Charles Nittrouer¹ and Neal Driscoll²

¹School of Oceanography, University of Washington, Seattle, WA 98195-7940
²Woods Hole Oceanographic Institution, Clark 260, Wood Hole, MA 02543

Towards a Sed/Strat Science Plan
Margins are the principal locus of sediment accumulation on Earth. The pathways followed by sediments on their journey from source to a sink (e.g., hill-slope erosion, river transport, biological production, temporary storage, seabed burial) have major impacts on the lives and livelihoods of people worldwide, ranging from natural hazards, to pollutant transport, shoreline erosion, and resource preservation. The eventual sinks for sediments are in carbonate and/or siliciclastic depositional settings, where their fate is determined by diverse factors (e.g., sea level, tectonics, climate, sediment supply, ocean hydrodynamics) that control sediment deposition and burial. The resultant stratigraphy on margins is a tape recording of Earth history, but the fidelity with which the stratigraphy records processes occurring on Earth is variable. A rich, but complex signal is created. This signal needs much better understanding than presently available, in order to unravel the interrelationships of past processes and to predict impacts of future processes (including applied scientific considerations, such as: erosion and landslide mitigation, river flooding, dredge-spoils disposal, channel navigation, fishing activities).

NSF will fund a meeting at which the science plan for the MARGINS sedimentology and stratigraphy community will be created (JOI support also has been requested). This plan will suggest important directions for future research, recommend strategies for accomplishing this research and will consider candidate sites for detailed interdisciplinary studies. The science plan is expected to provide a blueprint for taking geomorphologic, sedimentary and stratigraphic processes to a substantially higher level of understanding. The research goal is to discern the relationships among processes relevant to sediment production, transport, accumulation, and preservation on margins at multiple temporal and space scales, from turbulence to tectonics and from sedimentary fabric to sequence stratigraphy and basin analysis. Coupled

Land-Ocean Systems
The meeting and the science proposed will use a systems approach to examine coupled land and ocean environments (from mountain tops across shorelines to abyssal plains). It will involve understanding of drainage-system development and evolution, examination of the interplay between the drainage basin and sediment input to marine environments, assessment of how whole dispersal systems respond to climatic and base/sea-level perturbations, and information about transfer functions from sediment dispersal to the stratigraphic record. The many processes producing sediment on land (e.g., weathering, hill-slope erosion, fluvial transport, landscape evolution) will be considered in concert with those processes that control sediment burial on carbonate, mixed and siliciclastic margins (e.g., sea-level fluctuations, ocean hydrodynamics, biological productivity). These diverse processes are linked as part of the continuum forming a sediment dispersal system. In addition, consideration will be given to other processes, which impact both sides of the shoreline by themselves (e.g., tectonic activity, climate changes, groundwater variations). Emphasis will be placed on developing a significantly better understanding about the creation and interpretation of landscape evolution and the sedimentary record.

Understanding the linkageswithin entire sediment dispersal systems requires coordinated interdisciplinary investigations. Capturing this synergy will be important, and has the potential to foster much innovative research, as suggested below.

• Landscape-evolution models should be able to predict fluvial discharge of sediment, including hyperpycnal events that could transport sediment to deep portions of the margin.
• Margin stratigraphy can provide an independent check on terrestrial erosion rates from isotopic observations (e.g., ¹⁰Be, ²⁶Al) of land surfaces.
• Models using precipitation forecasts can predict hydrologic response in rivers, and can lead to stochastic models of sediment delivery to margins.
• Events impacting land and sea (e.g., river floods) can be investigated simultaneously through monitoring and rapid-response data collection.
• A fundamental question facing both geologic and oceanographic studies is how mass moves across isobaths on margins, especially across significant boundaries (e.g., shoreline, shelf break).
• Fluvial environments and marine environments can be investigated contiguously in a dispersal system, in order to elucidate linkages between them when base/sea level fluctuates.
• Many of the same fundamental physical mechanisms operate for transport of sediment in fluvial and marine environments, and theoretical advances in one area should help the other.
• Depositional environments form a spectrum from carbonate to mixed to siliciclastic, and should be studied as a depositional system in a process-oriented framework.
• Melt-water pulses from terrestrial ice sheets and catastrophic breaching of glacial lakes should be recorded in high-resolution sea-level curves and stable isotope (dO¹⁸) data.
• Integration of forward models, inverse one-, two-, and three-dimensional models, margin sequence stratigraphic records, and global oxygen isotopic variations will provide a testable record of past eustatic change.
• Reconstruction of sediment input, eustatic, and tectonic variations will allow testing of models for sedimentation changes within sequences.
• Reconstruction of erosion, transport and storage of sediment in large river valleys can illuminate the linkages between tectonic and climatic events on land, and the magnitude, mineralogy, and timing of signals recorded in margin stratigraphy.
• Integration across scales and environments will require partnerships between modeling and observations.

