Amplification of Shoreline Response To Sea-Level Change By Back-Tilted Subsidence

Abstract

Shorelines move in response to the balance of geodynamic processes acting on sedimentary basins; thus the stratigraphic record of shoreline migration is an important tool for reconstructing climate, tectonic, and eustatic histories from ancient deposits. Here we test whether subsidence geometry influences shoreline migration in response to sea-level change by comparing two physical experiments conducted in the Experimental EarthScape (XES) basin. The experiments had similar sediment supply, subsidence rate, and sinusoidal sea-level cycles, but one experiment had a fore-tilted subsidence profile, where subsidence rates increased with distance from the sediment source (similar to a passive-margin setting) and the other had a back-tilted subsidence profile, where maximum subsidence was close to the sediment source with subsidence rates decreasing downstream. In the recent back-tilted experiment, decreasing subsidence rates downstream resulted in a tendency for shoreline regressions to self-amplify during base-level fall, whereas increasing subsidence rates upstream caused a rapid shoreline retreat during base-level rise, causing amplified shoreline fluctuations during sea-level cycles compared to the previous fore-tilted experiment. These results indicate that the spatial pattern of subsidence in a basin has a significant effect on shoreline migration in response to eustatic cycles. Shorelines in back-tilted basins are substantially more sensitive to changes in relative sea level than comparable coastlines in passive-margin settings, all else being equal.

Identifying autogenic sedimentation in fluvial‐deltaic stratigraphy: Evaluating the effect of outcrop‐quality data on the compensation statistic

“…Similarly, there is a question about if and when the autogenic dynamics of deltaic systems should be controlled by the delta's fluvial topset ( H max ~channel depth) or the relief of the delta foreset ( H max ~basin depth) [e.g., Muto and Steel , ; Muto et al ., ; Kim and Jerolmack , ]. Basin depth and subsidence patterns influence how sediment is partitioned between the fluvial topset and the subaqueous foreset during delta growth [ Cederberg , ; Hajek et al ., ; Leva Lopez et al ., ]. When delta mass is sequestered in the fluvial topset, fluvial‐system scale may be the dominant influence on autogenic dynamics; however, in systems where the balance of sediment is in the delta foreset, basin depth and growth may set autogenic sedimentation patterns.…”

Accommodation and sediment‐supply controls on clastic parasequences: A meta‐analysis

“…Whether a sedimentary basin undergoes back‐tilting or fore‐tilting, or whether it presents syndepositional flexural bulges, will have an influence on sediment distribution and therefore on parasequence thickness, progradation distance and style of stacking (cf. Bhattacharya & Posamentier, ; Herbert, ; Emery & Myers, ; Hajek et al ., ; Leva López et al ., ).…”

Can the growth of deltaic shorelines be unstable?

“…Here our interest will focus on a new mechanism that might drive the instability of an advancing delta shoreline. Our motivation is the recent works from Hajek et al (2014) and López et al (2014), who have studied the growth of a sedimentary delta under a condition of a "back-tilted" subsidence rate; a condition that resulted in the water depth ahead of the shoreline decreasing with distance (i.e., the delta builds on an adverse slope). Such scenarios can arise in foreland basins where the sediment supply is sufficiently high relative to subsidence for progradation to occur, if a prograding delta approaches the opposite side of a lake or reservoir, or if the delta toe encounters an adverse slope on an offshore bar.…”