Week 6 - Microfossils Flashcards
What are the main learning outcomes of microfossil studies?
Constructing age-depth models, calculating sedimentation rates, identifying breaks in sedimentation, and understanding biostratigraphy.
What defines a microfossil?
Any fossilized part of an organism (usually skeletal) ranging from <1 μm to >1 mm in size.
What are the two main types of microfossils based on cellular structure?
Single-celled (e.g., radiolarians, foraminifera) and multicellular (e.g., ostracods).
How do microfossils obtain energy?
They can be photosynthetic (e.g., diatoms, coccolithophores)
heterotrophic (e.g., foraminifera, radiolarians),
or a combination of both.
What are the different scales used to measure microfossils?
1000 μm (1 mm): Visible to the eye, microscope needed for details.
100 μm (0.1 mm): Invisible to the eye, requires a light microscope.
1 μm (1000 nm): Requires high magnification (light or electron microscopes).
What are the three main uses of microfossils in geology?
Biostratigraphy – Dating rocks by identifying fossil species.
Palaeoclimate/Palaeoenvironment – Reconstructing past climate and ocean conditions.
Evolutionary Studies – Understanding evolutionary history through fossil records.
What are the three main types of microfossils based on composition?
Calcareous (CaCO₃) – Foraminifera, calcareous nannofossils, ostracods, pteropods.
Siliceous (SiO₂) – Diatoms, radiolarians.
Organic-walled – Dinoflagellates, acritarchs, chitinozoa, pollen.
What are calcareous nannofossils primarily composed of?
Calcium carbonate (CaCO₃), usually in the form of calcite.
What is the main group of calcareous nannofossils?
Coccolithophores.
What is the size range of calcareous nannofossils?
~5 – 10 μm.
Where are calcareous nannofossils commonly found?
Marine environments; they make up chalk deposits like the White Cliffs of Dover.
What are foraminifera?
Single-celled protists with CaCO₃ shells, found in both planktonic and benthic environments.
What is the size range of foraminifera?
50 μm – 2 mm (usually).
What are the two main types of foraminifera?
Planktic foraminifera – Float in the ocean; delicate, thin shells.
Benthic foraminifera – Live on the sea floor; thicker shells.
How are foraminifera used in geology?
For biostratigraphy, ocean temperature reconstructions, and geochemical analysis.
What are ostracods?
Microscopic crustaceans with bivalved calcite carapaces.
What is the size range of ostracods?
0.2 mm – 2 mm (up to 30 mm in rare cases).
What are pteropods?
Planktonic molluscs with aragonite shells.
What is the size ranges of pteropods?
0.2 mm – 5 mm (up to ~30 mm).
What are diatoms?
Photosynthetic algae with opaline silica (SiO₂) skeletons.
What is the size range of diatoms?
20 – 200 μm (up to 2 mm).
What is the economic importance of diatoms?
They form diatomaceous earth, used in filters, toothpaste, paints, and insecticides.
What are radiolarians?
Zooplankton with silica skeletons, floating at all ocean depths.
What are the size ranges of Radiolarians?
100 – 300 μm.
How are radiolarians used in geology?
Biostratigraphy, especially in deep-sea sediments with little CaCO₃.
What are dinoflagellates?
Primitive eukaryotic plankton, some photosynthetic, some heterotrophic.
What fossilized structures of dinoflagellates are found in the rock record?
Dinocysts (resting spores).
What is the size range of dinoflagellates?
~50 – 300 μm.
Why are dinoflagellates important in geology?
Used for biostratigraphy and climate reconstruction.
What are acritarchs and chitinozoa?
Organic-walled microfossils of uncertain biological affinity.
What is the size ranges of acritarchs and chitinozoa?
20 – 150 μm.
What do LO and FO mean?
LO (Last Occurrence) – The highest occurrence of a species, marking extinction.
FO (First Occurrence) – The lowest occurrence, marking its evolutionary origin.
How do scientists construct an age-depth model?
By plotting fossil occurrences against depth in a sediment core and assigning known ages.
What is sedimentation rate, and how is it calculated?
The rate at which sediments accumulate, calculated using age-depth data (cm/kyr).
