Research

Geobiology of the Precambrian-Cambrian Boundary.

 

Currently, my research is focused on a succession of mixed carbonate and siliciclastic sedimentary rocks outcropping in Western Mongolia which capture the transition between a microbial world and a world with complex, multicellular life. These rocks originally formed between the Ediacaran Period and the lower Cambrian Period in a transitional foreland basin system. In these basins were preserved many trace and body fossils of some of the earliest complex multicellular life in Earth history, alongside sedimentary structures mediated by communities of single-celled organisms. My work is to try to further reconstruct the sedimentary and chemical settings which hosted these fossil multi- and single-celled organisms, in an effort to understand how and why they became fossilized, and what the style and extent of their fossilization can tell us about the relationship between organisms and the environment at a pivotal moment in the history of life. Why these rocks in particular, though? Because the sediments, cements, and fossils within them are often highly rich in phosphorus, making them one of many uniquely phosphate-rich sedimentary deposits which formed during the major climate and ecological upheaval which characterized the Precambrian-Cambrian Boundary! This connects the rocks of Western Mongolia to the rocks of Eastern Brazil...

 

 

 

 

My doctoral dissertation centered on Ediacaran-age mostly-carbonate rocks in Eastern Brazil. Why then and there? Because during the Ediacaran Period (between about 650 million and 550 million years ago), the São Francisco Craton that forms much of what is now Eastern Brazil was host to a large seaway where carbonate minerals freely precipitated from the water column and at the seafloor. Microorganisms in this ancient sea influenced and were influenced by aqueous chemistry and sedimentation. The record they left behind of those influences includes a range of sedimentary structures and mineral deposits (specifically phosphate mineral deposits). My work is reading and interpreting that record, in an effort to understand both the environment that these microorganisms lived in and their lifestyle and metabolic strategies therein. I am particularly interested in the role they may or may not have played in the accumulation and mineralization of phosphate, which is — in sedimentary deposits of similar age elsewhere in the world — capable of preserving microbial fossils in exquisite detail. In the course of this work, I visit Bahia and Minas Gerais states in Brazil to collect sedimentological and stratigraphic data, as well as structural data, of the Ediacaran-age rocks there. I also collect samples, which I bring back to my institution Caltech and subject to a range of analytical methods to examine their chemical and isotopic compositions and microstructures. The tools I use include: scanning electron microscopy, energy dispersive X-Ray spectroscopy, Raman spectroscopy, and optical microscopy, secondary-ion mass spectrometry, ICP-MS, IRMS, elemental analyzers, and more!

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In addition to my research in Mongolia and Brazil, I have also assisted my colleagues in their work on Cryogenian-age carbonate rocks in the Namib-Naukluft National Park in Namibia. These rocks are more extensively recrystallized than the rocks I study in Brazil, in a way that has destroyed much of their primary microtexture and record of primary, depositional chemistry. However, they do contain microbially-influenced sedimentary structures that are visible on meso- and macro-scales, and they are an excellent case study in Neoproterozoic sequence stratigraphy and paleoclimate.

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I have also worked with petrographic thin sections of the Gunflint Chert (~1.88 billion years old), located in Ontario, Canada: identifying microfossils of putative bacteria preserved in microcrystalline quartz, and measuring their carbon isotopic composition via secondary ion mass spectrometry. This is part of a larger effort to determine what information of ancient microbial metabolic strategy and ecology can be extracted from microbial fossils.