Collaborative Research: Quantitative Reconstruction of Paleohydraulics of the Kayenta Formation - Implications for Paleoclimate Reconstruction

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Determination of paleoslopes in ancient fluvial systems has potentially broad, butlargely untapped, application to quantitatively constraining the history of tectonics andpaleoclimate in continental sequences. The objective of this project is to, first, flesh out anew approach to calculating paleoslope and associated information, such as water andsediment flux, from sandy braided stream deposits. The second objective is to apply themethod to the Kayenta Formation (Jurassic) on the Colorado Plateau to demonstrate theutility of the method in reconstructing aspects of long-term climate change from theancient record of fluvial deposits found on a regional scale. The key to reconstructingpaleoclimate as proposed here is to estimate paleowater flux from estimates of paleoflowdepth (as determined from bar forms) and calculations of paleoslope. Paleoslopecalculation follows a novel approach utilizing the Rouse Number, an indicator of grainsizefractionation between bed load and suspended load in water flows. The key tool toapplying the method is the use of high-precision, rapid, grain-size determinationsavailable using equipment housed at M.I.T. Preliminary results show the approach workswell in the modern and yields remarkably consistent comparisons with the KayentaFormation. Theoretical modeling of climate impact on fluvial systems suggests that longtermclimate change may produce a very different stratigraphic record than short-term(Milankovich scale) changes. Hence application of the method to the ancient not onlyprovides an example of what the method can do, but will help answer specific questionsregarding how the long-term change from dry to wet to dry conditions represented by theWingate-Kayenta-Navajo formations of the Glen Canyon Group, respectively, affectriver systems. By systematically applying the methodology to the Kayenta Formation, wewill obtain statistically significant probability distributions of aspects of paleoflow (slopeand water flux) that can be compared between sites within the unit to show how riversystems changed down basin and over time. Such an application will demonstrate theutility of the paleohydraulic reconstruction approach to paleoclimate reconstruction thatcan be applied to other sandy fluvial deposits in the ancient record.The broader aspects of the study include training a female Ph.D. student at theUniversity of Wyoming in quantitative methodologies of sedimentation. Anundergraduate at M.I.T. will also be trained in field and laboratory techniques as part ofthis project. In addition, the research includes a tie to an NCED (National Center forEarth-Surface Dynamics) facility, allowing for outreach of this NSF-funded Science andTechnology Center.