Unit 3 Rock Types Sedimentary Rocks Basic Rock

Unit 3 - Rock Types Sedimentary Rocks

Basic Rock Classifications ● Igneous ● Sedimentary ● Metamorphic

Sedimentary Rocks • Make up 5% of Earth’s 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 • Agents: water, ice, and wind – Over geological time, sediments transform into sedimentary rock.

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 oxide

Cementation

Classes of 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: grain size ● Clay (very fine) - shale ● Silt (fine) - siltstone ● Sand - sandstone Shale Sandstone Siltstone

Grain Shape ● Angular gravel particles - Breccia ● Rounded gravel particles- 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 size/shape? ⦿ Large grain size = (less current velocity) 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 from source

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, dolomite, nodular chert

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 Stala. Ctites: are icicle-like pendants that hang from the Ceiling. Water seeps through cracks in the ceiling of the cave. Stala. Gmites: form from the Ground. The precipitated limestone that makes up stalactites and stalagmites is called travertine.

Stalactites and Stalagmites

Biochemical Sedimentary Rocks Biochemical: Rocks that are formed from living material

Biochemical Sedimentary Rock Examples ⦿ Coquina – forms from the build-up, compaction, and cementation of shells from dead organisms (mostly on beaches).

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

Biochemical Sedimentary Rock Examples ⦿ Chert – forms from the accumulation of 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 Examples ⦿ Coral limestone – accumulations of coral 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 Examples ⦿ Coal – formed from the accumulation of 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). 1) Lignite – decreased levels of volatiles. 1) Bituminous – higher grade of coal than lignite. 1) 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 ⦿ Next Map for rocks class – Metamorphic Rocks