264 research outputs found
Spatial distribution of radionuclides in marine sediments from Djibouti seamounts (Alboran Sea, Western Mediterranean).
Sediment samples from two seamounts of the Djibouti Banks area – Avempace and Herradura - located at the Motril Marginal Plateau (northern Alboran Sea) were investigated to determine the radioactivity of natural and artificial radionuclides. Changes in the elemental composition of sediment from seamounts may be related to sources and oceanographic conditions in the water column, but also biogeochemical and geochemical processes can be involved during the vertical deposition of particles and in the sediment surface once particles are settled. The particular interest of this area is that the influence of fluvial supplies is scarce and therefore the contribution of aeolian dust inputs to sediments is expected to be high and largely responsible for the sediment’s composition. In this setting, the Sahara and northernmost part of North Africa or Sahel regions are the most likely areas providing dust particles to the Mediterranean Sea.
The tops of the Avempace and Herradura seamounts are relatively flat and shallow, with minimum depths of 260–275 m, respectively. In general, both seamounts presented similar average radiological load and the results showed that the spatial distribution of radionuclides was relatively uniform in surface sediments from these two banks. For the anthropogenic 137Cs, the radioactivity ranges from 1.8-6.9 Bq/Kg and can be mainly attributed to the significant supply of aeolian dust from North Africa to the Alboran Sea.Universidad de Málaga. Campus de Excelencia Internacional AndalucĂa Tec
Tectonic Control on Sedimentary Dynamics in Intraplate Oceanic Settings: A Geomorphological Image of the Eastern Canary Basin and Insights on its Middle-Upper Miocene to Quaternary Volcano-Tectonic-Sedimentary Evolution
This paper integrates sedimentary, tectonic and volcanic geological processes inside a model of volcano-tectonic activity in oceanic intraplate domains related to rifted continental margins. The study case, the eastern Canary Basin (NE Atlantic), is one of the few places in the world where giant MDTs and Quaternary volcanic and hydrothermal edifices take place in intraplate domains. In this paper, we analyse how two structural systems (WNW-ESE and NNE-SSW) matching with the oceanic fabric control the location of volcanic systems, seafloor tectonic reliefs and subsequently the distribution of main sedimentary systems. Linear turbidite channels, debris flow lobes and the lateral continuity of structural and volcanic reliefs follow a WNW-ESE trend matching the tracks of the oceanic fracture zones. Furthermore, escarpments, anticline axes and volcanic ridges follow a NNE-SSW trend matching normal faults delimiting blocks of oceanic basement. The morpho-structural analysis of all the above geomorphological features shows evidence of a volcanic and tectonic activity from the middle–upper
Miocene to the Lower–Middle Pleistocene spread over the whole of the eastern Canary Basin that reached the western Canary Islands. This reactivation changes the paradigm in the seamount province of Canary Islands reported inactive since Cretaceous. A tecto-sedimentary model is proposed for this period of time that can be applied in other intraplate domains of the world. A tectonic uplift in the study area with a thermal anomaly triggered volcanic and hydrothermal activity and the subsequent flank collapse and emplacement of mass transport deposits on the Western Canary Slope. Furthermore, this uplift reactivated the normal basement faults, both trending WNW-ESE and NNE-SSW, generating folds and faults that control the location of turbidite channels, escarpments, mass transport deposits and volcanic edifices.Versión del edito
Discovering the Fine-Scale Morphology of the Gulf of Cádiz: An Underwater Imaging Analysis
The dense and deep water flow that leaves the Mediterranean Sea to the Atlantic flows
through the upper and middle slope of the Gulf of Cádiz as a powerful bottom stream that model sand interacts with bathymetry. The detailed analysis of underwater images,obtained with a photogrammetric sled in the central area of the upper and middle slope of the Gulf of Cádiz, together with multibeam bathymetry and oceanographic and sediment types data, has allowed conducting a detailed study of the seafloor microtopography and the predominant oceanographic dynamics in the study area. Different fine-scale spatial bedforms were identified, such as ripples, dunes, burrows, mounds, obstacle marks, rock bottoms, and low-roughness bottoms using underwater images. Besides, a geostatistical study of the different video transects studied was carried out and allowed us to differentiate three types of bottoms depending on the processes that affect their microtopography.En prens
MorfometrĂa de montĂculos submarinos del talud inferior del margen continental canario (O de las Islas Canarias): Análisis basado en un MDT
We present a morphometric analysis of 41 mounded edifices located on the seafloor to the
west of Canary Islands, using a 150 m resolution DEM and very high-resolution seismic profiles. In
order to carry out morphometric computation a set of variables (slope, size and shape) were
calculated using ArcGIS Analyst tools. A mapping cluster has been generated using Grouping Analyst
ArcGIS Statistics toolset where seven differents morphometric groups have been distinguished. Four
main types of edifice shapes have been identified within the seven morphometric groups. The first
type is a single giant dome elevation that can be considered as an outlier mound. The second type is
