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Aluminosilicate haloes preserve complex life approximately 800 million years ago

DOI: 10.1098/rsfs.2020.0011 DOI Help

Authors: Ross P. Anderson (All Souls College, University of Oxford) , Nicholas J. Tosca (University of Oxford) , Gianfelice Cinque (Diamond Light Source) , Mark D. Frogley (Diamond Light Source) , Ioannis Lekkas (Diamond Light Source) , Austin Akey (Harvard University) , Gareth M. Hughes (University of Oxford) , Kristin D. Bergmann (Massachusetts Institute of Technology) , Andrew H. Knoll (Harvard University) , Derek E. G. Briggs (Yale University)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Interface Focus , VOL 10

State: Published (Approved)
Published: June 2020
Diamond Proposal Number(s): 15975 , 21059

Open Access Open Access

Abstract: Mudstone-hosted microfossils are a major component of the Proterozoic fossil record, particularly dominating the record of early eukaryotic life. Early organisms possessed no biomineralized parts to resist decay and controls on their fossilization in mudstones are poorly understood. Consequently, the Proterozoic fossil record is compromised—we do not know whether changing temporal/spatial patterns of microfossil occurrences reflect evolution or the distribution of favourable fossilization conditions. We investigated fossilization within the approximately 1000 Ma Lakhanda Group (Russia) and the approximately 800 Ma Svanbergfjellet and Wynniatt formations (Svalbard and Arctic Canada). Vertical sections of microfossils and surrounding matrices were extracted from thin sections by focused ion beam milling. Elemental mapping and synchrotron-based infrared microspectroscopy revealed that microfossils are surrounded by haloes rich in aluminium, probably hosted in kaolinite. Kaolinite has been implicated in Cambrian Burgess Shale-type (BST) fossilization and is known to slow the growth of degraders. The Neoproterozoic mudstone microfossil record may be biased to tropical settings conducive to kaolinite formation. These deposits lack metazoan fossils even though they share fossilization conditions with younger BST deposits that are capable of preserving non-mineralizing metazoans. Thus metazoans, at least those typically preserved in BST deposits, were probably absent from sedimentary environments before approximately 800 Ma.

Journal Keywords: metazoan antiquity; clay minerals; taphonomy; early eukaryotes; complex life; Proterozoic eon

Subject Areas: Earth Science

Instruments: B22-Multimode InfraRed imaging And Microspectroscopy