FIELD TECHNIQUES Flashcards
An essential piece of equipment for the detailed observation of all rock types and fossils materials.
Hand Lens
Most have a lens with ___ magnification
10x
Some lens contains both a (1)___ and a (2)___ or (3)___.
(1) 10x
(2) 15x
(3) 20x
- Essential for most geological fieldwork
- Used in breaking and collecting rock example
- Used to expose a fresh portion of the outcrop
Geologic hammer
In using a hammer, ____ must come first.
safety
Step on the sample and move your head (1)____ in the direction of hammer motion to avoid the (2)___ due to impact.
(1) away
(2) projectiles
Essential in taking down notes and sketching outcrops for better understanding
Field Notebook and Writing Materials
What to note?
- Date
- Weather
- GPS Reading/ Location
- Facing direction
- Scale
- Sketch
-Observations
-Pin point on your sketch where you get the strike where you get the strike and dip or observable features
Observations on Field Notebook
- Weathering
- Attitudes
- Structures
- Materials Present
- Sizes of grains or materials
- Remarks
(Typical Setting) Upper crust, outer zones of mountain belts
Pressure solution cleavage
(Typical Setting) Upper crust, outer zones of mountain belts; fine-grained rocks
Slaty cleavage
(Typical Setting) Upper crust, outer zones of mountain belts; competent rocks
Fracture cleavage
(Typical Setting) High strain faults and shear zones at all but shallowest depths
Mylonitic foliation
(Typical Setting) Middle crust, inner zones of mountain belts; metamorphosed rocks (1)
Schistosity
(Typical Setting) Middle crust, inner zones of mountain belts; metamorphosed rocks (2)
Crenulation cleavage
(Formed by) Dissolution of soluble grains to directed stress
Pressure solution cleavage
(Formed by) Alignment of platy grains by rotation, dissolution, and crystallization during applied stress
Slaty cleavage
(Formed by) Tensional failure under high fluid pressure* in competent rock types
Fracture cleavage
(Formed by) Extreme flattening and stretching in narrow, high-strain zones of shearing
Mylonitic foliation
(Formed by) Mineral alignment under applied stress, during metamorphic crystallization
Schistosity
(Formed by) Microfolding of a pre-existing planar fabric (tectonic and sedimentary)
Crenulation cleavage
(Clues in the Field) Dark/pale colour striping; partially dissolved fossils, clasts; stylolitic surfaces
Pressure solution cleavage
(Clues in the Field) Fine fabric that rock cleaves along; typically associated with folds
Slaty cleavage
(Clues in the Field) Spaced cracks in competent rock type
Fracture cleavage
(Clues in the Field) Strongly planar fabric; other high-strain features
Mylonitic foliation
(Clues in the Field) Visible mineral grains; millimeter to centimeter-scale folia, rougher than slaty cleavage
Schistosity
(Clues in the Field) Microfold hinges, crenulation lineation
Crenulation cleavage
Compass-clinometer is used to measure:
- The orientation of geological planes and lineation with respect to north
- Angle of dip of geological feature with respect to the horizontal
Can also use in conjuction with a topographic map to accurately determine location
Compass-clinometer
More sensitive device because of the in-built spirit levels and the graduation of scales in 1 degree and 2 degree increments
Brunton-type
Other type of Compass-clinometer
Silva-types
Sampling- Things to do:
- Know your sampling method
- Get the sample that has the bulk composition of the outcrop
- Get a fist size sample for petrology, and crushed sample for geochemistry
- Get a duplicate
- Name the sample properly
A sample of about __________ is usually sufficient for producing one or more thin sections provided the rock is not too coarse-grained
10cm thick x 5 cm x 5cm
If the rock is coarse-grained then a sample size that is appropriate to the _____________ should be taken
grain size
True or False:
The sample needs to be large enough to enable it to be clamped in the rock saw and care needs to be taken with sample position and shape if it needs to be orientated.
True
In deformed rocks it is useful to cut ___________ thin - sections at right angles to each other, so a slightly larger sample may be required.
two or even three
For sedimentary rocks the younging
direction is often required and is usually recorded on the face _____________ to bedding with an arrow.
perpendicular
True or False:
For sedimentary rocks if the bedding orientation is not clear then it may not be recorded.
False : If the bedding orientation is not clear this may also need to be recorded so that the section can be cut perpendicular to the bedding.
For igneous rocks the younging
direction may need to be recorded
for ______________________________
cumulates, pyroclastic rocks, and igneous rocks containing flow features and vesicles
For samples from metamorphic rocks it is also often necessary to record the top surface because of the need to obtain thin -sections in a particular orientation relative to the ______________.
structural fabric/s
Samples for Geochemical Analysis:
A _________ sample is usually sufficient for a range of major and minor element, trace element and isotopic analyses
200 g
Samples for Geochemical Analysis:
for very coarse - grained or heterogeneous rocks, about ________ sample may be required.
1 kg
Samples for Geochemical Analysis:
Particular care needs to be taken to ensure that the sample is __________.
fresh
Samples for Geochemical Analysis:
If possible it is better to remove the ______________ material in the field to
ensure that what you take back is a fresh sample
weathered material
Samples for Geochemical Analysis:
Color changes are a good indication of weathering, but also the ____________ and _________ of the rock tend to change.
fracture pattern and hardness
Sample for mineral extraction:
The amount of sample that needs to be collected for mineral analysis depends on the (1) __________ to be extracted and the (2) _________________
- minerals
- composition of the rock.
Sample for mineral extraction:
For heavy minerals such as zircon that are present only in low abundance, __________ kg of rock may be required.
1-2 kg
Sample for mineral extraction:
For volcanic glass and feldspars for « Ar —» Ar and K — Ar dating,generally at least ________ kg of rock is required
1kg
Sample for mineral extraction:
For pyroclastic and sedimentary rocks it is particularly important to collect from the _______________ as the coarser — grained minerals that are more easily picked out will be most abundant there.
base of the bed
Samples for megafossil analysis:
Megafossil samples and their supporting rock material tend to be large in which they are best wrapped in _________
paper.
Samples for megafossil analysis:
If they are fragile or the rock needs to dry out slowly, wrap them in __________ and then paper.
cling film/plastic food wrap
Samples for microfossil analysis:
The size of samples for microfossil analysis depends on the likely _________ of fossils within the sample.
abundance
Samples for microfossil analysis:
For an average abundance of foraminifers _______ g should be sufficient
200g
Samples for microfossil analysis:
For nanofossils and diatoms a small _____g sample is ample.
10g
Samples for microfossil analysis:
For palynology samples of ________ kg are required.
0.5 — 1kg
Samples for molecular fossils:
Very small samples are required for molecular fossils but the sample needs to be large enough about ______g to avoid contamination.
2-5 g
The samples should be packaged in
metal foil or glass or polythene bags of known composition.
On the sample bag or outside of the packing material itself it is useful to record the following as appropriate:
- sample number;
- cross reference to field notebook page and/or date collected;
- location;
- whether or not the sample is orientated;
- rock type;
- associated samples.
is a type of map characterized by large-scale detail and quantitative representation of relief, usually using contour lines, but historically using a variety of methods
Topographic Map
