A major shift in circumglobal circulation occurred in
the mid-to late Tertiary. From about 165 to 8 Ma,
circumglobal ocean circulation was possible through the
Tethys, located about 20–30
north of the equator. However, the Tethys consisted of many basins separated by
swells, both of which were constantly changing, affecting
the width and depth of shallow water passages. Connections at depth were even more variable, and it is possible
that a deep passage through the entire Tethys never
existed. As the Tethys closed, circumglobal circulation
shifted to the high latitudes of the Southern Hemisphere.
A continuous path for circulation around the Antarctic
continent became possible with the opening of the Drake
Passage and Tasman Gateway during the Eocene.
Seaways across the continental blocks were associated
with the high sea levels of the Cretaceous. These are shown
as dotted lines in Figure 1d. The Western Interior Seaway of
North America connected the Gulf of Mexico with the Arctic Ocean, but probably had an arm via the present Hudson
Bay region across Greenland to northern Europe. Finally,
during the middle of the Cretaceous, a seaway extended
across Africa from the northern South Atlantic to the Mediterranean. In the latest Cretaceous and early Tertiary, a very
shallow seaway extended across western Siberia periodically connecting the Tethys with the Arctic.
A shallow seaway from the North Atlantic to the Arctic
between Greenland and Europe (not shown in Figure 1d)
existed from the time of the separation of North America
and Africa until spreading began to separate Greenland
from Europe to form the Greenland-Iceland-Norwegian
(GIN) Sea. However, a deep connection between the Arctic and North Atlantic is blocked by the GreenlandIceland-Scotland Ridge.
The opening and closing of major interconnections
between the ocean basins are shown in Figure 1e. Although
very important over the long term, these were gradual
“events” that occurred over intervals of a few million years.
Opening passageways were initially shallow and became
deeper with time, just as closures initially restricted deep water
circulation and ended by shutting off surface circulation.
Summary
Events are episodes of change recorded by depositional,
erosional, or geochemical features. They may be only
local or regional in extent or global, reflecting significant
trends in ocean evolution.
Bibliography
Dercourt, J., Ricou, L. E., Adamia, S. A., Csaszar, G., Funk, H.,
Lefeld, J., Rakus, M., Sandulescu, M., Tollman, A., and
Tchoumatchenko, P., 1990. Northern Margin of Tethys; Paleogeographical Maps. Bratislava: Statny Geologicky Ustav
Dionyza Stura. 11 sheets.
Dercourt, J., Ricou, L.-E., and Vrielynck, B. (eds.), 1993. Atlas of
Tethys Paleoenvironmental Maps. Paris: Gauthier-Villars.
14 maps + explanatory notes.
Dercourt, J., Gaetani, M., Vrielynck, B., Barrier, E., Biju-Duval, B.,
Brunet, M. F., Cadet, J. P., Crasquin, S., and Sandulescu, M.,
2000. Peri-Tethys Paleogeographical Atlas. Paris: GauthierVillars. 24 maps + explanatory notes.
Erba, E., 2004. Calcareous nannofossils and Mesozoic oceanic
anoxic events. Marine Micropaleontology, 52, 85–106.
Haq, B. U., Hardenbol, J., and Vail, P. R., 1987. Chronology of fluctuating sea levels since the Triassic. Science, 235, 1156–1167.
Hay, W. W., Migdisov, A., Balukhovsky, A. N., Wold, C. N., Flögel,
S., and Söding, E., 2006. Evaporites and the salinity of the ocean
during the Phanerozoic: implications for climate, ocean circulation
and
life.
Palaeogeography
Palaeoclimatology
Palaeoecology, 240, 3–46.
Hohbein, M. W., Sexton, P. F., and Cartwright, J. A., 2012. Onset of
North Atlantic deep water production coincident with inception
of the Cenozoic global cooling trend. Geology, 40, 255–258.
Holser, W. T., 1977. Catastrophic chemical events in the history of
the ocean. Nature, 267, 403–498.
Holser, W. T., 1985. Gradual and abrupt shift in ocean chemistry
during Phanerozoic time. In Holland, H. D., and Trendall, A. F.
