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Non-Terrigenous Sediments and Rocks PowerPoint PPT Presentation


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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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Non terrigenous sediments and rocks l.jpg

Non-Terrigenous Sediments and Rocks

Carbonate-Chemical-Volcaniclastic

Sediments and Rocks


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No “Simple” Classification Scheme


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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


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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


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Siliceous Sediments/Rocks

  • Chert/diatomite (SiO2 );

    • Opaline tests

    • Chalcedony

    • microcrystalline quartz


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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


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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


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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


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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


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Importance of Volcaniclastics

  • Recognition of contemporaneous volcanism

    • Pyroclastic rocks and volcaniclastics with admixtures of proclasts

  • Voluminous strata at plate boundaries and hot spots


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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


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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


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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


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Composition of Tuffs

  • Crystals (intratelluric)

    • Euhedral +/- broken

    • Compositional zoning

  • Vitric (glassey) fragments

    • Bubble wall shards


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Composition of Tuffs

  • Vitric (glassy) fragments

    • Bubble wall shards

    • Hydroclastic shards

  • Lithic fragments

    • Volcanic rock fragments (cognate?)


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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.


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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


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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


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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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