COI Funded Project: Surface Exposure Dating in the Coastal Zone

Mark Kurz, Marine Chemistry and Geochemistry
Neal Driscoll, Geology and Geophysics

Project Duration: 6/1/98-12/31/99
Key Words: coastal erosion, radio isotope dating, beach cliffs, sediment transport

Proposed Research

Many important scientific and societal issues in the coastal zone require an accurate knowledge of the time scales on which erosional processes affect landforms, particularly within the last 10,000 years. The goal of the proposed research is to use measurements of cosmic-ray produced 3He as a dating method in the coastal zone. This method, referred to here as surface exposure dating, relies on the accumulation of nuclides produced by cosmic rays in the minerals within the top 3 meters of the earth's surface (cosmic radiation does not penetrate significantly below this). Although this method has been successfully used to date lava flows and glacial moraines, it has not yet been applied to the dynamic land forms in the coastal zone, and has never been applied on such short time scales.

Based on past results, it should be possible to date beach deposits and cliffs as young as 100 years, which would have wide applicability. In order to establish the practical age limits of the method, we propose a field sampling program at High Head (North Truro) on Cape Cod, and in the headlands of the Eel River (California), coupled with laboratory experimentation. The sampling at High Head will allow us to collect quartz rich sand and boulders from a variety of ages, ranging from zero age (present day beach sand and deeply buried sand) to the materials deposited by the late Wisconsin glaciation (~ 15,000 years). The cliffs at High Head are thought to be ~ 5000 years old, based on models of geomorphology and sea level change; if successful the new dates will provide a direct test of these models.

Sampling at the Eel River will allow direct measurement of erosion rates in the bedrock above the river system, which will then be compared with discharge rates at the river mouth, and extensive offshore studies of marine sedimentation. The bulk of the effort will be in laboratory studies of the samples, as this research will require adaptation of existing hardware, software and methodologies to measure the small amounts of cosmogenic 3He in such young materials. Without results from a coupled field/laboratory program such as proposed here, funding from traditional sources would be highly unlikely.