Geology Reference
In-Depth Information
The terms introduced by Logan and Semeniuk for
the description of rocks suffering from pressure solu-
tion were included by Logan (1984) in a more rigorous
classification that also considers deformation structures
caused by pressure response to burial and/or tectonism.
Carbonate rocks affected by compressional stress are
accommodated by compaction, pressure solution, and
shear fracture. The main response to tensional stress is
the formation of strain cavities - represented by veins,
vugs, and inter-fragment voids within breccias. Com-
pressional and tensional stress is often associated with
dolomitization, silicification, and other mineralization
processes.
Box 7.10.
Significance of compaction and pressure so-
lution.
Thickness and paleotopography of sedimentary
units
:
Stylolitization results in a considerable reduc-
tion of the thickness of a sequence. Differential com-
paction may control seafloor relief and reef geometry
(Anderson et al. 1996) and reduces the thickness of
adjacent facies units, e.g. reef and platform margins
(Matyszkiewicz 1999).
Burial cements
: Pressure solution increases the dis-
solution of calcite (Maliva and Siever, 1989). The
supply of CaCO
3
from pressure solution along sty-
lolites is a major source of late diagenetic cement
and may or may not (Kreutzberger and Peacor 1988)
affect also phyllosilicates within carbonate rocks.
Dolomitization
: Transformation of clay minerals by
burial diagenesis could be a source of magnesium
and dolomitization (McHargue and Price 1982;
Sternbach and Friedman 1984).
Economic importance
:
Compaction and stylolitization
reduce porosity depending on the degree of precom-
paction cementation and depending on the textural
rock type. Stylolites may enhance and inhibit reser-
voir quality (Abu Dhabi National Reservoir Research
1984). Stylolite surfaces may be important perme-
ability barriers, influencing the flow in aquifers and
petroleum reservoirs. Grain-to-grain pressure solu-
tion is the most detrimental process for permeability
(Budd 2002), followed by cementation. However,
stylolites can act as conduits for fluids (Braithwaite
1989), and permeability may be created by veining
activating the connectivity of stylolites (Smith 2000).
Controls on chemical compaction
Chemical compaction is controlled in a complex
manner and depends on
•
burial depth with attendant lithostatic load. Pressure
solution becomes effective at various depths. Many
authors favor burial of several hundreds to thousands
of meters, but stylolite formation has also been re-
corded after only some tens to hundreds of meters.
The paradigma of 900 m overload necessary for the
formation of stylolites (Dunnington 1967) is out of
date.
•
tectonic stress leading to tectonically controlled for-
mation of stylolites (Bathurst 1984),
•
vertical stress caused by overburden pressure result-
ing in preferential solution of the upper and lower
surfaces of grains, via solution films,
•
the chemistry of pore fluids. Mg-poor meteoric pore
waters will enhance pressure solution,
Pressure solution and rock types
Pressure solution in grain-supported carbonate rocks
with minor cementation starts with solution at grain-
to-grain contacts. Solution affects the more soluble
grains causing a ranking of grain solution.
Pressure solution subsequent to cementation results
in the formation of a fabric that distributes pressure
laterally, resulting in distinct stylolites or in a fitted fab-
ric (Buxton and Sibley 1981). Grain-rich carbonates
can be stylolitized under shallow burial of not more
than 30 m (Railsback 1993).
Lime mudstones, wackestones, packstones, and
weakly cemented grainstones exhibit preferential so-
lution seams that may indicate diagenetic bedding pro-
cesses (Ricken 1986). Solution seams can be pre- and
post-burial in origin (Bose et al. 1996).
•
the formation of stylolites can be retarded and pre-
vented by the presence of oil or organic films be-
tween and on grains,
•
pore fluid pressure in overpressing settings may re-
tard or stop pressure solution,
•
original mineralogy controls the early compactional
history. Aragonite mineralogy at times of burial
(shallow-marine carbonate muds) will enhance
chemical compaction; primary calcite mineralogy
(e.g. deep-marine carbonate oozes and chalk) will
retard pressure solution,
•
insoluble residues (clay, organic matter) seems to en-
hance pressure solution in fine-grained carbonates
(Oldershaw and Scoffin 1967, Sassen et al. 1987),
•
grain size and grain surface properties,
•
early dolomitization can inhibit or preclude stylo-
litization,
Solution resistance of grains?
Differences in solu-
tion resistance of different grain and matrix types have
been observed by various authors (e.g. Trurnit 1968;
Logan and Semeniuk 1976; Steiger 1981; Huber 1987).
Sandstone and dolomite extraclasts are more resistant
•
clay minerals; the presence or absence of minor
amounts of clay minerals appear to be a major con-
trol on whether or not pressure solution occurs in
carbonate rocks (de Boer 1977).
