Survey
* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project
Download GEOL 131: Syllabus
Document related concepts
no text concepts found
Transcript
SEDIMENTARY ROCKS TERMS • Weathering: breakdown of pre-existing rock – Physical or chemical breakdown • Erosion: transport of sediment on Earth’s surface • Erosional agents: processes that move sediment SEDIMENTARY ROCKS • • • • • • • Introduction Detrital Rocks Chemical/Organic Rocks Classification Lithification Sedimentary Environments Sedimentary Structures Sedimentary Rocks Introduction GEOL 131: Sedimentary Rocks INTRODUCTION • Origin – Only form at Earth’s surface – Weathering of pre-existing rock into soluble and insoluble sediments – Erosion of sediments – Deposition of solid sediment – Precipitation of dissolved sediment GEOL 131: Sedimentary Rocks INTRODUCTION • Importance – Record of past surface conditions – Fossils – Economically important materials • Fossil fuels, gypsum, phosphates, iron, gravel, etc. Sedimentary Rocks Detrital Rocks GEOL 131: Sedimentary Rocks Detrital Rocks • “Detrital” from “detritus” - debris • Composed of solid sediment grains • Distinguished by size of grains Detrital rock with smaller grains Detrital rock with large grains GEOL 131: Sedimentary Rocks Detrital Rocks: Common Minerals • Quartz – Physically durable • Feldspars – Physically durable – Break down chemically into clays • Clay minerals – Chemically stable GEOL 131: Sedimentary Rocks - Detrital Shale • Most abundant sedimentary rock – 2/3 of all sedimentary rock is shale • Made of clay grains – Microscopic sheets – From chemical weathering of feldspar GEOL 131: Sedimentary Rocks - Detrital Shale Scanning electron microscope image of shale showing flat clay grains. Scale bar is 0.005 cm. From: claysandminerals.com GEOL 131: Sedimentary Rocks - Detrital Shale Formation •Quiet environment •Burial and compaction of clay grains •Not cemented •Weak From: geoexpro.com GEOL 131: Sedimentary Rocks - Detrital Sandstone • Cemented sand-size grains • Sand: 1/16mm – 2mm diameter • Quartz is predominant mineral GEOL 131: Sedimentary Rocks - Detrital CONGLOMERATE/BRECCIA • Cemented gravel-size grains • Gravel: greater than 2mm CONGLOMERATE has rounded gravel BRECCIA has angular gravel Sedimentary Rocks Chemical Rocks GEOL 131: Sedimentary Rocks Chemical Rocks • Dissolved sediment precipitates out of solution as crystals • “Inorganic” processes: e.g. evaporation, chemical activity • “Biochemical” processes, e.g. growth of shells Bonneville Salt Flats, Utah From: rogerdhansen.wordpress.com GEOL 131: Sedimentary Rocks - Chemical Chemical Rocks: Limestones • Composed mainly of calcite (CaCO3) • Several kinds – Some biochemical and some inorganic • Most form in marine environments GEOL 131: Sedimentary Rocks - Chemical Biochemical Limestones From: proprofs.com From: www.pitt.edu From: seashellsbymillhill.com Fossil limestone Coquina - - Shells + matrix Hard Shells only Fragile Chalk - Microscopic plankton shells Very soft GEOL 131: Sedimentary Rocks - Chemical Biochemical Limestones Chalk under a scanning electron microscope, showing shells (round) and calcite crystals. Scale bar is 0.002 cm. From: greenelectron-images.co.uk GEOL 131: Sedimentary Rocks - Chemical Inorganic Limestones From: russianriverschoolhouse.com From: www4.uwm.edu Micrite Travertine - Microscopic calcite crystals - - Precipitated from oversaturated seawater “Cave rock” Porous From: www.newark.osu.edu Oolitic limestone - Round “ooids” + cement - Precipitation of crystals from seawater around a nucleus - Rolling back and forth GEOL 131: Sedimentary Rocks - Chemical Inorganic Limestones: Ooids Calcite layers Seafloor Ooid forming Nucleus Ooid cross-section - Ooids form when calcite precipitates from oversaturated seawater onto nuclei being rolled around on seafloor by currents - Nucleus can be any small solid particle: sand grain, piece of shell, etc. GEOL 131: Sedimentary Rocks - Chemical Chemical Rocks: Dolostone • Composed mainly of dolomite: CaMg(CO3)2 • Origin not well understood • Most dolostone is probably converted from limestone when Mg is added – Mg-rich groundwater? Seawater? GEOL 131: Sedimentary Rocks - Chemical Chemical Rocks: Chert • Biochemical • Composed mainly of microcrystalline quartz • Very hard; sharp edges • Made from compacted microscopic plankton shells GEOL 131: Sedimentary Rocks - Chemical Chemical Rocks: Evaporites • Inorganic • Evaporation of water (usually salt water) • Rock salt, rock gypsum Bonneville Salt Flats, the ancient floor of Lake Bonneville, a salty lake now mostly evaporated GEOL 131: Sedimentary Rocks - Chemical Chemical Rocks: Coal • Organic, no minerals • Chemically altered dead plant matter • Need oxygenpoor water From: eis.uow.edu.au Sedimentary Rocks Classification GEOL 131: Sedimentary Rocks Classification: Detrital GEOL 131: Sedimentary Rocks Classification: Chemical Sedimentary Rocks Lithification GEOL 131: Sedimentary Rocks - Lithification Lithification • How sediment becomes rock • “Lith” = stone GEOL 131: Sedimentary Rocks - Lithification Lithification Processes • Compaction • Cementation GEOL 131: Sedimentary Rocks - Lithification Lithification • Begins with deposition & burial of sediment under more sediment GEOL 131: Sedimentary Rocks - Lithification Compaction • Decreases porosity (empty space) • Drives out water • Can make flat grains stick together GEOL 131: Sedimentary Rocks - Lithification Cementation • New crystals form between grains • Precipitation out of groundwater • Fills in remaining porosity Original sand grain From: northstonematerials.com Cement crystals From: unibe.ch Sedimentary Rocks Sedimentary Environments GEOL 131: Sedimentary Rocks - Environments Sedimentary Environments • Any place where sediments accumulate • Rocks give clues to past environments • Reconstruct what Earth’s surface looked like in the past GEOL 131: Sedimentary Rocks - Environments From: neiu.edu Examples of some sedimentary environments GEOL 131: Sedimentary Rocks - Environments Categories of Sed. Environments • Nonmarine • Transitional • Marine GEOL 131: Sedimentary Rocks - Environments Sed. Rocks Represent Past Environments UTAH Ancient Lake Bonneville Bonneville Salt Flats (white areas): rock salt deposits represent ancient lake Sedimentary Rocks Sedimentary Structures GEOL 131: Sedimentary Rocks - Sedimentary Structures Layers (aka beds or strata) • Most common type of structure • Bedding planes: contacts between layers GEOL 131: Sedimentary Rocks - Sedimentary Structures Cross-bedding Cross-beds in a modern sand dune Cross-beds in sandstone GEOL 131: Sedimentary Rocks - Sedimentary Structures Cross-bedding shows depositional current’s flow direction • Wind, river, waves, etc. • Paleocurrent: ancient depositional current Flow direction Crossbeds GEOL 131: Sedimentary Rocks - Sedimentary Structures Graded beds Grains are sorted by size within a single layer GEOL 131: Sedimentary Rocks - Sedimentary Structures Ripple marks & mud cracks Mud cracks in modern sediment Ripple marks in sandstone End of Sedimentary Rocks Chapter
Related documents