152
surface sediments across the coastal plain which rest on top
of marine skeletal carbonates and organic-rich early Holocene lacustrine muds. The Coorong model should not be
used to explain widespread dolomitization in ancient
supratidal and shelf carbonates (Warren 1990).
Dolomitization largely destroys bio genie skeletons
and primary physical sedimentary structures. It often
leads to "secondary" porosity which can be of great
economic importance (cf. Sect. 13.3), but other
diagenetic processes may modify this trend. Longlasting burial diagenesis generally tends to close the
pore space completely.
3.4.8 Summary (Shallow-Marine Carbonates)
- Modem, shallow-marine carbonates form in
tropical, temperate, and arctic seas where little
terrigenous material dilutes bio genie carbonate
production. However, the carbonate-producing
communities vary with temperature, water depth,
and salinity (Chlorozoan association in tropical
seas, Foramol association in cooler waters).
Large-scale depositional environments of carbonates are ramps, rimmed carbonate shelves
and isolated platforms. They provide various
subenvironments (banks, different types of
reefs, mud mounds, forereef slope and backreef
lagoon, etc.) for carbonate production and redistribution of debris from syn-sedimentary reef
destruction.
Most rapid growth of reefs and composite carbonate buildups, including microbial and chemical carbonate precipitation, occurs in tropical
waters some meters below sea level. Ancient
Chapter 3 Coastal and Shallow Sea Sediments
Economic Aspects of Carbonate Diagenesis
The nature and duration of carbonate diagenesis in
relation to deposition largely control the great economic significance of carbonate buildups as reservoirs for hydrocarbons, groundwater, and host rocks
for mineral deposits, particularly Pb/Zn ores (Sect.
13.5). Reservoir potential and quality of reef carbonates as material for building and industrial purposes
vary significantly with regard to reef types (Flügel
1989). Organic reefs and reef mounds te nd to become exposed to sub aerial weathering and
karstification during their early his tory and therefore
commonly provide abundant pore space, whereas
mud mounds, often grown at greater depths below
sea level, seem to be of minor importance as reservoirs and host rocks.
carbonates formed in a similar way as today,
but the faunal associations differed from the
present ones.
Reefs and other carbonate buildups can easily
pro grade seaward or follow a moderately rising
sea level. They generally are sensitive to sealevel changes.
Lithification and dolomitization of shallow-water carbonates (early and late diagenesis ) are
favored by the presence of metastable carbonate
minerals, the high porosity and permeability of
many carbonate buildups, and emergence. Pervasive dolomitization requires a large Mgsource.
- The rock types of carbonate buildups displaya
great variety of microfacies due to the complex
growth of carbonate bodies, the importance of
resedimented material, and differences in
diagenesis.
surface sediments across the coastal plain which rest on top
of marine skeletal carbonates and organic-rich early Holocene lacustrine muds. The Coorong model should not be
used to explain widespread dolomitization in ancient
supratidal and shelf carbonates (Warren 1990).
Dolomitization largely destroys bio genie skeletons
and primary physical sedimentary structures. It often
leads to "secondary" porosity which can be of great
economic importance (cf. Sect. 13.3), but other
diagenetic processes may modify this trend. Longlasting burial diagenesis generally tends to close the
pore space completely.
3.4.8 Summary (Shallow-Marine Carbonates)
- Modem, shallow-marine carbonates form in
tropical, temperate, and arctic seas where little
terrigenous material dilutes bio genie carbonate
production. However, the carbonate-producing
communities vary with temperature, water depth,
and salinity (Chlorozoan association in tropical
seas, Foramol association in cooler waters).
Large-scale depositional environments of carbonates are ramps, rimmed carbonate shelves
and isolated platforms. They provide various
subenvironments (banks, different types of
reefs, mud mounds, forereef slope and backreef
lagoon, etc.) for carbonate production and redistribution of debris from syn-sedimentary reef
destruction.
Most rapid growth of reefs and composite carbonate buildups, including microbial and chemical carbonate precipitation, occurs in tropical
waters some meters below sea level. Ancient
Chapter 3 Coastal and Shallow Sea Sediments
Economic Aspects of Carbonate Diagenesis
The nature and duration of carbonate diagenesis in
relation to deposition largely control the great economic significance of carbonate buildups as reservoirs for hydrocarbons, groundwater, and host rocks
for mineral deposits, particularly Pb/Zn ores (Sect.
13.5). Reservoir potential and quality of reef carbonates as material for building and industrial purposes
vary significantly with regard to reef types (Flügel
1989). Organic reefs and reef mounds te nd to become exposed to sub aerial weathering and
karstification during their early his tory and therefore
commonly provide abundant pore space, whereas
mud mounds, often grown at greater depths below
sea level, seem to be of minor importance as reservoirs and host rocks.
carbonates formed in a similar way as today,
but the faunal associations differed from the
present ones.
Reefs and other carbonate buildups can easily
pro grade seaward or follow a moderately rising
sea level. They generally are sensitive to sealevel changes.
Lithification and dolomitization of shallow-water carbonates (early and late diagenesis ) are
favored by the presence of metastable carbonate
minerals, the high porosity and permeability of
many carbonate buildups, and emergence. Pervasive dolomitization requires a large Mgsource.
- The rock types of carbonate buildups displaya
great variety of microfacies due to the complex
growth of carbonate bodies, the importance of
resedimented material, and differences in
diagenesis.