Santander, February 19th-22nd 2008 - Aranzadi

Molluscs as sedimentary components. Another perspective of analysis
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The site was reoccupied at least ten times
during the 18th-19th century. The different occupation
periods can be detected by the superposition
of fire places and thin sedimentary layers
which cover them during a non occupation period.
We find those layers repeatedly in the same
depression area. The area where the Yamana
group would probably have located the huts is
delimited by a ring composed by sediment and
archaeological remains. Some post holes from the
huts were identified during the excavation. That
produced a complex sequence of occupation and
non-occupation processes of the site which is
reflected in the stratigraphic matrix (Orquera 1995,
Vila et al. i.p.). Moreover, every occupation unit is
formed by several stratigraphic subunits which
can be distinguished one from the other; those
subunits are the basic analysis units.
3. MALACOLOGICAL ANALYSES
Due to the complexity of the stratigraphic matrix,
the design of a method to evaluate the formation process
of the site and the quantity (MNI) of molluscs
consumed in the settlement was necessary.
Túnel VII was excavated extensively, isolating
very thin depositional subunits (inner stratification
layers) (Orquera and Piana 1992). The isolation of
each subunit followed a strict standardised and
objective protocol. The study of the shell midden
was done through sedimentary samples from every
stratigraphic subunit. Each sedimentary sample
was homogenized within their whole components of
the sedimentary matrix, therefore they reflected the
composition of each stratigraphic subunit. These
samples consisted of a standard measure, 4 litres of
sediment (4dm³) from each subunit, independently
of their total volume, which was proved to be statistically
representative enough and could be extrapolated
to quantify the total composition of each subunit,
considering their measured total volume
(Orquera and Piana 2000; 2001).
The study of the components of each subunit let
us evaluate the existence of differences among
them. These differences could be attributed to the
activities carried out in the settlement. In this case, it
could be possible to get social information and see
the molluscs not only as food. Furthermore, we can
get information about the formation processes of the
site which is also directly related to the management
of the residues by the Yamana. The information that
we can obtain is equally important for the reconstruction
of the social relations because it refers to
other aspects of the social activities.
4. MATERIALS AND METHODS
We selected random samples of 35 subunits
corresponding to different episodes of occupation
and coming from different places in the site. Their
whole volume and weight were measured and
then they were separated into their individual components:
valves, bones, flints, charcoal, soil and
pebbles. In turn, each component was weighed
and the volume was measured as well (Orquera
1997, Orquera and Piana 2000). Moreover, the
fragments of valves were identified taxonomically
and counted in order to estimate the MNI.
To estimate possible significant relations
among these components, we considered the
weight a variable of each component of the sediment
as indicator of differences in the contents of
one or another component. We applied inferential
statistics tests as Correspondence Analysis and
Principal Component’s tests to see if there was any
correlation between the components and their
weight (fig. 3).
After some data readjustments, the results
obtained are significant and very conclusive.
There are significant associations between the soil
and pebbles variables and they are completely
opposite to valves (fig. 4). That means that actually
a non-random relationship exists among some of
the components: the dynamics between the variables
soil and pebbles is similar between them,
while it differs from the dynamics of the variable
valves. The general tendency of the sample is that
the subunits with high content of sediments and
pebbles contain low quantity of valves and vice
versa (Orquera 1997, Verdún 2006).
These differences are related to the location of
each stratigraphic subunit inside or outside the
place where the hut would have been located in
the site: the subunits with higher content of pebbles
and soil are 100% and 87,5% respectively,
located inside the hut; whereas the subunits with
higher content of valves are outside the hut
(88,89%) (fig. 5).
At the same time, we calculated the density of
molluscs MNI/dm³ for each subunit. This is the reason
why the recount of MNI from the samples was
taken into account. If we consider the density of
molluscs/dm³ and the location of each subunit in
the site, the obtained results were similar to the
ones obtained through inferential statistics. The
range width of densities calculated from the subunits
goes from 19.75 individuals/dm³ to 224.25
indiv/dm³. The general mean is 89.56 individuals/dm
3 . In the density calculation all the identified
taxa are taken into account.
MUNIBE Suplemento - Gehigarria 31, 2010
S.C. Aranzadi. Z.E. Donostia/San Sebastián