Download SEDIMENTARY ROCKS - Sri Venkateswara College of Engineering

SEDIMENTARY
ROCKS
FORMATION OF SEDIMENTARY
ROCKS
• Sedimentary rocks are types of rock that are formed
by the deposition of material at the Earth's surface
and within bodies of water.
• The formation takes place by 4 methods.
Formation
Weathering Transportation Deposition Consolidation
WEATHERING:
• Weathering means “erosion of existing rocks”.
• This weathering takes place in 2 ways.
WEATHERING
MECHANICAL
WEATHERING
CHEMICAL
WEATHERING
TRANSPORTATION OF ERODED SEDIMENT:
• After the erosion process (weathering) the products are
transported .
• This transportation is mostly done by
running waters.
DEPOSITION OF THE ERODED SEDIMENT:
• This transportation continues till the velocity of
transporting medium id unchecked.
• When it reaches big waters like oceans the deposition
process takes place.
LITHIFICATION:
• The transformation of a loosely deposited sediment
into a rock is called as lithification.
• This is done in 2 ways.
Lithification
By Compaction
(or) Consolidation
By Cementation
CLASSIFICATION OF
SEDIMENTARY ROCKS
• Based on the processes responsible for their formation, sedimentary
rocks can be subdivided mainly into two groups:
1.Clastic Rocks
2.Non-Clastic Rocks
• The non-clastic rocks are again classified into two types.
• They are:
1.Chemical
2.Organic
• CLASTIC ROCKS:
• Clastic sedimentary rocks are composed of silicate minerals and rock
fragments that were transported by moving fluids (as bed load, suspended
load, or by sediment gravity flows) and were deposited when these fluids
came to rest. Clastic rocks are composed largely of quartz, feldspar, rock
(lithic) fragments, clay minerals, and mica; numerous other minerals may be
present as accessories and may be important locally.
SANDSTONE:
CONGLOMERATE:
CHEMICALLY FORMED ROCKS:
• Chemical sedimentary rock forms when mineral constituents
in solution become supersaturated and inorganically precipitate.
Common chemical sedimentary rocks include oolitic
limestone and rocks composed of evaporite minerals such
as halite (rock salt), sylvite, barite and gypsum.
ROCK SALT:
DOLOMITE:
• ORGANICALLLY FORMED ROCKS:
• Biochemical sedimentary rocks are created when organisms use materials
dissolved in air or water to build their tissue. Examples include:
• Most types of limestone are formed from the calcareous skeletons of organisms
such as corals, mollusks, and foraminifera.
• Coal which forms as plants remove carbon from the atmosphere and combine
with other elements to build their tissue.
• Deposits of chert formed from the accumulation of siliceous skeletons from
microscopic organisms such as radiolaria and diatoms.
COAL:
OIL SHALE:
TEXTURES
• The size, form and orientation of clasts or minerals in a rock is
called its texture. The texture is a small-scale property of a rock,
but determined many of its large-scale properties, such as the
density, porosity or permeability.
• The form of a clast can be described by using four parameters:
• Surface texture describes the amount of small-scale relief of the
surface of a grain that is too small to influence the general shape.
• Rounding describes the general smoothness of the shape of a
grain.
• 'Sphericity' describes the degree to which the grain approaches
a sphere.
• 'Grain form' describes the three dimensional shape of the grain.
STRUCTURES OF SEDIMENTARY
ROCKS
• The term structure signifies some large scale
features developed in the rock masses during the
process of their formation.
• Structure is of 3 types:
STRUCTURE
MECHANICAL
CHEMICAL ORGANIC
• MECHANICAL STRUCTURE:
• These are developed due to physical processes operating at the time of
deposition of the sediments.
• The various types of mechanical structures are as follows:
1.Stratification
2.Lamination
3.Cross Bedding
4.Graded Bedding
5.Mud Cracks
6.Rain Prints
7.Ripple Marks
CHEMICAL STRUCTURES:
• Many sedimentary rocks are formed due to the chemical processes
such as evaporation, precipitation and crystallization.
• A few types of chemically formed rocks are:
1.Concretionary structure
2.Nodular structure
3.Geode structure
ORGANIC STRUCTURES:
• Some structures develop in the sedimentary rocks due to the manner
in which the organic source material gets accumulated and compacted
to form a rock.
• They form 2 types of structures namely, fossilferrous and stromatolitic
structures.
SEDIMENTARY ROCKS
Iron Ore
Limestone
Shale
Flint
Conglomerate
Chert
Coal
Breccia
ENGINEERING PROPERTIES OF
SEDIMENTARY ROCKS:
• Compressive strength and deformability of sandstone is
influenced by its porosity, the amount and type of cement,
and matrix material, grain contact and composition.
• Shale mineral content influences geotechnical properties;
most important is the quartz-clay mineral ratio.
• Grain size and Cementation influence engineering
properties of carbonate sediments.