Macrofaunal assemblages from an inactive pockmark field in the Estremadura Spur (West Iberian margin)

Abstract During glacial times, the North Atlantic region was affected by serious climate changes corresponding to Dansgaard-Oeschger cycles that were linked to dramatic shifts in sea temperature and moisture transfer to the continents. However, considerable efforts are still needed to understand the effects of these shifts on terrestrial environments. In this context, the Iberian Peninsula is particularly interesting because of its close proximity to the North Atlantic, although the Iberian interior lacks paleoenvironmental information so far because suitable archives are rare. Here we provide an accurate impression of the last glacial environmental developments in central Iberia based on comprehensive investigations using the upper Tagus loess record. A multi-proxy approach revealed that phases of loess formation during Marine Isotope Stage (MIS) 2 (and upper MIS 3) were linked to utmost aridity, coldness, and highest wind strengths in line with the most intense Greenland stadials also including Heinrich Events 3–1. Lack of loess deposition during the global last glacial maximum (LGM) suggests milder conditions, which agrees with less-cold sea surface temperatures (SST) off the Iberian margin. Our results demonstrate that geomorphological system behavior in central Iberia is highly sensitive to North Atlantic SST fluctuations, thus enabling us to reconstruct a detailed hydrological model in relation to marine–atmospheric circulation patterns.

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Seasonal deposition and reworking at the sediment-water interface on the northwestern Iberian margin

Progress In Oceanography ◽

10.1016/s0079-6611(02)00014-9 ◽

2002 ◽

Vol 52 (2-4) ◽

pp. 331-348 ◽

Cited By ~ 21

Author(s):

S. Schmidt ◽

Tj.C.E. van Weering ◽

J.-L. Reyss ◽

P. van Beek

Keyword(s):

Water Interface ◽

Seasonal Deposition ◽

Iberian Margin

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A pockmark field in the Central Barents Sea; gas from a petrogenic source?

Polar Research ◽

10.1111/j.1751-8369.1985.tb00492.x ◽

1985 ◽

Vol 3 (1) ◽

pp. 11-19 ◽

Cited By ~ 30

Author(s):

ANDERS SOLHEIM ◽

ANDERS ELVERHøI

Keyword(s):

Barents Sea ◽

Petrogenic Source ◽

Pockmark Field

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EVIDENCE OF MANTLE INHERITANCE ON THE ULTRA-DISTAL WESTERN IBERIAN MARGIN FROM TRANSFORMED TOTAL MAGNETIC ANOMALY

Brazilian Journal of Geophysics ◽

10.22564/rbgf.v36i3.1957 ◽

2018 ◽

Vol 36 (3) ◽

pp. 1 ◽

Cited By ~ 2

Author(s):

Luizemara Soares Alves Szameitat ◽

Francisco José Fonseca Ferreira ◽

Gianreto Manatschal ◽

Monica da Costa Pereira Lavalle Helbron

Keyword(s):

