25th International Meeting on Organic Geochemistry IMOG 2011

P-134
Biomarkers preserved in cave sediments and their use as
indicators of environmental change in Trang An, Vietnam
Natalie F. Ludgate 1 , Thomas A. Griffiths 2 , Alison J. Blyth 1 , William D. Gosling 1 , Iain
Gilmour 1
1 The Open University, Milton Keynes, United Kingdom, 2 University College London, London, United
Kingdom (corresponding author:n.f.ludgate@open.ac.uk)
The aim of the Trang An archeological project is to
understand hunter-gatherer mobility at the end of the
last glacial maximum (LGM) [1]. Research into
terrestrial flora since the LGM is of key importance in
understanding hominid movement and cultural
development. Floral reconstructions can then be
integrated with cultural and dietary information
deduced from archaeological finds [1]. Clastic cave
sediments may thus provide an important terrestrial
record. Here we propose a novel technique using
biological markers found in clastic cave sediments.
The focus of this study is the use of lipids, including nalkanes,
and n-fatty acids, derived from higher plants
and molluscs from cave sediments in Vietnam.
Previous studies have shown that lipid biomarkers are
a valuable palaeoenvironmental resource in soils,
sediments and chemically precipitated speleothems
[e.g. 2,3,4]. Caves can provide an ideal environment
for lipid biomarker preservation. Within caves,
sediments are accumulated by aeolian or fluvial
deposition, with relatively little further digenesis or
post-depositional alteration. Lipid biomarkers from
local flora will therefore be transported into caves and
preserved.
Two caves in Vietnam (Ninh Bình province); Hang
Boi, and Hang Trong have been chosen as study
sites. Bulk sediment samples were taken from
stratigraphic layers within each archeological trench:
where strata were not determinable samples were
taken in 10 cm spits. Hang Boi is an open cave
situated at 78 m a.s.l. charcoal radiocarbon dates
indicate c.20 cm of sediment was deposited between
c. 12,400 and 12,100. The second site, Hang Trong,
is situated 142 m a.s.l. formed with openings on each
sides of a karst tower, allows detailed investigation of
airborne deposition. Radiocarbon dates, from
charcoal, indicate the immediate sub-surface
sediment is recent whilst at approximately 1.5 m from
the surface it dates to 18,500 yrs. b.p. The sites are
dominated by anthropogenic shell middens
interspersed with aeolian sediments and bed-rock
break down. For each stratum, freeze dried subsamples,
were Soxhlet extracted with 93:7
CH2Cl2/CH3OH. After evaporation of the excess
solvent, the samples were derivitised with boron
triflouride methanol in addition to BSTFA + TMCS.
Sample analysis is completed on a GC-MS; Agilent
Technology gas chromatograph coupled with a 5973
mass spectrometer. Separation was performed on a
J&W Scientific HP-5MS capillary column the He
carrier gas at a constant flow rate of 1.1 ml min -1 . The
GC oven temperature was held for 2 min at 50°C and
ramped to 300°C at 5°C min -1 and then held for 9 min.
A wide range of lipids in the extracted fraction
including: alkanes, alcohols, fatty acids, sterols, and
triterpenoids. The content of total extractable organic
matter in the sediment ranges from 110-880 µg/g of
dry sediment. Normal alkane homologues in the
extracts range from C26 to C34 with an average
maxima at C31. There is distinct odd-over-even carbon
predominance, indicating a vegetational source.
Normal fatty acids and alkanol range from C24 to C34
with average maxima at C30 and a strong even-overodd
carbon predominance.
This is first comprehensive investigation of lipid
biomarkers from plants preserved in clastic cave
sediments. The study will reconstruct the local
vegetational history using both palynological and lipid
biomarker analyses. The lipid biomarker time series
can then be compared with the palynological record to
determine the effectiveness of the method, providing
key insights into the local palaeoenvironmental
conditions and ecological impact on hominids. The
lipid analysis technique developed during this project
will support established methods and provide
information from sites where existing techniques are
unsuitable.
[1] Rabett, R., et al., (2010). Quaternary <strong>International</strong>, Article in Press
[2] Blyth, A.J., et al., (2007). Quaternary Research, 68(3), 314-324.
[3] Bull, I.D. et al (2000). Organic Chemistry, 31, 389-408.
[4] Meyers, P.A. et al., (2003). Organic Chemistry, 34, 261-289.
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