Browsing by Author "Alloway, Brent, V"

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    A century of ongoing silicic volcanism at Cordon Caulle, Chile: New constraints on the magmatic system involved in the 1921-1922, 1960 and 2011-2012 eruptions
    (2021) Seropian, Gilles; Schipper, C. Ian; Harmon, Lydia J.; Smithies, Sarah L.; Kennedy, Ben M.; Castro, Jonathan M.; Alloway, Brent, V; Forte, Pablo
    Cordon Caulle in southern Chile has produced three dacitic to rhyolitic fissure eruptions over the past century (in 1921-1922, 1960 and 2011-2012), and thereby provides an ideal opportunity to examine the architecture of its underlying silicic system. While the 2011-2012 eruption has been extensively studied, comparatively little is known about the 1921-1922 and 1960 events. Major-element matrix glass analyses from the 1960 products (71.5 wt.% SiO2) are indistinguishable from the 2011-2012 data (72.2 wt.% SiO2), but the 1921-1922 analyses form a discrete, slightly less evolved sub-population (69.0 wt.% SiO2). We utilise rhyolite-MELTS geobarometry to estimate both the storage and extraction depths of all three magmas. For all three eruptions, magma was stored in the shallow crust, between 80-150 MPa (3.5-6.6 km). The 2011-2012 magma body spanned this whole depth range but the 1921-1922 and 1960 magma bodies were more confined in pressure, at 90-112 MPa (4.0-5.0 km) and 123-143 MPa (5.4-6.3 km) respectively. Melt extraction from a parental crystal-mush occurred in the range 70-200 MPa (3.1-9.0 km) for all three eruptions, suggesting contiguous melt segregation and storage in the shallow crust. Finally, we discuss whether the deeper magma storage in 1960 reflects the influence of a seismic trigger by events associated with the Mw9.5 Great Chilean earthquake. (C) 2021 The Author(s). Published by Elsevier B.V.
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    An integrative geochronological framework for the pleistocene So'a basin (Flores, Indonesia), and its implications for faunal turnover and hominin arrival
    (2022) van den Bergh, Gerrit D.; Alloway, Brent, V; Storey, Michael; Setiawan, Ruly; Yurnaldi, Dida; Kurniawan, Iwan; Moore, Mark W.; Jatmiko; Brumm, Adam; Flude, Stephanie; Sutikna, Thomas; Setiyabudi, Erick; Prasetyo, Unggul W.; Puspaningrum, Mika R.; Yoga, Ifan; Insani, Halmi; Meijer, Hanneke J. M.; Kohn, Barry; Pillans, Brad; Sutisna, Indra; Dosseto, Anthony; Hayes, Susan; Westgate, John A.; Pearce, Nick J. G.; Aziz, Fachroel; Due, Rokus Awe; Morwood, Michael J.
    Flores represents a unique insular environment with an extensive record of Pleistocene fossil remains and stone artefacts. In the So'a Basin of central Flores these include endemic Stegodon, Komodo dragons, giant tortoises, rats, birds and hominins, and lithic artefacts that can be traced back to at least one million years ago (1 Ma). This comprehensive review presents important new data regarding the dating and faunal sequence of the So'a Basin, including the site of Mata Menge where Homo floresiensis-like fossils dating to approximately 0.7 Ma were discovered in 2014. By chemical fingerprinting key silicic tephra originating from local and distal eruptive sources we have now established basin-wide tephrostrati-graphic correlations, and, together with new numerical ages, present an update of the chronostratig-raphy of the So'a Basin, with major implications for the faunal sequence. These results show that a giant tortoise and the diminutive proboscidean Stegodon sondaari last occurred at the site of Tangi Talo-1.3 Ma, and not 0.9 Ma as previously thought. We also present new data suggesting that the disap-pearance of giant tortoise and S. sondaari from the sedimentary record occurred before, and/or was coincident with, the earliest hominin arrival, as evidenced by the first records of lithic artefacts occurring directly below the 1 Ma Wolo Sege Tephra. Artefacts become common in the younger layers, associated with a distinct fauna characterized by the medium-sized Stegodon florensis and giant rat Hooijeromys nusatenggara. Furthermore, we describe a newly discovered terrace fill, which extends the faunal record of Stegodon in the So'a Basin to the Late Pleistocene. Our evidence also suggests that the paleoenvir-onment of the So'a Basin became drier around the time of the observed faunal transition and arrival of hominins on the island, which could be related to an astronomically-forced climate response at the onset of the Mid-Pleistocene Transition (MPT;-1.25 Ma) leading to increased aridity and monsoonal intensity. (c) 2022 Published by Elsevier Ltd.
