Sedimentary Environments -Fossils and Dating
Sedimentary Environments -Fossils and Dating GLG 111
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This 0 page Class Notes was uploaded by Abigail Notetaker on Tuesday November 3, 2015. The Class Notes belongs to GLG 111 at Miami University taught by Jill Mignery in Summer 2015. Since its upload, it has received 18 views. For similar materials see The Dynamic Earth in Business at Miami University.
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Date Created: 11/03/15
Sedimentary Environments Fossils and Relative Dating 0 2 Methods of Determining Fossil Age 0 absolute dating measure of the amount of radioactive isotope left Within an igneous rock or carbon based fossil 39 parent amount of isotope number of half lives daughter amount of isotope 0 number of half lives X years it takes isotope to decay 1 half life exact age 0 relative dating determine the relative age of the rock based on its features trace fossils and the age of the rocks around it fossil remains of ancient life 0 types hard parts shells bones mineralized plant material carbon imprints of soft tissue microfossils trace fossils indications an organism was present 0 tracks burrows o excrements o feeding trails o 999 of all life that has ever existed is now extinct o Mineralized Plant Material 0 plants go through permineralization o permineralization when the pores of plant materials absorb minerals from ground groundwater or oceans their natural minerals get replaced by these invading minerals and the organism hardens into a fossil common minerals that form this type of fossil calcite iron silica 0 Law of Faunal Succession o Faunal Succession life forms have evolved over time in a definite recognizable order once extinct an organism never reappears fossils succeed each other vertically in a specific reliable order 0 INSERT DIAGRAM o fossils in older rocks show increasingly greater differences from species living now Sediment Layers Around the World 0 any two sediment layers with the exact same fossils must be the same age applies to sediment layers on a local regional continental andor global scale EX If a sedimentary layer has the same fossil assemblage as a sedimentary layer in the UK the two sedimentary layers are most likely the same age Even if two layers are different types of sedimentary rock and are from different areas they are most likely the same age 0 This idea allows Geologists to create a picture of any given time period using sedimentary rock layers 0 Index Fossils easily preserved geographically widespread and existed over a short period of time 0 index fossils help us determine the relative age of the rocks they are contained in index fossils have a set age because they only existed for a short time 0 Best example oating or swimming marine animals that evolved quickly 0 fossil types that overlap for short known periods of time also help with relative dating but they are not classified as index fossils 0 Key Beds rock layer that was deposited rapidly over a large area 0 thin easily recognized 0 help with absolute and relative dating 0 EX volcanic ash beds can be chemically correlated and radiometrically dated 0 Principle of Original Horizontality o sedimentary rocks metamorphosed sedimentary rocks and some volcanic rocks are originally deposited in horizontal layers if the layers have become warped or are folding or dipping then something has happened to them since they were deposited o Principle of Lateral Continuity 0 when deposited sedimentary layers extend laterally in all directions until they thin and pinchout or terminate against the edge of a depositional basin depositional basin places where sediments accumulate 0 place where the earth s surface shifts downward leaving a basin where sediments can be deposited fall into 0 Principle of Superposition o in an undisturbed stack of sediments or sedimentary rocks those on the bottom were deposited first followed by those above 0 INSERT DIAGRAM Principle of Inclusion o if a rock contains includes or encloses fragments of another rock then the included fragments are older than the rock they are contained in o INSERT PICTURE HERE 0 EX lithic fragments fragments of preexisting rocks in elastic sedimentary rocks xenoliths fragments of preserved country rock within an intruded mass of igneous rock Unconformity a section of discontinuity representing an interruption in sedimentation over a significant amount of geologic time 0 may be caused by erosion and or nondeposition o 3 types disconformity nonconformity angular unconformity Disconformity occurs when rock layers are missing due to erosion or nondeposition between two parallel sedimentary rock layers 0 erosion the action of natural forces wind water which remove soil and rock from one location and transport it to another where it is deposited o Nondeposition the failure to deposit Angular unconformity tilting and erosion of older layers followed by deposition of new layers Nonconformity occurs when sedimentary rocks overlie metamorphic or igneous rocks Peffer Park Oxford Geology 0 3 main geologic units Ordovician bedrock made up of shale and limestone o 450 million years old oldest layer at Peffer Glacial till from Pleistocene Ice Age 24000 years old stream deposits 3000 10000 years old depending on the location Within the park Type fossils represent the best or only example of a fossilized organism the ideal fossil Abundance of local fossils most to least abundant o Brachiopods o Bryozoa o Echinoderms o Trilobites o Other Fossils at Peffer Park Brachiopods look like shells most abundant Bryozoa look like coral they are not coral Crinoids look like stacks of pancakes Horn Corals Pelecypods clams Their shells were made of aragonite a mineral that transforms into calcite over time so they are not well preserved They look similar to brachiopods but they are much less abundant Trace Fossils fossils of tracks burrows feeding trails and excrement Trilobites look like pill bugs 0 History of Oxford Fossils 0 millions of years ago there was a storm that blew through Oxford 0 storm wiped out the organisms in the area o the ecosystem was repopulated by brachiopods which were then replaced by more complex organisms as the ecosystem recovered matured Table for Sedimentary Rock Identification Inorganic Sedimentary Rocks Texture Grain Size Composition Details Rock Name Clastic Pebbles Mostly quartz Rounded fragments Conglomerate fragmented boulders feldspars and clay embedded in Angular fragments Breccia sand silt or clay May contain fragments of other Fine to coarse Sandstone rocks Very fine grain Siltstone Compact may split Shale easily Chemically Organically Formed Sedimentary Rocks Texture Grain Size Composition Details Rock Name Crystalline Varied Halite Crystals from Rock Salt chemical precipitates Varied Gypsum and evaporates ROCk Gypsum Varied Dolomite Dolostone Bioclastic Microscopic to Calcite Cemented shell Limestone coarse fragments of biological origin contains marine organism fossils Varied Carbon From plant remains Coal
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