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1
Heine, Jan T. "Glacier advances at the Pleistocene/Holocene transition near Mount Rainier volcano, Cascade Range, USA /." Thesis, Connect to this title online; UW restricted, 1997. http://hdl.handle.net/1773/6748.
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Shunk, Aaron Driese Steven G. "Late Tertiary paleoclimate and stratigraphy of the Gray Fossil Site (eastern TN) and Pipe Creek Sinkhole (northcentral IN)." Waco, Tex. : Baylor University, 2009. http://hdl.handle.net/2104/5303.
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Smith, Alexander Ryan. "Sedimentology and Stratigraphy of Miocene-Age Glacial Deposits, Friis Hills, Antarctica." Thesis, North Dakota State University, 2011. https://hdl.handle.net/10365/29316.
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The Friis Hills is an isolated plateau standing as much as 600 m above surrounding topography in the McMurdo Dry Valleys region or Antarctica.Preserved on the plateau surface is a sequence of early to middle Miocene-aged dritis. At the eastern edge of the plateau, these drifts fill a shallow paleovalley to a depth of at least 35 m. The drills are exposed in a natural cross-section where modern topography crosscuts the paleovalley. Establishing an age and an environmental interpretation for these deposits is important because Antarctic paleoclimate records are lacking from the Mid-Miocene Climate Optimum. Two drifts fill the ancient paleovalley in the eastern Friis Hills. The upper drift is here named Cavendish drift: the lower is here named Friis drift. Cavendish can be subdivided into three units, whereas Friis drift can be subdivided into two units. Each of these units is a horizontal bed that laps on paleovalley sidewalls. The lowest, Friis II, is a compact diamicton that is overlain by a nearly in-situ bedded volvanic ash. Based on [20]Ar/[39]Ar dating, the ash is 19.76 [plus/minus] 0.07 Ma old. A second diamicton, Friis I, conformably blankets Friis II and was discovered to hold fossileferous interbeds. Both Friis I and II contain erratic clasts and both are lodgemont tills deposited from small, locally derived, alpine glaciers. Bedrock striations show ice flow to the northeast at azimuths between 025? to 032?, parallel to the trend of the paleovalley axis. Above these, Cavendish I. II. and III were deposited when thick ice covered the Friis Hills. Where the Cavendish drift laps onto paleovalley sidewalls, bedrock striations show ice flow from 077? to 150?. Cavendish drift was deposited sometime alter 19.8 Ma but before 14 Ma. when the Dry Valleys glacial records show that regional glaciers became cold-based. Downcutting eventually isolated the Friis Hills plateau, resulting in the preservation of the drift sequence. This event was most likely associated with growth or the East Antarctic Ice Sheet 14 Ma ago. This age constraint means that the tills preserved in the Friis Hills date from a time just before the East Antarctic Ice Sheet expanded and became a permanent feature. Based on the age-dated stratigraphy presented in this thesis, future work focusing on fossiliferious interbeds could provide unique and important constraints on Miocene climate change.North Dakota State University. Department of Geosciences
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Hartmann, Kerstin. "Jungquartäre Reliefentwicklung, Substratgenese, Klimageschichte und aktuelle Morphodynamik am Ostrand der Namib in der Region Hartmannstal-Marienflusstal (NW-Namibia) /." Köln : Geograph. Inst. der Univ. zu Köln, 2007. http://bvbr.bib-bvb.de:8991/F?func=service&doc_library=BVB01&doc_number=016293693&line_number=0002&func_code=DB_RECORDS&service_type=MEDIA.
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Kahmann-Robinson, Julia A. Driese Steven G. "Late Mississippian (Chesterian) high-frequency climate change in the Pennington Formation at Pound Gap, KY USA." Waco, Tex. : Baylor University, 2008. http://hdl.handle.net/2104/5293.
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Cleveland, David M. Atchley Stacy C. Nordt Lee C. "Fluvial sequence stratigraphy and paleoclimate of the Upper Triassic (Norian-Rhaetian) Chinle Strata, northern New Mexico." Waco, Tex. : Baylor University, 2007. http://hdl.handle.net/2104/5118.
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Thesis (Ph.D.)--Baylor University, 2007.In the abstract "[delta]13C" the "13" and "[delta]18O" the "18" are superscript; "pCO2" the "2" is subscript. Includes bibliographical references (p. 107-118).
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Holmes, Jonathan Anthony. "Pliocene and Quaternary environmental change in Kashmir, north-west Himalaya." Thesis, University of Oxford, 1989. http://ora.ox.ac.uk/objects/uuid:e9bb6cf8-93a8-4471-9c55-7ed84044dc3c.
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Late Cainozoic environmental changes in Kashmir (33°30' to 34°30' N: 74°10' to 75°30' E) have been reconstructed using a range of techniques. The sedimentary record in Kashmir consists of a thick (>1000m) basin-fill sequence known as the Karewa group, together with glacial and related sediments in the surrounding mountain flanks. The Karewa sediments are fluviolacustrine in origin and comprise alternations of conglomerates, sands and clayey silts. Work on the lower Karewa formation, which has previously been dated palaeomagnetically to between 4 and 0.4 MaBP, involved the semi- quantitative analysis of clay-mineral assemblages by X-ray diffraction.The clay minerals in the lower Karewa mudstones are interpreted as detrital clays which reflect weathering within Kashmir basin. The analyses showed a change in clay mineralogy between about 2.5 and 2.3MaBP, from abundant kaolinite to abundant smectite. Work on the upper Karewa formation involved field description and mapping of facies, sedimentological analysis, dating using thermoluminescence (TL) and amino-acid racemization, and analysis of ostracod assemblages from lacustrine sediments. Areal restriction of the lake in Kashmir occurred about 0.4MaBP with the rapid uplift of the Pir Panjal Range. Sedimentological data show that aeolian dust formed a major input into the lake. Ostracod assemblages show that the lake itself was cool, shallow, alkaline and had abundant plant macrophytes, The lake drained between 120 and SOkaBP. Stratigraphical, sedimentological and faunal evidence suggests that this was a result of tectonically-induced drainage rather than climatically-induced desiccation. The glacial history of the surrounding mountain flanks was reconstructed by field mapping of glacial sediments and dated using TL and radiocarbon methods. Present and past patterns of glaciation wore assessed by the determination of equilibrium-line altitudes (ELAs), glaciation thresholds (GTs) and cirque aJtitudes. Glaciers extended to 2150 m a.s.l in the Great Himalayan flank and 2600 m a.s.l. in the Pir Panjal. There is evidence for only 2 pre-Holucene advances in Kashmir, the older of which predates 35kaBP. Present patterns of glacierization indicate a SW to NE rise in the height of ELAs and GTs suggesting topographic and precipitation control. An apparent reversal of trends during the past is explained by Quaternary uplift of the Pir Panjal Range.
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Morgans, Helen Sarah. "Early to middle Jurassic stratigraphic development, vegetation and climate change in north-western Europe." Thesis, University of Oxford, 1997. http://ora.ox.ac.uk/objects/uuid:4b5cae3c-7562-45b9-b2a2-543b2649b24f.
