Littérature scientifique sur le sujet « Antarctica Ross Sea LGM Provenance »

AbstractGlacial till samples collected from beneath the Bindschadler and Kamb ice streams have a distinct U-Pb detrital zircon signature that allows them to be identified in Ross Sea tills. These two sites contain a population of Cretaceous grains 100–110 Ma that have not been found in East Antarctic tills. Additionally, Bindschadler and Kamb ice streams have an abundance of Ordovician grains (450–475 Ma) and a cluster of ages 330–370 Ma, which are much less common in the remainder of the sample set. These tracers of a West Antarctic provenance are also found east of 180° longitude in eastern Ross Sea tills deposited during the last glacial maximum (LGM). Whillans Ice Stream (WIS), considered part of the West Antarctic Ice Sheet but partially originating in East Antarctica, lacks these distinctive signatures. Its U-Pb zircon age population is dominated by grains 500–550 Ma indicating derivation from Granite Harbour Intrusive rocks common along the Transantarctic Mountains, making it indistinguishable from East Antarctic tills. The U-Pb zircon age distribution found in WIS till is most similar to tills from the west-central Ross Sea. These data provide new specific targets for ice sheet models and can be applied to pre-LGM deposits in the Ross Sea.

AbstractCores acquired from the Ross Sea continental shelf and continental slope during the XXX Italian Programma Nazionale di Ricerche in Antartide (PNRA) were analysed and yielded interesting micropalaeontological, biostratigraphic diatom results and palaeoceanographic implications. These multi-proxy analyses enabled us to reconstruct the glacial/deglacial history of this sector of the Ross embayment over the last 40 000 years, advancing our understanding of the Last Glacial Maximum (LGM) environmental and sedimentological processes linked to the Ross Sea ice sheet/ice shelf fluctuations in a basin and continental-slope environment, and allowed us to measure some of the palaeoceanographic dynamics. The central sector of the Ross Sea and part of its coast (south of the Drygalski Ice Tongue) enjoyed open marine conditions in the pre-LGM era (27 500–24 000 years bp). The retreat of the ice sheet could have been influenced by a southward shift of a branch of the Ross gyre, which triggered early deglaciation at c. 18 600 cal bp with a significant Modified Circumpolar Deep Water inflow over the continental slope at c. 14 380 cal BP. We assume that a lack of depositional material in each core, although at different times, represents a hiatus. Other than problems in core collection, this could be due to the onset of modern oceanographic conditions, with strong gravity currents and strong High Salinity Shelf Water exportation. Moreover, we presume that improvements in biostratigraphy, study of reworked diatom taxa, and lithological and geochemical analyses will provide important constraints for the reconstruction of the LGM grounding line, ice-flow lines and ice-flow paths and an interesting tool for reconstructing palaeo-sub-bottom currents in this sector of the Ross embayment.

AbstractDuring the Last Glacial Maximum (LGM), a grounded ice sheet filled the Ross Sea Embayment in Antarctica and deposited glacial sediments on volcanic islands and peninsulas in McMurdo Sound and coastal regions of the Transantarctic Mountains. The flow geometry and retreat history of this ice are debated, with contrasting views yielding divergent implications for the interaction between and stability of the East and West Antarctic ice sheets during late Quaternary time. Here, we present terrestrial geomorphologic evidence and reconstruct former ice-marginal environments, ice sheet elevations, and ice-flow directions in McMurdo Sound. Fossil algae in ice-marginal sediments provide a coherent radiocarbon chronology of maximum ice extent and deglaciation. We integrate these data with marine records to reconstruct grounded ice dynamics in McMurdo Sound and the western Ross Sea. The combined data set suggests ice flow toward the Transantarctic Mountains in McMurdo Sound during peak glaciation, with thick, grounded ice at or near its maximum position between 19.6 and 12.3 ka. Persistent grounded ice in McMurdo Sound and across the western Ross Sea after Meltwater Pulse 1a (14.0–14.5 ka) suggests that this sector of Antarctica did not significantly contribute to this rapid sea-level rise event. Our data show no significant advance of locally derived ice from the Transantarctic Mountains into McMurdo Sound during the local LGM.

AbstractA marine sediment core collected from the Nordenskjold Basin, to the south of the Drygalski Ice Tongue, provides new sedimentological and chronological data for reconstructing the Pleistocene glacial history and palaeoenvironmental evolution of Victoria Land. The core consists of an over consolidated biogenic mud covered with glacial diamicton; Holocene diatomaceous mud lies on top of the sequence. Radiocarbon dates of the acid insoluble organic matter indicate a pre-Last Glacial Maximum age (>24kyr) for the biogenic mud at the base of the sequence. From this we can presume that at least this portion of the western Ross Sea was deglaciated during Marine Isotope Stage 3 and enjoyed open marine conditions. Our results are consistent with recent findings of pre-Holocene raised beaches at Cape Ross and in the Terra Nova Bay area.

