Benjamin Kumpf

Topic

Evaporites Through Phanerozoic Time: Using GeoDeepDive, Macrostrat, and Geochemical Modeling to Investigate and Model Changes in Seawater Chemistry

School of Earth and Ocean Sciences

Date & location

• Tuesday, March 5, 2024
• 12:00 P.M.
• Virtual Defence

Examining Committee

Supervisory Committee

• Dr. Laurence Coogan, School of Earth and Ocean Sciences, University of Victoria (Co-Supervisor)
• Dr. Jon Husson, School of Earth and Ocean Sciences, UVic (Co-Supervisor)
• Dr. Jay Cullen, School of Earth and Ocean Sciences, UVic (Member)

External Examiner

• Dr. Robert Gaines, Geology Department, Pomona College

Chair of Oral Examination

• Dr. Patrick Rysiew, Department of Philosophy, UVic

Abstract

Marine evaporites provide a unique insight to the variation in paleo-seawater chemistry throughout the Phanerozoic Era which in turn provides information about various geologic processes and earth history. This study examines changes in paleo-ocean chemistry and evaporite minerology by utilizing GeoDeepDive and Macrostrat to derive records of evaporite occurrences and abundance throughout the Phanerozoic. This study provides a more comprehensive list of epsomite and sylvite evaporites, and their temporal occurrence, than has been available to-date. Changes observed in the abundance of epsomite, sylvite, halite, calcium sulfate and dolomite help contextualize changes in paleo-seawater composition and global sea-level fluctuations. Normalizng marine calcium sulfate occurrences to calcium sulfate and halite occurrences (RAC) shows a distinct difference in the abundance of sulfate-bearing evaporite before and after the Mid-Devonian. Prior to the Mid-Devonian the RAC was highly variable and after this it stabilized. Changes in the RAC were evaluated using batch evaporation modeling attempts in PHREEQC that suggest the main drivers of increased calcium sulfate to halite could be caused by increases in the product of Ca²⁺ and SO₄^2- which could constrain the assumption of a constant product of Ca²⁺ and SO₄^2- used in the calculation of seawater chemistry through fluid inclusion analyses. The occurrence and temporal abundance of marine evaporites yields unique insights into the role of global sea-level and its relationship to evaporites and their formation. Evaporite abundance tends to increase during periods of widespread continental flooding. The RAC tends to be elevated when global sea-level is decreasing and lower when sea-level has stabilized or is increasing. Dolomite abundance compared to these global evaporite records suggest that dolomite is primarily formed during continental flooding and less likely during widespread evaporite formation.