173 research outputs found
The influence of basin slope and fluvial flow on deltaic built-up processes off mountainous, seasonal rivers
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Evolución de los deltas submarinos de los ríos Guadalfeo y Adra en respuesta a las variaciones de los aportes sedimentarios
The Guadalfeo and the Adra submarine deltas off the northern coast of the Alboran Sea
have been built up under the direct influence of short and mountainous rivers. The area is subjected
to strong climatic seasonality, with sporadic winter torrential floods and high summer aridity. In
addition numerous anthropogenic activities have affected these systems, mostly during the last two
centuries. In order to decode the influence of climatic variability and anthropogenic impacts on
sediment supplies during the recent past, five sediment cores were collected from the Guadalfeo
and Adra submarine deltas. Benthic foraminiferal and sedimentological analyses, combined with
radiocarbon dating, were performed. The impact of torrential floods alternating with periods of low
rainfall or dry periods were recorded in the Adra and Guadalfeo prodeltas. Periods with low
abundance of benthic foraminifera and high amounts of coarse-grained sediments, were interpreted
as the result of enhanced sediment supply to the shelf triggered by major flood events. On the other
hand, periods with high amounts of fine-grained sediments and high abundances of colonizers and
opportunistic foraminiferal species indicate the establishment of new environments with distinct
ecological constraints. These environments were driven by lower sediment supplies during low
rainfall or dry periods. The most recent sedimentation seems to reflect the human interventions in
the rivers basins, such as deviation of the main river courses and dams construction, which reduced
the sediment input and promoted the deposition of shallow-water submarine deltas.Versión del edito
Relationship between the offlap-break location of Holocene prograding wedges on wave climate in southeastern Iberian Peninsula
Wave climate exerts a significant influence on the development of Holocene sedimentary prograding wedges. This is demonstrated by
the fact that near-bed orbital velocities between 0.10 and 0.14 m/s (threshold for resuspension) occur in the vicinity of the infralittoral
prograding wedges (IPW) offlap-breaks during storm-weather conditions, but during medium wave energy conditions in the case of
prodeltaic wedges
The evolution of the Guadalfeo submarine delta (northern Alboran Sea) during the last ca. 200 years
The Guadalfeo submarine delta is located on the northern Alboran Sea shelf in the western Mediterranean Sea. The sedimentary dynamics of the deltaic system is governed by the discharge of one of the major rivers in this area draining the western sector of the near-coastal Sierra Nevada Mountains. The area is under the influence of a Mediterranean climate, with high spatial and temporal (i.e., inter- and intra-annual) rain variability. Major anthropogenic forcing affected the river system during the 1930’s, with the deviation of the main river channel 2.5 km to the west, to its present position. More recently, the construction of Béznar (1977-1985) and Rules (1993-2003) dams have also contributed to limit the amount of sediments exported to the deltaic system.
In order to understand the interaction between river discharges and the evolution of the submarine delta at different timescales, sediment cores were collected off the ancient (core 13) and present-day (cores12 and 15) river courses. A chronological framework was performed and combined with sedimentological and benthic foraminiferal analyses.
Radiocarbon dating of plant debris from the base of the cores indicates that the sedimentary record goes back 200 years. In core 13, the variations between coarse and fine fractions along the core and the upward increase of benthic foraminiferal population density, would indicate that deposition possibly occurred until the deviation of the main river course to its present position. In the lower part of core 12, the strong alternation between coarse and fine sediment textures and the variable amounts of benthic foraminiferal species are interpreted as the result of an active fluvial regime. The upper part, with high percentages of fine sediments and high values of population density, could be attributed to the stabilization of the river course in its present-day location. Core 15, located at 11 m water depth, showed the highest content of gravel in the lower part of the core, high contents of silt at two core depths and increased percentages of sand to the top, indicating the strong influence of human interventions in the river basin and consequent changes in the sediment supply to the Guadalfeo submarine delta.info:eu-repo/semantics/publishedVersio
Multi-proxy evidence of rainfall variability recorded in subaqueous deltaic deposits off the Adra River, southeast Iberian Peninsula
The Adra River deltaic system, southeast Iberian Peninsula, shows a steep topography and is subjected to
strong climatic seasonality. This system has been affected by alternating wet and dry periods, and it has
also undergone numerous anthropogenic activities such as deforestation, mining activities, river channel
deviations and dam construction, particularly during the last two centuries. Two sediment cores were
retrieved off the Adra River, from the western (MS_V9) and eastern (MS_V4) lobes of the subaqueous
deltaic deposit. A multi-proxy study was carried out, including grain size, benthic foraminiferal assemblages,
magnetic susceptibility and geochemical element analyses, in order to understand the sedimentary
expression of recent climatic cycles and anthropogenic interventions in the river basin.