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The aim of work presented in this thesis was to explore the inter-relationships of cyclic sedimentation, relative sea-level change, and palaeoclimate as inferred from plant megafossils. To this end, the investigation focused on the classic plant-bearing Middle Jurassic succession of Yorkshire. The Middle Jurassic (Aalenian-Bathonian) Ravenscar Group of the Cleveland Basin (Yorkshire) comprises a predominantly fluvio-deltaic succession intercalated between thinner, laterally persistent marine units. There is a pronounced lateral facies change across the basin, from mainly alluvial sediments in the north to more marine deposits in the south. Although variable in character, the facies composing the sequence are described by four principal environments of deposition: alluvial, estuarine, lagoonal and marine. In an attempt to achieve a more accurate stratigraphic control on the succession, sequence-stratigraphic concepts are applied to outcrop exposures and subsurface cores. The identification of 'key surfaces' in the sequence resolves a series of lithological cycles which reflect relative sea-level fluctuations. Using this approach the Aalenian-Bathonian sequence can be subdivided into two large-scale (second-order) transgressive-regressive cycles onto which six medium-scale (thirdorder) cycles of transgression and regression are superimposed. The potential for correlating these lithological cycles regionally has been assessed by comparing coeval sections from southern Scandinavia. Plant-bearing fluvio-deltaic sequences from Bornholm and Scania were chosen as a means for appraising the lateral continuity of the cycles, and assessing what factors might have controlled their development. Study of floral remains from the Ravenscar Group within the context of this stratigraphic framework yields valuable palaeoclimatic information. Growth-ring analysis of fossil wood of Late Pliensbachian to Late Bathonian age indicates a distinctly seasonal climate with low to moderate interseasonal variation in tree growth. Significant intraseasonal influences on wood production are implicit in the abundance of false rings. Consideration of these results within a stratigraphic context suggests that conditions during the Bathonian were comparatively hostile: a finding which is interpreted to be due to more frequent and extended water shortages associated with a drier climate. These palaeoclimatic inferences are substantiated by evidence obtained from the examination of the flora using Correspondence Analysis (CA). This approach verifies the presence of a temporal fluctuation in the flora found by previous investigations and, furthermore, highlights physiognomic trends in the flora with time. The results from CA also indicate adverse growing conditions during the Bathonian, emphasized by the prevalence of xeromorphic taxa.
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Morse, David L. "Glacier geophysics at Taylor Dome, Antarctica /." Thesis, Connect to this title online; UW restricted, 1997. http://hdl.handle.net/1773/6801.
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Hawley, Robert L. "Borehole investigations of firn processes /." Thesis, Connect to this title online; UW restricted, 2005. http://hdl.handle.net/1773/6796.
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Marcott, Shaun Andrew. "A Tale of Three Sisters: Reconstructing the Holocene glacial history and paleoclimate record at Three Sisters Volcanoes, Oregon, United States." PDXScholar, 2005. https://pdxscholar.library.pdx.edu/open_access_etds/3386.
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At least four glacial stands occurred since 6.5 ka B.P. based on moraines located on the eastern flanks of the Three Sisters Volcanoes and the northern flanks of Broken Top Mountain in the Central Oregon Cascades. The youngest of these advances was the Little Ice Age (LIA) glaciation, which reached its maximum advance 150-200 yrs. B.P. and is defined by the large sharp crested and unvegetated moraines adjacent to the modern glaciers. In isolated locations less than 100 m downslope from these moraines, a second set of sparsely vegetated lateral moraines marks the Late-Neoglacial stand of the glaciers between 2.1 ± 0.4 and 7.7 ka B.P, A third set of Early-Neoglacial end moraines is 300-700 meters downslope of the modern glacier termini, and postdates 7.7 ka B.P. From SST temperature data (Barron et al., 2003) and a speleothem record (Vacco, 2003), we infer that this advance occurred between 4.5 and 6.5 ka B.P. Finally, the Fountonnor stand is marked by moraines 500-900 meters downslope of the modern glacier termini, and we infer these are latest Pleistocene or early Holocene.
Modem equilibrium line altitudes (ELAs) at the Three Sisters and Broken Top are approximately 2500 - 2600 m. During the LIA, the ELAs were 40 - 180 m lower, requiring cooler mean summer temperatures by 0.7 - 1.0°C and winter snowfall to increase by 10 - 60 cm water equivalent. The average Early Neoglacial and Fountonnor ELAs were 130 - 300 m and 290 - 320 m lower than modem glaciers, respectively, requiring air temperatures to be 0.7 - 1.6°C and 1.5 - 1.7°C cooler during the summer and winter snowfall to be 40 - 100 cm water equivalent and 90 - 100 cm water equivalent greater.
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Heimhofer, Ulrich. "Response of terrestrial palaeoenvironments to past changes in climate and carbon-cycling : insights from palynology and stable isotope geochemistry /." Zurich : [Swiss Federal Institute of Technlogy], 2004. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=15463.
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Birkos, Elizabeth. "Controls on Stable Oxygen Isotope Concentrations in Coropuna and Quelccaya Peruvian Ice Cores Over the Last 200 Years." The Ohio State University, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=osu1238093120.
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Brown, Thomas R. "Benthic foraminiferal paleoecology and sequence stratigraphy across the Cretaceous-Tertiary boundary at Braggs, Alabama." Virtual Press, 1992. http://liblink.bsu.edu/uhtbin/catkey/845938.
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Southern Alabama holds one of the world's most complete shallow shelf Cretaceous-Tertiary boundary sections. The boundary is exposed in a sequence of marl-limestone interbeds in a roadcut south-east of Braggs in Lowndes County, Alabama. Benthic foraminifera were extracted in 10cm intervals to obtain a high-resolution record of assemblage succession across this controversial boundary. A local sea level curve was then formulated using previous paleobathymetric foraminiferal assemblage models from the Gulf Coast and the Atlantic Coastal margin. Sea-level fluctuations thus evident have revealed a fourth-order cycle similar to those found by Briskin and Fluegeman (1990) with an average period of around 430 kyr through the Paleocene. This cycle includes a drop from outer slope to middle shelf conditions in the latest Cretaceous and a subsequent increase from inner shelf to outer shelf conditions in the earliest Paleocene. Within this cycle are several fifth-order cycles that are interpreted as having a periodicity of roughly 100 kyr. Sea-level cycles with Milankovitch frequencies occurring on an ice-free Paleocene Earth lend support to the concept of astronomical forcing of climate and thus sea-level.Department of Geology
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Young, Seth Allen. "A chemostratigraphic investigation of the late Ordovician greenhouse to icehouse transition oceanographic, climatic, and tectonic implications /." Columbus, Ohio : Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1201628490.
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Gudmundsson, Hjalti Johannes. "Holocene glacier fluctuations and tephrochronology of the Öræfi district, Iceland." Thesis, University of Edinburgh, 1999. http://hdl.handle.net/1842/15756.
