Earth Materi ials Unit: Sedimentary Rocks and Proces sses Maybe One Day Text: Chapters Fivee and Six Lab: Laboratory Six Name Page 1
Sedimentary Rocks and Processes Purpose: To classify sedimentary rocks and features by their physical and chemical properties. -By the end of this unit, students are expected to be able to: 1. Outline the origin and process of sedimentary rock formation. 2. Contrast clastic sediments with chemical (precipitate or biochemical) sediments and the rocks they become. 3. Describe the features of, and identify, the following sedimentary rocks: Conglomerate Limestone Breccia Chert Sandstone Gypsum Siltstone Rock Salt Shale Coal 4. Diagram and describe the following sedimentary features and use them to reconstructt hypothetical sedimentary environments: a) Sedimentary structures: Stratification, crossbedding, ripple marks, mud cracks, graded bedding, varves. b) Particle size, shape and sorting. c) Fossils and organic structures Page 2
s and Processes Part A: What is a Sedimentary Rock? -Sedimentary rock is rock that is composed of sediments. -Sediments are loose grains and chemical residues of rocks and minerals, and of plants and animals. -Sediments are formed from parent materials at a source location. At the source, the parent material is weathered (broken up or dissolved) into sediments or aqueous solutions. -The weathered material is eroded (removed from its source) and transported some distance, and then deposited. -The weathered material is then lithified (hardened into rock by pressure and/or cementation), or precipitates from solution. *95% of the earth s crust is composed of crystalline rock (igneous or metamorphic). However, sedimentary rock is the most common rock at or near Earth s surface! Part B: Sedimentary Rock Formation -Using the paragraph above, name the four basic steps in sedimentary rock formation: a) b) c) d) *In the following pages, we will explore each of these steps: Step 1: Weathering Processes -Weathering is the chemical or physical breakdown of Earth ss materials. 1. Mechanical (or Physical) Weathering -Mechanical weathering is the -Types of mechanical weathering include: a) Frost Wedging -What types of sediments and debris features are formed through frost wedging? Page 3
-In what environment would frost wedging be very prominent? _ -Where would frost wedging not be found? b) Thermal Expansion and Contraction -How can heat cause rocks to be broken down? _ -In what environment would thermal expansion be very prominent? _ c) Pressure Release -Describee how an exfoliation dome is created: -Exfoliation is a big concern in underground mining as it can result in rock bursts. d) Biotic Weathering -How can living organisms cause weathering? 2. Chemical Weathering Chemical weathering is the breakdown of rocks and minerals by chemical alteration of the parent material. -How does the product of chemical weathering differ from that of mechanical weathering? _ -Water is the most important agent in chemical weathering as it is a universal solvent and its chemical activity is increased by the addition of small amounts of dissolved materials. It plays a leading role in the three major types of chemical weathering: Page 4
a) Dissolution -Some minerals (such as Halite) dissolve easily in pure water,, but most minerals are insoluble. However, water containing acid (H+ ions) is a much more efficient weathering agent. -What are three sources for H+ ions? -For example, Calcite (Limestone, Marble) is a mineral dissolved completely by acidic water. No new minerals are created through this reaction! b) Hydrolysis -Reaction of acidic water with silicate minerals ( Feldspars, Quartz) that changes the silicate structure of the mineral and results in the production of ions and clay minerals. c) Oxidation -Oxygen combines with iron to form oxides (Hematite and Limonite). -What type of minerals would be most affected? -Why does oxidation occur more quickly in the presence of water? Page 5
*Chemical Weathering Produces: a) Changes to the internal structure of minerals: b) Physical changes to rocks: *Rates of Chemical Weathering are Affected by: a) Rock Characteristics s -Mineral Composition: -Physical Characteristics: Why would fractures or particle sizee affect the rate of weathering? b) Climate: What type of climate would promote greater chemical weathering? Page 6
c) Differential Weathering *Mechanical and chemical weathering occur at the same time and can work in concert: Page 7
Step 2: Erosion and Sedimentary Depositional Environments -Erosion is the movement of weathered materials from its source to depositional environment. -What are some processes of erosion? -Sediments can come in a variety of sizes and shapes and can be classified as: a) Detrital Sediments b) Chemical Sediments -Would you expect to find angular and very poorly sorted sediments close to or far away from their parent material? -Sorting and rounding become more prominent the further sediments are transported. -Transported sediments are eventually deposited in three mainn environments. Take your own notes from text 141 to 144. a) Continental Page 8
