Copyright (c) 2005 Pearson Education Canada, Inc.6-1 PowerPoint Presentation Stan Hatfield. Southwestern Illinois College Ken Pinzke. Southwestern Illinois College Charles Henderson. University of Calgary Chapter 6a Sedimentary Rocks: Environments & Processes PowerPoint Presentation Stan Hatfield. SW Illinois College Ken Pinzke. SW Illinois College Charles Henderson. University of Calgary Tark Hamilton. Camosun College

Copyright (c) 2005 Pearson Education Canada Inc.6-2 Sedimentary rocks are products of mechanical and chemical weathering They account for about 5 percent (by volume) of Earth’s outer 16 kilometres Contain evidence of past environments Sediment transport directions Macro-, Micro- & Trace fossils, evolution, time & changing ecologies Stable isotope records of past sea water & climates What is a sedimentary rock?

Copyright (c) 2005 Pearson Education Canada Inc.6-3 What is a sedimentary rock? Sedimentary rocks are important for economic considerations because they may contain: Coal Petroleum and natural gas Limestone for cement Gypsum for plaster & sheetrock Salt for roads & chemicals KCl in evaporites & Apatite in phosphate rock for fertilizers Sources of iron, aluminum, and manganese

Copyright (c) 2005 Pearson Education Canada Inc.6-4 Lithification: Turning Sediment into Sedimentary Rock Many changes occur to sediment after it is deposited Compaction Reduction or recycling of organic compounds Dewatering Cementation Recrystallization Diagenesis – all of the chemical, physical, and biological changes that take place after sediments are deposited, but prior to metamorphism Occurs within the upper few kilometres of Earth’s crust at temperatures generally less than 200ºC Clays persist in sediments (Micas form in Metamorphism) Reduction of porosity & permeability

Copyright (c) 2005 Pearson Education Canada Inc.6-5 Diagenesis Includes: Recrystallization – Pressure Solution: grains dissolve at corners Infilling of porosity Development of more stable minerals from less stable ones: Plagioclase  Clay + Calcite Lithification - Unconsolidated sediments are transformed into solid sedimentary rock by compaction and cementation –Cements include calcite, silica, clays, zeolites, iron oxide, pyrite Lithification: Turning Sediment into Sedimentary Rock

Copyright (c) 2005 Pearson Education Canada Inc.6-6 Types of Sedimentary Rocks Sediment originates from mechanical and/or chemical weathering Rock types are based on the source of the material Detrital sedimentary rocks – transported sediment as solid particles, earlier rocks & minerals Chemical sedimentary rocks – sediment that was once in solution Biochemical sedimentary rocks – sediment formed or shed from living organisms

Copyright (c) 2005 Pearson Education Canada Inc.6-7 Detrital (Clastic) Sedimentary Rocks The chief constituents of detrital sedimentary rocks include components shed from weathering on land (terrigenous debris): Clay minerals: kaolinite, illite, chlorite, smectite Quartz & Chert Feldspars (Kspar >> Plagioclase) Micas: Muscovite, Vermiculite, Chlorite, Serpentine Particle size is used to distinguish among the various types of detrital rocks Boulders, cobbles, gravel, sand, silt, clay

Copyright (c) 2005 Pearson Education Canada Inc.6-8 Detrital Sedimentary Rocks Particle size is important in the classification of detrital sedimentary rocks.

Copyright (c) 2005 Pearson Education Canada Inc.6-9 Shale and other Mudrocks (Argillite, Wackes) ~60% of all sedimentary rocks, best fossil records! Frequently organic rich and the source rocks for hydrocarbons Mud-sized particles in thin layers that are commonly referred to as laminae Deposited as a result of gradual settling in quiet environments: floodplains, deep lakes, deep ocean basins Shale exhibits fissility (splits into thin layers) and mudrock does not (sometimes bioturation or mixing destroys layers) Siltstone consists of silt-sized particles as well as mud Most common sedimentary rock, but often inconspicuous because they weather recessively and are covered by veg! Detrital Sedimentary Rocks

Copyright (c) 2005 Pearson Education Canada Inc.6-10 Shale is a type of mudrock. The shale above contains plant fossils. Detrital Sedimentary Rocks

Copyright (c) 2005 Pearson Education Canada Inc.6-11 Sandstone -20% of sedimentary rocks are sandstone; second only to mudrocks in abundance -Composed of sand-sized particles -Forms in a variety of environments and transported by wind and water -Sorting, shape, and composition of the grains can be used to interpret the rock’s history -Quartz is the predominant mineral in mature or long system sediments because it is so durable -Feldspars & Rock Fragments are abundant in younger immature sediments Detrital Sedimentary Rocks

