402-pp8 - UNIVERSITY OF SOUTH ALABAMA GY 402: Sedimentary...

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Unformatted text preview: UNIVERSITY OF SOUTH ALABAMA GY 402: Sedimentary Petrology Lecture 8: Sedimentary Facies Today's Agenda Sedimentary Facies 1. 2. 3. What are facies Defining characteristics of facies Facies and depositional environments Sedimentary Facies Why do sedimentologists collect all this data in the first place? . Sedimentary Facies Why do sedimentologists collect all this data in the first place? Ultimately, it is in order to interpret the environment of deposition of the sediment/sedimentary rocks. http://earthsci.org/mineral/rockmin/sed/clastics.gif http://earthsci.org/mineral/rockmin/sed/clastics.gif Sedimentary Facies There are literally dozens of different depositional environments that cover every imaginable marine and non-marine situation. And in most cases, there are multiple varieties of each basic environment of deposition. Sedimentary Facies There are literally dozens of different depositional environments that cover every imaginable marine and non-marine situation. And in most cases, there are multiple varieties of each basic environment of deposition. For example, rivers come in at least 3 "flavors": 1) Meandering 2) Braided 3) Anastimosing Sedimentary Facies Sedimentologists also need to consider the full range of variability within each depositional environment. Sedimentary Facies Sedimentologists also need to consider the full range of variability within each depositional environment. For example, a braided river channel has deep areas, flats and bars (longitudinal and transverse). Sedimentary Facies When you look closely at braided river depositional systems, it is clear that they consist of a lot of subcomponents. Not just a channel and a floodplain. So we lied (again!) in GY 111. Sedimentary Facies Ultimately, depositional environments are the sum of their various components and each of those components are distinguished from one another of the basis of geological characteristics. The components that collectively define depositional environments are called sedimentary facies (or just facies). http://www.kgs.ku.edu/PRS/publication/ofr2003-82/gif/figure1_06.gif http://www.kgs.ku.edu/PRS/publication/ofr2003- Sedimentary Facies Defining characteristics for facies include: Grain size Lithology Mineralogy Paleontology Sedimentary and biogenic structures Palaeocurrent orientations Obvious sedimentary trends Bedding (Bed thickness) Lamination Bedding contacts Lateral variations Anything else that you can think of Sedimentary Facies Facies can, and will, repeat vertically through a sedimentary sequence, but may vary in character as a result of environmental and/or evolutionary change through time. Sedimentary Facies Facies can, and will, repeat vertically through a sedimentary sequence, but may vary in character as a result of environmental and/or evolutionary change through time e.g., fossil content. offshore (10m) shoreface (5m) swash zone (0m) shoreface (5m) Sedimentary Facies Facies may also change laterally through a deposit as a result of changing environments with distance at the same time. Sedimentologists distinguish component facies in the outcrops that they are examining. Sometimes they go overboard. http://geology.isu.edu/Digital_Geology_Idaho/Module2/Belt_SedStruct_sml.jpg http://geology.isu.edu/Digital_Geology_Idaho/Module2/Belt_SedStruct_sml.jpg Then they determine which depositional environment best fits this variety of facies. This is called: Facies Modeling http://geology.isu.edu/Digital_Geology_Idaho/Module2/Belt_SedStruct_sml.jpg http://geology.isu.edu/Digital_Geology_Idaho/Module2/Belt_SedStruct_sml.jpg Facies Modeling Facies modeling is best done back at your lab/office where you can think about your data. Facies Modeling Facies modeling is best done back at your lab/office where you can think about your data. And drink a few beers to help you think about your data. Prograding Open Beach Facies Modeling And interpret what your data is implying Upcoming Stuff Homework 1) Grain Size Analysis introduction: Due at or before 2:00PM Today 2) Peer Review of Grain Size Introduction: Due Tomorrow 3) Get your field kits together Today's Lab 1) Peer Review protocol 2) Bogus Sedimentary Section activity/exercise (writing too!) Thursday Lecture/Lab: Scarborough School field trip (bring your stuff!) ...
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This note was uploaded on 02/05/2012 for the course GLY 402 taught by Professor Staff during the Fall '11 term at S. Alabama.

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