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From Ancient to Modern

Geology students went on a trip to the beach, but their shovels were a tool for studying depositional environments not for building sandcastles.

During the Fall of 2016, as part of the Petroleum Systems class (Geology 525), Dr. Hudson traveled with nine students to the Texas Gulf Coast to see for themselves the depositional environments they’d spent the semester studying in the classroom. From rivers to estuaries to shorelines and beyond, coastal settings are responsible for many of the conventional reservoirs from which we produce oil and gas. Seeing these environments first-hand gives students the opportunity to better grasp the scale and complexity of the architectural elements at the surface.

While this was a “trip to the beach,” students worked for their knowledge by digging trenches everywhere they went. At each field stop students (and instructors) got to work digging trenches to see the sedimentary structures being deposited and preserved in each environment. From sandy point bars to muddy bays, students worked to uncover what lay beneath the surface, breaking several shovels along the way.

Important reservoir analogues studied included fluvial point bars, which by themselves are not large accumulations of sand but which often stack up in the subsurface to create bigger reservoirs. Geomorphology and spatial/temporal evolution of rivers was discussed as the class saw evidence of recent flooding, as well as cutoff channels and oxbow lakes. The size of the active floodplain was contrasted with the size of the active channel, and comparisons to other modern systems, such as the nearby Mississippi River, were made.

Shoreface systems were a major focus of the trip, with multiple stops (and trenches) along the Texas Gulf Coast. At the bay head delta for the Trinity River, dry sandy trenches gave way to ankle-deep mud and discussions of invertebrate communities and their relationship to salinity variability. Distributary channels and mixing of water bodies as the delta evolves were shown to affect biological ecosystems, and the class discussed how the fossil record can show the evolution of the delta both spatially and through time.

Nearly half of the trip was spent along the shoreline of the Gulf of Mexico, looking at environments ranging from shoreface sands to backshore dunes to tidal channels and tidal deltas.

Discussions focused on determining the evolution of the shoreline through recent time, with trenches illuminating important changes that have happened just in the recent history of the Gulf Coast. Relationships between bedforms and processes was a major focus of the trip, and groups took turns presenting what they had uncovered at different parts of the system to the group. Studying the recent geologic record preserved within the sediment of the Gulf Coast while being able to turn around and look at the analogous modern environment is invaluable to picturing the process that led to the weathering, transport, and deposition of the sediment around which the discussions centered.

Aside from field learning, this was also a good introduction to applied research. The trip was modeled after a trip that Dr. Hudson used to help teach for new hires when he worked at ConocoPhillips and was co-led by Dr. Hudson’s former colleague who’s still working at this major energy company. Discussions not only focused on the processes at work in each environment but also focused on how the details of what they were seeing apply to oil and gas exploration. The way in which a reservoir performs deep in the subsurface is often affected dramatically by fine-scale details within the sedimentary rocks, and seeing these details in the modern coastal environment builds knowledge students and professionals can apply to similar systems deposited long ago.