STABLE ISOTOPE RECORD OF SOIL CARBONATES FROM

THE EOCENE-OLIGOCENE TRANSITION, BADLANDS NATIONAL PARK, SOUTH

DAKOTA, USAMichelle R.D. Mullin, MS Candidate

Richard H. Fluegeman, PhDBall State University Department of Geological

Sciences

Eocene-Oligocene Tectonics

Drake Passage Tasman Passage

38 Myr = pole of rotation 38 Myr = pole of rotation changes, affecting globalchanges, affecting global tectonicstectonics

Eocene-Oligocene Climate

Global Mean Annual Temperature Dropped 5 0C

Atmospheric CO2 decreased substantially

Marine extinctions

Development of large ice sheet on Antarctica

Goal of Research:

• Does North American terrestrial climate exhibit the same pattern as the global record?

• How does the changing regional climate affect terrestrial biota?

Stable Isotope Crash Course• Carbonate precipitates either biogenically or chemically in paleosols/sediments

via the following equation:Ca2+ + 2 HCO3

- → CaCO3 + CO2 + H2O. • δ18O is the deviation of the oxygen isotope ratio (R=18O/16O) of a sample from

that for a standard, typically Pee Dee Belemnite (V-PDB). This is calculated as:δ18O = 1000 x (Rsample-Rstandard)/Rstandard

• 18O is heavier than 16O, evaporation would thus enrich oceans in 18O– More so as temperatures drop and ice volume expands– Enrichment in 18O is described as “heavier”, δ18O becomes larger

• δ13C is the deviation of the carbon isotope ratio (R=13C/12C ) of a sample from that of a standard:

δ13C = 1000 x (Rsample-Rstandard)/Rstandard

• δ13C is used as a proxy for water chemistry: sea level change, ventilation, nutrient influx, plant root respiration, atmospheric CO2

Zachos et al., 2001

Current Research

Aims to answer question 1: Does North American terrestrial climate exhibit the same pattern as the global record?

Field MethodsConata 1 Conata 2 Dillon Pass

Chamberlain Pass

• Collection Permit obtained from park• Locations chosen for extensive previous sediment

characterization, biostratigraphy and magnetostratigraphy

• Hand specimens collected at every calcareous layer, and some non-calcareous

• Surface material scraped away, sample collected at depth

• “Lower Nodule” (LN) layer identified presence of Brule Formation

Results

Comparison to Global Climate

Key Findings

•Large variability in δ18O and δ13C in late Eocene and into the early Oligocene

•Large shift in δ18O occurs•Supports large drop in atmospheric CO2

•Indicates temperature decrease in the Badlands

•Changes lag the marine record•Decoupling of terrestrial and marine responses

•Increase in δ13C indicates increasing aridity

Regional Comparison: Gulf Coast•Different from Global Record•Fish otolith isotopes

•Eocene summer temps~ 20°C, winter temps down to 13.5°C•Oligocene summer temps same winter temps dropped 4°C

•Ice volume influences•Inverse P:B to d18O

Eocene–Oligocene global climate and sea-level changes: St. Stephens Quarry, AlabamaKenneth G. Miller*,1, James V. Browning1, Marie-Pierre Aubry1, Bridget S. Wade ,1, Miriam E. Katz ,1, Andrew A. Kulpecz1 and James D. Wright1

GSA Bulletin; January 2008; v. 120; no. 1-2; p. 34-53; DOI: 10.1130/B26105.1

Key Findings

•Large variability in δ18O and δ13C in late Eocene and into the early Oligocene

•Large shift in δ18O occurs•Supports large drop in atmospheric CO2

•Indicates temperature decrease in Gulf Coast

•Changes lag the marine record•Decoupling of terrestrial and deep marine responses

•Increase in δ13C indicates increasing seasonality

•Ice Volume played a significant role leading up to the E-O

Badlands Fossil Tooth Isotopes• Zanazzi et al. 2007 examined stable isotopes

from fossil teeth• Large drop in MAT (8.2°C +/- 3.1°C) over

400,000 years• Only small changes in increased temperature

seasonality, no change in aridity.

•Large shift in δ18O occurs•Supports large drop in atmospheric CO2

•Indicates temperature decrease in Gulf Coast

•Changes lag the marine record•Decoupling of terrestrial and deep marine responses

Badlands Chadronian NALMA

Allen Debus

•Large, drab-haloed root traces•Thin Paleosols with fine root traces•Hackberry endocarps

•Depth to calcic horizon = 500-1,000mm annual rain fall•Lacustrine Limestones

•Savannah adapted mammal migration, largely from Asia•Included dogs, camels, rhinos, pocket gophers, •beavers, squirrels, rabbits, and shrews

•Chadronian NALMA saw few extinctions, but many immigrations

Allen Debus

Question 2: How does the changing regional climate affect terrestrial biota?

•Native groups that existed were horses and oreodonts•All make up the White River Chronofauna

Badlands Orellan NALMA

•Vegetation similar to Chadron•Hackberry endocarps•Large drab-haloed root traces•Cracked and veined paleosols•Fine root traces replacing former wooded floodplain

•Sub-humid climate•Calcite depth indicates ppt. was half that of Eocene•Streams became less frequent and more confined

•Orellan NALMA, defined by FAD of Hypertragulus calcaratus

•No major faunal break, though Archaic groups such as brontothere, camel-like oromerycids and some rodents died out

Allen Debus

Allen Debus

Question 2: How does the changing regional climate affect terrestrial biota?

•First appearance of Leptomeryx eransi (deer-like), Palaeolagus intermedius (lagomorph)and Miniochoerus chadronensis (oreodont)•Most mammals typical of the Chadronian persisted with minor changes in abundance•Selection pressures favored animals with teeth appropriate for chewing grasses

Conclusions

•Badlands National Park Paleosol carbonates bridge the gap between stable isotopic data from the Gulf Coast and fossil teeth of the Badlands.

•Variability in the δ18O = decreasing atmospheric CO2 was not the onlyInfluencing factor on terrestrial climate

•Paleotopography may have had a significant role.•Ice volume increases probably led to increasing aridity

•Large fluctuation in δ18O does indicate a significant drop in temperature•Supports large drop in atmospheric CO2

•All three studies show that the δ18O shift lags the marine global record•Decoupling of marine and terrestrial records

Question 1: Does North American terrestrial climate exhibit the same pattern as the global record?

Answer: Somewhat

Conclusions

•Increased aridity and decreasing temperatures led to•Breakup of canopy structure•Increasing grasslands

•Mammals underwent subtle changes •Savannah adapted immigrants•Selection favored teeth appropriate for chewing grasses

•Reptiles and cold-blooded animals affected the most significantly

•Middle Eocene fauna experienced a more dramatic decline•Perhaps this is when the variability in temperatures began

Answer: Moderately

Question 2: How does the changing regional climate affect terrestrial biota?

•Long term variability in temperatures and aridity likely increased selection pressures throughout the Eocene- making a mass extinction less likely