Hunting for fractures: Fieldwork in the Neuquén Basin, northern Patagonia - by Ole Rabbel
As a Ph.D. student in the “Physics of Geological Processes” (PGP) research group at the University of Oslo, my project includes an integrated approach to quantify thermo-mechanical processes at the interface between igneous sill intrusions and organic-rich host rocks. The initial stage of the project requires fieldwork in areas where intrusions in organic-rich sediments are accessible in order to document the associated fracture networks in the rocks. Few places on Earth offer sufficient outcrop quality of such systems, and therefore I needed to make the long journey to the Neuquén Basin in northern Patagonia, Argentina.
Here, in the spectacular Cara Cura mountain range (Figure 1), abundant sill intrusions have been emplaced in the shales of the Vaca Muerta (“dead cow”) formation, leading to boiling of pore fluids, as well as the generation of hydrocarbons and greenhouse gases. One of the main hypothesis of my project is that the intense heating and fluid and gas generation leads to strong overpressure, which in turn causes increased fracturing close to the intrusion contacts.
With the help of my Argentinian colleagues, I was able to find many outcrops that display intense fracturing (Figure 2) where we could to gather much needed data along a several kilometer long section through the sedimentary succession. The work included manual structural measurements, dense sampling of rocks for laboratory analysis, as well as aerial photography with drones for 3D virtual outcrop models. Under fantastic conditions and with great teamwork we collected large amounts of data, which we will analyze throughout the coming months.
I could not have imagined a better start of my Ph.D. project, both scientifically and as a personal experience, and I would therefore like to thank DEEP for funding this valuable field trip.