Ways of Deciphering Compacted Sediments

Baldwin, Brewster

doi:10.1306/74d7224d-2b21-11d7-8648000102c1865d

Cited by 19 publications

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“…Sediment bulk density (herein we use dry bulk density, with units of g dry material per cm 3 wet volume) is known to increase with burial depth (and thus also with time) due to compaction (e.g., Baldwin, 1971;Van Asselen et al, 2011). However, details about the bulk density versus depth relationship are not well known.…”

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“…However, details about the bulk density versus depth relationship are not well known. Although there is an extensive literature on sediment compaction over large (10 3 m) depth intervals and long (>10 6 yr) timescales from the hydrocarbon industry (e.g., Baldwin, 1971;Rieke & Chilingarian, 1974), comparatively little is known about the compaction of shallower (10 −2 to 10 1 m) deposits over 10 0 -10 3 yr timescales. Here we address this knowledge gap, which is key to understanding the evolution and resilience of modern deltas and associated coastal wetland environments, by investigating shallow compaction with a new data set that is unprecedented in size, offering exceptionally high depth-time resolution.…”

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Organic Matter Accretion, Shallow Subsidence, and River Delta Sustainability

et al. 2021

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River deltas serve as critical nodes in the global water-energy-food nexus. They host large and rapidly growing populations (Edmonds et al., 2020) with associated economic assets, and many deltas provide important ecosystem goods and services. Thus, delta sustainability is a critical issue, and it is widely recognized that maintaining deltaic plains in the face of accelerating relative sea-level rise (RSLR) is a major priority that will become increasingly daunting in the future (e.g., Day et al., 2016;Hoitink et al., 2020;Nienhuis et al., 2020). On many deltaic plains, mineral sediment supply has decreased dramatically since the mid-twentieth century, largely due to the construction of dams, artificial levees, and other flood-control infrastructure (e.g., Giosan et al., 2014;Syvitski et al., 2005;Weston, 2014), a trend that is expected to continue in the 21st century (Dunn et al., 2019). In the Yangtze and Mississippi rivers, for example, dams have reduced the suspended sediment concentration by Abstract Globally, mineral sediment supply to deltaic wetlands has generally decreased so these wetlands increasingly rely on accretion of organic matter to keep pace with relative sea-level rise (RSLR). Because organic-rich sediments tend to be more compressible than mineral-dominated sediments, deltaic wetland strata are vulnerable to compaction and drowning. Using an unprecedented data set of almost 3,000 discrete bulk density and organic-matter measurements, we examine organic-rich facies from coastal Louisiana to quantify the thickness lost to compaction and investigate whether sediments are able to maintain sufficient volume for the associated wetlands to keep pace with RSLR. We find that organic content as well as overburden thickness and density (which together determine effective stress) strongly control sediment compaction. Most compaction occurs in the top 1-3 m and within the first 100-500 years after deposition. In settings with thick peat beds, successions up to 14 m thick have been compacted by up to ∼50%. We apply geotechnical modeling to examine the balance between elevation gained from accretion and elevation lost to compaction due to renewed sediment deposition over a 100-year timescale. Wetlands overlying mineral-dominated lithologies may support the weight of deposition and allow net elevation gain. Model results show that reintroduction of sediment to a representative Mississippi Delta wetland site will likely cause another ∼0.35-1.14 m of compaction but leave a net elevation gain of ∼0.01-1.75 m, depending on the sediment delivery rate and stiffness of underlying strata.Plain Language Summary River deltas constitute some of the most valuable but also most vulnerable environments on the planet. Their elevation right above sea level is controlled by a delicate balance between sediment deposition and compaction. If sediment delivery is reduced due to dam construction in the hinterland, for example, sedimentation rates decrease. Continued sediment compaction may prevent deltas from keeping up with sea-...

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