Marine terrace
Encyclopedia
A marine terrace, coastal terrace, raised beach or perched coastline is a relatively flat, horizontal or gently inclined surface of marine origin, mostly an old abrasion platform which has been lifted out of the sphere of wave activity (sometimes called "tread"). Thus it lies above or under the current sea level
, depending on its time of formation. It is bounded by a steeper ascending slope on the landward side and a steeper descending slope on the seaward side (sometimes called "riser"). Due to its reasonably flat shape it is often used for anthropogenic structures like settlements and infrastructure
.
range with commonly a linear to concave profile. The width is very variable, reaching up to 1000 m, and seems to differ between northern
and southern hemisphere
. The cliff
faces, delimiting the platform, can vary in steepness depending on the relative roles of marine and subaerial
processes. At the intersection of the former shore (wave-cut/abrasion-) platform
and the rising cliff face it commonly retains a shoreline angle or inner edge (notch) which indicates the location of the shoreline at the time of maximum sea ingression and therefore a paleo sea level
. Sub-horizontal platforms usually terminate in a low tide cliff and it is believed that the occurrence of these platforms depends on tidal activity. Marine terraces can extend for several tens of kilometers parallel to the coast
.
Older terraces are covered by marine and/or alluvial
or colluvial
materials while the uppermost terrace levels usually are less well-preserved. While marine terraces in areas of relatively rapid uplift rates (> 1 mm/year) can often be correlated to individual interglacial
periods or stages, those in areas of slower uplift rates may have a polycyclic origin with stages of returning sea level
s after times of exposure to weathering
.
Marine terraces can be covered by a wide variety of soil
s with complex histories and different ages. In protected areas allochtonous
sandy parent materials from tsunami deposit
s may be found. Common soil types found on marine terraces include Planosols and Solonetz
.
The formation of marine terraces is controlled by changes in environmental conditions and by tectonic activity
during recent geological times
. Changes in climatic conditions
have led to eustatic sea-level oscillations and isostatic movements of the earth’s crust
, especially with the changes between glacial
and interglacial
periods.
Processes of eustasy lead to glacioeustatic sea level fluctuations due to changes of the water volume in the oceans and hence to regressions
and transgressions of the shoreline. E.g. at times of maximum glacier extend during the last glacial period the sea level
was about 100 m lower compared to today. Eustatic sea level changes
can also be caused by changes of the void volume of the oceans, either through sedimento-eustasy or tectono-eustasy.
Processes of isostasy
involve the uplift of continental crust
s including their shorelines. Today the process of glacial isostatic adjustment
mainly applies to during Pleistocene
glaciated areas. In Scandinavia
, for instance, the present rate of uplift reaches up to 10 mm/year.
In general, eustatic marine terraces were formed during separate sea level
highstands of interglacial
stages and can be correlated to Marine Oxygene Isotopic Stages (MIS)
. Glacioisostatic marine terraces were mainly created during stillstands of the isostatic uplift. When eustasy was the main factor for the formation of marine terraces, derived sea level
fluctuations can indicate former climate change
s. This conclusion has to be treated with care, as isostatic adjustment
s and tectonic activities
can be extensively overcompensated by an eustatic sea level rise. Thus, in areas of both eustatic and isostatic
or tectonic
influences, the course of the relative sea level curve can be complicated. Hence most of today’s marine terrace sequences were formed by a combination of tectonic coastal uplift and Quaternary
sea level fluctuations.
Jerky tectonic
uplifts can also lead to marked terrace steps while smooth relative sea level
changes may not result in obvious terraces and their formations are often not referred to as marine terraces.
carried in the waves. Erosion
also takes place in connection with weathering
and cavitation
. The speed of erosion is highly dependent on the shoreline material (hardness of rock), the bathymetry
and the bedrock
properties and can be between only a few millimeters per year for granitic
rocks and more than 10m per year for volcanic ejecta
. The retreat of the sea cliff
generates a shore (wave-cut/abrasion-) platform
through the process of abrasion
. A relative change of the sea level
leads to regressions
or transgressions and eventually forms another terrace (marine-cut terrace) at a different altitude while notches in the cliff face indicate short stillstands.
It is believed that the terrace gradient increases with tidal
range and decreases with rock resistance. In addition the relationship between terrace width and the strength of the rock is inverse and higher rates of uplift and subsidence as well as a higher slope of the hinterland
increases the number of terraces formed during a certain time.
Furthermore shore platforms
are formed by denudation
and marine-built terraces arise from accumulations of materials removed by shore erosion. Thus a marine terrace can be formed by both erosion
and accumulation. However, there is an ongoing debate about the roles of wave erosion and weathering
in the formation of shore platforms
.
Reef flats or uplifted coral reefs are another kind of marine terrace found in intertropical regions. They are a result of biological activity, shoreline advance and accumulation of reef
materials.
While a terrace sequence can date back hundreds of thousands of years, its degradation is a rather fast process. On the one hand a deeper transgression of cliffs into the shoreline may completely destroy previous terraces; on the other hand older terraces might be decayed or covered by deposits, colluvia
or alluvial fan
s. Erosion and backwearing of slopes caused by incisive streams play another important role in this degradation process.
aerial photographic interpretation
(ca. 1 : 10,000 - 25,000), on-site inspections with topographic map
s (ca. 1 : 10,000) and analysis of eroded and accumulated material. Moreover the exact altitude can be determined with an aneroid barometer or preferably with a levelling instrument mounted on a tripod. It should be measured with the accuracy of 1 cm and at about every 50 - 100 m, depending on the topography. In remote areas technics of photogrammetry
and tacheometry
can be applied.
on the altitude as the most important criterion to distinguish coast lines of different ages. Moreover individual marine terraces can be correlated based on their size and continuity. Also paleo-soils as well as glacial, fluvial, eolian and periglacial
landforms and sediment
s may be used to find correlations between terraces. On New Zealand’s North Island, for instance, tephra
and loess
were used to date and correlate marine terraces. At the terminus advance of former glacier
s marine terraces can be correlated by their size, as their width decreases with age due to the slowly thawing glaciers along the coast line.
