CEE 1030 1st Edition Lecture 5 Review Question What two factors speed up rates of chemical weathering rocks 1 low temperature high rainfall 2 High temperature high rainfall Sedimentary rocks product of mechanical and chemical weathering 75 of rocks at earths surface are sedimentary but only 10 of outer 15 km Importance of sedimentary rocks economically important host oil gas coal gold and uranium deposits groundwater source source of sand and gravels for construction preserve a record of life on earth tell us about the environment preserve record of earth s climate history evidence for past environmental conditions verticle changes in the sedimentary rock types sedimentary rock types represent environmental changes through time chemical composition of marine sediments tells us about changes in ocean chemistry and temperature Sediments vs Sedimentary rocks sediments collection of loose solid particles sedimentary rock particles bound together to form a firm coherent rock lithification unconsolidated sediment to rock Types of sedimentary rocks detrital sediment transported as solid particles ex sandstone shale chemical sediment formed from material that was once in solution in water ex limestone inorganic and biological organic remains of decayed plants ex peat coal Detrital sedimentary rocks main constituents are clay minerals quartz feldspar mica and rock fragments particle size used to distinguish types particles greater than 2 mm in diameter conglomerate rounded particles places such like a river or a beach breccia sharp angular particles cliffs sand sized particles 0 0625 to 2mm sandstone quartz is dominant mineral fine particles are less than 0 0625 mm mudstone shale siltstone and claystone test by chewing rock shale shales siltstones mudstones difficult for water to penetrate little cementation poorly lithified and friable crumble easily Chemical sedimentary rocks material that was once in solution LOOK AT POWERPOINT limestone most abundant chemical rock composed of mineral calcite or its polymorph aragonite Oolitic limestone inorganic form in warm shallow agitated waters biogenic limestone coral reefs shell fragments microorganisms ex chalk made from tiny shell fragments of plankton conquina poorly cemented rock of shell fragments fossiliferous limestone shell fragments cemented with calcite cement chert hard compact microcrystalline SiO2 nodules and layers often in limestone beds also known as flint evaporates evaportation water triggers deposition of chemical precipitates ex halite gypsum carbonate marine environment Review Questions Select the answer that lists the common detrital sedimentary rocks in order of increasing particle size 1 shale conglomerate sandstone 2 sandstone shale conglomerate 3 conglomerate sandstone shale 4 shale sandstone conglomerate 5 sandstone conglomerate shale Which of the following lists the correct sequence of steps in the formation of a sedimentary rock 1 erosion weathering lithification deposition 2 erosion lithification weathering deposition 3 weathering erosion deposition lithification 4 lithification erosion deposition weathering 5 weathering lithification erosion deposition Sedimentary structures provide important information about environment of sedminenation most common characteristic of sedminary rocks form sub horizontal beds or strata bedding planes separate strata cross bedding and current ripples graded beds vertical change in particle size mud cracks evidence that sediment was alternately wet then dry Wet mud shrinks as it dries out forming cracks Sedimentary environments geographic settling where sediment accumulates determines the nature of the sediments that accumulate grain size grain shape etc continental environments rivers lakes deserts glacial transitional environments delta beach tidal flats marine environments deep sea continental shelf organic reefs Sedimentary facies different sediment types often accumulate adjacent to one another at the same time composed of particular sedimentary rock types