Shore Platforms in the Algarve (South Portugal) Rocky Coast, an Inheritance of the Last Interglacial Stage?

Shore platforms, notches, and marine caves are common yet distinctive morphological features along the southern coast of Portugal. The central Algarve rocky coast has provided a favorable setting in which to understand the processes contributing to shore platform development. This is because the morphology and characteristics of the features vary along the coast, as do several factors implicated in their development such as wave climate (including wave direction and frequency), seabed morphology and depth, bedrock lithology, karstification and geological structure

Interannual sub-aerial beach variability along a sector of the Tróia- Sines embayed coast

The comprehension of sub-aerial beach variability of sandy beaches is essential to describe and predict his behaviour after extreme events (e.g. storms). Around the world coastline beach monitoring plans are established in order to characterize the main morphodynamic changes at different spatial and temporal scales. Within this scope, four field surveys (19th to 28th May 2009; 30th October to 10th November 2009, 21th to 30th May 2010 and 14l to 21 April 2011), using a new coastal survey system named INSHORE system(Differential Global Positioning System) [1], were conducted along the Tróia-Sines embayed beach (INSHORE project -PTDC/AMB/73169/2006). The interannual variability of the sub-aerial beach topography along the Tróia-Sines embayed coast for the first three field surveys were analysed considering the DEM (Digital Elevation Model) analysis regarding the: alongshore coastline configuration; subaerial beach width; beach profile configuration and volumetric changes. The results points to the definition of eight main coastline sectors very similar to the results previously described by [2]. Although a general north-south increasing beach width trend can be observed, [3] one of these main sectors, Sector 6, presents a significant variation of the beach width and beach profile configuration. This sector was selected to describe the morphodynamic pattern responsible for the sediment accommodation (beach width, and profile configuration) during the studied period. The subtraction between the three DEMs points to the importance of the beach width variation that describes the landward or seaward subaerial beach displacement. Although this might affect the beach width, this variable should not be taken as the unique one to describe the shoreline change. In fact, this parameter does not describe the beach variability regarding the profile configuration (e.g. berm width and sediment accommodation). According to our results the volumetric changes are strictly related to the beach width variation but the profile configuration has a particular role in the final budget analysis. The proxies that were used (+2m, +3.4m and +4,3m MSL elevation contours) and the relation between the beach width and subaerial beach volume, has given high correlation values. These results proved that not only the MHW (mean high water) used by others authors [4] can be defined as a proxy to describe the shoreline evolution, but also other morphodynamic meaningful contour elevations can give reliable results

Palaeosurface reconstruction based on sedimentary record and in sea level evolution in the Guadiana Estuary (Southern Iberia)

The sedimentary infilling of the Guadiana estuary, in the Southern Iberian Peninsula, has been extensively studied using a variety of laboratory methods, namely geochemical and sedimentological analyses, foraminifera assemblages and palynological profiles, supported by 14C dating [1-3](...

Geophysical characterization of the Cercal Paleozoic structure, Iberian Pyrite Belt, from a mineral exploration perspective

ABSTRACT: The Cercal Volcano-Sedimentary Complex (Cercal VSC) structure is the westernmost sector of the Iberian Pyrite Belt (IPB) giant metallogenic province and was explored since Roman times for volcanogenic massive sulphides (VMS) and Fe–Mn (Ba) deposits. However, presently only a single deposit is known, the Salgadinho Cu-Ag-Au stockwork/disseminated deposit. Nevertheless, according to several mining companies that operated in the area during the last two decades, the Cercal area keeps a high potential for the discovery of new massive and stockwork mineralization deposits hosted in VSC felsic volcanic rocks. The lack of seismic data and deep drill holes (> 800 m), has been limiting the discovery of possible deep seated massive/stockwork deposits. The goal of this work is to provide new insights into the Cercal deep and near surface structure through the integrated interpretation of geophysical and geological data and contribute to the discovery of new stockwork or massive sulphide deposits. For this purpose, we reprocessed ground gravity, airborne magnetic/radiometric and electrical resistivity/induced polarization data which was interpreted and integrated with geological data. Data interpretation included 2.5D forward gravimetric modeling constrained by i) a new rock density database (from outcrops and drill-holes) built under the scope of this work, ii) the scarce available drill-holes and iii) geological information. A small magnetic susceptibility/conductivity database based on drill-hole core samples was also built to assist the magnetic and electrical/chargeability data interpretation. The integrated interpretation agrees with some of the expected geological scenarios predicted by surface mapping and exploration drill-hole logs in the IPB and provides further details on the deep structure of the Cercal Anticline, a NNW-SSE oriented VSC unrooted structure, controlled by variscan SW verging thrust faults and discordant strike-slip Late-Variscan faults. This geological scenario favors the possibility of new findings at relatively shallow depths (200–900 m), and a few sites for further exploration are indicated based on the integrated interpretation. Therefore, this work contributes to the understanding of the Cercal deep structure from a mineral exploration perspective and confirms the proposed structural models for the IPB’s westernmost region.info:eu-repo/semantics/publishedVersio