The lithostratigraphic
approach uses typical sequences of sediment
and rock strata to prove sea level
fluctuations on the basis of an alternation of terrestrial and marine sediments or littoral and shallow marine sediments. Those strata show typical layers of transgressive and regressive patterns. However, an unconformity
in the sediment sequence might make this analysis difficult.
The biostratigraphic
approach uses remains of organisms which can indicate the age of a marine terrace. For that often mollusc shell
s, foraminifera
or pollen
are used. Especially Mollusca
can show specific properties depending on their depth of sedimentation
. Thus they can be used to estimate former water depths.
Marine terraces are often correlated to Marine Oxygene Isotopic Stages (MIS)
(e.g. Johnson, M. E.; Libbey, L. K. 1997) and can also be roughly dated using their stratigraphic position.
, which is the most common one. E.g. this method has been used on the North Island of New Zealand to date several marine terraces. It utilizes terrestrial biogenic materials
in coastal sediment
s such as mollusc shell
s analyzing the 14C isotope
. In some cases dating based on the 230Th/234U ratio was applied though in case of detrital contamination or low Uranium
concentrations a high resolution dating was found to be difficult. In a study in southern Italy
paleomagnetism
was used to carry out paleomagnetic datings and luminescence dating (OSL)
was used in different studies on the San Andreas Fault
and on the Quaternary
Eupcheon Fault in South Korea
.
In order to calculate the eustatic sea level
for each dated terrace it is assumed that the eustatic sea-level position corresponding to at least one marine terrace is known and that the uplift rate has remained essentially constant in each section.
and earthquakes. They may show patterns and rates of tectonic uplift and thus may be used to estimate the tectonic activity
in a certain region. In some cases the exposed secondary landforms can be correlated with known seismic events such as the 1855 Wairarapa earthquake
on the Wairarapa Fault
near Wellington
/New Zealand
which produced a 2.7 m uplift. This figure can be estimated from the vertical offset between raised shorelines in the area.
Furthermore with the knowledge of eustatic sea level
fluctuations the speed of isostatic uplift can be estimated and eventually the change of relative sea levels for certain regions can be reconstructed. Thus marine terraces also provide information for the research on climate change
and trends in future sea level
changes.
When analyzing the morphology of marine terraces it must be considered, that both eustasy and isostasy
can have an influence on the formation process. This way can be assessed, whether there were changes in sea level or whether tectonic activities
took place.
influenced coastlines around the world.
Important sites include various coasts of New Zealand
, e.g. Turakirae Head south of Wellington
being one of the world’s best and most thoroughly studied examples. Also along the Cook Strait
in New Zealand
there is a well-defined sequence of uplifted marine terraces from the late Quaternary
at Tongue Point. It features a well preserved lower terrace from the last interglacial
, a widely eroded higher terrace from the penultimate interglacial and another still higher terrace, which is nearly completely decayed. Furthermore on New Zealand’s North Island at the eastern Bay of Plenty
a sequence of seven marine terraces has been studied.
Along many coasts of mainland and islands around the Pacific
, marine terraces are typical coastal features. An especially prominent marine terraced coastline can be found north of Santa Cruz
, near Davenport
, California
, where terraces probably have been raised by repeated slip earthquakes on the San Andreas Fault
. But also along the coasts of South America
marine terraces are present, where the highest ones are situated where plate margins lie above subducted oceanic ridges and the highest and most rapid rates of uplift occur. At Cape Laundi, Sumba Island
, Indonesia
an ancient patch reef can be found at 475 m above sea level
as part of a sequence of coral reef terraces with 11 terraces being wider than 100m. The coral marine terraces at Huon Peninsula
, New Guinea
, which extend over 80 km and rise over 600 m above present sea level
are currently on UNESCO
’s tentative list for world heritage sites under the name Houn Terraces - Stairway to the Past.
Other considerable examples include marine terraces rising up to 360 m on some Philippine Islands
and along the Mediterranean
Coast of North Africa
, especially in Tunisia
, rising up to 400 m.
Sea level
Mean sea level is a measure of the average height of the ocean's surface ; used as a standard in reckoning land elevation...
, depending on its time of formation. It is bounded by a steeper ascending slope on the landward side and a steeper descending slope on the seaward side (sometimes called "riser"). Due to its reasonably flat shape it is often used for anthropogenic structures like settlements and infrastructure
Infrastructure
Infrastructure is basic physical and organizational structures needed for the operation of a society or enterprise, or the services and facilities necessary for an economy to function...
.
Morphology
The platform of a marine terrace usually has a gradient between 1°- 5° depending on the former tidalTide
Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the moon and the sun and the rotation of the Earth....
range with commonly a linear to concave profile. The width is very variable, reaching up to 1000 m, and seems to differ between northern
Northern Hemisphere
The Northern Hemisphere is the half of a planet that is north of its equator—the word hemisphere literally means “half sphere”. It is also that half of the celestial sphere north of the celestial equator...
and southern hemisphere
Southern Hemisphere
The Southern Hemisphere is the part of Earth that lies south of the equator. The word hemisphere literally means 'half ball' or "half sphere"...
. The cliff
Cliff
In geography and geology, a cliff is a significant vertical, or near vertical, rock exposure. Cliffs are formed as erosion landforms due to the processes of erosion and weathering that produce them. Cliffs are common on coasts, in mountainous areas, escarpments and along rivers. Cliffs are usually...
faces, delimiting the platform, can vary in steepness depending on the relative roles of marine and subaerial
Subaerial
The term subaerial is mainly used in geology to describe events or structures that are located at the Earth's surface...
processes. At the intersection of the former shore (wave-cut/abrasion-) platform
Wave-cut platform
A wave-cut platform, or shore platform is the narrow flat area often found at the base of a sea cliff or along the shoreline of a lake, bay, or sea that was created by the action of waves. Wave-cut platforms are often most obvious at low tide when they become visible as huge areas of flat rock...
and the rising cliff face it commonly retains a shoreline angle or inner edge (notch) which indicates the location of the shoreline at the time of maximum sea ingression and therefore a paleo sea level
Sea level
Mean sea level is a measure of the average height of the ocean's surface ; used as a standard in reckoning land elevation...
