saline, occasionally poorly oxygenated deep layer and a
low-salinity surface layer marks the hydrography. In
fjords where a tidewater glacier is present, turbid meltwater from beneath the glacier rises as a plume into the
surface layer, where flocculation of silt and clay
particles leads to settling of these fine-grained particles
contributing to the bulk mass of the fjord deposits
(Mugford and Dowdeswell, 2011). Lamination may
occur due to the effect of seasonal melting on the
depositional process. These fine-grained sediments do,
however, often display intervals with coarser ice-rafted
debris which may reflect changes in iceberg calving activity of the local glacier (Andresen et al., 2012). A common
feature of fjord basins with a high sediment input is a wide
variety of slope failures along side-wall margins or basement highs and frequent occurrence of turbidites and
mass-flow deposits in the adjacent basin. This slope instability implies a potential geohazard risk in the form of a
local tsunami.
Bibliography
Andresen, C. S., Straneo, F., Ribergaard, M. H., Bjørk, A. A.,
Andersen, T. J., Kuijpers, A., Nørgaard-Pedersen, N.,
Kjær, K. H., Schjøth, F., Wecklström, K., and Ahlstrøm, A. P.,
2012. Rapid response of Helheim Glacier in Greenland to climate variability over the past century. Nature Geoscience, 5,
37–41.
Gilbert, R., 2000. Environmental assessment from the sedimentary
record of high-latitude fjords. Geomorphology, 32, 295–314.
Mugford, R. I., and Dowdeswell, J. A., 2011. Modelling glacial
meltwater plume dynamics and sedimentation in high-latitude
fjords. Journal of Geophysical Research, 116, F01023,
doi:10.1029/2010JF001735.
Syvitski, J. P. M., Burrel, D. C., and Skei, J. M., 1987. Fjords, Processes and Products. New York: Springer.
Syvitski, J. P. M., and Farrow, G. E., 1989. Fjord sedimentation as
an analogue for small hydrocarbon-bearing fan deltas. In
Whateley, M. K. G., and Pickering, K. T. (eds.), Deltas: Sites
and Traps for Fossil Fuels. Geological Society of London. Special Publication, Vol. 41, Department of Geology, The University Leicester, pp. 21–43.
Cross-references
Clay Minerals
Contourites
Currents
Grounding Line
Ice-rafted Debris (IRD)
Laminated Sediments
Layering of Oceanic Crust
Marine Sedimentary Basins
Moraines
Paleoceanography
Regional Marine Geology
Sea-level
Sediment Dynamics
Sediment Transport Models
Sedimentary Sequence
Shelf
Tsunamis
Turbidites
FORAMINIFERS (BENTHIC)
Anna Binczewska
1
, Irina Polovodova Asteman
2 and
Elizabeth J. Farmer
3
1
Institute of Marine and Coastal Sciences, University of
Szczecin, Szczecin, Poland
2
Bjerknes Centre for Climate Research, Bergen, Norway
3
Department of Earth Science, University of Bergen,
Bergen, Norway
Synonyms
Benthic foraminifera; Benthic foraminifers; Informally
benthic forams
Definition
Benthic foraminifera are unicellular, aquatic (marine and
brackish) eukaryotic organisms. They are benthic bottom
dwellers characterized by high diversity and abundance.
In benthic foraminifera, the cytoplasmic body is encased
in organic or mineralized test (shell), which provides a fossil record (Cambrian to recent). Due to the presence of the
test, benthic foraminifera are useful indicators of past and
present-day environmental changes. Foraminiferal shells
consist of single or multiple chambers interconnected with
each other by a channel, called foramen, which gives the
name to the entire Foraminifera group.
Introduction
One of the first findings on benthic foraminifera dates
back to the seventeenth century, and a drawing by Antonie
van Leeuwenhoek of a specimen nowadays recognized as
the genus Elphidium. Following numerous studies by,
e.g., A. d’Orbigny (1826), H.B. Brady, J.A Cushman
and A. R. Loeblich, and Jr. H. Tappan made a substantial
contribution to foraminiferal research (Sen Gupta,
1999a). These and subsequent investigations resulted in
benthic foraminiferal classification system consisting of
16 orders, Allogromiida, Astrorhizida, Litoulida,
Trochamminida, Textulariida, Fusulinida, Miliolida,
Carterinida, Spirillinida, Lagenida, Rotaliida, Buliminida,
Globigerinida, Involutinida, Robertinida, and Silicoloculinida (Loeblich and Tappan, 1988), which have been
recently placed in 3 to 4 major classes (Pawlowski et al.,
2013; Mikhalevich, 2013). Based on shell morphology,
about 5 000 modern and 40 000 fossil species are
described (Sen Gupta, 1999). Recent molecular studies
reveal a much higher genetic diversity due to numerous
cryptic species and genetically distinctive phylotypes
(Pawlowski et al., 2014).
