Premium
Cosmetic Isotope Analyses Applied to River Longitudinal Profile Evolution: Problems and Interpretations
Author(s) -
Seidl Michele A.,
Finkel Robert C.,
Caffee Marc W.,
Hudson G. Bryant,
Dietrich William E.
Publication year - 1997
Publication title -
earth surface processes and landforms
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.294
H-Index - 127
eISSN - 1096-9837
pISSN - 0197-9337
DOI - 10.1002/(sici)1096-9837(199703)22:3<195::aid-esp748>3.0.co;2-0
Subject(s) - bedrock , geology , cosmogenic nuclide , radionuclide , surface exposure dating , basalt , isotope , nuclide , physical geography , earth science , geochemistry , geomorphology , moraine , glacial period , geography , physics , quantum mechanics , cosmic ray , astrophysics
The use of cosmogenic isotopes to determine surface exposure ages has grown rapidly in recent years. The extent to which cosmogenic nuclides can distinguish between mechanistic hypotheses of landscape evolution is an important issue in geomorphology. We present a case study to determine whether surface exposure dating techniques can elucidate the role knickpoint propagation plays in longitudinal profile evolution. Cosmogenically produced 10 Be, 26 Al, 36 Cl, 3 He and 21 Ne were measured in olivines collected from 5·2 Ma basalt flows on Kauai, Hawaii. Several obstacles had to be overcome prior to the measurement of In situ ‐produced radionuclides, including removal of meteoric 10 Be from the olivine grains. Discrepancies between the radionuclide and noble gas data may suggest limits for exposure dating. Approximate surface exposure ages calculated from the nuclide concentrations indicate that large boulders may remain in the Hawaiian valley below the knickpoint for hundreds of thousands of years. The ages of samples collected above the knickpoint are consistent with estimates of erosion based on the preservation of palaeosurfaces. Although the exposure ages can neither confirm nor reject the nickpoint hypothesis, boulder ages downstream of the knickpoint are consistent with a wave of incision passing upvalley. The long residence time off the coarse material in the valley bottom further suggests that knickpoint propagation beneath a boulder pile is necessary for incision of the bedrock underlying the boulders to occur. © 1997 by John Wiley & Sons, Ltd.