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Coupling Textural, Magnetic, and Modeling Techniques to Understand Precambrian Paleoenvironments


Slotznick, Sarah Pearl (2016) Coupling Textural, Magnetic, and Modeling Techniques to Understand Precambrian Paleoenvironments. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/Z9HT2M8X.


The oxygenation of our planet is perhaps the greatest transition in its history, dramatically affecting geochemical cycles and the evolution of life. Major first-order questions still remain about late Archean and Proterozoic environments, even as newly developed geochemical techniques provide additional constraints and create subtle conundrums. I apply a new approach to classic localities to understand Precambrian redox character and paleoenvironmental conditions by combining textural observations from optical and electron microscopy, isotopic measurements, and (synchrotron-based) x-ray spectroscopy with scanning magnetic microscopy and bulk rock magnetic experiments. Models paired with data from the literature provide additional context for these measurement results.

The first portion of this dissertation focuses on understanding the predominant microbial metabolism recorded in the 2.72 Ga Tumbiana Formation stromatolites. I proposed that these stromatolites formed in shallow, anoxic waters and record a global signature of unique autotrophy distinct from younger systems dominated by oxygenic photosynthesis. The next portion of this dissertation uses the redox sensitivity of iron as a tool to investigate paleoredox conditions of the 1.45 Ga lower Belt Supergroup during a potentially transitional time-period in surface environments. Observations of primary mineralogy in early diagenetic pyrite and detrital iron oxides suggest an oxygenated water-column overlying anoxic, sulfidic pore-fluids very similar to the modern. The final portion of this dissertation assesses the effects of prevalent secondary overprints on the use of iron as a paleoredox proxy. Theoretical data-driven models combined with trends from the Belt Supergroup highlight the mobility of iron during progressive burial metamorphism as well as in diagenetic transformations and reactions with infiltrating fluids. Applying coupled techniques, specifically including textural methods, is vital for untangling secondary alterations from primary records of environmental conditions during the Precambrian.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:iron; rock magnetism; x-ray spectroscopy; C isotopes; Archean; Proterozoic
Degree Grantor:California Institute of Technology
Division:Geological and Planetary Sciences
Major Option:Geobiology
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Kirschvink, Joseph L. (co-advisor)
  • Fischer, Woodward W. (co-advisor)
Thesis Committee:
  • Sessions, Alex L. (chair)
  • Kirschvink, Joseph L.
  • Fischer, Woodward W.
  • Grotzinger, John P.
Defense Date:19 May 2016
Record Number:CaltechTHESIS:06032016-150348563
Persistent URL:
Related URLs:
URLURL TypeDescription adapted for ch. 2 adapted for ch. 4
Slotznick, Sarah Pearl0000-0001-8374-3173
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:9837
Deposited By: Sarah Slotznick
Deposited On:06 Jun 2016 20:28
Last Modified:22 Apr 2021 18:35

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PDF (Full Thesis) - Final Version
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PDF (Thesis--Front Material, Chapters 1 to 4) - Final Version
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PDF (Thesis--Chapter 5) - Final Version
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PDF (Thesis--Chapter 6) - Final Version
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