SEDIMENTARY PETROLOGY (BIOGENIC, CHEMICAL, AND VOLCANICLASTICS) Flashcards
Differenatiate Calcareous and Carbonaceous?
Calcareous are used to describe sediments which soliidy to form limestones which are rich in CaCO3 while Carbonacous are used fro materials rich in carbon such as coal
How would you differentiate quartz from calcite?
Calcite is soft with hardness of 3 and can be scratched easily by pen-knife while quartz is 7 and is harder than the metal blade.
How many % of mg to qualify for low and high-Mg Calcite?
Low: <4%,
High: 11-19%
Organisms that have high Mg Calcite?
Echinoderms, Barnacles, Foraminifers
Difference between calcite and aragonite?
Calcite is hexagonal while aragonite is orthorhombic. Aragonite is more densely packed and isthus denser with G=2.95. Calcite is 2.74-2.94. Aragonite is harder (3.5-4).
Inverterbrates which has aragonitic composition for hard parts
Bivalves and Corals
Chemical formula of dolomite?
CaMg (CO3)2
When you stain dolomite with Alizarin Red-S, what would be the contrast with other carbonates?
No change in color but for makes other carbonates pink
This dye is used to distinguish between ferroan and non-ferroan carbonates?
Potassium ferricyanide
What would be the color if iron in the carbonate reacts with potassium ferricyanide?
Blue
How can you make thin sections for carbonates?
Acetate peels
Organisms which usually appear as single crystals?
Crinoids, Echinoids and calcareous sponges
Homogenous crystals?
Trilobites, Ostracods, and molluscs
Lamellar form?
molluscs
primsatic form?
Molluscs
Foliated form?
brachiopods and other moluscs
granular form
Foraminifera and mollluscas
nacreous
molluscs
Radial form?
belemnites
Spherulitic?
Corals
modern calcitic bivalves
oysters and scallops
molluscs which have distinct coiled form and have calcitic or aragonitic layered structure
Gastropods
have layered shell structure, which includes modern nautilus and the coiled chambered ammonites
Cephalopods
A cephalopod that has cigar-shape guard of radial fibrous calcite which is common in Mesozoic Sed Rocks
Belemnites
shelly organisms with 2 shells similar to bivalves but are made up of low magnesium calcite nad a two-layer structure of fibrous crystals which may be preserved
Brachiopods
The exoskeletons of these organism as made up of prisms of calcite that are elongate perpendiular to the edges of the plates
Trilobites
Examples of Arthropods?
Triblobite and Barnacles
sea urchins?
Echinoids
Sea lilies?
Crinoids
small single celled marine organisms which range from few tens of microns in diameter to tens of mm
Foraminifera
Contrast planktonic and Benthic?
Planktonic means floating while benthic are those which live on the sea floor
Hard outer parts of forams made up possibly of high and low mg calcite
Tests
What is the class of corals?
Cnidaria
Whats the contrast between older and younger corals?
Older are made primarily of calcite while the
younger ones are aragonite-rich
Corals which have symbiotic relationship with algae that require clear, warm, shallow marine waters
Hermatypic Corals
Corals that do not have algae and can exist in cooler, deeper water?
Ahermatypic Corals
Singe-celled protozoans w/c are mainly encrusting organism made up of aragonite and/or high mg calcite
bryozoa
sedentary organisms that may form hard parts of calcite which some may also be of silica or protein composition
Sponges (Porifera)
Calcareous sponges that were common in Palaeozoic
Stromatoporoids
Annelid worms which secrete tubes of carbonates (Calcitic, or aragonitic) as they encrust pebbles or other hard parts of other organisms
Serpulid
A carbonate producing alage which isknown as corraline algae which have a layered structure and are effective at binding soft substrate
Red algae (Rhodophyta)
Algae that have calcified stems and branches and often sgmented which contribute fine grains and rods of Calcite when the organism dies
Green Algae (Chlorophyta)
these are spherical bodies of few tens of microns made of of plates which are important constituent of pelagic limestone such as cret chalk
Cocolithophores
These are flat or domes structures formed by trapping of finegrained carbonates by the filaments and stick surfaces of cyanbacteria. These are also considered as some of the earliest lifeforms on Earth
Stromatolites
Cyanobacterial communities which have an irregular form
Thrombolites
irregular concentric structures mm to cm accross formed of layers bound by cyanobacteria found as clasts w/in carbonate sediments
Oncoids
The action of cyanobacteria to alter original structure of a shell into fine-grained micrite
Micritisation
spherical bodies of CaCO3 less than 2mm in diamter which have an internal strucure of concentric layers which suggest precipitation of CaCO3 aroun the surface of the sphere
Ooids
what may be the nucleus of an ooid?
