The sedimentary rocks of macaronesia

Mitchell-Thomé, Raoul C.

doi:10.1007/bf01821329

Cited by 10 publications

(6 citation statements)

References 25 publications

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“…The precise age of the marine sequence at Corgo do Barrinho has proven difficult to date. It was initially considered as “Vindobonian” (15.5–11.0 Ma) on the basis of its macrofauna [ Romariz , ; Mitchell‐Thomé , ; Zbyszewski et al ., ], using criteria that are now considered invalid [ Mata et al ., ]. Later, Ferreira et al .…”

Section: Discussionmentioning

confidence: 99%

“…The precise age of the marine sequence at Corgo do Barrinho has proven difficult to date. It was initially considered as ''Vindobonian' ' (15.5-11.0 Ma) on the basis of its macrofauna [Romariz, 1971a[Romariz, , 1971bMitchell-Thom e, 1974;Zbyszewski et al, 1975], using criteria that are now considered invalid [Mata et al, 2013]. Later, Ferreira et al [1988] considered it to be younger than 5.2 Ma, based on a K-Ar age on a seemingly subjacent lava flow.…”

Section: Discussionmentioning

confidence: 99%

“…As previous studies note, the absence of obvious submarine volcanic products on the exposed Madeira shield edifice is noteworthy (except for very recent littoral volcanism). However, the presence of in‐sequence marine sediments exposed at Sítio dos Lameiros—a locality within São Vicente Valley and at 300–450 m in elevation (Figure c)—is well documented [e.g., Romariz , ; Mitchell‐Thomé , ; Zbyszewski et al ., ; Mata , ] and recognized as possible evidence for a complex history of vertical movements affecting the island edifice [ Mata , ]. The stratigraphic reconciliation between the presence of marine sediments at those elevations and the apparent absence of submarine volcanic morphologies anywhere on the island is still largely unresolved, a fact mainly attributed to the scarcity of exposures and the lack of detailed island‐scale stratigraphic studies.…”

Section: Geological Settingmentioning

confidence: 99%

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The emergence of volcanic oceanic islands on a slow‐moving plate: The example of Madeira Island, NE Atlantic

Ramalho

Silveira

Fonseca

et al. 2015

Geochem Geophys Geosyst

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The transition from seamount to oceanic island typically involves surtseyan volcanism. However, the geological record at many islands in the NE Atlantic-all located within the slow-moving Nubian plate-does not exhibit evidence for an emergent surtseyan phase but rather an erosive unconformity between the submarine basement and the overlying subaerial shield sequences. This suggests that the transition between seamount and island may frequently occur by a relative fall of sea level through uplift, eustatic changes, or a combination of both, and may not involve summit volcanism. In this study, we explore the consequences for island evolutionary models using Madeira Island (Portugal) as a case study. We have examined the geologic record at Madeira using a combination of detailed fieldwork, biostratigraphy, and 40 Ar= 39 Ar geochronology in order to document the mode, timing, and duration of edifice emergence above sea level. Our study confirms that Madeira's subaerial shield volcano was built upon the eroded remains of an uplifted seamount, with shallow marine sediments found between the two eruptive sequences and presently located at 320-430 m above sea level. This study reveals that Madeira emerged around 7.0-5.6 Ma essentially through an uplift process and before volcanic activity resumed to form the subaerial shield volcano. Basal intrusions are a likely uplift mechanism, and their emplacement is possibly enhanced by the slow motion of the Nubian plate relative to the source of partial melting. Alternating uplift and subsidence episodes suggest that island edifice growth may be governed by competing dominantly volcanic and dominantly intrusive processes.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Geological Settingmentioning

confidence: 99%

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The emergence of volcanic oceanic islands on a slow‐moving plate: The example of Madeira Island, NE Atlantic

