Flysch is a sequence of
sedimentary rocks that is deposited in a deep
marine facies in the
foreland basin of a developing
orogen. Flysch is typically deposited during an early stage of the
orogenesis. When the orogen evolves, the foreland basin becomes shallower and
molasse is deposited on top of the flysch. It is therefore called a
syn-orogenic sediment (deposited contemporaneously with mountain building).