Bremen. Dissertation.
http://nbn-resolving.de/urn:nbn:de:
gbv:46-00102438-18
Römer, M., Sahling, H., Pape, T., Bohrmann, G., and Spieß, V.,
2012. Quantification of gas bubble emissions from submarine
hydrocarbon seeps at the Makran continental margin (offshore
Pakistan). Journal of Geophysical Research, 117, C10015,
doi:10.1029/2011JC007424.
Saffer, D. M., and Tobin, H. J., 2011. Hydrogeology and mechanics
of subduction zone forearcs: fluid flow and pore pressure.
Annual Review of Earth and Planetary Sciences, 39, 157–186.
Sloan, E. D., and Koh, C. A., 2008. Clathrate Hydrates of Natural
Gases, 3rd edn. Boca Raton, FL: CRC Press. 752pp.
Suess, E., 2010. Marine cold seeps Handbook of Hydrocarbon and
Lipid Microbiology. Berlin: Springer, pp. 188–203, doi:10.1007/
978-3-540-77587-4_12. ISBN 978-3-540-77587-4.
Teichert, B. M. A., Bohrmann, G., and Suess, E., 2005.
Chemoherms on Hydrate Ridge – unique microbially-mediated
carbonate build-ups growing into the water column. Paleogeography, Paleoclimatology, Paleoecology, 227, 68–85.
Torres, M. E., McManus, J., and Huh, C.-A., 2002. Fluid seepage
along the San Clemente fault scarp: impact on the geochemical
barium cycles on a basin-wide scale. Earth and Planetary Science Letters, 203, 181–194.
Torres, M.E., J-H. Kim, J. Choi, J-B Ryu, J-J Bahk, M. Riedel, T.
Collett, W-L. Hong and M. Kastner. 2011. Occurrence of high salinity fluids associated with massive near-seafloor gas hydrate deposits.
In: Proceedings of the 7th International Conference on Gas Hydrates
(ICGH 2011), Edinburgh, Scotland, United Kingdom, July 17–21.
Torres, M. E., Bohrmann, G., Dubé, T. E., and Poole, F. G., 2003.
Barite deposition at modern cold seeps: analogue to paleozoic
bedded barite. Geology, 31, 897–900.
Tréhu, A. M., Flemings, P. B., Bangs, N. L., Chevalier, J., Gracia, E.,
Jonhson, J., Liu, C. S., Liu, X., Riedel, M., and Torres, M. E.,
2004. Feeding methane vents and gas hydrate deposits at south
hydrate ridge. Geophysical Research Letters, 31, L23310.
Valentine, D. L., 2011. Emerging topics in marine methane biogeochemistry. Annual Review of Marine Science, 3, 147–171.
Westbrook, G. K., Thatcher, K. E., Rohling, E. J., Piotrowski,
A. M., Pälike, H., Osborne, A. H., and Aquilina, A., 2009.
Escape of methane gas from the seabed along the West Spitsbergen continental margin. Geophysical Research Letters, 36,
L15608, doi:10.1029/2009GL039191.
Cross-references
Intraoceanic Subduction Zone
Marine Gas Hydrates
Methane in Marine Sediments
Mid-ocean Ridge Magmatism and Volcanism
Mud Volcano
Passive Plate Margins
Transform Faults
CONTINENTAL RISE
William W. Hay
Department of Geological Sciences, University of
Colorado at Boulder, Estes Park, CO, USA
Definition
The continental rise is the gently inclined slope between
the base of the continental slope and the deep ocean floor.
The expression “continental rise” was first used by
Bruce Heezen and Maurice Ewing in their account of the
effects of the 1929 Grand Banks earthquake. It was formally defined in 1959 by Heezen et al. in GSA Special
Paper 65. The Floors of the Ocean: I, The North Atlantic:
“Since we have limited the continental slope to gradients
greater than 1:40, we split off this lower portion of the continental margin into a separate province, the continental
rise” (p. 19).
In many areas, local morphologic features interfere
with the general slopes so that neither the upper nor lower
limits of the continental rise are well defined (Figure 1).
The geologic basis for the continental rise
The concept of the continental rise arose in the classic passive margin region of the western North Atlantic. There
the continental rise overlies the ocean crust bordering the
faulted and fractured continental margin. It is the site
where sediment shed from the continent into the deep
sea accumulates.
Along active margins where ocean crust is being
subducted beneath continental crust, the margin is often
marked by an ocean trench; there is no continental rise.
However in some areas where there is a great thickness
of sediment on the ocean floor entering the subduction
zone, or where the supply of sediment from the continent
into the subduction zone completely fills the trench, a narrow continental rise may develop.
What controls the configuration of the
continental rise
Nature of the crust
Where the continents have broken up, in the Atlantic,
Indian, and Arctic oceans, the continental rise overlies
the oldest ocean crust. Because the ocean crust subsides
with age, this is the region where the differences in elevation between continental and ocean crust are maximal.
Detrital sediment supply
The continental rise is the ultimate site of deposition of
sediment eroded off the continents. The current rate of
detrital sediment eroded from land and delivered to the
sea is estimated to be about 24 Â 10
12 kg/year. However,
the continental shelves can only accommodate about
10 % of this load at high sea-level stands and almost none
at sea-level lowstands. This means that most of the detrital
sediment load must be passed on to the continental slope,
where again accommodation space is very limited, and to
the deep sea. The continental rise represents the site of
accumulation of most of the sediment eroded off the continental blocks. These conditions have changed over time.
