Pedro Costa | University of Coimbra (original) (raw)

Papers by Pedro Costa

Resumo: Cada ambiente sedimentar é caracterizado por uma dinâmica peculiar e por condições especí... more Resumo: Cada ambiente sedimentar é caracterizado por uma dinâmica peculiar e por condições específicas de energia que se traduzem em atributos de natureza estrutural, estratigráfica, textural e composicional dos sedimentos. Algumas características são impostas no local da deposição, outras são herdadas da área ou material-fonte e outras ainda serão impostas durante o transporte. Sendo as microtexturas superficiais muito sensíveis a modificações dos parâmetros ambientais, é expectável que a superfície de cada grão de quartzo corresponda a um palimpsesto, no qual as microtexturas mais recentes correspondam essencialmente às condicionantes impostas pelo último episódio de remobilização ou de remodelação da superfície do grão. O capítulo inclui um atlas de microtexturas, comentadas, obtidas em grãos de quartzo colhidos em diferentes locais da costa algarvia, que ilustram o conjunto de microtexturas mais frequentes em ambientes litorais e peri-litorais. A reorganização das 18 marcas/atributos microtexturais aqui descritas em 5 tipos fundamentais (rolamento, superfícies recentes, marcas de percussão, dissolução e partículas aderentes) parece suficiente para diferenciar os ambientes e discriminar assinaturas microtexturais impressas pelo transporte dos grãos. O número de grãos de quartzo da mesma classe granulométrica necesssários à caracterização microtextural de uma amostra de areia é, no mínimo, de 12 e, preferivelmente, ≥30. A aplicação de análise microtextural em estudos sedimentares tem sido especialmente orientada no sentido de determinar a origem dos grãos de quartzo e identificar os processos activos até à sua deposição ou os pós-deposicionais, com incidência especial nos episódios de imobilização (pedogénese), transporte em contextos recentes, fluviais e glaciais.

Planetary and Space Science, 2010

Martian gullies are widespread landforms in the mid-latitudes of Mars. When the first reports of ... more Martian gullies are widespread landforms in the mid-latitudes of Mars. When the first reports of these kilometre-scale features were published in 2000, they were controversially hailed as a sign of recent flows of liquid water on the surface of Mars. This supposition was contrary to our understanding of recent environmental conditions on Mars, under which water should not exist in its liquid form. In response to their discovery, researchers proposed a wide range of scenarios to explain this apparent paradox, including scenarios driven by CO 2 , climate change or the presence of a liquid water aquifer. This Special Publication is a collection of papers arising from the topics discussed at the Second International Workshop on Martian Gullies held at the Geological Society, London. A review paper opens the Special Publication and thereafter the papers are presented under three themes: Martian remote sensing, Earth analogues and laboratory simulations. This Special Publication establishes the state of the art in Martian gully research, presents the latest observations and interpretations of the present-day activity and long-term evolution of Martian gullies, explores the role of Earth analogues, highlights novel experimental work and identifies future avenues of research. The importance of gullies as a potential marker of habitable environments on Mars underlines their importance in framing space exploration programmes. Gold Open Access: This article is published under the terms of the CC-BY 4.0 license.

The Holocene, 2019

Estuaries are sensitive to changes in global to regional sea level, to climate-driven variation i... more Estuaries are sensitive to changes in global to regional sea level, to climate-driven variation in rainfall and to fluvial discharge. In this study, we use source and environmentally sensitive proxies together with radiocarbon dating to examine a 7-m-thick sedimentary record from the Sado estuary accumulated throughout the last 3.6 kyr. The lithofacies, geochemistry and diatom assemblages in the sediments accumulated between 3570 and 3240 cal. BP indicate a mixture between terrestrial and marine sources. The relative contribution of each source varied through time as sedimentation progressed in a low intertidal to high subtidal and low-energy accreting tidal flat. The sedimentation proceeded under a general pattern of drier and higher aridity conditions, punctuated by century-long changes of the rainfall regime that mirror an increase in storminess that affected SW Portugal and Europe. The sediment sequence contains evidence of two periods characterized by downstream displacement of...

Marine Geology, 2017

Southern cliffs on Santa Maria Island in the Azores archipelago (North Atlantic Ocean) feature su... more Southern cliffs on Santa Maria Island in the Azores archipelago (North Atlantic Ocean) feature submarine volcanic sequences inter-bedded with Pliocene coralline algal limestone, shelly coquinas, and mixed volcaniclastic-calcarenite sandstone. Within the 20-m sedimentary succession at Malbusca, a singular, 5-m sandstone bed is distinguished by dark and light laminae dominated alternately by heavy minerals and carbonate detritus. Carbonate grain-size varies between that of coarse silt and very fine sand. The basal part shows coarser and more poorly sorted sand in an upward transition to increasingly finer carbonates. Accessible over a lateral space of 34 m, the big bed is shouldered against and overlaps the remnants of a drowned rocky shore with a paleorelief of 4 m that preserves intertidal to shallow subtidal biotas. Extrapolated from the big bed's rock face (1,830 m 2) and the width of the eroded shelf on which it resides (8 m), calculations yield a projected volume of 14,500 m 3. Unique to the island, the big bed is interpreted as a major hurricane deposit that moved sand from an offshore bar in an onshore path. Such an event fits the context of the Pliocene Warm Period, during which global El Niño conditions were more intense than today.