(eds.), Patterns of Change in Earth Evolution, Dahlem
Konferenzen 1984. Berlin: Springer, pp. 123–143.
Jenkyns, H. C., 1999. Mesozoic anoxic events and paleoclimate.
Zentralblatt für Geologie und Paläontologie, Teil I 1998. Heft,
5–6, 943–949.
Kazmin, V. G., and Napatov, L. M. (eds.), 1998. The Paleogeographic Atlas of Northern Eurasia. Moscow: Institute of Tectonics of the Lithospheric Plates, Russian Academy of Natural
Sciences. 26 maps.
Knauth, L. P., 2005. Temperature and salinity history of the Precambrian ocean: implications for the course of microbial evolution.
Palaeogeography Palaeoclimatology Palaeoecology, 219, 53–69.
Müller, R. D., Sdrolias, M., Gaina, C., and Roest, W. R., 2008. Age,
spreading rates, and spreading asymmetry of the world’s ocean
crust. Geochemistry, Geophysics, Geosystems, 9, Q04006,
doi:10.1029/2007GC001743. 19 pp.
Schlanger, S. O., and Jenkyns, H. C., 1976. Cretaceous oceanic
anoxic events: causes and consequences. Geologie en Mijnbouw,
55, 179–184.
Sclater, J. G., Jaupart, C., and Galson, D., 1980. The heat flow
through oceanic and continental crust and the heat loss of the
Earth. Reviews of Geophysics and Space Physics, 18, 269–311.
Cross-references
Anoxic Oceans
Calcite Compensation Depth (CCD)
Erosion-Hiatuses
Marine Evaporites
Sedimentary Sequence
EXPLOSIVE VOLCANISM IN THE DEEP SEA
Christoph Helo
Institute of Geosciences, Johannes Gutenberg-University
Mainz, Mainz, Germany
Definition
Explosive
eruption
Eruption characterized by magma
fragmentation at the vent, producing
pyroclasts.
Effusive
eruption
Extrusion of magma as lava flow.
EXPLOSIVE VOLCANISM IN THE DEEP SEA
241
the mid-to late Tertiary. From about 165 to 8 Ma,
circumglobal ocean circulation was possible through the
Tethys, located about 20–30
north of the equator. However, the Tethys consisted of many basins separated by
swells, both of which were constantly changing, affecting
the width and depth of shallow water passages. Connections at depth were even more variable, and it is possible
that a deep passage through the entire Tethys never
existed. As the Tethys closed, circumglobal circulation
shifted to the high latitudes of the Southern Hemisphere.
A continuous path for circulation around the Antarctic
continent became possible with the opening of the Drake
Passage and Tasman Gateway during the Eocene.
Seaways across the continental blocks were associated
with the high sea levels of the Cretaceous. These are shown
as dotted lines in Figure 1d. The Western Interior Seaway of
North America connected the Gulf of Mexico with the Arctic Ocean, but probably had an arm via the present Hudson
Bay region across Greenland to northern Europe. Finally,
during the middle of the Cretaceous, a seaway extended
across Africa from the northern South Atlantic to the Mediterranean. In the latest Cretaceous and early Tertiary, a very
shallow seaway extended across western Siberia periodically connecting the Tethys with the Arctic.
A shallow seaway from the North Atlantic to the Arctic
between Greenland and Europe (not shown in Figure 1d)
existed from the time of the separation of North America
and Africa until spreading began to separate Greenland
from Europe to form the Greenland-Iceland-Norwegian
(GIN) Sea. However, a deep connection between the Arctic and North Atlantic is blocked by the GreenlandIceland-Scotland Ridge.
The opening and closing of major interconnections
between the ocean basins are shown in Figure 1e. Although
very important over the long term, these were gradual
“events” that occurred over intervals of a few million years.
Opening passageways were initially shallow and became
deeper with time, just as closures initially restricted deep water
circulation and ended by shutting off surface circulation.
Summary
Events are episodes of change recorded by depositional,
erosional, or geochemical features. They may be only
local or regional in extent or global, reflecting significant
trends in ocean evolution.
