all the way to Patagonia to look at deep-sea sedimentary rocks? This particular sedimentary basin, the Cretaceous Magallanes Basin, is a foreland basin. Many outcrops of sedimentary successions come from foreland basins because they end up getting uplifted into the evolving fold-thrust belt. Compared to most foreland basins of this type, the Magallanes Basin had a unique tectonic history that resulted in a basin that was deep enough for long enough time to accumulate approximately 4,000 m of deep-sea sediments. If you’re interested in the details, my colleagues and I discuss this tectonic history at length in this paper.
This geologic history provides a situation to study a thick succession of deep-sea stratigraphy that evolved over 20 million years and resulted in a diverse assemblage of turbidite (the deposits of turbidity currents) architectures. Check out this paper that my colleagues and I published last year for the best ‘start here’ review of the Magallanes Basin.
There are numerous scientific questions about how these sedimentary systems work and how they relate to the evolution of the Andes in this region. But, how are the results of this kind of work actually used in applied Earth science? The deposits of deep-sea sedimentary systems that are still buried in the subsurface are important reservoirs that we extract fluids from (oil, gas, water) and that we inject fluids into (CO2). These subsurface reservoirs are not homogenous layers, rather they are heterogeneous 3D bodies. Subsurface geology is as rich and complex as geology at the surface, but we have only low-resolution remote sensing and dimensionally challenged observations to characterize it. These examples exposed at the Earth’s surface, in outcrop belts like the Magallanes Basin, provide an opportunity to characterize the complex relationships at scales we may never be able to achieve deep in the subsurface. Qualitative insights and quantitative information (e.g., sedimentary body dimensions) derived from outcrops like this are used to constrain models and, importantly, improve prediction of complex subsurface geology.
Image at top of post: This mountain, called Cerro Divisadero, is where I did a big chunk of my PhD research in 2004-2006. I haven’t been back since those days (it’s rather difficult to get to) but we got close enough last week to get this view. Here’s the paper that came out of that work.