Introduction to tufas and speleothems - Tufas and Speleothems: Unravelling the Microbial and Physical Controls - page 5

seasonal geochemical proxy signals within them in
favour of certain seasons. Fairchild et al. explore
the seasonality which is encoded in speleothems.
All samples show visible autumnal laminations
which are associated with increases in trace
element concentrations. Within these laminae syn-
chrotron studies have resolved mm-scale Pb and
Zn enrichments. The study is an excellent demon-
stration of how chemical variations within laminae
express seasonal physiology in temperate caves.
Mattey et al. monitored the water chemistry at
three speleothems drip sites and demonstrate a
strong link between local microclimate and the
proxy-record. The data reveal a strong seasonal
drip-water chemistry pattern with the calcite satur-
ation being linked closely to regular seasonal vari-
ations in cave air pCO 2 . The relationships between
stable isotope rations, Sr/Ca and speleothem
laminae are consistent with a degassing - calcite
precipitation process. In these modern speleothems
rapid degassing controls the d 13 C of drip water
and calcite whereas the slower rate of calcite pre-
cipitation caused seasonal Sr cyclicity. Neverthe-
less, caution is advised when linking paired
speleothem fabrics to specific seasons because of
the local processes operative within caves.
Clearly, there is a dominantly physico-chemical
control on the geochemical signals within spe-
leothems but this need not be exclusive to subterra-
nean sites. In fact, on a widespread macro-scale
Hammer et al. presents a thoughtful study of the
dominantly physico-chemical controls governing
travertine terracing patterns. Such terracing occurs
at a range of incremental scales though this study
pays particular attention to micro-terrace develop-
ment. The terrace morphologies are the product
of interactions between any combination of water
chemistry, precipitation kinetics, topography,
hydrodynamics, carbon dioxide degassing, erosion,
sedimentation and even biology. However,

article provides some pointers to the likely process
combinations controlling each development.
Collectively, these research articles illustrate a
wide range of modern calcium carbonate precipi-
tation processes and related carbonate precipitates.
All demonstrate that small scale variations in
water chemistry correlate directly to changes in
environmental conditions. Many of the articles
confirm that such variations are faithfully recorded
in the precipitated carbonate fabrics as proxy-
palaeoenvironmental indicators. Preservation
quality appears excellent for the Holocene but has
yet to be confirmed for older Quaternary and
Neogene deposits. Research continues to seek new
approaches (e.g. synchrotron analysis) which will
reveal fine scale variations within the carbonate
precipitation processes though much remains to
be done. Nevertheless, it is already clear that
depositional karst offers an unrivalled opportunity
to fine-tune our understanding of Quaternary envi-
ronmental change at the global scale. Speleothems
provide the absolute chronometer of environmental
change and monitor of hydrological regime within
the aquifer whereas tufas provide a detailed view
of karst surface processes and their influence on
environment-driven ecological change. The next
step in this Geobiology research domain is to
resolve the dynamic choreography between these
subaerial and subterranean karst players.

References

C ACCHIO , P., C ONTENTO , R., E RCOLE , C., C APPUCCIO ,
G., M ARTINEZ ,M.P.&L EPIDI , A. 2004. Involvement
of microorganisms in the formation of carbonate
speleothems in the Cervo Cave (L'Aquila-Italy).
Geomicrobiology Journal, 21(8), 497-509.
N OFFKE , T. 2005. Geobiology - a holistic scientific
discipline. Palaeogeography, Palaeoclimatology,

the Palaeoecology, 219,1-3.