There were major changes in temperature across the Ordovician that have been recorded using oxygen isotopes. Figure 2 (Trotter et al., 2008) shows a compilation of several carbonate and apatite oxygen isotope signatures during this period from around the globe. Use the 18O highlighted in the gray bar to make the interpretations for this exercise. Note that an increase in 18O of 1 is approximately equivalent to a decrease in temperature of 4C in this figure.

1. When do you see the highest oxygen isotopic values?

2. When do you see the lowest oxygen isotopic values?

3. During what stage is it the hottest in the Ordovician?

4. During what stage is it the coldest in the Ordovician?

5. What is the general trend in temperature change across this interval?

6. There is a short hiatus where temperatures were not greatly changing. About how long was this interval (in millions of years)?

7. There is a major extinction event during the Ordovician that is primarily associated with mass glaciation. When do you think this might have occurred?

Figure 2. Oxygen isotope compilation through the Ordovician (from Trotter et al., 2008). Both carbonate and apatite 18O values are included, with scales for both at top and bottom. The gray bar indicates the general trend in oxygen isotopes during this interval. For the time scale on the left, Dap stands for Dapingian and H stands for Hirnantian.

8"Ocart (%o V-PDB) - 10 -9 -8 -7 -6 -5 Wenlock 430 Telych SILURIAN 435 Llandovery Aeron 440 Rhud I Laurentia (Canada) O Newfoundland Devon is Manitoba O Anticosti Is . Cornwallis Is Gondwana (Australia) Georgina Basin Canning Basin Amadeus Basin Literature (conodonts) Bassett et al. 2007 A Wenzel et al. 2000 Literature (brachiopods) Shields et al. 2003 x Azmy et al. 1998 6C 6b 445 0 Katian 5d 450 UPPER ORDOVICIAN 50 455 5b 5a 460 4C 4b Dap Darriwilian Sandbian 465 MID ORD 4a 3b 3a 2c 470 Floian 475 00 2b 2a 1d 480 Epoch | LOWER ORDOVICIAN Tremadocian 1c 485 1b Myr Stage 8"00 1a 12 13 14 15 16 17 18 19 20 Papetite (%o V-SMOW) Figure 2. Oxygen isotope compilation through the Ordovician (from Trotter et al., 2008). Both carbonate and apatite 8180 values are included, with scales for both at top and bottom. The gray bar indicates the general trend in oxygen isotopes during this interval. For the time scale on the left, Dap" stands for Dapingian and H stands for Hirnantian. 8"Ocart (%o V-PDB) - 10 -9 -8 -7 -6 -5 Wenlock 430 Telych SILURIAN 435 Llandovery Aeron 440 Rhud I Laurentia (Canada) O Newfoundland Devon is Manitoba O Anticosti Is . Cornwallis Is Gondwana (Australia) Georgina Basin Canning Basin Amadeus Basin Literature (conodonts) Bassett et al. 2007 A Wenzel et al. 2000 Literature (brachiopods) Shields et al. 2003 x Azmy et al. 1998 6C 6b 445 0 Katian 5d 450 UPPER ORDOVICIAN 50 455 5b 5a 460 4C 4b Dap Darriwilian Sandbian 465 MID ORD 4a 3b 3a 2c 470 Floian 475 00 2b 2a 1d 480 Epoch | LOWER ORDOVICIAN Tremadocian 1c 485 1b Myr Stage 8"00 1a 12 13 14 15 16 17 18 19 20 Papetite (%o V-SMOW) Figure 2. Oxygen isotope compilation through the Ordovician (from Trotter et al., 2008). Both carbonate and apatite 8180 values are included, with scales for both at top and bottom. The gray bar indicates the general trend in oxygen isotopes during this interval. For the time scale on the left, Dap" stands for Dapingian and H stands for Hirnantian