The Continent-ocean boundary (COB) or continent-ocean transition is the boundary between 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...

 and oceanic crust

Oceanic crust

Oceanic crust is the part of Earth's lithosphere that surfaces in the ocean basins. Oceanic crust is primarily composed of mafic rocks, or sima, which is rich in iron and magnesium...

 on a passive margin

Passive margin

A passive margin is the transition between oceanic and continental crust which is not an active plate margin. It is constructed by sedimentation above an ancient rift, now marked by transitional crust. Continental rifting creates new ocean basins. Eventually the continental rift forms a mid-oceanic...

. The identification of continent-ocean boundaries is important in the definition of plate boundaries at the time of break-up when trying to reconstruct the geometry and position of ancient continents e.g. in the reconstruction of Pangaea

Pangaea

Pangaea, Pangæa, or Pangea is hypothesized as a supercontinent that existed during the Paleozoic and Mesozoic eras about 250 million years ago, before the component continents were separated into their current configuration....

.

Techniques used in identification

• Gravity data inversion - Moho
  Moho
  -Birds:* Moho , a genus of birds in the family Meliphagidae* The Hawaiʻian name of the Hawaiian Rail, an extinct species* The Māori name of the North Island Takahē, an extinct species-Computers:...
  
   depth can be derived by the inversion of satellite gravity data and thereby crustal thickness

• Magnetic stripe data - Most areas of oceanic crust show characteristic stripes due to periodic magnetic reversals
  Geomagnetic reversal
  A geomagnetic reversal is a change in the Earth's magnetic field such that the positions of magnetic north and magnetic south are interchanged. The Earth's field has alternated between periods of normal polarity, in which the direction of the field was the same as the present direction, and reverse...
  
   during formation at a mid-oceanic ridge. The continental crust is by contrast typically magnetically quiet.

• Seismic refraction
  Seismic refraction
  Seismic refraction is a geophysical principle governed by Snell's Law. Used in the fields of engineering geology, geotechnical engineering and exploration geophysics, seismic refraction traverses are performed using a seismograph and/or geophone, in an array and an energy source...
  
   and wide-angle reflection
  Reflection seismology
  Reflection seismology is a method of exploration geophysics that uses the principles of seismology to estimate the properties of the Earth's subsurface from reflected seismic waves. The method requires a controlled seismic source of energy, such as dynamite/Tovex, a specialized air gun or a...
  
   data - These data give a precise location for the COB by determining the P-wave
  P-wave
  P-waves are a type of elastic wave, also called seismic waves, that can travel through gases , solids and liquids, including the Earth. P-waves are produced by earthquakes and recorded by seismographs...
  
   velocities along a profile. The two types of crust have distinct P-wave velocities.

Economic importance

As hydrocarbon exploration moves further offshore to look for the remaining potential on passive margins, understanding the location of the COB is critical to predicting possible hydrocarbon occurrence. This is both from the likely location of source and reservoir rocks and the need to model the thermal effects of break-up in basin modelling

Basin modelling

Basin modelling is the term broadly applied to a group of geological disciplines that can be used to analyse the formation and evolution of sedimentary basins, often but not exclusively to aid evaluation of potential hydrocarbon reserves....