Steady State ◽

Magnetic Anomaly ◽

Oceanic Crust ◽

Oceanic Lithosphere ◽

Magnetic Data ◽

Continental Lithosphere ◽

Flow Lines ◽

Passive Margins ◽

Magnetic Features ◽

Iberian Margin

ABSTRACT. Inheritance on continental lithosphere is considered as an important aspect on passive margins, since they may control magmatic budget and strain evolution during rifting and lithospheric breakup. On the distal Western Iberian margin, the transition to a steady state oceanic crust was little sampled and less investigated, in comparison to the more proximal parts near to the continental edge. In this work, we use marine magnetic data to analyze some aspects of the transition between the zone of exhumed continental mantle (ZECM) and the unequivocal oceanic crust, using transformed magnetic data. We observe that the end of the ZECM presents some straight magnetic features, especially at the eastern limit of the J anomaly. These magnetic lineaments are consistent with Early Cretaceous flow lines of the Iberian Plate. Straight structures are not expected in a newly formed oceanic lithosphere. Instead, it seems to be controlled by mantle inheritance. These straight magnetic features may indicate basement inheritance controlling magmatic insertions at the beginning of the oceanic crust formation.Keywords: Iberia, Magnetometry, Ocean-Continent Transition, Inherited Structures, Magma-Poor Margin. RESUMO. Estruturas herdadas na litosfera continental são um aspecto importante em margens passivas, pois poderão condicionar a entrada de magma e a evolução da deformação durante o rifteamento e quebra litosférica. Na porção distal da Margem Ibérica Ocidental, a transição da crosta continental até a crosta oceânica bem estabelecida possui menos dados e é menos investigada em comparação com a porção junto do limite de crosta continental. Neste trabalho, usamos dados magnéticos marinhos para analisar alguns aspectos entre a zona de exumação mantélica e a crosta oceânica inequívoca, através de dados magnéticos transformados. Observa-se que o final da zona de exumação mantélica apresenta algumas feições retilíneas, especialmente no limite leste da Anomalia J. Estes lineamentos magnéticos estão em conformidade com linhas de fluxo mesozoicas da Placa Ibérica. Feições retilíneas não são esperadas em uma litosfera oceânica neoformada. Ao contrário, estas aparentam ser um controle dado por estruturas pretéritas do manto. Portanto, estas feições magnéticas retilíneas sugerem uma herança do embasamento continental controlando as intrusões magmáticas no início da formação da crosta oceânica.Palavras-chave: Ibéria, Magnetometria, Transição Continente-Oceano, Estruturas Herdadas, Margem Pobre em Magma.

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How deep does sand deposits in the Alentejo basin (Gulf of Cadiz) reach? Evaluating slope stability from bottom-current activities through time

10.5194/egusphere-egu2020-18904 ◽

2020 ◽

Author(s):

Davide Mencaroni ◽

Roger Urgeles ◽

Jonathan Ford ◽

Jaume Llopart ◽

Cristina Sànchez Serra ◽

...

Keyword(s):

Pore Pressure ◽

Sediment Supply ◽

Excess Pore Pressure ◽

Bottom Current ◽

Gulf Of Cadiz ◽

Strait Of Gibraltar ◽

Gulf Of Cádiz ◽

The Stability ◽

Iberian Margin ◽

Excess Pore

Contourite deposits are generated by the interplay between deepwater bottom-currents, sediment supply and seafloor topography. The Gulf of Cadiz, in the Southwest Iberian margin, is a famous example of extensive contourite deposition driven by the Mediterranean Outflow Water (MOW), which exits the Strait of Gibraltar, flows northward following the coastline and distributes the sediments coming from the Guadalquivir and Guadiana rivers. The MOW and related contourite deposits affect the stability of the SW Iberian margin in several ways: on one hand it increases the sedimentation rate, favoring the development of excess pore pressure, while on the other hand, by depositing sand it allows pore water pressure to dissipate, potentially increasing the stability of the slope.In the Gulf of Cadiz, grain size distribution of contourite deposits is influenced by the seafloor morphology, which splits the MOW in different branches, and by the alternation of glacial and interglacial periods that affected the MOW hydrodynamic regimes. Fine clay packages alternates with clean sand formations according to the capacity of transport of the bottom-current in a specific area. Generally speaking, coarser deposits are found in the areas of higher MOW flow energy, such as in the shallower part of the slope or in the area closer to the Strait of Gibraltar, while at higher water depths the sedimentation shifts to progressively finer grain sizes as the MOW gets weaker. Previous works show that at present-day the MOW flows at a maximum depth of 1400 m, while during glacial periods the bottom-current could have reached higher depths.In this study we derived the different maximum depths at which the MOW flowed by analyzing the distribution of sands at different depths along the Alentejo basin slope, in the Northern sector of the Gulf of Cadiz.Here we show how changes in sand distribution along slope, within the stratigraphic units deposited between the Neogene and the present day, are driven by glacial &#8211; interglacial period alternation that influenced the hydrodynamic regime of the MOW.By deriving the depositional history of sand in the Alentejo basin, we are able to correlate directly the influence that climatic cycles had on the MOW activity. Furthermore, by interpreting new multi-channel seismic profiles we have been able to derive a detailed facies characterization of the uppermost part of the Gulf of Cadiz.An accurate definition of sand distribution along slope plays an important role in evaluating the stability of the slope itself, e.g. to understand if the sediments may be subjected to excess pore pressure generation. As sand distribution is a direct function of the bottom-current transport capacity, the ultimate goal of this study is to understand how climate variations can affect the stability of submarine slope by depositing contourite-related sand.

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