Geology Reference
In-Depth Information
13.3 Organic Matter in Carbonate
Rocks
anoxia, hypersalinity, microbial sulfate-reducing activ-
ity, algal blooming, paleo-upwelling and paleo-surface
seawater temperature are indicated by molecular and/
or isotopic characteristics.
Most work on organic petrology and palynofacies
concerns siliciclastic rocks. But biomarkers are also
promising and sensitive paleoenvironmental and depo-
sitional indicators in carbonate rocks as demonstrated
by the distinct differences in autochthonous biomarkers
in reef, platform and basin carbonates allowing facies
interpretations to be refined with respect to salinity, oxy-
genation and water stratification (Marynowski et al.
2000). Cyclicity and its bearing on sequence stratigra-
phy is another tool that can be elucidated by organic
matter distribution in limestones (Bombardiere and
Gorin 2000). The identification of silt-sized remains of
organisms may be facilitated by biomarkers as well,
e.g. the differentiation of grains derived from calcare-
ous algae and from corals (Böhm et al. 1980).
The formation of carbonate rocks can be considered as
a part of a three-component system (Ricken 1993). Or-
ganic matter, carbonate and siliciclastic sediment may
settle concurrently, but at different rates, and intermix
at the sea floor resulting in a particular sediment com-
position. A change in the flux of one component can
cause diluting or concentrating of the other two com-
ponents expressed by the ratio of organic carbon to
carbonate.
Organic matter is a trace constituent of calcareous
skeletons (Crick 1989), carbonate cements (Dravies and
Yurewicz 1985), carbonate particles (Davies et al. 1978)
and speleothems (Shopov et al. 1994). The presence
and composition of organic matter in carbonates is used
as a tool in
• estimating the productivity and the origin of 'black
shales'.
• recognizing depositional facies and delineate diage-
netic fabrics,
• understanding the controlling effect of organic con-
stituents on mineral growth,
• providing fingerprints for the source of organic mat-
ter in sediments and the origin of source rocks, and
•
Basics: Organic matter
Crick, R.E. (ed., 1989): Origin, evolution and modern as-
pects of biomineralization in plants and animals. - 536
pp., New York (Plenum Press)
De Leeuw, J.W., Frewin, N.L., Van Bergen, P.F., Sinninghe
Damste, J.S., Collinson, M.E. (1995): Organic carbon as
a paleoenvironmental indicator in the marine realm. - In:
Bosence, D.W., Allison, P.A. (eds.): Marine paleoenviron-
mental analysis from fossils. - Geological Society of Lon-
don, Special Publication,
83
, 43-71
Gautier, D.L. (ed., 1986): Roles of organic matter in sedi-
ment diagenesis. - Soc. Econ. Paleont. Miner., Special
Publications,
38
, 203 pp.
Huc, A.Y. (1990): Deposition of organic facies. - American
Association of Petroleum Geologists, Studies in Geology,
30
, 234 pp.
Marynowski, L., Narkiewicz, M., Grelowski, C. (2000): Bio-
markers as environmental indicators in a carbonate com-
plex, example from the Middle to Upper Devonian, Holy
Cross Mountains, Poland. - Sedimentary Geology,
137
,
187-212
Peters, K.E., Moldovan, J.M. (1993): The biomarker guide -
interpreting molecular fossils in petroleum and ancient
sediments. - 363 pp., Englewood Cliffs (Prentice Hall)
Ramseyer, K., Miano, T.M., D'Orazio, V., Wildberger, A.,
Wagner, T., Geister, J. (1997): Nature and origin of or-
ganic matter in carbonates from speleothems, marine ce-
ments and coral skeletons. - Organic Geochemistry,
26
,
361-378
Ricken, W. (1993): Sedimentation as a three-component sys-
tem. - Lecture Notes in Earth Science,
51
, 211 pp., Berlin
(Springer)
Tyson, R.V. (1995): Sedimentary organic matter. Organic fa-
cies and palynofacies. - 615 pp., London (Chapman and
Hall)
Whelan, J.K., Farrington, J.W. (eds., 1992): Organic matter:
productivity, accumulation and preservation in recent and
ancient sediments. - 533 pp., New York (Columbia Press)
Further reading:
K069
determining the timing of hydrocarbon migration.
The molecular structure of organic matter controls
mineral growth (Ramseyer et al. 1997). Inorganically
precipitated carbonates (speleothems, cements; Dravies
and Yurewicz 1985) incorporate during growth adsorbed
organic matter between submicroscopic subunits of
crystals. Biologically secreted carbonates incorporate
biogenic tissue between crystals. The organic matter is
derived from soils (speleothem calcite), dissolved or-
ganic matter (marine carbonates) and biological decay
products (aragonitic coral skeletons).
Biogeochemical proxies:
Sedimentary compounds
within sedimentary rocks supply important biomarkers
and paleoenvironmental indicators (de Leeuw et al.
1995). Marine as well as non-marine environments are
characterized by the combined presence of specific
compounds.
Biomarkers
are (a) proxies for various groups of bac-
teria, cyanobacteria, algae, vascular higher plants, and
animals (Peters and Moldovan 1993); (b) assist in es-
timating shoreline proximity of modern carbonates, and
allow paralic margins dominated by mangroves, and
subtidal mud-banks characterized by sea grass to be
distinguished; and (c) are fundamental for evaluating
of organic-rich carbonate rocks (Hopf et al. 2001). Pa-
leoenvironmental characteristics, such as photic zone,
