Classification of

Clastic Sedimentary Rock

*formed from broken rock fragments weathered and eroded by river, glacier, wind and sea waves. These clastic sediments are found deposited on floodplains, beaches, in desert and on the sea floors.

CLASTIC ROCKS

Clastic rockssolidify

• Clastic rocks are classified on the basis of the grain size: conglomerate, sandstone, shale etc.

*Clastic rocks mainly comprise broken fragment of older rock – they are also know as Terrigenous rocks

Clastic Rock:-

Clastic Process-

RUDACEOUS Rock

ARENACEOUS Rock

ARGILLACEOUS Rock

•RUDACEOUS ROCKS:- •These include all coarse grained clastic rock of heterogeneous These include all coarse grained clastic rock of heterogeneous composition. composition. •Made up of rounded or sub-rounded Pebbles - cobbles (Conglomerate) and angular to subangular Pebbles - cobbles ( breccia ) .•Example-1.Conglomerate 2.Breccia

It is consist rounded fragments of various sizes, but generally above 2 mm. Conglomerate rock is a Conglomerate rock is a

common sedimentary common sedimentary rock. rock.

Conglomerate is a Conglomerate is a sedimentary rock formed sedimentary rock formed from rounded gravel and from rounded gravel and boulder sized clasts more boulder sized clasts more than 30% by volume than 30% by volume cemented together in a cemented together in a matrix.matrix.

• Rounded clasts.Rounded clasts.• Unique clast Unique clast

composition.composition.• Uniform clast-size.Uniform clast-size.• Chaotic clast Chaotic clast

orientation.orientation.

Conglomerate

(A) (B)

(A) Extraformational Conglomerate:-(A) Extraformational Conglomerate:-

Clasts derived from a Clasts derived from a distant source.distant source.

A conglomerate in which clasts are A conglomerate in which clasts are exotic (i.e., derived from outside the exotic (i.e., derived from outside the depositional basin). Clasts are depositional basin). Clasts are normally very well rounded and well normally very well rounded and well sorted as they have been transported sorted as they have been transported for larger distance.for larger distance.

1.OrthoConglomerate:-:-conglomerates may have no matrix between clasts (open conglomerates may have no matrix between clasts (open framework) or spaces between clasts may be filled by less framework) or spaces between clasts may be filled by less

than 15 % matrix of finer sediment (closed framework).than 15 % matrix of finer sediment (closed framework). 2.ParaConglomerate:-conglomerate conglomerate in which most clasts are not in contact; i.e., the in which most clasts are not in contact; i.e., the matrix supports the clasts which is more than 15%matrix supports the clasts which is more than 15%

Oligomictic conglomerate :-Oligomictic conglomerate :-A conglomerate in which the clasts are made up of A conglomerate in which the clasts are made up of only one rock type.only one rock type.Suggests that the source area was nearby Suggests that the source area was nearby and have one or similar source rock.and have one or similar source rock.

Polymictic conglomerate :-Polymictic conglomerate :-Conglomerates that include clasts Conglomerates that include clasts from a wide-variety of source rocks, from a wide-variety of source rocks, possibly derived over a wide possibly derived over a wide geographical area or a smaller but geographical area or a smaller but geologically complex areageologically complex area..

(B) Intraformational conglomerate :-(B) Intraformational conglomerate :-

A conglomerate in A conglomerate in which clasts are which clasts are derived locally from derived locally from within the within the depositional basin depositional basin (e.g., clasts composed (e.g., clasts composed of local muds torn up of local muds torn up by currents; such by currents; such clasts are commonly clasts are commonly termed "rip-up termed "rip-up clasts" or "mud clasts" or "mud clasts").clasts").

Deposition in an Deposition in an environment environment where muds where muds accumulated. accumulated. Muds were in very Muds were in very close proximity to close proximity to the site of the site of deposition as the deposition as the clasts would not clasts would not withstand withstand considerable considerable transport. transport.

