Laboratory Experiments of Incised Valley Systems: Influence of Sediment Concentration and Sea Level Rise

Abstract

Incised valleys have been widely recognized and studied by many researchers (Cason 1982, Hansen 1984, Dalrymple, Zaitlin et al. 1992, Zaitlin 1994, Posamentier 2001, Li, Wang et al. 2002). The original description of incised valleys of the Mississippi river was established by Fisk in 1944 and later defined as a “fluvial eroded, elongate topographic low that is typically larger than a single channel” (B.A. Zaitlin 1994). Valley fills generally contain a complex range of alluvial architecture linked to laterally amalgamated sandy channel belts in lowstand systems tracts (Martinsen 1994, Zaitlin 1994, Posamentier 2001) to channel avulsion process and backstepping deltaic deposit (Harris 1994) during highstand systems tracts. However, some fundamental questions still need to be investigated, in particular 1)what is the influence of upstream controls (e.g., sediment concentration) versus downstream controls (e.g., base level rise) on channel geometrical records in the paleo-valley, and 2) what is the signature of autogenic processes sedimentary records in the incised valley depositional stratigraphy? To answer these questions, we performed several experiments of incised valley infilling deposition during a single base-level rise in the Saint Antony Falls Laboratory (SAFL, University of Minnesota). We designed and built a 2m × 0.8m × 0.12m V-shape valley placed into a 5m × 5m basin. The water level of this basin is totally controlled and allows reproducing sea-level rise at different rates. We performed 10 sets of experiments, during which we systematically changed the water discharge and the rate of base level rise. The topography is measured over the whole surface of the valley at regular time intervals (every 10 minutes) by computer-controlled laser scanner. In addition, the geometry of the channel sandbodies is acquired by cross-section photos after each runs. The experimental results are then compared with the stratigraphic record of the paleo-incised valley in the Esplugafreda section of the central Tremp-Graus basin (Spanish South-Pyrenees). This section is composed of sandbodies and well-developed soils (Esplugafreda Fm.) capped by a massive conglomerate (Claret Fm.). Preliminary results suggest that water discharge could influence the variability of sandbodies geometry in the incised valley and the stratigraphic sequence in Esplugafreda Section could the inevitable autogenic signature of valley filling, rather than the record of an upstream perturbation.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016