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Dinosaur eggshell isotope geochemistry from Upper Cretaceous of Spain



From: Ben Creisler
bcreisler@gmail.com


A new online paper:


V. Riera, P. Anadón, O. Oms, R. Estrada & E. Maestro (2013)
Dinosaur eggshell isotope geochemistry as tools of paleoenvironmental
reconstruction for the Upper Cretaceous from the Tremp Formation
(Southern Pyrenees).
Sedimentary Geology (advance online publication)
http://dx.doi.org/10.1016/j.sedgeo.2013.06.001,
http://www.sciencedirect.com/science/article/pii/S0037073813001255


The isotopic compositions (delta13C and delta18O) of dinosaur
eggshells have been widely used in paleoenvironmental studies,
although the geochemical signatures of eggshells are not usually
contrasted with other proxies. In this work, the isotopic signatures
of eggshells from a large Maastrichtian succession from the Tremp
formation (Southern Pyrenees, Spain) are compared to those of
carbonate pedogenic nodules occurring in the same levels. The isotopic
signatures of eggshells vary according to the stratigraphic unit and
geographical location. A group of samples from several localities
corresponding to eggshells without significant diagenetic imprints has
isotopic values differing from the associated nodules; The Late
Cretaceous isotopic composition record from the Tremp Fm is consistent
that is, the eggshells have distinct primary signatures preserved.

However, the eggshells from another locality, which exhibit neomorphed
textures, display isotopic signatures similar to the associated
pedogenic carbonate, which suggests a diagenetic isotopic signature
and confirms alteration in the eggshells. Both microscopic and
geochemical data suggest that an early meteoric diagenesis
(pedogenesis) is responsible for the secondary signatures. The
delta13C values in the carbonate pedogenic nodules indicate a carbon
isotopic composition typical of C3 plants, although the slight
difference in delta13C between the paleosol carbonate of coeval
successions may be due to slightly different paleoenvironmental
conditions. The small discrepancy in the delta13C calculated for C3
plants, from carbonate nodules and from eggshells may be because the
paleosol carbonate gives the isotopic composition of the vegetation
grown at a local site whereas the delta13C from eggshells is a proxy
for the ingested food in the area in which the dinosaurs lived. The
oxygen isotopic compositions from paleosol carbonate nodules have been
used for calculation of the air temperature, and we may conclude that
the mean air temperature in the studied area during the late
Cretaceous was approximately 21ºC. The use of this temperature gives
rational results in the calculation of the oxygen isotopic composition
of paleosol carbonate by means of the isotopic composition of the
eggshell carbonate. Additionally, a relatively continuous isotopic
record of nodules shows an overall vertical trend towards negative
delta13C values and a high relative and steady delta18O content
throughout the Maastrichtian. The K/Pg boundary was recorded by a
negative excursion in delta13C in the carbonate nodules.