Geology Reference
In-Depth Information
Fig. 15.7.
Pisolitic travertine
. One of the most spectacular
pisolitic travertines is the 'Karlsbad Sprudelstein', a pea-stone
composed of densely packed, well-developed spherical and
egg-shaped pisoids and composite pisoid grain aggregates.
The pisoids consist of extremely fine concentric laminae ar-
ranged in layers that differ in thickness and color. The lami-
nae consist of tangentially arranged aragonite crystals with
submicroscopic micropores in between. A conspicuous fea-
ture of most pisoids is color banding caused by different iron
compounds and organic impurities. The nuclei of the pisoids
are very small rock and mineral fragments. The pisoids are
poorly sorted. Some samples may be longer than 15 mm in
size, but most lie between > 0.5 mm and < 2 mm. The pisoids
occur in alluvial deposits and originated from hot, mineral-
rich springs situated along tectonic faults in a basement of
crystalline and volcanic rocks.
A:
Pisoids differing in size
and shape. Note the large composite grain near the bottom.
B:
Concentric pisoids connected by circumgranular arago-
nite meniscus cement.
C:
The cement fringes consist of
densely spaced acicular aragonite needles. Fringes are almost
uniformly thick (200 to 250
m). Pores are still open. Karlovy
Vary (Karlsbad), a famous spa in Bohemia, Czech Republic.
Scale is 1 mm.
Characteristic criteria are layers consisting of cal-
cite or aragonite crystals growing vertically to the sub-
strate. The fabric is characterized by long-prismatic
crystals or corresponds to bundles of fibrous crystals
(Pl. 2/4). Crystal layers are separated by thin partings
of microcrystalline carbonate.
Basics: Travertine, calcareous tufa and calcareous sinter
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mation in a hard-water creek (Deinschwanger Bach, Fran-
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, 1-22
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52
, 1-47
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chemical composition of some calcareous tufa from the
Schwäbische Alb, Germany. - In: Müller, G., Friedman,
G.M. (eds.): Recent developments in carbonate sedimen-
tology in central Europe. - 157-171, Berlin (Springer)
Koban, C.G., Schweigert, G. (1993): Microbial origin of trav-
ertine fabrics - two examples from Southern Germany
(Pleistocene Stuttgart travertines and Miocene Riedöschin-
gen travertine). - Facies,
29
, 251-263
Perry, C.T. (1994): Freshwater tufa stromatolites in the basal
Purbeck Formation (Upper Jurassic), Isle-of-Portland,
Dorset. - Geological Journal,
29
, 119-135
Platt, N.H. (1992): Freshwater carbonates from the Lower
Freshwater Molasse (Oligocene, western Switzerland):
sedimentology and stable isotopes. - Sedimentary Geol-
ogy,
78
, 81-99
Schweigert, G. (1996): Vergleichende Faziesanalyse, Paläo-
ökologie und paläogeographisches Umfeld tertiärer Süß-
wasserkarbonate auf der westlichen Schwäbischen Alb und
im Hegau (Baden-Württemberg). - Profil,
9
, 1-100
Walter, M.B., Desmarais, D., Farmer, J.D., Hinman, N.W.
(1996): Lithofacies and biofacies of mid-Paleozoic ther-
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Further reading:
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