Bibliography
Dercourt, J., Ricou, L. E., Adamia, S. A., Csaszar, G., Funk, H.,
Lefeld, J., Rakus, M., Sandulescu, M., Tollman, A., and
Tchoumatchenko, P., 1990. Northern Margin of Tethys; Paleogeographical Maps. Bratislava: Statny Geologicky Ustav
Dionyza Stura. 11 sheets.
Dercourt, J., Ricou, L.-E., and Vrielynck, B. (eds.), 1993. Atlas of
Tethys Paleoenvironmental Maps. Paris: Gauthier-Villars.
14 maps + explanatory notes.
Dercourt, J., Gaetani, M., Vrielynck, B., Barrier, E., Biju-Duval, B.,
Brunet, M. F., Cadet, J. P., Crasquin, S., and Sandulescu, M.,
2000. Peri-Tethys Paleogeographical Atlas. Paris: GauthierVillars. 24 maps + explanatory notes.
Erba, E., 2004. Calcareous nannofossils and Mesozoic oceanic
anoxic events. Marine Micropaleontology, 52, 85–106.
Haq, B. U., Hardenbol, J., and Vail, P. R., 1987. Chronology of fluctuating sea levels since the Triassic. Science, 235, 1156–1167.
Hay, W. W., Migdisov, A., Balukhovsky, A. N., Wold, C. N., Flögel,
S., and Söding, E., 2006. Evaporites and the salinity of the ocean
during the Phanerozoic: implications for climate, ocean circulation
and
life.
Palaeogeography
Palaeoclimatology
Palaeoecology, 240, 3–46.
Hohbein, M. W., Sexton, P. F., and Cartwright, J. A., 2012. Onset of
North Atlantic deep water production coincident with inception
of the Cenozoic global cooling trend. Geology, 40, 255–258.
Holser, W. T., 1977. Catastrophic chemical events in the history of
the ocean. Nature, 267, 403–498.
Holser, W. T., 1985. Gradual and abrupt shift in ocean chemistry
during Phanerozoic time. In Holland, H. D., and Trendall, A. F.
(eds.), Patterns of Change in Earth Evolution, Dahlem
Konferenzen 1984. Berlin: Springer, pp. 123–143.
Jenkyns, H. C., 1999. Mesozoic anoxic events and paleoclimate.
Zentralblatt für Geologie und Paläontologie, Teil I 1998. Heft,
5–6, 943–949.
Kazmin, V. G., and Napatov, L. M. (eds.), 1998. The Paleogeographic Atlas of Northern Eurasia. Moscow: Institute of Tectonics of the Lithospheric Plates, Russian Academy of Natural
Sciences. 26 maps.
Knauth, L. P., 2005. Temperature and salinity history of the Precambrian ocean: implications for the course of microbial evolution.
Palaeogeography Palaeoclimatology Palaeoecology, 219, 53–69.
Müller, R. D., Sdrolias, M., Gaina, C., and Roest, W. R., 2008. Age,
spreading rates, and spreading asymmetry of the world’s ocean
crust. Geochemistry, Geophysics, Geosystems, 9, Q04006,
doi:10.1029/2007GC001743. 19 pp.
Schlanger, S. O., and Jenkyns, H. C., 1976. Cretaceous oceanic
anoxic events: causes and consequences. Geologie en Mijnbouw,
55, 179–184.
Sclater, J. G., Jaupart, C., and Galson, D., 1980. The heat flow
through oceanic and continental crust and the heat loss of the
Earth. Reviews of Geophysics and Space Physics, 18, 269–311.
Cross-references
Anoxic Oceans
Calcite Compensation Depth (CCD)
Erosion-Hiatuses
Marine Evaporites
Sedimentary Sequence
EXPLOSIVE VOLCANISM IN THE DEEP SEA
Christoph Helo
Institute of Geosciences, Johannes Gutenberg-University
Mainz, Mainz, Germany
Definition
Explosive
eruption
Eruption characterized by magma
fragmentation at the vent, producing
pyroclasts.
Effusive
eruption
Extrusion of magma as lava flow.
EXPLOSIVE VOLCANISM IN THE DEEP SEA
241