Abstract
The presence of clay-sized particles and clay minerals in modern sands and ancient sandstones has long presented an interesting problem, because primary depositional processes tend to lead to physical separation of fine- and coarse-grained materials. Numerous processes have been invoked to explain the common presence of clay minerals in sandstones, including infiltration, the codeposition of flocculated muds, and bioturbation-induced sediment mixing. How and why clay minerals form as grain coats at the site of deposition remains uncertain, despite clay-coated sand grains being of paramount importance for subsequent diagenetic sandstone properties. We have identified a new biofilm mechanism that explains clay material attachment to sand grain surfaces that leads to the production of detrital clay coats. This study focuses on a modern estuary using a combination of field work, scanning electron microscopy, petrography, biomarker analysis, and Raman spectroscopy to provide evidence of the pivotal role that biofilms play in the formation of clay-coated sand grains. This study shows that within modern marginal marine systems, clay coats primarily result from adhesive biofilms. This bio-mineral interaction potentially revolutionizes the understanding of clay-coated sand grains and offers a first step to enhanced reservoir quality prediction in ancient and deeply buried sandstones.
Highlights
Bio-sediment interactions have been recognized in rocks from almost all geological time periods (Noffke et al, 2006)
Biofilms have been shown to play a fundamental role in sediment dynamics and the subsequent diagenesis of marginal marine sedimentary systems (Stal, 2003), affecting grain-size heterogeneity (Garwood et al, 2015), sediment stability (Vignaga et al, 2013), sediment transport, and bedform stability (Malarkey et al, 2015; Schindler et al, 2015)
Intertidal biofilms typically result from the secretion of extracellular polymeric substances (EPSs) by microphytobenthic (MPB) communities that are composed of algae, cyanobacteria, and other photosynthetic bacteria (Jesus et al, 2009)
Summary
Bio-sediment interactions (microbially induced sedimentary structures) have been recognized in rocks from almost all geological time periods (Noffke et al, 2006). Biofilms in intertidal sediments have been reported to form an adhesive coat on sand grains that acts as a binding agent capable of forming aggregates of diatoms, organics, and clay minerals (Kessarkar et al, 2010) and that is responsible for fine particle entrapment in sand-dominated estuarine tidal flats (Garwood et al, 2015).
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