Exceptional Preservation

Question 1

What are lagerstatten?

Answer 1

Extraordinarily preserved organisms

Question 2

What are the two types of lagerstatten?

Answer 2

• Concentration deposits: fossils occur in unusual concentrations, e.g. bone beds, mass kills
• Conservation deposits: exceptional preservations. 3 types:
  
  • preservation of organisms that are not usually preserved (slugs, jelly fish, embryos)
  • preservation of parts of an organism not usually preserved (internal organisms, skin)
  • organisms preserved unusually articulated (full articulated skeleton)

Question 3

What are the major controls of exceptional preservation?

Answer 3

• Exclusion of bioturbators and scavengers
• Unusual chemical environment, often resulting from catastrophic events.

Question 4

What do microbial mats do during preservation?

Answer 4

Microbial mats form a ‘death mask’ which stabilises sediment and sets up favourable geochemical gradients to promote early mineralisation.

Question 5

What are some conservation traps?

Answer 5

• Amber (sticky, catches debri and preserves)
• Ice (permafrost, freezes organisms and preserves)
• Tar pits (e.g. La Brea tarpits in LA, oil sucked to surface, water sits on top, birds land on top and get preserved
• Hot silicious springs (silicon is deposited around organism and preserves
• Tufa (calcium carbonate, lime stone
• Ashfall (covers organisms and immediately forms rocks

Question 6

Do all tissues decay at the same rate?

Answer 6

Tissues display a spectrum of resistance to decay
recalcitrant <-> labile

Question 7

When are decay prone tissues preserved well?

Answer 7

When they are replicated quickly by authigenic minerals which either:
- precipitate around the tissue to form a mould/cast
- precipitate on or within the tissue, preserving the cells

Question 8

What minerals can cause exceptional preservation?

Answer 8

• Apatite (phosphate, preserves with most fidelity)
• Clay minerals (preserve in cold glacial environments)
• Iron pyrite
• Metal sulphides
• Silica (like in silicious hot springs)
• Calcite (tufa)

Question 9

How can lagerstatten divert us and promote bias?

Answer 9

Lagerstatten can preferentially occur during certain periods of geological time
Some unusual environments and overrepresented.

Question 10

What are two examples of places of lagerstatten?

Answer 10

Messel
- Cenozoic, Germany
- Organisms fell into lake and got preserved
Hunsruck Slate
- Devonian, Germany
- Anoxic mud

Question 11

What is an example of dinosaur lagerstatten?

Answer 11

The Jehol Biota
- Cretaceous, China
- Volcanic eruption killed organisms which were preserved in ash

Question 12

What does a fine rock grain mean?

Answer 12

Fine rock grain = finer intricacy observed