MARCH 2025 LUNCHEON MEETING
DALLAS DUNLAP
presents:
An Experimental Model of the Influence from Obstructed Subaqueous Channels on Turbidity Current Deposition/Erosion and the Potential for Channel Avulsion
11:30 AM Wednesday, March 19, 2025
at Willow Brook Country Club
3205 W Erwin St.
Tyler, TX 75702
Cost: $25 if you RSVP
$30 at the door if you do NOT reserve
Abstract
The Death Valley region has long been an important study site for our understanding of continental extension, transtension, and the evolution between the two. It is the type locality of the “pull-apart basin” and one of the early suggestions for the applicability of the “rolling-hinge model.” This presentation will discuss the evolution of southern Death Valley, which has been overprinted by multiple generations of extension, and the implications on previously applied extensional models for the region. In particular, this talk will suggest a refinement of the rolling-hinge model to southern Death Valley as detailed mapping suggests a lack of a singular detachment surface, necessary to the model. Additionally, recent thermochronology provides new constraints on the timing of extension and, when paired with geochronology of the adjacent syn-extensional basin, helps to define an updated model for extension in this part of the Death Valley region.Recent availability of high-quality and laterally expansive 3D marine seismic-reflection data revealed unusual high-angle meander bend character in deep-water channels adjacent to structural highs and local areas of remobilized sediments. Subaqueous leveed-channels have been shown to influence the path of debris flows and the spatial distribution of resulting deposits. What has been less studied is how turbidity currents interact with channel-emplaced debris flow deposits and how these interactions influence sediment deposition/erosion and the potential for channel avulsion. To investigate these interactions, we have conducted a series of 3D laboratory experiments using similar shape but different size (height, width) and relative attack angle (90 and 60 degrees) obstructions that were placed within a 2 m long by 0.65 m wide by 0.06 m deep straight channel submerged within an 8 m x 4 m x 2 m tank. Both saline gravity flows and sediment-laden turbidity currents were released into the channel. High resolution topographic scans were used to identify the spatial and temporal evolution of deposition/erosion and 3D current velocity fields were measured on a 0.04 m x 0.04 m grid using a profiling acoustic doppler velocimeter.
For all obstruction sizes and turbidity current attack angles, two relatively large horizontal eddies with depth-limited vertical heights formed upslope of the obstruction within the channel thalweg and along the sloping channel walls. Near the obstructions, currents were accelerated by these eddies, resulting in localized erosion or reduced sedimentation and increased deposit reworking within the channel thalweg. These eddies were also associated with the redirection of the lowermost portions of the currents to the channel margins, while the portions of the currents above the eddies travelled over the obstruction. For a 90-degree attack angle (perpendicular to the channel), a portion of the currents were re-routed out of the channel for a large (approximately channel filled) obstruction, whereas the entire current flowed over a small obstruction (approximately 84% channel filled). For a 60-degree attack angle, a portion of the currents were re-routed out of the channel for both large and small obstructions. Additionally, for the large obstruction more current was re-routed out of the channel for the 60-degree orientation than for the 90-degree orientation. It’s estimated that approximately 10-30% of the current’s volume was re-routed out of the channel axis, highlighting the often-overlooked impact of emplaced debris flow and slump deposits on post-emplacement turbidity current re-routing and potential avulsion of submarine channels and the implications for reservoir quality and facies distributions.
Biography
Dallas B. Dunlap is a Project Manager at the University of Texas, Bureau of Economic Geology. He received his B.S. degree from the University of Texas at Austin in 1996. That year, he joined the BEG’s International projects group focused on reservoir characterization studies in Austria, Mexico, and Venezuela. Dunlap further received a M.S. from UT in 2013 and is currently completing a Ph.D. (2025) focused on the impacts to channel migration and evolution from the emplacement of submarine landslides and sediment mass-movements. Dunlap continues to work in geologically complex deep-water settings which include the Northern Atlantic, Gulf of Mexico, and offshore Brazil and most recently developing benchmarked seismic datasets for machine learning and artificial intelligence applications.