Pitman, W., and Heirtzler, J., 1966. Magnetic anomalies over the
Pacific-Antarctic ridge. Science, 154, 1164–1171.
Raff, A. D., and Mason, R. G., 1961. Magnetic survey off the west
coast of North America, 40
N latitude to 50
N longitude. Geological Society of America Bulletin, 72, 1267–1270.
Rapp, R. P., Shimizu, N., and Norman, M. D., 2003. Growth of early
continental crust by partial melting of eclogite. Nature, 425,
605–609.
Runcorn, S. K., 1959. Rock magnetism. Science, 129, 1002–1012.
Scholl, D. W., and von Heune, R., 2007. Crustal recycling at
modern subduction zones applied to the past – issues of
crustal growth and preservation of continental basement crust,
mantle geochemistry, and supercontinent reconstruction. In
Hatcher, R. D., Jr., Carlson, M. P., McBride, J. H., and Martínez
Cataln, J. R. (eds.), 4-D Framework of Continental Crust. Boulder: Geological Society of America, Memoir, Vol.
200, pp. 9–32.
Scott, D. J., St-Onge, M. R., Lucas, S. B., and Helmstaedt, H., 1991.
Geology and chemistry of the Early Proterozoic Purtuniq
ophiolite, Cape Smith Belt, northern Quebec, Canada. In Peters,
T., et al. (eds.), Ophiolite Genesis and Evolution of the Oceanic
Lithosphere. Sultanate of Oman: Ministry of Petroleum and
Minerals, pp. 817–849.
Shirey, S. B., and Richardson, S. H., 2011. Start of the Wilson Cycle
at 3 Ga shown by diamonds from subcontinental mantle. Science, 333, 434–436.
Smithies, R. H., van Kranendonk, M. J., and Champion, D. C.,
2005. It started with a plume – early Archaean basaltic protocontinental crust. Earth and Planetary Science Letters, 238,
284–297.
Stern, R. J., 2005. Evidence from ophiolites, blueschists, and
ultrahigh-pressure metamorphic terranes that the modern episode of subduction tectonics began in Neoproterozoic time.
Geology, 33, 557–560.
Strik, G. M. H. A., Blake, T. S., Zegers, T. E., White, S. H., and
Langereis, C. G., 2003. Paleomagnetism of flood basalts in the
Pilbara Craton, Western Australia: late Archaean continental
drift and the oldest known reversal of the geomagnetic field.
Journal of Geophysical Research, 108(B12), 2551,
doi:10.1029/2003JB002475.
Valley, J. W., Peck, W. H., King, E. M., and Wilde, S. A., 2002.
A cool early Earth. Geology, 30, 351–354.
Van Kranendonk, M. J., 2011. Onset of plate tectonics. Science,
333, 413–414.
Vine, F. J., and Matthews, D. M., 1963. Magnetic anomalies over
ocean ridges. Nature, 199, 947–949.
Wilde, S. A., Valley, J. W., Peck, W. H., and Graham, C. M., 2001.
Evidence from detrital zircon for the existence of continental
crust and oceans on the Earth 4.4 Gyr ago. Nature, 409,
175–178.
Willbold, M., Hegner, E., Stracke, A., and Rocholl, A., 2009. Continental geochemical signatures in dacites from Iceland and
implications for models of early Archaean crust formation. Earth
and Planetary Science Letters, 279, 44–52.
Wilson, J. T., 1965. A new class of faults and their bearing on continental drift. Nature, 207, 343–347.
Cross-references
Driving Forces: Slab Pull, Ridge Push
Hot Spots and Mantle Plumes
Intraplate Magmatism
Plate Tectonics
Subduction
Wilson Cycle
ANOXIC OCEANS
Christian März
1 and Hans-Jürgen Brumsack
2
1
School of Civil Engineering and Geosciences (CEGS),
Newcastle University, Newcastle upon Tyne, UK
2
Institute for Chemistry and Biology of the Marine
Environment, University of Oldenburg, Oldenburg,
Germany
Definition
A large body of open marine water free of dissolved
molecular oxygen and potentially containing dissolved
hydrogen sulfide.
