From shelf break to marine terraces, the morphological record of eustasy and interseismic deformation

Aug 31, 2020, 13:15 Uhr

MARUM Research Seminar

via ZOOM, register with jtitschack@marum.de

Luca Malatesta

The coastlines of active margins evolve under the combined action of two primary forcings: rock uplift and wave erosion. Here, I present two aspects of this system, long-term interseismic deformation and the eustatic record of marine terraces.

First, we show that the location of the continental shelf break at subduction zones reflects the position of the seismic locking depth based on a global compilation of coseismic ruptures and interseismic coupling.

The erosive shelf of a subduction margin results from continuous uplift and active wave erosion. The long-term uplift at subduction zones is driven by 1) the non-recoverable fraction of interseismic deformation 2) structural and 3) isostatic uplift. We combine a wave erosion model with an elastic deformation model to show how the hinge line that marks the transition from interseismic subsidence to uplift pins the location of the shelf break and how the coastline is removed from it.

Second, I focus on the use of marine terraces to derive uplift rates and eustatic history at the coast by interrogating the bijective assumption that each marine terrace records a singular marine high stand and that the next older high-stand is preserved by the next higher terrace. We show the emergent complexity and non-linearity of the marine terrace record in two steps.

Firstly, the elevation datums most often occupied by sea level, and thereby most likely to host wide terraces, are unevenly distributed and depend on local uplift rate; they do not necessarily correspond to sea level high-stands. Secondly, we use a model coupling tectonic deformation with wave-base erosion to identify the translation of vertical sea level rise and fall into horizontal transgression and regression of the coastline. This model sheds light on the intrinsically transient nature of marine terraces and the parameters, such as optimal uplift windows that control it.