Ordovician Paleogeography

Ordovician Paleogeography - Ordovician Paleogeography Early...

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon
Ordovician Paleogeography Early in Ordovician time, Baltica was centered midway between the equator and the south pole It moved Northward By the end of this period Baltica moved into the tropics Tropical limestone’s accumulated in this area of the present day Baltic Sea – some of these limestone’s including oolite deposits resembled those forming today in the Bahamas banks Gondwanaland shifted so that its southern margin encroached on the south pole Neat the end of Ordovician time, a large glacier grew in the southern region + associated changed in the world’s oceans caused a profound global extinction event Glaciation and sea level lowering occurred at the end of the Ordovician The ice cap that grew on Gondwanaland was centered near the south pole (Now northern Africa) Evidence of this glacial episode is seen with Tillites, scratches on bedrock and drop stones in marine sediments Near the end of the Ordovician period, a global drop in sea level caused an unconformity to form on the top of shallow water strata throughout the world Sea levels fell due to the ice caps on Gondwanaland; it removed a significant amount of water from the global water cycle In the central U.S, rivers cut deep valleys near the end of the Ordovician It eroded rapidly downward to reach the lower level of the sea Depths of their canyon like valleys indicated the global sea level fell by about 50 metres Late Ordovician glacial interval lasted no longer than a million years – shorter than the other Phanerozoic ice ages Resulted from a brief reduction of greenhouse warming Late Ordovician Climatic change caused a two-step mass extinction During the Late Ordovician Glacial event, marine Life suffered mass extinctions in Earth’s history Man groups of Brachiopods, Trilobites, bryozoans and corals died out on the sea floor In the waters above, many species of acritarchs, graptolites, conodonts and nautiloids disappeared There were two pulses of extinction in the Late Ordovician crises First pulses coincided with the onset of Glaciation Second with the end of the glacial interval The first pulse is marked in the stratigraphic record by the disappearance of many fossil groups at the level of unconformity when the sea level dropped Climate cooling caused the extinction of many taxa adapted to warm conditions The second pulse was marked by the disappearance of many fossil groups adapted to cool conditions of the ice age Earth System Shift: Glaciation results in Mass extinction One of the largest mass extinctions of all time accompanied the ice age
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
It occurred near the end of the Ordovician period It once seemed the Late Ordovician Glacial episode lasted several million years Oxygen isotope ratios contradicted it When large glaciers grow on land, isotopically light H2O accumulates in them; Sea water becomes correspondingly enriched in oxygen 18 (Heavier Isotope)
Background image of page 2
Image of page 3
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 12/05/2011 for the course BIO 211 taught by Professor Jessica during the Spring '11 term at University of Toronto.

Page1 / 10

Ordovician Paleogeography - Ordovician Paleogeography Early...

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online