AbstractThick successions of turbidites are widespread in the Ross–Delamerian and Lachlan orogens and are now dispersed through Australia, Antarctica and New Zealand. U-Pb detrital zircon age patterns for latest Precambrian, Cambrian and Ordovician metagreywackes show a closely related provenance. The latest Neoproterozoic–early Palaeozoic sedimentary rocks have major components, at c. 525, 550, and 595 Ma, i.e. about 40–80 million years older than deposition. Zircons in these components increase from the Neoproterozoic to Ordovician. Late Mesoproterozoic age components, 1030 and 1070 Ma, probably originate from igneous/metamorphic rocks in the Gondwanaland hinterland whose exact locations are unknown. Although small, the youngest zircon age components are coincident with estimated depositional ages suggesting that they reflect contemporaneous and minor, volcanic sources. Overall, the detrital zircon provenance patterns reflect the development of plutonic/metamorphic complexes of the Ross–Delamerian Orogen in the Transantarctic Mountains and southern Australia that, upon exhumation, supplied sediment to regional scale basin(s) at the Gondwana margin. Tasmanian detrital zircon age patterns differ from those seen in intra-Ross Orogen sandstones of northern Victoria Land and from the oldest metasediments in the Transantarctic Mountains. A comparison with rocks from the latter supports an allochthonous western Tasmania model and amalgamation with Australia in late Cambrian time.

In this thesis the application of multi-disciplinary provenance methods to the study of late Quaternary sediments deposited along the edge of the continental shelf of Ross Sea and in the coastal area of McMurdo Sound (Southern Victoria Land) is treated. In particular, petrographic analysis of gravel fraction (clasts of different grain size) has been applied to glacimarine intervals related to the last advance and consequent retreat of the Antarctic Ice Sheet on the continental shelf at the Last Glacial Maximum. The sediments were analyzed using a petrographic approach, with logging and classification of gravel-sized clasts of various lithologies in cores distributed along an E-W transect along the entire Ross Embayment. The classification and quantitative approach applied on the gravel fraction, coupled with geo and thermo- chronological techniques on sandy fractions from the same stratigraphic intervals, allowed to refine the existing data in the region dealing with drainage pattern of paleo-ice flows during the Last Glacial Maximum. In particular, in the region of Eastern Ross Sea, the acquired new data allowed to better constrain the contribution of West Antarctica Ice Sheet to the ice drainage in the Ross Embayment, while in the Central and Western Ross Sea the contribution of East Antarctic Ice Sheet has been revealed by new petrographic data that have qualitatively refined existing provenance models. In addition, a petrographic approach on onshore unconsolidated sediments (Ross Sea Drift) transported by a grounded Ice Sheet in the McMurdo Sound region (Southern Victoria Land) has been carried out, applying a quantitative approach to various granulometric fractions. Deposits have been classified according to thelithological composition of clasts that composed these sediments. The data obtained allowed to refine the existing ice transport models in the region and to hypothesize paleo ice flow depending on the provenance of glacial erratics.

