On the rise and fall of oceanic islands:Towards a global theory following the pioneering studies of Charles Darwin and James Dwight Dana

The careers of Charles Darwin (1809–1882) and James Dwight Dana (1813–1895) are intimately linked to circumnavigations of the globe with the British mapping expedition on the H.M.S. Beagle (1831–1836) under Captain Robert FitzRoy and the United States Exploring Expedition (1838–1842) under Lieutenant Charles Wilkes. The former expedition mainly surveyed coastal South America, but also visited many volcanic islands in the Atlantic, Pacific, and Indian oceans. The latter expedition followed a similar path through the Atlantic, but devoted more time to Pacific Ocean islands. Remembered more today for his visit to the Galapagos Islands and its subsequent impact on understanding the mechanisms of biological evolution, Darwin was motivated early on during his stopover in the Cape Verde Islands to compile studies on the geology of volcanic islands. Better known for his theory of atoll development from the subsidence of volcanic islands stimulated by his visit to the Keeling Islands and published in 1842, Darwin also wrote a related volume published in 1844 with an equally strong emphasis on island uplift. Dana was influenced by Darwin's theory of atoll development, and published his own independent observations on coral reefs and island subsidence in 1843, 1849, and 1853. The work of both geologists matured from primary observations using inductive logic during fieldwork (i.g. unconformable position of limestone on and between basalt flows as an indicator of paleo-sea level) to the advancement of broader theories regarding the behavior of the Earth's oceanic crust. Notably, Dana recognized age differences among islands in Pacific archipelagos and was strongly influenced by the orientations of those island groups. The classic Hawaiian model that features a linear string of progressively older and subsiding islands does not apply easily to many other island groups such as the Galapagos, Azores, Canary, and Cape Verde islands. Geologists and coastal geomorphologists increasingly find that the original observations on island uplift covered in Darwin's, 1844 treatment provide an alternative pathway to understanding the complexities of island histories in oceanic settings. Original work by Darwin and Dana also led to ongoing studies on the trans-oceanic migrations of marine organisms, such as barnacles, corals and non-attached coralline red algae represented by rhodoliths. This work gives added importance to oceanic islands as way stations in the dispersal of biotas over time.</p

What Darwin did not see : Pleistocene fossil assemblages on a highenergy coast at Ponta das Bicudas, Santiago, Cape Verde Islands

Two distinct Pleistocene assemblages from SE Santiago Island are comparable to modern analogues elsewhere in the Cape Verde Islands. A low-diversity Siderastrea radians assemblage lived atop basalt knobs surrounded by sand on a slope below a cliff. A Millepora alcicornis–Megabalanus azoricus assemblage occupied the cliff. The latter was a typical rocky-shore assemblage from a high-energy setting belowthe tidal zone.Bioerosion structures in basalt produced by Circolites kotoncensis and Gastrochaenolites isp. also occur there. Despite extensive studies on local limestone deposits in 1832 and 1836, lack of exposure prevented Darwin from seeing these fossils.Funding for fieldwork on Santiago Island in June 2011 was provided under grant CGL2010-15372-BTE from the Spanish Ministry of Science and Innovation to project leader Eduardo Mayoral (University of Huelva). Financial support to A. Santos came from the Spanish Ministry of Science and Technology (Juan de la Cierva subprogram, Ref: JCI-2008-2431). Additional support by the Junta de Andalucia (Spanish government) to the Research Group RNM276 is also acknowledged. Partial funding to J. Ledesma-Vazquez on this project came from the Programma Integral de Fortalecimiento Institucional 2010. We thank Christopher K. Pham, Department of Oceanography and Fisheries, University of the Azores, Portugal, for help with identification of the fossil barnacles and Ricardo Ramalho, Institut fur Geophysik, Westphalishe-Wilhelms Universitat, Germany, for discussions about bioerosion by sea urchins on basalt surfaces

A biometric re-evaluation of the Silurian brachiopod lineage Stricklandia lens/S. laevis

Volume: 29Start Page: 187End Page: 20

The Llandovery enteletacean brachiopods of the central Oslo region, Norway

Volume: 31Start Page: 1101End Page: 112

Septate gastropods from the Upper Devonian of the Canning Basin: implications for palaeoecology

Cook, A.G., Jell, P.A., Webb, G.E., Johnson, M.E. & Baarli, B.G., 21.4.2015. Septate gastropods from the Upper Devonian of the Canning Basin: implications for palaeoecology. Alcheringa 39, 519–524. ISSN 0311-5518 Septate murchisoniid gastropods are documented from the Upper Devonian (Frasnian) Pillara Limestone, Canning Basin, Western Australia. Two localities were investigated corresponding to a peri-island and back reef setting. Extensive septation is reviewed for Palaeozoic gastropods and is interpreted to be an adaptation to shallow water, apical breakage in non-euomphaloidean gastropods, or combined with the possible need to adjust calcium levels in the mantle. Fletcherviewia from the Middle Devonian of north Queensland is reassigned to the Murchisoniidae. Alex G. Cook [[email protected]], Peter A. Jell [[email protected]] and Gregory E. Webb [[email protected]], School of Earth Sciences, The University of Queensland, Queensland, 4072, Australia; Markes E. Johnson [[email protected]] and B. Gudveig Baarli [[email protected]], Department of Geosciences, Williams College, Williamstown, MA 01267, USA. Received 7.2.2015; revised 16.4.2015; accepted 21.4.2015

