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Non Life Sciences => Geology, Palaeontology & Archaeology => Topic started by: Exodus on 16/08/2004 13:49:59

Title: The use of Palynology
Post by: Exodus on 16/08/2004 13:49:59

Palynology

Organic-Walled Phytoplankton

Chloropyceae – Carboniferous to recent,  algae.
Used for palaeoenvironmental analysis à Still, shallow freshwater.

Prasinophyceae – Ordivician to recent, algae, mass occurrence in black shales

Acritarcs – Central body with ornament. Major biostratigraphic role
      Extinction – snowball earth
      Nearshore/offshore analysis

à Nearshore – low diversity, thin walled spheres
     Offshore – High diversity, varied forms.
     Deep waters – Low diversity, thick walled spheres.   

Dinoflagellates – Have a life cycle that involves a cyst production, cyst lies dormant benthically. Encystment follows when cyst comes out of protective layer (naked), then forms cell wall.
>2000 species.

High variation in ornamentation, some similar to acritarchs.
Cysts may have several wall layers and varying plate patterns.

à taphonomic issues
·   Not all are cyst producing
·   Cyst walls vary in resistance
·   Gap between Silurian and Triassic.
·   Little knowledge of modern life cycles.

Applications à
·   Variety, abundance and small size = powerful tool.
·   Hydrocarbon tool.
·   Biostratigraphy and evolution
·   Boundary events.


Onshore/Offshore indicators. à
FRESHWATER – Proximate cysts, a smooth structure.
MARINE – Chorate cysts, ornamentation.

ACMEs – peaks in abundance (e.g. Palaeocene/Eocene) possibly short lived global warming à higher productivity.


Palaeoceanography à
Upwelling zones – peridinoid cysts
Blooms
Sea syrface temperatures
CRETACEOUS – Bivalves all ages killed by dinoflagellate bloom.




PLANTS

Plants were thought to have invaded the land in the late Ordivician/early Devonian. The major radiation of spores occurred at the end of the Silurian during the period Pridoli. Diversification of  the spore assemblages rocketed during the Devonian.

Examples of Early Devonian spores –

Retusotriletes
Perotriletes
Ephanisporites

About Ephanisporites

Originated in the Silurian with some radial ribbing. Moving into the Devonian saw evolution leading to increasing radial ribbing and the development of an Anulus.


The Devonian  saw the vast majority of the spores being miospores although the middle Devonian saw the introduction of Megaspores. These were considerably larger which would provide the germinating spore to have more food for growth. Megaspores were over 200 micrometers in size.

The late Devonian saw more complexity in spores with the formation of grapnel spines, these may have been to aid in their transportation OR to link Miospores to Megaspores.

During the Devonian the stratigraphic range was very thin around the equatorial regions à End of the Devonian saw many of the spores go extinct.




The Carboniferous saw radial thickening of spores
e.g. Tripartities, Triquitrities, Murospora.


Also there is diversification of ornamentation. The upper Carboniferous was principally spore dominated e.g. LYCOPSID











Order of evolution of reproduction:


Homospore
Microspore
Prepollen
Pollen (cycad) – have fertilising pollen tube.
Pollen (pinus) – have fertilising pollen tube.


Leads on to à


·   Homospory involves the seed having the male and female gametes and occurred proximally, Heterospory has the megaspores (female) and microspores (male). This occurred proximally, both involved spores

·   Early seeds were the gymnosperms which were also proximal. They involved a megaspore like bud containing the gametophyte. The prepollen enters the megaspore and germination occurs inside.

·   Recent gymnosperms have a similar gametophyte and involve pollen with a central part called a sulcus. These can travel further and are therefore classed as distal

·   Angiosperms involve fruits but have microspores with a sulcus like the gymnosperms.



The first pollen: MONOLETES (shape)
       : Saccate Pollen (Saccus is outer sheaths)


More stability in late carboniferous, The Devonian to Carboniferous is the best time for land plant biostratigraphy.

Monosaccate – one air sack
Bisaccate – Two air sacks   
Disaccate – Mickey mouse appearance



Megaspores à Increasing ornamentation, echinate as in spiny, have hooks on the end.
Many of the upper carboniferous spores were of lycopsids.




SUMMARYà
Radial thickening in early carboniferous
Late carboniferous dominated by lycopsid and fern spores
Large saccate pollen common in late carboniferous.
Major extinctions towards end of carboniferous. (climate change)




Permian, Triassic Jurassic and Cretaceous

Bisaccate pollen, esp. striates dominate assemblages in Permian/Triassic.
Also present are trilete spores, mainly from ferns.
Monolete spores of lycopsids present



Megaspores in the Mesozoicà
·   Banksisporites
·   Bowenispora

Appear trilete, some have heavy ornamentation.



·   Rhaetic (Triassic/Jurassic) – e.g. Ricciisporites – 4 spores joined together. – palaeomarker for end Triassic. (END TRIASSIC DRIER)


·   Jurassic saw spore dominated assemblages, also sees diversification of gymnosperm pollen.



·   Classopollis (EARLY CRETACEOUS) occurs in clumps with doughnut shape.
·   Lower cretaceous also sees first angiosperm pollen

·   HUGE radiation of angiosperm pollen through Cretaceous.


Overall, a major vegetation turnover  in cretaceous.








TERTIARY à

Asseblages include à
·   Pteridophyte spores (ferns, lycophytes)
·   Fungal spores (often grey/brown)
·   Freshwater algae – chlorophyta e.g. Botryococcus, colony of cells.
·   Dynoflagellates.
·   Fauna (conodonts)
·   Plant debris – Cuticles, compressed wood, fibre bundles, charcoal.



Angiosperm pollen à
Exine wall à Has pillars in the cell wall. Has outer sticking out things – Columella with TECTUM on the end. TECTUM = flowering plant.


APERTURES –
Pores à
One pore = monoporate.
Three pores = Triporate.
Many pores = Polyporate.

Gaps as in pieces à colpate -à monocolpate, tricolpate, hexacolpate.


ORNAMENT –
Ornament variety – Rugulate, Echinate
Microechinate – Variation in echinae, ridges, clustered, even distribution.


PRESERVATION –
Sporopollenin – makes pollen resistant
Algaenan – makes algae resistant.
Fungal Chitin – Makes fungi resistant.

Insect vs wind pollination à
Insect – Large, spiny, sticky (stick to insect).
Wind – Small, smooth, dry.

PREPARATION
Like Palaeozoic/Mesozoic BUT à
Small pollen of angiosperms.
·   Seive size 10 or 5 micrometers
·   Search at higher magnification.
·   Easy to miss
·   HIGH DIVERSITY.

APPLICATIONS
Paleaeoenvironmental analysis
Climate reconstruction.
Biostratigraphy and evolution
Boundary events
Climate change


VEGETATION & CLIMATE RECONSTRUCTION
Use à
In situ grains
Detailed comparisons with NLR.
Diversity trends
Facies associations.

NEAREST LIVING RELATIVE
Look for likenesses that would stand little chance of appearing again in evolution e.g. ornament, colpate etc…

BIOSTRATIGRAPHY
Pollen and spores have most attributes of good zone fossils – resistant, easy to characterise. (Use Juglandaceae).

K/T BOUNDARY EVENTS
Massive floral turnover, and recovery palynoflora.
South to North variation in dominant taxa.
Therefore colonising vegetation at different latitudes



SUMMARY>>>

Palynology Disadvantages
May not be species diagnostic
Bias
Mixing of local communities
Reworking

Palynology Advantages
Durability & small size
Variety
Abundance
In absence of macrofossils
Widspread