Geology Reference
In-Depth Information
Table 6 The four categories of marine sedimentary components with examples
of mineral phases
Classification
Mineral example
Chemical formula
Lithogenous
Quartz
SiO
2
Microcline
KA1Si
3
O
8
Kaolinite
Al
4
Si
4
O
10
(OH)
8
Montmorillonite
Al
4
Si
8
O
20
(OH)
4
nH
2
O
Illite
K
2
Al
4
(Si, Al)
8
O
20
(OH)
4
(Mg,Fe
21
)
10
Al
2
(Si,Al)
8
O
20
(OH,F)
16
Chlorite
Hydrogenous
Fe-Mn mineral
FeO(OH) - MnO
2
Carbonate fluoroapatite
Ca
5
(PO
4
)
3
x
(CO
3
)
x
F
11x
Barite
BaSO
4
Pyrite
FeS
2
Aragonite
CaCO
3
Dolomite
CaMg(CO
3
)
2
Biogenous
Calcite
CaCO
3
Aragonite
CaCO
3
SiO
2
nH
2
O
Opaline silica
Apatite
Ca
5
(F,Cl) (PO
4
)
3
Barite
BaSO
4
Organic matter
Cosmogenous
Cosmic spherules
Meteoric dusts
Source: adapted from Harrison and de Mora, 1996.
23
The relative contribution of lithogenous material to the sediments will
depend on the proximity to the continent and the source strength of
material derived elsewhere. The most important components in the
lithogenous fraction are quartz and the clay minerals (kaolinite, illite,
montmorillonite and chlorite). The distribution of the clay minerals
varies considerably. Illite and montmorillonite tend to be ubiquitous in
terrestrial material, but the latter has a secondary origin associated with
submarine volcanic activity. Kaolinite typifies intense weathering ob-
served in tropical and desert conditions. Therefore, it is relatively
enriched in equatorial regions. On the other hand, chlorite is indicative
of the high-latitude regimes where little chemical weathering occurs. The
lithogenous components tend to be inert in the water column and
represent detrital deposition. Nonetheless, the particle surfaces can act
as important sites for adsorption of organic material and trace elements.
Hydrogenous components, also known as chemogenous or halmeic
material, are those produced abiotically within the water column. This
may comprise primary material formed directly from seawater upon
exceeding a given solubility product, termed authigenic precipitation.
The best-known examples of authigenic material are the various types of
ferromanganese nodules found throughout the oceans. Alternatively,