Morphological features and processes in the central Algarve rocky coast (South Portugal)

Morphological features along the Algarve rocky coast, South Portugal, are identified and described, with an emphasis on shore platforms and notches. The contributions of processes, such as wave attack, chemical weathering and bioerosion, to sculpting the shore platforms are discussed. The preferential localization of shore platforms on sites exposed to waves, and the lack of significant chemical weathering, point to wave erosion as the first-order factor in platform formation, whilst bioerosion/bioprotection, lithology and geological structure determine platform morphological variations. In addition, platforms above the present intertidal zone appear to have a polygenetic evolution, being inherited from former sea-level highstands and currently undergoing chemical weathering. The occurrence of notch features is independent of the degree of exposure to waves, but they mostly occur where the substratum is sand. Hydrostatic pressure appears to be an important factor in the formation of marine caves in the more sheltered sites.Fundação para a Ciência e a Tecnologia. COCHAL Project (POCTI/34162/CTA/00

Holocene sea level fluctuations and coastal evolution in the central Algarve (southern Portugal)

In Armação de Pêra Bay, southern Portugal, environmental changes during the Holocene can be interpreted based on the morphological and sedimentological similarities between older geomorphic features (cemented beach and dune rocks) and present coastal features. Using knowledge of the present beach and dune processes, we propose a two-step model for the evolution of Armação de Pêra Bay. First, during the rapid sea level rise between about 8800 and 6600 yr cal BP, the bay changed from a positive to a negative budget littoral cell and transgressive dunes formed, favoured by drought conditions. At about 5000 yr cal BP, during a sea level maximum, beach width was less than the critical fetch and dunes stabilized and underwent cementation during the wetter Atlantic climatic event. The second phase of dune accumulation started at about 3200 yr cal BP, due to a regression of sea level during which the bay changed back to a positive budget littoral cell in which beach width was greater than the critical fetch. Currently, the beach width is less than the critical fetch, dunes are inactive, and the sedimentary budget is negative due to sediment storage in local river systems.Fundação para a Ciência e a Tecnologia. FEDER, and OE (Project POCTI/CTA/34162/2000

A avaliação de risco sísmico no Algarve: efeito de sítio

As características físicas locais traduzem no seu todo, aquilo a que se designa por efeito de sítio, ou seja, a resposta do substrato geológico a um determinado estímulo como é, neste caso, a propagação de uma onda sísmica. Face a este estímulo, a conjugação dos vários atributos físicos locais, pode resultar na amplificação do movimento do substrato, no aumento do tempo do movimento e na geração de movimentos diferenciais. Este tipo de efeito designa-se por agravamento.Autoridade Nacional de Protecção Civi

Variações do nível médio do mar no Algarve ao longo do Quartenário superior: sector praia da Galé- praia de S. Rafael

Dissertação de mest., Estudos Marinhos e Costeiros, Faculdade de Ciências do Mar e do Ambiente, Univ. do Algarve, 200

Equilibrium configuration of sandy embayed beaches from the Southwest Portuguese rocky coast

The planform of five embayed sandy beaches (São Torpes, Furnas, Amoreira, Monte Clérigo and Arrifana), from the Southwest Portuguese rocky coast were compared to theoretical equilibrium curves (logarithmic spiral and parabolic). The beach planform configurations were defined based on aerial photography and the 2 m (MSL) contour extracted from DGPS field surveys (Furnas and Amoreira beaches). In order to analyse beaches morphodynamic, the volumetric active sediment changes, wave climate characteristics and wave propagation effects to nearshore were characterized. The wave breaking height and beach configuration is responsible for different degrees of exposure to the dominant NW wave direction. Major volumetric changes were largely associated with storm incidence. Comparison between real beach planform and predicted static equilibrium configurations suggests that the Arrifana beach represents a perfect example of a fully developed parabolic bay shape while, the other four beaches are not represented by any theoretical curve approach. In fact, the 2 m (MSL) contour at the Amoreira beach describes a convex beach planform tendency. The effect of the wave direction over the diffraction point was tested but the results points to a low diffraction effect. The Furnas beach revealed a high width variation at the northern extreme related with a more energetic wave climate, dominant from West, with lower diffraction. This study shows that the studied beaches presents a complex dynamic equilibrium that is a function of the subaerial beach configuration, the intertidal bar system variation, the degree of exposure to the dominant NW wave direction and the storm incidence.publishe