Introduction
Today’s world oceans are dominated by oxic water
masses, except for some marginal basins like the Black
Sea, fjords, upwelling areas, and so-called coastal “anoxic
dead zones.” However, since the formation of oceans on
Earth, anoxic (oxygen-free) conditions have occurred frequently in parts of the global ocean, leading to the deposition of organic-rich sediments that subsequently generated
oil or gas, the main energy source for our modern civilization. Here we will focus on deep ocean anoxia, their environmental controls, and their geological expressions.
The Proterozoic
Throughout large parts of the Precambrian, the oceans
were anoxic. Oxygen-producing photosynthetic organisms like algae were only beginning to evolve, and atmospheric oxygen levels were orders of magnitude lower
than at present. Due to this oxygen-poor atmosphere, sulfate was not produced in significant quantities by chemical
weathering of magmatic rocks on land, and sulfate concentrations in the early oceans were low. In contrast,
dissolved Fe concentrations were very high due to hydrothermal input related to ocean crust formation, reductive
weathering on land, and possibly diagenetic Fe release
from sediments. These oxygen-free, sulfate-poor but
iron-rich (ferruginous) oceans persisted over much of the
Proterozoic until the Great Oxidation Event (Canfield,
1998), which initiated the global deposition of banded iron
formations (BIFs). When atmospheric oxygen concentrations reached a threshold, the oxidative weathering of sulfide minerals led to the establishment of the marine sulfate
pool. Consequently, organic matter degradation by microbial sulfate reduction started to release hydrogen sulfide
into the water column. As the dissolved Fe in the water
column reacted with hydrogen sulfide to form pyrite, ferruginous conditions were gradually replaced by sulfidic
(euxinic) conditions in the marine environment. With
increasing atmospheric oxygen, the spatial extent of
marine anoxia/euxinia was reduced, only persisting in certain ocean regions (Poulton et al., 2010). While the expansion and duration of Proterozoic deep ocean anoxia were
never reached again, there were still periods in the Phanerozoic with widely distributed deep ocean anoxia.
20
ANOXIC OCEANS
Pacific-Antarctic ridge. Science, 154, 1164–1171.
Raff, A. D., and Mason, R. G., 1961. Magnetic survey off the west
coast of North America, 40
N latitude to 50
N longitude. Geological Society of America Bulletin, 72, 1267–1270.
Rapp, R. P., Shimizu, N., and Norman, M. D., 2003. Growth of early
continental crust by partial melting of eclogite. Nature, 425,
605–609.
Runcorn, S. K., 1959. Rock magnetism. Science, 129, 1002–1012.
Scholl, D. W., and von Heune, R., 2007. Crustal recycling at
modern subduction zones applied to the past – issues of
crustal growth and preservation of continental basement crust,
mantle geochemistry, and supercontinent reconstruction. In
Hatcher, R. D., Jr., Carlson, M. P., McBride, J. H., and Martínez
Cataln, J. R. (eds.), 4-D Framework of Continental Crust. Boulder: Geological Society of America, Memoir, Vol.
200, pp. 9–32.
Scott, D. J., St-Onge, M. R., Lucas, S. B., and Helmstaedt, H., 1991.
Geology and chemistry of the Early Proterozoic Purtuniq
ophiolite, Cape Smith Belt, northern Quebec, Canada. In Peters,
T., et al. (eds.), Ophiolite Genesis and Evolution of the Oceanic
Lithosphere. Sultanate of Oman: Ministry of Petroleum and
Minerals, pp. 817–849.
Shirey, S. B., and Richardson, S. H., 2011. Start of the Wilson Cycle
at 3 Ga shown by diamonds from subcontinental mantle. Science, 333, 434–436.
Smithies, R. H., van Kranendonk, M. J., and Champion, D. C.,
2005. It started with a plume – early Archaean basaltic protocontinental crust. Earth and Planetary Science Letters, 238,
284–297.
Stern, R. J., 2005. Evidence from ophiolites, blueschists, and
ultrahigh-pressure metamorphic terranes that the modern episode of subduction tectonics began in Neoproterozoic time.