The amount of material eroded off the continental blocks
depends on topographic relief and changing climatic conditions. The amount of sediment that can accumulate on
shelves has decreased with time as subsidence of the shelf
areas has slowed. Major erosion of the continental shelves
has occurred since the lowering of sea levels associated
122
CONTINENTAL RISE
http://nbn-resolving.de/urn:nbn:de:
gbv:46-00102438-18
Römer, M., Sahling, H., Pape, T., Bohrmann, G., and Spieß, V.,
2012. Quantification of gas bubble emissions from submarine
hydrocarbon seeps at the Makran continental margin (offshore
Pakistan). Journal of Geophysical Research, 117, C10015,
doi:10.1029/2011JC007424.
Saffer, D. M., and Tobin, H. J., 2011. Hydrogeology and mechanics
of subduction zone forearcs: fluid flow and pore pressure.
Annual Review of Earth and Planetary Sciences, 39, 157–186.
Sloan, E. D., and Koh, C. A., 2008. Clathrate Hydrates of Natural
Gases, 3rd edn. Boca Raton, FL: CRC Press. 752pp.
Suess, E., 2010. Marine cold seeps Handbook of Hydrocarbon and
Lipid Microbiology. Berlin: Springer, pp. 188–203, doi:10.1007/
978-3-540-77587-4_12. ISBN 978-3-540-77587-4.
Teichert, B. M. A., Bohrmann, G., and Suess, E., 2005.
Chemoherms on Hydrate Ridge – unique microbially-mediated
carbonate build-ups growing into the water column. Paleogeography, Paleoclimatology, Paleoecology, 227, 68–85.
Torres, M. E., McManus, J., and Huh, C.-A., 2002. Fluid seepage
along the San Clemente fault scarp: impact on the geochemical
barium cycles on a basin-wide scale. Earth and Planetary Science Letters, 203, 181–194.
Torres, M.E., J-H. Kim, J. Choi, J-B Ryu, J-J Bahk, M. Riedel, T.
Collett, W-L. Hong and M. Kastner. 2011. Occurrence of high salinity fluids associated with massive near-seafloor gas hydrate deposits.
In: Proceedings of the 7th International Conference on Gas Hydrates
(ICGH 2011), Edinburgh, Scotland, United Kingdom, July 17–21.
Torres, M. E., Bohrmann, G., Dubé, T. E., and Poole, F. G., 2003.
Barite deposition at modern cold seeps: analogue to paleozoic
bedded barite. Geology, 31, 897–900.
Tréhu, A. M., Flemings, P. B., Bangs, N. L., Chevalier, J., Gracia, E.,
Jonhson, J., Liu, C. S., Liu, X., Riedel, M., and Torres, M. E.,
2004. Feeding methane vents and gas hydrate deposits at south
hydrate ridge. Geophysical Research Letters, 31, L23310.
Valentine, D. L., 2011. Emerging topics in marine methane biogeochemistry. Annual Review of Marine Science, 3, 147–171.
Westbrook, G. K., Thatcher, K. E., Rohling, E. J., Piotrowski,
A. M., Pälike, H., Osborne, A. H., and Aquilina, A., 2009.
Escape of methane gas from the seabed along the West Spitsbergen continental margin. Geophysical Research Letters, 36,
L15608, doi:10.1029/2009GL039191.
Cross-references
Intraoceanic Subduction Zone
Marine Gas Hydrates
Methane in Marine Sediments
Mid-ocean Ridge Magmatism and Volcanism
Mud Volcano
Passive Plate Margins
Transform Faults
CONTINENTAL RISE
William W. Hay
Department of Geological Sciences, University of
Colorado at Boulder, Estes Park, CO, USA
Definition
The continental rise is the gently inclined slope between
the base of the continental slope and the deep ocean floor.
The expression “continental rise” was first used by
Bruce Heezen and Maurice Ewing in their account of the
effects of the 1929 Grand Banks earthquake. It was formally defined in 1959 by Heezen et al. in GSA Special
Paper 65. The Floors of the Ocean: I, The North Atlantic:
“Since we have limited the continental slope to gradients
greater than 1:40, we split off this lower portion of the continental margin into a separate province, the continental
rise” (p. 19).
In many areas, local morphologic features interfere
with the general slopes so that neither the upper nor lower
limits of the continental rise are well defined (Figure 1).
The geologic basis for the continental rise
The concept of the continental rise arose in the classic passive margin region of the western North Atlantic. There
the continental rise overlies the ocean crust bordering the
faulted and fractured continental margin. It is the site
where sediment shed from the continent into the deep
sea accumulates.
Along active margins where ocean crust is being
subducted beneath continental crust, the margin is often
marked by an ocean trench; there is no continental rise.
However in some areas where there is a great thickness
of sediment on the ocean floor entering the subduction
zone, or where the supply of sediment from the continent
into the subduction zone completely fills the trench, a narrow continental rise may develop.
What controls the configuration of the
continental rise
Nature of the crust
Where the continents have broken up, in the Atlantic,
Indian, and Arctic oceans, the continental rise overlies
the oldest ocean crust. Because the ocean crust subsides
with age, this is the region where the differences in elevation between continental and ocean crust are maximal.
Detrital sediment supply
The continental rise is the ultimate site of deposition of
sediment eroded off the continents. The current rate of
detrital sediment eroded from land and delivered to the
sea is estimated to be about 24 Â 10
12 kg/year. However,
the continental shelves can only accommodate about
10 % of this load at high sea-level stands and almost none
at sea-level lowstands. This means that most of the detrital
sediment load must be passed on to the continental slope,
where again accommodation space is very limited, and to
the deep sea. The continental rise represents the site of
accumulation of most of the sediment eroded off the continental blocks. These conditions have changed over time.
The amount of material eroded off the continental blocks
depends on topographic relief and changing climatic conditions. The amount of sediment that can accumulate on
shelves has decreased with time as subsidence of the shelf
areas has slowed. Major erosion of the continental shelves
has occurred since the lowering of sea levels associated
122
CONTINENTAL RISE