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The aims of this thesis are to refine the tephrochronology of the Öræfi district, SE Iceland and assess the Holocene glacier fluctuations of the Öræfajökull ice cap. The pattern and timing of glacier fluctuations are determined using glacial geomorphology and tephrochronology, and the implications for palaeoclimate are assessed. Iceland is important to the study of global and regional climatic change because it is located close to both the marine and atmospheric Polar Fronts widely regarded as the key factors in the climate of the North Atlantic region. Six outlet glaciers were studied: Svinafellsjökull, Virkisjökull, Kotárjökull and Kviárjökull originating from the Öræfajökull ice cap and Skaftafellsjökull and Morsárjökull originating from the Vatnajökull ice cap. A long history of glacier fluctuations were found with a similar temporal pattern of glacier oscillation between the outlets of Vatnajökull and Öræfajökull. A maximum of eight advances have been identified. The oldest advance is inferred to date from the maximum of the last Glaciation ca. 18000 yrs BP. The first advance in the Holocene occurred ca. 9700 BP during a still-stand of the last Termination. The onset of the Neoglaciation occurred between 6000 BP and 4600 BP with an expansion of all of the studied glaciers. Subsequent smaller advances have been dated to ca. 3200 BP, ca. 1800 BP, ca. 700 BP, ca. 200 BP and ca. 80 BP. The most significant movement of the Polar front during the Holocene is likely to have occurred around 5000 BP, and, as a consequence, an estimated temperature cooling of ca. 2.5°C took place in Iceland, perhaps the greatest cooling since the last Termination. Within the broad pattern of change, glaciers in the study area show variability which represents local precipitation patterns, contrasting topography and change in glacier process. In this thesis a total of 22 silicic tephra layers are identified from over 90 profiles in the study area. The majority of these layers are dated to the latter part of the Holocene. Three silicic tephras were deposited during historical time (post 900 AD) namely, Vö ca. 900AD,HI104 and Ö1362. The Vö ca. 900 AD and the H1104 tephras are located for the first time. Specific prehistoric (pre 900 AD) tephras identified include Hekla-Ö, Hekla-4 and Hekla-S. The tephrochronology of the Öræfi district is also used to assess the eruption history of the Öræfajökull stratovolcano during the Holocene. Prehistoric eruptions are dated to ca. 9200 BP, ca. 6500 BP(?), ca. 4700 BP, ca. 2800 BP and ca. 1500 BP. Jökulhlaups accompanied the eruptions of 1727 AD, 1362 AD and ca. 1500 BP and are likely to have followed older eruptions of the volcano. A strong relationship occurs between volcanic activity of the Öræfajökull stratovolcano and the pattern of glacier fluctuations. This is explained as a response to isostatic crustal adjustment during ice cap growth and decay, and indicates a general relationship between volcanic activity and climate change.
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Tomescu, Iulia. "The Ordovician : a window toward understanding abundance and migration patterns of biogenic chert and implications for paleoclimate /." Ohio University / OhioLINK, 2004. http://www.ohiolink.edu/etd/view.cgi?ohiou1103302033.
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Buffen, Aron Maurice. "Abrupt Holocene climate change: Evidence from a new suite of ice cores from Nevado Coropuna, southwestern Peru and recently exposed vegetation from the Quelccaya Ice Cap, southeastern Peru." Columbus, Ohio : Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1218568566.
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Metcalfe, Elisabet Joan. "Late-glacial through Holocene Stratigraphy and Lake-level Record of Rangely Lake, Western Maine." Fogler Library, University of Maine, 2007. http://www.library.umaine.edu/theses/pdf/MetcalfeEJ2007.pdf.
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Gregory, Kathryn Mary. "Late Eocene paleoaltitude, paleoclimate, and paleogeography of the Front Range region, Colorado." Diss., The University of Arizona, 1992. http://hdl.handle.net/10150/185985.
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Erosion beveled the Laramide Front Range uplift in Colorado to a surface of low relief by the end of the Eocene. This study uses paleobotanic climate analysis techniques to determine the paleoelevation of this regional surface by examining the overlying 34.9 Ma Florissant flora. Multiple regression models explaining 93.4% of the variance in mean annual temperature (MAT), 86.1% of the variance in growing season precipitation (GSP) and 65.7% of the variance in rainfall distribution were derived from J. A. Wolfe's dataset of 31 leaf physiognomic character states from 86 modern vegetation sites. When applied to a new collection of 29 species from the Florissant flora, estimates of MAT = 10.7 ± 1.5°C, and GSP = 55.6 ± 12.5 cm, with precipitation occurring mostly during the growing season, are derived. This paleoclimate estimate is corroborated by data from late Eocene Sequoia affinis from Florissant. Higher mean ring width of the fossil trees as compared to modern counterparts can be explained by a climate with summer mean monthly temperatures ≥ 14°C and summer mean monthly rainfall >1.5 cm. The estimated MAT, when combined with coeval sea level MAT and terrestrial lapse rate, implies an elevation of 2.3-3.3 km for Florissant, which is indistinguishable from the modern elevation of 2.5 km. The elevation of Florissant is tied to that of the Great Plains by the Wall Mountain Tuff, so the Great Plains were also high. The elevation was created either by underplating and/or mass transfer in the Laramide, or by mantle uplift of crust thickened by pre-Laramide tectonics. This elevation estimate implies that: (1) Pliocene uplift is not required to explain the present elevation. Thus, late Tertiary plateau uplift in the western US was not a contributing factor to the marked global cooling since 15 Ma; and (2) in the late Eocene, regional surfaces of planation could be formed at elevations significantly above sea level but below tree line. The surface was possibly formed from a lack of storminess; a preponderance of small storm events will diffusively smooth topography.
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Avila, Teresa D. "Seafloor weathering and the Middle to Late Ordovician seawater 87Sr/86Sr inflection point preserved in conodont apatite." The Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu1565961269717394.
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Gouldey, Jeremy C. "Strontium and Carbon Isotope Stratigraphy of the Llandovery (Early Silurian): Implications for Tectonics and Weathering." Columbus, Ohio : Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1221528660.
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Eddleman, James L. "Elevation, Longitudinal Profile, And Schmidt Hammer Analysis Of Strath Terraces Through Capitol Reef National Park, Utah: Bedrock Channel Response To Climate Forcing?" Diss., CLICK HERE for online access, 2005. http://contentdm.lib.byu.edu/ETD/image/etd936.pdf.
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Hansen, Christel Dorothee. "The characterisation of an openwork block deposit, northern buttress, Vesleskarvet, Dronning Maud Land, Antarctica." Thesis, Rhodes University, 2014. http://hdl.handle.net/10962/d1013138.
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Investigating openwork block accumulation has the potential to further our understanding of rock weathering, the control of geological structure on landforms, the production of substrates for biological colonisation and the impacts of climate change on landform development and dynamics. Various models for the development of these landforms have been proposed. This includes in situ weathering, frost heave and wedging. Furthermore, it has been suggested that cold-based ice has the potential to preserve these features rather than to obliterate them. Blocky deposits are also frequently used as proxy evidence for interpreting palaeoclimates. The morphology and processes acting on a blockfield located on the Northern Buttress of the Vesleskarvet Nunataks, Dronning Maud Land, Antarctica (2°W, 71°S) were investigated and characterised. Given block dimensions and orientations that closely resembled the parent material and only small differences in aspect related characteristics observed, the blockfield was found to be autochthonous with in situ block production and of a young (Holocene) age. Small differences in rock hardness measurements suggest some form of aspect control on rock weathering. South-facing sides of clasts were found to be the least weathered. In comparison, consistently low rock hardness rebound values for the north-facing aspects suggest that these are the most weathered sides. Additional indicators of weathering, such as flaking and pitting, support analyses conducted for rock hardness rebound values. Solar radiation received, slope gradients and snow cover were found to influence weathering of clasts across the study site. Furthermore, ambient temperatures and wind speed significantly influenced near-surface ground temperatures dynamics. However, the lack of a matrix and paucity of fine material in textural analyses suggest a limited weathering environment. It is suggested that the retreat of the Antarctic ice sheet during the last LGM led to unloading of the surface, causing dilatation and subsequent fracturing of the bedrock along pre-existing joints, leading to in situ clast supply. Subsequent weathering and erosion along other points or lines of weakness then yielded fines and slight edge rounding of clasts.