Copyright (c) 2005 Pearson Education Canada Inc.6-12 Quartz sandstone (bottom) and wind-blown layers of sandstone (above) from Zion National Park (Jurassic Desert!). Detrital Sedimentary Rocks

Copyright (c) 2005 Pearson Education Canada Inc.6-13 Conglomerate and breccia –Both are largely composed of particles > 2mm –Indicative of high energy currents or steep slopes –Conglomerate consists primarily of rounded gravels –Grain supported have been sorted, winnowed, redeposited –Matrix supported usually just deposited once as a thick slurry or debris flow –Breccia is composed largely of large angular particles –Less sedimentary transport –May result from avalanche or talus in mountainous terrain Detrital Sedimentary Rocks

Copyright (c) 2005 Pearson Education Canada Inc.6-14 Conglomerate is composed primarily of rounded gravel-size particles. Detrital Sedimentary Rocks

Copyright (c) 2005 Pearson Education Canada Inc.6-15 Breccia is composed of angular gravel-sized particles. Detrital Sedimentary Rocks

Copyright (c) 2005 Pearson Education Canada Inc.6-16 Chemical Sedimentary Rocks Consist of precipitated material that was once in solution Precipitation of material occurs in two ways Inorganic processes (precipitation, crystallization from solution in briny or saturated fluids) Organic processes (biochemical origin) –Clams grow shells –Calcareous algae –Wood in bayous, oxbow lakes –Fish poop on shelf!

Copyright (c) 2005 Pearson Education Canada Inc.6-17 Common chemical sedimentary rocks Limestone –Most abundant chemical rock; 10% of all sedimentary rocks –Composed chiefly of the mineral calcite (CaCO 3 ) –Marine biochemical limestones form as coral reefs, coquina (broken shells; also called bioclastic grainstone), and chalk (microscopic organisms) –Inorganic limestones include travertine and oolitic limestone (comprises small spherical grains or ooids formed in high wave-energy environments) Chemical Sedimentary Rocks

Copyright (c) 2005 Pearson Education Canada Inc.6-18 Bioclastic limestone with shell fragments of biochemical origin. Chemical Sedimentary Rocks

Copyright (c) 2005 Pearson Education Canada Inc.6-19 Modern coral reef (A) and Paleozoic fossil reef in Arctic Canada (B). Chemical Sedimentary Rocks But Reefs form in the Tropics?

Copyright (c) 2005 Pearson Education Canada Inc.6-20 Common chemical sedimentary rocks Dolostone –Typically formed secondarily from limestone when magnesium replaces some calcium Chert –Made of microcrystalline silica (SiO 2 ) –Occurs as nodules in limestone and as tabular layers (siliceous organisms like diatoms and radiolarians often provide silica related to chert origin) –Varieties include flint and jasper (banded form is called agate) –Banded Iron Formation (Hematite & Jasper) from Precambrian evolution of cyanobacteria  Free O 2 Chemical Sedimentary Rocks

Copyright (c) 2005 Pearson Education Canada Inc.6-21 Banded Iron Formation Precambrian between 3.8 and 1.7 Ga (Archean)

Copyright (c) 2005 Pearson Education Canada Inc.6-22 Common chemical sedimentary rocks Evaporites –Evaporation triggers deposition of chemical precipitates –Examples include rock salt (NaCl) and rock gypsum (CaSO 4.2H 2 O), anhydrite (CaSO 4 ), sylvite (KCl; potash, which is used as a fertilizer) Phosphate Rock –Phosphate Rock is apatite rich marine sediment also used as fertilizer –Forms on sediment starved shelves –Upwelling and biological activity exceeds clastic input Chemical Sedimentary Rocks

Copyright (c) 2005 Pearson Education Canada Inc.6-23 Common chemical sedimentary rocks Coal –Different from other rocks because it is composed of organic material –Stages in coal formation (in order) –1. Accumulation of plant material (often in swamps) –2. Partial decomposition into peat –3. Shallow burial forming lignite –4. Deeper burial forming bituminous coal Chemical Sedimentary Rocks

Copyright (c) 2005 Pearson Education Canada Inc.6-24 Successive stages in the formation of coal. Chemical Sedimentary Rocks

Copyright (c) 2005 Pearson Education Canada Inc.6-25 End of Chapter 6a