Graduation Year

2004

Document Type

Thesis

Degree

M.S.

Degree Granting Department

Geology

Major Professor

Peter J. Harries.

Keywords

Permian climate, sclerochronology, oxygen isotopes, paleoclimate, climate models

Abstract

Sclerochronology was conducted on the pedicle valves of four Sakmarian-age brachiopods (Squamaria moorei) to constrain climate model predictions of temperature seasonality along western equatorial Pangaea (WEP). The brachiopods are from a Lower Permian section within the Robledo Mountains, NM, and they reveal seasonal trends of δ¹⁸O and temperature for that interval that suggest global warming and moderation of seasonality. Elemental and SEM analyses verified the specimens were well preserved. δ¹⁸O profiles show a relatively rapid and consistent two-year growth rate corresponding to the organism's juvenile stage, followed by a slower, seasonal growth rate corresponding to the organism's sexually mature stage typical of most organismal growth. Their initial two-year cycles show consistent, high-amplitude profiles that captured virtually complete records of annual δ¹⁸O values, and these profiles were used for seasonality interpretations.

The specimen from the stratigraphically lowest layer shows δ¹⁸O values varying from -4.26 to -2.17 minimum winter temperatures (MWT) and maximum summer temperatures (MST) of 25.2C and 35.7C, respectively; and a seasonal temperature variation ΔTs of 10.0C. The overlying horizon yielded two specimens showing δ¹⁸O values ranging from a minimum of -4.54 to a maximum of -2.79; MWT ranging from 28.2 to 29.6C; MST ranging from 34.9 to 37.2C; and ΔTs ranging from 6.7 to 7.6C. The uppermost layer yielded a specimen that shows δ¹⁸O values ranging from -4.49 to -3.03; MWT of 31.3C; MST of 37.0C; and ΔTs of 5.7C. The specimens show overall high seasonality for an equatorial regime, but the general trend shows increasing winter temperatures and a moderation of seasonality. The data supports climate-model predictions for the Permian of more equable temperatures, higher winter temperatures, and decreased seasonality.

Three numerical climate models of Permian temperatures were evaluated against the brachiopod data, and their model predictions for Δs along WEP range from as high as 10C to as low as C. The models were supported somewhat by the independently derived temperature proxy data measured in this study.

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