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

No “Simple” Classification Scheme

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

Classification of Volcaniclastic Rocks 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 Pyroclastic rock or sediment >75% material fragmented by volcanic eruptions Tephra: unconsolidated pyroclastic deposit Hydroclastic rocks or sediment Water interaction fragmentation Pyroclastic Ejecta Juvenile Cognate Accidental Erupting magma, Crystals and glass Co-magmatic volcanic rock Country rock inclusions

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

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

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

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.

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

Volcanic Fragmentation Processes and Products Hydroclastics; Water interaction fragmentation (typically basaltic lavas) Great volumes of hydroclastics on the sea floor and in the edifice of submarine volcanoes Highly subject to alteration –> clay minerals, microcrystalline silica, and zeolite

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

Orthochemical Sediment: Evaporites Stratified rock consisting of minerals precipitated from high concentration brines, typically hypersaline sea water Anhydrite (CaSO4) Gypsum (CaSO4 )*H2O Halite (NaCl) Others

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

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

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

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

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

Organic Rich Sedimentary Rock Oil 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.

Non-Terrigenous Sediments and Rocks Carbonate Sediments and Rocks

No “Simple” Classification Scheme

Most Common non-Terrigenous Sedimentary Rocks Carbonates (>50% primary carbonate minerals) Limestone (CaCO3) Chemical biochemical Dolomite (CaMg(CO3)2)

The Origin of Carbonate Sediments Most form as biogenic particles (essentially the only source) in warm (tropical; 30oN to 30oS latitude), shallow (shelf; within the photic zone), (mostly <10-20 m) marine water Also accumulate in deepwater ooze limestone (fine-grained) made up of skeletons of pelagic microorganisms such as Globigerina

The Origin of Carbonate Sediments Why? Any process that decreases [CO3] forces rxn (2) to the left, CO2 is less soluble in warm water; CaCO3 has retrograde solubility (1) H2O + CO2 <---> 2H2CO3 <–->H+ + HCO3- <-->H+ + CO3-2 CaCO3 <-–> Ca+2 + CO3-2 (pH dependant reaction)

Carbonates: General Characteristics The majority of carbonate sediment forms in subtidal to supratidal environments and gives rise to widespread tabular deposits along continental (trailing edge) margins and epicontinental seas Important occurrence in reefs, mounds or banks (bio-buildups)

Carbonate Minerals in Sedimentary Rocks The physical and chemical conditions of the environment in which calcites, dolomites and aragonites are formed are reflected in their composition. bivalent metal cations Ca+2 Calcite, aragonite Mg+2 Magnesite, dolomite Fe +2 Siderite, ankerite + CO3 -2

Carbonate Minerals in Sedimentary Rocks Several factors control the crystal habits and crystal sizes of these minerals, most important: salinity ratio of magnesium to calcium of in the solution (time dependant) bivalent metal cations Ca+2 Calcite, aragonite Mg+2 Magnesite, dolomite Fe +2 Siderite, ankerite + CO3 -2

Most modern Carbonate sediments (mostly biogenic) Magnesian Calcite = small crystals > 4% Mg++ (4-9%), Mg++ = 3 x Ca++ in normal sea water (main site of CaCo3 ppt) “poisons” (interferes with calcite crystallization) and results in formation of meta-stable Aragonite (neomorphosis) Aragonite (orthorhombic polymorph of CaCo3) (Mg,Ca)CO3 (Mg,Fe,Ca)CO3 (Aragonite)

Most ancient carbonate rock is Calcite: <4% Mg++ (CaCO3) Dolomite (CaMg{Co3}2) 42% - 58% CaCo3. Not readily formed at low temperatures; almost always 2nd ary mineral or very rare primary ppt “the dolomite problem”: Primary or Secondary/Authigenic?? (Mg,Ca)CO3 (Mg,Fe,Ca)CO3 (Aragonite)

Other, (mainly diagenetic) Sedimentary Carbonate Minerals Siderite Fe Co3 Ankerite: Ca(Mg,Fe)Co3

Carbonates: General Characteristics An antipathetic relationship exists between carbonate sediments and siliciclastic sediments due in large part to the biology of carbonate sediment-forming organisms high terrigenous sedimentation rates increase turbidity, which inhibits photosynthesis by benthic organisms gill breathers (such as the coral) get clogged up and die The structures and textures of carbonate rocks mostly reflect intrabasinal, biological AND physical factors

Carbonates: General Characteristics Carbonate sediments are particulate and subject to physical processes at the site of deposition just like TC sediments Kinetic energy (currents) in the depositional environment influence: grain size and sorting BUT, carbonate sediments are mostly biogenic (“born” not “made”) and may not experience physical transport This can confound grain size-sorting / depositional energy relationship

Source and Type of Sediments Produced in Modern and Ancient Carbonate Environments

