Publication Date
Fall 2024
Degree Type
Thesis
Degree Name
Master of Science (MS)
Department
Moss Landing Marine Laboratories
Advisor
Ivano Aiello; John Sarao; Maxime Grand
Abstract
The International Ocean Discovery Program (IODP) Expedition 385 to the Guaymas Basin in the Gulf of California explored carbon cycling in the hot subseafloor of a nascent ocean basin. Roughly 50 km from the modern spreading axis, we compared adjacent sites U1545 and U1546. While the sites are ~1 km apart and have highly similar sediment compositions, a ~70 m igneous sill crosses U1546 at ~300 mbsf. The depth of the sulfate-methane transition zone (SMTZ) at U1546 is 100 mbsf, while at U1545 it is 50 mbsf. Solid phase carbonates capture geochemical conditions of porewater over time. Using smear slide petrography, XRD, XRF, and SEM/EDX, we determined concentration and type of solid phase carbonates to reconstruct a time-averaged view of the SMTZ against which modern porewater chemistry was compared. Micrite %cover and coccolith %cover are negatively correlated (U1545: R2= 0.315, p=1.18e-9) (U1546: R2=0.212, p=2.78e-5), while Ca wt% correlates with solid-phase carbonate (U1545: r2=0.404, p=5.873) (U1546: r2=0.302, p=4.93e-7). Carbonate dissolution is apparent in the upper 30 meters at both sites. ACs at U1545 occurred at ~70 mbsf (consistent with porewater data), while Authigenic Carbonate (ACs) at U1546 occurred at ~60 mbsf, within the sulfate reduction zone, inconsistent with porewater geochemistry. The inconsistency between porewater and the solid phase at U1546 suggests the intrusion of the sill was a significant disturbance that resulted in the deepening of the SMTZ at this site.
Recommended Citation
Clifford, Rachel W., "Analysis of Solid Phase Mineralogy to Explore Past Biogeochemical Conditions of the Deep Biosphere in the Guaymas Basin" (2024). Master's Theses. 5589.
DOI: https://doi.org/10.31979/etd.bs99-h22g
https://scholarworks.sjsu.edu/etd_theses/5589
