Geology Reference
In-Depth Information
basins. Detrital quartz grains within the silt fraction
should be specifically studied with respect to crystal
habit and surface features (Krinsley and Doornkamp
1973).
Box 13.1.
Use of insoluble residues (IR) of limestones
in facies analysis.
•
Differentiating carbonate platforms and ramps.
Land-
locked platforms are more commonly affected by silici-
clastic input than open-marine oceanic platforms whose
carbonates are generally very poor in non-carbonate resi-
dues. Different parts of carbonate platforms can be char-
acterized by different mineralogical composition of the
insoluble residues (Adatte and Rumley 1984).
•
Distinguishing depositional settings
. Diagrams of IR
content versus the silt/clay ratios of limestones can sepa-
rate limestones formed in different basins (Bausch 1987).
IR contents increase in platform-slope-basin transverses
from platform-edge reefs to near-reef basinal facies and
to off-reef basinal sediments (Dürkoop et al. 1986).
•
Assessing sedimentation patterns.
Bed-per-bed stud-
ies of limestone sequences reveal quantitative differences
in the composition of IR that may reflect cyclic deposi-
tional patterns and allow regressive and transgressive
phases to be defined.
•
Quantifying sedimentation rates.
The proportion of
carbonate and non-carbonate within limestone beds and
bed thickness are useful for describing depositional rates.
•
Recognizing hidden discontinuities in limestone se-
quences.
Abrupt and significant changes in IR contents
and marked differences in the mineralogical composi-
tion and in grain sizes from bed to bed may indicate depo-
sitional breaks.
•
Understanding source areas and hinterland erosion
.
Changes in erosion and the topography of the source
areas are reflected by clay mineral composition, the il-
lite/kaolinite proportions, grain sizes and IR amounts
(e.g. Weaver and Stevenson 1971).
•
Understanding conditions in transitional terrestrial-
marine areas.
Clay-mineralogical assemblages of marls
at the top of shallowing-upward sequences reflect fluc-
tuating freshwater and marine conditions affecting shal-
low-water carbonates (Deconinck and Strasser 1987).
•
Reconstructing transport mechanisms
. SEM surface
features of quartz grains are helpful in reconstructing
source area and transport mechanisms of terrigenous in-
put into carbonate environments (Cater 1984; Piller and
Mansour 1994).
•
Correlating platform and basin carbonates:
Compo-
sitional patterns of IR are used for stratigraphic correla-
tion of shallow- to deep-marine carbonates on a regional
scale (Gygi and Persoz 1986; Bausch 1996; Schweizer
1996). Changes in the amount of quartz and feldspars
studied in IR and in thin sections of carbonates offer a
possibility for recognizing time lines and time units
(Bolliger and Burri 1967).
•
Approaching an understanding of major paleocli-
matic differences.
The abundance and composition of
specific clay minerals in association with other proxies
are used as key indicators for humid versus arid climates.
The criteria used to define humid climate are the abun-
dance of kaolinite, Th-enriched clays, siliciclastics, posi-
tive δ
13
C values and wood. Arid climate may be indi-
cated by the abundance of illite, U and K-rich clays,
evaporites and carbonates, and negative δ
13
C values
(Ruffell et al. 2002).
Significance.
The mineralogical composition of in-
soluble residues of carbonate rocks is commonly ex-
plained as the result of terrigenous input. However, the
possibility of transformation or neoformation of min-
erals in the course of burial diagenesis must be kept in
mind.
The amount of clay in limestones varies strongly
within a range of less than 1% and more than 10%.
Clay content is often higher in micritic rocks than in
high-energy grain-supported limestones that are win-
nowed with respect to fine-grained constituents. These
differences are controlled by hydrodynamic conditions
and depositional settings.
Combined investigations of insoluble residues and
microfacies have been successfully applied to facies
analysis (Box 13.1) as well as to applied studies of car-
bonate rocks (see Chap. 17).
Basics: Insoluble residues in limestones
Adatte, T., Rumley, G. (1984): Microfaciès, minéralogie,
stratigraphie et évolution des milieux de depôts de la plate-
forme berriaso-valanginienne des régions de Sainte-Croix
(VD), Cressier et du Landeron (NE). - Bulletin de la So-
cieté Neuchâteloise des Sciences Naturelles,
107
, 221-239
Bausch, W. (1980): Tonmineralprovinzen in Malmkalken. -
Erlanger Forschungen, Reihe B,
8
, 78 pp.
Bausch, W. (1996): Noncarbonates as controlling factor in
reef growth and as a tool in reef stratigraphy (with ex-
amples from the Upper Jurassic of southern Germany). -
Göttinger Arbeiten zur Geologie und Paläontologie, Sonder-
band,
2
, 203-205
Bolliger, W., Burri, P. (1967): Versuch einer Zeitkorrelation
zwischen Plattformkarbonaten und tiefermarinen Sedi-
menten mit Hilfe von Quarz-Feldspat-Schüttungen (mitt-
lerer Malm des Schweizer Jura). - Eclogae geologicae
Helvetiae,
60
, 491-507
Cater, J.M.L. (1984): An application of scanning electron
microscopy of quartz sand surface textures to the envi-
ronmental diagnosis of Neogene carbonate sediments,
Finestrat Basin, south-east Spain. - Sedimentology,
31
,
717-731
Chamley, H. (1989): Clay sedimentology. - 623 pp., Berlin
(Springer)
Chamley, H., Proust, N.-J., Mansy, J.-L., Boulvain, F. (1997):
Diagenetic and paleogeographic significance of clay, car-
bonate and other sedimentary componentes in the Middle
Devonian limestones of the western Ardennes, France. -
Palaeogeography, Palaeoclimatology, Palaeoecology,
129
,
369-385
Dürkoop, A., Richter, D.K., Stritzke, R. (1986): Fazies, Alter
und Korrelation der triadischen Rotkalke von Epidauros,
Adhami und Hydra /Griechenland). - Facies,
24
, 105-150
Piller, W., Mansour, A.M. (1994): Origin and transport mecha-
nisms of non-carbonate sediments in carbonate-dominated