. Sub-horizontal platforms usually terminate in a low tide cliff and it is believed that the occurrence of these platforms depends on tidal activity. Marine terraces can extend for several tens of kilometers parallel to the coast
Coast
A coastline or seashore is the area where land meets the sea or ocean. A precise line that can be called a coastline cannot be determined due to the dynamic nature of tides. The term "coastal zone" can be used instead, which is a spatial zone where interaction of the sea and land processes occurs...
.
Older terraces are covered by marine and/or alluvial
Alluvium
Alluvium is loose, unconsolidated soil or sediments, eroded, deposited, and reshaped by water in some form in a non-marine setting. Alluvium is typically made up of a variety of materials, including fine particles of silt and clay and larger particles of sand and gravel...
or colluvial
Colluvium
Colluvium is the name for loose bodies of sediment that have been deposited or built up at the bottom of a low-grade slope or against a barrier on that slope, transported by gravity. The deposits that collect at the foot of a steep slope or cliff are also known by the same name. Colluvium often...
materials while the uppermost terrace levels usually are less well-preserved. While marine terraces in areas of relatively rapid uplift rates (> 1 mm/year) can often be correlated to individual interglacial
Interglacial
An Interglacial period is a geological interval of warmer global average temperature lasting thousands of years that separates consecutive glacial periods within an ice age...
periods or stages, those in areas of slower uplift rates may have a polycyclic origin with stages of returning sea level
Sea level
Mean sea level is a measure of the average height of the ocean's surface ; used as a standard in reckoning land elevation...
s after times of exposure to weathering
Weathering
Weathering is the breaking down of rocks, soils and minerals as well as artificial materials through contact with the Earth's atmosphere, biota and waters...
.
Marine terraces can be covered by a wide variety of soil
Soil
Soil is a natural body consisting of layers of mineral constituents of variable thicknesses, which differ from the parent materials in their morphological, physical, chemical, and mineralogical characteristics...
s with complex histories and different ages. In protected areas allochtonous
Allochthon
thumb|right|250px|Schematic overview of a thrust system. The hanging wall block is called a [[nappe]]. If an [[erosion]]al hole is created in the nappe that is called a [[window |window]]...
sandy parent materials from tsunami deposit
Tsunami deposit
A tsunami deposit is a sedimentary unit deposited as the result of of a tsunami. Such deposits may be left onshore during the inundation phase or offshore during the 'backwash' phase. Such deposits are being used to identify past tsunami events and thereby better constrain estimates of both...
s may be found. Common soil types found on marine terraces include Planosols and Solonetz
Solonetz
Solonetz is a type of soil in FAO soil classification. They have, within the upper 100 cm of the soil profile, a so-called "natric horizon" . There is a subsurface horizon , higher in clay content than the upper horizon, that has more than 15% exchangeable sodium...
.
Causes
Tectonics
Tectonics is a field of study within geology concerned generally with the structures within the lithosphere of the Earth and particularly with the forces and movements that have operated in a region to create these structures.Tectonics is concerned with the orogenies and tectonic development of...
during recent geological times
Geologic time scale
The geologic time scale provides a system of chronologic measurement relating stratigraphy to time that is used by geologists, paleontologists and other earth scientists to describe the timing and relationships between events that have occurred during the history of the Earth...
. Changes in climatic conditions
Climate change
Climate change is a significant and lasting change in the statistical distribution of weather patterns over periods ranging from decades to millions of years. It may be a change in average weather conditions or the distribution of events around that average...
have led to eustatic sea-level oscillations and isostatic movements of the earth’s crust
Crust (geology)
In geology, the crust is the outermost solid shell of a rocky planet or natural satellite, which is chemically distinct from the underlying mantle...
, especially with the changes between glacial
Glacial period
A glacial period is an interval of time within an ice age that is marked by colder temperatures and glacier advances. Interglacials, on the other hand, are periods of warmer climate within an ice age...
and interglacial
Interglacial
An Interglacial period is a geological interval of warmer global average temperature lasting thousands of years that separates consecutive glacial periods within an ice age...
periods.
Processes of eustasy lead to glacioeustatic sea level fluctuations due to changes of the water volume in the oceans and hence to regressions
Marine regression
Marine regression is a geological process occurring when areas of submerged seafloor are exposed above the sea level. The opposite event, marine transgression, occurs when flooding from the sea covers previously exposed land....
and transgressions of the shoreline. E.g. at times of maximum glacier extend during the last glacial period the sea level
Sea level
Mean sea level is a measure of the average height of the ocean's surface ; used as a standard in reckoning land elevation...
was about 100 m lower compared to today. Eustatic sea level changes
Sea-level curve
The sea-level curve is the representation of the changes of the sea level throughout the geological history.The first such curve is the Vail curve or Exxon curve. The names of the curve refer to the fact that in 1977 a team of Exxon geologists from Esso Production Research headed by Peter Vail...
can also be caused by changes of the void volume of the oceans, either through sedimento-eustasy or tectono-eustasy.
Processes of isostasy
Isostasy
Isostasy is a term used in geology to refer to the state of gravitational equilibrium between the earth's lithosphere and asthenosphere such that the tectonic plates "float" at an elevation which depends on their thickness and density. This concept is invoked to explain how different topographic...
involve the uplift of continental crust
Continental crust
The continental crust is the layer of igneous, sedimentary, and metamorphic rocks which form the continents and the areas of shallow seabed close to their shores, known as continental shelves. This layer is sometimes called sial due to more felsic, or granitic, bulk composition, which lies in...
s including their shorelines. Today the process of glacial isostatic adjustment
Post-glacial rebound
Post-glacial rebound is the rise of land masses that were depressed by the huge weight of ice sheets during the last glacial period, through a process known as isostasy...
mainly applies to during Pleistocene
Pleistocene
The Pleistocene is the epoch from 2,588,000 to 11,700 years BP that spans the world's recent period of repeated glaciations. The name pleistocene is derived from the Greek and ....
glaciated areas. In Scandinavia
Scandinavia
Scandinavia is a cultural, historical and ethno-linguistic region in northern Europe that includes the three kingdoms of Denmark, Norway and Sweden, characterized by their common ethno-cultural heritage and language. Modern Norway and Sweden proper are situated on the Scandinavian Peninsula,...
