Bethany P. Theilinga,b and Maya Elricka

aUniversity of New MexicobPurdue University

Evidence for high-frequency (104-105 yr) glacial-eustasy during Paleozoic

greenhouse intervals

Purdue Stable Isotope (PSI) Facility1) 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 flowδ13C, δ15N, C/N, %C and %N-Carlo Erba EA-Gilson Gas Chromatograph

3) Delta V Plus IRMS, continuous flowδ2H, 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

Greenhouse High pCO2Globally high sea LevelGlobally high temperaturesLittle to no glacial iceSluggish atmospheric and oceanic circulation

IcehouseLow pCO2Globally low sea levelGlobally low temperaturesVast expanses of continental glacial iceVigorous atmospheric and oceanic circulation

Temperaturecurve

(Modified from Scotese 2007)

Also in greenhouse depositsGlacial dropstonesEvidence of cyclic changes in water depthGeochemical fluctuations best described by changing ice-volume

High-frequency (104-105 yr) cycles

Pietras et al. (2003)

(S. Atchley)

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

1.8 ‰

3.2 ‰

1.9 ‰

0.8 ‰

Upper SilurianPleistocene δ18O:

0.5-2.0 ‰

Upper Devonian cycles

China, Europe, Middle East, Nevada, Pennsylvania, New York

early Late Devonian (Frasnian)

central Nevada cycles

Upper Devonian

1.0 ‰

0.2 ‰

1.0 ‰

0.1 ‰1.6 ‰

0.5 ‰

0.4 ‰

1.3 ‰

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.

Conclusions1) δ18O is generated by a combination of ice-volume fluctuations,

SST changes, and evaporation2) Isotopic trends support the hypothesis of glacio-eustasy driving

late Silurian and early Late Devonian cycle formation3) Magnitude of glacio-eustatic change over cycle development is

~10s of meters

Implications1) Significant glacial ice existed and fluctuated over 104 - 105 yr timescales2) Indicates that these “greenhouse” intervals are not ice-free3) Climate models must address the large latitudinal temperature gradients needed to generate polar ice and high

seawater surface temperatures.

AcknowledgementsFundingNSF-EAR 0920830LabViorel Atudorei, Dani Gutierrez

FieldAndy Yuhas, Stephanie

Yurchyk