EXAM and QUIZ #1 In 2 weeks, September 30. Exam on chapters 1-5 in Pinet’s text. 1 - 1.5 h length Multiple choice, short answer. Study material at end of chapters: keywords Review of basic concepts questions Critical thinking essays questions Discovering with numbers questions Quiz questions taken directly from laboratory exercises
Classification of marine sediments based upon size. SedimentTypeDiameter (mm) Gravel Boulder>256 Cobble65-256 Pebble4-64 Granule2-4 Sand Very coarse1-2 Coarse0.5-1 Medium0.25-0.5 Fine0.123-0.25 Very fine0.0625-0.125 Mud (silt & clay) 0.0002-0.004 Colloid <0.0002
Classification of marine sediments based upon Mode of Formation. Terrigenous: Sands and mud produced by weathering and erosion of rocks on land. Biogenic : CaCO 3 (calcium carbonate) and SiO 2 (silica) muds and oozes composed of hard parts of organisms. Authigenic : formed by precipitation of minerals in seawater (Manganese (Mn) and Phosphorus (P) nodules). Volcanogenic : ejected from volcanoes (ash). Cosmogenous : pieces of meteorites that survive trip thru atmosphere.
Worldwide distribution of recent shelf sediments by composition is strongly related to latitude and climate. Calcareous biogenic sediments dominate tropical shelves. River-supplied sands and muds dominate temperate shelves. Glacial till and ice-rafted sediments dominate polar shelves.
Geologic controls of continental shelf sedimentation must be considered in terms of a time scales. For a time scale up to 1000 (10 3 ) years, sedimentation controlled by: –Waves –Wind-induced currents –Tidal currents (all related to water depth)
Million-year time scale. For a time scale up to 1,000,000 (10 6 ) years, sedimentation controlled by: –Glaciation and its effect on position of coastline
Relict Sediment: deposited in the past under conditions that are no longer present.
If influx of terrigenous sediment is low and the water is warm, carbonate sediments and reefs will dominate. Carbonate Shelves
Passive (Atlantic) vs. Active (Pacific) Type Margins. Atlantic (passive) type margin: Passive boundary Long history of sedimentation Sedimentation rate = subsidence rate Broad, smooth continental shelf Pacific (active) type margin: Convergent boundary Sedimentary layers compressed and deformed Volcanic sediment Seismic activity causes slumps and slides of sediments to deep-sea trenches.
Passive (Atlantic) vs. Active (Pacific) Type Margins.
Bulk emplacement: –Slumps: sediment transport by mass with little deformation or folding of layers –Slurries: debris flows and mud flows- destroy any previous bedding or layering. Turbidity currents –Deep-Sea canyons formed by these processes. –Ice Rafting Polar latitudes, debris from melting icebergs. Glacial marine sediment Modes of sedimentation in deep sea
Modes of sedimentation in deep sea Pelagic sedimentation: –Pelagic muds: Inorganic red or brown clays and silt –Fine-grained (0.0002 – 0.0004 mm) –Quartz, feldspar, kaolinite & chlorite minerals –Terrigenous, wind- bourne, cosmogenous source –Kaolinite in tropical & subtropical waters –Chlorite in temperate & subpolar –Dominate below waters with little planktonic production.
Pelagic sedimentation: –Pelagic muds: biogenic oozes –>30% of debris from planktonic organisms –Calcareous oozes (CaCO 3 ) »Shells of foraminifera & pteropods (zooplankton) and coccolithophorids (phytoplankton). »Accumulate on seafloor above CCD. »Forms hard limestone under pressure –Siliceous oozes (SiO 2 ) »Shells of radiolaria (zooplankton) and diatoms (phytoplankton). »Accumulate on seafloor below CCD. »Accumulate below regions of high diatom production (equator, poles, upwelling areas) Modes of sedimentation in deep sea
CaCO 3 (calcite) is a solid material produced by biological or abiological processes in seawater: Ca 2+ + CO 3 2- CaCO 3 –The reaction can go both ways, depending on the pH, pressure. –When the seawater is undersaturated with respect to CaCO 3, calcite will dissolve: Ca 2+ + CO 3 2- CaCO 3 –But when seawater is saturated with respect to CaCO 3, calcite will remain in its solid form and not dissolve: Carbonate Chemistry
Depth in ocean at which seawater becomes undersaturated with respect to calcite and rate of dissolution of CaCO 3 equals its rate of delivery. –CCD ~ 4500 m (or deeper in regions of high surface productivity). –Depths below CCD: Seawater undersaturated w.r.t. CaCO 3 Chemical properties of deep water dissolves calcite CaCO 3 oozes less common than SiO 2 oozes. –Depths above CCD: Seawater saturated w.r.t. CaCO 3 CaCO 3 remains intact. CaCO 3 oozes more common than SiO 2 oozes. Question: Why is the CCD sometimes referred to as the “snow-line”? Carbonate Compensation Depth, CCD
Foraminifera (zooplankton with CaCO 3 shell) Size ~ 1mm
Diatoms (phytoplankton with SiO 2 shell) Size ~ 0.01mm
TYPE COMPO- SITION ATLANTIC (%) PACIFIC (%) INDIAN (%) GLOBAL (%) Foram. oozeCarbonate65365447 Pteropod ooze Carbonate20.1-0.5 Diatom oozeSilica7102012 Radiolarian ooze Silica-50.53 Red clayAluminum silicate 26492538
Formed by chemical or biochemical reactions on ocean floor Nodules of ferromanganese (Fe and Mn) or phosphorite (P). Concentric layers of metal oxides accrete on particles over millions of years (1-4 mm per 10 6 y). Contain economically important metals Cu, Zn, Co and Pb. (but too expensive to harvest). Origin uncertain (biological?) Authigenic deposits
Ferromanganese nodules Floor of South Pacific Ocean. Nodule size 1-5 cm diameter