Signs of photosynthesis on a neoproterozoic snowball Earth ...

• Main Author: Olcott, Alison Nicola author
• Format: Thesis
• Language: English
• Published: University of Southern California Digital Library (USC.DL) 2006
• Subjects: Geological Sciences degree program; Doctor of Philosophy degree; College of Letters, Arts and Sciences school; Sea ice
• Online Access: https://dx.doi.org/10.25549/usctheses-m60; https://digitallibrary.usc.edu/asset-management/2A3BF1FVIJO3

Laterally extensive black shales were deposited on the S�o Francisco craton in southeastern Brazil during one of the low-latitude Neoproterozoic glaciations. The effect these glaciations had on the biosphere has long been controversial, but there has not been sufficient data to assess the impact. This study, the first organic geochemical investigation of synglacial sediments, synthesizes geological observations and biomarkers information from subsurface cores drilled through the glacial sediments. These rocks contain up to 3.0 wt.% organic carbon and pseudomorphs of the hydrated carbonate mineral ikaite, which are interpreted as representing the preserved record of abundant marine primary productivity from glacial times. Extractable biomarkers reflect a complex and productive microbial ecosystem, including both phototrophic bacteria and eukaryotes, living in a stratified ocean with thin or absent sea ice, oxic surface waters, and euxinic conditions within the photic zone. Furthermore, this environment is ...