Foraminifera and tidal notches: Dating neotectonic events at Korphos, Greece

Abstract

Fossil assemblages of foraminifera and thecamoebians from three salt-marsh cores recovered at Korphos, Greece, provided evidence for five transgression events since the mid Holocene. Marsh accretion rates based on radiocarbon-dated peat and geomorphic evidence from a series of discrete, v-shaped, submerged tidal notches indicated that these transgression events were rapid and episodic. Correlation of the tidal notches with the transgression horizons in the salt-marsh stratigraphy revealed a stepwise pattern of relative sealevel change at Korphos, which is best explained by coseismic subsidence related to fault displacement (earthquakes) associated with the Hellenic subduction zone. A comparison between the Korphos data and a model of Holocene sea-level change for the Peloponnesus reinforces this interpretation as sea-level rose in a series of jumps by amounts greater than accounted for by eustatic and glacio-hydro-isostatic factors (up tõ 2.0 m). This study illustrates that by combining microfossil, sedimentary and geomorphic records of past sea-level change, problems frequently encountered with each record individually (e.g. dating submerged notches and autocompaction of marsh sediments) may be overcome.

Significance of active growth faulting on marsh accretion processes in the lower Pearl River, Louisiana

“…Evidence of fault motion could be expressed in the geomorphology, surface sediments and shallow stratigraphy of this environment as follows: 1) geomorphologic change that includes formation of open water areas and expansion of water bodies into unique geometries within the marsh interior (White and Morton, 1997;Gagliano et al, 2003;Nichol et al, 2007); 2) quantifiable changes or patterns in fluvial geomorphology, including variations of river and distributary planforms, channel sinuosity, and gradients (Burnett and Schumm, 1983;Maroukian et al, 2008); 3) localized and accelerated wetland loss and rates of subsidence (Morton et al, 2002;Shinkle and Dokka, 2004); 4) quantifiable lateral discontinuities near fault surface traces in sediment accumulation rates over small spatial scales; and 5) subsurface indicators including lateral chronostratigraphic offsets of dated facies, and/or lithostratigraphic or biostratigraphic offsets of facies or fossil assemblages over short distances (400 m), and/or high-resolution seismic reflectors that display deformation in the form of offsets, unique terminations, and abrupt changes of reflector orientations and trends (e.g., Bourgeois and Johnson, 2001;Hayward et al, 2004;Ferranti et al, 2008;Nixon et al, 2009). Other studies focused on the geomorphology and stratigraphy of coastal Louisiana have noted similar physical relationships with fault motion (e.g., Holbrook and Schumm, 1999;Dokka et al, 2006;Morton et al, 2006).…”

Global sea-level rise and the disappearance of tidal notches

“…Pirazzoli, 1980;Fouache et al, 2000;Faivre and Fouache, 2003;Antonioli et al, 2004;Benac et al, 2004Benac et al, , 2008Nixon et al, 2009;Evelpidou et al, 2011a, b;Furlani et al, 2011).…”

Submerged notches on the coast of Skyros Island (Greece) as evidence for Holocene subsidence

“…In tectonically active coastal areas sudden relative sea-level changes occur before, during and after earthquake events (Hawkes et al, 2005;Shennan and Hamilton, 2006;Nixon et al, 2009). Relicts of former sea-level stands, such as raised or submerged notches, benches, beachrocks, caves, provide valuable data for detecting relative sea-level changes.…”