The Great Ordovician Biodiversification Event Flashcards
What is the GOBE?
Great Ordovician Biodiversification Event
What developed from phylla?
Classes which are the taxonomic level below phylla
What are the series of the Ordovician?
Lower
Middle
Upper
What are the ages of the Ordovician?
Tremadocian
Floian
Dapingian
Darriwilian
Sandbian
Katian
Hirnantian
What dispute was resolved by Charles Lapworths discovery of the Ordovician?
Between Murchinson wanting to extend the Silurian down in the rock record and Sedgewick wanting to extend the Cambrian up
What do golden spikes represent on the chronostratigraphic chart?
where a rock sequence has been identified to represent type of sequence for that boundary
What is an example of the “golden spike” for the base of the Ordovician system?
Green Point, Newfoundland
FAD (first appearance datum) - Iapetognathus fluctivagus
What biostratigraphy can be used to identify the base of the Ordovician?
Taxon which look like conodonts - soft eel like (occur globally)
What debate is ongoing concerning the Ordovician?
Whether its a continuation of the Cambrian or its own event
What is the variation of substrate mobility between the Cambrian and the Ordovician?
Substrate mobility increased due to increased burrowing and movement into the water column
What name was given to organisms which moved into the water column in the Ordovician?
Macro plankton
What is also evidence of a shift to more life in the water column?
Suspension feeder (nutrients and food off the sediment floor)
Zooplankton - animals in water column
What cased a revolution in the oceanic trophic levels in the Ordovician?
Acritarch’s
What are acritarch’s?
Small flask shape organic fossils (suggested low level part of Ordovician food chain)
What is class Graptolithina?
Mode of life Graptolids
Wholly planktonic
Wide variety of sediments
What was a “kick” for biodiversification in the Ordovician?
Establishment of reef communities (modern day hotspots for diversification)
What are the causes of GOBE?
Elevated sea levels
Global cooling
Raised atmospheric O2
Elevated oceanic nutrients
Asteroid shower
How did elevated sea levels cause GOBE?
Cratonic flooding- increased area due to dispersal of continental areas (produced many shallow shelf environment, high energy and reef environment)
How is it thought that global cooling caused the GOBE?
Decline of ocean temp into the middle Ordovician, corresponding with diversification pulses (temp decreased to modern day equatorial temp)
What is the EPI?
Early Palaeozoic Ice house
How is EPI linked to GOBE?
Ice caps can lead to diversification and help generation of ocean currents distributing nutrients and factor of weathering
How is increased atmospheric O2 linked to GOBE?
Increased atmo O2 men more dissolved in ocean, O2 is fundamental part of respiration for many organisms
What caused increased oceanic nutrient levels?
Growth of polar icecap drives deep water currents creating upwelling zones ventilating depth
How are asteroids linked GOBE?
Intermediate disturbance hypothesis
What is the intermediate disturbance hypothesis?
asteroid causes small change in surface conditions which forces adaptation and diversification of species
What are found with Ordovician rocks in Sweden?
Lumps of asteroid
What evidence of extra terrestrial rock is there in the Darriwilian?
Spikes in Chromite
Where is there evidence of elevated flux of cosmic spherules? (Ordovician)
Durness group NW scotland
What was mortality rate of the End Ordovician extinction?
Global - 49-60% marine genera
85% marine species
What was the main cause of the Ordovician extinction?
Feedback created by the development of a continental ice sheet which expanded rapidly reducing sea level and removing shallow cratonic pools
When were the 2 phase extinctions of the Ordovician?
1st End of Katian
2nd midway Hirnantian
What are some examples of species greatly affected by the 1st extinction phase?
Chitinozoa
Conodonts
Graptolites
Trilobites
Brachiopods
What are chitinozoa?
microscopic flask structures assigned to the zooplankton
What are conodonts?
primitive vertebrates Largely known from their tooth- like feeding structures some thought to be pelagic, some swimming close to sea-floor (nekto-benthonic)
What was the effect of the end Oreo on graptolites?
Major reduction in graptolites, but already in decline from earlier in the Ordovician
How are trilobites affected by end Ordo?
pretty much all the free-swimming trilobites, such as Opipeuterella and
the cyclopygids go in the first strike
How are benthic assemblage zones and end Ordovician extinction linked?
1st strike sea level decline causing compression of sections 4 and 5 (shelf area)
2nd strike upward compression of segments