a carbonate materials or a clastic sand grain
A rock made up of carbonate ooids?
Oolitic Limestones
How does ooids form?
Chemical precipitation out of agitated water saturated in CaCO3 in calcium cabonate in warm waters
How can you differentiate Pisoids from ooids?
Pisoids have a dimater of over 2mm and are more irregular in shape but similar in form and origin to ooids
Round particles made up of fine-grained clacites found in sediments which do not show any concentric structures and didnt grow in water
Peloids or Faecal Pellets
What organisms usually produced these particles which are less than a mm across?
gastropods
fragments of CaCO3 material that has been partly lithifed, an then broken up an reworked to form a clast which is incorporated into the sediment
Intraclasts
rounded carbonate grains consisting of several fragments of CaCO3 cemented together
Grapestone
Fine -grained carbonate particles less than 4microns across which may be purely precipitated from CaCO3 saturated water, from breakdown of skeltal framents or algal or backerial origin
Lime Mud,Carbonate Mud or Micrite
the most widely used schme for limestone description in the field both in mesoscopic and microscopic scale which is based on texture, including the proportion of carbonate mud present and the overall framework of the rock
Dunhman Classficcation
A rock consisting entirely of ooids with no matrix?
OOlitic Grainstone
Rock with 75% shelly fragments in a matrix of carbonate mud
bioclastic packstone
In limestone petrographic analysis, a high proportion of fine-grained carbonate materials imply that?
rock was formed in a relatively low-energy setting
Absence of mud in a limestone imply that?
High energy environment of roc formation
What does high concentration of ooids indicate?
Shallow, wave-dominated coastl setting
What would be the depositional evnrionment of a rock composed of biogenic material of same group of organisms such as bivalves or gastropods?
Lagoonal Setting
What would be the indicator if shells are composed mainly of aragonite or high mg calcite?
When primary fabric is lost due to recrystallisation
organism which te to retain primary structures
LowMg Calcite such as brachiopods and Bivalves
Minerals formed by precipitation our of solutions as ions became more concentrated when water evaporates?
Evaporites
Ave dissolve ions in Sewater?
35 part per thousands
Order of precipitation of evaporite minerals?
CaCO3, Calcium Sulphate, Sodium Chloride then Potassium and Magnesium Chlorides
This will precipiate once evaporation concretae seawater to 19% of its original volume
Cacium Suplhate
Differntiate Anhydrite and Gypsum?
Gypsum is hydrous
Slender crystals of Gypsum?
Selenite
forms as a results of rehydration of anyhdrite and has fine crystalline form in nodules
Alabaster
How can you distinguidh Gypsum from Calcite and Halite
Gypsum is softer with hardness of 2 and can be scratched by fingernail and does not taste salty
How can you differentiate gypsum and anhydrite?
Gypsum is less denser and softer while Anhyrite is harder and cannot be scracthed by fingernail (3.5), under the microscpore, Gypsum has low relief and has interference color of low-order grays while anhydrite has high relief and have moderate high-rder colours
When will calcite precipitate from Sewater?
when evaporation concentrate seawater to <50% of its original volume
Precipitates our of seater once it as been concentrated to 9.5% of its orignal volume
Halite (NaCl)
Halite with stepped or stairlike crystal face?
Hoppe Crystal
Contrast haltie and sylvite
Halite is Sodium chloride and has salty taste while sylvite is potassium chlorid with bitter taste
Striking characteristics of halite under microscope?
