A marine transgression occurs if the rate of relative
sea-level rise cannot be compensated by sediment supply
and the coastline shifts landward (Posamentier et al.,
1988; Posamentier and Allen, 1999; Catuneanu, 2002),
so that former land is submerged and converted into seafloor. The relative sea-level change is an effect of eustacy
modified by tectonic/isostatic vertical displacements of
the Earth’s crust. The opposite of transgression is “regression”, which occurs if the relative sea-level drops,
emerging former seafloor as land. During a transgression,
the advancing highly dynamic coastal zone reworks
the surface of the submerged land, resulting in the formation of coarse coastal sediments. These sediments can
be used as “transgression horizons” in the geological
record as an indicator of an advancing ancient sea
and form ideal markers in stratigraphic correlation of
well sections and seismic records (sequence stratigraphy,
seismic stratigraphy). In the seismic record, reflectors
marking transgressive strata are characterized by
“onlapping” at their lower boundary. Relative sea-level
changes bound cycles in the Earth’s history which can
be hierarchically ordered based on the time spans of millions of years to millennia (Suess et al., 1906; von
Bubnoff, 1954; Vail et al., 1991; Seibold and Berger,
1993).
Bibliography
Catuneanu, O., 2002. Sequence stratigraphy of clastic systems: concepts, merits, and pitfalls. Journal of African Earth Sciences,
35(1), 1–43.
Posamentier, H. W., and Allen, G. P., 1999. Siliciclastic Sequence
Stratigraphy: Concepts and Applications. SEPM Concepts
Sedimentol. Paleontol. Ser. vol. 7, Tulsa, Oklahoma: Society
for Sedimentary Geology.
Posamentier, H. W., Jervey, M. T., and Vail, P. R., 1988. Eustatic
controls on clastic deposition. I. Conceptual framework. In:
Wilgus, C. K., Hastings, B. S., Kendall, C. G. St. C.,
Posamentier, H. W., Ross, C. A., and Van Wagoner, J. C.
(eds.), Sea Level Changes – An Integrated Approach. SEPM
Special Publication No 42, Tulsa, Oklahoma: Society for Sedimentary Geology. pp. 110–124.
Seibold, E., and Berger, W. H., 1993. The Sea Floor – An Introduction to Marine Geology. Berlin/Heidelberg: Springer.
Suess, E., Sollas, W. J., and Sollas, H. B. C., 1906. The Face of the
Earth. Oxford: Clarendon.
Vail, P. R., Audemard, I. P., Bowman, S. A., Eisner, P. N., and PerezCruz, C., 1991. The stratigraphic signatures of tectonics, eustasy
and sedimentology – an overview. In Einsele, G. (ed.), Cycles
and Events in Stratigraphy. Berlin: Springer.
von Bubnoff, S., 1954. Grundprobleme der Geologie. Berlin:
Akademie Verlag.
Cross-references
Marine Regression
Relative Sea-level (RSL) Cycle
Sea-Level
Sedimentary Sequence
Sequence Stratigraphy
MASS WASTING
Jan Sverre Laberg, Tore O. Vorren and Matthias Forwick
Department of Geology, University of Tromsø, Tromsø,
Norway
Synonyms
Mass movement; Slope failure
Driven by the pull of gravity, mass wasting comprises all
the sedimentary processes related to remobilization of sediments deposited on slopes including creep, sliding,
slumping, flow, and fall. The initial stage of
remobilization is limited to a layer or zone of weakness,
i.e., a stratigraphic interval with physical properties
allowing liquefaction from an external trigger. This interval may be located from meters to >100 m below the
sea floor. Following the initial liquefaction, the overlying
succession is mobilized as blocks, slabs, or ridges and
deformation mainly occurs in a basal shear zone. During
further movement, disintegration into debris flows or
mudflows with or without blocks of consolidated sediments may occur. The incorporation of ambient water during disintegration may lead to the development of
turbidity currents due to erosion of the frontal part. If the
velocity of the flow reaches a critical value, hydroplaning
may occur (Mohrig et al., 1998).
The initial stage of mass wasting may be located anywhere on a slope and involve gradients <1
. Many slope
failures have a retrogressive development, i.e., that
shallower parts of the slope successively get affected due
to the loss of support from below (Kvalstad et al., 2005).
In such cases, weak layers or zones at different stratigraphic levels may be involved. Such a development
may last from hours to days, and individual flows can vary
in volume and run-out distance.
The shallowest part of the slide scar is delineated by a
slope-parallel or amphitheater-shaped headwall or scarp
that may be >100 m high. Sidewalls form by lateral shear
in downslope direction. However, they sometimes also
involve compressional features. Where weak layers at different stratigraphic depths are involved, prominent escarpments within the slide scar develop. Slide scars may be
partly or completely evacuated.
Parts of the evacuated material are frequently deposited
in areas with marked reductions in slope gradients, as, e.g.,
at the transition from the continental slope to the continental rise. Due to the reduction in slope gradient, the shear
stress drops below the shear strength of the reworked sediments, leading, e.g., to freezing “en masse” of debris
flows/mudflows. However, some debris flows/mudflows
may proceed beyond the base of the continental rise and
onto the abyssal plain. Run-out distances of debris flows
Tore O. Vorren is deceased.
