Lecture 3 - exceptional preservation Flashcards
what is exceptional preservation?
the preservation of material other than hard parts e.g. eyes, muscle fibres etc
define Lagerstatten
fossil sites containing exceptionally preserved material
2 basic types of fossil lagerstatten:
- konzentrat-Lagerstatten/ concentration deposits = where fossils occur in unusual concentrations e.g. bone beds, mass killings
- Conservation deposits = where preservation is of unusual quality
3 basic types of conservation deposits:
- preservation of organisms not usually preserved
- preservation of PARTS of organisms not usually preserved
- organisms are preserved unusually articulated or in unusual configurations
2 major controls of exceptional preservation are:
- the exclusion of scavengers and bioturbators e.g. by anoxia, rapid burial, elevated salinity
- unusual chemical environment, permitting exceptional preservation e.g. nodule formation and microbial mats creating a ‘death mask’
what are conservation traps?
special conditions; occur unusually but allows exceptional preservation
examples of conservation traps:
amber ice tar pits hot siliceous springs tufa ashflows
define tufa
porous rock composed of calcium carbonate, e.g. limestone, formed by precipitation from water
what is a bioturbator?
burrowing/digging animals which carry out bioturbation (the disturbance of sedimentary deposits)
tissues at the top of the spectrum of decay
biomineralised endo- exo skeletons e.g. bones, teeth
tissues in the middle of the spectrum of decay
robust structural tissues e.g. cuticle, lignin
tissues with low resistance to decay
decay prone muscle e.g. eyes
how are decay prone tissues preserved?
when they are inundated very rapidly by authigenic minerals
define authigenic
minerals formed in their present position
authigenic minerals do 2 main things to preserve, these are:
- precipitate around the tissue and is replicated by a mould/cast
- precipitate on/with tissues - preserving cells
what is the best way to preserve material?
using apatite, a complex phosphate mineral which preserves little crystallites e.g. muscle fibres
exceptional preservation may also occur from:
iron pyrite
other metal sulphides
silica
calcite
how may fossil Lagerstatten confuse us?
- by creating false biodiversity peaks
- by preferentially occurring during certain periods of geological time e.g. cambrian, when bioturbators hadn’t evolved
- certain unusual environments are over-represented
examples of exceptional preservation sites:
- Messel (Germany) - Cenozoic stratified lake, therefore no bioturbators at the bottom
- Hunsruck slate (Devonian Germany) an anoxic layer - iron pyrite precipitates out and preserves soft tissue
exceptional preservation site of dinosaours =
The Jehol Biota (Cretaceous China)
