Val et al., 2014: CHEMICAL PREPARATION OF DINOSAUR EGGSHELLS
INTRODUCTION
This work summarizes preliminary results on
carbonated matrices, matrices with a high
cleaning fossil eggshells. These treatments can
content of iron oxides, as well as matrices with
be used for the study of the surface under
a high silicic composition. The main feature
electronic microscope of both small fragments
common to all those matrices was their
and complete fossil eggs.
hardness and their resistance to many cleaning
Cleaning of the surface of fossil eggshells for
agents and techniques.
electron microscopy is usually very difficult. In
The
herein
presented
preliminary
study
order to be able to study its microstructure
consists of an analysis made using an electron
under the microscope, the elimination of the
microscope to study the effects of various
matrix that covers the eggshells without
chemical treatments on eggshells.
damaging them is crucial. Eggshells cannot be
protected with any resin layer to prevent them
METHODOLOGY
from being damaged by cleaning products,
since it would prevent thorough cleaning of the
eggshell surface, and it would not allow us to
Preparation techniques were conducted on
clearly observe the structure of the eggshell.
dinosaur eggshell fragments collected from
The difficulty of the cleaning techniques used in
several Late Cretaceous deposits (Tremp Fm.)
these first tests lies in finding a good cleaning
in the South-Pyrenean basins (Catalonia, NE
product that could not damage the eggshell. In
Iberian Peninsula; see Figure 1). Sampled
our case, fossil eggshells are mainly composed
localities occur in continental facies that include
of calcium carbonate, and thus very similar to
mudstones, marls, oncolite limestone and fine
the types of matrix that cover them, which are
to medium, well-cemented sandstones. In most
usually very rich in calcium carbonate (Quinn,
cases, eggshells are imbedded in a highly
1994).
carbonated matrix that strongly hinders the
Traditionally, cleaning fossil eggshells for
removal of secondary deposits.
electron microscopy has been done using
The different treatments were conducted with
organic acids such as acetic acid (Jeppsson et
different volume concentrations, starting with
al., 1985; Quinn, 1994; Rutzky et al., 1994;
2% until reaching the percentage of optimal
Shelton, 1994). However, this technique
cleaning. All the samples were subjected to the
usually damaged the eggshells, and did not
same dilution percentage, at the same
allow accurate observations of their surface.
temperature and the same time of exposition.
The research team "Àrea de recerca del
Following the first standard tests, we tried to
Mesozoic"
of
the
Institut
Català
de
find, in each case, the best percentage of
Paleontologia
Miquel
Crusafont
(ICP)
is
dissolution and the best time of exposition of
continuously studying dinosaur fossil eggshells
each one. In order to observe the results
and, for this reason, members of our team
obtained for each treatment in detail, we used
have been working for years trying to find the
an environmental SEM (FEI Quanta 200) at the
best cleaning techniques for these fossil
Serveis Cientifico Tècnics of the Universitat de
eggshells that need to be studied after
Barcelona. We compared the damage suffered
preparation. Our first studies on cleaning
by the eggshells with each treatment. An image
techniques were performed on Titanosaur fossil
of a non-treated eggshell was included as
eggshells from the Fumanya area (Berguedà,
control (Figure 2). The optimal cleaning was
Catalonia, Spain), which were embedded in
defined as the one that allowed us to identify
marls with a composition of 50% calcium
the oxygenation channels properly, and where
carbonate and 50% silicate (Val, 2007). During
the morphology of the surface of the eggshell
these first studies, we tried to dissolve the
was not or minimally altered in comparison
noncarbonated part of the matrix in order to
with the eggshell used as control.
prevent damaging the carbonate in the
All trials were made with fragments of similar
eggshells. To do so, we used chemicals that
size (1 cm2 approximately) and with a volume
dissolve the silicate part of the matrix. The
of 40 ml of dissolution for the different
results obtained using these alkaline agents
percentages of each chemical agent. Cleaning
were
better
than
other
acid
cleaning
essays were performed using ultrasonic baths
techniques. Highly alkaline agents dissolve
(with a duration of 15 min), which accelerated
silicates converting them into very soluble
the cleaning process and increased the
crystals (San Andres Moya and de la Viña
penetration capacity of the cleaning agents. It
Ferrer, 2004). Afterwards, we performed more
is important to emphasize that these cleaning
cleaning trials with other types of matrix, the
techniques
are
useful
for
individualized
results of which were presented in Val et al.
eggshells that need to be studied under the
(2010). Those essays were performed with
microscope, but when cleaning complete fossil
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Journal of Paleontological Techniques