Transcript Indicators of different environments

Indicators of different
environments - recap
Fragmental?
• Made of fragments
• Clasts
•  sedimentary rock
What environment
does this picture
show?
• Shallow marine
• What features in rocks would you see?
• Fossils – Corals are the main here – environmental
indicators (clear, warm, shallow, marine, aerated seas) –
TROPICAL
• Rocks? – Limestone
• Texture: well sorted, fine grain size, test with dil HCl  fizz
reaction (therefore it is a carbonate)
• If you can see BROKEN fossils or fragments – it implies …
strong currents
What environment
does this picture
show?
• River aka Fluvial
• Fluvial is when a river or a stream where
there are sediments that are being
transported down by water. The deposits
are formed by a river.
• What features in rocks would you see?
• Coarse debris such as boulders and sand
are the type of sediments in fluvial.
• Texture: coarse grain size (indicates
strong current/fast flow), finer material
shows processes of abrasion and
attrition have worn the fragments down
What environment
does this picture
show?
• Lake aka Lacustrine
• Lacustrine environments consist of sediments that
have been transported by a river or stream but
the water has ponded up and settled
• What features in rocks would you see?
• The sediments are fine grained and consist of silt
and clay.
• Texture: fine grain size (indicates little current)
What environment
does this picture
show?
• Desert aka Aeolian
• Deserts are types of areas that almost have no rain and
are considered to be very warm and dry areas.
• What features in rocks would you see?
• The most common type of sediment in the desert is sand.
• The colour might be RED – as any iron has been OXIDISED
• Texture: fine grain sizes (the wind can only blow small
grains – the process is called deflation)
• Cross bedding
• Sediment blown up the gentle stoss side, is dumped on
the leeward side
What environment
does this picture
show?
• Swamp
• still shallow water which tends not to move very much
(stagnant).
• What features in rocks would you see?
• The sediments in swamps mostly consist of very dark
brown mud which was created due to the water.
• Texture: Plant material rich (peat), partly rotted with fine
grained sediments
What environment
does this picture
show?
• Delta
• Landform created at the mouth of a river or a stream
where water most likely to flow into large body of still
water
• What features in rocks would you see?
• Sediment deposition which water carries the sediments
in rivers, suddenly stops
Texture: coarse material dropped first (proximal - closest
to land), finer material carried further away (distal)
What environment
does this picture
show?
• Alluvial fan
• when a river dumps sediment in a shape of a fan at the
mouth of a mountain canyon.
• What features in rocks would you see?
• The rocks that have formed on the alluvial fan have some
large pieces of sediment
• Texture: coarsest closest to land, angular fragments
Igneous rocks ….
• Cooling history?
• Interlocking crystals  igneous
• Coarse crystal size  slow cooling  PLUTON
deep underground
• Mineralogy  quartz, feldspar, mica 
granite
• What if porphyritic?
Felsic or Mafic?
• The most common felsic/acidic rock is granite,
mineralogy includes quartz, muscovite,
orthoclase, and plagioclase feldspars.
• Common rock-forming mafic/basic minerals
include olivine, pyroxene, amphibole, and
biotite. Common mafic rocks include basalt,
dolerite and gabbro.
Igneous rocks ….
• Cooling history?
• Interlocking crystals  igneous
• Medium crystal size  moderately slow
cooling  large mass, not on surface, but not
deep crust
• Dyke, sill …. Check for concordance
• Mineralogy  dark-coloured hornblende
crystals and white feldspar crystals  dolerite
Igneous rocks ….
• Cooling history?
• Interlocking crystals  igneous
• Fine crystal size  fast cooling  on surface
 lava flow
• Vesicles – trapped gases
• Columnar jointing - cooling cracks
• Mineralogy  plagioclase feldspar, pyroxene,
olivine, low quartz content  basalt
Igneous rocks ….
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Cooling history?
Interlocking crystals  igneous
Olive green colour  olivine
Peridotite  mantle composition