characteristics of sedimentary rocks

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Sedimentary Rocks

compaction of the sediments.

• Sedimentary rocks are formed due to the aggradations and compaction of the sediments.

• The word sedimentary has been derived from the Latin word which means settling down..

Stratified or layered rocks

• The sedimentary rocks are also Called as Stratified or layered rocks and hence Consists of different types of layers and strata of various sediments. Some sedimentary rocks do not consist of layers, ex: loess.

Characteristics of Sedimentary rocks

• Sedimentary rocks are formed of sediments derived from older rocks, Plants and animal remains thus these rocks contains fossils of animals and plants

Characteristics of Sedimentary rocks

• The sedimentary rocks are widespread about 75 % of the globe consists of sedimentary rocks and the remaining 25% by igneous and metamorphic rocks. Nevertheless the sedimentary constitute only 5 % of the composition of earth’s crust

Characteristics of Sedimentary rocks

• The deposition of sediments takes place in a certain sequence. The size of the Sediments decreases from the littoral margins to the centre of the water bodies.

littoral margins

Characteristics of Sedimentary rocks

• The sedimentary rocks are consolidated and compacted by cementing elements Such as Silica, iron compounds, Calcite, Clay Etc

Characteristics of Sedimentary rocks

• of cementing materials and the rocks are Seldom found in their original manner because of the lateral compressive and tensile forces

Characteristics of Sedimentary rocks

• Sedimentary rocks are seldom crystalline but are Characterized by Joints perpendicular to the bedding Planes

Characteristics of Sedimentary rocks

• The connecting Plane between two consecutive beds or layers is called as bedding Plane.

Types of formation in Sedimentary rocks

• When two beds are uniform along the bedding Plane then this type of formation is called conformity.

two beds

• conformity.

Types of formation in Sedimentary rocks

• When two beds are not uniform then the structure is called as Unconformity.

Types of Unconformity

• Non-conformity (where sedimentary rocks succeed igneous & metamorphic rocks)

• Angular unconformity (where horizontal sedimentary beds are deposited over the previously folded strata)

• Disconformity (where two conformable beds are separated by Changes in sediment type.

• Paraconfirmity ( where two sets of conformable beds are Separated by same set of sediments)

Disconformity AND Angular unconformity

• Sedimentation units in the rocks which are more than One centimeter is called BEDS

• The upper and lower surface of the beds are called BEDDING PLANE or BOUNDING PLANES

• Sometimes the lower surface of the bed is called SOLE. There are further sedimentary units within a bed. The units having more than one centimeter is called layer or Strata Where as the units below one centimeter are Called laminae

strata and laminae

• Thus several strata and laminae make up a bed. When beds are deposited at an angle to the depositional surface they are called cross beds and the general phenomena of inclined layers are called cross lamination or cross bedding.

MUD CRACKS

• Soft mud or alluvial deposits by rivers develop cracks when baked in sun and these cracks are generally of Polygonal Shape, such cracks are Called MUD CRACKS OR SUN CRACKS.

Permeable and Porous

• Most of the sedimentary rocks are Permeable and Porous but few of them are nonporous and Impermeable

Classification of sedimentary rocks

• ON THE BASIS OF NATURE OF SEDIMENTS

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Classification of sedimentary rocks

– ON THE BASIS OF NATURE OF SEDIMENTS

– Mechanically formed or clastic rocks

• Sandstones

• Conglomerates

• Clay rock

• Shale

• Loess

Classification of sedimentary rocks

– ON THE BASIS OF NATURE OF SEDIMENTS

– Chemically formed sedimentary rocks

• Gypsum

• Salt rock

Classification of sedimentary rocks

– ON THE BASIS OF NATURE OF SEDIMENTS

– Organically formed sedimentary rocks

• Limestone

• Dolomites

• Coals

• Peats

ON THE BASIS OF TRANSPORTING AGENTS

– Argillaceous or aqueous rocks

• Marine rocks

• Lacustrine rocks

• Riverine rocks

ON THE BASIS OF TRANSPORTING AGENTS

– Aeolian sedimentary rocks

• Loess

ON THE BASIS OF TRANSPORTING AGENTS

– Glacial sedimentary rocks

• Till

• Moraines

Mechanically formed sedimentary Rocks

• Mechanically formed sedimentary Rocks

Mechanically formed sedimentary Rocks

• Previously formed rocks are subjected to mechanical or physical disintegration these are called fragmental rock materials or Clasticmaterials which become the source materials for the formation of mechanical or clasticsedimentary rocks. These materials are further broken down in to fragments during their transportation by the exogenous process such as wind, running water glacier etc, some of the important members of this group are Sandstones, conglomerates, Silt, shale, Clay etc.

