Marine notches in coastal cliffs: indicators of relative sea-level change, Perachora Peninsula, central Greece

Abstract

In several sites in the complex faulted western part of Perachora Peninsula, central Greece, three principal marine notches in rocky coasts are present. In each site, no Holocene notches occur above the upper of the three notches; only subaerial weathering affected the rocks. Lateral variation in the heights of notches demonstrates differential uplift due to fault control, and illustrates the complexity of application of marine notches in interpretation of tectonic history. The lower (undated) notch is prominent in places, coincides with modern sea level, and is interpreted to be forming now; it suggests that the western part of the peninsula has been stable for a considerable time. The middle and upper notches vary in height between sites, and may not be time-equivalent, but represent earlier sea level positions. In the harbour adjacent to the Heraion archaeological site, the middle and upper notches are preserved in most places as notch roofs, so that gradual uplift led to removal of notch floors by physical, chemical and biotic processes in exposed locations. However, within a few hundred metres west of the harbour, four uplifted (plus a fifth, forming now) notches have been illustrated by Pirazzoli et al. [Tectonophysics, 229 (1994) 201] that cannot be readily correlated to the harbour site, and indicate differential uplift by fault displacement. In a more complex situation at Mylokopi (6 km NE of Heraion), three different notch profiles occur in three blocks separated by two faults. However, within the central block of the three, two very different profiles are preserved only tens of metres apart, beneath one continuous upper notch roof at the same height. This complex arrangement, interpreted as variability of exposure to marine processes on different parts of this irregular embayment, such that one profile (containing three notches) was controlled largely by abrasion, and formed notches that are vertically more extensive, while the other profile (containing five narrow notches) formed by dissolution and/or biological erosion at the same time, in the protected east end of the block. However, if only one or the other profile was visible, very different tectonic interpretations would result. The bedrock of Perachora Peninsula also shows important variations in resistance to erosion, affecting the resulting notch profiles, and some sites are influenced by structurally controlled differential subaerial weathering, forming ridges and grooves, giving the false impression of extra minor notches; the distinction between dissolution-controlled and structure-controlled minor notches may not be possible in some places. The interpretations of notch profiles can be highly complex, and influence views of tectonic history in a given region. Overall, the occurrence of three principal notches beneath one uplifted notch roof in several sites, indicates that (a) Holocene uplift rates outpaced post-glacial sea-level rise; (b) there were three principal periods of relative sea-level stillstand affecting the Perachora Peninsula; and (c) uplift of the entire western part of the Perachora Peninsula is an important component of its tectonic processes, probably more important than fault movement within the peninsula.