Fluvial response to sea‐level changes: a quantitative analogue, experimental approach

Abstract

Quantitative evaluation of fluvial response to allogenic controls is crucial for further progress in understanding the stratigraphic record in terms of processes that control landscape evolution. For instance, without quantitative insight into time lags that are known to exist between sea‐level change and fluvial response, there is no way to relate fluvial stratigraphy to the sea‐level curve. It is difficult to put firm constraints on these time‐lag relationships on the basis of empirical studies. Therefore, we have started to quantify time‐averaged erosion and deposition in the fluvial and offshore realms in response to sea‐level change by means of analogue modelling in a 4 × 8‐m flume tank. The rate of sea‐level change was chosen as an independent variable, with other factors such as sediment supply, discharge and initial geometry kept constant over the course of 18 experiments. Our experimental results support the common view that neither fall nor rise in sea level affects the upstream fluvial system instantaneously. An important cause for the delayed fluvial response is that a certain amount of time is required to connect initial incisions on the newly emergent shelf (canyons) with the fluvial valley. Lowering of the fluvial longitudinal profile starts only after the connection of an active shelf canyon with the fluvial valley; until that moment the profile remains steady. We quantified the process of connection and introduced the quantity ‘connection rate’. It controlled, in conjunction with the rate of sea‐level fall: (1) the amount of fluvial degradation during sea‐level fall; (2) the total sediment volume that bypasses the shelf edge; (3) the percentage of fluvial relative to shelf sediment in the lowstand delta; (4) the volume of the transgressive systems tract and (5) the amount of diachroneity along the sequence boundary. Our experiments demonstrate also that the sequence‐stratigraphic concept is difficult to apply to continental successions, even when these successions have been deposited within the influence of sea level.

Conceptual assessment of (dis)connectivity and its application to the Ganga River dispersal system

“…In this case, longitudinal connectivity will also be defined by downstream to upstream connectivity, as variations in sea level at different temporal scales will affect geomorphic processes in the LGP through headward propagation of incision following a base-level fall. The downstream to upstream connectivity in the LGP will depend on sediment supply from upstream, channel slope and sea floor slope, and rate of sea level fall (Schumm, 1993;Van Heijst and Postma, 2001). The high sediment supply, high channel slope in comparison to the sea floor slope, and the slow rate of sea level change decrease the downstream-upstream connectivity (Schumm, 1993;Van Heijst and Postma, 2001).…”

Biostratigraphy and sedimentology of the Fluviatile Untere Serie (Early and Middle Miocene) in the central part of the North Alpine Foreland Basin: implications for palaeoenvironment and climate

“…Sea-level, and therefore the sequence stratigraphic base-level (Richards 1996;van Heijst and Postma 2001;Howell and Flint 2003), directly affected the sedimentary record of the basal UFM. Zweigel (1998) attributes sequence boundaries in the NAFB mainly to eustatic sea-level changes rather than to tectonics or climate.…”

Wave train model for knickpoint migration

“…Rates of knickpoint migration generally range between 0.001 and 0.1 m y − 1 (e.g. Van Heijst and Postma, 2001) with exceptional values greater than 1 m y − 1 as for the Niagara Falls or for active orogens (Philbrick,1970;Tinkler et al,1994;Wohl,1998;Crosby and Whipple, 2006). Several field and experimental studies have emphasized the correlation between the rate of knickpoint migration and the upstream drainage area, which is considered as a proxy for water discharge (Parker, 1977;Schumm et al, 1987;Rosenbloom and Anderson, 1994;Bishop et al, 2005;Crosby and Whipple, 2006;Berlin and Anderson, 2007).…”