Clinoform architecture influenced by salt tectonics and Quaternary Sea level changes: The Acheloos delta complex, Gulf of Patras, Greece

Abstract

This study focuses on the evolution of the Acheloos river-dominated delta in western Greece. It is an area with limited published data, that serves as a link between the well-studied rift basin of the Gulf of Corinth and the active Kephalonia Transform Fault. The examination of a newly acquired 3D seismic cube and vintage well data in this area offers a rare opportunity to: i) develop a stratigraphic scheme for the evolution of river-dominated deltas in restricted basins influenced by salt tectonics, which can be applied as an analogue to similar deltas worldwide, and ii) re-evaluate the deformation style of the study area and challenge the widely accepted concept of its tectonic behavior as a rigid block.

Detailed 3D seismic stratigraphy and well data revealed eleven progradational packages. These are attributed to the Acheloos activity during Pleistocene and exhibit distinctive spatial variation. Thickness distribution and trajectory analysis show that the delta developed in three stages: (i) poorly developed progradational units in a weakly subsiding basin, (ii) retrogradational delta units in a strongly subsiding basin and (iii) stabilization of the accommodation space and gradual basin infill through progradational units.

Although the study area has been considered a rigid block, stratigraphic analysis revealed multiple subsidence events linked to the structural history of the basin. Additionally, seismic data reveal that salt tectonics have a significant impact on its evolution, affecting the locus of the depocenters and the subsidence rates. The deformation of the underlying strata shows that the salt diapiric activity intensified from 435 ka to present. This can either be attributed to the differential loading due to the continuous deltaic sedimentation and/or to the structural activity within the study area. Notably, the paroxysmal phase of salt tectonics occurs right after a large subsidence of the area of interest between 860 and 550 ka.