If grains are rounded, the rock is termed as ‘Breccia’

• GRAIN SIZE-2mm to several cm, in finer matrix

volcanismte

cton

ismweathering

Meteoric impact

ARGILLACEOUS ROCKS:- Made up of clay size sediments. This is fine grained rock

and grain size 1/250mm to 1/64mm.Example-1. Shale2. Mudstone3. Claystone

*Shales are clastic rocks, made up mainly fine silt/clay*They are most abundant

sedimentary rocks, accounts for about 80% of them*Often contain fossils*Mostly hydrous aluminum

silicate in composition = from weathered feldspars

• Shales are made of fine well sorted silt and clayey sediments, where normally one can expect high porosity and permeability.

Shale= Quartz + feldspar + mica

Rock Type

Sediment Grain Size

Shale Clay less than 0.001 mm

Shale

Three type on the basis of their Origin-1.Residual Shales2.Transported Shales3.Hybrid Shales

• A grey or black rock formed from mud, mudstones contain both detrital minerals, such as quartz and feldspar, and clay minerals and carbonaceous matter. Individual grains, however, are too small to be seen without a hand lens. Some mudstones are fossiliferous, others are calcareous and react with acid.

• GRAIN SIZE-Less than 0.1mm.• ESSENTIAL COMPONENTS-

Quartz, feldspar.

Grey mudstone in Namibia

• Clay is typically dark to light grey but a pure white variety called china clay can occur. Individual grains may be seen only under powerful microscopes.

• GRAIN SIZE - Less than 0.005mm. ESSENTIAL COMPONENTS - Clay minerals, such as

kaolinite, illite

•ARENACEOUS ROCKS:-• Made up of mainly sand e.g. Sandstone. These rocks are either accumulated by wind action or deposited under water action or marine to non marine. This rock is medium grained and grain size is 1/16mm to 2mm.•Example-1.Sandstone2.Silt stone3.Arkose 4.Greywacke5.Grit This rock other name is Terrigenous.

Sandstone:- One of the most common sedimentary rocks,

sandstone is usually quartz-dominated with visible sandy grains.

• GRAIN SIZE-0.1–2mm. ESSENTIAL COMPONENTS-

Quartz, feldspar. ADDITIONAL COMPONENTS-

Mica and many others.

Classification of Sand Stone

Silica (SiO3) is cementing material

In cementing material is CaCO3 & Mg

Cementing material is clayey in character

Cementing material is fe composition

Siltstone:-

GRAIN SIZE 0.1–2mm. ESSENTIAL COMPONENTS-Quartz,

feldspar. ADDITIONAL COMPONENTS-Mica and

many others.

Siltstone is another detrital sedimentary rock, lying in grain size between sandstone and mudstone. Like sandstone, it can form in different environments and have different colours and textures, but reds and greys, and planar bedding are typical. Plant fossils and other carbonaceous matter are common in darker-coloured siltstones. The presence of mica may produce a flaggy siltstone.

A pink sandstone, the colour of which is due to an abundance of feldspar, especially pink alkali feldspars.Arkose forms by the fast deposition of sand weathered from granites and gneissesGRAIN SIZE= 0.1–2mm. ESSENTIAL COMPONENTS- Feldspar, quartz.

• Greywacke has formed from a mixture of sand and, proportionately less, mud. It is a dark-coloured rock( grey, dark green, or black) containing .

• Poorly sorted angular fragments of quartz and basic igneous rock and fine grained chlorite or clay material.

• Greywacke's may contain as much as 30% fine grained clay or chlorite or both.

• GRAIN SIZE 0.005–2mm. • ESSENTIAL COMPONENTS-

Rock and mineral fragments.

Grit or Grit stone:-Grit is a hard,coarse grained rock , siliceous sandstone.It is a sandstone containing sharply angular grain that May rub off easily.Most grit are formed in water.

The chief mineral components are quartz , feldspar and mica.

This term is especially applied to such sandstone that are Quarried for building material.