25th International Meeting on Organic Geochemistry IMOG 2011

P-458
220 ka palaeoenvironmental reconstruction of the Fuentillejo
maar-lake record (Central Spain) using biomarker analysis
Laura Moreno 1 , José E. Ortiz 1 , Trinidad Torres 1 , Juana Vegas 2 , Blanca Ruiz-Zapata 3 ,
Ángel García-Cortés 2 , Luis Galán 2 , Alfredo Pérez-González 4
1 Biomolecular Stratigraphy Laboratory. E.T.S.I. Minas, Universidad Politécnica Madrid. Ríos Rosas 21,
Madrid, Spain, 2 Instituto Geológico y Minero de España (IGME). Ríos Rosas 23, Madrid, Spain, 3 Dpto.
Geología. Facultad Ciencias. Campus Universitario. Universidad Alcalá, Alcalá de Henares, Spain, 4 Centro
Nacional de la Evolución Humana. Avda. de la Paz 28, Burgos, Spain (corresponding
author:laura.moreno@upm.es)
The sedimentary record of the volcanic lake-maar of
Fuentillejo (Central Spain) offers the opportunity to
determine palaeoenvironmental evolution during the
Middle and Upper Pleistocene of the Central-
Southern part of the Iberian Peninsula, a warmsteppe
zone with peculiar environmental
characteristics. The complete sedimentary record was
obtained from a continuous core (142.4 m long),
although here we addressed only the upper 88 m, in
which a total of 439 samples were taken at 20-cm
intervals. Biomarkers were extracted using an ASE-
200 and analyzed in a CG-MS (Agilent 6890/5973).
Several radiometric datings ( 14 C and U/Th) allowed us
to determine an age-depth function and the record
was calculated to cover a time span of 350 ka.
Here we present results on the n-alkane distribution,
although we also include other biomarkers such as nketones,
n-alkanoic acids, organic sulphur and
sterols.
We used a number of n-alkane indexes, such as the
predominant n-alkane chain, the aquatic macrophytes
proxy index (Paq), the carbon preference index (CPI),
and the relative percentage of high molecular weight
n-alkanes.
At the bottom of record we interpreted a mixed input
of terrestrial plants and algae in which a bimodal
distribution of C17 and high molecular weight nalkanes
was observed. C27 and C29 n-alkanes were
dominant from 76.80 to 71.80 m, thus indicating a
major input of terrestrial vegetation, while again a
mixed input was detected between 71.80 and 60 m.
However, there was a clear record of organic matter
of algal origin from 60 to 22.5 m. Low CPI values and
C29 n-alkane dominance were observed in the upper
25.5 m of the record, these linked to organic matter
derived from terrestrial plants.
Using the wide range of information obtained from the
n-alkane indexes, we perform a series of statistical
analyses (cluster and spectral analysis) to synthesize
geochemical data. We identified six biomarker
associations from the cluster analysis, these ranging
from group 1 (the wettest environmental conditions) to
6 (the driest phases). Thus, we constructed a
palaeoenvironmental index of the Fuentillejo record.
This index showed marked variations that can be
linked to distinct palaeoclimatic scenarios (more
humid vs. drier phases). The spectral analysis
showed palaeoenvironmental variations linked to 100,
41 and 26 ka periods (Milankovitch cycles).
Figure 1. Palaeoenvironmental index along the upper
88 m of Fuentillejo record.
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