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Lopes, Renato Pereira. "Reconstituição paleo-climática e paleo-ambiental do pleistoceno tardio no sul da planície costeira do Rio Grande do Sul." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2013. http://hdl.handle.net/10183/81220.
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A Planície Costeira do estado do Rio Grande do Sul (PCRS) foi estruturada ao longo do Quaternário por sucessivas oscilações do nível do mar. Alem das oscilações eustáticas, o clima também afetou a região, influenciando nos padrões deposicionais representados pelas fácies expostas em afloramentos e na distribuição dos organismos. O objetivo da presente tese é reconstituir condições climáticas e ambientes da região durante o Pleistoceno tardio, a partir de levantamentos estratigráficos, sedimentologia, datações, e análises de fósseis. A área escolhida para o desenvolvimento da tese foi o Arroio Chuí, localizado no sul da PCRS entre as barreiras II e III, onde afloram seqüências deposicionais que representam ambientes marinho e terrestre. Os resultados mostram que a porção marinha da seqüência exposta ao longo do arroio representa a fácies marinha do sistema deposicional Laguna-Barreira II. Datações em sedimentos e conchas de bivalves coletados nesta fácies indicam que este sistema teria sido formado pelo máximo transgressivo marinho ocorrido durante o estágio isotópico marinho (MIS) 7, há aproximadamente 230 mil anos. As temperaturas do oceano na região durante esse intervalo eram mais quentes do que nos dias de hoje, como evidenciado por espécies de moluscos bivalves e foraminíferos indicativos de águas mais quentes. A camada acima da fácies marinha representa paleossolos e antigos sistemas fluviais, onde ficaram preservados fósseis de grandes mamíferos. Datações feitas nos fósseis desses animais mostraram idades entre 226 e 34 mil anos; análises de isótopos estáveis (13C e 18O) em dentes fósseis mostram que o ambiente era caracterizado por pradarias compostas por gramíneas, arbustos e possivelmente matas de galeria. As características sedimentológicas mostram intercalações entre períodos mais úmidos e outros mais secos. Na camada acima do horizonte que contem os restos de grandes mamíferos não foram encontrados fósseis ate agora, e o aumento na quantidade de silte e presença de nódulos e concreções carbonáticas indicam clima mais seco, provavelmente relacionado ao ultimo máximo glacial (LGM).The Coastal Plain of Rio Grande do Sul state (CPRS) was formed during the Quaternary by successive sea-level oscillations. Besides the eustatic oscillations, the region was also affected by climate changes, which influenced the depositional patterns represented by the facies exposed along outcrops and the distribution of organisms. The objective of this thesis is to reconstruct late Pleistocene climate conditions and environments of the region, using stratigraphic surveys, sedimentology, datings ands analysis on fossils. The area chosen for this work was the Chui Creek, located in the southern CPRS between the barriers II and III, where depositional sequences that represent marine and terrestrial environments are exposed. The results show that the marine portion of the sequence exposed along the banks of the creek represents the marine facies of the depositional system Barrier-Lagoon II. Datings on sediments and bivalve shells from this facies indicate that this system would have been formed by the marine highstand during the marine isotope stage (MIS) 7, around 230 thousand years ago. The ocean temperatures during this interval were higher than today, as indicated by bivalves and foraminifers that indicate warmer waters. The layer above the marine facies represents paleosoils, and ancient fluvial systems where fossils of large mammals were preserved. Datings on these fossils revealed ages between 226 and 34 thousand years; analyses of stable isotopes (13C and 18O) in fossil teeth showed that the landscape consisted of prairies composed by grasses, shrubs and possibly gallery forests. The sedimentary record show intercalated humid and dry periods. The layer above the horizon with large mammalian remains provided no fossils so far, and the increase in silt-sized particles and the presence of carbonate nodules and concretions indicate very dry conditions, probably correlated with the last glacial maximum (LGM).
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Álvarez, Amado Fernanda. "Evolución Paleoclimática Basada en el Estudio de una Estalagmita, Caverna “Perte du Temps”, Isla Madre de Dios, Patagonia, Chile." Tesis, Universidad de Chile, 2009. http://repositorio.uchile.cl/handle/2250/103396.
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En este trabajo se muestra el potencial para establecer una evolución climática en una estalagmita perteneciente a la caverna “Perte du Temps”, Isla Madre de Dios. El objetivo es interpretrar el registro paleoclimático almacenado en ella, a través del estudio petrográfico de la muestra. Se pretende establecer un modelo cronoestratigráfico utilizando como proxy climático las variaciones de espesor de láminas en función de la temperatura y precipitación.
Se recolectaron muestras de rocas, estalagmitas y agua, se estudió en detalle la petrografía de la estalagmita EMD01. Para construir el modelo cronoestratigráfico se realizó un conteo y caracterización de bandas, luego se definieron dominios en base a diferencias de espesor y naturaleza de éstas, color y fábrica de la calcita y/o discontinuidades en el crecimiento.
A lo largo de la muestra se observa la repetición de la secuencia: lámina clara gruesa – lámina oscura delgada, lo cual sugiere la misma unidad de tiempo. Se propone que es de un año, ya que existe una ritmicidad anual del clima en superficie, la cual es transmitida a la estalagmita. Las variaciones en el color y espesor de las capas, coincidirían con las estaciones verano/otoño e invierno/primavera, que presentan cambios en tasas de precipitaciones y temperatura, factores relacionados con tasas de goteo, vegetación sobre la caverna y concentración de Ca2+ en el agua, que finalmente son los que controlan la tasa de crecimiento de la calcita. Se plantea que la mayor concentración de Ca2+ en el agua ocurriría en verano/otoño, por lo que las láminas claras se desarrollarían en estas estaciones y las láminas oscuras durante el invierno.
En la estalagmita se definieron 13 dominios, cuyos límites coinciden con máximos y mínimos en las tasas de crecimiento. Para delimitarlos se utilizaron criterios que dependen del clima, por lo tanto los límites entre cada dominio se asocian a cambios climáticos de orden mayor a los registrados al interior de cada uno. Los dominios con mayor tasa promedio de crecimiento (C, E y L) indican que la estalagmita creció bajo condiciones de temperatura media mayor a los otros.
A una escala mayor, es posible dividir la estalagmita en dos partes en base a la fábrica de los cristales, la primera se habría formado en un ambiente de menor temperatura que el de la segunda parte, donde las láminas crecieron bajo una temperatura mayor. Debido a que el cambio en la fábrica es gradual se piensa que el cambio de temperatura también lo es.
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Partin, Judson Wiley. "Stalagmite reconstructions of western tropical pacific climate from the last glacial maximum to present." Diss., Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/22556.