Experiment Design and Equipment
Interdisciplinary field, lab, and modeling efforts, with a range of tools from computer and flume-tank simulations to airborne surveying and shallow ocean drilling, will be required to understand the dynamic components controlling erosion, sediment transport, and sediment dispersal from source to sink across the coupled land-ocean system. Although the potential study areas are not constrained prior to the creation of a science plan, a major contribution of the proposed meeting will be to identify several candidate areas best suited for future investigation. Scientific priorities and financial resources require a focused effort.

Certain field equipment is recognized as central to our quest for a quantum step in understanding landscape evolution, sedimentary processes and stratigraphy. High-resolution digital topography/bathymetry and other forms of remote sensing (such as side-looking sonar and radar, and hyperspectral imagery) will be essential, as will ground-penetrating radar/seismic systems and drilling at all elevations/ depths (including shallow water 0-100 m). Multiple dating techniques (radiochemical, paleontological, cosmogenic radiochronology) will be important. Studies on land and sea are anticipated to provide time-series data regarding many important processes. Fiber-optic cables or telemetry systems would be ideal for these observations. Rapid response to events (e.g., floods, landslides, storms, earthquakes) also will be needed to maximize the information obtained for some processes, and this will require creative uses of ships, aircraft, and unmanned platforms (drones and AUVs).

Numerical modeling will be an important component to many studies, and the development of robust models may control the sequence of observations. In cases where models exist, they can help delineate the variables that must be measured. In cases where they donšt exist, experimental designs may have to wait. In other cases, observations will be needed before models can be formulated. Such evaluation of sequential timing for these and other considerations will occur at the meeting. In the context of a large, interdisciplinary effort, special attention shall be paid to designing tests and calibrations of mathematical models.

Timetable, Funding and Applications
The four-day meeting will be held at Lake Quinault, WA, on Sept 28-October 1, 1999. An organizing committee will help identify speakers, who will give educational presentations during the first two days. Prior to the meeting, participants will be asked to express thoughts about criteria for choosing topics and sites of investigation. These will be used to frame and focus the discussions on the final two days, when the science plan is written. Shortly after the meeting, a draft of the science plan and descriptions of 2-3 candidate study sites will be disseminated through the MARGINS web page and mailing list. Final consideration of these will occur during a community meeting at the December 13-17 AGU meeting. The goal is to build a consensus about topics and regions to study, and to prepare the community for submitting MARGINS proposals; i.e., to have a science plan for the Sedimentology and Stratigraphy portion of MARGINS in place by the end of 1999. Approximately 50 participants are expected, and funds are available for travel support. Applications to attend the workshop should be submitted to the MARGINS Office. The MARGINS Steering Committee will be asked to evaluate candidates. To apply, send a one page (or less) e-mail message to margins@soest.hawaii.edu containing

1. address and contact information, including web site,
2. description of research interests
3. statement of potential contributions to the meeting.

Organizing Committee
C. Nittrouer* (U. Washington), convenor
N. Driscoll* (Woods Hole OI), convenor
J. Austin (UT Austin)
W. Dietrich* (UC Berkeley)
T. Dunne (UC Santa Barbara)
G. Eberli (U. Miami)
C. Fletcher (U. Hawaii)
A. Hine (U. South Florida)
G. Karner* (Lamont-Doherty EO)
K. Miller (Rutgers U.)
G. Parker (U. Minnesota)
L. Pratson (Duke U.)
J. Trowbridge (Woods Hole OI)
M. Underwood* (U. Missouri) (*MARGINS steering committee member)

 

This page was last updated June 4, 1999