Publication Date

2016-04-27

Availability

Embargoed

Embargo Period

2017-04-27

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PHD)

Department

Marine Geology and Geophysics (Marine)

Date of Defense

2016-03-31

First Committee Member

Peter K. Swart

Second Committee Member

Gregor P. Eberli

Third Committee Member

James S. Klaus

Fourth Committee Member

Brad E. Rosenheim

Abstract

The formation of low-temperature dolomite (CaMg(CO3)2) continues to be enigmatic. By using a newly developed carbonate paleothermometer based on the measurement of clumped isotopes, the abundance of which is controlled by a thermodynamic isotope exchange reaction that promotes the combination of multiple heavy isotopes into single molecules with decreasing temperature, it is believed that understanding the environments of formation for dolomites can be elucidated. The advantage of this technique over other carbonate paleothermometers is that the technique is completely independent of the composition of the precipitating fluid, making clumped isotopes ideal for use in ancient carbonates and in dolomites where the formation fluid is difficult to discern. In this work, the dolomite problem is approached by measuring clumped isotopes in samples from five different cores from the Bahamas, where their relatively young age and comparably simple history make them ideal for calibrating clumped isotopes to dolomites. The first study attempts to measure the temperature of acid digestion fractionation factor in dolomites relative to calcites and aragonites and finds that the fractionation in dolomite (0.153‰) is significantly larger than for calcite (0.089‰) or aragonite (0.091‰). Using the new acid fractionation factor, it is shown that temperatures calculated from clumped isotopes agree with the expected formation temperatures based off previous research and the average fluid temperatures of seawater in the Bahamas and new insights are made as to the fluid flow regimes that formed the dolomites. Using the clumped isotope temperatures, an attempt to reduce the number of viable d18Ofluid-dolomite calibrations is made. The clumped isotope technique is then applied to a less ideal sedimentary system, the Clino core, where mixed carbonates and a complex geological history make interpretation difficult. Guidelines are developed for the application of end-member mixing to clumped isotopes in mixed carbonate samples and the implications for having carbonates that formed from different parent fluids and varying temperatures is discussed. Ultimately, the Clino core clumped isotope temperatures do not agree with any known model of formation known from the Bahamas as the temperatures are exceedingly too high. By measuring carbonate associated sulfate d34S in the Clino bulk samples and comparing the measurements to sights where clumped isotope temperatures are agreeable, it is found that a unique correlation exists between elevated d34S and the formation temperatures recorded by the clumped isotopes in Clino. It is proposed that bacterial sulfate reduction and associated processes is capable of causing disequilibrium in clumped isotopes which has significant implications for the application of clumped isotopes in diagenetic settings.

Keywords

Bahamas; Dolomite; Clumped Isotope; Sulfate Reduction

Table S.1.xlsx (171 kB)
Table S.2.xlsx (124 kB)
Table S.3.xlsx (138 kB)
Table S.4.xlsx (19 kB)

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