the most frequent and can be considered as the standard type mound on the Canary continental
slope due to its intermediate morphology. They show extrusive seismic characteristics in seismic
profiles. The third type is morphologically derived from type 2, representing steeper and higher
mounds related with extrusive processes whereas the fourth type represents smoother and flatter
mounds related to faulting. This study shows that an elaborated geomorphometry resolves between
types of extrusive edifices from those under tectonic conditionsVersiĂłn del edito
A preliminary characterization of greenhouse gas (CH4 and CO2) emissions from Gulf of Cadiz mud volcanoes
Morphological characterization of contourite and mass-wasting recent processes at the Guadalquivir Bank Margin uplift, Gulf of Cádiz
The Gulf of Cadiz records the interplay of a variety of sedimentary processes related to the
circulation of water masses. The most important one is the Mediterranean Outflow Water (MOW) that
exits the Mediterranean Sea, but other water masses also affect the seafloor, with complex variations
along time and space. This work studies the interplay between oceanographic and gravitational
sedimentary processes on the Guadalquivir Ridge, based on bathymetry and high-resolution seismic
profiles. A series of morphological features including flat terraces, circular/elliptical depressions, semicircular
scarps and valley-shaped features are analysed in order to better understand the interaction
between water masses circulation and mass-wasting processes of the Gulf of Cadiz.VersiĂłn del edito
Los Montes Submarinos de la Plataforma Marginal de Motril, Mar de Alborán: Interacción con las Masas de Agua Profunda
VersiĂłn del edito
From hyperextended rift to convergent margin types: mapping the outer limit of the extended Continental Shelf of Spain in the Galicia area according UNCLOS Art. 76
European Geosciences Union General Assembly (2017. Viena)Spain presented on 11 May 2009 a partial submission for delimiting the extended Continental Shelf in respect to the area of Galicia to the Commission on the Limits of the Continental Shelf (CLCS). The Galicia margin represents an example of the transition between two different types of continental margins (CM): a western hyperpextended margin and a northern convergent margin in the Bay of Biscay. The western Galicia Margin (wGM 41Âş to 43Âş N) corresponds to a hyper-extended rifted margin as result of the poly-phase development of the Iberian-Newfoundland conjugate margin during the Mesozoic. Otherwise, the north Galicia Margin (nGM) is the western end of the Cenozoic subduction of the Bay of Biscay along the north Iberian Margin (NIM) linked to the Pyrenean-Mediterranean collisional belt.Instituto GeolĂłgico y Minero de España, EspañaCentro Oceanográfico de Málaga, Instituto Español de OceanografĂa, EspañaInstituto Hidrográfico de la Marina, Españ
Modelización de los end-members para reconocer fuentes de aporte sedimentario en contornitas: un caso de estudio en el Mar de Alborán
Contourite drifts are one the main morphosedimentary features in the Alboran Sea and
their sediments are important archives of the past oceanographic conditions and sedimentary
processes. The end-member modelling approach lets to decompose multimodal grain-size
distribution into genetically meaningful subpopulation that may be related to different sediment
transport mechanisms and source areas. Three end-members have been identified in the contourite
drift and moat system located at the southern side of the Dijbouti Ville seamount that have been
interpreted in terms of sediment sources. Two end-members point to an eolian source and comprise
fine silt (EM1) and coarse silt (EM2) as modal grain-sizes, characterized by high and low contents,
respectively, of terrigenous elements (Al, Si, Ti and K). The third end-member (EM3) indicates a
fluvial origin and is mainly defined by a clay modal grain-size of intermediate and homogeneous
content in terrigenous elements. Downcore variation of the relative proportion of these EMs can be
used to decipher paleocenographic and paleoclimatic conditions in the Alboran Sea.VersiĂłn del edito
Caracterización preliminar de emisiones de gases de efecto invernadero (CH4 y CO2) procedentes de volcanes de fango del Golfo de Cádiz
Mud volcanism represents an important migration pathway for methane and other gases
from deeper reservoirs to the surface; however most submarine sources remain poor quantified.
During SUBVENT2 cruise, water column over several mud volcanoes were surveyed for gas seepage
characterization. Water samples of ROV Niskin and Rosette-CTD Niskin bottles were recovered above
the Bonjardim, El Cid, Las Negras, Mercator, Algacel, Mvseis, Madrid and Yuma mud volcanoes, and
at three newly discovered, mud volcano like structures, to quantify overall gases release fluxes from
seabed. CO2 and CH4 concentrations were measured by potentiometric titration and using a gas
chromatograph, respectively, in order to understand the relationship between physicochemical and
geological processes. Gases concentrations decreased from shallower to deeper mud volcanoes.
Values varied widely within 50 to 200 nM for CH4 and between 400 to 1500 ÎĽatm for fCO2.
Greenhouse gases variations were large influenced by water column depth, temperature, salinity
and possibly by anaerobic oxidation of methane (AOM). Our observations suggest that the emission
of methane and carbon dioxide from the mud volcanoes structures studied here may be relevant at
the present as a part of the carbon global cycle.VersiĂłn del edito
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