Full textAbstract:
The West Pacific Warm Pool (WPWP) plays an important role in the global heat budget and global hydrologic cycle, so knowledge about its past variability would improve our understanding of global climate. Variations in WPWP precipitation are most notable during El Niño-Southern Oscillation events, when climate changes in the tropical Pacific impact rainfall not only in the WPWP, but around the globe. The stalagmite records presented in this dissertation provide centennial-to-millennial-scale constraints of WPWP precipitation during three distinct climatic periods: the Last Glacial Maximum (LGM), the last deglaciation, and the Holocene. In Chapter 2, the methodologies associated with the generation of U/Th-based absolute ages for the stalagmites are presented. In the final age models for the stalagmites, dates younger than 11,000 years have absolute errors of ±400 years or less, and dates older than 11,000 years have a relative error of ±2%. Stalagmite-specific 230Th/232Th ratios, calculated using isochrons, are used to correct for the presence of unsupported 230Th in a stalagmite at the time of formation. Hiatuses in the record are identified using a combination of optical properties, high 232Th concentrations, and extrapolation from adjacent U/Th dates. In Chapter 3, stalagmite oxygen isotopic composition (d18O) records from N. Borneo are presented which reveal millennial-scale rainfall changes that occurred in response to changes in global climate boundary conditions, radiative forcing, and abrupt climate changes. The stalagmite d18O records detect little change in inferred precipitation between the LGM and the present, although significant uncertainties are associated with the impact of the Sunda Shelf on rainfall d18O during the LGM. A millennial-scale drying in N. Borneo, inferred from an increase in stalagmite d18O, peaks at ~16.5ka coeval with timing of Heinrich event 1, possibly related to a southward movement of the Intertropical Convergence Zone (ITCZ). An inferred precipitation maximum (stalagmite d18O minimum) during the mid-Holocene in N. Borneo supports La Niña-like conditions and/or a southward migration of the ITCZ over the course of the Holocene as likely mechanisms for the observed millennial-scale trends. In Chapter 4, stalagmite Mg/Ca, Sr/Ca, and d13C records reflect hydrologic changes in the overlying karst system that are linked to a combination of rainfall variability and cave micro-environmental effects. Dripwater and stalagmite geochemistry suggest that prior calcite precipitation is a mechanism which alters dripwater geochemistry in slow, stalagmite-forming drips in N. Borneo. Stalagmite Mg/Ca ratios and d13C records suggest that the LGM climate in N. Borneo was drier and that ecosystem carbon cycling may have responded to the drier conditions. Large amplitude decadal- to centennial-scale variability in stalagmite Mg/Ca, Sr/Ca and d13C during the deglaciation may be linked to deglacial abrupt climate change events.
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Avilés, Nahuelpán Julio Esteban. "Estratigrafía y sedimentología de registros marinos de las bahías de Tongoy y Guanaqueros (~30° S), y sus implicancias paleohidrológicas." Tesis, Universidad de Chile, 2016. http://repositorio.uchile.cl/handle/2250/143344.
Full textAbstract:
GeólogoLas bahías de Tongoy y Guanaqueros son parte de la costa semi-árida de Chile, una zona de transición climática entre el desierto hiperárido de Atacama y el clima mediterráneo de Chile Central, donde la mayoría de las lluvias están fuertemente condicionadas por la influencia del Anticiclón Subtropical del Pacifico Suroriental y El Niño-Oscilación del Sur, afectando fuertemente la disponibilidad de agua cuando éstas se ausentan y ocasionando desastres cuando son muy intensas. Estas bahías se encuentran protegidas del viento dominante del suroeste, por la Punta Lengua de Vaca y Guanaquero, y están a su vez fuertemente influenciadas por la surgencia costera adyacente a este rasgo geomorfológico. Además, las bahías reciben descargas aluviales esporádicas desde las quebradas de las hoyas hidrográficas, lo que resulta en condiciones favorables para la acumulación de restos biogénicos derivados de la productividad océanica impulsada por la surgencia, así como material litogénico por escorrentía hacia el fondo de las mismas. Por tanto, el estudio estratigráfico y sedimentológico de los depósitos del fondo marino de ambas bahías permite determinar las variaciones paleoclimáticas a escala del Pleistoceno terminal-Holoceno, lo que fue estudiado en este trabajo de título, así como la relación de estas variaciones con cambios océano-climáticos a escala regional y/o global. El estudio sedimentológico de los testigos marinos TK2 y GUK1 de las bahías de Tongoy y Guanaqueros, respectivamente, permitió definir las siguientes unidades, que de base a techo son: unidad 4 (Holoceno temprano) en GUK1, presenta un gran porcentaje y tamaño de conchillas que disminuye al techo, que se interpreta por el paso de un ambiente con hidrodinámica litoral somera a uno hemipelágico y que se asocia al alto estadio global marino post-Último Máximo Glacial (UMG) desde los 7 ka AP. La unidad 3 (Holoceno medio) presenta el menor tamaño de grano y en GUK1 aparecen múltiples laminaciones lo que sugiere sedimentación rítmica, y posibles variaciones en la surgencia y productividad primaria asociada, que generaría ambientes hipóxicos a anóxicos. Esto se evidenciaría por la presencia del foraminífero Bolivina plicata, pirita en ambos testigos y olor a ácido sulfhídrico. La unidad 2 (Holoceno tardío) registra un abrupto aumento del tamaño de grano para TK2 y un mayor tamaño y % de volumen de minerales para GUK1, que se mantiene hacia el techo y que se inicia a los 5.500-5300 años cal AP, basado en edades radiocarbónicas. Esto se interpreta como un aumento en la frecuencia de flujos de detrito esporádicos de gran energía y concuerda con otros registros que indican que para tales edades ocurriría una mayor frecuencia de intensas lluvias asociada al comienzo de El Niño, como se conoce hoy en día (Rodbell et al., 1999; Jenny et al., 2002; Vargas et al., 2006). Finalmente, para la unidad 1 (último siglo datado a través de exceso 210Pb) se identifica un aumento del tamaño y % de volumen de la moda secundaria para TK2 y un aumento gradual de la mediana d(0,5) en GUK1, que sugiere que el tamaño y aporte de líticos para TK2 y el tamaño de líticos para GUK1 arrastrados por flujos aluvionales hacia el fondo de las bahías sería mayor desde, al menos, el último siglo. A partir del análisis sismoestratigráfico se identifican 4 unidades. En el substrato estratificado subhorizontal se diferencian 2 system tracts asociados a cambios eustáticos: una unidad transgresiva post-UMG (15-7 ka AP) con probables aportes aluviales asociado al UMG (30-19 ka AP) caracterizada por terminaciones onlap, downlap y toplap, y geometría agradacional-progradacional. A esta unidad la sobreyace una unidad de alto estadio asociado al alto estadio marino global post 7 ka AP caracterizada por terminaciones downlap y geometría progradacional. Ambas unidades incorporan facies caóticas en el relleno sedimentario del fondo de la bahía de Tongoy, que son interpretadas como slumps producto de inestabilidad de sedimentos a menor profundidad. Los slumps, junto con nítidos escarpes morfológicos en el norte de la estrecha plataforma continental de la bahía de Tongoy se consideran evidencias para sugerir fallas normales secundarias ubicadas a los pies de los escarpes producto del reacomodo de los estratos ante reactivaciones normales de la Falla Puerto Aldea (FPA). Por tanto, la FPA tendría una prolongación submarina y un carácter activo a escala del Cuaternario tardío.
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Solari, Corvalan Marcelo Alberto. "Paleo-Termometría y Evolución del Sistema Hidrológico del Parque Nacional Torres del Paine, Patagonia." Tesis, Universidad de Chile, 2010. http://repositorio.uchile.cl/handle/2250/102347.
