SCIENTIA GEOGRAPHICA SINICA ›› 2014, Vol. 34 ›› Issue (1): 116-121.doi: 10.13249/j.cnki.sgs.2014.01.116

• Orginal Article • Previous Articles     Next Articles

Impact of Surface Rock Erosion Rate on In-situ Cosmogenic Exposure Dating Method

Zhi-gang ZHANG1(), Jian WANG1,2(), Shi-biao BAI1,2, Xiao-bin XU3, Zhi-yang CHANG1   

  1. 1. School of Geographical Sciences, Nanjing Normal University, Nanjing, Jiangsu 210023, China
    2. Key Laboratory of Virtual Geographical Environment, Nanjing Normal University, Nanjing, Jiangsu 210023, China
    3. Jiangsu College of Education, Nanjing, Jiangsu 210024, China
  • Received:2013-03-05 Revised:2013-04-20 Online:2014-01-10 Published:2013-06-13

Abstract:

The cosmogenic exposure dating method that measures trace cosmogenic nuclide concentrations present in terrestrial surface rocks developed in the late 1980s. This method has become a widely used tool to address scientific questions in the fields of geomorphology, glaciology, palaeoclimatology, palaeoseismology, soil science, volcanology and geohazard research. Until now, three types of uncertainty affect the precision and accuracy of cosmogenic isotope dates; these include: analytical uncertainties including systematic errors, production rate uncertainties and sampling uncertainties. The cosmogenic nuclide concentration on the surface of rocks is a function of exposure time and erosion rate. However, it is usually hypothesized that the sample erosion rate is zero when dating the age using cosmogenic exposure dating method due to poorly constrained rock surface erosion rates. Recent research suggests that the assumption of “zero erosion” may underestimate true exposure age and the effect will increase with increasing sample age. In order to explore the impact of different erosion rates to the different exposure ages sample, we gathered 56 rock cosmogenic 10Be datum from different areas in the literature of 2009-2012. We analyzed the effects of zero erosion between 0.5, 1 and 2 mm/ka for the 1×104 a, 10×104 a and 50×104 a scale samples respectively. The erosion rates datum stem from mircro-weathering measurements and maximum erosion rates of the oldest sample using the cosmogenic exposure dating method in different areas. The results suggest, that the age for 1×104 a is underestimated approximately by 0.5%, 1% and 2% for erosion rates of 0.5, 1 and 2 mm/ka, respectively. For the age of 10×104 a, the underestimate is approximately should be 5%, 7% and 20%, and for 50×104 a approximately 40%, 70% and even more than 100%, respectively. The results are consistent with previous research results which suggest that our results are reliable. At the same time the result means that the erosion rates of surface rock significantly affect the accuracy of cosmogenic exposure dating method, and in particular for the older exposure age samples. Thus, future studies should pay attention to this issue.

Key words: cosmogenic isotope, beryllium-10, exposure dating, erosion rate

CLC Number: 

  • P931.4