Publication Date

2019

Document Type

Honors Project

Degree Name

Bachelor of Arts

Department

Geosciences

Advisors

Sara B. Pruss

Keywords

Benthic foraminifera, Iron sulfides, Ecology, Taphonomy, Shark Bay, Replacement fossil

Abstract

Modern benthic foraminifera from Carbla Beach may contain insights into the previously poorly understood early diagenesis pathways involving iron sulfide formation in warm shallow marine settings. Although the activity of pyrite (FeS2) in carbonate fossils is well studied, the specifics of how this reaction begins remains less clear. EDS analyses of chemical composition of test walls shows that the mineral pyrrhotite is replacing foraminiferal calcite in tests observed at Carbla Beach, Shark Bay, Western Australia. The foraminiferal assemblage is low in diversity (25 species) with high abundance of porcelaneous species, with the dominant taxa being Dendritina striata (24%), Peneroplis pertuses (19%), Spirolina arietina (16%), and Peneroplis planatus (11%). Other species present include Coscinospira acicularis (6%), Spiroloculina scrobluculata (2.4%), Unknown Sp. 29 (2%), Sorites orbiculus (1.7%),Vertebralina striata (0.7%), Triloculina (1.4%), Quinqueloculina (0.02%), Neoconorbina (0.05%), Amphisorus (0.15%), Pseudotriloculina (0.19%), and Lamellodiscorbis (0.01%). Extreme hypersalinity, high summer temperatures (30oC+), and high evaporation rates, makes this setting naturally very stressful for the organisms that live there. Chemical maps of thin sections demonstrates that abundant sulfur is present in the test wall of foraminifera, likely providing a locally abundant source of ulfur atoms for subsequence iron sulfide forming reactions. In thin section, the iron sulfide replacement reaction appears to be clustered along the inner most organic matter lining of the chambers, with pyrrhotite crystals growing from the inside to the outside of the test wall. These benthic foraminifera of Carbla Beach could provide insight into the early stages of iron sulfide replacement and contribute to our knowledge of the stages of iron sulfide replacement fossils through the fossil record.

Rights

©2019 Daniel Eli Wood. Access limited to the Smith College community and other researchers while on campus. Smith College community members also may access from off-campus using a Smith College log-in. Other off-campus researchers may request a copy through Interlibrary Loan for personal use.

Language

English

Comments

90 pages : illustrations (some color). Includes bibliographical references (pages 54-62)

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