Mechanically formed sedimentary Rocks

• Previously formed rocks are subjected to mechanical or physical disintegration these are called fragmental rock materials or Clasticmaterials which become the source materials for the formation of mechanical or clasticsedimentary rocks. These materials are further broken down in to fragments during their transportation by the exogenous process such as wind, running water glacier etc, some of the important members of this group are Sandstones, conglomerates, Silt, shale, Clay etc.

Mechanically formed sedimentary Rocks

• Sandstones

• Sandstones are formed mostly due to the deposition, Cementation, compaction of Sand grains. The Sand grains are divided into five categories on the basis of their size

Classification of sands by grain size

Sand types Grain size (in mm)

Very Coarse sand 1.0 to2.0

Coarse Sand 0.5 to 1.0

Medium sand 0.25 to 0.5

Fine sand 0.125 to 0.25

Very Fine sand 0.0625 to 0.125

•

• These grains are deposited in the water bodies, and are aggravated and consolidated by Cementing elements such as Silica, Calcium, iron oxide Clay etc. The Colourof the sandstone Varies according to the nature of the cementing elements. Sandstones become red and gray when cemented by iron oxide and in to white when the cementing element is replaced by calcium Carbonate. They become hard and resistant when cemented by Silica. On an average the sandstones are generally porous rocks.

•

• These grains are deposited in the water bodies, and are aggravated and consolidated by Cementing elements such as Silica, Calcium, iron oxide Clay etc. The Colourof the sandstone Varies according to the nature of the cementing elements. Sandstones become red and gray when cemented by iron oxide and in to white when the cementing element is replaced by calcium Carbonate. They become hard and resistant when cemented by Silica. On an average the sandstones are generally porous rocks.

•

• These grains are deposited in the water bodies, and are aggravated and consolidated by Cementing elements such as Silica, Calcium, iron oxide Clay etc. The Colourof the sandstone Varies according to the nature of the cementing elements. Sandstones become red and gray when cemented by iron oxide and in to white when the cementing element is replaced by calcium Carbonate. They become hard and resistant when cemented by Silica. On an average the sandstones are generally porous rocks.

• Sandstones

• On the basis of mineralogical and textural Characteristics sandstones are classified in to the following types

• Quartz Arenites (composed entirely of quartz grains)

• Quartz Arenites (composed entirely of quartz grains)

• Arkose Sandstones (feldspar being the dominant Mineral)

• Lithic Arenites (composed of fine grained rock fragments derived from Shales, schist, slates and volcanic rocks).

• Greywackle Sandstones (Composed of feldspar, rock fragments, quartz).

• Note: The English word Arsenite is derived from Latin word Arena-meaning thereby Sand.

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• Conglomerates

• They are formed due to the consolidation and cementing of pebbles of various Sizes with Sands. Polished round fragments of size with 4 mm of diameter are called Pebbles and those with a diameter 256mm are called boulders. Angular rock fragments are Called breccia.

• Clay rock and shale

• They are formed due to the deposition and cementation of fine sediments.

• Clay rock and shale

• . Sediment having grain size of 0.3mm to O.4mm are called silts where as Clays are formed When the grain size is between 0.4mm to O. 00012 mm are Cemented or consolidated.

• Clay rock and shale

• . Clay rocks are formed exclusive Kaolin minerals and pure White in colour but they Change to different colours because of being mixed with impurities.

Chemically formed sedimentary Rocks

• When Running Water containing chemicals come in touch with the rocks containing Soluble materials are washed away and come in contact with the Chemicals. The Chemical materials are then settled down, compacted and cemented to form Chemical sedimentary rocks such as gypsum and salt rocks.

