Our research generally focuses on two major themes --

1)  Stratigraphic development and character of alluvial systems (fluvial, alluvial fan, etc.)

• "sequence stratigraphy" of continental depositional systems (especially alluvial fans!).
• accommodation controls and preservation potential in aggradational fluvial regimes.
• continental basin fill, basin-scale variability (basin analysis).

2)  Hydrostratigraphic characterization (using stratigraphic concepts to characterize the aquifer system)

• modeling the 3D hydrofacies distributions using stratigraphic concepts and tools.
• characterizing the various scales of hydrologic heterogeneity based on sedimentologic characteristics.
• outcrop analog modeling - evaluation of the influence of heterogeneity on non-Fickian transport.

Classified Advertising:  Does any of this sound interesting to you?????  Are you interested in getting involved in hydrostratigraphic analysis of fluvial systems?  Do you like to study fluvial stratigraphy and are into innovative approaches to understanding the subsurface character of these strata?  Contact Gary Weissmann at weissman@unm.edu or by phone at 505/ 277-3636.

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Active Projects:

Fluvial Stratigraphic Form in Actively Aggrading Continental Sedimentary Basins

Collaborators:

• Dr. Adrian Hartley, University of Aberdeen, Scotland
• Dr. Gary Nichols, Royal Holloway, London
• Dr. Louis Scuderi, Center for Rapid Environmental Assessment and Terrain Evaluation (CREATE), UNM
• Dr. Timothy Wawrzyniec, UNM Lidar Laboratory

Funding Sources:  FSRG consortium. NSF (through CREATE)

When we think of fluvial systems and their preservation in the rock record, we typically draw upon our experiences with tributary rivers that are most common in the world. Indeed, most facies models that we use to interpret the ancient rock record have been developed on tributary rivers that exist outside active sedimentary basins or, if the river studied lies within a sedimentary basin, the models developed typically do not place the studied reach into the context of the basin.  A review of over 700 modern continental sedimentary basins around the world (e.g., those that have a chance to be preserved in the rock record) shows that fluvial depositional form in these basins is not tributary in nature; rather they form either (1) distributive fluvial systems (DFS), commonly called megafans, fluvial fans, and alluvial fans in the literature, or (2) axial stream systems that parallel the basin trend, with the vast majority of sedimentation in the basin occurring on the DFS (up to 95%).  In these continental sedimentary basins, we have identified ~400 fluvial megafans (defined as DFS that are greater than 30km in length), with countless smaller DFS filling the basins.  Thus, most sedimentary basins undergoing aggradation do not contain tributary fluvial systems.  The implications of this observation could significantly affect our ability to reasonably interpret ancient fluvial deposits.

 

The Alaska Range Foreland Basin near Fairbanks, Alaska. Notice how this basin is dominated by DFS. The Taquari River DFS, Pantanal Basin, Brazil

The Shargyn Basin, Mongolia. The Seimchan Basin, Siberia.

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Evaluation of the influence heterogeneity has on non-Fickian transport: outcrop analogs of aquifers and geologically-based upscaling approaches Collaborators: Dr. Timothy Wawrzyniec, UNM Lidar Laboratory Kate Klise, Sandia National Laboratory Dr. Vince Tidwell, Sandia National Laboratory Dr. Sean McKenna, Sandia National Laboratory Dr. David Benson, Colorado School of Mines Funding Source:  Department of Energy - Basic Energy Science Program Most model of contaminant or solute transport use a Gaussian assumption for dispersion (in other words, the velocity distribution around a mean velocity, given to us by Darcy's Law calculations, is normal, or Gaussian). This is also called Fickian transport. Many studies have shown that this is not a reasonable assumption, and the dispersion or velocity variability is better characterized by a power law distribution. We are exploring what of the physical heterogeneity causes this non-Fickian dispersion, and what are the parameters that we should use in a given depositional setting and scale. To accomplish this, we use terrestrial lidar to acquire a high-resolution (down to 2mm) image of an outcrop, segment lithofacies from this 3D image, and develop groundwater models based on these images. So far, we've only constructed 2D models, but Beth Nichols will soon show results of 3D imaging. The images to the right show preliminary results from a 3m x 1.5m exposure. Notice the significant groundwater focusing in gravels shown by particle tracking simulations in the bottom image. We are expanding this work to image outcrops at large scales (350x350m area) in order to develop concepts on geologically-based upscaling techniques. We also plan to use such 3D characterizations to aid in evaluating groundwater issues such as potential impacts of in-situ uranium mining.

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Geochemical and Physical Aquifer Property Heterogeneity: A Multiscale Sedimentologic Approach to Reactive Transport Collaborators: Dr. Richelle Allen-King, University of Buffalo Dr. Chris Murray, Pacific Northwest National Laboratory Dr. Tim Scheibe, Pacific Northwest National Laboratory Funding Source:  Department of Energy - Environmental Management Science Program (EMSP) Often, only physical heterogeneity is considered as affecting contaminant transport, however geochemical heterogeneity, potentially correlated to lithofacies variability, may also significantly affect movement of contaminants in the subsurface. We are testing this at the Hanford 200 West site through both subsurface studies and outcrop analogs.

 

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