5
Texts and exercises :
Lesson N° 1 :
Sediment in the sea :
Sediment is produced by the weathering (chemical and mechanical
breaking down) of rock such as granite or basalt into particles that are
moved then by air , water or ice .Sediment can also form by the
accumulation of shells od dead organisms .Therefore ,sediment can
consist of either mineral or fossil particles , and both types can be found
in many places on the bottom of the sea.
1-Classification of marine sediment :
The first step in classifying anything is to establish criteria for defining
categories.Sediments can be subdivided on the basis of the size of the
particles(grain size) or on the basis of their mode of formation.
Sediments can be subdivided into five categories , based on the way
they form ;
a- Terrigenous sediment :
fine and coarse grains that are produced by the weathering and erosion
of rocks on land ; typically sand and mud.
b- Biogenous sediment :
Fine and coarse grains that are derived from the hard parts of organisms
, such as shells and skeletal debris .
c- Hydrogenous sediment :
Particles that are precipitated by chemical or biochemical reactions
in seawater near the seafloor.
d- Volcanogenous sediment :
Particles that are ejected from volcanoes ; ash is an example.