, for instance, the present rate of uplift reaches up to 10 mm/year.
In general, eustatic marine terraces were formed during separate sea level
Sea level
Mean sea level is a measure of the average height of the ocean's surface ; used as a standard in reckoning land elevation...
highstands of interglacial
Interglacial
An Interglacial period is a geological interval of warmer global average temperature lasting thousands of years that separates consecutive glacial periods within an ice age...
stages and can be correlated to Marine Oxygene Isotopic Stages (MIS)
Marine isotope stage
Marine isotope stages , marine oxygen-isotope stages, or oxygen isotope stages , are alternating warm and cool periods in the Earth's paleoclimate, deduced from oxygen isotope data reflecting changes in temperature derived from data from deep sea core samples...
. Glacioisostatic marine terraces were mainly created during stillstands of the isostatic uplift. When eustasy was the main factor for the formation of marine terraces, derived sea level
Sea level
Mean sea level is a measure of the average height of the ocean's surface ; used as a standard in reckoning land elevation...
fluctuations can indicate former climate change
Climate change
Climate change is a significant and lasting change in the statistical distribution of weather patterns over periods ranging from decades to millions of years. It may be a change in average weather conditions or the distribution of events around that average...
s. This conclusion has to be treated with care, as isostatic adjustment
Post-glacial rebound
Post-glacial rebound is the rise of land masses that were depressed by the huge weight of ice sheets during the last glacial period, through a process known as isostasy...
s and tectonic activities
Tectonics
Tectonics is a field of study within geology concerned generally with the structures within the lithosphere of the Earth and particularly with the forces and movements that have operated in a region to create these structures.Tectonics is concerned with the orogenies and tectonic development of...
can be extensively overcompensated by an eustatic sea level rise. Thus, in areas of both eustatic and isostatic
Isostasy
Isostasy is a term used in geology to refer to the state of gravitational equilibrium between the earth's lithosphere and asthenosphere such that the tectonic plates "float" at an elevation which depends on their thickness and density. This concept is invoked to explain how different topographic...
or tectonic
Tectonics
Tectonics is a field of study within geology concerned generally with the structures within the lithosphere of the Earth and particularly with the forces and movements that have operated in a region to create these structures.Tectonics is concerned with the orogenies and tectonic development of...
influences, the course of the relative sea level curve can be complicated. Hence most of today’s marine terrace sequences were formed by a combination of tectonic coastal uplift and Quaternary
Quaternary
The Quaternary Period is the most recent of the three periods of the Cenozoic Era in the geologic time scale of the ICS. It follows the Neogene Period, spanning 2.588 ± 0.005 million years ago to the present...
sea level fluctuations.
Jerky tectonic
Tectonics
Tectonics is a field of study within geology concerned generally with the structures within the lithosphere of the Earth and particularly with the forces and movements that have operated in a region to create these structures.Tectonics is concerned with the orogenies and tectonic development of...
uplifts can also lead to marked terrace steps while smooth relative sea level
Sea level
Mean sea level is a measure of the average height of the ocean's surface ; used as a standard in reckoning land elevation...
changes may not result in obvious terraces and their formations are often not referred to as marine terraces.
Processes
Marine terraces often result from marine erosion along rocky coast lines in temperate regions due to wave attack and sedimentSediment
Sediment is naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of fluids such as wind, water, or ice, and/or by the force of gravity acting on the particle itself....
carried in the waves. Erosion
Erosion
Erosion is when materials are removed from the surface and changed into something else. It only works by hydraulic actions and transport of solids in the natural environment, and leads to the deposition of these materials elsewhere...
also takes place in connection with weathering
Weathering
Weathering is the breaking down of rocks, soils and minerals as well as artificial materials through contact with the Earth's atmosphere, biota and waters...
and cavitation
Cavitation
Cavitation is the formation and then immediate implosion of cavities in a liquidi.e. small liquid-free zones that are the consequence of forces acting upon the liquid...
. The speed of erosion is highly dependent on the shoreline material (hardness of rock), the bathymetry
Bathymetry
Bathymetry is the study of underwater depth of lake or ocean floors. In other words, bathymetry is the underwater equivalent to hypsometry. The name comes from Greek βαθύς , "deep", and μέτρον , "measure"...
and the bedrock
Bedrock
In stratigraphy, bedrock is the native consolidated rock underlying the surface of a terrestrial planet, usually the Earth. Above the bedrock is usually an area of broken and weathered unconsolidated rock in the basal subsoil...
properties and can be between only a few millimeters per year for granitic
Granite
Granite is a common and widely occurring type of intrusive, felsic, igneous rock. Granite usually has a medium- to coarse-grained texture. Occasionally some individual crystals are larger than the groundmass, in which case the texture is known as porphyritic. A granitic rock with a porphyritic...
rocks and more than 10m per year for volcanic ejecta
Volcanic rock
Volcanic rock is a rock formed from magma erupted from a volcano. In other words, it is an igneous rock of volcanic origin...
. The retreat of the sea cliff
Cliff
In geography and geology, a cliff is a significant vertical, or near vertical, rock exposure. Cliffs are formed as erosion landforms due to the processes of erosion and weathering that produce them. Cliffs are common on coasts, in mountainous areas, escarpments and along rivers. Cliffs are usually...
generates a shore (wave-cut/abrasion-) platform
Wave-cut platform
A wave-cut platform, or shore platform is the narrow flat area often found at the base of a sea cliff or along the shoreline of a lake, bay, or sea that was created by the action of waves. Wave-cut platforms are often most obvious at low tide when they become visible as huge areas of flat rock...
through the process of abrasion
Abrasion (geology)
Abrasion is the mechanical scraping of a rock surface by friction between rocks and moving particles during their transport by wind, glacier, waves, gravity, running water or erosion. After friction, the moving particles dislodge loose and weak debris from the side of the rock...