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    Fires and rates of change in the temperate rainforests of northwestern Patagonia since-18 ka
    (2023) Moreno, Patricio, I; Mendez, Cesar; Henriquez, Carla A.; Fercovic, Emilia, I; Videla, Javiera; Reyes, Omar; Villacis, Leonardo A.; Villa-Martinez, Rodrigo; Alloway, Brent, V
    We examine the temporal and spatial structure of wildfires and rates of vegetation change in the Pacific sector of northwestern Patagonia (40 degrees-44 degrees S) over the last-18,000 years. Macroscopic Charcoal Accu-mulation Rates (CHAR), a proxy of past local fires, shows a geographic variation that mirrors the modern north-to-south and low-to-high elevation increase in annual precipitation and decrease in precipitation seasonality, and the frequency of explosive volcanic events. Variability in past fires is evident at multiple timescales, with a significant multi-millennial low between-18-13.1 ka, an abrupt rise between-13.1 -12.5 ka, and heightened fire activity between-11.4-8.2 ka with significant high values between-10 -9.4 ka. A subsequent decline led to the lowest Holocene values between-6-5.4 ka, which rose and led to significant high values between-3.1 ka and the present. Andean and Western Upwind Environments share a multi-millennial structure of fire activity since-18 ka, overprinted by millennial and centennial -scale divergences. These differences underscore the role of explosive volcanism as a trigger or modulator of fire activity in the vicinity of Andean eruptive centers. We posit that fire activity in Western Upwind Environments was driven primarily by hydroclimate variations, namely changes in the intensity of the Southern Westerly Winds. Compilations of CHAR and the Rates of Change (ROC) parameter, a measure of the magnitude and rapidity of changes in the pollen records, covary during the onset of the interglacial fire regime at-13.1 ka and the last-4000 years, suggesting that fires catalyzed vegetation changes during specific intervals since the last glaciation. Highly mobile human occupations deployed along the coasts started at-6.2 ka, increased in pulses, and spread widely during the last two millennia. Covariation with CHAR and ROC since-4 ka suggests that hunter-gatherer -fishers contributed to enhanced fire activity and abrupt vegetation changes at regional scale. The ubiquitous fire maximum over the last four cen-turies relates to widespread settlement and associated large-scale land clearance conducted by Euro-pean/Chilean settlers.(c) 2022 Elsevier Ltd. All rights reserved.
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    Glacial geomorphology of the central and southern Chilotan Archipelago (42.2 degrees S-43.5 degrees S), northwestern Patagonia
    (TAYLOR & FRANCIS LTD, 2022) Soteres, Rodrigo L.; Sagredo, Esteban A.; Moreno, Patricio, I; Lowell, Thomas, V; Alloway, Brent, V
    We present a geomorphic map of the glacial landforms associated with the Golfo Corcovado ice lobe in northwestern Patagonia. Built upon prior studies, our map elaborates on the central and southern sectors of Isla Grande de Chiloe and neighboring islands. Through a combination of remote sensing techniques and exhaustive fieldwork, we identified a suite of ice-marginal, subglacial, and glaciofluvial features created by the Golfo Corcovado ice lobe during four maxima within the last glacial cycle, in none of which the ice-front reached the Pacific coast of Isla Grande de Chiloe. Our mapping builds a foundation and provides insights for future interdisciplinary research on the Late Quaternary sequence of glacial and paleoclimatic events in this key sector of northwestern Patagonia.
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    The role of climate and disturbance regimes upon temperate rainforests during the Holocene: A stratigraphic perspective from Lago Fonk (-40 degrees S), northwestern Patagonia
    (PERGAMON-ELSEVIER SCIENCE LTD, 2021) Henriquez, Carla A.; Moreno, Patricio, I; Lambert, Fabrice; Alloway, Brent, V
    Climate and disturbance regimes play key roles in shaping the structure, composition and functioning of terrestrial ecosystems. Despite this importance, very few stratigraphic studies in the temperate rainforests from northwestern Patagonia have explored this relationship in detail along a time continuum through the entire Holocene. Here we present a high-resolution fossil pollen and charcoal record from Lago Fonk (median resolution: 20 years), a small closed-basin lake in the lowlands of the Chilean Lake District (41 degrees S), where wildfires and explosive volcanism have intermittently taken place during the Holocene, along with pronounced human-induced disturbance in post-colonial time. Our results show persistence of temperate rainforest throughout the Holocene, with changes in the composition and structure of Valdivian rainforests (VRF) at millennial timescales. We detect centennial-scale alternations in dominance between the VRF tree Eucryphia/Caldcluvia and generalist trees found in VRF and North Patagonian rainforests after-6.5 cal ka BP. Intervals dominated by VRF coincide with enhanced fire occurrence signaling negative hydroclimate anomalies with a mean duration of-150 years, which alternate with positive hydroclimate anomalies lasting-312 years on average. Our results suggest that the magnitude and rapidity of vegetation changes detected at 10.2-9.9, 4.0-3.0,-1.0, and-0.7 cal ka BP were amplified by disturbance regimes, and led to the establishment and maintenance of Eucryphia/Caldcluvia-dominated forests in the Longitudinal Valley of the Chilean Lake District. On several occasions the higher incidence of fire disturbance during warm/dry climate intervals coincided with episodes of heightened explosive volcanic activity from multiple eruptive centers within the Southern Andean Volcanic Zone. (c) 2021 Elsevier Ltd. All rights reserved.