Transcript Evidence for High-Frequency (10E4 - 10E5 yr) Glacial-Eustasy during Paleozoic Greenhouse Intervals

Evidence for high-frequency (104-105 yr)
glacial-eustasy during Paleozoic
greenhouse intervals
Bethany P. Theilinga,b and Maya Elricka
aUniversity of New Mexico
bPurdue University
Purdue Stable Isotope (PSI) Facility
1) Sercon 20-20 IRMS, continuous flow
δ13C, δ15N, C/N, %C and %N
-PDZ Europa Elemental Analyzer (EA)
-Gilson Trace Gas Analyzer
2) Sercon 20-22 IRMS, continuous flow
δ13C, δ15N, C/N, %C and %N
-Carlo Erba EA
-Gilson Gas Chromatograph
3) Delta V Plus IRMS, continuous flow
δ2H, δ18O, δ13C, and δ15N
-Thermo TC-EA
-GasBench II-PAL
4) Delta V Advantage IRMS, dual inlet and continuous flow
δ15N, δ18O, and Δ17O
-Headspace extraction of denitrifiers and gold tube thermal decomposition for δ15N, δ18O, and Δ17O
-Vacuum line: thermal decomposition of solids for δ18O and Δ17O on dual inlet
-Laser ablation of solids for δ15N, δ18O and Δ17O (in preparation)
Tim Filley
Greg Michalski
Objectives
Demonstrate the power of interdisciplinary
paleoclimate research (stable isotopes +
stratigraphy and sedimentology)
Present evidence that continental glacial ice existed
and fluctuated on orbital timescales during late
Silurian (424-419 Ma) and early Late Devonian
(382-372 Ma) global greenhouse time intervals
Greenhouse vs. icehouse
time intervals
Temperature
curve
Greenhouse
Icehouse
High pCO2
Globally high sea Level
Globally high temperatures
Little to no glacial ice
Sluggish atmospheric
and oceanic circulation
Low pCO2
Globally low sea level
Globally low temperatures
Vast expanses of
continental glacial ice
Vigorous atmospheric
and oceanic circulation
Also in greenhouse deposits
Glacial dropstones
Evidence of cyclic changes in water
depth
Geochemical fluctuations best
described by changing ice-volume
(Modified from Scotese 2007)
High-frequency (104-105 yr) cycles
(S. Atchley)
Pietras et al. (2003)
Oxygen isotopes
Oxygen isotopes: Conodonts
Ca5Na0.14(PO4)3.01(CO3)0.16F0.73(H2O)0.85
(Sweet,1988)
Convert to Ag3PO4
upper Silurian cycles
Oklahoma, Ontario, Pennsylvania, England
upper Silurian (Ludlow-Pridoli)
paleoequator
central Oklahoma cycles
Upper Silurian
Pleistocene δ18O:
0.5-2.0 ‰
0.8 ‰
1.9 ‰
3.2 ‰
1.8 ‰
Upper Devonian cycles
China, Europe, Middle East, Nevada, Pennsylvania, New York
early Late Devonian (Frasnian)
central Nevada cycles
Upper Devonian
1.3 ‰
0.4 ‰
0.5 ‰
1.6 ‰
0.1 ‰
1.0 ‰
0.2 ‰
1.0 ‰
Δ δ18O
70% ice: 30% SST
30% ice: 70% SST
0.2 ‰
~15 m: <1°C
~5 m: <1°C
1.0 ‰
~65 m: ~1°C
~30 m: ~5°C
2.0 ‰
~120 m: ~3°C
~50 m: ~6°C
3.0 ‰
~200 m: ~4°C
~90 m: ~10°C
Evaporation
5 m of surface seawater would have to
evaporate to generate a 0.5‰ increase in
δ18O, increasing surface salinity by ~2 ppt
20 m of surface seawater would be evaporated
to generate a 2‰ increase in δ18O, increasing
surface salinity by ~10 ppt.
Conclusions
1) δ18O is generated by a combination of ice-volume fluctuations,
SST changes, and evaporation
2) Isotopic trends support the hypothesis of glacio-eustasy driving
late Silurian and early Late Devonian cycle formation
3) Magnitude of glacio-eustatic change over cycle development is
~10s of meters
Implications
1) Significant glacial ice existed and fluctuated over 104 - 105 yr
timescales
2) Indicates that these “greenhouse” intervals are not ice-free
3) Climate models must address the large latitudinal
temperature gradients needed to generate polar ice and high
seawater surface temperatures.
Acknowledgements
Field
Funding
Andy Yuhas, Stephanie
NSF-EAR 0920830
Yurchyk
Lab
Viorel Atudorei, Dani Gutierrez