WEEK 4 – 3040 Notes on FACIES & ENVIRONMENTS Reading: http://www.seddepseq.co.uk/SEQ_STRAT/WALTHER.htm FACIES (Latin meaning face, look, appearance) = important internal characteristics, properties A way to divide and group rocks Informal and adaptable (can use at all kinds of scales, tailor it to your needs) Uses of Facies (here using examples that may all refer to the same set of rocks) 1. Descriptive/objective (factual) – our preferred usage e.g., graded ss facies 2. Process/genetic e.g, turbidite facies (implying process of density driven turbidity currents) 3. Environmental e.g., deep sea fan facies (environment such rocks may form in) Facies patterns – designed to depict important features of the rocks, standard patterns and colors, but it’s always a good idea to have a legend! Facies Models (often expressed as 3-D block diagrams), show facies relationships, associations to help interpretations *** Walther’s Law: laterally adjacent facies can be vertically imposed /stacked, assuming no major break- unconformity or fault, etc. 1 Transgression – shoreline moves landward (retrogradational stacking) Regression – shoreline moves seaward (progradational stacking) Facies Rules, Facies Models and relationships STRATIGRAPHIC SECTIONS – watch short 5 min. video 1) Title at the top, centered, all capital letters. Ex: STRATIGRAPHIC SECTION OF THE CRETACEOUS BLACKHAWK FORMATION NEAR HELPER, UT 2) Time divisions and scale along the far left side of the column shows series, stage, formation and meters (or feet) above base. 3) Label the lithologic column “Grain size” or “Weathering profile” (standard has been 1” = most resistant, ½” = least resistant, but sometimes we exaggerate that to fit more in, and/or if we will need to reduce the column for publication, etc.). Some columns use tick marks for the different grain size divisions. 4) Use standard lithologic symbols. If you have several units, color the beds to match your map units. 5) Use standard symbols to represent scoured (erosional surfaces, unconformities), faults or sedimentary structures, keyed to a legend. 4) Include where samples, data, fossils or photographs were collected. 5) Give brief lithologic descriptions (in a consistent ordered format): Letter neatly or use computer graphics for the lithologic descriptions. Each description must be across from the beds it is describing. Align all descriptions (left-justify). 2 Phrases or common abbreviations are O.K.! You do not need completed sentences. 6) Include “Drawn by” and the date in the bottom right corner or on the top right below the title. -See Template examples Here’s an example from Dinosaur National Monument below. The descriptions are short because this is only exhibiting the basic formations. Sometimes what you include is a function of your purpose. Some sections can be very details where the measurements included each bed, even at cm scales! Some sections are very generalized. If you can’t fit all the words or descriptions in, you can also list basics, with an extra appendix of the full details Choose appropriate scale so that the entire section can be represented at an appropriate level of detail (in a paper world, this means multiple pages or a fold out, but could be a lot of scrolling or nested details in a digital format). . 3 4 DEPOSITIONAL ENVIRONMENTS Watch this 14 min. video as an overiew (though admittedly the video imagery can be tough if you get carsick!) https://www.youtube.com/watch?v=lt05PRFfkCg DEPOSITIONAL ENVIRONMENTS Sedimentary realms or envts distinguished by parameters: • physical (velocity, direction, wind, waves, climate. T, tectonics, etc.) • chem (comp of water, geochem of rx, provenance) • bio (flora, fauna, affects of animals, reefs, etc.) CONTINENTAL Glacial Eolian/desert Alluvial Fluvial Lacustrine Swamp Cave (Spelean) TRANSITIONAL Deltaic Estuarine – Lagoon Tidal MARINE Barrier Isl. – Strand Plain Beach – Shoreline Shelf (Neritic) 5 Slope (Bathyal) Deep – Sea Fan Basin Abyssal GLACIAL Ice as geol agent Combo of : Low T, high rates of ppt with extremely low rates of evap Processes: 1. Glacial flow : 2. Glacial Erosion (striations): 3. Glacial Transport: 4. Glacial Deposits (Till) glacial-marine drift Recognition: 1. types of glacial depos (10s m thick) 2. landforms 3. gradation of glacial sheet to glacio-fluv outwash plain Reading http://geowiki.ucdavis.edu/Wikitexts/UCD_GEL_109/Alluvial_Fans/Glacial_Environments 6 LACUSTRINE / LAKES A. Formed by: tectonic subsidence, faulting, glacial erosion B. Waters: water chem., water temp. vary widely in character, with variable degrees of permanence, salinity (fresh, brackish, saline, hypersaline), alkalinity etc. C. Sed supply D. Climate E. Facies (ideal – concentric patterns from shoreline to basin center) G. Recognition H. Economics – oil shale, evaporite minerals, some coals o o o o o o o Need subsidence: usually tectonic Others formed by damming (glacial, volcanic, mass wasting, etc.) Not that common in the