Geological evidence bearing on the Miocene to Recent structural evolution of the New Hebrides arc

The New Hebrides archipelago is a complex reversed-arc system that can be divided into four major volcanic provinces. The Western Belt is an Early to Middle Miocene extinct volcanic arc that, as a result of polarity reversal, is now incorporated into the frontal arc of the present-day configuration. The Eastern Belt initially received detritus in the early Middle Miocene from a tholeiitic arc complex but in the Mio-Pliocene became the locus of a more calc-alkaline arc volcanism. Volcanic activity then ceased in the Eastern Belt but is well-represented as a third and largely submerged Marginal Province through the Pliocene into the Early Pleistocene. The present volcanic line, the Central Chain, is essentially a continuation of the Marginal Province volcanism into Recent times.Initial tectonic events in the New Hebrides arc were associated with the regional disruption in the Middle Miocene of an east-facing system, with consequent termination of Western Belt arc volcanism. The Western Belt remained as a landmass during the lowermost Late Miocene but subsided following a Late Miocene renewal of island arc volcanism to the east. This latest phase was coeval with initial expansion of the North Fiji Basin and marked the advent of the New Hebrides as a westwards-migrating reversed-arc system. During arc migration there were apparent hiatuses in island arc volcanism, the most notable being a Middle Pliocene to Late Pleistocene period of quiescence in the central sector.Tectonism in the Early Pleistocene-Recent raised the fore-arc, brought about rifting and extension to the rear and concentrated volcanism along the presently-active Central Chain.     

The Holme Pierrepont sand and gravel and the timing of Middle and Late Devensian floodplain aggradation in the English Midlands

This paper provides the first detailed, multi-proxy environmental record for the character of Lateglacial conditions in the lowest Pleistocene terrace of the main valley floor of the River Trent at Holme Pierrepont near Nottingham. The analysis of pollen, plant, insect and mollusc remains preserved within organic channels near the base of the terrace, named the Holme Pierrepont Sand and Gravel by the British Geological Survey (historically known as the Floodplain Terrace), provided evidence of cool, though not fully arctic climatic conditions and a largely treeless landscape, roamed by large herbivores. Radiocarbon dating indicates that these sediments were deposited during the Loch Lomond Stadial (Younger Dryas GS-1). Comparison of these dates from Holme Pierrepont with those from morphostratigraphically similar deposits in the wider Trent catchment suggests that the Holme Pierrepont Sand and Gravel may have been laid down in two separate pulses of braidplain aggradation either side of the ‘Last Glacial Maximum’. It has been demonstrated from historical documentation and riverine archaeological evidence that the middle Trent has been particularly sensitive to changing flood frequency and magnitude associated with climatic oscillations during the late Holocene; this study demonstrates that such sensitivity appears to extend back into the late Pleistocene. The timing of fluvial aggradation recorded at Holme Pierrepont agrees broadly with that recorded from other sites across England and north-west Europe.     

“The mangrove preserves life”: Habitat of African survival in the Atlantic world

Mangroves emerged a crucial habitat for Africans and their descendants during the transatlantic slave trade. Europeans avoided mangroves because of the deadly fevers that frequently claimed the lives of those who ventured there. Many were felled by lethal falciparum malaria, against which Africans alone carried genetic resistance. The transatlantic slave trade spread the disease‐causing plasmodium to New World Anopheles mosquitoes through infected bloodstreams, extending African mangroves’ pestilential reputation to the Neotropics. On both sides of the Atlantic, an environment Europeans feared provided Africans food, basic necessities, and sometimes, refuge from slavery. In Neotropical mangroves Africans largely replaced declining Amerindian populations, who were also immunologically vulnerable to the introduced plasmodium. Today, African descendants in Old and New World mangroves demonstrate longstanding human use of this ecosystem. Comparison of shellfish gathering and gendered collection patterns in mangroves recognizes Amerindian and African influences in Neotropical mangroves and illuminates the connections to transatlantic diasporic history. The discussion considers how a more‐than‐human geography shaped “place‐based knowledge” of mangrove swamplands that remained marginal to European territorializing during the colonial period. African and Afro‐descendant place‐making underscores the ways people, plants, insects, microbes, shellfish, and tides framed geography and diasporic identity at the periphery of the Atlantic world.     

Hypotaurine and thiotaurine as indicators of sulfide exposure in bivalves and vestimentiferans from hydrothermal vents and cold seeps

Vesicomyid clams, vestimentiferans, and some bathymodiolin mussels from hydrothermal vents and cold seeps possess thiotrophic endosymbionts, high levels of hypotaurine and, in tissues with symbionts, thiotaurine. The latter, a product of hypotaurine and sulfide, may store and/or transport sulfide non‐toxically, and the ratio to hypotaurine plus thiotaurine (Th/[H + Th]) may reflect an animal's sulfide exposure. To test this, we analyzed seep and vent animals with in situ sulfide measurements. Calyptogena kilmeri clams occur at high‐sulfide seeps in Monterey Canyon, while C. (Vesicomya) pacifica clams occur at seeps with lower levels but take up and metabolize sulfide more effectively. From one seep where they co‐occur, both had gill thiotaurine contents at 22–25 mmol kg⁻¹ wet mass, and while C. (V.) pacifica had a higher blood sulfide level, it had a lower Th/[H + Th] (0.39) than C. kilmeri (0.63). However, these same species from different seeps with lower sulfide exposures had lower ratios. Bathymodiolus thermophilus [East Pacific Rise (EPR 9°50′ N)] from high‐(84 μm ) and a low‐(7 μm ) sulfide vents had gill ratios of 0.40 and 0.12, respectively. Trophosomes of Riftia pachyptila (EPR 9°50′ N) from medium‐(33 μm ) and low‐(4 μm ) sulfide vents had ratios of 0.23 and 0.20, respectively (not significantly different). Ridgeia piscesae vestimentiferans (Juan de Fuca Ridge) have very different phenotypes at high‐ and low‐sulfide sites, and their trophosomes had the greatest differences: 0.81 and 0.04 ratios from high‐ and low‐sulfide sites, respectively. Thus Th/[H + Th] may indicate sulfide exposure levels within species, but not in interspecies comparisons, possibly due to phylogenetic and metabolic differences. Total H + Th was constant within each species (except in R. piscesae); the sum may indicate the maximum potential sulfide load that a species faces.     

Sea floor responses to hydrocarbon seeps,Louisiana continental slope

Observations and samples from research submersible dives confirm that brines, crude oil, fluid mud, and gases are common seep products. Through this mechanism a unique interplay of geochemical, geologic, and biological processes resulting in unusual sea floor features ranging from carbonate-rich nodular sediments to mounds with tens of meters relief. Stable carbon isotopes occluded in the carbonates provide a permanent imprint that links these authigenic carbonates to by-products of microbial breakdown of crude oil and gas. Recent DSV ALVIN dives confirm that hydrocarbon seeps and their accompanying chemosynthetic communities and authigenic carbonate mounds occur over the entire depth range of the slope.