Geology Reference
In-Depth Information
The mean tufa growth rate at the Karw
´
w site is
1.0124 mg/cm
2
/day, less than at L ´
ˇ
ky but more
than in the two other sites. Mineralization of water
(mean TDS of 522.2 mg/l) seems the most likely
cause of the relatively high tufa growth rate at the
Karw
´
w site. Thus, the case of Karw
´
w is to some
extent similar to that of L ´
ˇ
ky. The Karw
´
w site
is fed by water ascending along a fault; however
the water temperature, TDS and probably residence
time are all significantly lower than those of
the deep-circulating component of water that feeds
the L´
ˇ
ky site. It is worth mentioning that other
tufa-depositing streams are present in the vicinity.
Moreover, Gruszczy
´
ski et al. (2004) described
an inactive travertine dome 7 m high and
60 m across, which started to grow in early
Holocene and lies 30 km west of Karw
´
w also on
a fault line.
Mean annual rates of tufa growth differ radically
also between the Z´zriv´ and H´j sites: 0.1592 mg/
cm
2
/day and 0.4027 mg/cm
2
/day, respectively.
Although the data concern only two sites, some ten-
tative explanations can be offered. The mean annual
temperatures and the SI
calc.
values of parent fluids
clearly influenced tufa growth rate at the studied
sites (Fig. 27). Such influence was suggested in lit-
erature, as based on the interrelation between temp-
erature, amount of soil CO
2
, the rate of carbonate
bedrock dissolution and SI
calc.
of parent water (e.g.
Hennig et al. 1983; Pedley et al. 1996; Pentecost
1995, 2005, p. 281). Direct comparison of the data
presented here with those of Bono et al. (2001),
who studied Tartare karst spring in Italy, leads to a
similar conclusion. In the Tartare spring, the mean
growth rate measured by Bono et al. (2001)
for dam settings, so similar to those presently
studied, was 1.86 mg/cm
2
/day. The mean annual
temperature in the vicinity of Tartare karst spring
is over 12 8C. Hence, both the tufa growth and temp-
erature are higher there than the studied herein.
A mean rate of tufa growth in a tropical karst
region in northern Australia reaches 4.15 mm a
21
(Drysdale & Gillieson 1997). In that region the
mean annual temperature is around 25 8C, which
fits well to the above tendency. Similar relationship
was noted in Japan (Kano et al. 2007). However, a
further study is needed in this field, because no
other tufa sites were studied systematically in this
respect that could be used for comparison.
2. Deposition of tufa is more efficient in setting
with fast flow of water in comparison with
neighbouring setting with sluggish flow.
3. Growing tufa contains many different biogenic
components and displays a wide spectrum of
textures. Fast-growing tufa exhibits crystalline
texture or is composed of highly encrusted
algae building fibrous texture. The crystalline
texture results from inhibition of microbial
colonization by quickly growing crystals,
while the fibrous texture is the result of acceler-
ated growth of micro-organisms forced by
quick crystallization of calcite on their cells.
Both textures developed under SI
calc.
. 0.8
and both are characteristic of fast-flow
setting. Slowly growing tufa shows mainly
micritic texture.
4. Algae were calcified on the surface of their
cells, while cyanobacteria on their sheaths.
Thus, the process is one of external surficial
precipitation. It took place under the condition
of SI
calc.
. 0.45. Unicellular desmid Oocar-
dium stratum calcified under SI
calc.
, 0.78.
Diatom frustules were commonly overgrown
by calcite but they acted as nucleation surface
only when SI
calc.
value was higher than 1.
5. No universal common seasonal trend was
detected in tufa growth rate. This demonstrates
the importance of local factors, specific for par-
ticular sites. A clear seasonal sequence of tex-
tures was not detected, either, though some
textures, such as clotted micrite with numerous
diatoms, are common in winter, and encrusted
algal filaments are abundant in spring and
summer. The high growth rate of tufa in the
summer of 2003 was the result of exceptionally
warm and dry conditions prevailing at that time.
6.
Chemistry of parent water is the main agent
governing the tufa growth. This is confirmed
by the higher net growth rate at the L ´
ˇ
ky
and Karw ´w sites (4.994 mg/cm
2
/day and
1.0124 mg/cm
2
/day respectively), where
water had the highest content of TDS, which
reflects the deep-circulation origin of this
water. The net tufa growth rates at the mountain
Z
´
zriv
´
site and at the upland H
´
j site are
0.1592 mg/cm
2
/day and 0.4027 mg/cm
2
/
day, respectively, which suggests that this
process may be influenced by local climatic
conditions.
Conclusions
The study is financed by the State Committee of Scientific
Research grant 6PO4D 001 21. While conducting the
experiment the author was supported by the Foundation
for Polish Science in the frame of Grant for Researchers
to Professor J´ zef Ka´mierczak. Professor Wolfgang
Dreybrodt let the author know how he calculated the tufa
growth
The field experiment carried out in Slovakia and
Poland in 2002 and 2003 have led to the following
conclusions:
1.
Micro-organisms and high values of SI
calc.
of
parent water favour growth of tufa.
rate
in
Hunaglong
and
Tartare
sites.
Roman
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