1
The Solid Phase of Marine Sediments
8
teristically depends on the type of parent rock.
On account of its iron content, chlorite is prone
to chemical weathering. Chlorite distinctly displays a distribution pattern of latitudinal zonation and due to its abundance in polar regions it
is considered as the “mineral of high latitudes”
(Griffin et al. 1968). The grain size of chlorite minerals is – similar to illite – not limited to the clay
fraction (< 4 µm), but in addition encompasses
the entire silt fraction (4 - 63 µm) as well.
1.2.2
Biogenous Sediments
Biogenous sediments generally refer to bioclastic
sediments, hence sediments which are built of
remnants and fragments of shells and tests produced by organisms – calcareous, siliceous or
phosphatic particles. In a broader sense, biogenous sediments comprise all solid material
formed in the biosphere, i.e. all the hard parts inclusive of the organic substance, the caustobioliths. The organic substance will be treated
more comprehensively in Chapter 4, therefore they
will not be discussed here.
The amount of carbonate which is deposited in
the oceans today is almost exclusively of biogenous origin. The long controversy whether
chemical precipitation of lime occurs directly in
the shallow waters of the tropical seas, such as
the banks of the Bahamas and in the Persian Gulf
(Fig. 1.5), during the formation of calcareous
ooids and oozes of acicular aragonite, has been
settled in preference of the concept of biomineralization (Fabricius 1977). The tiny aragonite
Fig. 1.5 SEM photographs of calcareous sediments composed of aragonite needles which are probably of biogenic origin.
Upper left: slightly etched section of a calcareous ooid from the Bahamas showing subconcentric laminae of primary ooid
coatings; upper right: close-up showing ooid laminae formed by small acicular aragonite needles. Lower left: silt-sized
particle of aragonite mud from the Persian Gulf; lower right: close-up showing details of acicular aragonite needles measuring up
to 10 µm in length, scalebar 5 µm.
The Solid Phase of Marine Sediments
8
teristically depends on the type of parent rock.
On account of its iron content, chlorite is prone
to chemical weathering. Chlorite distinctly displays a distribution pattern of latitudinal zonation and due to its abundance in polar regions it
is considered as the “mineral of high latitudes”
(Griffin et al. 1968). The grain size of chlorite minerals is – similar to illite – not limited to the clay
fraction (< 4 µm), but in addition encompasses
the entire silt fraction (4 - 63 µm) as well.
1.2.2
Biogenous Sediments
Biogenous sediments generally refer to bioclastic
sediments, hence sediments which are built of
remnants and fragments of shells and tests produced by organisms – calcareous, siliceous or
phosphatic particles. In a broader sense, biogenous sediments comprise all solid material
formed in the biosphere, i.e. all the hard parts inclusive of the organic substance, the caustobioliths. The organic substance will be treated
more comprehensively in Chapter 4, therefore they
will not be discussed here.
The amount of carbonate which is deposited in
the oceans today is almost exclusively of biogenous origin. The long controversy whether
chemical precipitation of lime occurs directly in
the shallow waters of the tropical seas, such as
the banks of the Bahamas and in the Persian Gulf
(Fig. 1.5), during the formation of calcareous
ooids and oozes of acicular aragonite, has been
settled in preference of the concept of biomineralization (Fabricius 1977). The tiny aragonite
Fig. 1.5 SEM photographs of calcareous sediments composed of aragonite needles which are probably of biogenic origin.
Upper left: slightly etched section of a calcareous ooid from the Bahamas showing subconcentric laminae of primary ooid
coatings; upper right: close-up showing ooid laminae formed by small acicular aragonite needles. Lower left: silt-sized
particle of aragonite mud from the Persian Gulf; lower right: close-up showing details of acicular aragonite needles measuring up
to 10 µm in length, scalebar 5 µm.