25th International Meeting on Organic Geochemistry IMOG 2011

P-470
Organic-geochemical Proxys for Tsunami-Events in sediment
cores of the Thermaikos Gulf
Frederike Wittkopp, Klaus Reicherter, Jan Schwarzbauer
RWTH Aachen University, Aachen, Germany (corresponding author:schwarzbauer@lek.rwth-aachen.de)
Nowadays, researchers have access to a broad range
of indicators for palaeotsunamis, such as
stratigraphical and sedimentological, archaeological
and palaeontological methods. Although
palaeosalinity is used very often as a proxy, there is a
lack in use of geochemistry as an indicator for
palaeotsunamis. In particular, the usage of organic
geochemical proxies is limited to the values of loss on
ignition although there is a lot more potential.
Therefore, this study was initiated to test sediment
samples of proposed tsunami layers using organicgeochemical
parameter. The overall aim was to
identify organic-geochemical proxies to trace and to
quantify the effect of mixing marine and terrigenous
matter in sedimentary material by a tsunami event
A 4 m sediment core from a lagoon at Thermaikos
Gulf (Northern Greece) was taken in 2008. Distinct
layers have been selected for which a tsunami event
has been postulated (based on sedimentological
methods) as well as unaffected layers. These
samples have been subjected to extensive organicgeochemical
analyses. Beside the extractable low
molecular compounds also the molecular composition
of the non-extractable fraction as released either by
alkaline hydrolysis or pyrolysis has been investigated.
Beside the loss of ignition (LOI) a special focus was
laid on a preselected set of common biomarkers. In
detail the following compounds and corresponding
ratios have been analyzed:
� n-alkanes (extractable and non-extractable) -
LHCPI, TAR
� isoprenoids (extractable and nonextractable)
- pr/ph
� fatty acids (extractable and non-extractable)
� sterenes (extractable and non-extractable)-
C27,C28,C29 composition
� n-aldehydes
� aromatic functionalized substances and nalkanes
(pyrolysis products)
Generally, compound ratios were calculated to
differentiate marine and terrigenous contributions.
Example is the TAR ratio, which expresses the
contribution of higher n-alkanes as representatives of
higher land plant input and, consequently, represents
terrigenous matter.
The organic-geochemical analyses revealed on the
one hand differences between the biomarker
compositions of the extractable and non-extractable
fractions, but also points to different qualities of
individual substance classes or biomarker groups to
act as tsunamite-indicators. In particular, specific
variations in n-alkane and isoprenoid distributions
were detected, whereas e.g. for aldehydes and
FAMEs no clear correlation of pattern with tsunami
affected layers was observed.
However, using LHCPI, TAR and pr/ph ratio two
layers, for which tsunami related events have been
postulated, were clearly differentiated from other core
material as illustrated in Fig 1.
To our knowledge this is the first study testing a
comprehensive set of organic-geochemical
parameters as indicators for tsunamites.
a)
b)
Fig. 1: Selected biomarker ratios detected in the
extractable (a) and hydrolysable fraction (b) of
different core layers. Based on the relative proportion
it was able to differentiate layers that were either
affected or unaffected by tsunami related events.
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