Avulsion and Crevassing in the Sandy, Braided Niobrara River: Complex Response to Base‐Level Rise and Aggradation

The Pennsylvanian Springhill Mines Formation: sedimentological framework for a portion of the Joggins Fossil Cliffs UNESCO World Heritage Site

“…Channel margins are not exposed, but abundant internal erosion surfaces and low-angle laminae suggest that fast, erosive, poorly-channelized flows were present within the confines of the river. These deposits, particularly the large channel body at 386.5 m, are comparable with Miall's (2006) shallow, perennial, sand-bed braided river facies model and may have formed in association with rivers similar to the lower Niobrara or South Saskatchewan Rivers (Cant and Walker 1978;Ethridge et al 1999;Skelly et al 2003). These bodies are similar to ancient examples described from the Solling Formation (Olsen 1988) and the multistory channel body from 581 m in the underlying Joggins Formation (Rygel and Gibling 2006).…”

River Avulsions and Their Deposits

“…Support for a causal connection between channel aggradation rate and avulsion frequency comes from Törnqvist (1994) who points out that the number of avulsions during Holocene development of distributaries in the Rhine-Meuse delta increased during times of rapid sea-level rise (when sedimentation rates were high) and decreased when the rate of sea-level rise decreased (but see Stouthamer & Berendsen 2000, p. 597, using the same Rhine-Meuse data for an alternative interpretation). The high number of partial avulsions of the Niobrara River where it enters the Missouri River is interpreted by Ethridge et al (1999) to be caused by channel aggradation owing to base level rise, and experimental evidence also suggests that avulsion frequency rises with increasing sedimentation rate (Bryant et al 1995, Heller & Paola 1996. Similar support is given by Makaske (1998), who shows that among different anastomosing rivers, avulsion frequencies decline with decreasing channel aggradation rates.…”

Late Glacial and Holocene avulsions of the Rio Pastaza Megafan (Ecuador–Peru): frequency and controlling factors

“…However, the principal characteristic of these areas is the presence of diverted/rejoining channels forming anastomosing patterns still apparent in spite of vegetation growth. This suggests sustained avulsive flow transforming a floodplain into an avulsion belt showing abandoned anastomosed channels and small isolated flood basins as in the modern Saskatchewan River (Morozova and Smith 2000;Slingerland and Smith 2004) or other avulsion belts formed under various climatic regimes (e.g., Schumm et al 1996;Smith et al 1997;Bristow 1999;Ethridge et al 1999;and other refs in Slingerland and Smith 2004). According to Slingerland and Smith's (2004) review, anastomosing reaches are results of progradational avulsions (Morozova and Smith 2000) characterized by deposition out of the parent channel into the invaded floodplain and favoured by slow runoff promoted by low floodplain slopes (Slingerland and Smith 2004, p. 264).…”

“…2 in Slingerland and Smith 2004). In most of the modern avulsion belts such the Saskatchewan River (Morozova and Smith 2000), the Niobrara River (Ethridge et al 1999), the Ovens and King rivers, Australia (Schumm et al 1996) or the Brahmaputra River (Bristow 1999), the causes of avulsions are entirely autocyclic and related to the high sedimentary discharge and deposition of these rivers even though the trigger was occasionally extrinsic (e.g., damming as for the Niobrara River, Ethridge et al 1999). However, for Smith et al (1997), neotectonic movement is the underlying cause of avulsion and anastomosis in the panhandle (upper entry corridor) of the Okavango fan situated in a 'relative' valley gradient depression inferred to represent a small graben.…”