Exceptional Preservation Flashcards
What is a Fossil-Lagerstätten?
Areas of extraordinary fossil preservation
What are the two types of Fossil-Lagerstätten?
- Konzentrat-Lagerstätten
- Exceptional preservation
What is Konzentrat-Lagerstätten?
Where fossils occur in unusual concentrations
Examples of Konzentrat-Lagersträtten
- Lake dries up quickly and kills all the fish - large quantity of fish preserved in a concentrated area.
- Mass kills / Bone beds etc
What is exceptional preservation?
When preservation is of unusual quality.
What are the types of exceptional preservation?
- Preservation of organims that are not usually preserved.
- Preservation of parts of organisms that are not usually preserved
- Organisms are preserved unusually articulated or in unusual configurations
Preservation of organism that are not usually preserved examples
Jellyfish, embryos, soft bodied organisms etc
Preservation of parts of organisms that are not usually preserved examples
- Soft tissue
- E.g. Ichthyosaur skin
Examples of when organisms are preserved unusually articulated or in unusual configurations.
Entire Ichthyosaur skeleton with embryos.
What permits exceptional preservation?
- Exclusion of scavengers and bioturbators (anoxia, rapid burial, elevated salinity)
- Unusual chemical environment
Effects of unusual chemical environment
- Nodule formation
- Microbial mats - death mask
What is nodule formation?
- Concentrations form around the fossil which protect it from future decay.
- organims is buried in sediment and water is excluded - high pressure.
- E.g. flint nodules in chalk cliffs
What can nodules be made out of?
Exceptional preservation
- Silica, flint, iron pirate, calcium carbonate.
What are microbial mats?
Mats of microbes that form over organims and mineralise it effectively
Examples of conservation traps
- Amber.
- Ice: permafrost deposits. Doesn’t date back that far (ice age).
- Tar pits.
- Hot silicious springs (geezers).
- Tufa: calcium carbonate areas - stalactites & stalagmites.
- Ash falls: ash and hot gas collapse down in pyroclastic flows. Can get up to 1000 degrees C and travel 450 mph - everything in the way gets preserved.
Tissues display a spectrum of decay from recalcitrant to labile, what are these?
- Biomineralised endo- or exoskeletons e.g. bones, chitin.
- Robust structural tissue e.g. arthropod cuticle, woody tissue.
- Decay prone e.g. muscles, eyes etc
How are decay prone tissues preserved?
They are only preserved when they are rapidly replicated by authigenic minerals
E.g. an eye needs to be preserved in a day otherwise it’ll rot away
How do authigenic minerals preserve decay prone tissues?
- Precipitate around the tissue and replicate it by mould/cast.
- Precipitate on and within the tissues (often filling or preserving actual cells)
Microbes often perfom a critical role as they mineralise themselves
Examples of minerals that preserve
Apatite: phosphate mineral. Small minerals that preserve small structures (muscles fibres etc).
Clay minerals: Also preserve minute structures. Not sure how this is done. (cold glacial environments).
Phosphate preservation
During the pre-cambrian there was a abundance of phosphate.
Many tiny organims / structures were preserved.
Phosphate can only perserve very small structures.
How can fossil-largerstattens confuse/divert us?
- False biodiversity peaks
- Preferentially occur during certain periods of geological time (e.g. cambrian)
- Certain unusual envronments are over-presented
As well as apatite (phosphate) and clay minerals exceptional preservation may result from:-
- Iron pyrite (‘fools gold’)
- Other metal sulphides
- Silica (e.g. hot springs, nodule/concretion formation (flint), wood permineralisation) lignin has affinity for silica.
- Calcite (coal balls and other nodules/concretions) peat swamps
Examples of some Fossil-Lagerstatten: Messel
- Cenozoic: Germany
- Volcanic erruption that caused a collpase of the surrounding environment.
- Big deep lake forms, bottom layers are anoxic, anything that falls down gets preserved as there is nothing to eat / decay it.
- Occational carbon monoxide clouds released into the environment which means anything surrounding / flying etc will die and fall into the lake to be preserved.
Examples of Fossil-Lagerstatten: Hunsruck Slate
- Devonian: Germany.
- Shallow sea with stratified water column.
- Black mud containing anoxic bacteria.
The Jehol biota (Cretaceous: China)
Dinosaur case study - exceptional preservation
- Series of lakes that dammed up due to volcanic activity
- Ash and water reacted to form weird chemical environments
- Unusual things like feathers preserved
- Ash is very fine grain so very fine intricate preservation
- Colour preservation in insects
- Lots of fish preserved
- Some cases where behaviours can be assumes due to how they are preserved (e.g. example of brooding with 2 adults and 2 juveniles)
The Jehol biota (Cretaceous: China). What do we know about dinosaur colouration from these fossils?
- The Melanosomes in the feathers are the same as today
- Using a scanning electron microscope we can see what colours the feathers were.
