Late Neogene rift-basin evolution and its relation to normal fault history and climate change along the southwestern margin of the Gerania Range, central Greece

摘要

The south- to southwest-dipping North and South Saros normal faults occupy the southeastern margin of the Gerania Range, a major massif of Mesozoic limestone and ophi-olite in the eastern Gulf of Corinth Rift, central Greece. The history of the Saros faults is constrained by adjacent basin-fill sediments and modern drainage patterns. Older basin fill (Pliocene-lower Pleistocene?), which consists of terrestrial fine sands, carbonaceous muds, marls, and micrite limestones, is uplifted on the South Saros fault block and onlaps the North Saros fault footwall block on its northern side to near its crest, suggesting that it predates major fault activity. In contrast, younger basin fill (middle Pleistocene?) was deposited and locally deformed during fault activity in a main basin south of the faults and in a perched basin on the South Saros fault block. Main-basin deposits consist of alluvial-fan, fan-delta, and shallow-marine sediments up to 50 m thick, whereas perched-basin fanglomerates are 5-15 m thick. Fault-scarp retreat and sediment onlap indicate that the faults became inactive late in the history of deposition of the younger basin fill. The perched and main basins are currently undergoing incision, allowing modern sediment to bypass the basins and to be deposited on modern fan deltas and beaches along the Gulf of Megara coast. The absence of knickpoints and upstream deepening of the canyons suggest that a climatically driven increase in catchment runoff was responsible for basin incision, although uplift and sea-level change may have contributed as well. The North and South Saros faults each consist of three segments characterized by different strikes. The major drainages cross the Saros faults at or near segment boundaries, suggesting that the drainages may have initially flowed between the tips of isolated fault segments. As the segments became linked, the antecedent drainages maintained their course and cut deep gorges. At the scale of the entire eastern Gulf of Corinth region, however, older unlinked faults were abandoned, and new faults were created in a general northward and basinward direction; the origin of this process remains controversial.