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

Abstract

<p> Foraminiferal and thecamoebian biofacies were documented in the modem Korphos marsh located on the western coast of the Saronikos Gulf, Greece in order to define the general ecological features (such as salinity and proximity to marine influence) of the environments they occupied. These constraints were later used to identify fossil biofacies in subsurface marsh sediments at Korphos. </p> <p> Positive marine tendencies identified in fossil biofacies distributions were used for the first time to radiocarbon date relative changes in sea-level implied by a series of discrete, submerged tidal notches and beach rock adjacent to the marsh along the coast. Magnitude of subsidence events based on notch and beach rock data were measured to 2.9m, 0.5m, 1.3m, 0.39m, 0.47m, and 0.34m. The relatively unaltered v-shape of each notch profile suggested that sea-level rise was rapid and episodic. </p> <p> A comparison between the tidal notches and beach rock and an isostatically corrected model of sea-level for this area isolated the tectonic contribution to sea-level change and revealed that at least four of the six sea-level indicators plotted well-below predicted sea-level during subsidence. Therefore, the gradual sea-level rise of the late Holocene was interrupted by at least four sub-meter to meter-scale, step-wise increases in relative sea-level during coseismic subsidence of the Korphos marsh. The results of this study show how the combination of geomorphological and salt-marsh records have the potential to remove errors stemming from a lack of datable material for notches and autocompaction of marsh sediments when reconstructing local sea-level change. </p>