Periods of increased deposition of coarse-grained sediments, low absolute abundance of benthic
foraminifera and high elemental ratios indicative of terrigenous contributions, were interpreted as periods
of increased sediment supply to the shelf. Four flooding events were recorded in core MS_V9 and
three events on core MS_V4, of which two were observed in both cores. They were related to periods
with major floods that were documented on the southern Iberian Peninsula around 1770e1810 and 1860
e1870 AD. On the other hand, sediment core intervals exhibiting increasing proportion of fine-grained
sediments and higher abundances of foraminiferal species assigned as successful colonizers (Textularia
earlandi) and opportunistic species that feed on bacteria or terrestrial organic matter (Bolivina ordinaria,
Bulimina elongata, Eggerelloides scaber and Ammonia beccarii or tepida), indicate the establishment of new
environments with new ecological constraints. They were related to significant decreases of terrigenous
sediment input during low rainfall or dry periods. The increase of opportunistic species feeding on fresh
phytodetritus (Nonionella iridea, Nonionella stella, Nonionella sp., Brizalina dilatata, Epistominella vitrea
and Bolivinellina pseudopuntata), under more stable environmental conditions, also point to a stronger
marine influence on the prodeltaic environments during these periods. The human interventions on the
river basin after 1872 AD, with the deviation of the main river channel to the east, led to a drastic
reduction of the sediment exported to the western delta lobe. This study showed that the sedimentation
on the Adra subaqueous deltaic deposit was mainly controlled by rainfall variability from 1663 to 1872
AD, and afterwards by anthropogenic interventions.En prensa2,247
Gravitational and oceanographic processes interaction in the upper slope gullies of the Gulf of Cadiz
Submarine deltaic geometries linked to steep, mountainous drainage basins in the northern shelf of the Alboran Sea: Filling the gaps in the spectrum of deltaic deposition
A comprehensive analysis of small deltaic environments linked to short, mountainous, and seasonal fluvial systems
in the northern shelf of the Alboran Sea was undertaken in order to define the controlling parameters of
the geomorphological variability. The database includes multibeam and backscatter imagery, surficial sediment
samples, and high-resolution seismic profiles. Additionally, geomorphological and hydrodynamic modeling
and statistical analysis (principal component and cluster analysis) of hydrological and physiographic variables
were performed.Most of the studied deltaic systems have high-gradient, coarse-grained deposits with preferential
development of the submarine portions to the detriment of the deltaic plains. The geomorphological analysis
identified three basic types of plan-viewdistributions according to the length-to-width ratios: elongate, linguoid
and lobate. Cross-slope profiles evidence dominant concave-upward geometries, fewer occurrences of planar geometries,
and no sigmoid profiles. Sediment depocenters are extremely thick in proximal locations, but thin out
rapidly seawards. The geometric distribution patterns of the deltaic systems are characterized by a predictable
pattern in plan-view according to the type of fluvial system, ranging from a relatively large river to ephemeral
creeks. Prevailing concave and secondary planar profiles support strong sediment progradation in the submarine
realmand lowsediment retention in the emerged deltaic environment. Two different types of systems are distinguished:
(1) larger rivers,where deltaic deposition is largely controlled by basin dimensions, ultimately dictating
themagnitude of water and sediment discharges; and (2) smaller rivers and creeks,where deltaic geometries are
related to the basin slopes. The influence of hydrodynamic variables on defining the submarine deltaic geometry
has been observed in the case of concave-upward geometries, where geomorphological boundaries are defined
by medium- and high-energy wave conditions.Versión del editor2,520
The role of late Quaternary tectonic activity and sea-level changes on sedimentary processes interaction in the Gulf of Cadiz upper and middle continental slope (SW Iberia)
A morphological and seismic-stratigraphic analysis of the Gulf of Cadiz area near the Strait of Gibraltar is presented
in this work, focused on the sedimentary evolution of the upper and proximal middle-continental slope
since the Mid-Pleistocene. Based on the analysis of seismic reflection profiles and swath bathymetry data, this
work analyses the close influence of the activity of buried and outcropping diapiric ridges and late Quaternary
sea-level changes on the evolution of contouritic features related to the Mediterranean Outflow Water (MOW)
and Eastern North Atlantic Central Water (ENACW), gravitational features and fluid-escape structures. The
stratigraphic architecture reveals that, under active diapiric deformation, the upper slope plastered drift grew
during low sea-level stages, when sediment supply was high and the ENACW swept the upper slope, contrasting
with the present-day highstand situation dominated by northwest-trending MOW flow. The south-estward
ENACW flow forced asymmetry and lateral migration of gullies incised in the plastered drift. Two evolutionary
stages have been established: 1) After the Mid Pleistocene, activity of diapirs with a NE trend determined
the location of the deepest depressions which were infilled by plastered contouritic drifts; 2) Between Late
Quaternary and present, a drastic change of buried diapirs growth pattern and orientation to a NW trend
enhanced slope-derived gravitational processes affecting the bottom current dynamics. Adjustments to tectonic
changes led to a phase of plastered drift growth on the upper slope during which depocenters varied their distribution
and orientation. In a long-term the structural control on sedimentation shows a northwestward
displacement of deformation, resulting in an overall extension of the contourite depositional system to the NW.
In a short-term, sea-level changes favored drift deposition, gullies incision and the strengthening of water masses.
This work evidences the importance of tectonic deformation in sedimentation at recent time scales, and the twodirectional
interplay between recent tectonic activity and bottom current dynamics.Versión del edito
Last ca. 250 years shifts of benthic foraminiferal assemblages in response to natural and anthropogenic impacts, Northern Alboran Sea
Episodios de construcción de un delta mediterráneo: Cambio climático y modificaciones antropogénicas en el delta del río Adra
The evolutionary stages of the submarine delta off the Adra River are investigated in this
study, under the context of climatic fluctuations entangled with increasing human activities and
interventions in the drainage basins and adjacent shores during the Middle to Late Holocene. To
achieve that goal, we used an extensive database comprising a set of bathymetric data covering
different time slices, a dense grid of high-resolution seismic data and several sediment cores
collected in the two submarine lobes of the Adra River delta. Two main evolutionary phases can be
identified. The first one extended through most of the construction history and was mediated by
major climatic events at the Mediterranean scale; this phase included three major progradational
events occurring during the Mid Holocene, the Roman time and the Little Ice Age. The most recent
phase is strongly determined by human modifications of the fluvial channels, and resulted in a
drastic transformation of the submarine sedimentary environment.Versión del edito
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