Unit 3 - Rock Types Sedimentary Rocks

Basic Rock Classifications Igneous Sedimentary Metamorphic

Make up 5% of Earth’s outer 16 km and 75% of continental crust. 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.

Weathering: The break up of existing rocks 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 Compaction 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 Sedimentary Rocks are classified in three ways: Clastic (formed from weathering) Chemical (formed from precipitates) Biochemical (formed from living material)

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

Clastic/Detrital Rocks Clastic rocks are classified based on: Grain size Grain Shape Sorting

Clastic Sedimentary Rock classification: grain size Shale Clay (very fine) - shale Silt (fine) - siltstone Sand - sandstone 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 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

Beach Fluvial Fluvial Shallow Marine

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 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 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: Peat – earliest stage of plant accumulation. Contains large amounts of volatiles. (PEAT IS NOT A ROCK). Lignite – decreased levels of volatiles. Bituminous – higher grade of coal than lignite. Anthracite – final stage of coal formation. It is classified as a metamorphic rock due to heat, pressure, and hot chemical fluids. It burns cleaner. Small amount available world-wide. Increasing Grade

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