Ramalho

Silveira

Fonseca

et al. 2015

Geochem Geophys Geosyst

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“…Disseminated ash occurred over a longer sequence, but at both sites the discrete ash beds are restricted to the middle Miocene. The middle Miocene occurrences correlate with the age of diabase intrusions at Site 368 (Duncan and Dalrymple, this volume); the age of major volcanism around Dakar, Senegal (Furon, 1963); Canary Island volcanism (Furon, 1963;Dillon and Sougy, 1974;Grunau, et al, 1975); and Cape Verde Island volcanism (Furon, 1963;Mitchell-Thome, 1974;Grunau et al, 1975). We are surprised to find so few volcanic ash beds in the Miocene with all this volcanic activity.…”

Section: Volcanic Ash Recovered At Sites 368 and 369mentioning

confidence: 92%

Sediments Recovered from the Northwest African Continental Margin, Leg 41, Deep Sea Drilling Project

Gardner¹,

Dean²,

Jansa³

1978

Initial Reports of the Deep Sea Drilling Project

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“…A 65‐m‐thick sequence of volcaniclastic and fossil‐bearing limestone beds is exposed at Paredes and Forno on the east side of Ilhéu de Baixo, as summarized by da Silva () and Mitchell‐Thomé (). The reef limestone with the dominant coral Pocillopora madreporacea (Lamarck) is from a lens‐like deposit 1.6 m thick, sitting on volcaniclastic rocks 45 m above sea level (Boekschoten and Best, ; Best and Boekschoten, ).…”

Section: Location and Geological Settingmentioning

confidence: 99%

A Middle Miocene carbonate embankment on an active volcanic slope: Ilhéu de Baixo, Madeira Archipelago, Eastern Atlantic

et al. 2013

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Carbonate factories on insular oceanic islands in active volcanic settings are poorly explored. This case study illuminates marginal limestone deposits on a steep volcanic flank and their recurring interruption by deposits linked to volcaniclastic processes. Historically known as Ilhéu da Cal (Lime Island), Ilhéu de Baixo was separated from Porto Santo, in the Madeira Archipelago, during the course of the Quaternary. Here, extensive mines were tunnelled in the Miocene carbonate strata for the production of slaked lime. Approximately 10 000 m3 of calcarenite (−1 to 1ø) was removed by hand labour from the Blandy Brothers mine at the south end of the islet. Investigations of two stratigraphic sections at opposite ends of the mine reveal that the quarried material represents an incipient carbonate ramp developed from east to west and embanked against the flank of a volcanic island. A petrographic analysis of limestones from the mine shows that coralline red algae from crushed rhodoliths account for 51% of all identifiable bioclasts. This material was transported shoreward and deposited on the ramp between normal wave base and storm wave base at moderate depths. The mine's roof rocks are formed by Surtseyan deposits from a subsequent volcanic eruption. Volcaniclastic density flows also are a prevalent factor interrupting renewed carbonate deposition. These flows arrived downslope from the north and gradually steepened the debris apron westwards. Slope instability is further shown by a coral rudstone density flow that followed from growth of a coral reef dominated by Pocillopora madreporacea (Lamarck), partial reef collapse, and transport from a more easterly direction into a fore‐reef setting. The uppermost facies represents a soft bottom at moderate depths in a quiet, but shore‐proximal setting. Application of this study to a broader understanding of the relationship between carbonate and volcaniclastic deposition on oceanic islands emphasizes the susceptibility of carbonates to dilution and complete removal by density flows of various kinds, in contrast to the potential for preservation beneath less‐disruptive Surtseyan deposits. Copyright © 2013 John Wiley & Sons, Ltd.

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The sedimentary rocks of macaronesia

Cited by 10 publications

References 25 publications

The emergence of volcanic oceanic islands on a slow‐moving plate: The example of Madeira Island, NE Atlantic

The emergence of volcanic oceanic islands on a slow‐moving plate: The example of Madeira Island, NE Atlantic

Sediments Recovered from the Northwest African Continental Margin, Leg 41, Deep Sea Drilling Project

A Middle Miocene carbonate embankment on an active volcanic slope: Ilhéu de Baixo, Madeira Archipelago, Eastern Atlantic

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