My research focuses on the interaction between subsurface fluid migration, lithology, and tectonics. This interaction affects a wide range of geologic processes from the mechanical properties of faults to the distribution of mineral resources and is of immediate societal interest for its influence on hazardous waste remediation, water resources management, and slope stability issues. In the marine environment, the influence of fluid/sediment interactions on methane gas hydrate distribution has been a topic of recent interest because this compound, an ice-like crystalline solid in which a lattice cage of water molecules traps a molecule of methane gas, has been touted as an agent for climate change, is a potential new source of economically recoverable organic carbon, and likely influences sub-marine slope stability.

Hydrate Ridge

Hydrate Ridge, OR is an accretionary ridge located ~100 km offshore central Oregon. It is formed by the subduction of the Juan de Fuca Plate beneath the North American Plate. Scientific interest in Hydrate Ridge has made it the focus of several international, interdisciplinary, studies in recent years. I participated in Ocean Drilling Program (ODP) Leg 204, to southern Hydrate Ridge as a sedimentologist/structural geologist in order to determine the role of subsurface fluids in controlling the distribution of hydrate in this complex geologic environment.

Infrared Camera

ODP Leg 204 used an infrared camera to image gas hydrate deposits recovered in the cores. I analyzed these images and compared them to the sampled lithologies in order to establish a link between gas hydrate formation and grain size at Hydrate Ridge. I have shown a few sample images below. The blue colors are cold spots in the core and indicate the location of gas hydrate. The hydrate is colder than the surrounding sediment because it is dissociating at surface temperature and pressure conditions. This dissociation is an endothermic process.

Resistivity-at-the-Bit

Resistivity-at-the-bit (RAB) data are also useful for determining the location of hydrate in the ODP boreholes. These data are taken by the logging-while-drilling (LWD) suite of tools, which measure the physical properties of the sediments while the borehole is being drilled. Resistivity, a measure of how difficult it is to send an electric current through the formation, varies with the amount of salt water filling the pore space. Where this pore fluid has been displaced by gas hydrate, free gas, or other mineral cements, the formation is highly resistive. In the images below, the bright white areas are more resistive and indicate gas hydrate in fractures in the formation.

The two images on the ends are round, core images. The one in the middle is an “unwrapped” image of the borehole. In this central image, the two vertical sides can be re-wrapped together to meet, and when this happens the bright while sinusoid in the middle of this image, turns into a plane. Therefore these images can be used to examine the structural orientation of gas hydrate. I took these data and determined that the crest of Hydrate Ridge is undergoing gravitational collapse, creating strikingly (note the geology pun) different patterns of hydrate orientation at the ridge crest than the flanks.

Soil Mechanics

Another way to assess stress state, burial history, and fluid over-pressures in sediments is to examine how much of their void space they lose when placed under stress. This relationship is unique for each sediment type, and can be measured in the lab using a consolidometer. At Hydrate Ridge, I determined that the basin site (to the east of the ridge) is highly over-pressured. This excess fluid pressure is related to an increase in sedimentation rate within the last 300k.y..