Morphology and taxonomy
Foraminifera belong to the kingdom Protista because their
body consists of a single cell filled with cytoplasm. Cellular structures include mitochondria, vacuoles, and nuclei
placed in a cytoplasmic body and encased in a shell
(test). Foraminiferal shells can be calcareous
FORAMINIFERS (BENTHIC)
251
low-salinity surface layer marks the hydrography. In
fjords where a tidewater glacier is present, turbid meltwater from beneath the glacier rises as a plume into the
surface layer, where flocculation of silt and clay
particles leads to settling of these fine-grained particles
contributing to the bulk mass of the fjord deposits
(Mugford and Dowdeswell, 2011). Lamination may
occur due to the effect of seasonal melting on the
depositional process. These fine-grained sediments do,
however, often display intervals with coarser ice-rafted
debris which may reflect changes in iceberg calving activity of the local glacier (Andresen et al., 2012). A common
feature of fjord basins with a high sediment input is a wide
variety of slope failures along side-wall margins or basement highs and frequent occurrence of turbidites and
mass-flow deposits in the adjacent basin. This slope instability implies a potential geohazard risk in the form of a
local tsunami.
Bibliography
Andresen, C. S., Straneo, F., Ribergaard, M. H., Bjørk, A. A.,
Andersen, T. J., Kuijpers, A., Nørgaard-Pedersen, N.,
Kjær, K. H., Schjøth, F., Wecklström, K., and Ahlstrøm, A. P.,
2012. Rapid response of Helheim Glacier in Greenland to climate variability over the past century. Nature Geoscience, 5,
37–41.
Gilbert, R., 2000. Environmental assessment from the sedimentary
record of high-latitude fjords. Geomorphology, 32, 295–314.
Mugford, R. I., and Dowdeswell, J. A., 2011. Modelling glacial
meltwater plume dynamics and sedimentation in high-latitude
fjords. Journal of Geophysical Research, 116, F01023,
doi:10.1029/2010JF001735.
Syvitski, J. P. M., Burrel, D. C., and Skei, J. M., 1987. Fjords, Processes and Products. New York: Springer.
Syvitski, J. P. M., and Farrow, G. E., 1989. Fjord sedimentation as
an analogue for small hydrocarbon-bearing fan deltas. In
Whateley, M. K. G., and Pickering, K. T. (eds.), Deltas: Sites
and Traps for Fossil Fuels. Geological Society of London. Special Publication, Vol. 41, Department of Geology, The University Leicester, pp. 21–43.
Cross-references
Clay Minerals
Contourites
Currents
Grounding Line
Ice-rafted Debris (IRD)
Laminated Sediments
Layering of Oceanic Crust
Marine Sedimentary Basins
Moraines
Paleoceanography
Regional Marine Geology
Sea-level
Sediment Dynamics
Sediment Transport Models
Sedimentary Sequence
Shelf
Tsunamis
Turbidites
FORAMINIFERS (BENTHIC)
Anna Binczewska
1
, Irina Polovodova Asteman
2 and
Elizabeth J. Farmer
3
1
Institute of Marine and Coastal Sciences, University of
Szczecin, Szczecin, Poland
2
Bjerknes Centre for Climate Research, Bergen, Norway
3
Department of Earth Science, University of Bergen,
Bergen, Norway
Synonyms
Benthic foraminifera; Benthic foraminifers; Informally
benthic forams
Definition
Benthic foraminifera are unicellular, aquatic (marine and
brackish) eukaryotic organisms. They are benthic bottom
dwellers characterized by high diversity and abundance.
In benthic foraminifera, the cytoplasmic body is encased
in organic or mineralized test (shell), which provides a fossil record (Cambrian to recent). Due to the presence of the
test, benthic foraminifera are useful indicators of past and
present-day environmental changes. Foraminiferal shells
consist of single or multiple chambers interconnected with
each other by a channel, called foramen, which gives the
name to the entire Foraminifera group.
Introduction
One of the first findings on benthic foraminifera dates
back to the seventeenth century, and a drawing by Antonie
van Leeuwenhoek of a specimen nowadays recognized as
the genus Elphidium. Following numerous studies by,
e.g., A. d’Orbigny (1826), H.B. Brady, J.A Cushman
and A. R. Loeblich, and Jr. H. Tappan made a substantial
contribution to foraminiferal research (Sen Gupta,
1999a). These and subsequent investigations resulted in
benthic foraminiferal classification system consisting of
16 orders, Allogromiida, Astrorhizida, Litoulida,
Trochamminida, Textulariida, Fusulinida, Miliolida,
Carterinida, Spirillinida, Lagenida, Rotaliida, Buliminida,
Globigerinida, Involutinida, Robertinida, and Silicoloculinida (Loeblich and Tappan, 1988), which have been
recently placed in 3 to 4 major classes (Pawlowski et al.,
2013; Mikhalevich, 2013). Based on shell morphology,
about 5 000 modern and 40 000 fossil species are
described (Sen Gupta, 1999). Recent molecular studies
reveal a much higher genetic diversity due to numerous
cryptic species and genetically distinctive phylotypes
(Pawlowski et al., 2014).
Morphology and taxonomy
Foraminifera belong to the kingdom Protista because their
body consists of a single cell filled with cytoplasm. Cellular structures include mitochondria, vacuoles, and nuclei
placed in a cytoplasmic body and encased in a shell
(test). Foraminiferal shells can be calcareous
FORAMINIFERS (BENTHIC)
251