Geology, 33, 557–560.
Strik, G. M. H. A., Blake, T. S., Zegers, T. E., White, S. H., and
Langereis, C. G., 2003. Paleomagnetism of flood basalts in the
Pilbara Craton, Western Australia: late Archaean continental
drift and the oldest known reversal of the geomagnetic field.
Journal of Geophysical Research, 108(B12), 2551,
doi:10.1029/2003JB002475.
Valley, J. W., Peck, W. H., King, E. M., and Wilde, S. A., 2002.
A cool early Earth. Geology, 30, 351–354.
Van Kranendonk, M. J., 2011. Onset of plate tectonics. Science,
333, 413–414.
Vine, F. J., and Matthews, D. M., 1963. Magnetic anomalies over
ocean ridges. Nature, 199, 947–949.
Wilde, S. A., Valley, J. W., Peck, W. H., and Graham, C. M., 2001.
Evidence from detrital zircon for the existence of continental
crust and oceans on the Earth 4.4 Gyr ago. Nature, 409,
175–178.
Willbold, M., Hegner, E., Stracke, A., and Rocholl, A., 2009. Continental geochemical signatures in dacites from Iceland and
implications for models of early Archaean crust formation. Earth
and Planetary Science Letters, 279, 44–52.
Wilson, J. T., 1965. A new class of faults and their bearing on continental drift. Nature, 207, 343–347.
Cross-references
Driving Forces: Slab Pull, Ridge Push
Hot Spots and Mantle Plumes
Intraplate Magmatism
Plate Tectonics
Subduction
Wilson Cycle
ANOXIC OCEANS
Christian März
1 and Hans-Jürgen Brumsack
2
1
School of Civil Engineering and Geosciences (CEGS),
Newcastle University, Newcastle upon Tyne, UK
2
Institute for Chemistry and Biology of the Marine
Environment, University of Oldenburg, Oldenburg,
Germany
Definition
A large body of open marine water free of dissolved
molecular oxygen and potentially containing dissolved
hydrogen sulfide.
Introduction
Today’s world oceans are dominated by oxic water
masses, except for some marginal basins like the Black
Sea, fjords, upwelling areas, and so-called coastal “anoxic
dead zones.” However, since the formation of oceans on
Earth, anoxic (oxygen-free) conditions have occurred frequently in parts of the global ocean, leading to the deposition of organic-rich sediments that subsequently generated
oil or gas, the main energy source for our modern civilization. Here we will focus on deep ocean anoxia, their environmental controls, and their geological expressions.
The Proterozoic
Throughout large parts of the Precambrian, the oceans
were anoxic. Oxygen-producing photosynthetic organisms like algae were only beginning to evolve, and atmospheric oxygen levels were orders of magnitude lower
than at present. Due to this oxygen-poor atmosphere, sulfate was not produced in significant quantities by chemical
weathering of magmatic rocks on land, and sulfate concentrations in the early oceans were low. In contrast,
dissolved Fe concentrations were very high due to hydrothermal input related to ocean crust formation, reductive
weathering on land, and possibly diagenetic Fe release
from sediments. These oxygen-free, sulfate-poor but
iron-rich (ferruginous) oceans persisted over much of the
Proterozoic until the Great Oxidation Event (Canfield,
1998), which initiated the global deposition of banded iron
formations (BIFs). When atmospheric oxygen concentrations reached a threshold, the oxidative weathering of sulfide minerals led to the establishment of the marine sulfate
pool. Consequently, organic matter degradation by microbial sulfate reduction started to release hydrogen sulfide
into the water column. As the dissolved Fe in the water
column reacted with hydrogen sulfide to form pyrite, ferruginous conditions were gradually replaced by sulfidic
(euxinic) conditions in the marine environment. With
increasing atmospheric oxygen, the spatial extent of
marine anoxia/euxinia was reduced, only persisting in certain ocean regions (Poulton et al., 2010). While the expansion and duration of Proterozoic deep ocean anoxia were
never reached again, there were still periods in the Phanerozoic with widely distributed deep ocean anoxia.
20
ANOXIC OCEANS