. A relative change of the sea level
Sea level
Mean sea level is a measure of the average height of the ocean's surface ; used as a standard in reckoning land elevation...
leads to regressions
Marine regression
Marine regression is a geological process occurring when areas of submerged seafloor are exposed above the sea level. The opposite event, marine transgression, occurs when flooding from the sea covers previously exposed land....
or transgressions and eventually forms another terrace (marine-cut terrace) at a different altitude while notches in the cliff face indicate short stillstands.
It is believed that the terrace gradient increases with tidal
Tide
Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the moon and the sun and the rotation of the Earth....
range and decreases with rock resistance. In addition the relationship between terrace width and the strength of the rock is inverse and higher rates of uplift and subsidence as well as a higher slope of the hinterland
Hinterland
The hinterland is the land or district behind a coast or the shoreline of a river. Specifically, by the doctrine of the hinterland, the word is applied to the inland region lying behind a port, claimed by the state that owns the coast. The area from which products are delivered to a port for...
increases the number of terraces formed during a certain time.
Furthermore shore platforms
Wave-cut platform
A wave-cut platform, or shore platform is the narrow flat area often found at the base of a sea cliff or along the shoreline of a lake, bay, or sea that was created by the action of waves. Wave-cut platforms are often most obvious at low tide when they become visible as huge areas of flat rock...
are formed by denudation
Denudation
In geology, denudation is the long-term sum of processes that cause the wearing away of the earth’s surface leading to a reduction in elevation and relief of landforms and landscapes...
and marine-built terraces arise from accumulations of materials removed by shore erosion. Thus a marine terrace can be formed by both erosion
Erosion
Erosion is when materials are removed from the surface and changed into something else. It only works by hydraulic actions and transport of solids in the natural environment, and leads to the deposition of these materials elsewhere...
and accumulation. However, there is an ongoing debate about the roles of wave erosion and weathering
Weathering
Weathering is the breaking down of rocks, soils and minerals as well as artificial materials through contact with the Earth's atmosphere, biota and waters...
in the formation of shore platforms
Wave-cut platform
A wave-cut platform, or shore platform is the narrow flat area often found at the base of a sea cliff or along the shoreline of a lake, bay, or sea that was created by the action of waves. Wave-cut platforms are often most obvious at low tide when they become visible as huge areas of flat rock...
.
Reef flats or uplifted coral reefs are another kind of marine terrace found in intertropical regions. They are a result of biological activity, shoreline advance and accumulation of reef
Reef
In nautical terminology, a reef is a rock, sandbar, or other feature lying beneath the surface of the water ....
materials.
While a terrace sequence can date back hundreds of thousands of years, its degradation is a rather fast process. On the one hand a deeper transgression of cliffs into the shoreline may completely destroy previous terraces; on the other hand older terraces might be decayed or covered by deposits, colluvia
Colluvium
Colluvium is the name for loose bodies of sediment that have been deposited or built up at the bottom of a low-grade slope or against a barrier on that slope, transported by gravity. The deposits that collect at the foot of a steep slope or cliff are also known by the same name. Colluvium often...
or alluvial fan
Alluvial fan
An alluvial fan is a fan-shaped deposit formed where a fast flowing stream flattens, slows, and spreads typically at the exit of a canyon onto a flatter plain. A convergence of neighboring alluvial fans into a single apron of deposits against a slope is called a bajada, or compound alluvial...
s. Erosion and backwearing of slopes caused by incisive streams play another important role in this degradation process.
Mapping and surveying
For exact interpretations of the morphology extensive datings, surveying and mapping of marine terraces is applied. This includes stereoscopicStereoscopy
Stereoscopy refers to a technique for creating or enhancing the illusion of depth in an image by presenting two offset images separately to the left and right eye of the viewer. Both of these 2-D offset images are then combined in the brain to give the perception of 3-D depth...
aerial photographic interpretation
Aerial photographic and satellite image interpretation
Photographic interpretation can be defined as: “the act of examining photographic images for the purpose of identifying objects and judging their significance” ....
(ca. 1 : 10,000 - 25,000), on-site inspections with topographic map
Topographic map
A topographic map is a type of map characterized by large-scale detail and quantitative representation of relief, usually using contour lines in modern mapping, but historically using a variety of methods. Traditional definitions require a topographic map to show both natural and man-made features...
s (ca. 1 : 10,000) and analysis of eroded and accumulated material. Moreover the exact altitude can be determined with an aneroid barometer or preferably with a levelling instrument mounted on a tripod. It should be measured with the accuracy of 1 cm and at about every 50 - 100 m, depending on the topography. In remote areas technics of photogrammetry
Photogrammetry
Photogrammetry is the practice of determining the geometric properties of objects from photographic images. Photogrammetry is as old as modern photography and can be dated to the mid-nineteenth century....
and tacheometry
Tacheometry
Tacheometry , is a system of rapid surveying, by which the positions, both horizontal and vertical, of points on the earth surface relatively to one another are determined without using a chain or tape or a separate levelling instrument....
can be applied.
