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Non-Terrigenous Sediments and Rocks

Non-Terrigenous Sediments and Rocks. Carbonate-Chemical-Volcaniclastic Sediments and Rocks. No “Simple” Classification Scheme. Orthochemical Sediment: Evaporites. Stratified rock consisting of minerals precipitated from highly concentrated brines, typically hypersaline sea water

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Non-Terrigenous Sediments and Rocks

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  1. Non-Terrigenous Sediments and Rocks Carbonate-Chemical-Volcaniclastic Sediments and Rocks

  2. No “Simple” Classification Scheme

  3. Orthochemical Sediment:Evaporites • Stratified rock consisting of minerals precipitated from highly concentrated brines, typically hypersaline sea water • Anhydrite (CaSO4) • Gypsum (CaSO4 )*H2O • Halite (NaCl) • Others

  4. Evaporites • Indicative of unusual climatic or oceanographic conditions • Severe circulation restriction • Climatic aridity • Highly subject to secondary alteration/solution • Anhydrite<--->gypsum due to hydration/dehydration • Physical deformation: enterolithic structure • Occurrence • Bedded • Nodular • Chicken wire

  5. Siliceous Sediments/Rocks • Chert/diatomite (SiO2 ); • Opaline tests • Chalcedony • microcrystalline quartz

  6. Bedded chert (most) Pelagic sediment consisting of siliceous zoo- and phytoplanktonic tests Siliceous sediment experience apredictable transformation from amorphous opal to chalcedony and eventually to microcrystalline quartz due to time/temperature dependant chemical reaction Siliceous Sediments/Rocks C= lam chert, s= sandstone layers, f= fractures

  7. Siliceous Sediments/Rocks • Nodular Chert; diagenetic origin (typical) • Silica derived from the solution of siliceous fossil material in predominantly carbonate rich successions • Sponge spicules and other siliceous bioclasts N=chert nodules, b=bedded chert

  8. Organic Rich Sedimentary Rock • Organic compound-rich rocks • Coal • Humic coal • vascular {land} plant derived organic compounds altered by elevated temperature and burial pressure • Sapropelic coal • Formed from non-vascular (algal) plant material

  9. Organic Rich Sedimentary Rock • Oil (black) Shale • Primary, organic carbon (OC)-rich shale (>2% to > 10% OC) • Formed in low energy environments through suspension and deposition in stagnant (anaerobic) conditions • Most common source of long chain, liquid and gaseous hydrocarbons that can migrate into porous reservoir rocks and from economic accumulations of petroleum Spontaneous combustion of Kimmeridge oil-shale, Dorset, UK., probable source for most North Sea oil

  10. Importance of Volcaniclastics • Recognition of contemporaneous volcanism • Pyroclastic rocks and volcaniclastics with admixtures of proclasts • Voluminous strata at plate boundaries and hot spots

  11. Volcanic particulate material Any fragmentation mechanism Any transport process Any environment Pyroclastic Particles broken by volcanism Epiclastic (epiclasts) Any fragment of volcanic (composition) origin Classification of Volcaniclastic Rocks

  12. Pyroclastic rock or sediment >75% material fragmented by volcanic eruptions Tephra: unconsolidated pyroclastic deposit Hydroclastic rocks or sediment Water interaction fragmentation Classification of Volcaniclastic Rocks Pyroclastic Ejecta

  13. Classification of Pyroclastic Rocks • Basic classification otbo (on the basis of) particle size • Blocks (solid) and bombs (molten) (>64mm) • Volcanic breccia deposits • Lapilli (2-64mm) • Lapillistone • Ash (<2mm) • Tuff • Additional Classification otbo composition • Crystals • Lithic • Vitric fragments

  14. Composition of Tuffs • Crystals (intratelluric) • Euhedral +/- broken • Compositional zoning • Vitric (glassey) fragments • Bubble wall shards

  15. Composition of Tuffs • Vitric (glassy) fragments • Bubble wall shards • Hydroclastic shards • Lithic fragments • Volcanic rock fragments (cognate?)

  16. Fragmentation Processes • Explosive (gas expansion) comminution (fragmentation): mainly intermediate to silicic (high silica) magmas. • Ash fall; Laterally extensive air fall; Typically silicic and vitric rich. • Mantles topography. • Consists of glass (bubble-wall) shards.

  17. Volcanic Fragmentation Processes and Products • Continental silicic (high silica) magmas; Calderas and pyroclastic sheet deposits • Ash flow {nuee ardante or ignimbrite, as in “great flaming ignimbrites”. • Follow topographic lows (high density fluid). • Create gigantic pyroclastic sheet deposits • Can be hot enough after deposition to weld, annealed vitric fragments welded tuff Kaguyak volcano, Alaska

  18. Volcanic Fragmentation Processes and Products • Hydroclastics; Water interaction fragmentation (typically basaltic lavas) • Great volumes of hydroclastics on the sea floor and in the edifice (sticky-up topographic/bathymetric feature) of submarine volcanoes • Highly subject to alteration –> clay minerals, microcrystalline silica, and zeolite

  19. Subject to extensive diagenetic alteration during burial Typically occur in high heat flow geological settings Typically poor fluid reservoir rocks Significance of Volcaniclastic Rocks

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