Unit 3 - Rock Types

Unit 3 - Rock Types

Unit 3 - Rock Types Sedimentary Rocks Basic Rock Classifications Igneous Sedimentary

Metamorphic Sedimentary Rocks Make up 5% of Earths outer 16 km and 75% of continental crust. Originate from sediment produced from: (i) physical breakdown of pre-existing

rock (ii) chemical weathering followed by precipitation of dissolved materials. Sedimentary Rocks Sediment becomes eroded then

deposited in water or air and later lithified into a solid mass. Weathering: The break up of existing rocks Two Types: Chemical and Mechanical Erosion: The movement of eroded rock material Lithification - pg. 158

Lithification: The process of when sediments form into rock Two sub processes 1. Compaction 2. Cementation Lithification: Compaction

Compaction: Occurs when sediments get buried deep underground pressure from the burial solidifies material into rock. This results in reduced porosity (less space)

and permeability. Lithification: Cementation Cementation: Minerals precipitate from groundwater and fill the spaces between sediments It is crystallization of minerals in the pore

space. Reduces porosity and permeability Precipitates include: Silica, calcite, iron Cementation Classes of Sedimentary Rocks

Sedimentary Rocks are classified in three ways: 1. Clastic (formed from weathering) 2. Chemical (formed from precipitates) 3. Biochemical (formed from living material)

1. Clastic/Detrital Rocks Formed from mechanical weathering of preexisting rocks e.g., shale, siltstone, sandstone, conglomerate, breccia 1. Clastic/Detrital Rocks

Clastic rocks are classified based on: 1. Grain size 2. Grain Shape 3. Sorting Clastic Sedimentary Rock classification: Shale

grain size Clay (very fine) - shale Sandstone Silt (fine) - siltstone Sand - sandstone Siltstone

Grain Shape Angular gravel particles - Breccia Rounded gravel particles- Conglomerate Conglomerate

Breccia Sorting Is the degree of similarity in particle size in a sedimentary rock well sorted sediment: all the particles are the same size

- wind blown, - transported a great distance, - deposited slowly Sorting poorly sorted sediment: show variation in size and shape

- wave action, - turbulent streams, - transported a short distance, - deposited rapidly Sorting Degree of rounding indicates the distance or time

involved in transportation in air or water Size of sediment indicates strength of current/wind Sorting

The faster flowing the wind/water the finer the sediment and more rounded High Velocity Low Velocity

Breccia, Conglomerate Sandstone Siltstone Shale COARSE FINE

Horizontal Sorting Vertical Sorting What can we tell from grain Large grain size = (less current velocity) size/shape?

closer to source Smaller grain size = (more current velocity) father

from source Angular grains = (less current velocity) closer to source

Rounded grains = (more current velocity) farther Clastic Depositional Environments

Sedimentary rock types form in specific places Fluvial (Rivers/streams) Conglomerate, Breccia, Sandstone, Siltstone, Shale Lagoonal/Bays Siltstone, Shale Beaches Conglomerate, Sandstone Clastic Depositional Environments

Deep Marine Conglomerate, Sandstone, Siltstone, Shale, but is dominated by chemical sedimentary rocks. Shallow Marine Conglomerate, Sandstone,

Siltstone, Shale Fluvial Beach Fluvial

Shallow Marine 2. Chemical Sedimentary Rocks 2 Types of Chemical sedimentary rocks: 1) Evaporites

2) Precipitates Chemical Sedimentary Rocks types 1) Evaporites When water evaporates dissolved minerals are left behind e.g., halite (rock salt), gypsum, sylvite

Salt flats Chemical Sedimentary Rocks types 2) Precipitates Due to Changes in Environmental

conditions. E.g., Temperature change, chemical change, concentration change. Chemical weathering dissolving of chemicals e.g., compact limestone, travertine,

Chemical Depositional Environments: 1. Shallow Marine e.g., gypsum, halite, sylvite, limestone and dolomite 2. Deep Marine e.g., limestone, dolomite and nodular

chert 3. Cave - Stalactites and stalagmites Stalactites and stalagmites StalaCtites: are icicle-like pendants that hang from the Ceiling. Water seeps through cracks in the ceiling of the cave.

StalaGmites: form from the Ground. The precipitated limestone that makes up stalactites and stalagmites is called Stalactites and Stalagmites

Biochemical Sedimentary Rocks Biochemical: Rocks that are formed from living material Biochemical Sedimentary Rock Coquina forms from the build-up,

Examples compaction, and cementation of shells from dead organisms (mostly on beaches). Biochemical Sedimentary Rock

Chaulk forms from the accumulation, Examples compaction, and cementation of microscopic marine organisms such as formaminifera (i.e. deep marine) Biochemical Sedimentary Rock

Chert forms from the accumulation of Examples microscopic marine organisms, such as radiolaria and diatoms, that form a very hard rock consisting of microcrystalline

silica. E.g. of chert include jasper, flint, and agate (i.e. deep marine) Biochemical Sedimentary Rock Coral limestone accumulations of coral

Examples can be compacted and cemented into coral limestone (i.e. shallow marine) What are corals? Corals: organisms that are capable of

creating large quantities of marine limestone from their shells and external skeletons which are composed of calcium carbonate. Biochemical Sedimentary Rock

Coal formed from the accumulation of Examples plant material, which is buried and chemically altered over millions of years. The Formation of Coal - Swamps

There are 4 stages of coal formation: 1) Peat earliest stage of plant accumulation. Contains large amounts of volatiles. (PEAT IS NOT A ROCK). 2) Lignite decreased levels of volatiles.

3) Bituminous higher grade of coal than lignite. 4) Anthracite final stage of coal formation. It is Increasing Grade classified as a metamorphic rock due to heat,

pressure, and hot chemical fluids. It burns cleaner. Small amount available world-wide. Depositional Environments

Swamp Coal Shallow Marine Coquina, Limestone (Coral) Beach Coquina Deep Marine Chaulk, Chert

Think about the concept of systems. How do biochemical sedimentary rocks and coral represent interaction of the spheres? Core Lab 3 Sedimentary Rocks

Concept Map for rocks Next class Metamorphic Rocks

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