It is isotropic, has stronge cleavage planes because it is isometric
Lakes that have the same dissolved ions as sewater?
Saline Lakes
Minerals which may precipitate from Saline lakes?
Trona Na2CO3, Mirabilite Na2SO4, and Epsomite (MgSO4)
Silica which is made up of radating fibers a few tens to hundreds microns long?
Chalcedony
Fine-grained siliceous sed rocks made up of microcrystalline quartz and chalcedony
Cherts
These froms on the seafloor or lake floor by accumulation of siliecous skeletons of microscopic oranism which becomes chert
Siliecous Ooze
siliecous microoganism in lakes or in freshwater?
Diatoms
Common siliceous microoganism marine environments?
Radiolaria
differentiate radiolaria and diatoms
Radiolaria are zooplankton while diatoms are phytoplankton
Cyrptocrystalline silca with water in mienral strcuture
Opal
Depositional evnironment of Cherts?
Deep-Marine
How does diagenetic Cherts form?
when SiO2 replaces unstable materials in a rock by water rich in silica flowing through the rock
Texture of Diagenetic Cherts
Nodular
Dark Chert
Flint
Hardest Sedimentary Rock
Cherts
What gives jasper its strong red color?
Hemattite
What does chert look like under the microscope?
Radiating fibers of chalcedony or completely interlocking microquartz grains
What depositonal environemnt are phosphatic materials usally associated?
Shallow marine continental shelf deposits
Calcium phospahtes which occur as accessory minerals in granitic rocks
Apatite
Where does phosphates usually occur?
High organic Productivity envir and with low oxygen content
Rocks with concenration of 5-35% P2O5
Phosporites
calcium hydroxl fluorapatite?
Francolite
Fossilated faeces of fishes or animals
Coprolite
Sed rocks with at least 15% iron
Ironstones or iron formations
from which age are most iron rock mined today came from?
Precambrian
black mineral which occurs as accessory mineral in igneous rocks and as detrital in seds
Magnetite (Fe3O4)
most common oxide mineral which is bright red to black and occurs as weathering or altertion product in seds and sed rocks?
Haematite (Fe2O3)
Iron hydroxide that is widespread in sediments as yellow-brown mienrals which may be primary deposit or weathering product representing less oxidizing conditions than haematite
Goethite (FeO.OH)
Why are young deserts yellowish in color?
Because of Geothite content
Why are ancient deserts reddish in color?
Because Geothite already oxidized ,cause by post depositional processes, into haematite giving it a reddish color
A hyrated iron oxide that is amorphous
Limonite
Differentiate Goethite, Limonite, Magnetite and Hematite in Thin Section
Iron Oxides are opaque while magnetite is black and often euhedral while haematite occurs in variety of form which is red in reflected light. Geothite and Limonite are yellow-brown in thin sections and are anisotropic
Common iron rich sulphide minerals found in ign and met rocks as brassy cubic crystals and occurs finely disseminated particles which may give dark coloration to sediments
Pyrite (FeS)
Iron rich phyllosilicates minerals found in ironstones and formed either as authigenic and diagenetic
Greenalite (Serpentine)
and Chamosites (Chlorite)
A phyllosilicate formed through authigenetic processes in shallow marine environments
Glauconite
siderite rich mudstones are associated with what environment?
Freshwater reducing conditions such as
non-saline marshes
A sed rocks consisting of alternating laminated or thin bedded alternations of heamatite rich seds and other material which is typically siltsone or chert (Silica Rich) which there is no equivalent forming today
Banded Iron Formations (BIFs)
Age range of BIFs
2.5-1.9 Ga Precambrian
an example of ferromanganese deposit form at any depth authigenically in a very slow manner and are only found concentrated deep in the oceans where the rate of deposition of other sed is even slower
Manganese Nodules
Seds or sed rocks with high conc of organic matter
Carbonaceous
whats the range for a mudrock to be considered as carbonaceous?
> 2%
Whats the range for a limestone to be carbonaceous?
> 0.2%
Whats the range of organic matter content for a sandstone to be carbonaceous?
