Introduction to Sedimentary Rock Forms
Sedimentary rocks are formed by the deposition of sediments transported by streams,
ocean or wave currents, ice, or wind. Most sediments are remnants of previously decomposed
and disintegrated igneous, sedimentary, and metamorphic rocks, but some are derived from
chemical reactions an organic sources. When a particular transporting agent can no longer carry
their mass, the sediments are deposited. Variations in the velocity of the transporting agent
produce layers or beds whose particles vary in texture, and it is the presence of bedding plains
that distinguishes sedimentary from igneous rocks, the latter tend to be massive and nonbedded.
The bedding planes in sedimentary rock, are originally laid down parallel to the earth’s surface,
but later may be tilted by movements of the earth’s crest.
Sedimentary rocks accounting for approximately 75 percent of the earth’s exposed land
surface occur in two categories. The first category includes clastic or fragmental rocks, such as
shales, sandstones, and conglomerates, originally from other rocks. The second category are
formed from chemical and biochemical (organic) sediments precipitated from solution (examples
are calcium carbonate, and limy parts of organisms such as corals, algae, foraminifers, clams and
snails). These sediments include limestone, gypsums, and salt. Large organic or swamp deposits
upon lithification become coal and are commonly found interbedded with other sedimentary
materials. Coal is not included here. Most sedimentary deposits originate underwater in oceans
resulting from stream and river flow. The sediments consist of gravels, sands, silts and clays; the
resulting deposits vary in texture according to the distance from shore and water velocities at the
time of deposition.
Distribution- Some regions of the World containing well-consolidated sedimentary rocks are
listed in the following paragraphs.

North America, United States, and Canada- The regions include only those where
residual soils have developed from weathered sedimentary rocks. In the United States,
sedimentary rocks of all types and attitudes are found in areas adjacent to the
Appalachian Mountains, the central plains, and scatterings throughout the Rockies.
 A band of interbedded sedimentary rock extends across most of Saskatchewan and
eastern Alberta, across the Northwest Territories just west of Great Bear Lake and into
the Alaskan north slope.
 South and Central America- Sedimentary rocks are found in southern Argentina and
throughout parts of Brazil.
 Africa- Sedimentary rocks are widespread across Africa with surfaces of residual soils.
 Asia- Large portions of western Russia and central Siberia consist of Sedimentary rock,
with scattered systems occurring through Tibet. Less exposures can be found in
Cambodia and Thailand.
 Australia- Sedimentary rocks are found in most of Queensland, parts of South Australia,
and parts of Western Australia.
 Pacific and Caribbean Regions- Well-consolidated rocks occur in the islands of coral
formations and coquina.
 Sedimentary deposits are found in parts of Cuba, Haiti, the Dominican Republic, and
Puerto Rico; limestone formations are most common.
Source: Terrain analysis procedural guide for surface configuration, US Army engineer
topographic laboratories, p. 7-69