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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

The late Quaternary tephrochronology of the Adriatic region : implications for the synchronisation of marine records

Bourne, Anna Julie January 2012 (has links)
Tephrochronologies for three marine core sequences from the Adriatic Sea have been constructed. Two of the sequences, PRAD 1-2 and RF93-77, are located in the central Adriatic and the third, SA03-03, lies in the southern Adriatic. Isotopic and biostratigraphic records are available for all three sequences, features of which have been used as isochronous markers in the region. This project aimed to establish whether tephra layers provide (a) secure, independent isochronous tie-lines and (b) a robust methodology for testing correlations based on other methods. A total of 54 tephra layers have been identified within these sequences, of which only 8 are visible layers, the remainder being classified as cryptotephras. Geochemical characterisation of the ash layers has been undertaken using electron microprobe analysis and laser-ablation trace element methods. Geochemical correlation to the detailed tephra record from Lago Grande di Monticchio was performed using chemical element biplots and discriminant function analysis. Bayesian-based age models were generated for the three Adriatic records using available chronological information that are independent of assumptions of synchroneity between proxy marker events. These models allowed comparisons with tephra and palaeoenvironmental data from Lago Grande di Monticchio and other Mediterranean sites. The results support some assumptions of synchronous regional changes, but not others. The key outcomes are (a) the recognition of additional (non-visible) distal ash layers that enhance the potential for correlating marine and terrestrial records in the central Mediterranean; (b) volcanic ash records preserved in Lago Grande di Monticchio and in some localities proximal to volcanic sources appear to be incomplete; and (c) isotopic records in Adriatic sediment sequences reflect regional forcing factors more than local conditions.
2

The Quaternary Stratigraphy of the Henrys Fork and Western Browns Park, Northeastern Uinta Mountains, Utah and Wyoming

Counts, Ronald C. 01 May 2005 (has links)
The landscape evolution of the northeastern Uinta Mountains and the manner in which climatic and tectonic forcing have influenced it are not well constrained. Surficial deposits covering ~325 km2 below the glacial termini in the Henrys Fork and ~50 km2 along the Green River in western Browns Park were mapped at 1:24,000 scale to develop a Quaternary stratigraphic framework for the northeastern Uinta Mountains. The Henrys Fork mapping area spans from late Wisconsinan moraines to Flaming Gorge Reservoir. The Henrys Fork stratigraphy contains 10 mainstem gravels, six piedmont gravels, and landslide deposits. Terraces preserved along the Henrys Fork converge downstream and are strath terraces underlain by clast-supported, cobble gravel derived from the Uinta Mountain Group and Paleozoic limestone units. The Henrys Fork terrace stratigraphy was correlated to the Wind River terrace stratigraphy for age control, and incision rates were estimated at 80-110 m/m.y. The Browns Park mapping area includes Little Hole and continues through lower Red Canyon into westernmost Browns Park, ending at the Warren Draw-Swallow Canyon quadrangle boundary. The Browns Park stratigraphy includes eight mainstem gravels, five piedmont gravels, and various landslide, colluvial, and eolian deposits. A tuffaceous bed with Lava Creek Bash (640 ka) was identified near the top of a deposit at Little Hole that was previously mapped as Miocene basin fill. Minimum Green River incision rates were estimated between 90 and 115 m/m.y. using the Lava Creek Bash for age control. These rates are comparable to estimates for the Henrys Fork, but are about half of the rates reported for the south flank of the Uintas and other central Rocky Mountain ranges. A series of three distinct deposits in western Browns Park are interpreted as evidence for the landslide impoundment and subsequent outburst flooding of the Green River. These include slackwater deposits at Little Hole, an outburst flood deposit in western Browns Park, and a large paleolandslide deposit that lies between them. Estimates of sediment accumulation rates behind the paleolandslide dam suggest it was stable for ~605 years. Peak discharge estimates from impounded water volume estimates and paleoflow competence indicators suggest that the resulting outburst flood was ~22,000 m3/s.
3

Enregistrements stratigraphiques des cycles glacio-eustatiques et de la déformation durant le Pléistocène le long de la marge centrale d’Équateur : exploitation des données de la campagne ATACAMES / Stratigraphic record of the glacio-eustatic cycles and the deformation during the Pleistocene along the central Ecuadorian margin : using the ATACAMES data campaign

Martillo Bustamante, Carlos 11 May 2016 (has links)
L’objectif de cette étude est de contraindre les déformations au cours du Pléistocène d'une marge active à partir de l’analyse sismo-stratigraphique des sédiments conservés sur la plate-forme et la pente supérieure, le long de la marge centrale d’Equateur. A partir les données de sismique haute résolution et de carottage collectées pendant l'expédition Atacames (2012), plusieurs bassins ont été identifiés. La répartition latérale et de la succession des séquences T-R dans ces bassins montrent une distribution complexe des sédiments dans le temps et l'espace. Ce travail montre que, le long des marges actives, l’analyse sismo-stratigraphique de l’enregistrement des séquences liées aux cycles eustatiques du Pléistocène est un outil très puissant. A l'échelle locale, la subduction de seamounts perturbe et renforce l'effet de déformation régionale de la ride de Carnegie. / The aim of this study is to constrain recent deformation and stratigraphic evolution of an active margin, using sismo-stratigraphic analysis of Pleistocene sediment preserved on the margin shelf and upper slope along of the Central Ecuadorian margin. From the extensive geophysical and sedimentological investigations carried out during the ATACAMES expedition (2012), we are identified serveral basins in the Ecuadorian margin. A detailed analysis of the thickness, the lateral distribution and stacking patterns in these basins show a complex distribution of sediments in time and space. The seismic-sequence stratigraphy analysis related to eustatic cycles of the Pleistocene shows a regional regional unconformity at the base (1782-Ka as minimum age), which can correspond to the signature of the beginning of the Carnegie ridge collision.
4

Late Quaternary Louisiana Shelf-Margin Deltaic Deposition, North-Central Gulf of Mexico

Mobley, Casey 20 May 2005 (has links)
This study aims to establish a depositional framework for an area of the Louisiana shelf, north-central Gulf of Mexico. The depositional history of the study area is poorly understood, especially within the last cycle of major eustatic fluctuation (~18, 000 yrs BP – present). Data sets used in this study include pre-existing and previously unanalyzed two-dimensional, highresolution seismic profile records (Acadiana 86 and Acadiana 89), geotechnical foundation boring data (Coleman and Roberts, 1988a), and an industry lease block survey report (Cole, 1983). Seismic sequence stratigraphic methods are employed in this study to analyze seismic profile data. Seismic sequence analysis results indicate the presence of five unconformable surfaces and five seismic facies units. Through correlation of seismic profile data with lithologic and chronologic data, it is possible to conclude that these seismic facies units represent shelf-margin deltaic deposition during the last lowstand of sea level (~18, 000 yrs BP), sourced by the Pearl River. .

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