Multi-scale and multi-parametric analysis of Late Quaternary event deposits within the active Corinth Rift (Greece)

Abstract

A major challenge in subaqueous paleoseismology is to understand the relationship between an earthquake/tsunami and a sedimentary event recorded in drillcores. Expedition 381 of the International Ocean Discovery Program was dedicated to the development of the Corinth Rift, and its drilled cores provide a potentially important resource to better understand depositional mechanisms of sedimentary events within changing open marine to (semi-)isolated environments. To achieve this, we analyse U-channels and spatula samples from the topmost part (0-65 m below seafloor maximum depth) of cores M0078B and M0079A (~0-25 ka), using high-resolution X-Ray microtomography in combination with grainsize, magnetic and XRF measurements. Structures and grain array are resolved down to 12 µm in voxel size, characterizing the geometry of the basal surface of homogenite+turbidite sedimentary events, and the internal base-upwards evolution at high-resolution scale. The analysed events suggest these types of deposits are more complex than previously proposed, especially at the transition between the basal coarse turbidite sub-unit and the fine-grained homogenite upper sub-unit, as well as within the homogenite. Combined with the other observations and parameters, X-ray microtomography reinforces the interpretation of the Corinth HmTu deposits as having predominantly originated from paleoearthquake or paleotsunamis effects, despite subtle differences according to depositional environment. 1-Introduction Over previous decades, the discipline of "subaqueous paleoseismology" developed with the aim of contributing efficiently to earthquake hazards assessment (e.g. McCalpin, 2009). This approach needs to build on a tripartite relationship between 1) a sedimentary event bed 2) an earthquake with or without an associated tsunami wave, occasionally reported or recorded for historical times, and 3) an identified active fault, with possibly a localized rupture. Such paleoseismological methods are applied, event-by-event, to sedimentary records (either marine or lacustrine) that can span as much as tens of thousands of years (e.g.

Did the Younger Dryas to Holocene climate transition favour high seismicity rates in the north‐western Alps?

“…This suggests that Hm deposition was mainly controlled by sediment settling rather than by flow velocity (Arnaud et al ., 2012; Wilhelm et al ., 2016). This type of event layer has been described as a ‘turbidite + homogenite’ (Tu + Hm) facies in marine environments (Campos et al ., 2013; de Gelder et al ., 2022).…”

Late Quaternary mud‐dominated, basin‐floor sedimentation of the Gulf of Corinth, Greece: Implications for deep‐water depositional processes and controls on syn‐rift sedimentation

“…Density underflows may be triggered by: (i) extended periods of hyperpycnal fluvial discharge some of which may evolve into lofted flows, (ii) shorter‐lived, storm‐triggered fluvial discharges causing hyperpycnal flows, (iii) slope instability events creating subaqueous landslides or slumps that undergo disaggregation and dilution downslope into debris flows and/or turbulent underflows; some of which may be triggered during storms (Ferentinos et al, 1988), (iv) “seismites”, essentially a seismically‐triggered subset of (iii), and (v) possible saline inflow into the axis of the basin when sea‐level rise over‐topped the level of the structural sill. Campos et al (2013) and De Gelder et al (2021) explored whether there may be characteristics of homogenite‐turbidite couplets that might distinguish earthquake‐triggered events from non‐earthquake triggered deposits, specifically deposition of the upper homogenous mud component being by prolonged suspension fall‐out from an initially‐oscillating cloud of suspended sediment. However, as outlined above, there are multiple combinations of processes which may lead to sediment bypass and deposition of bipartite beds (Stevenson et al, 2015).…”