Correlation and dating
Different methods for dating and correlation of marine terraces can be used and combined.Correlational dating
The morphostratigraphic approach focuses especially in regions of marine regressionMarine regression
Marine regression is a geological process occurring when areas of submerged seafloor are exposed above the sea level. The opposite event, marine transgression, occurs when flooding from the sea covers previously exposed land....
on the altitude as the most important criterion to distinguish coast lines of different ages. Moreover individual marine terraces can be correlated based on their size and continuity. Also paleo-soils as well as glacial, fluvial, eolian and periglacial
Periglacial
Periglacial is an adjective originally referring to places in the edges of glacial areas, but it has later been widely used in geomorphology to describe any place where geomorphic processes related to freezing of water occur...
landforms and sediment
Sediment
Sediment is naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of fluids such as wind, water, or ice, and/or by the force of gravity acting on the particle itself....
s may be used to find correlations between terraces. On New Zealand’s North Island, for instance, tephra
Tephra
200px|thumb|right|Tephra horizons in south-central [[Iceland]]. The thick and light coloured layer at center of the photo is [[rhyolitic]] tephra from [[Hekla]]....
and loess
Loess
Loess is an aeolian sediment formed by the accumulation of wind-blown silt, typically in the 20–50 micrometre size range, twenty percent or less clay and the balance equal parts sand and silt that are loosely cemented by calcium carbonate...
were used to date and correlate marine terraces. At the terminus advance of former glacier
Glacier
A glacier is a large persistent body of ice that forms where the accumulation of snow exceeds its ablation over many years, often centuries. At least 0.1 km² in area and 50 m thick, but often much larger, a glacier slowly deforms and flows due to stresses induced by its weight...
s marine terraces can be correlated by their size, as their width decreases with age due to the slowly thawing glaciers along the coast line.
The lithostratigraphic
Lithostratigraphy
Lithostratigraphy is a sub-discipline of stratigraphy, the geological science associated with the study of strata or rock layers. Major focuses include geochronology, comparative geology, and petrology...
approach uses typical sequences of sediment
Sediment
Sediment is naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of fluids such as wind, water, or ice, and/or by the force of gravity acting on the particle itself....
and rock strata to prove sea level
Sea level
Mean sea level is a measure of the average height of the ocean's surface ; used as a standard in reckoning land elevation...
fluctuations on the basis of an alternation of terrestrial and marine sediments or littoral and shallow marine sediments. Those strata show typical layers of transgressive and regressive patterns. However, an unconformity
Unconformity
An unconformity is a buried erosion surface separating two rock masses or strata of different ages, indicating that sediment deposition was not continuous. In general, the older layer was exposed to erosion for an interval of time before deposition of the younger, but the term is used to describe...
in the sediment sequence might make this analysis difficult.
The biostratigraphic
Biostratigraphy
Biostratigraphy is the branch of stratigraphy which focuses on correlating and assigning relative ages of rock strata by using the fossil assemblages contained within them. Usually the aim is correlation, demonstrating that a particular horizon in one geological section represents the same period...
approach uses remains of organisms which can indicate the age of a marine terrace. For that often mollusc shell
Mollusc shell
The mollusc shell is typically a calcareous exoskeleton which encloses, supports and protects the soft parts of an animal in the phylum Mollusca, which includes snails, clams, tusk shells, and several other classes...
s, foraminifera
Foraminifera
The Foraminifera , or forams for short, are a large group of amoeboid protists which are among the commonest plankton species. They have reticulating pseudopods, fine strands of cytoplasm that branch and merge to form a dynamic net...
or pollen
Pollen
Pollen is a fine to coarse powder containing the microgametophytes of seed plants, which produce the male gametes . Pollen grains have a hard coat that protects the sperm cells during the process of their movement from the stamens to the pistil of flowering plants or from the male cone to the...
are used. Especially Mollusca
Mollusca
The Mollusca , common name molluscs or mollusksSpelled mollusks in the USA, see reasons given in Rosenberg's ; for the spelling mollusc see the reasons given by , is a large phylum of invertebrate animals. There are around 85,000 recognized extant species of molluscs. Mollusca is the largest...
can show specific properties depending on their depth of sedimentation
Sedimentation
Sedimentation is the tendency for particles in suspension to settle out of the fluid in which they are entrained, and come to rest against a barrier. This is due to their motion through the fluid in response to the forces acting on them: these forces can be due to gravity, centrifugal acceleration...
. Thus they can be used to estimate former water depths.
Marine terraces are often correlated to Marine Oxygene Isotopic Stages (MIS)
Marine isotope stage
Marine isotope stages , marine oxygen-isotope stages, or oxygen isotope stages , are alternating warm and cool periods in the Earth's paleoclimate, deduced from oxygen isotope data reflecting changes in temperature derived from data from deep sea core samples...
(e.g. Johnson, M. E.; Libbey, L. K. 1997) and can also be roughly dated using their stratigraphic position.
Direct dating
There are various methods for the direct dating of marine terraces and their related materials including 14C radiocarbon datingRadiocarbon dating
Radiocarbon dating is a radiometric dating method that uses the naturally occurring radioisotope carbon-14 to estimate the age of carbon-bearing materials up to about 58,000 to 62,000 years. Raw, i.e. uncalibrated, radiocarbon ages are usually reported in radiocarbon years "Before Present" ,...
, which is the most common one. E.g. this method has been used on the North Island of New Zealand to date several marine terraces. It utilizes terrestrial biogenic materials
Biogenic substance
A biogenic substance is a substance produced by life processes. It may be either constituents, or secretions, of plants or animals. A more specific name for these substances is biomolecules.-Examples:...
in coastal sediment
Sediment
Sediment is naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of fluids such as wind, water, or ice, and/or by the force of gravity acting on the particle itself....
s such as mollusc shell
Mollusc shell
The mollusc shell is typically a calcareous exoskeleton which encloses, supports and protects the soft parts of an animal in the phylum Mollusca, which includes snails, clams, tusk shells, and several other classes...
s analyzing the 14C isotope
Isotope
Isotopes are variants of atoms of a particular chemical element, which have differing numbers of neutrons. Atoms of a particular element by definition must contain the same number of protons but may have a distinct number of neutrons which differs from atom to atom, without changing the designation...
