Practical Flashcards
Dip
Angle at which the plane is inclined from the horizontal
Calculate tanD= v(contour height)/h(distance between contours)
Dip direction
Direction in which the structure contour lines decrease in topographical height
Outlier
Younger rock surrounded by older
Mainly in ridges
Inlier
Older rock surrounded by younger
Mainly in valleys
What is a syncline fold?
When younger rocks are in the middle
What is an anticline fold?
When the older rocks are in the middle
Ecology, Taphonomy and Time scale of Stromatolites
Microbial mats
Deposition around and got preserved
Pre-cambrian to present
Ecology, Classification and Time scale of Trilobites
Burrowing, scavenger feeders
Moulting behaviour
Rapid burial perhaps
Phylum: Arthropoda
Cambrian- end Permian (251.9Ma)
Ecology, Classification and Time scale of Graptolites
Filter feeders, colonial
Phylum: Hemichordata
mid Cambrian (520Ma)- mid Carboniferous (320Ma)
Ecology, Classification and Time scale of Bivalves
Burrow (mya), Swimmers (Pecten), Cementers (Ostrea)
Benthic and epifaunal/infaunal
Phylum: Mollusca
Cambrian to present
Ecology, Classification and Time scale of Brachiopods
Filter feeders, pedicle attaches, toothed hinges (rarely found open)
Mollusca Brachiopoda
Cambrian to present
Ecology, Classification and Time scale of Echinoids
Filter feeder/ grazer dorsal at the top ventral underneath with teeth
Pentaradial symmetry
Phylum: Echinodermata
Cambrian to present
Ecology, Classification and Time scale of Crinoids
Suspension feeders, attach to logs and float
Ossicles often preserved
Phylum: Echinodermata, Class: Crinoidea
mid Cambrian to present
Ecology, Classification and Time scale of plants
Autotrophic, photosynthesise, respire, sessile
e.g. Genus Stigmaria, from Plantae kingdom
Cambrian to present
Ecology, Classification and Time scale of Bryozoan
Colonial, filter feeders, provide shelter
Phylum: Bryozoa, class of Gymnolaemata most successful
Ordovician (485Ma)
Ecology, Classification, Preservation and Time scale of ammonoids
Free swimmers, carnivorous
Aragonite shell, and moulds
Phylum: Mollusca, Class: Cephalopoda, Orders: Goniatitic, Ceratitic, Ammonitic
G=Dev (420-360Ma) -Permian (300Ma-251.9Ma)
C= Triassic (251.9Ma-200Ma)
A=Triassic- Cretaceous (66Ma)
Ecology, Classification, Preservation and Time scale of Nautiloids
Jet propulsion, Carnivores
Aragonite shell
Phylum: Mollusca, Class: Cephalopoda, Subclass: Nautiloid
Cambrian, then Triassic (251.9Ma-200Ma) coiled only
Ecology, Classification and Time scale of corals
Solitary/ Colonial
Phylum: Cnidaria, Subclasses: Scleractinia, Rugosa, Tabulata
T+ R= Ordovician (485Ma)- Permian (251.9Ma), in calcite
S= Triassic (250Ma) - present, in aragonite
Ecology, Classification, Presevation and Time scale of belemnites
Mesozoic squid, swimmers, carnivorous
Phylum: Mollusca, Class: Cephalopoda, Order: Belemnitida
Calcite guard
Jurassic (200Ma-145Ma) - Cretaceous (145Ma-66Ma)
How does a schist differ to a gneiss in thin section?
Schist- tiny crystals barely visible in clear lineation, muscovite, biotite
Gneiss- larger quartz crystals present, banding when looking with naked eye, quartz, feldspar
What are the optical differences between Clinopyroxene and Orthopyroxene?
Clinopyroxene- Inclined extinction, Colourless/ greyish, Pink to orange with CP
Orthopyroxene- Straight extinction, Colourless/ reddish/ green, Grey to purple with CP
Describe the optical properties of magnetite
Black in Plane and cross polars
Small
Can be found as intrusion
What are the optical properties of Olivine?
Curving cracks
Bright second order colours CP
Pale yellow PP
High relief
Quite euhedral usually
What are the optical properties of plagioclase feldspar?
Lamellar twinning CP
Low relief
Distinct cleavage
Inclined extinction
What are the optical properties of Amphibole/ Hornblende?
Pleochroic green to brown
Clear cleavage 56 and 124 degrees
Shows twinning
High second order interference
What are the optical properties of quartz?
Low relief
No cleavage
Low 1st order colours
What are the optical properties of garnet?
Colourless
Isotropic
High relief
What are the optical properties of biotite/ mica?
Speckled extinction
Straight extinction
May contain zircons
Low relief
Pleochroic
What are the optical properties of orthoclase/ K+ feldspar?
Straw colour
Lack of striations
Low birefringence
Pleochroic
Cleavage
No barcode extinction
What are the optical properties of microcline feldspar?
Cross hatch extinction
Low relief
Colourless
Inclined extinction
What are the optical properties of muscovite/ mica?
Rainbow coloured CP
Moulted appearance
Green tint in PP
Straight speckled extinction
What are the optical properties of chlorite?
Some pleochroism
Some twinning
Green tint PP
Brown/ Dark green/ blue CP (not on chart)
What are the optical properties of epidote?
Yellow- green pleochroic
High relief
purple w/orange outline in CP
Some lamellar twinning
Inclined extinction
What does a red colour in a rock suggest? What type of magma/ minerals are likely to be present?
