We recommend that a step-by-step approach be used in
the Dunham scheme. The order of questions to be asked is:
1. Is the depositional texture recognizable?
No – called crystalline limestone
Yes – go to 2.
2. Was the rock bound together during deposition?
Yes – boundstone
No – go to 3.
3. Components deposited as distinct grains
Grain supported – no mud – grainstone
Grain supported – some mud – packstone
Mud supported > 10% grains – wackestone
Mud < 10% grains – mudstone
This classification key can be represented in a diagrammatic
way (see Dunham Classification Scheme diagram).
Summary
A variety of classification schemes have been proposed for
limestones that provide information relating to their origin, component composition, grain size, presence of
matrix or cement, and depositional setting. The first universally accepted scheme was that of Folk, developed in
1959 to integrate the origin, component composition,
grain size, and depositional setting. This was elaborated
further in 1962. Folk’s scheme is most suited for the study
of thin sections of limestones.
An alternative classification scheme was proposed by
Dunham in 1962. This is more suited for limestone
descriptions made when using a hand lens or binocular
microscope. It was further modified in 1971 by Embry
and Klovan. Dunham’s scheme is now commonly used
by the oil/gas exploration industry.
A subsequent modification was proposed by James in
1984. It enables these various earlier schemes to be used
interchangeably. The classification schemes can be
represented in diagrammatic form.
Bibliography
Carrozzi, A. V., 1960. Microscopic Sedimentary Petrography. New
York/London: Wiley.
Dunham, R. L., 1962. Classification of carbonate rocks according to
depositional texture. Memoir American Association Petroleum
Geologists, 1, 108–121.
Embry, A. F., and Klovan, J. E., 1971. A late Devonian reef tract on
Northeastern Banks Island, NWT. Canadian Petroleum Geology
Bulletin, 19, 730–781.
Folk, R. L., 1959. Practical petrographic classification of limestones.
Bulletin American Association Petroleum Geologists, 43, 1–38.
Folk, R. L., 1962. Spectral subdivision of limestone types. In Ham,
W. E. (ed.), Classification of Carbonate Rocks. American Association of Petroleum Geologists Memoir I, pp. 62–84.
Folk, R. L., 1965. Some aspects of recrystallization in ancient limestones. Society of Economic Paleontologists and Mineralogists
(spec. pub.), 13, 14–48.
Illing, L. V., 1954. Bahaman calcareous sands. Bulletin American
Association of Petroleum Geologists, 38, 1–95.
James, N. P., 1984. Shallowing-upwards sequences in carbonates. In
Walker, R. G. (ed.), Facies Models. Canada: Geological Association of Canada, Geoscience Canada, (Rpr. Series 1), pp. 213–228.
Pettijohn, F. J., 1952. Sedimentary Rocks. New York: Harper &
Brothers.
Reid, R. P., Macintyre, I. G., and James, N. P., 1990. Internal precipitation of microcrystalline carbonate: a fundamental problems of
sedimentologists. Sedimentary Geology, 68, 163–170.
Scholle, P. A., and Ulmer-Scholle, D. S., 2003. A color guide to the
petrography of carbonate rocks. AAPG Memoir, 77, 474.
Twenhoffel, W. H., 1932. Treatise on Sedimentation. Baltimore,
MD: Williams & Wilkins.
Wolf, K. H., 1961. An introduction to the classification of limestones. Neues Jahrbuch for Geology and Paleontology –
Monatschefte, 5, 236–250.
Wright, P. V., 1992. A revised classification of limestones. Sedimentary Geology, 76, 177–185.
Cross-references
Bindstone
Floatstone
Framestone
Micrite
Packstone
Rudstone
Wackestone
CLIMATE CHANGE AND CORAL REEFS
Janice M. Lough
Australian Institute of Marine Science, Townsville, QLD,
Australia
Definition
Climate: Weather expected at given location and time of
year, based on observations over at least 30 years, including average values and range of variability.
Climate change: Significant and persistent change in average and/or variability of climate.
Greenhouse gas: Constituent of atmosphere that absorbs
and emits thermal infrared radiation.
Greenhouse effect: Trapping by atmospheric greenhouse
gases of thermal infrared radiation, which otherwise
would be lost to space, within climate system. Without
the natural greenhouse effect, the earth would be about
30
C cooler and uninhabitable.
A rapidly changing climate
Climate change is not new. Global and regional climate
has varied and changed in the past on a range of time
scales due to a variety of internal and external causes
(IPCC, 2007a, Chap. 1). Organisms and ecosystems, such
as coral reefs, have survived, changed their distribution,
and adapted to many of these past changes.
We are, however, in a new era of rapidly changing global
climate as a consequence of human activities. The evidence
for increasing greenhouse gases due to burning of fossil fuels,
land-use changes and agriculture activities since the late eighteenth century is unequivocal (IPCC, 2007a, Chap. 2). The
atmospheric concentration of the main greenhouse gas, carbon dioxide (CO 2 ), has risen about 40% from 280 ppm in
1750 to 383 ppm in 2007, the highest concentration of the last
650,000 years and possibly the last 20 million years. Not only
198
CLIMATE CHANGE AND CORAL REEFS
the Dunham scheme. The order of questions to be asked is:
1. Is the depositional texture recognizable?
No – called crystalline limestone
Yes – go to 2.
