Undergraduate Honors Thesis

Alternative Title

• The Formation of Guttulatic Crystal
• Guttulatic Crystal as Cold Climate Proxy

Abstract

• The metastable pseudomorph of calcium carbonate known as ikaite (CaCO₃.6H₂O) is a reliable tool for recognizing frigid ancient climates. Its recognition is aided by the unique guttulatic structure. This structure appears as ellipsoidal overgrowths surrounding pseudohexagonal to ellipsoidal cores. These cores are surrounded by more Mg-rich sparry or micritic cement.

  This study employs Transmitted Light (TL) microscopy, Cathodoluminescence (CL) microscopy paired with Plane Polarized Light (PPL) and Cross Polarized Light (XPL) microscopy, alongside stable isotope δ¹³C and δ¹⁸O analyses. These are used to investigate the crystallography of ikaite. The aim is to discern the frigid ancient climate of Creede, Colorado during the Oligocene period. A key focus is on identifying the guttulatic crystal structure of ikaite. Traditionally, it has been described as possessing a sole pseudo-hexagonal core with overgrowth in various cold locations. However, our examination reveals core variations in Creede. These include tear-drop, oval, triangular, circular almond, and irregular rounded corner shapes. This indicates the presence of guttulatic structures as the second most abundant form. Furthermore, our analysis of the water chemistry of ancient Lake Creede suggests complexities in interpretation. We observe a non-luminescent core, the shape of which is consistent with vaterite. We hypothesize its formation in a highly oxygenated environment. Subsequent overgrowth with lighter orange CL luminescence suggest a transition to a low-oxygen environment. Macroscopic observations of ikaite pseudomorphs, specifically glendonite formation, offer insights of environmental conditions. The transformation of guttulatic crystals into stable vaterite hexagonal cores with overgrowth, accompanied by sparry calcite filling, suggests warming and loss of water. Calcite with cleavage angles exceeding 78° and 102° indicates temperatures surpassing 8°C of the stability range of ikaite. While a dislocation of guttulatic crystal is hypothesized to be deformed during uplift event such as the Neogene uplift and Rio Grande incision. Analysis of δ¹³C and δ¹⁸O values are consistent with a cold-water environment during the Oligocene. Low δ¹³C values imply organic carbon incorporation, possibly influenced by decaying organic matter in mud deposits. Higher δ¹⁸O values suggest colder climate conditions, indicative of a cold and dry evaporative ancient Creede Lake approximately 26.9 million years ago. This comprehensive approach enhances our understanding of Creede's paleoclimate and geological evolution.

Creator

• Romly, Amir

Date Awarded

• 2024-04-10

Academic Affiliation

• Geological Sciences

Advisor

• Trower, Lizzy

Committee Member

• Hynek, Brian Michael
• Lininger, Katherine

Granting Institution

• University of Colorado Boulder

Contributors

• CU Chemical Sedimentology Research Group
• Dr. Zawaski

Subject

• Oligocene Climate
• Calcium Carbonate
• Guttulatic Crystals
• Ancient Creede Lake
• Ikaite
• Vaterite
• Glendonite

Last Modified

• 2024-04-18

Location

• Creede

Resource Type

• Undergraduate Honors Thesis

Rights Statement

• In Copyright

Language

• English [eng]

License

• Creative Commons BY-NC Attribution-NonCommercial 4.0 International

Relationships

In Collection:

• Arts and Sciences Honors Program

Items

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	Amir_Romly_A_Proposed_Formation_of_Unique_Crystallographic_Ikaite_as_a_Key_Proxy_for_Identifying_Frigid_Ancient_Climates_in_Creede__Colorado_During_the_Late_Oligocene.pdf	2024-04-17	Public	Download