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Diagenesis

Diagenesis. Opal ? ChertCarbonate ooze ? chalk ? limestoneBasalt ? smectite (montmorillonite)Reduction of organic matterMost organics along the marginsOxic vs. suboxic vs. anoxic conditionsAlteration of claysMore common under anaerobic conditions. Deep Sea Diagenesis. Sediment ? record of his

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Diagenesis

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    1. Diagenesis Diagenesis Low temperature Chemical alteration Within the sediments Interaction with interstitial fluids Authigenesis In the water column, or sed/water interface From seawater Metamorphism High temperature

    2. Diagenesis Opal ? Chert Carbonate ooze ? chalk ? limestone Basalt ? smectite (montmorillonite) Reduction of organic matter Most organics along the margins Oxic vs. suboxic vs. anoxic conditions Alteration of clays More common under anaerobic conditions

    3. Deep Sea Diagenesis Sediment ? record of history Sediment patterns environment of deposition Sedimentation rates Productivity Proximity to source regions Chemistry- d18O, d13C, Mg/Ca, 87Sr/86Sr… Ice volume, temperature, water mass age, carbon budget, weathering, hydrothermal activity…

    4. Sediments are altered with time Interstitial fluids (pore fluids) more sensitive monitor of changes in the sediment through time Deep Sea Diagenesis

    5. Sediment Diagenesis Sediments Wide range of initial compositions Chemistry not very sensitive to sed/water reactions Example: Sr calcite ~1000 ppm Sr Interstitial Fluids Well-defined seawater composition Chemistry very sensitive to sed/water reactions Example: Sr seawater ~ 87 mM Sr or 7.9 ppm

    6. Interstitial Fluids Significant as recorders of sediment reactions Alteration of igneous material Basalt and ash layers Recrystallization of sedimentary components Calcite, silica, clay Degradation of organic matter Formation of in situ mineral Celestite (CaSO4), calcite

    7. Sampling Interstitial Fluids Squeeze Squeeze at 0°C- minimize T effect on mineral stability Squeeze under N2 or He- minimize effects of oxidation state on reduced species Centrifuge Corks- Osmotic chambers Benthic flux chambers (shallow)

    8. Squeeze Cakes

    9. Osmopumps

    10. Processes Affecting Interstitial Fluid Composition Sedimentation Advection Diffusion Reactions

    11. Processes Affecting Interstitial Fluid Composition Sedimentation Water introduced to system during burial Advection- flow of fluid Compaction- porosity reduction, flow < sediment burial rate (minor effect) Tectonic- convergent margins (subduction)- can transport material

    12. Interstitial Fluids

    14. Interstitial Fluids

    16. Reactions Within sediment In underlying crust Source or sink of ions (? diffusion) Diffusion- molecular Net motion of matter resulting from random motion of molecules Created by concentration gradients = flux into or out of sediment Processes Affecting Interstitial Fluid Composition

    17. Diffusion

    18. Diffusion Fick’s First Law (steady state)

    19. Ds is a function of: Pressure Temperature Porosity Tortuosity (permeability) Decreases with depth in the sediment Diffusion

    20. Diffusion Fick’s Second Law (Rate- nonsteady state))

    21. Diffusion Fick’s Second Law If there is a concentration gradient there is a flux of material normal to the gradient The flux is proportional to the gradient D (the diffusion coefficient) is the proportionality constant

    22. Diffusion

    23. Diffusion Diffusion rates > Sedimentation rates Bioturbation rates Diffusion in and out of sediment column ? profiles (gradients)

    24. Pore Fluid Composition Deposition- sediment and water Reactions Concentration gradients Diffusion Net result = pore fluid profiles

    25. General Diagenetic Equation

    27. Interstitial Fluid Profiles

    28. Interstitial Fluid Profiles

    29. Conservative Profiles

    30. Conservative Profiles

    31. Nonconservative Profiles

    32. Nonconservative Profiles

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