2019 AAPG Annual Convention and Exhibition:

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Understanding Muddy Sedimentary Strata on Continental Margins: Significance, Knowledge Gaps, and One Perspective on What We Need for the Future


Mud is a mix of sediments < 63 microns in size and is a major building block of Earth’s sedimentary record. Mud comprises about 80% of all sediments exported from rivers to the ocean. It is the dominant sedimentary material within continental-margins: it builds coastal river deltas, deep-sea fans, and hydrocarbon reservoirs. The geological prevalence of mud suggests that understanding how mud moves, deposits, and builds sedimentary strata is critical for us to understand how coastlines will evolve in a changing climate, and we can more efficiently and safely find and extract hydrocarbons. We have conducted much insightful research on mud Dispersal, Deposition, and Diagenesis (3Ds) over the last several decades. However, we still cannot confidently predict the 3Ds of muddy sedimentary strata, especially compared to sandy deposits, which are less geomechanically complex.

This may be largely due to the shape-shifting qualities of mud, with respect to how it is deposited, eroded, and later modified within sedimentary deposits. For example, the shear strength and erodibility of mud evolve as functions of time, burial history, and diagenetic processes such as (but not limited to) bioturbation and self-weight consolidation. Similarly, viscosity and density of muddy suspensions can change radically during transport, to enhance or reduce deposition rates. Numerous mathematical solutions for the 3Ds of mud have been developed, but are often highly simplified, or very complex, and generally undersupported by adequate experimental or observational data. Because of this, formation and evolution of muddy sedimentary strata on continental margins remains, to some extent, just as opaque as the suspensions that create these deposits. As a result, we cannot confidently predict how coastal salt marsh in a river delta, or behind a barrier island, will erode during a storm. We cannot confidently predict stratigraphic properties of sedimentary layers that build a subaqueous delta clinoform, such as the vast deposits offshore of the Amazon, Ganges-Brahmaputra, Po, Mekong, and many other coastal river deltas on which one in 14 people worldwide live.While these knowledge gaps are a hindrance, addressing them outlines an exciting research agenda for the 3Ds of mud in continental margin strata that is powerfully relevant to society, touching both the security and sustainability of human communities and coasts for years to come. Such an agenda will be the focus of this talk.