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

Massachusetts Institute Of Technology, Cambridge MA

Investigators

Abstract

Determination of paleoslopes in ancient fluvial systems has potentially broad, but largely untapped, application to quantitatively constraining the history of tectonics and paleoclimate in continental sequences. The objective of this project is to, first, flesh out a new approach to calculating paleoslope and associated information, such as water and sediment flux, from sandy braided stream deposits. The second objective is to apply the method to the Kayenta Formation (Jurassic) on the Colorado Plateau to demonstrate the utility of the method in reconstructing aspects of long-term climate change from the ancient record of fluvial deposits found on a regional scale. The key to reconstructing paleoclimate as proposed here is to estimate paleowater flux from estimates of paleoflow depth (as determined from bar forms) and calculations of paleoslope. Paleoslope calculation follows a novel approach utilizing the Rouse Number, an indicator of grainsize fractionation between bed load and suspended load in water flows. The key tool to applying the method is the use of high-precision, rapid, grain-size determinations available using equipment housed at M.I.T. Preliminary results show the approach works well in the modern and yields remarkably consistent comparisons with the Kayenta Formation. Theoretical modeling of climate impact on fluvial systems suggests that longterm climate change may produce a very different stratigraphic record than short-term (Milankovich scale) changes. Hence application of the method to the ancient not only provides an example of what the method can do, but will help answer specific questions regarding how the long-term change from dry to wet to dry conditions represented by the Wingate-Kayenta-Navajo formations of the Glen Canyon Group, respectively, affect river systems. By systematically applying the methodology to the Kayenta Formation, we will obtain statistically significant probability distributions of aspects of paleoflow (slope and water flux) that can be compared between sites within the unit to show how river systems changed down basin and over time. Such an application will demonstrate the utility of the paleohydraulic reconstruction approach to paleoclimate reconstruction that can 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 the University of Wyoming in quantitative methodologies of sedimentation. An undergraduate at M.I.T. will also be trained in field and laboratory techniques as part of this project. In addition, the research includes a tie to an NCED (National Center for Earth-Surface Dynamics) facility, allowing for outreach of this NSF-funded Science and Technology Center.