INVESTIGADORES
ORFEO Oscar
artículos
Título:
Scales and causes of heterogeneity in bars in a large multi-channel river: Río Paraná, Argentina
Autor/es:
REESINK, A.; ASHWORTH P,; SAMBROOK SMITH, G.; BEST, J; PARSONS, D.; AMSLER, M.; HARDY, R,; LANE, S.; NICHOLAS, A.; ORFEO, O.; SANDBACH, S.; SIMPSON C,; SZUPIANY, R.
Revista:
SEDIMENTOLOGY
Editorial:
WILEY-BLACKWELL PUBLISHING, INC
Referencias:
Lugar: Londres; Año: 2014 p. 1 - 31
ISSN:
0037-0746
Resumen:
To date, published studies of alluvial bar architecture in large rivers have
been restricted mostly to case studies of individual bars and single locations.
Relatively little is known about how the depositional processes and sedimentary
architecture of kilometre-scale bars vary within a multi-kilometre
reach or over several hundreds of kilometres downstream. This study presents
Ground Penetrating Radar and core data from 11, kilometre-scale bars
from the R_ıo Paran_a, Argentina. The investigated bars are located between
30 km upstream and 540 km downstream of the R_ıo Paran_a ? R_ıo Paraguay
confluence, where a significant volume of fine-grained suspended sediment
is introduced into the network. Bar-scale cross-stratified sets, with lengths
and widths up to 600 m and thicknesses up to 12 m, enable the distinction
of large river deposits from stacked deposits of smaller rivers, but are only
present in half the surface area of the bars. Up to 90% of bar-scale sets are
found on top of finer-grained ripple-laminated bar-trough deposits. Bar-scale
sets make up as much as 58% of the volume of the deposits in small, incipient
mid-channel bars, but this proportion decreases significantly with
increasing age and size of the bars. Contrary to what might be expected, a
significant proportion of the sedimentary structures found in the R_ıo Paran_a
is similar in scale to those found in much smaller rivers. In other words, large river deposits are not always characterized by big structures that allow
a simple interpretation of river scale. However, the large scale of the depositional
units in big rivers causes small-scale structures, such as ripple sets,
to be grouped into thicker cosets, which indicate river scale even when no
obvious large-scale sets are present. The results also show that the composition
of bars differs between the studied reaches upstream and downstream
of the confluence with the R_ıo Paraguay. Relative to other controls on downstream
fining, the tributary input of fine-grained suspended material from
the R_ıo Paraguay causes a marked change in the composition of the bar
deposits. Compared to the upstream reaches, the sedimentary architecture of
the downstream reaches in the top ca 5 m of mid-channel bars shows: (i) an
increase in the abundance and thickness (up to metre-scale) of laterally
extensive (hundreds of metres) fine-grained layers; (ii) an increase in the percentage
of deposits comprised of ripple sets (to >40% in the upper bar
deposits); and (iii) an increase in bar-trough deposits and a corresponding
decrease in bar-scale cross-strata (