Full textAbstract:
Un conjunto de complejos morrénicos se distribuyen desde el margen este de la Cuenca de Drenaje de Torres del Paine
hasta las cercanías del margen actual de los Campos de Hielo Patagónicos. Regionalmente se reconocen en el paisaje un conjunto
de terrazas lacustres vinculadas a las fluctuaciones glaciares. Las evidencias geomorfológicas y sedimentarias lacustres
encontradas apoyan la existencia de un único lago proglacial denominado en el presente estudio como Gran Paleo-Lago
Tehuelche (GPT), mejoran la cronología de los eventos glaciales y permiten una comprensión de la evolución del sistema
hidrológico de Torres del Paine.
Los avances glaciares previamente denominados por Marden (1993) como A, B y C, se desarrollaron durante el Último
Máximo Glacial y alimentaron al GPT con aguas de fusión, permitiéndole al lago alcanzar su mayor extensión y altitud. El
hallazgo de trombolitos en Laguna Amarga fue clave para determinar que el desagüe del GPT hacia el Seno de Última Esperanza
se produjo hace 7110 años calibrados antes del presente (años cal AP) producto de la fusión de una gran barrera glacial existente
durante el avance E, que posteriormente dio paso al complejo sistema hidrológico de ríos y lagos existente. Para dicho período, se
proponen condiciones de mayor aridez en el sector de Laguna Amarga debido al descenso en las precipitaciones. Desde otra
perspectiva, la temporalidad del avance E sumado a otras evidencias encontradas en Patagonia por otros investigadores, hacen
referencia de un evento frío en Patagonia durante el Holoceno temprano. Mayores estudios deben realizarse en Patagonia para
dilucidar si existe una relación con el evento frío ampliamente descrito en el Hemisferio Norte entre 8000 y 9000 años AP.
La regresión fría registrada en la Región de los Lagos (11.8-13.2 ka AP) respecto a los eventos de inversión fríos
sincrónicos en Antártica y Torres del Paine (12.6-14.8 ka AP), se pueden explicar por la modulación de los Vientos
Predominantes del Oeste (VPO) causada por el reforzamiento de los Vientos Tropicales del Este/ENSO y por la expansión hacia
el norte de la celda atmosférica de Bajas Presiones Subpolar. Esta hipótesis muy preliminar busca recalcar la necesidad de
comprender sobre la base de registros paleoclimáticos los reajustes espaciales y temporales de las diferentes células atmosféricas
y la circulación oceánica, y con ello conceptualizar y modelar como la atmósfera y los océanos se comportan e interactúan frente
a la una renovada teoría de forzamiento orbital propuesta por Davis y Bewer el año 2009.
Con posterioridad al desagüe del GPT, Lago Sarmiento y Laguna Amarga se transforman en cuencas endorreicas en las
cuales se observan terrazas lacustres locales, las que entregan nuevas evidencias y aportan un conjunto de resultados de
importancia paleoclimática regional.
Lago Sarmiento y Laguna Amarga actualmente están localizados al este de una de las mayores sombras orográficas de
precipitaciones del mundo, generada al este del Campo de Hielo Patagónico Sur. Grandes colonias de trombolitos están presentes
en Lago Sarmiento, mientras que extensas colonias de estromatolitos están presentes en Laguna Amarga. Basados en las
características del sistema hidrológico de ambas cuencas, en conjunto con la estimación del balance isotópico y el análisis de las
condiciones de equilibrio entre el agua y los carbonatos biológicamente inducidos, se concluyó que las microbialitas de Lago
Sarmiento presentan mejores condiciones que Laguna Amarga para ser utilizadas como indicadores de paleo-temperaturas. Los
trombolitos de Lago Sarmiento presentan una única especie mineral la cual precipita cerca de las condiciones de equilibrio
isotópico y la variación de la temperatura controla el fraccionamiento isotópico de oxígeno en el lago. En los trombolitos se
observan con claridad cuatro niveles lacustres, en los cuales fue posible cuantificar la temperatura:
• Hace 1215 años cal AP el nivel del lago fue 85 m s.n.m con una temperatura cercana a 9,3ºC, y hace 600 Cal
años AP el nivel descendió a 82 m s.n.m con una temperatura cercana a los 8,5ºC. Estos períodos cálidos en el
lago coinciden temporalmente con el Periodo Cálido Medieval (1200 a 800 años Cal AP) registrado
ampliamente en el Hemisferio Norte, pero mayor cantidad de evidencias regionales son necesarias para
establecer una correlación.
• Hace 183 años cal AP el nivel del lago fue de 80 m s.n.m con una temperatura de 7,7ºC, representando un
periodo de menor temperatura del lago coincidente con la Pequeña Edad de Hielo.
• La superficie de Lago Sarmiento disminuyó entre 1986 y 1999 debido a cambios en los patrones de
precipitación y evaporación. Estos se relacionan probablemente con uno de los efectos del cambio climático
detectado en el calentamiento troposférico al sur de Sudamérica en las últimas décadas, lo cual se asocia a la
disminución de casi la totalidad de los grandes glaciares en los Campos de Hielo Patagónicos.
Un resultado importante de la tesis fue que la señal de δ13C en carbonatos es una herramienta efectiva para distinguir el
proceso que produce su precipitación. Valores negativos de δ13CVPDB son característicos de la precipitación inorgánica y valores
positivos son característicos de la precipitación biológicamente inducida.
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Rocha, Lucas Sarmento Neves da. "Calibração dos Registros Ambientais em Esqueletos de Colônias do Coral Siderastrea Stellata Verril, 1868." Instituto de Geociências, 2015. http://repositorio.ufba.br/ri/handle/ri/21564.
Full textAbstract:
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Lucas Rocha (2015) - mestrado.pdf: 14637707 bytes, checksum: 996b70d370a5333486ee80bf8542477b (MD5)Made available in DSpace on 2017-02-21T01:16:25Z (GMT). No. of bitstreams: 1 Lucas Rocha (2015) - mestrado.pdf: 14637707 bytes, checksum: 996b70d370a5333486ee80bf8542477b (MD5)
Considerando a indisponibilidade de longas séries temporais para registros instrumentais, torna-se imprescindível a utilização de proxies capazes de fornecerem medidas precisas do clima e de ambientes pretéritos. As bandas alternadas de densidade nos esqueletos de corais permitem quantificar e datar características relacionadas ao seu crescimento. Este padrão anual está diretamente relacionado às variações sazonais de parâmetros ambientais que caracterizam a água do mar. A calibração entre o proxy utilizado e o comportamento da variável ambiental investigada é fundamental para estabelecer a relação entre o estímulo ambiental e sua resposta no organismo. Deste modo, o objetivo deste trabalho foi realizar a calibração dos indicadores proxy de temperatura e turbidez da água do mar nos corais da espécie Siderastrea stellata Verril, 1868, para duas regiões específicas: Baía de Todos os Santos (Salvador, Bahia) e Arquipélago de Tinharé (Cairu, Bahia). Para isto, foram geradas placas de aproximadamente 5 mm de espessura do esqueleto de oito colônias de coral, posteriormente radiografadas e analisadas esclerocronologicamente no software Coral XDS®. A partir desta análise, pôde-se estimar as taxas de extensão linear, densidade e taxas de calcificação médias anuais e mensais para cada uma das colônias. As séries mensais da temperatura da superfície do mar (TSM) foram obtidas através do sistema operacional OSTIA. As séries mensais das variáveis ambientais Radiação Fotossinteticamente Ativa (PAR), Coeficiente de Atenuação Difusa da Luz (K490) e Concentração de Clorofila Superficial (CHLO) foram obtidas dos sensores MODIS e SeaWiFS. A comparação realizada entre os dois sítios de amostragem evidenciou uma diferença estatisticamente significativa para os três parâmetros esclerocronológicos analisados, enfatizando a influência dos fatores locais sobre os padrões de crescimento desta espécie de coral. As taxas de calcificação obtidas para as duas sub-áreas mostraram-se principalmente determinadas pela variabilidade da extensão linear, com a densidade exercendo um papel secundário. Colônias de S. stellata no sitio de amostragem Comunidade coralina do Yatch Clube da Bahia mostraram-se mais sensíveis a possíveis alterações nas variáveis ambientais. TSM e PAR exerceram maior influência sobre o padrão de densidade dos esqueletos desta espécie de coral em comparação às outras variáveis analisadas.