Zeitschrift für Geomorphologie, Supplementary Issues, 2018

This article is a response to the publication by Nick Marriner, David Kaniewski, Christophe Morha... more This article is a response to the publication by Nick Marriner, David Kaniewski, Christophe Morhange, Clément Flaux, Matthieu Giaime, Matteo Vacchi and James Goff entitled "Tsunamis in the geological record: Making waves with a cautionary tale from the Mediterranean", published in October 2017 in Science Advances. Making use of radiometric data sets published in the context of selected palaeotsunami studies by independent research groups from different countries, Marriner et al. (2017) carried out statistical and time series analyses. They compared their results with an assessment of Mediterranean storminess since the mid-Holocene that was previously published by Kaniewski et al. (2016) based on a single-core study from coastal Croatia. Marriner et al. (2017) now present "previously unrecognized" 1500-year "tsunami megacycles" which they suggest correlating with Mediterranean climate deterioration. They conclude that up to 90% of all the 'tsunamis&#...

Remote Sensing

Coastal monitoring is a topic continuously developing, which has been applied using different app... more Coastal monitoring is a topic continuously developing, which has been applied using different approaches to assess the meteo-marine features, for example, to contribute to the development of improved management strategies. Among these different approaches, coastal video monitoring coupled with recent machine learning and computer vision techniques has spread widely to assess the meteo-marine features. Video monitoring allows to obtain large spatially and temporally datasets well-distributed along the coasts. The video records can compile a series of continuous frames where tide phases, wave parameters, and storm features are clearly observable. In this work, we present LEUCOTEA, an innovative system composed of a combined approach between Geophysical surveys, Convolutional Neural Network (CNN), and Optical Flow techniques to assess tide and storm parameters by a video record. Tide phases and storm surge were obtained through CNN classification techniques, while Optical Flow techniqu...

A key issue in coastal hazards research is the need to distinguish sediments deposited by past ex... more A key issue in coastal hazards research is the need to distinguish sediments deposited by past extreme storms from those of past tsunamis. This study contributes to this aim by investigating patterns of sedimentation associated with extreme coastal flood events, in particular, within the Lagoa deÓbidos (Portugal). The recent stratigraphy of this coastal lagoon was studied using a wide range of techniques including visual description, grain-size analysis, digital and x-ray photography, magnetic susceptibility and geochemical analysis. The sequence was dated by 14 C, 210 Pb and Optically Stimulated Luminescence. Results disclose a distinctive coarser sedimentary unit, within the top of the sequence studied, and shown in quartz sand by the enrichment of elements with marine affinity (e.g., Ca and Na) and carbonates. The unit fines upwards and inland, thins inland and presents a sharp erosive basal contact. A noticeable post-event change in the sedimentary pattern was observed. The likely agent of sedimentation is discussed here and the conceivable association with the Great Lisbon tsunami of AD 1755 is debated, while a comparison is attempted with a possibly synchronous deposit from a tsunami in Martinhal (Algarve, Portugal). The possibility of a storm origin is also discussed in the context of the storminess of the western Portuguese coast and the North Atlantic Oscillation. This study highlights certain characteristics of the sedimentology of the deposits that may have a value in the recognition of extreme marine inundation signatures elsewhere in the world.

have been distinguished in TAH17-1 core (Fig. 5). These layers present at least one of the follow... more have been distinguished in TAH17-1 core (Fig. 5). These layers present at least one of the following characteristics: a well-defined sandy layer, interbedded in fine estuarine sediments; an enrichment in Ca and Zr indicating a marine source of the sediment, and depletion in terrigenous elements (Rb); the presence of sedimentation structures such as rip-up clasts and/or sediment discontinuity"

Dear authors, thanks for the opportunity to review your work on Reconstruction of flow conditions... more Dear authors, thanks for the opportunity to review your work on Reconstruction of flow conditions from 2004 Indian Ocean tsunami deposits at the Phra Thong island using a deep neural network inverse model. I deeply appreciated your effort and I consider that this manuscript has potential to be accepted for publication at NHESS after some major revisions. I detailed them on over 100 comments on the annotated version attached.

Earth-Science Reviews, 2021

This paper reviews the evidence for onshore sedimentary imprints of tsunami inundation known from... more This paper reviews the evidence for onshore sedimentary imprints of tsunami inundation known from the geological record of the Atlantic basin. The central aim of the paper is to offer a broad overview on the main deposits and key localities that have been documented along the Atlantic coastlines, and which attest to the local or regional impact of tsunamis during historical, pre-historical and recent geological times. Considerable detail is devoted to summarising key diagnostic criteria used to identify the deposits as tsunami-derived, and to set each deposit in its own unique geomorphological setting and context, always referring to the latest scientific knowledge of the events that generated them. The paper also discusses the relationships between the different tsunamigenic sources that concurred to the formation of the deposits, as well as critical information on magnitude and frequency, as inferred from the sedimentary responses preserved in the sediment archives. Documented case studies range from the well-studied landslide-triggered and earthquake-triggered Storegga and 1755 Lisbon tsunamis, respectively, to collapse-and eruption-triggered tsunamis in the Atlantic archipelagos, to other less well-known events in the south Atlantic, Caribbean and Arctic. Despite its less frequent tsunami recurrence, the Atlantic coastal stratigraphy presents some world-class case studies and outstanding outcrops, from which critical knowledge can be gained with respect to some of the most enigmatic aspects of tsunami science.

