Sedimentology and Palaeontology Lecture 2: Biominerals and Rock forming organisms

Question 1

What are the materials that organisms will use to create their skeletons?

Answer 1

-Calcium carbonate
- Silica
- Hydroxyapatite
- Magnetite
- Chitin
- Lignin

Question 2

Go into detail about Calcium carbonate (CaCO3) in a palaeontological context

Answer 2

Common biomineral, occurring in nannoplankton,
echinoderms, molluscs, cnidarians, bryozoans,
foraminiferans, some arthropods and others.

Question 3

Go into detail about Calcite in a palaeontological context

Answer 3

Calcite
* Stable and abundant
* High preservation
potential

Question 4

Go into detail about Aragonite in a palaeontological context

Answer 4

Aragonite
* Metastable at normal
temperatures and
pressures
* Relatively rare in the
fossil record
* Only preserves in
mudstones

Question 5

What are the two things fossil dissolution/a fossil dissolving can create

Answer 5

Mould:
the external
impression of an organism in
the surrounding sediment

Cast:
replacement minerals
infilling the mould. When this
happens, original textures
are generally obliterated

Question 6

What are Coccolithophores?

Answer 6

Coccolithophores are nannoplankton less than 63 µm, typically 5 – 50 µm. They are Photosynthetic, unicellular algae

Skeletons formed of calcite plates

Arose in the Triassic, reaching highest diversity in Late
Cretaceous.

Question 7

What sedimentary rock are Coccolithophores/the skeletons of Coccolithophores made up of?

Answer 7

Chalk, which is a substance made up of calcium carbonate (CaCO3)

Question 8

Calcium carbonate rocks dissolve under a certain depth (compensation depths) and therefore cannot contribute rock record in these areas.
What are the compensation depths?

Answer 8

Calcite Compensation Depth (CCD) is 4-5 km

Aragonite Compensation Depth (ACD) 1-2 km

These depths vary with latitude, pressure, and the
availability/amount of dissolved of CO2

Compensation depths have changed significantly over time.

Question 9

Define carbonate reefs

Answer 9

Topographic highs of biologically-produced carbonate

Question 10

What are Cnidarians

Answer 10

Cnidaria is a phylum including:

-Anthozoans(corals)

-Scyphozoans(Mostly pelagic jellyfish)

-Hydrozoans(Hydroids, fire corals and other jellyfish).

Question 11

Describe the anatomy of Cnidarians

Answer 11

Simplest metazoans

Can be colonial or solitary
organisms

Either Radial or bilateral symmetry

Single body cavity: the enteron

Diploblastic tissues
(comprised of two main
layers)

Nematocysts, stinging
cells, found on
tentacles.

Question 12

Describe the life stages of the Cnidarian

Answer 12

Medusa life stage: free swimming,
sexual reproduction. Mouth is facing up.

Polyp life stage: sedentary, asexual reproduction. Mouth is facing down.

Question 13

Define Zoantharian corals

Answer 13

Predominantly sessile life strategy
- Eight major groups of extinct forms, but only three have
substantial fossil records
- Mesenteries secrete CaCo3
skeletons, the coralite (in solitary
animals) or corallum (colonial)

Question 14

Define Rugose Corals/Rugosa

Answer 14

Range from Ordovician to Permian

Well-developed septa

Bilaterally symmetrical

Colonial and solitary

Most possess tabulae

Calcite skeletons

Weakly anchored to sea
floor

Question 15

Define Tabular corals

Answer 15

Ranges from Ordovician to Permian

Always colonial

Radial symmetry

Weak or absent septa

Well developed
tabulae

Calcite skeleton

Question 16

Define Scleractinian corals/Scleractinia

Answer 16

Triassic to Recent

Colonial and solitary

Well developed septa

Tabulae absent

Aragonite skeleton

Radial symmetry

Question 17

Define Stromatolites

Answer 17

Photosynthetic cyanobacteria that Precipitate calcite that binds
sediment together.

Are occasionally buried, forcing
the microbes to migrate
upwards towards the light. This
produces calcite-rich, stratified
mounds.

Oldest confirmed stromatotlites date to c.3.5 Ga
(Precambrian)
- Declined in abundance throughout the Phanerozoic as grazing
metazoans developed

Question 18

What are some other CaCO3 rock builders?

Answer 18

-Foraminifera
- Crinoids
- Stromatoporoids
- Calcisponges
- Bivalves (oyster reefs)
- Bryozoans
- Rhodophytes (red algae)

Question 19

Define Porifera(Sponges)

Answer 19

Developed 1.8 Ga

Are Parazoans: animals with no
differentiated body tissues

Have Multiple methods of
reproduction

Different ecomorphs reflect
different environments

Marine and freshwater forms

Many sponges have
flexible, siliceous
skeletons

Skeletons comprised of
spicules held together
with spongin