Organically formed sedimentary rocks

• The sediments derived from the disintegration and decomposition of Plants and animals deposit and consolidate to form organic sedimentary rocks. The rocks are divided in to three categories on the basis of its carbon and lime content. They are

Organically formed sedimentary rocks

• Calcareous rocks

• Carbonaceous rocks

• Siliceous rocks

• Calcareous rocks

Organically formed sedimentary rocks

• Calcareous rocks are formed due to the deposition and consolidation of sediments derived from the remnants of animals and plants which contain lime. Limestone is one of the examples of the calcareous rocks. Limestone is formed in the following Manner

Organically formed sedimentary rocks

• Calcium oxide (Cao) reacts with water to form Calcium hydroxide Ca (0H) 2. This is given by the following equation,

Limestone is formed in the following Manner

• Then Calcium hydroxide reacts with Carbon dioxide (CO2) to give Calcium carbonate CaCo3 this is given by the following equation,

Limestone is formed in the following Manner

Limestone : calcareous rocks

•

• The calcareous rocks are collectively called as carbonate rocks or carbonates. Calcium carbonate (Caco3), Magnesium carbonate (Mgco3), dolomite (CaMg (co3)2 are important calcareous rocks. Limestone is both thinly beaded and thickly bedded. The most dominant minerals are calcite (Hexagonal), Aragonite (orthorhombic).

Limestone : calcareous rocks

• Though Limestone are weak rocks in humid regions they become more resistant when exposed to dry climate, because of its uniform or homogenous structure they are not easily affected by differential expansion and contraction due to temperature.

Limestone : calcareous rocks

• The Carbonate rocks after Chemical weathering give birth too karst topography. Chalks another form of Carbonate rocks are formed due to the Precipitation of Carbonate minerals desired from microorganisms like foraminifera.

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ARGONITE ROCKS (ORTHOTHROMBIC) CALCITE ROCKS

(HEXAGONAL)

Ex 9-igneous rock-Page 63The Palisades rising above the Hudson

River

Location map of the Palisades Sill (red) within the Newark Basin (yellow)

• The outcrop of the Palisades Sill is quite recognizable for its prominent cliffs above the Hudson River; it is easily seen from the western portions of Manhattan

• The exposure is approximately 80 kilometers (50 mi) long, most of it following the Hudson River. It first emerges in Staten Island in New York City.[1] The sill then crosses the state line into New Jersey, where Hoboken, Jersey City, Union City, Fort Lee, and Englewood Cliffs all lie on it

• The sill eventually crosses back into New York, following the Hudson River north until reaching Haverstraw. It is at this point that the sill makes a turn to the west, where it disappears near Pomona. At this turn, the sill cuts across local strata, making it a dike in that area, not a sill.

• It has been proposed that the sill reemerges in two locations in Pennsylvania (where the outcrops are also discordant with local strata), but this idea is not generally agreed upon, and discussion of the Palisades Sill is usually limited to the exposure in New York and New Jersey.

Figure 11

• Separate host of granite from the mafic (Mg and Fe)

• Suggest a origin of these zones:

• 1. partial melting-produces basalt

• 2. magnetic differentiation is best answer: it separates early formed-denser material from magma

Figure 11

• 3. also assimilation: since as magma rises-it may add ions by melting

• As new material is incorporated –the magma composition may change enough to enable crystal to form –which might not ever been otherwise able to be produced

Figure 11

• 4. lastly-magma mixing-evidence suggests some intermediate rocks did not crystalize

• So they formed when-felsic and mafic were mixed

Figure 12

• Tectonic settings for major igneous rock types

• Convergent boundaries

• Subduction zones

• Volcanic island arcs

• Andean –type mountains

Divergent boundaries

• Ocean hot-spot islands-basalt

• Ocean floors-basalt (MORB)

• Mid ocean ridges-basalt (MORB)

• Continental rift zones (Ryolite)

• Continents (granite, ryolite, basalt

Ex 10-page 65

• A. mid ocean ridges

• B. continental rifts

• C. oceanic and continental volcanic arcs

• D. hot spots