Foraminifera Flashcards
What are Rhizaria?
- formerly referred to as protista
- unicellular eukaryotes
- heterotrophic, symbiotic or parasitic
- no test or skeleton
- Radiolaria and Foraminifera (Cambrian to recent)
What are Radiolaria?
- skeleton of opaline silica, organic and silica mix, or even strontium sulphate
- 50 -200 microns
- sometimes colonial assemblages 1m diameter
- Cambrian to recent
What is a pseudopodia?
the tentral stream of cellular tissue from a radiolarian skeleton
What are Foraminifera composed of?
CaCO3 skeleton
How long have Foraminifera existed and what is their nickname?
- from the early cambrian to recent marine and brackish conditions
- ‘armoured amoeba’ typically 0.5 -1mm in diameter
What is the Foram protoplasm divided into?
- endoplasm (food vacuoles and nucleus)
- ectoplasm (pseudopodia fro eating organics)
Why build a test?
Reduce biological pressure, physical and chemical stress
What were the giant forams called?
Nummulites, 10cm diameter, 1 cell from the Eocene
Name the Forams important features
- wall structure
- wall layering
- chamber arragement
- apertures
- ornament
Name the types of wall structure:
- Tectinous (organic, Allogromia)
- Agglutinated (possibly organic, Texturlarina)
- Porcelaneous (Milliolina)
- Microgranular (Fusulinina, Globigerinina)
- Hyaline (Rotallina)
Why are Fusilinids important?
great biostratigraphic markers
- rapidly evolving (esp. Carboniferous)
- multilocular
Describe test morphology variables:
- Diamorphism, change from sexual to asexual
- Coiling direction, varies from sinistral to dextral usually related to temperature (goes back to 3Ma showing polar front and interglacials and glacials)
What are the main foram palaeoecologies
- marine and brackish water
- planktonic, benthic and encrusting
What era are forams most useful for?
application of oceanography and climate in the cenozoic
Glutinated forams live…
below the CCD
What are the main foram applications?
- Oceanography and climate
- Biostratigraphy
What controls rotaliniid coiling?
ocean temperature, they help track thermocline and polar front
the thermocline rises when?
at 0 degrees lattitude
Why is plankton distribution not completely controlled by their lattitude (temperature)?
because the gulf stream interrupts it
How are forams indicators of oceanic conditions?
looking at modern species using the transfer function of 18O/Mg/Ca however some specimens could have been dissolved or moved post mortem
- some are tropical (25 degrees C), seasonal (15) or polar and down in the thermocline (4-0)
What are problems with using forams for predicting climate
- some species could have changed their tolerances through time
- bioturbation smears the signal
- diagenesis
- sample size
- sediment accumulation is not constant
Give an example of past climate reflected in foram record:
Palaeocene - Eocene Thermal maximum +5 degrees at the equator from greenhouse carbon increase! O2 foram isotopes spike as benthic foram extinction
occurs
- reefs were decimated expelling dinoflagellates and decreasing ocean alkalinity
- Large benthic forams (e.g. Nummulites) fill the niche
Another example in Eocene - Oligocene boundary
How are forams used in oceanography?
- O2 isotopes in benthic foram shells using a mass spectrometer
- Example: Cenozoic cooling; recorded ratio of 18O: 16O as glacial and interglacial periods ensued
Give an example for foram application in biostratigraphy:
Forams are widespread and short rangeing;
- Eocene; Morozovella a planktonic foram are surface dwellers in the tropics and characteristic of palaeogene followed by a mass extinction in Mid Eocene ~38Ma
- Possibly a response to eutrophication of surface waters and demise of symbiotic relationships with dinoflagellates that provided nutrients
