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  <dc:title xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:ows="http://www.opengis.net/ows">Chinese Loess Plateau 700KYr Amino Acid Racemization Data</dc:title>
  <dc:creator xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:ows="http://www.opengis.net/ows">Oches, E.A.; McCoy, W.D.</dc:creator>
  <dc:creator xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:ows="http://www.opengis.net/ows">Oches, E.A.</dc:creator>
  <dc:creator xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:ows="http://www.opengis.net/ows">McCoy, W.D.</dc:creator>
  <dc:subject xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:ows="http://www.opengis.net/ows">earth science/paleoclimate/others</dc:subject>
  <dc:subject xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:ows="http://www.opengis.net/ows"> (Luochuan&gt;LATITUDE 35.7&gt;LONGITUDE 109.4)</dc:subject>
  <dc:description xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:ows="http://www.opengis.net/ows">Amino acid geochronology provides important chronostratigraphic 
insight in the regional correlation and paleoclimatic evaluation 
of loess-paleosol sequences in the midwestern US, throughout western, 
central, and eastern Europe, and in China. In general, loess of 
the last four glacial cycles, corresponding to marine oxygen-isotope 
stages (OIS) 2-4, 6, 8, and 10, respectively, can be distinguished 
on the basis of alloisoleucine/isoleucine (A/I) ratios measured in 
fossil gastropod shells preserved in the loess. The racemization 
reaction is much slower in older samples, resulting in decreased 
temporal resolution. In the midwestern US and Europe, it is not 
possible to confidently subdivide the last glacial cycle on the 
basis of aminostratigraphic data. However, in China, where effective 
temperatures were higher during the Late Pleistocene, loess above 
and below L1SS1, the OIS-3 interstadial paleosol, can be distinguished 
using amino acid racemization data. 
With improvements in analytical methods, multiple amino acid D/L 
enantiomers are now being measured using reverse-phase liquid 
chromatography. Aspartic acid racemizes at a higher rate than 
the traditionally measured alloisoleucine/isoleucine diastereomers 
and can be measured more rapidly. This development offers hope for 
better temporal resolution and enhanced stratigraphic subdivision 
of loess units than has been achieved previously. 
 
          STUDY NOTES: Alloisoleucine/isoleucine data from fossil snail shells recovered 
from loess strata of the Chinese loess plateau in the region near 
Luochuan, Shaanxi Province, China. 

Fossil gastropod shells collected from large exposures of stratified 
loess and paleosols in the vicinity of Luochuan, Shaanxi Province, 
China, are analyzed by cation-exchange HPLC to determine the extent 
of isoleucine epimerization.  Three of the sample sites (Lower Heimu, 
Upper Heimu and Potou) are within about three kilometers of the 
village of Luochuan and are near branches of a large, deep gully 
system (Heimugou).  The fourth site is at an excavation for a railroad 
grade about 20 km southwest of Luochuan and close to the city of 
Huangling.  The ratio of D-alloisoleucine/L-isoleucine (AI) 
progressively increases in shells from strata of increasing 
stratigraphic age over several loess (glacial) cycles from L1 
(youngest) to L5 (oldest sampled for this report).  The AI values 
provide clear discrimination of loess stratigraphic units L1, L2 and 
L3.  Although AI values continue to increase in units older than L3, 
resolution decreases.  Confounding the inevitable reduction of 
resolution with increasing age is the fact that shells are much less 
abundant in the older strata and, therefore, few shell samples were 
recovered.  Due to this scarcity of data, the extent of isoleucine 
epimerization in shells from these older units remains poorly 
characterized.  On the other hand, the resolution in the youngest 
loess, L1, is good enough that it appears possible to discriminate 
between the two loess strata within it, L1LL1 and L1LL2. </dc:description>
  <dc:publisher xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:ows="http://www.opengis.net/ows">NCDC-Paleoclimatology</dc:publisher>
  <dc:publisher xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:ows="http://www.opengis.net/ows">https://www.ncdc.noaa.gov/data-access/paleoclimatology-data - Bauer Bruce</dc:publisher>
  <dc:contributor xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:ows="http://www.opengis.net/ows">Investigator : Oches, E.A.</dc:contributor>
  <dc:contributor xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:ows="http://www.opengis.net/ows">Investigator : McCoy, W.D.</dc:contributor>
  <dc:date xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:ows="http://www.opengis.net/ows">2011-06-01</dc:date>
  <dc:type xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:ows="http://www.opengis.net/ows">ONLINE Files</dc:type>
  <dc:format xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:ows="http://www.opengis.net/ows">online, ASCII</dc:format>
  <dc:identifier xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:ows="http://www.opengis.net/ows">https://www.ncdc.noaa.gov/paleo/study/11200</dc:identifier>
  <dc:identifier xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:ows="http://www.opengis.net/ows">https://www1.ncdc.noaa.gov/pub/data/paleo/aar/oches2001loess/oches2001loess.xls</dc:identifier>
  <dc:identifier xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:ows="http://www.opengis.net/ows">https://www1.ncdc.noaa.gov/pub/data/paleo/aar/oches2001loess/oches2001loess.txt</dc:identifier>
  <dc:source xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:ows="http://www.opengis.net/ows">https://www1.ncdc.noaa.gov/pub/data/paleo/aar/oches2001loess/oches2001loess.xls</dc:source>
  <dc:source xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:ows="http://www.opengis.net/ows">https://www1.ncdc.noaa.gov/pub/data/paleo/aar/oches2001loess/oches2001loess.txt</dc:source>
  <dc:language xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:ows="http://www.opengis.net/ows">English</dc:language>
  <dc:relation xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:ows="http://www.opengis.net/ows">https://www.ncdc.noaa.gov/paleo/study/11200</dc:relation>
  <dc:relation xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:ows="http://www.opengis.net/ows">https://www1.ncdc.noaa.gov/pub/data/paleo/aar/oches2001loess/oches2001loess.xls</dc:relation>
  <dc:relation xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:ows="http://www.opengis.net/ows">https://www1.ncdc.noaa.gov/pub/data/paleo/aar/oches2001loess/oches2001loess.txt</dc:relation>
  <dc:relation xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:ows="http://www.opengis.net/ows">Oches, E.A. and W.D. McCoy. 2001. 
Historical developments and recent advances in amino acid 
geochronology applied to loess research: examples from 
North America, Europe, and China. 
Earth-Science Reviews, Vol. 54, Issues 1-3, June 2001, pp. 173-192. 
doi:10.1016/S0012-8252(01)00047-2 </dc:relation>
  <dc:coverage xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:ows="http://www.opengis.net/ows">START YEAR: 700000 cal yr BP  * END YEAR: 0 cal yr BP</dc:coverage>
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