35 documents found, page 1 of 4
Age dependent variation of the magnetic fabric of dike swarms and implications ...
Moreira, Mário; Mata, João; Madeira, José; Represas, Patricia; Martins, SofiaABSTRACT: Magnetic fabric analysis of dikes is a powerful technique when assessing magma transfer processes. This study presents an integrated analysis combining magnetic susceptibility and anisotropy of magnetic susceptibility, magnetic mineralogy, geochemistry and new 40Ar/39 Ar dating of dikes intruding formations ranging from the Lower Cretaceous to the Miocene on the island of Maio, in the Cabo Verde archi...
Investigating the hydrothermal activity at Fogo volcano (Cape Verde) using geoc...
Candeias, Carla; Rocha, Fernando; Dumont, Stéphanie; Maineult, Alexis; Ramalho, Ricardo; Madeira, José; Antunes, JoãoABSTRACT: Characterizing hydrothermal systems at volcanoes is particularly important as they play a crucial role in controlling eruptive dynamics. On the long term, hydrothermal systems participate in the geochemical alteration of both rocks and soils, through hydrolysis, dissolution, mineral precipitation, and secondary mineralization contributing in the gradual destabilization of volcanic structures. Fogo vol...
A glycymeris-rich unit as evidence of a late pleistocene tsunami event from NW ...
Doukani, Mohamed Amine; Satour, Linda; Ozer, Caner Kaya; Belkebir, Lahcene; Voelker, Antje; Tedjeddine, Hassane; Landau, Bernard; Uchman, AlfredCompared to the extensive research carried out on the Neogene deposits of the Lower Chelif Basin, the Pleistocene series is still poorly studied, with no detailed lithological succession published to date. This study focuses on the Glycymeris-rich Unit (GRU) along the coastal area of the Hachacha Plateau in Northwestern Algeria. This unit unconformably overlies Miocene, Pliocene, and Pleistocene basements. The ...
First evidence of ants (Hymenoptera, Formicidae) in the early Pleistocene of Ma...
Marques, Carlos A. Góis; Correia, Pedro; Nel, Andre; Madeira, José; Sequeira, Miguel Menezes deTo be successfully established on oceanic islands, native ants (Hymenoptera: Formicidae) have to migrate from the mainland or from nearby islands, crossing the ocean barriers, to find a suitable habitat. Despite the general interest on oceanic islands biotas, nothing is known about the deep-time migration and settling of native ants in these insular ecosystems. Palaeoentomological studies on oceanic islands tha...
The bicentenary of Georg Hartung, a German pioneer geologist, explorer and illu...
Marques, Carlos A.Góis; Sequeira, Miguel Menezes de; Madeira, JoséWe present a tribute to Georg Friedrich Karl Hartung (1821–1891), a less-known, non-academic German geologist, on his 200th birthday anniversary. Influenced by eminent 19th century scientific personalities, such as Oswald Heer, Charles Lyell, and Alexander von Humboldt, he performed pioneer geological observations and sampling in the Azores, Madeira, and Canary Islands volcanic archipelagos. Later in his life, ...
Diverse bioerosion structures in lower Pliocene deposits from a volcanic oceani...
Dávid, Árpád; Uchman, Alfred; Ramalho, Ricardo Dos Santos; Madeira, José; Melo, Carlos; Madeira, Patrícia; Rebelo, Ana Cristina; Berning, BjörnPliocene body fossils from Santa Maria Island, Azores, have been studied for decades, but only more recently have ichnofossils received their due attention. Calcareous Pliocene deposits from the Baía de Nossa Senhora section contain numerous, diverse, well-preserved natural casts of invertebrate borings. The study of this type of fossils adds to knowledge on the dispersal of benthic faunas across oceans to volc...
Megatsunamis Induced by Volcanic Landslides in the Canary Islands: Age of the T...
Ferrer, Mercedes; González de Vallejo, Luis; Madeira, José; Andrade, César; García-Davalillo, Juan C.; Freitas, Maria Da Conceição; Meco, JoaquínEvidence for frequent, large landslides on the flanks of the volcanic edifices forming the Canary Islands include outstanding landslide scars and their correlative submarine and subaerial rock and debris avalanche deposits. These landslides involved volumes ranging from tens to hundreds of km3. The sudden entry of large volumes of rock masses in the sea may have triggered tsunamis capable of affecting the sourc...
The bicentenary of Georg Hartung, a German pioneer geologist, explorer, and ill...
Góis-Marques, Carlos A.; Menezes de Sequeira, Miguel; Madeira, JoséWe present a tribute to Georg Friedrich Karl Hartung (1821–1891), a less-known, non-academic German geologist, on his 200th birthday anniversary. Influenced by eminent 19th century scientific personalities, such as Oswald Heer, Charles Lyell, and Alexander von Humboldt, he performed pioneer geological observations and sampling in the Azores, Madeira, and Canary Islands volcanic archipelagos. Later in his life, ...
Tracing insular woodiness in giant Daucus (s.l.) fruit fossils from the Early P...
Góis-Marques, Carlos A.; Nascimento, Lea de; Fernández‐Palacios, José María; Madeira, José; Sequeira, Miguel Menezes dePlants on oceanic islands can evolve insular syndromes such as secondary woodiness, a generalized trend found in island floras worldwide. This phenomenon occurs through evolution in situ. It is triggered by ecological and physiological stimuli that trans form herbaceous annuals into woody perennials. However, well-dated and informative fossils that could help track and frame the evo lution of this syndrome are ...
A geological record of multiple Pleistocene tsunami inundations in an oceanic i...
Madeira, José; Ramalho, Ricardo S.; Hoffmann, Dirk L.; Mata, João; Moreira, MárioIn the Central Atlantic archipelagos - the Canaries, Cape Verde, Madeira and the Azores - tsunami hazard is often regarded as low, when compared with other extreme wave events such as hurricanes and storms. The geological record of many of these islands, however, suggests that tsunami hazard may be underestimated, notwithstanding being lower than in areas adjacent to subduction zones, such as the margins of the...