Geology Reference
In-Depth Information
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Hottinger, L. (1987): Conditions for generating carbonate
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, 265-271
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8
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Further reading:
K212
during drowning. Nutrient excess has various causes.
Reef carbonates that are overlain by shales may be vic-
tims of nutrients in terrestrial runoff. Rapid transgres-
sion that flooded subaerially exposed platforms and
ramps may have supported the influx of soils and nu-
trients to areas of reef growth. Other mechanisms for
drowning by excess nutrients include rapid pulses of
sea-level fluctuations and local or regional upwelling.
Studies of modern coral reefs indicate that an in-
crease in nutrient input and the related increase in pro-
ductivity lead to changes in dominant species, in an
increase in fast-growing and smaller taxa, and in greater
competition for space. Corals may be less abundant than
algae, sponges and bryozoans. This change can be re-
corded in ancient reefs by distinct differences in suc-
cessions and growth types.
Note that the relations between reef builders and
nutrients summarized by the Hallock and Schlager
model can be used to explain changes in ancient reefs
formed by zooxanthellate corals, but can not be applied
to reefs formed by siliceous sponges, bryozoans or mi-
crobes.
Basics: Productivity and nutrients
Berger, W.H., Smetacek, V.S., Wefer, G. (eds., 1989): Pro-
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Chichester (Wiley)
Birkeland, C. (1988): Second-order ecological effects of nu-
trient input into coral communities. - Galaxea,
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, 91-100
Bombardière, L., Gorin, G.E. (2000): Stratigraphical and lat-
eral distribution of sedimentary organic matter in Upper
Jurassic carbonates of SE France. - Sedimentary Geol-
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132
, 177-203
Brasier, M.D. (1995a): Fossil indicators of nutrient levels.
1. Eutrophication and climate change. - In: Bosence,
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analysis from fossils. - Geological Society, London, Spe-
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83
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Brasier, M.D. (1995b): Fossil indicators of nutrient levels. 2.
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Bosence, D.W.J., Allison, P.A. (eds.): Marine palaeo-
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Caplan, M.L., Bustin, R.M., Grimm, K.A. (1996): Demise of
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34
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Dupraz, C., Strasser, A. (2002): Nutritional modes in coral-
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17
, 449-471
Föllmi, K.B., Weissert, H., Bisping, M., Funk, H. (1994):
Phosphogenesis, carbon-isotope stratigraphy, and carbon-
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Hallock, P. (1988): The role of nutrient availability in bioero-
sion: consequences to carbonate buildups. - Palaeogeo-
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Hallock, P., Schlager, W. (1986): Nutrient excess and the de-
12.2 Estimating Paleoclimatic Con-
ditions: Grain Association Analysis
Shelf carbonates from warm- and cool-water regimes
can be recognized by identifying the dominant skeletal
constituents. Grain association analysis is one of the
most promising tools of microfacies studies, but the
results should be verified on the basis of accumulated
evidence (James 1997). Cold climatic settings, for ex-
ample, are indicated by specific grain associations, but
are more clearly proven by ice-rafted dropstones or
calcite pseudomorphs after ikaite, a metastable hexahy-
drate of calcium carbonate (see Sect. 2.4.1.5). Grain
association patterns have a high potential in understand-
ing climate change and paleolatitude shifts of carbon-
ate ramps and platforms.
The following text deals with the grain composi-
tion patterns of modern and ancient shelf carbonates.
Examples of facies models deduced from these patterns
are described in Chap. 14.
12.2.1 Concepts
Modern shelf carbonates are formed in tropical and non-
tropical zones. The criteria of these sediments were al-
ready discussed in Sect. 2.4.4. Tropical carbonate sedi-
mentation at low latitudes takes place in warm-water
environments. Non-tropical sedimentation occurs at
mid- and high latitudes in warm-temperate and cool-
