The avulsion of the Saskatchewan River (Cumberland Marshes, east-central Saskatchewan, Canada) has resulted in new floodplain deposition over an area of more than 500 km 2 since beginning in the 1870s. The avulsion deposits are predominantly fine grained and could be otherwise classifiable as "overbank" sediments in alluvial floodplains presumed to be supplied by intermittent flooding of dominant master channels. The North Angling and Cadotte channels are older pre-existing channels that were intercepted and appropriated by the expanding avulsion. Following annexation of the North Angling Channel, stable cohesive banks inhibited channel enlargement and crevassing, forcing the increasing discharges to be accommodated by overbank flow and in the process, enhancing new levee aggradation. These levee deposits coarsen upward and thin downstream as a result of greater competence and higher proximal deposition rates brought on by the larger flows. In contrast, the Cadotte Channel responded to increasing discharges by levee breaching, giving rise to splay progradation and floodbasin filling. The Cadotte splay complex, formed from the avulsively annexed Cadotte Channel, represents a small but typical area of the avulsion belt. Facies characteristics and interrelationships examined from auger borings and vibracores are presented to illustrate patterns of deposition and floodplain development. Avulsive flooding initially raised local water-surface elevations, deepening small existing lakes and creating new shallow (1-2 m deep) lakes on the floodplain surface. Deposition began when levees of the Cadotte Channel were breached, allowing water and coarser sediment to spread as sheet-like flows while finer sediment was carried and deposited farther into the basin. Later, as the proximal splay sheets coalesced and grew basinward, flows became channelized, and progradation of mouth bars into marshes and shallow lakes, together with deposition of interchannel fines, became dominant, forming coarsening-upward sequences. Further floodplain aggradation developed by overbank flooding when splay channels became stabilized and bordered by levees. Gradual abandonment was accompanied by de-position of organic-rich fine-grained sediment on top of the progradational sequences. Throughout the avulsion, the North Angling Channel has stood as an older alluvial ridge separating two broad areas of avulsive deposition. Its recent levee deposits now grade basinward into these new floodplain sediments composed of thicker heterogeneous, predominantly upward-coarsening, and rapidly deposited facies of the avulsion.

Geophysical, structural, geochronological and geomorphological data indicate that the Psatha, East Alkyonides, Skinos and Pisia faults are Holocene-active structures whereas the status of the West Alkyonides, Strava, Perachora and Loutraki faults is less certain. We see no evidence for significant lateral surface fault growth. New data for late Pleistocene footwall uplift of the Psatha fault are comparable with previously estimated Holocene rates. Pre-Holocene stratigraphic sequences in the Alkyonides Gulf allow calculation of vertical displacement on the Skinos fault of 1.42–1.60 km over a period of >0.6 Ma. Previous palaeoseismological studies indicate comparable displacement rates extrapolated to 0.61–2.20 Ma, whereas extrapolation of previous geodetic data indicate a range of 0.17–0.46 Ma. The latter is too short given the evidence of the stratigraphic record, signifying either that these data may not be representative of longer-term rates, or that significant deformation has taken place elsewhere, for example, on offshore antithetic faults. A case is established for uniform late Quaternary (post-MIS 7) uplift of the Perachora peninsula at rates of c . 0.2–0.3 mm a ⁻¹ . The lack of regional tilting over Perachora–Corinth–Isthmia is in marked contrast to the situation in the Alkyonides–Megara basins to the east.