Heavy-mineral weight in total sediment fraction presented a mean value of 31%, ranging between 18... more Heavy-mineral weight in total sediment fraction presented a mean value of 31%, ranging between 18 and 59%. The magnetite weight percentage present in the heavy-mineral fraction has a mean of 26% ranging between 14 and 43%. Considering the mean frequency of the transparent heavy minerals it was identified the presence of orthopyroxenes (67%), followed by clinopyroxenes (30%). These results indicate that the main original source of heavy minerals are basic volcanic rocks. The

Natural Hazards and Earth System Sciences Discussions, 2019

The 2004 Indian Ocean Tsunami and the 2011 Great East Japan earthquake and tsunami caused largesc... more The 2004 Indian Ocean Tsunami and the 2011 Great East Japan earthquake and tsunami caused largescale topographic changes in coastal areas. Whereas much research has focused on coastlines that have or had large human populations, little focus has been paid on coastlines that have little or no infrastructure. The importance of examining erosional and depositional mechanisms of tsunami events lies in the rapid reorganisation that coastlines must undertake immediately after an event. Through understanding the precursor conditions to this reorganisation is paramount to the reconstruction of the coastal environment. This study examines the locations of sediment erosion and deposition during the 2004 Indian Ocean Tsunami event on the relatively pristine Phra Thong Island, Thailand. Coupled with satellite imagery, we use numerical simulations and sediment transportation models to determine the locations of significant erosion and the areas where much of that sediment was redeposited during the tsunami inundation and backwash processes. Our modelling approach confirms that beaches on Phra Thong Island were significantly eroded by the 2004 tsunami, predominantly during the backwash phase of the first and largest wave to strike the island. Although 2004 tsunami sediment deposits are found on the island, we demonstrate that most of the sediment was deposited in the shallow coastal area, facilitating quick recovery of the beach when normal coastal processes resume.

Geomorphology, 2018

A comparison of younger post-Olduvai paleosol horizons with older buried horizons of Plio/Pleisto... more A comparison of younger post-Olduvai paleosol horizons with older buried horizons of Plio/Pleistocene age shows that primary and secondary minerals and organic molecules in sand coatings in these paleosols remain intact and provide a record of past weathering events. From IR spectra, concentrations of organic and some inorganic constituents within these coatings reveal supporting evidence of variable weathering trends from Late Pliocene to Holocene time. With some variability, hematite and goethite concentrations in sand coatings parallel similar variable concentrations of secondary Fe-extractable concentrations previously determined for pre-and post-Olduvai paleosols in these Mt. Kenya sections. Negative correlations between metahalloysite and gibbsite, previously determined to result from aggressive leaching of Si from metahalloysite in paleosols, tend to follow similar distributions in the sand coatings reported here. Similarly, additions of gibbsite in selected paleosol horizons are followed by reductions of lesser concentrations of metahalloysite, suggesting that individual horizons within paleosols have independent leaching histories different from the entire paleo-pedon. As with these paleosols

Journal of Sedimentary Research, 2017

The aim of this work is to identify and characterize microtextural signatures in silica glass gra... more The aim of this work is to identify and characterize microtextural signatures in silica glass grains (used as analogous to quartz) that are produced during aqueous transport at different flow velocities, with variable sediment concentrations, transport distances, and time intervals. To achieve this, an open-channel flow experiment was conducted with a mixture of sand and silica glass microspheres in varying conditions-velocity (from 0.67 to 1.4 m/s), duration (1 or 10 minutes), distance (0 to 2.5 m) and sediment concentration (60 or 80%). Experimental conditions were used to replicate natural phenomena such as river superficial velocity or coastal swash processes. Before the experiment the microsphere surfaces were imaged and clear of any microtextural imprint. Increasing velocity, distance, and sediment concentration exhibited a strong correlation with higher numbers of surfaces abundantly covered with microtextures of mechanical origin (i.e., craters, abrasion marks, and v-shaped percussion marks). SEM microphotographs of silica were analyzed and classified to provide examples of the specific microtextures produced during the open-channel flow experiment. The purpose of the experiment was to characterize surface microscopic signatures in quartz grains replicating hydrodynamic conditions of coastal and fluvial environments. The results demonstrated a strong correlation between higher velocities (and higher sediment concentrations) and a larger presence of microtextural mechanical imprints in the grains analyzed, thus demonstrating a clear relation between microtextural imprints and water flow modes. These results have important implications for future microtextural works analyzing grain imprints and their relation to sediment transport types. An example demonstrated here is that the higher presence of v-marks could be used as an indicator of supercritical flow conditions.