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Exposure dating (10Be, 26Al) of natural terrain landslides in Hong Kong, China

By
Roderick J. Sewell
Roderick J. Sewell
Hong Kong Geological Survey, Geotechnical Engineering Office, Civil Engineering and Development Department, 101 Princess Margaret Road, Kowloon, Hong Kong SAR, China
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Timothy T. Barrows
Timothy T. Barrows
Department of Nuclear Physics, Research School of Physical Sciences and Engineering, Australian National University, ACT, 0200, Canberra, Australia
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S. Diarmad G. Campbell
S. Diarmad G. Campbell
Hong Kong Geological Survey, Geotechnical Engineering Office, Civil Engineering and Development Department, 101 Princess Margaret Road, Kowloon, Hong Kong SAR, China
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L. Keith Fifield
L. Keith Fifield
Department of Nuclear Physics, Research School of Physical Sciences and Engineering, Australian National University, ACT, 0200, Canberra, Australia
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Published:
January 01, 2006

We successfully apply exposure dating using cosmogenic nuclides to natural terrain landslides in Hong Kong. Forty-five samples from eight landslide sites were exposure dated using 10Be, and a subset of six samples was also dated using 26Al. The sites comprised four large, deep-seated landslides featuring well-preserved rock scarps and associated debris lobes; two sites of rock and boulder fall; and two sites where scarps only are preserved. All of the deep-seated landslides gave ages within the last 50,000 yr, and the largest landslide gave an age of ∼32,000 yr. The youngest (∼2000 yr) and oldest (∼57,000 yr) landslide events dated came from the two sites of rock and boulder fall. Exposure ages from the deep-seated landslide scarps generally gave the most internally consistent ages for the landslides. However, only in rare cases did the landslide scarp ages overlap with those of boulders in the associated debris. Generally, boulders in the debris appeared to contain significant inheritance of cosmogenic nuclides from previous exposure and so yielded ages greater than those from the scarps. Surface exposure ages of ∼285,000 yr from boulders in the debris of two deep-seated landslides provide minimum ages considered to represent the original rock surfaces. This study has shown that it is possible to measure exposure ages of surfaces associated with large landslides from 70,000 yr down to a few thousand years old, despite low cosmogenic isotope production rates in Hong Kong due to low latitude and low altitude.

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Contents

GSA Special Papers

In Situ-Produced Cosmogenic Nuclides and Quantification of Geological Processes

Ana María Alonso-Zarza
Ana María Alonso-Zarza
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Lawrence H. Tanner
Lawrence H. Tanner
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Geological Society of America
Volume
415
ISBN print:
9780813724157
Publication date:
January 01, 2006

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