. In some cases dating based on the 230Th/234U ratio was applied though in case of detrital contamination or low Uranium
Uranium
Uranium is a silvery-white metallic chemical element in the actinide series of the periodic table, with atomic number 92. It is assigned the chemical symbol U. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons...
concentrations a high resolution dating was found to be difficult. In a study in southern Italy
Italy
Italy , officially the Italian Republic languages]] under the European Charter for Regional or Minority Languages. In each of these, Italy's official name is as follows:;;;;;;;;), is a unitary parliamentary republic in South-Central Europe. To the north it borders France, Switzerland, Austria and...
paleomagnetism
Paleomagnetism
Paleomagnetism is the study of the record of the Earth's magnetic field in rocks. Certain minerals in rocks lock-in a record of the direction and intensity of the magnetic field when they form. This record provides information on the past behavior of Earth's magnetic field and the past location of...
was used to carry out paleomagnetic datings and luminescence dating (OSL)
Optical dating
Optical dating is a method of determining how long ago minerals were last exposed to daylight. It is useful to geologists and archaeologists who want to know when such an event occurred....
was used in different studies on the San Andreas Fault
San Andreas Fault
The San Andreas Fault is a continental strike-slip fault that runs a length of roughly through California in the United States. The fault's motion is right-lateral strike-slip...
and on the Quaternary
Quaternary
The Quaternary Period is the most recent of the three periods of the Cenozoic Era in the geologic time scale of the ICS. It follows the Neogene Period, spanning 2.588 ± 0.005 million years ago to the present...
Eupcheon Fault in South Korea
South Korea
The Republic of Korea , , is a sovereign state in East Asia, located on the southern portion of the Korean Peninsula. It is neighbored by the People's Republic of China to the west, Japan to the east, North Korea to the north, and the East China Sea and Republic of China to the south...
.
In order to calculate the eustatic sea level
Sea level
Mean sea level is a measure of the average height of the ocean's surface ; used as a standard in reckoning land elevation...
for each dated terrace it is assumed that the eustatic sea-level position corresponding to at least one marine terrace is known and that the uplift rate has remained essentially constant in each section.
Relevance for other research areas
Marine terraces play an important role in the research on tectonicsTectonics
Tectonics is a field of study within geology concerned generally with the structures within the lithosphere of the Earth and particularly with the forces and movements that have operated in a region to create these structures.Tectonics is concerned with the orogenies and tectonic development of...
and earthquakes. They may show patterns and rates of tectonic uplift and thus may be used to estimate the tectonic activity
Tectonics
Tectonics is a field of study within geology concerned generally with the structures within the lithosphere of the Earth and particularly with the forces and movements that have operated in a region to create these structures.Tectonics is concerned with the orogenies and tectonic development of...
in a certain region. In some cases the exposed secondary landforms can be correlated with known seismic events such as the 1855 Wairarapa earthquake
1855 Wairarapa earthquake
The 1855 Wairarapa earthquake occurred on 23 January at about 9 p.m. In Wellington, close to the epicenter, shaking lasted for at least 50 seconds. The magnitude of the earthquake is estimated to have been in the range 8.1-8.3, the most powerful recorded in New Zealand since systematic European...
on the Wairarapa Fault
Wairarapa Fault
The Wairarapa Fault is an active seismic fault in the southern part of the North Island of New Zealand. It is a dextral strike-slip fault with a component of uplift to the northwest as expressed by the Rimutaka Range...
near Wellington
Wellington
Wellington is the capital city and third most populous urban area of New Zealand, although it is likely to have surpassed Christchurch due to the exodus following the Canterbury Earthquake. It is at the southwestern tip of the North Island, between Cook Strait and the Rimutaka Range...
/New Zealand
New Zealand
New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...
which produced a 2.7 m uplift. This figure can be estimated from the vertical offset between raised shorelines in the area.
Furthermore with the knowledge of eustatic sea level
Sea level
Mean sea level is a measure of the average height of the ocean's surface ; used as a standard in reckoning land elevation...
fluctuations the speed of isostatic uplift can be estimated and eventually the change of relative sea levels for certain regions can be reconstructed. Thus marine terraces also provide information for the research on climate change
Global warming
Global warming refers to the rising average temperature of Earth's atmosphere and oceans and its projected continuation. In the last 100 years, Earth's average surface temperature increased by about with about two thirds of the increase occurring over just the last three decades...
and trends in future sea level
Sea level
Mean sea level is a measure of the average height of the ocean's surface ; used as a standard in reckoning land elevation...
changes.
When analyzing the morphology of marine terraces it must be considered, that both eustasy and isostasy
Isostasy
Isostasy is a term used in geology to refer to the state of gravitational equilibrium between the earth's lithosphere and asthenosphere such that the tectonic plates "float" at an elevation which depends on their thickness and density. This concept is invoked to explain how different topographic...
can have an influence on the formation process. This way can be assessed, whether there were changes in sea level or whether tectonic activities
Tectonics
Tectonics is a field of study within geology concerned generally with the structures within the lithosphere of the Earth and particularly with the forces and movements that have operated in a region to create these structures.Tectonics is concerned with the orogenies and tectonic development of...
took place.
Prominent examples
Marine terraces can be found on many geodynamicallyGeodynamics
Geodynamics is a subfield of geophysics dealing with dynamics of the Earth. It applies physics, chemistry and mathematics to the understanding of how mantle convection leads to plate tectonics and geologic phenomena such as seafloor spreading, mountain building, volcanoes, earthquakes, faulting and...
influenced coastlines around the world.
Important sites include various coasts of New Zealand
New Zealand
New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...
, e.g. Turakirae Head south of Wellington
Wellington
Wellington is the capital city and third most populous urban area of New Zealand, although it is likely to have surpassed Christchurch due to the exodus following the Canterbury Earthquake. It is at the southwestern tip of the North Island, between Cook Strait and the Rimutaka Range...
being one of the world’s best and most thoroughly studied examples. Also along the Cook Strait
Cook Strait
Cook Strait is the strait between the North and South Islands of New Zealand. It connects the Tasman Sea on the west with the South Pacific Ocean on the east....
in New Zealand
New Zealand
New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...
there is a well-defined sequence of uplifted marine terraces from the late Quaternary
Quaternary
The Quaternary Period is the most recent of the three periods of the Cenozoic Era in the geologic time scale of the ICS. It follows the Neogene Period, spanning 2.588 ± 0.005 million years ago to the present...
at Tongue Point. It features a well preserved lower terrace from the last interglacial
Interglacial
An Interglacial period is a geological interval of warmer global average temperature lasting thousands of years that separates consecutive glacial periods within an ice age...