ABSTRACT - Considering the unavailability of long time series for instrumental records, mainly in the South Atlantic Ocean, it is essential to use indirect or proxy indicators to provide accurate measures of past climates and environments. The alternating density bands in coral skeletons allows dating and quantify characteristics related to its growth. This annual pattern is directly related to seasonal changes in environmental parameters that characterize the seawater. The calibration between the proxy used and the behavior of the investigated environmental variables is critical in establishing the relationship between the environmental stimulus and the organism response. Thus, the aim of this work was to perform the calibration of proxy indicators of temperature and turbidity of sea water in the coral specie Siderastrea stellata Verril, 1868, for two specific regions: Todos os Santos Bay (Salvador, Bahia) and Archipelago of Tinharé (Cairu, Bahia). For this, plates of approximately 5 mm were generated from skeletons of eight coral colonies, then x-rayed and analyzed sclerochronologically in the XDS® Coral Software. From this analysis, it was possible to estimate the annual and monthly averages of densities, linear extent and calcification rates for each colony. Sea surface temperature (SST) monthly series were obtained through the operating system OSTIA. The monthly series of environmental variables Photosynthetically Active Radiation (PAR), Diffuse Attenuation Coefficient (K490) and Superficial Chlorophyll Concentration (CHLO) was obtained from the MODIS and SeaWiFS sensors. The comparison between the two sampling sites showed a statistically significant difference for the three sclerochronological parameters analyzed, emphasizing the influence of local factors on the growth patterns of this species of coral. Calcification rates obtained for the two sub-areas were shown to be mainly determined by the variability of the linear extension, with the density as a secondary factor. Colonies of S. stellata in YCB sampling site were more sensitive to possible changes in environmental variables. TSM and PAR had the greatest influence on the pattern density of the skeletons of this species of coral compared to other variables.
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Allen, Jonathan Patrick. "The carboniferous evolution of the Maritimes Basin complex, Atlantic Canada." 2009. http://proquest.umi.com/pqdweb?did=1825907771&sid=13&Fmt=2&clientId=14215&RQT=309&VName=PQD.
Full textAbstract:
Thesis (Ph.D.)--University of Nebraska-Lincoln, 2009.Title from title screen (site viewed January 5, 2010). PDF text: xx, 547 p. : ill. (chiefly col.) ; 47.3 Mb. UMI publication number: AAT 3360491. Includes bibliographical references. Also available in microfilm and microfiche formats.
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Pierce, Elizabeth Lane. "Antarctica's Geologic and Ice Sheet History from Isotopic Sedimentary Provenance Studies." Thesis, 2012. https://doi.org/10.7916/D8P84K0J.
Full textAbstract:
Within the constraints of uncertainty in the nature of erosion and transport in the sub-glacial environment, the study of glacialy-derived material from marine sediments located off the margin of East Antarctica provides a means for characterizing the sub-glacial geology obscured by the more than 98% ice cover of the continent. These insights into the geology of East Antarctica in turn provide characterization of sedimentary source areas, the knowledge of which can be applied to sediment provenance studies of ice rafted detritus (IRD) and thus about East Antarctic ice sheet history. Much of what has been learned of East Antarctica's Cenozoic ice sheet evolution has been achieved through the study of marine sediments, as ice sheets tend to erode their own history and much of what is preserved is, like the geology, obscured the ice sheet. Determining the provenance of ice-rafted detritus allows for spatial and temporal reconstructions of ice sheet behavior. Accordingly sedimentary provenance studies are key to documenting how Antarctica's ice sheet evolved through the Cenozoic. In this work, I have taken samples of marine sediments and used grain size and physical properties to separate different terrigenous components, and I have examined the sand fractions under a microscope. Following the sedimentological characterization, I have separated specific minerals from the sand fraction and employed isotopic measurements - 40Ar/39Ar on detrital hornblende and biotite grains, U-Pb on detrital zircons. I have also employed Nd isotope measurements on the terrigenous fine (< 63µm) fractions of these same samples. Chapter 2 is published in the journal Paleoceanography, and chapters 3 and 4 are to be submitted to Earth and Planetary Sciences and Paleoclimatology, Palaeoecology & Paleoceanography, respectively. In Chapter 2, I demonstrated that (1) four main sectors between the Ross Sea and Prydz Bay, separated by ice drainage divides, are distinguishable based upon the combination of 40Ar/39Ar ages of detrital hornblende and biotite grains and the εNd of the bulk fine fraction, (2) 40Ar/39Ar biotite ages can be used as a robust provenance tracer for this part of East Antarctica, and (3) sediments shed from the coastal areas of the Aurora and Wilkes sub-glacial basins can be clearly distinguished from one another based upon their isotopic fingerprints. This is particularly significant as the Aurora and Wilkes sub-glacial basins have elevations significantly below sea level, and thus are likely prone to being destabilized during warm climates. My work confirms and extends previous published evidence for episodes of massive ice rafting from these sectors. In Chapter 3, I addressed the relative merits of U-Pb zircon and the 40Ar/39Ar hornblende and biotite systems for sedimentary provenance studies. U-Pb zircon is a widely used detrital provenance tool. In polar and subpolar regions where chemical weathering is minor, hornblende and biotite are viable alternatives, and because they are more abundant in crystalline rocks it is possible to find significant populations in the relatively small samples that are available from marine sediment cores. My work has demonstrated that (1) detrital U-Pb zircon, 40Ar/39Ar hornblende and 40Ar/39Ar biotite ages all faithfully record the geologic history of East Antarctica, as expressed in their respective age populations, although different aspects may be accentuated in one or another (2) a number of previously unknown source regions have been identified (though not found on the continent yet) with this method (3) there is benefit to combining the three chronometers where possible as they are not completely redundant. Chapter 4 concerns the middle-Miocene climate transition (MMCT) on the Wilkes Land margin. In this study I combined 40Ar/39Ar with εNd of the terrigenous fine fraction across the MMCT in IODP Site U1356. The results from the two size fractions tell different stories and provide further support for the application of multiple tools. Specifically I found that (1) the hornblende ages in the MMCT of Site U1356 have a very dominant 1400-1550 Ma age population, which is not commonly found on the Wilkes land margin. I interpret these results, in the context of published geophysical interpretations of the sub-glacial geological boundaries, to require that the EAIS was greatly retreated in the Wilkes sub-glacial basin prior to and during the MMCT, and sat along the extension of the Mertz Shear Zone, at the western edge of the Wilkes Basin (2) While the hornblende evidence for provenance does not indicate large changes in iceberg sources, the εNd of the bulk fine fraction shows excursions to more radiogenic Nd values, 8 epsilon units higher than the local signal during times of elevated IRD concentrations at this site. The data reveal evidence for three events, which closely correspond with periods of glacial outburst floods responsible for carving part of the spectacular scabland topography (the Labyrinth) found in the Dry Valleys, and with provenance signals consistent with a significant sediment contribution from such a source and (3) the major pulse of dropstones to IODP Site U1356 occurs between ~14.0 and ~13.7 Ma, corresponding to the timing of the major pulse of IRD at ODP Site 1165 from near Prydz Bay, as well as to the timing of published records interpreted to indicate significant ice volume growth from oxygen isotope records and eustatic sea-level reconstructions. Collectively these observations allow tying together direct evidence for EAIS growth from proximal glacial-marine sediments and results from far field proxies. Overall, this work demonstrates the efficacy of isotopic and geochronological provenance tools for studying East Antarctica's geologic and ice sheet history. Furthermore the application of this approach to studying East Antarctic ice-sheet dynamics across the mid-Miocene Climate Transition (~14 Ma), one of the most important periods of East Antarctic ice sheet growth, highlights the powerful potential for future discoveries.
