Geology Reference
In-Depth Information
pounds considered in geochemical prospecting are
CaCO
3
, MgCO
3
, SiO
2
, SO
3
, Fe
2
O
3
, Al
2
O
3
, Mn
2
O
3
,
K
2
O as well as various minor elements. Combina-
tions of geochemical prospecting and microfacies
analysis of samples has proved quite successful (e.g.
Städter 1989).
Ultra-poor limestones are usually white limestones
characterized by a very high calcium carbonate and very
low iron contents (>99% CaCO
3
, <0.5% Fe
2
O
3
). An
example are Late Jurassic limestones (particle-rich
sponge boundstones, packstones and grainstones) oc-
curring in Swabia in lenses that extend laterally sev-
eral hundreds of meters to several kilometers across.
Quality variations are controlled by diagenesis, sec-
ondary alterations and karstification. Exploration in-
cludes detailed mapping related to the lithology, facies,
alterations and structure, and requires continuous sam-
pling along drill cores with a close spacing (Koch et al.
1997; Aigner and Schauer 1998).
•
Thin-section studies:
Differentiation of facies types
based on textural criteria and diagenetic character-
istics (recrystallization, dolomitization, dedolomit-
ization, stylolitization; see Chap. 7).
•
Assessment of a
'facies model'
describing the lat-
eral and vertical spatial relationships of the facies
types. This model is used in further interpreting
samples studied during the exploration phase. This
phase demands investigation of cuttings or cores.
18.3 Facies and Physical-Chemical
Properties of Carbonate Rocks
•
Exploration wells:
Study of cores and cuttings. Cut-
tings are washed, differentiated into lithotypes us-
ing a binocular, and characterized by microfacies
criteria. In addition, the total carbonate content as
well as mineralogical and geochemical properties
of core samples are determined (clay minerals, do-
lomite, main and rare elements). The number of
samples analyzed depends on the rock qualities de-
manded (Langbein et al. 1982).
Physical properties
important for the industrial use of
carbonate rocks include the textural composition, po-
rosity, permeability, specific surface and the distribu-
tion of pore throat diameters, water sorption and bulk
density, rock hardness; compressive, tensile and shear
strength; rigidity and elasticity, refractive properties
and thermal conductivity (Harben and Purdy 1991;
Bellanger et al. 1993; Winkler 1994). Both physical
and chemical properties are at least partly facies-con-
trolled.
Specific interrelationships exist between deposi-
tional facies, rock color and the amount of non-car-
bonate contents and assist in the differentiation of the
purity of limestones (Dimke 1997). The relationships
between depositional facies, diagenesis and porosity
explain weathering types (see Sect. 18.4). Frost dam-
age is the result of tensile stresses caused by water freez-
ing in the pores of limestones. The saturation state and
water distribution are a function of pore geometries.
Depositional facies, porosity, mineralogical and chemi-
cal composition influence burning behavior and quick
lime production (Gotthardt et al. 1967; Gotthardt and
Wilder 1981, 1984; Gosh 1981; Butenuth et al. 1993;
Ellmies 1995; Rossner and Michel in Koch et al. 1997).
•
Samples should be grouped statistically
according
to their spatial occurrence or according to particular
features. This approach leads to the visual presenta-
tion of rock bodies consisting of carbonate facies
units with particular physical and/or chemical prop-
erties.
•
Mapping
and differentiation of facies-controlled
carbonate bodies with regard to boundaries, exten-
sion and volumes.
Exploration of pure limestones.
Pure limestones with
high calcium carbonate and very low non-carbonate
contents are used in the glass, paper and chemical in-
dustries for water desulfurization of flue gasses, and
for producing fertilizers and animal food (Kimmig et
al. 2001). Pure carbonate rocks are represented by
marbles and by platform and reef limestones (see Fig.
14.22).
Distinct correlations exist between total carbonate
content and depositional conditions: Open-marine bio-
herms and reefs, sand piles and open-marine platform
carbonates often correspond to 'pure limestones', be-
cause of low or missing siliciclastic input or deposi-
tion in high-energy environments. Reasons for the high
purity of many limestones are winnowing of fine-
grained carbonate and non-carbonate impurities in
high-energy environments and rapid early cementation
(Flügel 1977; Bertle 1982; Koch et al. 1984, Dimke
1997). White marbles are often pure carbonates and
are industrially sought after raw materials.
Different lithotypes exhibit specific burning behav-
iors. High quality soft quick lime is produced by pure
calcilutites and calcarenites. Grain size and porosity
do not affect burning or slacking. In contrast non-car-
bonate contents and clay admixtures reduce the qual-
ity of quick lime (Ellmies 1995; Koch et al. 1997; Frey
1998). The controls on density, porosity, permeability,
hardness and strength by the original depositional tex-
ture and the course of cementation are responsible for
different physical properties, which in turn influence
the technological properties of limestones and dolo-