> 0.05%
Enviroment with very limited to no oxygen?
Anaerobic
This may form from long term accumulation of dead vegatation favored by wet anaerobic conditions of mires, bogs, and swamps
Peat
At present where does peat forms?
from Subarctic boggy regions to mangrove swamps in the tropics
What is the ideal area for pure peat formation?
areas with little clastic input
Remains of planktonic algae, spores and very fine detritus from larger plants that accumulates underwater in anaerobic conditions?
Sapropel
Organisms whose remains will ultimatey form liquid and gaseous hydrocarbons?
Zoonplankton and Phytoplanktons and bacteria
how much of a rock must be organic matter to qualify as coal?
2/3
Non organic, non combustible material of Coals
Ash
When will a coal be economic?
If ash content is less than 10%
this is a heterogenous type of coal made up of different types of vegetation
Peat
Coals that is bright, shiny black that usually breaks cubically and consisting of woody tissues
Vitrain
Black or grey in color, dull and rough usually contains a lot of spore and detrital plant material
Durain
Black fibrous with a silky luster, friable and soft coal that represent fossil charcoal
Fusain
Banded, layered coal that consists of alternation of the other three types
Clarain
A coal with chonchoidal fracture
Sapropelic
Sapropelic Coal with dull black luster rich with spores
Cannel Coal
Saproperlic Coal with black/brown color rich with algae
Boghead Coal
Particle types making up the coal
Macerals
How do you observe coal under thin section?
Polished surfaces under a thin layer of oil using reflected light
Macerals in which the oirgin is mainly cell walls of woody tissues and leaves
Vitrinite
Macerals which comes mainly from spores ,cuticles and resins
Liptinite
Macerals which are burnt, oxidised, or degraded plant material
Inertinite
A technique used to analyse coal by measuring the amount of light reflcted from the polished surface
Reflectance
Differentiate Macerals in terms of reflectance?
Liptinite have low reflectance while inertinite have high reflectance and vitrinite reflectance varies on coal rank
A technique used to determine the rank of coal and is a measure of the burial temperature of the bed and also provides a measure of the burial depth of a bed in basin analysis
Vitrinite reflectance
relation of coal rank with T
As T in burial increases, Rank increases
Mudrocks which contains high proportion of organic material that can produce liquid oil or gas
Oil Shales
Organic material, usually of algae, which are broken down to form long chain of hydrocarbons
Kerogen
Most important source rock
Shale
Environment which favors source rock formations?
Lakes, restricted shallow marine environments
Clastic sediments that are saturated with hydrocarbons and they are exposed equivalents of oil reservoirs
Tar sands/ Oil Sands
What happens to organic matter in the formation of tar sands?
Biodegraded into bitumen
Differentiate Basaltic and Silicic Magma in terms of Volcanoclastic content
Basaltic usually ejects large volumes of lava but small volcanic ash while silicic are those which have large amounts of molten rocks ejected
Collective terms for pyroclastic materials?
Tephra
Diferentiate pyroclastic and volcanoclastic?
Pyroclastic is mainly particles ejected by the volcano while volcaniclastic are those which are composed mainly of volcanic detritus
Differentiate volcanic blocks and bombs
Both are coarse materials over 64mm in diameter but blocks are ejected in a solid form while bombs are those which were partially motlen and have cooled in the air
Blocks that are consolidated into a rock?
VOlcanic Breccia
Bombs consilidated into a rock
Agglomerate
Pyroclastic materials with 2-64 mm diameter or granule to pebble size
Lapilli
Consolidated lappili?
Lapillistone
Speherical aggreggates of fine ash formed during air fall which is a bit moist
Accretionary Lapilli
Unconsolidated sand, silt, and clay grade pryoclastic materials
Ash
Lithified ash from volcanic eruptions
Tuff
3 usual compositions of vocaniclastic rocks?
Mineral grains, Lithic fragments and Vitric materials (Glass Shards and Pumice)
These are small dark lenses of glassy material usually of pumice that were softened and compressed in flame like structures during welding of tuff
fiamme
A rock that have fiamme structures
Ignimbrite / Welded Tuff