Questo lavoro di tesi riguarda principalmente lo studio di provenienza di sedimenti e rocce deposti in ambienti glaciali nel continente antartico in due contesti temporali estremamente differenziati, ovvero durante la LPIA (Late Paleozoic Ice Age) che ha interessato il Gondwana, e durante i cicli glaciale-interglaciale del Cenozoico, attraverso un approccio multidisciplinare. Il filo conduttore tra due contesti così distanti è stato quello di confrontare sistemi di trasporto glaciali e di ricostruzione della provenienza dei sedimenti in frangenti temporali, climatici, paleogeografici e geodinamici estremamente diversi, seppure relativi sempre al continente antartico. Questo confronto può anche evidenziare affinità e differenze dei due sistemi glacigenici, che possono essere utili sia per ricostruzioni paleoclimatiche e paleogeografiche, che per la previsione di scenari futuri. Il lavoro di tesi si è basato principalmente sullo studio della frazione grossolana (ciottoli > 2mm) di facies glaciali (diamictiti e conglomerati), attraverso analisi petrografiche, che permettono un confronto diretto con le litologie affioranti nel bacino di alimentazione dei ghiacciai. Alle analisi petrografiche sono state affiancate altre tecniche analitiche in modo da rafforzare le ipotesi di provenienza. In particolare, alla petrografia dei ciottoli sono state affiancate analisi chimiche di alcune fasi mineralogiche. Questi dati preliminari sembrano evidenziare il fatto che la composizione chimica delle biotiti che si trovano all’interno di rocce intrusive può essere un marker discriminante per la provenienza, con particolare riferimento alle rocce intrusive che costituiscono l’Antartide Orientale e Occidentale. Inoltre, sono state effettuate analisi geocronologiche sugli zirconi della frazione sabbiosa, una tecnica largamente utilizzata che fornisce ottimi risultati ai fini di discriminare la provenienza dei sedimenti. In particolare, quest’ultima tecnica permette, se applicata a sistemi fossili molto antichi, di ricostruire indirettamente il contesto tettono-morfologico nell’area di studio. Tali metodologie analitiche sono state applicate su due casi studio estremamente diversi tra di loro. Il primo ha riguardato i sedimenti glaciali deposti durante la Late Paleozoic Ice Age ed attualmente affioranti nella Terra Vittoria in Antartide; le analisi petrografiche e geocronologiche, unite ad indagini sedimentologico-stratigrafiche, hanno permesso di andare a dettagliare la distribuzione della copertura glaciale nel Gondwana durante il Permiano inferiore, rafforzando l’ipotesi che usa serie di calotte glaciali si fossero sviluppate asincronamente durante una delle più durature fasi glaciali della storia della Terra. Il secondo caso studio è inquadrato all’interno della IODP Expedition 374 che mira alla comprensione delle dinamiche delle calotte antartiche nel Mare di Ross (Antartide) dal Miocene Inferiore all’attuale. Sui carotaggi sono stati identificati e descritti dettagliatamente i ciottoli che, confrontando i dati di questo studio, con indagini geocronologiche, termocronologiche e geochimiche tuttora in corso, hanno permesso di avanzare ipotesi sui flussi glaciali presenti nel Mare di Ross negli ultimi 18 Milioni di anni, mettendo in luce la nascita della Calotta Antartica Occidentale marina nel Miocene Inferiore.
This thesis focus on the provenance study with multidisciplinary approach of sediments and rocks deposited in glacial environments in Antarctica in two distinct temporal contests: the Late Paleozoic Ice Age (LPIA) which involved Gondwana, and the Cenozoic glacial-interglacial cycles. The common point between the two distinct context is the comparison of glacial depositional systems and the provenance study of different temporal, climatic, paleogeographic, and continental settings, whereas both in the Antarctic continent. The comparison could highlight differences between the two studied glacial settings, and it could be useful both for paleo-geographic and paleo-climatic reconstructions and for future previsions. This work is focused on the study of the gravel fraction (clasts larger than 2 mm), constituting glacial sedimentological facies (i.e., diamictite and conglomerate), through petrographic analyses which allow the direct comparison between clasts and outcropping geology of the glacier’s catchments. Other analytical technologies were used to constrain provenance hypothesis based on clast petrography; in particular, chemical analyses on selected mineralogical phases were carried out. These preliminary data seem to show variations in the chemical composition of biotite in intrusive rocks, and it could be used as a marker for the provenance discrimination of intrusive rocks constituting East and West Antarctica. Moreover, geochronological analyses on detrital zircons, from sand size, were carried out; this is an analytical technique largely used for provenance analysis. This technique allows, if applied on fossil systems, the indirect reconstruction of the paleo-tectonic and paleo-morphologic setting of the study region. The methodologies described have been applied in two different cases study extremely different. The first concerns the glacial sediments deposited during the Late Paleozoic Ice Age which currently crop out in Victoria Land (Antarctica); the petrographic and geochronological analyses, coupled with sedimentological and stratigraphic investigations, allow to better define the distribution of the glacial cover across Gondwana in the early Permian, strengthening the hypothesis of multiple and diachronous ice sheets which developed one of the longest glacial phases of the Earth. The second case study is framed inside the IODP Expedition 374, which aims the understanding of the Antarctic Ice sheets dynamics in the Ross Sea (Antarctica) since early Miocene. Gravel sized clasts within sediment cores were identified and described. The clast petrology, compared with ongoing geochronological, geochemical and thermochronological analyses, allows the reconstruction of the paleo-ice flows in the Ross Sea in the early Miocene to Pliocene.

Thesis (M.S.)--Indiana University, 2008.
Department of Earth Sciences, Indiana University-Purdue University Indianapolis (IUPUI). Advisor(s): Kathy J. Licht, Andrew P. Barth, R. Jeffery Swope, Gabriel M. Filippelli. Includes vitae. Includes bibliographical references (leaves 182-191).