Chemical weathering and the onset of biomineralization on the Planet during the Late Ediacaran

• Applicant: Gustavo Macedo de Paula Santos, Ph.D.
• Subject Area: Geology ; Mineralogy, Petrology and Geochemistry
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 497339722

The onset of skeletal evolution is one of the most remarkable innovations of life on our planet. Calcareous biomineralizing animals appeared globally in the late Ediacaran ocean (ca. 550 Ma) and spread rapidly to a diverse range of phyla. Exoskeleton biomineralization was an outstanding evolutionary achievement, especially given the increasing ecological complexity of marine systems that marked that period with evidences for predation. However, the causes for this biological event is a matter of a longstanding debate in the literature. The main hypothesis is that a major switch in seawater chemistry occurred in the late Ediacaran, with a change from dolomite-argonite to aragonite seas. These highly alkaline and Ca-supersaturated marine systems were probably favourable for calcium carbonate secretion by early metazoans. The Earth System processes responsible for such turnover remain unknown. Several studies suggest that the assembly of large continental masses continuously exposed fresh rocks for weathering, causing a large discharge of ions into the ocean that could have raised seawater alkalinity and lowered its Mg/Ca ratio. However, the role of chemical weathering in these ocean chemistry changes has never been tested with adequate proxies. To investigate this relationship between continental weathering and biomineralization this project aims to construct lithium, magnesium and calcium isotope profiles from marine carbonate rocks retrieved from boreholes in Late Ediacaran sections from three locations spread across the globe: Brazil, Namibia and China. We focus on the time period between 560 to 545 Ma, during which the target sections record the appearance of the first skeletal fauna on the Planet. By using multiple proxies, it will be possible to track changes in continental weathering during the Ediacaran and determine whether these changes caused the transition to aragonite seas that may have triggered biomineralization. Collaborators on this project will also obtain paleontological and isotope biogeochemical data for the same set of samples providing valuable information on past ecology and biochemistry to effectively test the impact of chemical weathering on the evolution of life.

• DFG Programme: Infrastructure Priority Programmes
• Subproject of: SPP 1006: International Continental Scientific Drilling Program (ICDP)
• International Connection: Brazil, United Kingdom
• Co-Investigator: Professorin Dr. Simone A. Kasemann
• Cooperation Partners: Professorin Marly Babinski; Professor Ricardo Trindade; Professorin Dr. Rachel Wood