Carbonate Rock Classification Allochems Carbonate sand Micrite Micro Crystalline calcite Cement (spar)

Carbonate Rocks Constituents The sand-sized grains that occur in carbonate rocks are called allochemical particles or allochems. Intraclasts (rock fragments): formed, transported and redeposited within the basin Ooliths: concentrically laminated carbonate structures, including: oolites -concentrically laminated structures,less than 2mm in diameter, thought to be abiogenic in origin pisolites - same as oolites, but greater than 2mm in diameter oncolites - spheroidal stromatolites (> 1-2 cm) Peloids: silt to fine grained sand sized carbonate particles with no distinctive internal structure; most thought to be fecal pellets Skeletal particles (bioclasts): whole microfossils, whole megafossils, broken shell fragments algae, forams, corals, bryozoans, brachiopods, gastropods, pelecypods, ostracods, etc.

Carbonate Rocks Constituents The sand-sized grains that occur in carbonate rocks are called allochemical particles or allochems. Intraclasts Ooliths Peloids Skeletal particles (bioclasts) The interpretation of the depositional setting of carbonates is based on grain types, grain packing or fabric, sedimentary structures, and early diagenetic changes.

Carbonate Rocks Constituents The sand-sized grains that occur in carbonate rocks are called allochemical particles or allochems. Intraclasts (early lithified carbonate fragments): irregularly-shaped grains that form by syndepositional erosion of partially lithified sediment.

Carbonate Rocks Constituents The sand-sized grains that occur in carbonate rocks are called allochemical particles or allochems. Ooliths: concentrically laminated carbonate structures, including: oolites -concentrically laminated structures,less than 2mm in diameter, thought to be abiogenic in origin pisolites - same as oolites, but greater than 2mm in diameter oncolites - spheroidal stromatolites (> 1-2 cm)

Carbonate Rocks Constituents The sand-sized grains that occur in carbonate rocks are called allochemical particles or allochems. Pelloids: silt to fine grained sand sized carbonate particles with no distinctive internal structure; most thought to be fecal pellets

Carbonate Rocks Constituents The sand-sized grains that occur in carbonate rocks are called allochemical particles or allochems. Skeletal particles (bioclasts): whole microfossils, whole megafossils, broken shell fragments algae, forams, corals, bryozoans, brachiopods, gastropods, pelecypods, ostracods, etc. Standard microfacies (fossil fragment type -> environment)

Carbonate Rocks Constituents Micrite: microcrystalline carbonate particles of clay (<1-4 micron) size (subtranslucent matrix) formed by chemical or biochemical ppt abrasion of allochems implies deposition in a low energy environment just like in terrigenous mudstones

Carbonate Rocks Constituents Cement: sparry (twinkling crystalline) orthochemical material formed in interstitial pore spaces of “grainy” carbonate sediment cement in pores indicates original void space also recrystallized allochems or micrite

Carbonate Rocks Constituents Insoluble Residues – minor amounts of clay minerals and quartz occur in limestones, as insoluble residues, (so called because they do not dissolve in HCl) Most insoluble material is chert (siliceous) chert mostly originates from the shells of silica secreting organisms including diatoms, radiolarians, and some sponges.

Classification Schemes: Folk Classification Type I limestone, Sparry Allochemical rocks: allochems > 50%, spar cement > micrite mud [4 rock types] more energetic environment, some sorting Type II limestone, Micritic Allochemical rocks: allochems >10%, micrite mud > spar cement [4 rock types]lower energy environment, more poorly sorted than Type I Type III limestone: Micrite: allochems < 10% very low energy at the site of deposition (carbonate mudrock) “Biolithite”: Reef rock

Classification Schemes: Dunham Classification Texture and allochem type incorporated into classification sediment deposited in calm vs agitated waters mud-bearing vs mud-free sediment grain vs mud support bound (biologically) depositional texture recognizable

5 Principles of Dunham Classification Presence or absence of lime mud; is there any mud at all. Calm waters allow for the accumulation of lime mud and indicates the absence of current induced agitation Grain Support: self supporting framework: fluid circulation, diagenesis Grain kind: standard microfacies types Grain size, rounding, and coating: hydrologic interpretations Biogenically ppt masses bound at time of deposition: Boundstone organic framework laminations not consistent with gravity (stromatolite) roof over sediment filled cavities

Folk Textural Spectrum Classification Concocted to incorporate textural characteristics comparable to textural maturity in TC sediments Mud component Sorting Rounding

Dolomitic Rocks Typically devoid of primary textures and structures; if primary textures are preserved <10% dolomite: “dolomitized” (rock name) >10% dolomite: dolomitic (rock name) recrystallized carbonate: dolostone saddle dolomite: “burial” dolomite of hydrothermal origin