lesson 5 sedimentary processes , rocks and fossils

Question 1

What properties can tell us about the rock story?

Answer 1

• -> Grain sizes
• -> Sorting
• -> Roundness
• -> Other: chemical composition can provide info abt the chemical weathering processes

Question 2

What do grain sizes review about the rock?\

Answer 2

Low energy environment –> can cause Small grains
e.g shallow marine
This is due to the low energy currents, which may not be able to deposit the rock into other environments, as higher energy environment tend to ERODE the rock.

Question 3

What does sorting tell us (hint: energy)

Answer 3

Poorly sorted rock –> indicate sudden change in energy that CAUSED the deposition
e.g meandering river (outer edge of the water is moving faster then inner)

Well sorted rock –> indicate gradual change in energy
e.g gradual widening of river

Question 4

What can roundness reveal about the distance that the source rock has deposited?

Answer 4

Well rounded grains –> indicate a LONG distance travelled from the source rock to deposition.
LONG distance –> long time / higher speed –> more time to be weathered
e.g mountain top to estuary

Angular grains –> short distance travelled (inversive)

Question 5

What does minerals in a rock indicate about its rock story?

Answer 5

The chemical composition of a mineral can provid info about the chemical weathering process
e.g feldspar –> typically weather into clay,
thus feldspar rich sedimentary rock –> likely lithified close to the source rock

Question 6

What are the four notable depositional environment?

Answer 6

• -> floodplains (mudstone)
• -> meandering rivers (conglomerate)
• -> shallow marine (sandstone, limestone)
• -> deep marine (chalk, chert)

Question 7

Recall how sediments are presented in floodplains

Answer 7

• sediments build up by –> floods of low-lying plains adjacent to a river
• typically small particle size –> due to low energy

Question 8

Properties of meandering rivers (conglo_?)

Answer 8

• rock: conglomerate
• fast flowing rivers that sweep from side to side (whee-Whee, like ~~~~~~)
• fastest flow on outside of curves, slowest flow on inside, possibly even low energy
• deposition (stays still) when sediments moved from inside and upstream to outside (^^^^ to ——>)
• mixed! grain sizes due to SUDDEN change in energy

Question 9

Properties of shallow marine? (sand_?, lime_?)

Answer 9

–> on the continental shelf, a part of the continent that is a bit below the ocean

Question 10

deep marine (cha?, cher?)

Answer 10

• past the continental shelf, DEEP OPEN WATER

* LOW ENERGY , fine particles

Question 11

What is biological sedimentary rocks?

Answer 11

Lithified results of biological activity

–> formed from matter that was used for biological structures

Question 12

Notable habits of biological sedimentary rocks?

Answer 12

–> shallow marine
–> deep marine
–> swamp
(basically where animals or life existed, or can survive in)

Question 13

Shallow marine properies in biological manner?

Answer 13

• -> on continental shelf
• -> corals, shelled creatures
• -> biological strucures made from calcite / aragonite

Question 14

Deep marine properties in biological manner?

Answer 14

• -> deep and very low energy (water waves can’t move through easily, heavy)
• ->only very small particles from shallow marine can make it to deep marine and settle
• -> chalk (calcium carbonate), chert(silica - used for biological structure of some small reatures)

Question 15

Swamp

Answer 15

• plants buried and pressured to form coal

* blurs the line between the rock and fossils, as it is made from organic materials

Question 16

Chemical Sedimentary rocks definition

Answer 16

• -> chemical sediments formed from chemical reactions
• -> most important PRECIPITATION REACTIONS
  * (solution) aq + (solution_1)aq = (soluable)aq + (precipitate)solid
  * when two liquid solutions react together and form a new substance that exits the water as a solid.

Question 17

Example of banded iron formations in Australia?

Answer 17

The first organisms on Earth, cyanobacteria, photosynthesises, filling the atmosphere with oxygen and so much that some are DISSOLVED into the oceans.
–> iron ions within ocean REACTED with the oxygen to precipitate IRON OXIDE (red substance), which then settles on ocean floor and form banded iron formations
–> chemical sediments as such –> evaporation of seawater –> dissolved minerals and left behin insoluble sediments
!!! most common minerals: halite (salt) and gypsum.

Question 18

Define fossils

Answer 18

Fossils are traces of past life, fossilised either directly or indirectly, on a macro or micor scale.

Question 19

Examples and types of fossils

Answer 19

• hard parts that do not decompose (bones, scales)
• remains of soft parts that have escaped decomposition (a chemicla reaction was avoided)
• chemical traces (Molecular fossils and isotope ratios)
• physical traces (like foot prints)

Question 20

We do we care about these old dead things?

Answer 20

• -> past extinctions, past climates, changes that have occured over time
• -> develop geologic time scale, date rocks relative to each other, and determine better understanding of stratigraphy

Question 21

original material:

Answer 21

–> hard parts of organisms can be very durable and are sometimes buried and left unchanged for millions of years.

Question 22

permineralisation

Answer 22

when cells of fossils are pentrated by mineral rich water.

• -> after long periods of time, minerals within the water crystallise and take the place of cells
• -> causes the fossil to become a rock, but shaped like the original material: petrified wood

Question 23

mold/cast

Answer 23

Hard parts of organisms can sometimes be buried and the sediment around it lithified. After long periods of time, the original material can be dissolved by slightly acidic water.

• -> remaining space is where the hard part use to be –> mold
• -> mineral rich water fills mold & crystallises –> resulting fossil is cast –> calcium carbonate shells of sea creatures

Question 24

Traces

Answer 24

• -> traces are only preserved : paw prints, dinosaur footprints or fossils of worm tunnels.
• -> often trace fossils are casts

Question 25

What are index fossils?

Answer 25

an index fossils must:

• -> have wide distribution –> correlate rock layers from all over the globe
• -> be part a species that existed for a SHORT time,
• -> be easily recognisable, be sure of what it is

Question 26

Function of index fossils?

Answer 26

Extremely useful in relative dating

–> sedimentary layers –> that have same types of index fossils –> can be deduced to have the same or similar ages

Question 27

Notable fossils recalling: 8

Answer 27

1. Athropoda
   * all animals with exoskeletons and segmented bodies : flies, carbs and spiders
   * 521-252 million years ago
2. Brachiopoda
   * 500 million, 500-250 million years ago
   * shelled creatures that were once the most prominent, but now not really
   * symmetric across face, asymmetric across hinge

3. Mollusca
Ammonities
* 400-66million years old
* internal segments
* look like weird shaped snails

Bivalves

• 500 million years old when its present, proliferous from 250 million years old
• most prominent shelled creatures currently
• symmetric across hinge, often asymmetric across face

4. Hemichordata
   Graptolites
   * 510-320 million years old
   * worm-like organisms, are tubular and elongated
   * have quite a variety of different shapes
   * found as carbon film, a cast of its past shapes
5. Vertebrates
   * 520 million present
   * animals with an internal skeleton
   * bony fish, and boring organisms like humans
6. Vascular plants
   * plants with internal vascular structures (xylem and phloem) to transport water and nutrients
   * trees, most plants with leaves, pollen from vascular plants
   * present from 425 million years ago
7. Non-vascular plants
   * plants lacking vascualr system
   * mosses algae (structurally delicate bryophyte tissues )
   * fossil records are quite rare
8. Stromatolites
   * “living fossils”
   * sedimentary rock structures formed by cyanobacteria and other microorganisms that trap and layer grains
   * made by simple life, are some of the oldest records of life

Question 28

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