b) Transitional c) Marine Step 3: Lithification -Finally, after being deposited sediments can be transformed into sedimentary rock by lithification, which involves two processes: 1. Compaction _ 2. Cementation Precipitation of minerals onto the sediments, eventually filling the pore space and joining sediments together. -What are the most common mineral cements? _ -Most sedimentary rocks are formed through lithification, but some are products of crystal growth and are called evaporates. We will explore these later in the package. Page 9
-Which of the rocks below was transported the farthest from its source? How do you know? -Which of the rocks below was deposited deeper in an ocean or lake? How do you know? Page 10
Part C: Types of Sedimentary Rocks Detrital Sedimentary Rocks - Detrital sedimentary rocks are separated from Chemical and d Biochemical Sedimentary Rocks as they are composed of: -Detrital rocks are also called Siliclastic because their main constituents are: a) _; b) -This rock category is divided into different rock types according to grain/sediment size (examine Lab Book Figure 6.3 on page 131). -What can grain size reveal about the depositional environment? -Take your own notes on the different types of Detrital Sedimentary rocks: : a) Mudstone (Claystone, Shale, Siltstone) Particle Size: _ Depositional Environment: _ Strength: Breakage: Other Characteristics: Page 11
b) Sandstone (Quartz, Arkose, Wacke) Particle Size: Depositional Environment: Sorting: Roundness Composition _ Types: i) Quartz Sandstone: ii) Arkose Sandstone: iii) Wacke Sandstone: _ *The Folk Classification System for Sedimentary Rocks takess the ratio of mud to sand very seriously Page 12
c) Conglomerate and Breccia Particle Size: _ -Compare and contrastt Conglomerate and Breccia depositional environments as revealed by their constituent particles: Chemical Sedimentary Rocks -Are the product of materials carried in solution when it precipitates to form chemical sediments. -Precipitation occurs as a product of evaporation (crystalline texture) and the chemical activity of organisms like corals (clasticc texture). a) Limestone Composition: Formation Process: Types: i) Organic Limestone: ii) Inorganic Limestone: Page 13
b) Chert (Flint, Jasper, Agate) Composition: Formation Process: d) Evaporites -Evaporation results in the precipitation of minerals (halite, gypsum) out of solution. Coal -Take your own notes on coal formation from text pages 1555 to 166. Page 14
Part D: Reading the Rock Record -The rocks making up Earth s crust form the only record of prehistory. -Sedimentary rocks are very valuable as they contain evidencee of the environment at the type of deposition as their properties result from the physical, chemical and biological processes that existed. -Additionally, the structures that sedimentary rocks form and the fossils they contain can provide further information. Sedimentary Structures A sedimentary structure is any feature in sedimentary rock formed at or shorty after deposition. a) Strata or Beds: b) Bedding Planes: c) Cross-Bedding: Animationn 1, Animation 2 -What direction was the current/wind moving in the various strata? Page 15
d) Gradedd Bedding: -What type of environment does graded bedding form in? -Commonly associated with turbidity currents (an underwater flow of sediments and water with a greater density than sediment free water) or storms. e) Ripple Marks: -What are the differences between Current Ripple Marks and Oscillation (Wave) Ripple Marks? Page 16
-In what direction was the current flowing in the image below? -What type of sedimentary rock is most likely to show ripple marks? f) Mud Cracks: Mudstone from the Cambrian period g) Varves: Annual layers of rocks deposited by galcier melt. Page 17
Part D: Fossils Fossils are the remains or traces of prehistoric life. Why are they important to science today? _ Fossils are grouped into two categories: a) Body fossils: b) Trace fossils: _ Have all organisms that lived on Earth been fossilized? Why or why not? Soft Body Part Preservation Methods *All of the methods below involve quick burial and low O 2 levels which isolate the remains from scavengers and microbes (decomposers). 1. Unaltered Soft Body Part Preservation 2. Altered Soft Body Part Preservation a) Carbonization: Page 18
b) Imprints: Impression of organism in sediments. Typical off Pre- Cambrian organisms, such as the Jellyfish to the left. Hard Body Part Preservation Methods: 1. Unaltered Hard Body Part Preservation 2. Altered Hard Body Part Preservation a) Permineralization (Petrifaction): b) Replacement: Page 19
Geology 1 c) Externa d) Interna e) Cast: 12: Sediment al Mold: _ al Mold: _ tary Rock Pa age 20