C. R. Woltz, R. P. Anderson, N. J. Tosca, S. M. Porter
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引用次数: 0
Abstract
Precambrian organic-walled microfossils (OWMs) are primarily preserved in mudstones and shales that are low in total organic carbon (TOC). Recent work suggests that high TOC may hinder OWM preservation, perhaps because it interferes with chemical interactions involving certain clay minerals that inhibit the decay of microorganisms. To test if clay mineralogy controls OWM preservation, and if TOC moderates the effect of clay minerals, we compared OWM preservational quality (measured by pitting on fossil surfaces and the deterioration of wall margins) to TOC, total clay, and specific clay mineral concentrations in 78 shale samples from 11 lithologic units ranging in age from ca. 1650 to 650 million years ago. We found that the probability of finding well-preserved microfossils positively correlates with total clay concentrations and confirmed that it negatively correlates with TOC concentrations. However, we found no evidence that TOC influences the effect of clay mineral concentrations on OWM preservation, supporting an independent role of both factors on preservation. Within the total clay fraction, well-preserved microfossils are more likely to occur in shales with high illite concentrations and low berthierine/chamosite concentrations; however, the magnitude of their effect on preservation is small. Therefore, there is little evidence that bulk clay chemistry is important in OWM preservation. Instead, we propose that OWM preservation is largely regulated by physical properties that isolate organic remains from microbial degradation such as food scarcity (low TOC) and low sediment permeability (high total clay content): low TOC increases the diffusive distances between potential carbon sources and heterotrophic microbes (or their degradative enzymes), while high clay concentrations reduce sediment pore space, thereby limiting the diffusion of oxidants and degradative enzymes to the sites of decay.
期刊介绍:
The field of geobiology explores the relationship between life and the Earth''s physical and chemical environment. Geobiology, launched in 2003, aims to provide a natural home for geobiological research, allowing the cross-fertilization of critical ideas, and promoting cooperation and advancement in this emerging field. We also aim to provide you with a forum for the rapid publication of your results in an international journal of high standing. We are particularly interested in papers crossing disciplines and containing both geological and biological elements, emphasizing the co-evolutionary interactions between life and its physical environment over geological time.
Geobiology invites submission of high-quality articles in the following areas:
Origins and evolution of life
Co-evolution of the atmosphere, hydrosphere and biosphere
The sedimentary rock record and geobiology of critical intervals
Paleobiology and evolutionary ecology
Biogeochemistry and global elemental cycles
Microbe-mineral interactions
Biomarkers
Molecular ecology and phylogenetics.