Molecular fossil and paleovegetation records of paleosol S4 and adjacent loess layers in the Luochuan loess section, NW China

Using gas chromatography-mass spectrometry (GC-MS) technique, a series of biomarkers were identified, including n-alkanes, n-alkane-2-ones, isoprenoid etc. from the loess-paleosol samples collected from the S4 and adjacent L5, L4 of the Luochuan loess section, Northwestern China. Based on these data, especially n-alkanes and high-resolution magnetic susceptibility and grain size data, the paleoenvironment and paleovegetation history during S4 was reconstructed. The CPI (Carbon Predominance Index) and correlation between n-alkanes and magnetic susceptibility and grain size data demonstrated that the molecular fossils in paleosol and loess layers can reflect the vegetation condition during the loess-paleosol formation, if the allochthonous organic inputs could be excluded reasonably. The ACL (average chain length) index is correlated well with paleomagnetic susceptibility and grain size variations, displaying their good synchrony with warm and humid climate. However, it relatively lagged behind the paleomagnetic susceptibility and the grain size variations when the climate began to deteriorate. During the formation period of paleosol, the n-alkanes was dominated by C31 homologue, indicating that the primary organic input originated from herbs. Our study also demonstrated that the herbs were more flourish than wood plants in Loess Plateau, especially in the Luochuan area during the warm and humid phase, and there was no typical forest vegetation developed in the studied period.

[1]  S. Clemens,et al.  Summer monsoon intensity controls C4/C3 plant abundance during the last 35 ka in the Chinese Loess Plateau: Carbon isotope evidence from bulk organic matter and individual leaf waxes , 2005 .

[2]  P. Cranwell.  Chain‐length distribution of n‐alkanes from lake sediments in relation to post‐glacial environmental change , 1973 .

[3]  T. Bianchi,et al.  Terrestrially derived dissolved organic matter in the Chesapeake Bay and the Middle , 2000 .

[4]  G. Kukla,et al.  Pleistocene climates in China dated by magnetic susceptibility , 1988 .

[5]  G. Eglinton,et al.  A north to south transect of Holocene southeast Atlantic continental margin sediments: Relationship between aerosol transport and compound‐specific δ13C land plant biomarker and pollen records , 2003 .

[6]  P. Peng,et al.  Long-chain alkenones in Hotong Qagan Nur Lake sediments and its paleoclimatic implications , 1999 .

[7]  L. Thompson,et al.  Geochemical analyses of a Himalayan snowpit profile: implications for atmospheric pollution and climate , 2000 .

[8]  G. Kukla.  Loess stratigraphy in central China , 1987 .

[9]  S. Blackburn,et al.  Alkenones in Gephyrocapsa oceanica: Implications for studies of paleoclimate , 1995 .

[10]  J. Hayes,et al.  Origins of lipid biomarkers in Santa Monica Basin surface sediment: a case study using compound-specific Δ 14 C analysis , 2001 .

[11]  S. Hanisch,et al.  The biomarker record of Lake Albano, central Italy—implications for Holocene aquatic system response to environmental change , 2003 .

[12]  L. Schwark,et al.  Reconstruction of postglacial to early Holocene vegetation history in terrestrial Central Europe via cuticular lipid biomarkers and pollen records from lake sediments , 2002 .

[13]  E. Peltzer,et al.  The importance of atmospheric input of terrestrial organic material to deep sea sediments , 1986 .

[14]  B. Simoneit,et al.  Molecular marker study of extractable organic matter in aerosols from urban areas of China , 1991 .

[15]  Zhang Hucai,et al.  Branched aliphatic alkanes of shell bar section in Qarhan Lake, Qaidam Basin and their paleoclimate significance , 2007 .

[16]  M. Collins,et al.  Lipid distribution in a subtropical southern China stalagmite as a record of soil ecosystem response to paleoclimate change , 2003, Quaternary Research.

[17]  G. Eglinton,et al.  Lipids of aquatic organisms as potential contributors to lacustrine sediments—II☆ , 1984 .

[18]  J. Grimalt,et al.  Aliphatic and aromatic hydrocarbons in different sized aerosols over the Mediterranean Sea: Occurrence and origin , 1987 .

[19]  L. Frakes,et al.  A carbon isotope record of the upper Chinese loess sequence: estimates of plant types during stadials and interstadials , 1994 .

[20]  J. Damsté,et al.  Carbon isotope analyses of n-alkanes in dust from the lower atmosphere over the central eastern Atlantic , 2003 .

[21]  A. Taira,et al.  Molecular paleoclimatology : reconstruction of climate variabilities in the late Quaternary , 1997 .

[22]  G. Eglinton,et al.  AEOLIAN-DERIVED HIGHER PLANT LIPIDS IN THE MARINE SEDIMENTARY RECORD: LINKS WITH PALAEOCLIMATE , 1989 .

[23]  Fahu Chen,et al.  The occurrence of a grassy vegetation over the Chinese Loess Plateau since the last interglacier: the molecular fossil record , 2002 .

[24]  J. Schneider,et al.  Particle size distributions of n-alkanes and 210Pb in aerosols off the coast of Peru , 1983, Nature.

[25]  Huayu Lu,et al.  Lower temperature as the main cause of C4 plant declines during the glacial periods on the Chinese Loess Plateau , 2003 .

[26]  Dongsheng Liu,et al.  Loess and the environment , 1985 .

[27]  Weijian Zhou,et al.  Reconstruction of late glacial and Holocene climate evolution in southern China from geolipids and pollen in the Dingnan peat sequence , 2005 .

[28]  P. Meyers,et al.  Lacustrine organic geochemistry—an overview of indicators of organic matter sources and diagenesis in lake sediments , 1993 .

[29]  G. Eglinton,et al.  Leaf wax lipids as paleovegetational and paleoenvironmental proxies for the Chinese Loess Plateau over the last 170 kyr , 2006 .

[30]  B. Simoneit,et al.  An assessment of terrestrial higher molecular weight lipid compounds in aerosol particulate matter over the south atlantic from about 30–70°S , 1991 .

[31]  R. Evershed,et al.  Peat molecular fossils recording paleoclimatic change and organism replacement , 2001 .