In areas where major accumulation takes place, along the margins of continents, sedimentary layers will undergo progressive burial. Most sedimentary rocks are marine in origin and contain sea water which was trapped between the sedimentary particles during deposition. In passive margins, as the underlying crust deforms under the weight of accumulated sediments, these sediments are buried deeper, and pressures and temperatures increase. Sediments may also be affected by deformation and igneous activity, especially along active continental margins.