Geology Reference
In-Depth Information
spring, 1.6 - 4.6 8C in autumn and 4.8 8C in winter
with respect to the splash zone. These variations in
water temperature are dependent on seasonal air
temperature. In the city centre of Denizli according
to long-term meteorological data, average air temp-
eratures are 5.9 8C in January, 14.5 8C in April,
27.5 8C in July and 11 8C in November.
The pH value increases in downflow direction,
from 7.2 - 7.4 at the spring orifice (measurements at
Sp-4), to 7.7 at waterfall head (point GW-1 in
Fig. 6), and to 8.0 at the waterfall bottom (point
GW-2) as a result of CO
2
-degassing. The biggest pH
variation has occured during the flow from top to
bottom (7.7- 8.1) of the waterfall in winter season
(Table 1). Similarly, the HCO
3
value also decreases
rapidly downflow, from Sp-4 to GW-3 (see Fig. 6).
The CO
2
value in the water of Sp-4 is higher
(53 - 65 ppm) in winter and spring seasons. It is
lower (6 - 15 ppm) in summer and autumn seasons.
Maximum CO
2
- degassing from the water
occured in January. The calcium content of the
Sp-4 was almost constant with 64 ppm in five
sampling period. The Ca values decrease sharply
in the splash zone. The Mg ratio ranged from 7.8 -
12.7 (Table 1). Mg/Ca molar ratios of the Sp-4
are lower in wet season compared with dry period
because of dilution. According to hydrochemical
analysis, the dominant ions in the spring waters
are calcium and bicarbonate (Table 1) and conse-
quently, all spring waters in the tufa site are type
of Ca - HCO
3
.
The calcite saturation indices (SIC) in the spring
orifice are within borderline scale potential (20.02-
0.06); however, they increase rapidly along the
flow path because of CO
2
-degassing and the waters
are supersaturated with respect to calcite at splash
zone of the waterfall (Table 1). These values reach
up to 0.6 at the waterfall bottom. The SIC values
are highest in the summer season and lowest during
the winter. Similarly, the pCO
2
and DIC values of
the spring water change naturally like the SIC
values. The CO
2
partial pressure of the water in
GW-3 location is close to the atmospheric pressure.
The tritium value of the spring Sp-1 and Sp-4 is
5.9 TU. These isotopic data indicate that the spring
waters are of meteoric origin and ascend to the
surface following shallow circulation. The d
13
Cin
dissolved inorganic carbon (DIC) of the Sp-4 is
23.71‰, indicating that the inorganic carbon was
derived mainly by dissolution of marine carbonate.
The calcite is mostly micrite and microspar (5 -
20 m) in size. The microspar calcite occurred as
cement readily distinguishable from the micritic
groundmass, and commonly fills pores (Fig. 7e - g).
Micropores on some of the crystal surfaces are
possibly from dissolution of inclusions (perhaps
loss of organic fragments) (Fig. 7h). The quartz
grains, which are scattered throughout the micritic
ground and commonly single quartz grains in silt
size, probably derived from the schists around the
tufa site.
Biological composition
Apart from hydrophytic macrophytes, the tufa
deposits also include bryophytes, cyanobacterial
filaments, and diatoms. Bryophytes dominate in
the waterfall area. The diatom frustules were deter-
mined as species Cymbella sp. and Synedra sp.
(Figs 7b & 8e, f - h). In some cases, pulmonate gas-
tropods were observed occasionally within the fine
grained detrital tufa of the lower slope deposits.
Chemical composition
The eleven recent and old tufa samples were taken
from different parts of the site. The results of
major and trace element analyses of the samples
were given in Table 2. The Mg content ranged
from 1380 - 7440 with an average of 3235 ppm.
The MgCO
3
of the tufa deposits ranges from
0.59 - 3.40 mol% with an average of 1.43 mol%.
According to these values, the calcite in the tufa is
clearly low magnesian calcite. The Mg contents of
the tufa samples are more or less similar with the
Urrea de Jal ˜n tufa deposit, Ebro basin, NE Spain
(Arenas et al. 2000), whereas the higher values
were reported from some travertine occurances in
hiydrothermal origin (Minissale et al. 2002). Ba
and Sr compositions of the tufa samples are 33 -
192 ppm and 222 - 322 ppm, respectively. The Ba
and Sr contents are similar or slightly higher than
those in fluvio-lacustrine tufas in the central Ebro
Depression, NE Spain (Arenas et al. 2000), while
Ba content in Quaternary tufa stromatolite from
central Greece is also in similar value (Andrews &
Brasier 2005).
Radiocarbon and stable-isotope
composition
Preliminary results of
14
C and stable-isotope (d
13
C
and d
18
O) composition of these tufa deposits were
reported in Horvatinˇi´ et al. (2005). The
14
C
activity of recent tufa samples in the G¨ney spring-
line tufa site are 60 - 70% of modern carbon (pMC)
(Table 2, sample 1, 3, 4 and 12). This A
o
value is
Mineralogical, chemical and biological
composition of the tufa deposits
Mineralogical composition
Tufa samples are mainly composed of calcite
(Fig. 7) with minor amound of quartz and feldspar.
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