Listric faulting, sedimentation, and morphological evolution of the Quaternary eastern Corinth rift, Greece: First stages of continental rifting

Abstract

The 30-km-wide Corinth rift is one of a series of west-northwest-trending Quaternary grabens in western Greece. In the north, a major listric fault marks the southern edge of a deep asymmetric graben filled by the sea.The footwall of this fault, which forms the southern part of the rift, has experienced epeirogenic uplift and 18% Quaternary extension along smaller listric faults. Rates of motion are determined by offsets in Quaternary rift-filling sediments. The uplift and listric extension of the southern part of the rift took place in the first two million years of rifting.This tectonic style occurs in other Greek Quaternary rifts, but comparable records have been destroyed by erosion in older rifts. Quaternary sediments exposed in the uplifted southern part of the rift comprise a northward-prograding deltaic sequence, the deposition of which continues today in the Gulf of Corinth. These Quaternary sediments are principally alluvial fan and coastal lacustrine conglomerates in the south, lacustrine Gilbert-type fan-delta conglomerates and marls in the center, and predominantly lacustrine marls overlain by thin marine or fluvial in the north. The oldest marine is mid-Pleistocene; this facies is generally transgressive over the lacustrine deltaic deposits. Mesoscopic structural features are unusually well developed in these sediments. Large listric faults are accommodated by minor synthetic or antithetic faults, rollover structures with counter faults, and low-dipping shear zones in the place where mesoscopic listric faults meet the decollement horizon. Some extension joints have been reactivated to form shear faults. The landscape on the uplifted southern part of the rift has flights of terraces previously interpreted as providing a detailed record of sea-level changes in the past 0.5 m.y. Most terraces result from fault disruption of the same delta-top surface, in places with marine caprock, that was also influenced by synsedimentary faulting. The marine caprock and associated alluvial facies are thin, and there is no evidence for river dissection due to lowered base level prior to the middle Pleistocene isotopic stage 6 (130-180 Ka); this indicates that marine highstands were only a little higher than normal lake level. In the late Pleistocene, lake levels dropped substantially during marine lowstands, leading to the dissection of the landscape and the deposition of thick alluvium during marine highstands. Caprock sediments preserve only an incomplete record of marine highstands.