Red suggests oxidised iron
Minerals: Quartz, feldspar
Magma: Rhyolitic
What are the 3 low density igneous rocks and their differences?
Pumice- light coloured
Scoria- dark coloured
Tuff- orange, brown, more sediment like
What are the features of a QFP and Quartz porphyry?
Large crystals of quartz and feldspar, in a fine ground mass
May have some iron staining
Rhyolitic magma origins, high Si content
What are the features of a breccia?
Large angular clasts
In a fine ground matrix
Large variety of minerals
Poorly sorted
What are the features of eclogite and its original environment?
Green - pyroxene
Pink- garnet
Basaltic origins, undergone metamorphism
Some quartz, amphibole
What are the features of amphibolite and its origins?
Black- hornblende, slightly shiny
White- K+ feldspar
Regional metamorphism, from basaltic origins
What are the features of quartzites?
Sandpaper glassy texture
Pink and white crystals (Q and K feldspar)
What are the features of pelites and its origin?
Fine grained
Dark coloured
Originally mudstone/ siltstone
What are the features in ooids and their origins?
Small spherical spheres
Dark brown radial rings
Made of calcite
Formed in shallow tropical waters
What are the features of conglomerates and their origins?
Rounded clasts in a fine grained matrix
From floods
Matrix may be sand (quartz)
What are the properties of a limestone and its origin?
Easily scratched
Light coloured
Reasonably small grain size
Formed from precipitation out of water due to biological and non-biological processes
What are the properties and origin of chalk?
Low density
White
Formed from remain of marine organisms
What are the properties and origins of dolomite?
Slight red colour Ca:Mg 1:1
May have cavities due to alteration shrinkage
Formed in high intertidal and sabkhas (coastal mudflat)
What are the properties and origins of chert/ flint?
Conchoidal fracture
Dark brown/ grey colour
Non-clastic formed from microcrystalline quartz
Form as nodules
Give a technical description of a brachiopod
- Contains a pedicle which it uses to attach - filter feeder
- Pedicle is at the posterior end
- Diductor muscles for opening
- Adductor muscles for closing
- Leaves less muscle scars and has less muscle mass
- Has tooth and socket system
Give a technical description of a bivalve
-Only has adductor muscles
- Open when adductor muscles relax
- Beak is called the umbo, and points towards anterior
- Has pallial line inside- marks where muscles attached
- Very clear muscle scars
- Contain ligament near tooth
- Has tooth and socket system
Why does calcium carbonate sometimes biomineralize in calcite and sometimes aragonite?
Depends on the minerals present in the water
If no Mg present then will biomineralize in stable calcite, if Mg present will form metastable aragonite
Original composition of skeletal material of trilobites
Calcium carbonate- specifically calcite
Original composition of skeletal material of echinoids
Calcium carbonate- specifically calcite
Ossicles formed of small calcite crystals
Original composition of the skeletal material of bivalves
Calcium carbonate
How do muscovite and biotite differ?
Hand specimen
Biotite- black, dark
Muscovite- light, w/green tinge
PP
Biotite- Brown/ green
Muscovite- colourless
CP
Both show straight speckled extinction
What are the optical properties of augite?
Clear cleavage, many parallel to each other
Second order blue, orange CP
Pale colourless in PP
Moderate relief
Clinopyroxene so inclined extinction
What are examples of black minerals in hand specimen?
Magnetite
Biotite mica
Augite pyroxene (dark green)
Hornblende/Amphibole
What are the properties of Diorite?
White- plagioclase
Black- biotite
Present are also pyroxene and amphibole
Intrusive rock (large crystals), acidic origins
What are the properties of gabbro?
Coarse grained intrusive mafic rock
Dark minerals- Pyroxene
Lighter minerals- feldpspars
What are the properties and the environment formation of blueschists ?
Blue colour
Blue- glaucophane
Green- epidote, jadeite
Pink- garnet
Metamorphism at subduction plate
Originally basaltic (oceanic plates)
What are the properties and environments of formation for marble?
White, pink
Granular texture
Metamorphosed limestone
What are the differences between nautiloids and ammonoids?
Nautiloids thicker shell
Nautiloids simpler suture lines
Ammonoids septa curve inwards into body
Nautiloid siphuncle central, ammonoid is lateral
How can tectonic setting be inferred from thin sections?
Large crystals- intrusive vice versa
Quartz- rhyolitic magma, olivine/ pyroxene- basalt
Presence of muscovite, chlorite, glaucophane, epidote- suggest metamorphism
What are the optical properties of glaucophane?
Blue
Good cleavage
Twinning
Accompanied with epidote and jadeite
What are the optical properties of spinel?
Isotropic
No cleavage
High relief
Brown in PPL
In mafic igneous rocks
What are the optical properties of serpentine?
Green in PPL
Low relief
1st order birefringence
‘skin of a serpent’
What part of a belemnite is commonly preserved?
(Rostrum)
Calcitic guard
What are the key features on an echinoid?
Periproct (anus)
Peristome (mouth)
ambulacra (where spines attach 5 radial things)
Interambulacra (inbetween the above)
Spine attachement
Ventral and dorsal
How to calculate stratigraphic thickness?
Cos(Dip) x vertical thickness (calculate by the contour structure difference between top and bottom of boundary)
How to estimate dip direction?
If valley, then direction of veeing
If ridge then opposite direction to veeing
What 4 labels should be added to graptolites?
Nema
Sicula
Thecae
Stipe
