5. SEDIMENTARYMATERIALS
• Most sedimentary rocks are varieties of sandstone, clay or limestone
• Mineral grains: mostly quartz, also muscovite (the physically and
chemically stable minerals)
• Rock fragments and volcanic debris (not yet broken down to their
constituent minerals) – SANDSTONES
• Breakdown products: clay minerals (formed by reaction of water with
feldspar or mafic minerals) – MUDSTONE
• Organic debris: plant material to form peat and coal (animal soft
parts form oil) – minor rocks
• Organic debris: dominated by calcite from marine shell debris
• Solutes: dominantly calcite precipitated from sea water largely
due to biological activity – LIMESTONES
• Solutes: including gypsum and salt, and other less abundant soluble
compounds – minor rocks
14. LITHIFICATI
ON
The processes by which a weak, loose sediment is turned
into a stronger sedimentary rock. Induced by burial
pressure and slightly increased temperature beneath a
kilometer or more of overlying sediment.
The processes of lithification are also known as diagenesis by
geologists, referring to the changes which take place after
deposition.
The results of lithification, notably the increase in
strength, are referred to as consolidation by engineers.
Three main processes of lithification:
16. LITHIFICATI
ON
Cementation
The filling of the inter-granular pore
spaces by deposition of a mineral
cement brought in by circulating
groundwater. Rock strength is largely
dependent on the type of cement,
which may be silica (strongest), iron
oxides, calcite or clay (weakest). The
dominant process in sandstones
18. LITHIFICATI
ON
Compaction Restructuring and
change of grain packing, with
decrease in volume, due to burial
pressure, with consequent reduction
of porosity as water is squeezed out.
Increase in strength is due to more
grain to grain contact. The dominant
process in clays
19. LITHIFICATI
ON
Recrystallization Small scale solution
and redisposition of mineral, so that
some grains become smaller and
some larger. Result may be similar to
cementation, but may produce stronger
mosaic texture. Can also include change
of state and growth of new, more stable
minerals.
The dominant process in limestone.
20. Structure of sedimentaryrocks
Sediment are usually deposited so that new
layers is placed on the top and the older ones
at the bottom. Subsequent earth movements
may raise the beds of
sedimentary rock above sea level; erosion
and removal of the overlying rocks (to form
the source material for another generation of
sediments and sedimentary rocks)
then exposes the old sedimentary rocks in
outcrops in a landscape far removed from
contemporary seas and in an environment
very different from that of the sedimentation.
21. Stratifications
The modern principles of stratigraphy
represent a derivation of the original
principles defined by Steno. According
to such principles, younger strata are
found at the top, while older strata
occur at the base of sedimentary
sequences (principle of
superposition), strata deposit as
horizontal layers (principle of
original horizontality), and are
laterally continuous throughout the
sedimentary basin (principle of
strata continuity).
27. Ex
Indicate the origin of rock ( clastic ,chemical or
biochemical) & the basic mineral
SN Sedimentary rock
name
Origin of rock Basic mineral
1 Limestone
2 Sandstone
3 Conglomerate
4 shale
5 Rock salt
28. Ex
SN Clast type Sedimentary rock name
1 Gravel
2 Sand
3 Silt
4 clay
Indicate the name of sedimentary
rock
