Geology Reference
In-Depth Information
(3) Fine- and very fine-grained sands (< 0.25 mm):
Common in central parts of lagoons, in innerplatform
basins, in deeper depressions of topographically dif-
ferentiated subtidal areas, in small or large protected
areas and in areas covered by seagrass or mangroves.
Vegetation favors the accumulation of fine-grained
well-sorted bioclastic sediment; the sediment consists
of small calcareous organisms living on the plants and
allochthonous grains trapped within the plants.
terpreted as indicators of different water energy
(Plumley et al. 1962; Sect. 12.1.1.2).
The combination of grain-size parameters (mean,
skewness, kurtosis) separates predominantly those en-
vironments which differ strongly in their hydrodynamic
controls. These environments are not restricted to spe-
cific depositional settings.
Box 6.1.
Selected grain-size studies of modern and an-
cient carbonates.
* Studies of calcareous sands in reef
complexes.
Sorting
Specific sorting values of shallow-marine calcare-
ous sands measured by inclusive standard deviation and
skewness are not limited to particular depositional en-
vironments but are important in combination with other
grain-size parameters.
Well to moderately well sorted, coarse calcareous
sands are common on beaches and at reef rims.
Moderately sorted coarse sands occur on beaches,
submarine ridges, near inner platform and lagoonal
patch reefs, on inner carbonate ramps and open-ma-
rine platforms.
Moderately to poorly sorted sands are widely dis-
tributed. Coarse sands occur in tidal and shallow sub-
tidal environments.
Fine and very fine moderately to poorly sorted fine
sands are known from tidal environments, the leeward
part and the central parts of reefs and in lagoons of
platform reefs.
Poorly to very poorly sorted fine-grained sands oc-
cur in protected basins and topographic depressions.
Modern environments
Shallow-marine banks, platforms and reefs:
Anwar
et al. 1984; Basan 1972*; Davies and Conley 1977; Early
and Goodell 1968; Emery 1963; Flood and Orme 1977*;
Folk 1962, 1967; Folk and Robles 1964*; Ginsburg
1956*; Gischler 1994*; Hoskin and Nelson 1971;
Hubbard et al. 1981; Jindrich 1969; Kench and McLean
1997; Khalaf et al. 1984; Koopmann et al. 1979; Land
1979*; Lewis 1969*; Lynts 1966; Mallik 1976*, 1979*;
Maxwell and Flemming 1961*; Maxwell et al. 1961*;
McKee 1959*; Milliman 1973; Montaggioni et al. 1986*;
Müller 1964; Müller and Müller 1967; Passega 1964;
Pilkey et al. 1967; Piller and Mansour 1990*; Purdy
1963; Rao and Amini 1995; Rizzini 1968; Sarnthein
1971; Scoffin et al. 1980*; Upchurch 1972
Size and hydrodynamics of carbonate grains:
Braithwaite 1973;
Chave 1960; Chardy et al. 1988;
Driscoll and Wettin 1973; Force 1969; Hoskin et al. 1983;
Maiklem 1968; Swinchatt 1965; Wanless et al. 1981
Ancient environments
Shallow-marine platforms and reefs:
Boccaletti et al.
1969 (Jurassic); Carozzi 1958, 1961* (Devonian);
Carozzi and Diaby 1981 (Early Carboniferous); Carozzi
and Hulse 1963* (Devonian); Carozzi and Lundwall
1959* (Devonian); Carozzi and Reichelderfer 1987
(Early Carboniferous); Carozzi and Zadnik 1959* (Sil-
urian); Carss and Carozzi 1965* (Devonian); Dawson
and Carozzi 1986* (Late Carboniferous); Fabricius 1967
(Late Triassic and Early Jurassic); Flügel and Flügel-
Kahler 1963* (Late Triassic); Faugères 1974 (Jurassic);
Gindy and Sultan 1978 (Miocene); Hötzl 1966 (Late Ju-
rassic); Jaanusson 1952 (Ordovician); Merta 1991 (Ju-
rassic); Ott 1969 (Late Jurassic); Rad 1974 (Tertiary and
Quaternary); Rao and Carozzi 1973 (Mississippian);
Rogen et al. 2001 (Cretaceous chalk); Usdowski 1962
(Triassic); Zacher 1973 (Cretaceous)
Summary
Grain-size distributions reflect the availability of
skeletal grains, i.e. the occurrence of certain organisms
in specific subenvironments, the degree of water en-
ergy controlled by tides, waves and storms, and the dif-
ferentiation of hydrodynamic conditions by submarine
bottom topography. Grain size reflects only some of
the variability of the sedimentary bottom facies.
Well sorted to moderately sorted sands appear to be
commonly controlled by high-energy conditions,
brought about by wave action and/or currents. Poor sort-
ing may be caused by tidal and bottom currents or re-
flect just the deposition of larger eroded grains (e.g.
coral detritus) within finer sediment.
In larger reef complexes, the grain-size distribution
of the bioclastic sediments is indicative of hydrody-
namic processes acting within defined depositional en-
vironments. Large-scale grain-size studies based on
multivariate analyses (e.g. Flood and Orme 1977) sup-
port the classification of carbonate rocks according to
textural criteria (grain size, sorting, etc.) which are in-
Turbidites:
Babek and Kalvoda 2001 (Late Devonian
and Early Carboniferous); Carozzi and Baneree 1984
(Devonian); Carozzi and Frost 1966 (Silurian); Eder
1971; Engel 1974 (Early Tertiary); H.W. Flügel and
Pölsler 1965 (Late Jurassic); Herbig and Mamet 1994
(Early Carboniferous); Meischner 1964 (Devonian);
Steiger 1981 (Late Jurassic)