2. Was the rock bound together during deposition?
Yes – boundstone
No – go to 3.
3. Components deposited as distinct grains
Grain supported – no mud – grainstone
Grain supported – some mud – packstone
Mud supported > 10% grains – wackestone
Mud < 10% grains – mudstone
This classification key can be represented in a diagrammatic
way (see Dunham Classification Scheme diagram).
Summary
A variety of classification schemes have been proposed for
limestones that provide information relating to their origin, component composition, grain size, presence of
matrix or cement, and depositional setting. The first universally accepted scheme was that of Folk, developed in
1959 to integrate the origin, component composition,
grain size, and depositional setting. This was elaborated
further in 1962. Folk’s scheme is most suited for the study
of thin sections of limestones.
An alternative classification scheme was proposed by
Dunham in 1962. This is more suited for limestone
descriptions made when using a hand lens or binocular
microscope. It was further modified in 1971 by Embry
and Klovan. Dunham’s scheme is now commonly used
by the oil/gas exploration industry.
A subsequent modification was proposed by James in
1984. It enables these various earlier schemes to be used
interchangeably. The classification schemes can be
represented in diagrammatic form.
Bibliography
Carrozzi, A. V., 1960. Microscopic Sedimentary Petrography. New
York/London: Wiley.
Dunham, R. L., 1962. Classification of carbonate rocks according to
depositional texture. Memoir American Association Petroleum
Geologists, 1, 108–121.
Embry, A. F., and Klovan, J. E., 1971. A late Devonian reef tract on
Northeastern Banks Island, NWT. Canadian Petroleum Geology
Bulletin, 19, 730–781.
Folk, R. L., 1959. Practical petrographic classification of limestones.
Bulletin American Association Petroleum Geologists, 43, 1–38.
Folk, R. L., 1962. Spectral subdivision of limestone types. In Ham,
W. E. (ed.), Classification of Carbonate Rocks. American Association of Petroleum Geologists Memoir I, pp. 62–84.
Folk, R. L., 1965. Some aspects of recrystallization in ancient limestones. Society of Economic Paleontologists and Mineralogists
(spec. pub.), 13, 14–48.
Illing, L. V., 1954. Bahaman calcareous sands. Bulletin American
Association of Petroleum Geologists, 38, 1–95.
James, N. P., 1984. Shallowing-upwards sequences in carbonates. In
Walker, R. G. (ed.), Facies Models. Canada: Geological Association of Canada, Geoscience Canada, (Rpr. Series 1), pp. 213–228.
Pettijohn, F. J., 1952. Sedimentary Rocks. New York: Harper &
Brothers.
Reid, R. P., Macintyre, I. G., and James, N. P., 1990. Internal precipitation of microcrystalline carbonate: a fundamental problems of
sedimentologists. Sedimentary Geology, 68, 163–170.
Scholle, P. A., and Ulmer-Scholle, D. S., 2003. A color guide to the
petrography of carbonate rocks. AAPG Memoir, 77, 474.
Twenhoffel, W. H., 1932. Treatise on Sedimentation. Baltimore,
MD: Williams & Wilkins.
Wolf, K. H., 1961. An introduction to the classification of limestones. Neues Jahrbuch for Geology and Paleontology –
Monatschefte, 5, 236–250.
Wright, P. V., 1992. A revised classification of limestones. Sedimentary Geology, 76, 177–185.
Cross-references
Bindstone
Floatstone
Framestone
Micrite
Packstone
Rudstone
Wackestone
CLIMATE CHANGE AND CORAL REEFS
Janice M. Lough
Australian Institute of Marine Science, Townsville, QLD,
Australia
Definition
Climate: Weather expected at given location and time of
year, based on observations over at least 30 years, including average values and range of variability.
Climate change: Significant and persistent change in average and/or variability of climate.
Greenhouse gas: Constituent of atmosphere that absorbs
and emits thermal infrared radiation.
Greenhouse effect: Trapping by atmospheric greenhouse
gases of thermal infrared radiation, which otherwise
would be lost to space, within climate system. Without
the natural greenhouse effect, the earth would be about
30
C cooler and uninhabitable.
A rapidly changing climate
Climate change is not new. Global and regional climate
has varied and changed in the past on a range of time
scales due to a variety of internal and external causes
(IPCC, 2007a, Chap. 1). Organisms and ecosystems, such
as coral reefs, have survived, changed their distribution,
and adapted to many of these past changes.
We are, however, in a new era of rapidly changing global
climate as a consequence of human activities. The evidence
for increasing greenhouse gases due to burning of fossil fuels,
land-use changes and agriculture activities since the late eighteenth century is unequivocal (IPCC, 2007a, Chap. 2). The
atmospheric concentration of the main greenhouse gas, carbon dioxide (CO 2 ), has risen about 40% from 280 ppm in
1750 to 383 ppm in 2007, the highest concentration of the last
650,000 years and possibly the last 20 million years. Not only
198
CLIMATE CHANGE AND CORAL REEFS