geologic record Strongly affected by climate Hard to differentiate from marine at times 25 largest today: 10 glacial dam, 7 cratonic depressions, 4 rift valley (Baikal, E Africa) Good oil source – Found: faulted grabens or other subsiding basins, internal drainage & limited outflow. – Sensitive to changing subsidence and climate patterns. Lake margins, water chemistry, and lake ecology are variable over short stratigraphic intervals. – Lake shorelines can move basinward either by progradation or by withdrawal of water. Withdrawal (lake level fall) leaves only a limited rock record (mainly dessication features). – Gradual lake ‘filling’ would show upward-coarsening from distal lake environments to deltaic/fluvial environments. This is only one of several possible vertical successions. – May find: laminated, kerogen-rich mudstones (good source for oil), turbidite beds, fresh or saline-water fossils (absence of marine invertebrates), limestones, transition to fluvial-deltaic facies. 7 Other references, Recommended watching: WATCH Youtube ppt video of Matthew Clapham on Facies https://www.youtube.com/watch?v=Bs7z_2081T4 If you want additional help understanding these, you can also try: Identifying Transgression and Regressions (Jennifer Lewis, 7 mins) https://www.youtube.com/watch?v=WE9fkQ9a2xA Ref: If you want more reinforcement of these ideas, you can Watch Dawn Sumner’s Youtube video http://www.youtube.com/watch?v=ZSsULiPouTo Transgression, Regression Ref. for more explanations see: http://www.geologyin.com/2015/09/how-to-identify-transgression-and.html 8 Lab 4 GEO 3040 Name: Sedimentary Structures Due Date: Sept 23, 2020 (beginning of lab) Objective: You have focused on texture and classification of sedimentary rocks. Now you will examine sedimentary structures that provide valuable clues for hydrodynamic conditions and interpreting depositional environments. Parts 1 & 2 can be completed at home. Part 3 should be done at field sites. Materials Needed: Internet access, Calculator/Computer (for calculating ripple index) Part I – Common Sedimentary Structures Carefully examine each rock sample and answer the associated questions. You will want to refer to the recommended Boggs text and lecture notes as well for additional (web, youtube, etc.) references for identifying and interpreting the samples. From SketchFab – https://sketchfab.com/nate_sid/collections/sedimentary-structures 1. Trough Cross Bedding https://sketchfab.com/3d-models/sedimentary-structures-troughcross-bedding-aaaf6655e6234227a052379773da8aca A. What characteristics justify the cross-bedding name of this sample? B. What would be the Froude number/conditions this would have formed under? (And you should understand why!) a) Fr >1 b) Fr = 1 c) Fr < 1 2. Ripples https://sketchfab.com/3d-models/ripple-marks-prac-specimen-test7d96d73707e341c4b452044698e1fbbe A. What kind of ripples are these? d) Current e) Wave f) Interference g) Adhesion h) Eolian B. Cite evidence: C. Give an approximate estimate of the Ripple Index (R.I.), and make sure this is consistent with your answer to A. above. 1 3. Ripple Marks 3 https://sketchfab.com/3d-models/sedimentary-structures-ripple-marks-32b1AbftpeRwqBiYwJbyGb7Cxd7RCxvDw3 A. What kind of ripple marks are these? a) Current b) Wave c) Interference d) Adhesion B. Cite evidence: a) Asymmetrical in cross-sectional view b) Symmetrical in cross-sectional view c) Presence of fossils d) Presence of salt minerals C. Describe the shape of the ripples at or over the crest, (peaked or rounded) 1 pt a) Peaked b) Rounded D. Describe the shape of the ripples along the crest a) totally, perfectly straight, b) slightly curved though relatively straight c) very curved, linguoid shape E. In one upper left corner- give a description of what happens to the crest that lends further support to your interpretation of what type of ripple this is: 4. Raindrop Impressions https://sketchfab.com/3d-models/sedimentary-structures-raindropimpressions-bbdd19454c374c64bf2d41a141d7f3c4 A. Do you see perfect circular impressions? a) Yes, all are totally, perfectly circular b) Only a few are truly circular c) Not a single one is circular B. Choose what type of structure this is: a) Intrabed b) Bedding plane c) Trace fossil d) Diagenetic C. Describe the shape of the ripples in cross section, (symmetrical or asymmetrical) 2 5. Synaerisis (??) Cracks https://sketchfab.com/3d-models/sedimentary-structures-synaerisis-cracksf5a4cd1861a94b128c7841e1c51083dc A. Give the correct spelling for what this post meant the structure to be: B. Is this a good interpretation or not? Cite the weakness of this interpretation. C. What do you think it could be instead and why? 6. Now look at what he has labeled Mud Cracks 2 https://sketchfab.com/3d-models/sedimentary-structures-mud-cracks-2e76afb108e954d37910ed5b79759ec76 A. Choose the correct description for these: a) Complete, well-formed polygons b) No co
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