Geology Reference
In-Depth Information
the distinctive control of travertine microfacies types
and dominating organisms (eucaryonts, photosynthetic
and chemosynthetic bacteria) by water temperatures and
pH values (Farmer 2000).
Pamukale near Denizli (southeastern Turkey) is an-
other famous locality where thermal spring waters at a
hill built, and still build, large rimstone pools of traver-
tine while flowing down in cascades about 100 m of
height difference. Because of the large surface of the
very thin layer of water, the water looses deep-source
carbon dioxide, resulting in carbonate precipitation.
The resulting white travertines have been used since
Roman times as building stones. The Turkish name
Pammukale means 'cotton castle' and refers to the strik-
ingly white color of the large steps.
fabric-selective porosity patterns. Changes in porosity,
permeability, specific surface, and water sorption due
to the dissolution and precipitation of calcite within
pores lead to a decrease in porosity and increase in rock
hardness with time (Koch et al. 1999).
The rapid precipitation of carbonate favors the pres-
ervation of fossil faunas and floras, and of archeologi-
cal artifacts. Chronological dating of Pleistocene trav-
ertines aids greatly in the age determination of prehis-
toric archeological material (Kahlke 1984).
2.4.1.7 Lacustrine Carbonates: Lakes
Lacustrine environments differ from marine environ-
ments in the properties, kinetics, chemistry and pro-
ductivity of lake waters as well as in the sedimentation
patterns originating in hydrologically open and hydro-
logically closed lakes. Lakes are dynamic systems.
Short-term and long-term changes in climate, water
chemistry and bathymetry of lakes result in significant
variations of litho- and biofacies, and their lateral and
vertical distribution patterns.
Phytoherms:
Plant-dominated freshwater calcareous
tufa, formed in river systems, are called 'phytoherms'
(Cipriani et al. 1977; Pedley 1987, 1992) underlining
the dominant role of macrophytes and procaryote-
microphyte biofilms in the construction of carbonate
buildups (Collinson 1988). Phytoherms of river sys-
tems, capable of damming the water courses to pro-
duce chains of lakes (e.g. Plitvica region, Croatia: Emeis
et al. 1987), are characterized by rapid growth in cool,
agitated waters. Continuous water circulation is neces-
sary for bringing in nutrients and providing replenish-
ment of CaCO
3
for the extensive precipitation of Low-
Mg-calcite cements within organic frameworks. The
primary frameworks are provided by the in-situ growth
of erect and trailing hydrophytes and semi-aquatic mac-
rophytes. Secondary frameworks are formed by oscilla-
toriacean cyanobacteria, diatoms and insect larvae colo-
nizing exposed surfaces. The shelly fauna associated
with the phytoherms contains ostracods, gastropods,
rare bivalves and crustaceans.
The stability of these bioconstructions and also their
preservation in the fossil record is provided by a con-
comitant development of thick Low-Mg calcite calcite
cements (micrite fringes and bladed calcite spar fringes)
and by an intra-frame sediment infill. Both micritic
fringe cements and the abundant small-scaled peloids
are interpreted as the product of biological mediation
associated with a procaryote-microphyte biofilm and
the presence of organic detritus.
Our review focuses on the carbonates formed in
lakes. Carbonates are only a part of lacustrine sediments,
which in addition, often include claystones, marls and
also sandstones. The review neglects the siliciclastic
sediments as well as some chemical deposits (cherts,
phosphorites).
Lacustrine carbonates are a specific type of terres-
trial carbonate deposited within a lake or at the shore-
lines of a lake. Fluctuating shorelines may result in a
pedogenic overprint of lacustrine sediments leading to
the formation of 'palustrine carbonates' (Sect. 2.4.1.2),
which were defined as 'near-shore deposits of extremely
shallow lakes with oscillating lake levels and densely
vegetated shorelines' (Freytet and Plaziat 1982). Fre-
quently, lake deposits are associated with paleosols as
well as with fluvial sediments.
Because wind-driven currents and waves often do
not affect the lake bottom, lake waters tend to become
permanently or seasonally stratified: Warmer and lighter
waters (epilimnion) overlie colder and denser waters
of the bottom zone (hypolimnion). These zones are
separated by a zone characterized by a rapid rate of
change of temperature with depth (mesolimnion). Per-
manent stratification is characteristic of tropical
oligomictic lakes with temperature stratification and of
meromictic lakes in which the bottom water has a higher
salinity than the surface water. In both cases, the bot-
tom water can become completely stagnant and be de-
pleted of nutrients and oxygen, resulting in the accu-
mulation of laminated muds rich in organic matter.
Significance:
Travertines are important building and
decoration stones, used since antique times. High qual-
ity travertine possesses a great mechanical strength and
remarkable resistance to weathering as compared with
other building stones. Technological qualities of trav-
ertines are strongly controlled by depositional facies
and early diagenesis. Differences in technological prop-
erties of travertines and tufas are primarily caused by