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

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

Recent Rhodolith Deposits Stranded on the Windward Shores of Maio (Cape Verde Islands):Historical Resource for the Local Economy

Johnson, M.E.; Baarli, B.G.; da Silva, C.M.; Cachão, M.; Ramalho, R.S.; Santos, A., and Mayoral, E.J., 2016. Recent rhodolith deposits stranded on the windward shores of Maio (Cape Verde Islands): Historical resource for the local economy.Maio is a volcanic island with an area of 269 km2 in the Cape Verde archipelago off the west coast of Africa. Although considered a leeward island, it absorbs NE trade winds that typically register 5 to 6 on the Beaufort Scale (moderate to fresh breeze). The trade winds produce ocean swells commonly 3.5 m in height that scour the island's north coast but also generate eastern longshore currents. Outcrops with Pleistocene rhodoliths occur on the SE and south shores and include lithified dunes mainly composed of crushed rhodolith debris. In contrast, the modern beaches and Pleistocene dunes on the more sheltered west coast are practically devoid of rhodoliths. Present-day rhodolith banks off the north coast would seem to be precluded by intense wave action. This study examines rhodoliths from overwash and beach-rock deposits around Ponta Cais in the far north. Lumpy rhodoliths (likely Lithothamnion sp.) are concentrated in a sheltered corner on the bay south of Ponta Branca. A more extensive overwash deposit covers an area of 27,000 m2 that is 1 m above mean sea level with a surface exposure of 450 rhodoliths/m2. A unique specimen nucleated around a ceramic fragment indicates that the deposit is historical in context. Rhodolith beach rock extends all along Praia Real east of Ponta Cais. A northern bank clearly exists, but it does so at a water depth normally adequate to protect larger rhodoliths from all but major storms. Abandoned limekilns behind Praia Real demonstrate that the local economy on a volcanic island used rhodoliths as a source of mortar and whitewash

Miocene–Pliocene rocky shores on São Nicolau (Cape Verde Islands): Contrasting windward and leeward biofacies on a volcanically active oceanic island

North Atlantic islands in the Cape Verde Archipelago off the coast of West Africa commonly feature an elongated N–S shape in which reduced northern coasts and longer eastern shores absorb the brunt of wave activity and long-shore currents generated by prevailing North East Trade Winds. Located in the middle windward islands, São Nicolau is unusual in profile with an elongated E–W configuration that offers a broad target against high-energy, wind-driven waves. Conversely, the south shore of São Nicolau provides relatively wide shelter in a leeward setting. Reconstruction of the proto-island prior to the onset of the Main Eruptive stage during the Late Miocene at ~ 5.1 Ma reveals a moderately smaller island with essentially the same E–W orientation. This study combines previous data with results from a detailed stratigraphic log based on Upper Miocene limestone deposits on the island's south flank for comparison with stratigraphic profiles of Upper Miocene limestone from the island's northeast quarter. Logs from a Pliocene sandy limestone outcropping on the south-central coast of São Nicolau give added context to the diversity of marine invertebrates, including branching coral colonies and delicate ramose bryozoans that found shelter in a leeward setting. Whole rhodoliths contribute the main fabric of carbonates deposited against rocky shores on the northern, exposed side of the Miocene island, whereas only traces of worn rhodoliths and rhodolith sand occur as in finer Miocene grainstone on the island's southern, protected side. Miocene and Pliocene carbonate deposits were terminated by submarine flows on an actively growing volcanic island. The passage zone from submarine to subaerial flows on the island's flanks makes a useful meter-stick to gauge absolute water depth at the moment of local extinction by volcanic activity.This study was funded under grant CGL2010-15372-BTE from the Spanish Ministry of Science and Innovation to project leader Eduardo Mayoral (University of Huelva). Support from Research Group RNM276 also is acknowledged. Extra support for work on calcareous nannofossils came from PTDC/MAR/102800/2008. R. Ramalho was funded by an FP7-PEOPLE-2011-IOF Marie Curie Postdoctoral Fellowship, which is gratefully acknowledged. We thank Dr. Bjorn Berning (Upper Austrian State Museum, Leonding, Austria) for identification of the Pataca bryozonas to genus level and Dr. Davide Bassi (Department of Earth Sciences, Ferrara University, Italy) for identification of the Castilhano rhodoliths to genus level. The editor and two anonymous reviewers provided useful comments that helped to improve the final manuscript