AAPG Annual Convention and Exhibition

Datapages, Inc.Print this page

Sequence Variability in Shallow Marine/Deltaic Syn-Rift Systems: Impact of Fault Network Evolution and Sediment Supply Variations, Plio-Pleistocene of the Corinth Rift

Abstract

Shallow marine and deltaic environments are particularly sensitive to changes in relative sea-level and variations in sediment supply making them key environments for developing sequence stratigraphic concepts. In this presentation we focus on the Plio-Pleistocene, abandoned portion of the Corinth Rift, to investigate variability in sequence stratigraphic evolution. Fault evolution and preserved sediment source areas allow us to investigate the controls on sequence variability, making the Corinth Rift an ideal natural laboratory for source-to-sink sequence stratigraphic studies. In the western part of the rift, Pliocene deposition is dominated by north-flowing alluvial systems that over-filled available accommodation space associated with several major normal faults. Northward localization of faulting onto the Pirgaki-Mamoussia Fault at 1.8 – 1.5 Ma, lead to increased hangingwall subsidence, but hinterland drainage maintained a northerly course, cutting through uplifting footwalls and supplying sediment to giant, fan-deltas. These fan-deltas have a radius of 2 – 4 km, display a strongly aggradational stacking pattern and are formed of individual, 30 – 100 m thick aggradational to progradational stratal units, bounded by flooding surfaces. There is little or no evidence of abrupt shallowing events or subaerial exposure, until faulting shifted further northward and began to uplift the fan-deltas around 0.6 Ma. In contrast, the central part of the rift was already the site of a deep, underfilled lake during the late Pliocene, with localized giant fan-deltas along the active southern border fault. Northward localization of faulting onto the Xylocastro and Lykoporia faults, located some 20 km north of the southern border fault, caused uplift in their footwalls, leading to progressive shallowing, exposure and fluvial incision. This resulted northward offlap and downstepping of the southern margin fan deltas creating a series of forced regressive wedges. Deltaic forced regression ended, not as a result of increasing accommodation space, but because of reversal of hinterland drainage, terminating the supply of coarse, clastic sediment to the shoreline. The study highlights the marked local variability in sequence development that is common in tectonically active areas and the need to integrate source-to-sink studies within an evolving structural framework.