490
MASS WASTING
sea-level rise cannot be compensated by sediment supply
and the coastline shifts landward (Posamentier et al.,
1988; Posamentier and Allen, 1999; Catuneanu, 2002),
so that former land is submerged and converted into seafloor. The relative sea-level change is an effect of eustacy
modified by tectonic/isostatic vertical displacements of
the Earth’s crust. The opposite of transgression is “regression”, which occurs if the relative sea-level drops,
emerging former seafloor as land. During a transgression,
the advancing highly dynamic coastal zone reworks
the surface of the submerged land, resulting in the formation of coarse coastal sediments. These sediments can
be used as “transgression horizons” in the geological
record as an indicator of an advancing ancient sea
and form ideal markers in stratigraphic correlation of
well sections and seismic records (sequence stratigraphy,
seismic stratigraphy). In the seismic record, reflectors
marking transgressive strata are characterized by
“onlapping” at their lower boundary. Relative sea-level
changes bound cycles in the Earth’s history which can
be hierarchically ordered based on the time spans of millions of years to millennia (Suess et al., 1906; von
Bubnoff, 1954; Vail et al., 1991; Seibold and Berger,
1993).
Bibliography
Catuneanu, O., 2002. Sequence stratigraphy of clastic systems: concepts, merits, and pitfalls. Journal of African Earth Sciences,
35(1), 1–43.
Posamentier, H. W., and Allen, G. P., 1999. Siliciclastic Sequence
Stratigraphy: Concepts and Applications. SEPM Concepts
Sedimentol. Paleontol. Ser. vol. 7, Tulsa, Oklahoma: Society
for Sedimentary Geology.
Posamentier, H. W., Jervey, M. T., and Vail, P. R., 1988. Eustatic
controls on clastic deposition. I. Conceptual framework. In:
Wilgus, C. K., Hastings, B. S., Kendall, C. G. St. C.,
Posamentier, H. W., Ross, C. A., and Van Wagoner, J. C.
(eds.), Sea Level Changes – An Integrated Approach. SEPM
Special Publication No 42, Tulsa, Oklahoma: Society for Sedimentary Geology. pp. 110–124.
Seibold, E., and Berger, W. H., 1993. The Sea Floor – An Introduction to Marine Geology. Berlin/Heidelberg: Springer.
Suess, E., Sollas, W. J., and Sollas, H. B. C., 1906. The Face of the
Earth. Oxford: Clarendon.
Vail, P. R., Audemard, I. P., Bowman, S. A., Eisner, P. N., and PerezCruz, C., 1991. The stratigraphic signatures of tectonics, eustasy
and sedimentology – an overview. In Einsele, G. (ed.), Cycles
and Events in Stratigraphy. Berlin: Springer.
von Bubnoff, S., 1954. Grundprobleme der Geologie. Berlin:
Akademie Verlag.
Cross-references
Marine Regression
Relative Sea-level (RSL) Cycle
Sea-Level
Sedimentary Sequence
Sequence Stratigraphy
MASS WASTING
Jan Sverre Laberg, Tore O. Vorren and Matthias Forwick
Department of Geology, University of Tromsø, Tromsø,
Norway
Synonyms
Mass movement; Slope failure
Driven by the pull of gravity, mass wasting comprises all
the sedimentary processes related to remobilization of sediments deposited on slopes including creep, sliding,
slumping, flow, and fall. The initial stage of
remobilization is limited to a layer or zone of weakness,
i.e., a stratigraphic interval with physical properties
allowing liquefaction from an external trigger. This interval may be located from meters to >100 m below the
sea floor. Following the initial liquefaction, the overlying
succession is mobilized as blocks, slabs, or ridges and
deformation mainly occurs in a basal shear zone. During
further movement, disintegration into debris flows or
mudflows with or without blocks of consolidated sediments may occur. The incorporation of ambient water during disintegration may lead to the development of
turbidity currents due to erosion of the frontal part. If the
velocity of the flow reaches a critical value, hydroplaning
may occur (Mohrig et al., 1998).
The initial stage of mass wasting may be located anywhere on a slope and involve gradients <1
. Many slope
failures have a retrogressive development, i.e., that
shallower parts of the slope successively get affected due
to the loss of support from below (Kvalstad et al., 2005).
In such cases, weak layers or zones at different stratigraphic levels may be involved. Such a development
may last from hours to days, and individual flows can vary
in volume and run-out distance.
The shallowest part of the slide scar is delineated by a
slope-parallel or amphitheater-shaped headwall or scarp
that may be >100 m high. Sidewalls form by lateral shear
in downslope direction. However, they sometimes also
involve compressional features. Where weak layers at different stratigraphic depths are involved, prominent escarpments within the slide scar develop. Slide scars may be
partly or completely evacuated.
Parts of the evacuated material are frequently deposited
in areas with marked reductions in slope gradients, as, e.g.,
at the transition from the continental slope to the continental rise. Due to the reduction in slope gradient, the shear
stress drops below the shear strength of the reworked sediments, leading, e.g., to freezing “en masse” of debris
flows/mudflows. However, some debris flows/mudflows
may proceed beyond the base of the continental rise and
onto the abyssal plain. Run-out distances of debris flows
Tore O. Vorren is deceased.
490
MASS WASTING