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EES 450: Sedimentary Geology

Breccia Conglomerate Diamictite Sandstone Siltstone Shale. Rudites. Mechanical Weathering. Clastic or Detrital. EES 450: Sedimentary Geology. New Clay Minerals. Shale. Source Rocks. Limestone Chert Diatomite. Biochemical. Solution. Evaporites Chert Limestone Ironstone.

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EES 450: Sedimentary Geology

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  1. Breccia Conglomerate Diamictite Sandstone Siltstone Shale Rudites Mechanical Weathering Clastic or Detrital EES 450: Sedimentary Geology New Clay Minerals Shale Source Rocks Limestone Chert Diatomite Biochemical Solution Evaporites Chert Limestone Ironstone Mudrocks – mudstones, shales and siltstones Chemical Weathering Chemical Peat Coal Bitumen Resins Plant Extraction Organic Crustal, upper mantle melts Explosive Eruption Tuff, Bentonite Agglomerate Volcaniclastic

  2. EES 450: Sedimentary Geology Mudrocks– mudstones, shales and siltstones ● Simple classification of mudrocks based on the percentage of silt and clay and the presence or absence of fissility.

  3. EES 450: Sedimentary Geology Mudrocks– mudstones, shales and siltstones ● Simple classification of mudrocks based on the percentage of silt and clay and the presence or absence of fissility. Shale:Laminated or fissile. Mudstone:No lamination or fissility.

  4. EES 450: Sedimentary Geology Mudrocks– mudstones, shales and siltstones ● Energy conditions conducive to mudstone deposition/accumulation. - What is the significance of the wave base? Wave base Muds

  5. EES 450: Sedimentary Geology Mudrocks– mudstones, shales and siltstones ● How is clay deposited? - Clays supplied to marine environments will aggregate to form flocs(ionic strength of sea water). Flocswill attract/incorporate organic matter from the water column and settle out to be deposited on the substrate. SEM image of clay aggregates or flocs. Megascopic view of clay flocs settling out of suspension from water in a beaker. Clay flocsmay be moved by currents.

  6. EES 450: Sedimentary Geology Mudrocks– mudstones, shales and siltstones ●Mudrocks and oxidation state. - What is the pycnocline? How does it figure in here? - Are ocean basins typically anaerobic? How does [O2] figure in here?

  7. EES 450: Sedimentary Geology Mudrocks– mudstones, shales and siltstones ● Structures and features in “anoxic” black shales. - Do these shales really represent anoxia? Why or why not? Bioturbation Ripple marks Erosional surfaces

  8. EES 450: Sedimentary Geology Mudrocks– mudstones, shales and siltstones ● What are oil shales? Is their a difference between oil shale, and oil-bearing shale? - Oil shale: Organic-rich fine-grained rock, contains significant kerogen (solid mix of organic compounds) from which liquid hydrocarbons called shale oil can be produced. Upon cooling of vapor, the liquid shale oil is separated from combustible oil-shale gas. “Excuse me, but your rock is on fire” Why is this good? Why is this bad?

  9. EES 450: Sedimentary Geology Mudrocks– mudstones, shales and siltstones ● What is shale gas? - Shale gas: Natural gas produced from shales, which often have low permeability, which doesn’t allow significant fluid flow to a well bore, so most are not commercial sources of natural gas. Commercial gas production requires fractures to provide permeability.

  10. EES 450: Sedimentary Geology Mudrocks– mudstones, shales and siltstones ● What is shale gas? - Hydraulic Fracturing “Fracking”:Fracturing of rock by pressurized fluids.

  11. EES 450: Sedimentary Geology Mudrocks– mudstones, shales and siltstones ● What is shale gas? - Hydraulic Fracturing “Fracking”:Problems? Air: Flaring of hydrogen sulfide, methane leaks, truck traffic. Water: Of some ~2,500 fluid components, ~650 are known carcinogens; “flowback” water often enriched in salts, uranium, thorium and radon (radioactivity). Possibility of polluting groundwater with H2S, CH3 and the rest. Seismicity: Process induces small-scale seismicity; also evidence of larger-scale earthquakes caused by hydraulic fracturing.

  12. EES 450: Sedimentary Geology Mudrocks– mudstones, shales and siltstones ● How do oil and gas shales form? - More on kerogen… ο Comprised of high molecular weight organic compounds. ο Relatively insoluble = kerogen; relatively soluble = bitumen (soluble in organic solvents). ο If heated to the right temps., (60-160 °C or 150-200 °C), some kerogens will release crude oil or natural gas, respectively. Give some examples of the source materials for kerogen…

  13. EES 450: Sedimentary Geology Mudrocks– mudstones, shales and siltstones ●Kerogen types…

  14. EES 450: Sedimentary Geology Mudrocks– mudstones, shales and siltstones ● Late Devonian time on Laurentia… - What conditions favor deposition of oil and gas shales?

  15. EES 450: Sedimentary Geology Mudrocks– mudstones, shales and siltstones ● Late Devonian time on Laurentia…

  16. EES 450: Sedimentary Geology Mudrocks– mudstones, shales and siltstones ● Late Devonian time on Laurentia… Marcellus Shale – Washingtonville, PA (left), Leroy, NY (right) Marcellus Shale – Elimsport, PA (left), Antis Fort, PA (right)

  17. EES 450: Sedimentary Geology Mudrocks– mudstones, shales and siltstones ● Challenges in studying mudrocks: Comprise ~50% of all sedimentary rocks! (1) Mudrocks are the least understood, and are relatively understudied as compared to other sedimentary rocks. (2) Challenging to study mudrock constituents, due to their diminutive size and susceptibility to weathering on outcrops. (3) Multiple classification schemes accepted/used by scientists. Claystone– Glacial Lake Missoula Claystone – Slovakia Ragged Reef Fm. – Nova Scotia

  18. EES 450: Sedimentary Geology Mudrocks– mudstones, shales and siltstones ● Historically, and often still interpreted to represent quiet, deep-water environments, current research indicates deposition in higher energy settings as well. Alluvial environments Glaciers Non-glacial lakes Deltas Coastlines Marine environments

  19. EES 450: Sedimentary Geology Mudrocks– mudstones, shales and siltstones ● Historically, and often still interpreted to represent quiet, deep-water environments, current research indicates deposition in higher energy settings as well. Marine environments

  20. EES 450: Sedimentary Geology Mudrocks– mudstones, shales and siltstones ● Why is the study of mudrocks important? (1) Most abundant of all sedimentary rocks. (2) They contain a lot of information regarding the geologic history of Earth’s surface. (3) They are major hydrocarbon source rocks. (4) They often form important hydrocarbon seals. (5) They are rapidly becoming very important gas reservoir rocks (shale gas). Deltas Coastlines Marine environments

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