, a widely eroded higher terrace from the penultimate interglacial and another still higher terrace, which is nearly completely decayed. Furthermore on New Zealand’s North Island at the eastern Bay of Plenty
Bay of Plenty
The Bay of Plenty , often abbreviated to BOP, is a region in the North Island of New Zealand situated around the body of water of the same name...
a sequence of seven marine terraces has been studied.
Along many coasts of mainland and islands around the Pacific
Pacific Ocean
The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...
, marine terraces are typical coastal features. An especially prominent marine terraced coastline can be found north of Santa Cruz
Santa Cruz, California
Santa Cruz is the county seat and largest city of Santa Cruz County, California in the US. As of the 2010 U.S. Census, Santa Cruz had a total population of 59,946...
, near Davenport
Davenport, California
Davenport is a census-designated place in Santa Cruz County, California. Davenport sits at an elevation of . The 2010 United States census reported Davenport's population was 408.-Situation:...
, California
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...
, where terraces probably have been raised by repeated slip earthquakes on the San Andreas Fault
San Andreas Fault
The San Andreas Fault is a continental strike-slip fault that runs a length of roughly through California in the United States. The fault's motion is right-lateral strike-slip...
. But also along the coasts of South America
South America
South America is a continent situated in the Western Hemisphere, mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. The continent is also considered a subcontinent of the Americas. It is bordered on the west by the Pacific Ocean and on the north and east...
marine terraces are present, where the highest ones are situated where plate margins lie above subducted oceanic ridges and the highest and most rapid rates of uplift occur. At Cape Laundi, Sumba Island
Sumba
Sumba is an island in eastern Indonesia, is one of the Lesser Sunda Islands, and is in the province of East Nusa Tenggara. Sumba has an area of 11,153 km², and the population was officially at 611,422 in 2005...
, Indonesia
Indonesia
Indonesia , officially the Republic of Indonesia , is a country in Southeast Asia and Oceania. Indonesia is an archipelago comprising approximately 13,000 islands. It has 33 provinces with over 238 million people, and is the world's fourth most populous country. Indonesia is a republic, with an...
an ancient patch reef can be found at 475 m above sea level
Sea level
Mean sea level is a measure of the average height of the ocean's surface ; used as a standard in reckoning land elevation...
as part of a sequence of coral reef terraces with 11 terraces being wider than 100m. The coral marine terraces at Huon Peninsula
Huon Peninsula
Huon Peninsula is a large rugged peninsula on the island of New Guinea in Morobe Province, eastern Papua New Guinea. It is named after French explorer Jean-Michel Huon de Kermadec who discovered it along with his personal assistant and porter, Henry Ole. The peninsula is dominated by the steep...
, New Guinea
New Guinea
New Guinea is the world's second largest island, after Greenland, covering a land area of 786,000 km2. Located in the southwest Pacific Ocean, it lies geographically to the east of the Malay Archipelago, with which it is sometimes included as part of a greater Indo-Australian Archipelago...
, which extend over 80 km and rise over 600 m above present sea level
Sea level
Mean sea level is a measure of the average height of the ocean's surface ; used as a standard in reckoning land elevation...
are currently on UNESCO
UNESCO
The United Nations Educational, Scientific and Cultural Organization is a specialized agency of the United Nations...
’s tentative list for world heritage sites under the name Houn Terraces - Stairway to the Past.
Other considerable examples include marine terraces rising up to 360 m on some Philippine Islands
Philippines
The Philippines , officially known as the Republic of the Philippines , is a country in Southeast Asia in the western Pacific Ocean. To its north across the Luzon Strait lies Taiwan. West across the South China Sea sits Vietnam...
and along the Mediterranean
Mediterranean Sea
The Mediterranean Sea is a sea connected to the Atlantic Ocean surrounded by the Mediterranean region and almost completely enclosed by land: on the north by Anatolia and Europe, on the south by North Africa, and on the east by the Levant...
Coast of North Africa
North Africa
North Africa or Northern Africa is the northernmost region of the African continent, linked by the Sahara to Sub-Saharan Africa. Geopolitically, the United Nations definition of Northern Africa includes eight countries or territories; Algeria, Egypt, Libya, Morocco, South Sudan, Sudan, Tunisia, and...
, especially in Tunisia
Tunisia
Tunisia , officially the Tunisian RepublicThe long name of Tunisia in other languages used in the country is: , is the northernmost country in Africa. It is a Maghreb country and is bordered by Algeria to the west, Libya to the southeast, and the Mediterranean Sea to the north and east. Its area...
, rising up to 400 m.
See also
- BeachBeachA beach is a geological landform along the shoreline of an ocean, sea, lake or river. It usually consists of loose particles which are often composed of rock, such as sand, gravel, shingle, pebbles or cobblestones...
- BenchBench (geology)In geomorphology, geography and geology, a bench or benchland is a long, relatively narrow strip of relatively level or gently inclined land that is bounded by distinctly steeper slopes above and below it...
- Fluvial terrace
- LandformLandformA landform or physical feature in the earth sciences and geology sub-fields, comprises a geomorphological unit, and is largely defined by its surface form and location in the landscape, as part of the terrain, and as such, is typically an element of topography...
- Raised beachRaised beachA raised beach, marine terrace, or perched coastline is an emergent coastal landform. Raised beaches and marine terraces are beaches or wave-cut platforms raised above the shore line by a relative fall in the sea level ....
- Raised shorelinesRaised shorelinesA raised shoreline is an ancient shoreline exposed above current water level. These landforms are formed by a relative change in sea level due to global sea level rise, isostatic rebound, and/or tectonic uplift. These surfaces are usually exposed above modern sea level when a heavily glaciated...
- Terrace
- Wave-cut platformWave-cut platformA wave-cut platform, or shore platform is the narrow flat area often found at the base of a sea cliff or along the shoreline of a lake, bay, or sea that was created by the action of waves. Wave-cut platforms are often most obvious at low tide when they become visible as huge areas of flat rock...