1. Permo-Carboniferous Glaciation Charlie Boland 11/25/09ESS433

2. The Paleozoic

11. Estimates of Earth’s spin (geographic) axis relative to Gondwana from glacial sediments and paleomagnetism A.G. Smith October 1996

12. An estimation of Paleozoic ice centers Using a Quaternary analog Paleomagnetism Glacial sediments

13. Paleozoic ice ages All glaciation centered on Gondwana Milankovitch frequencies of early Paleozoic analogous to Quaternary Widespread distribution of glacial sediments: South America, Africa, Madagascar, Arabia, India, Antarctica, Australia Paleozoic glacial sediments in China previously from Gondwana Some evidence lost to tectonic processes

14. Some uncertainty of the extent of ice mass Ice sheet assumed to be extensive, perhaps reaching up to 50° Paleo-South pole estimated to be at 30° S, 47° E during maximum glaciation (uncertainty of 5°)

15. Permo-Carboniferous Ice Sheet

16. Using a Quaternary Analog Data from most recent glaciation considered a possible analog for Paleozoic Similar Milankovitch frequencies Known pole distribution Lowest latitudes ice reached Predicts that ice would be unlikely to extend North of 40°S or deviate over 17° from South pole

17. Paleomagnetism Iron-bearing minerals leave paleomagnetic signatures Because there are no known hot spots for Paleozoic Gondwana, all non-stratigraphic evidence is paleomagnetic All data is from averaging VGPs to determine a geocentric axisymmetric dipole field for Paleozoic and Quaternary

18. Selecting Paleomagnetic data- Quaternary All poles selected were from the ORACLE databases All poles selected had primary magnetization the same age as rocks selected from Initial dataset of 313 poles, dropped 75 that had not been magnetically tested Mean pole is 89.3°N, 189°E with α 95 of 1.2° Mean pole indistinguishable from spin axis

19. α 95 Standard method for evaluating paleomagnetic errors The value implies that there is a 1/20 chance that the mean pole lies outside a circle with radius α 95 outside the mean Measure of precision

20. Selecting Paleomagnetic data- Quaternary All poles selected were from the ORACLE databases All poles selected had primary magnetization the same age as rocks selected from Initial dataset of 313 poles, dropped 75 that had not been magnetically tested Mean pole is 89.3°N, 189°E with α 95 of 1.2° Mean pole indistinguishable from spin axis

21. Paleomagnetic data- Paleozoic Gondwanan poles from 490-250 Ma selected from ORACLE database Again, all poles had magnetization ages in common with the rocks were used Poles with uncertainties of over 40 Ma were excluded All demagnetized poles discarded All poles with significant error were found to be from areas of complex tectonic folding or strike- slip faults

22. Paleozoic Paleomagnetism Data Small number of poles in Paleozoic data set– sliding window of 60 Ma applied Mean pole calculated at 20 m.y. intervals

23. Permo-Carboniferous Paleomagnetic Data

24. Interpretations Datasets are compatible with Quaternary analog provided the ice center migrated eastwards Presumed ice cover of Gondwana as asymmetric as Pleistocene ice sheets were

25. Summary Glacigenic sediments indicate the ice cover varied across the Permo- Carboniferous Glaciation originated west and migrated east over time (centroid migrated as well) Permo-Carboniferous South pole estimate falls within 20° of the centroid Present-day South pole centroid lies 5° from magnetic South pole The 20° circle around Permo- Carboniferous centroid overlaps all α 95 values Paleomagnetic and sedimentological data agree with each other Besides shallow marine glacial deposits, the Paleozoic glaciation events were very similar to Quaternary

26. Reevaluation of the timing and extent of late Paleozoic glatiation in Gondwana: Role of the Transantarctic Mountains J. Isbell, P. Lenaker, R. Askin, M. Miller, L. Babcock 2003

27. Claims Early paleogeographic reconstructions assume Permo-Carboniferous ice sheet was very large and centered on Transantarctic Mountains Weathering profiles show evidence to the contrary Isbell claims no evidence exists that shows the Transantarctic Mountains were ever close to a glacial spreading center Carboniferous glaciation less widespread than previously assumed?

28. Contrasting Evidence Cyclothems: alternating sequences of marine and nonmarine sediments (unique to Permo-Carboniferous) Glacioeustatic fluctuations of 60-200m Ice sheet calculated to have volume of 35- 115x10 6 km 3

29. Previous Assumptions Most paleogeographic reconstructions show Victoria Land, Darwin Glacier region and central Transantarctic Mountains as buried under centroid of Paleozoic ice sheet

30. Beginnings of glaciation towards the end of Mississippian based on glacial grooves in deposits along the Pensacola Mountains and large unconformity separating Pennsylvanian from the Devonian

31. Conflicting Evidence Palynological data found in glacigenic deposits in the Transantarctic Mountains supports a Permian age for deposits Unconsolidated sediments in Victoria Land and Darwin glacier region suggest that the area was not glaciated during Carboniferous– these sediments would not have survived multiple future glacial advances if this were the case