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Albert, Ashley Lisbeth. "A laminated carbonate record of late holocene precipitation/evaporation from Pretty Lake, Lagrange County, Indiana." Thesis, 2016. https://doi.org/10.7912/C29656.
Full textAbstract:
Indiana University-Purdue University Indianapolis (IUPUI)Late Holocene hydroclimate variability in the midcontinental United States is not well understood because there is a lack of high-resolution paleoclimate records constraining historical climate patterns for the region. Here, a 2500-year-long multi proxy lake sediment record from a northern Indiana kettle lake is used to examine spatial and temporal scales of drought and pluvial patterns in the Midwest. Oxygen (18Ocal) isotope analysis of authigenic carbonate and the sedimentary lithic abundance (%lithics) are the primary datasets used to evaluate hydroclimate trends with supporting information from total organic matter, total carbonate and magnetic susceptibility. We additionally derive a record of local evaporation by subtracting the isotopic composition of precipitation (18Oprecip) as characterized by the nearby Martin Lake, IN, record, from the Pretty Lake 18Ocal record. The combined Pretty Lake hydroclimate record documents climate variability during the last 2 millennia and shows that the Midwest has experienced a wide range of evaporative regimes during the late Holocene. We notice a consistent relationship between the Pretty and Martin Lake multi-proxy records; where reduced (increased) evaporative periods and higher (lower) lake levels at Pretty Lake mostly align with increased (decreased) Gulf sourced precipitation and stream erosion with longer (shorter) warm seasons at Martin Lake. Early periods of much drier, and weakened warm-season evaporation patterns dominated from 600 BCE to 900 CE. Evidence of a prolonged period of enhanced warm-season pluvial conditions, with less evaporation and higher lake levels, during the Medieval Climate Anomaly (MCA) between 900 to 1350 CE; and a pronounced century of arid conditions throughout the Little Ice Age (LIA) from 1350 to 1700 CE followed by a gradual decrease in evaporation and rising lake levels starting at 1700 CE and continuing to present. These trends track other Midwest regional hydroclimate climate records, but show an anti-phased relationship with records from the High Plains and western United States regions. This supports the idea that a hydrocilmate dipole exists between the Midwest and western United States driven largely by mean state changes in the Pacific North American teleconnection pattern, but with modification by local and in-lake responses to mean climate states.
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Nace, Trevor. "Late Quaternary Paleoclimatology and Paleoceanography of the Amazon Continental Margin, Brazil." Diss., 2012. http://hdl.handle.net/10161/5556.
Full textAbstract:
The tropics are a significant source of heat and moisture export, which drive global circulation patterns, thus it is vital to systematically understand the land, ocean and sedimentological interactions within the tropics. The Brazilian continental margin is an ideal region to characterize the tropics due to its unique local oceanography and proximity to the atmospheric engine that is the Amazon Basin. A combination of: 1) terrestrial organics and hydrology; 2) oceanographic temperature, isotopic composition, and salinity and 3) early diagenesis and geochemistry of sedimentary interstitial water and methane hydrate, provide a detailed understanding of the primary constituents that influence the South American tropics.
Sedimentological, organic and paleoceanographic reconstructions of the Amazon Basin, Brazilian Nordeste, and western equatorial Atlantic have been undertaken on two sediment cores located on the Brazilian continental slope representing 30 and 110 ka, respectively. High-resolution XRF analyses of Fe, Ti, K and Ca are used to define the sedimentological history of the Amazon Basin and northern Nordeste. Here we present elemental ratios of Ti/Ca and Fe/K, in addition to magnetic susceptibility, to determine variability in Amazon Basin and Nordeste hydrology. Bulk organic proxies d13C and d15N of sedimentary organic carbon are used to define the organic history of the Amazon Basin. Peaks in Ti/Ca and Fe/K ratios largely correlate in both the Amazon Basin and in the Nordeste Record. These excursions correlate with commonly modeled global slowdown of the Atlantic meridional overturning circulation (AMOC) during increased northern hemisphere glaciation. Differences in the Fe/K and Ti/Ca records suggest periods of increased chemical weathering independent of precipitation driven sediment discharge in the Brazilian Nordeste. Bulk organic geochemistry indicates the vegetative history of the Amazon Basin has been relatively stable during the late Quaternary.
High-resolution stable oxygen isotopic analysis and Mg/Ca paleothermometry undertaken on the near-surface-dwelling planktic foraminiferal species Globierinoides ruber provide a picture of paleoceanographic forcings in the western equatorial Atlantic. The Nordeste core exhibits a rapid warming of ~3.5ºC between the last glacial maximum and the early Holocene. Furthermore, in almost all cases during the last glacial stage, there was a 0.5 to 2ºC warming of the western equatorial Atlantic during the periods of high Ti/Ca ratios that correlate with slowdown of AMOC. Thus, as observed in some previous studies, the western equatorial Atlantic was warm and the adjacent southern tropical continent was wet coincident with increased glaciation in the high latitude northern hemisphere.
Interstitial pore waters were analyzed from the Amazon Fan and Brazilian continental slope to determine early diagenesis, methane hydrate potential and its geographic variability. Interstitial waters were measured for total Mg, Ca, SO4, alkalinity, Cl, and d18O, combined with seismic bottom simulating reflectors (BSRs) to investigate early diagenesis. Interpolated maps of sulfate reduction, sedimentation rate and maximum alkalinity were produced to examine geographic variability in early diagenesis and methane hydrates. Inorganic precipitation of calcium and magnesium, likely via dolomite and siderite, correlates with a decrease in alkalinity through inorganic carbonate precipitation and methanogenesis, but alternatively increases through redox pathways, specifically sulfate reduction.
Through multiple lines of evidence it is likely that there is extensive methane hydrate occurrence on the Amazon continental shelf. A combination of: 1) A rapid linear decline in sulfate at an unusually shallow depth; 2) Uncommonly high sedimentation rates and terrestrial organic carbon input; 3) Significant variability in what should be conservative chloride concentrations; 4) Large variability in interstitial oxygen isotopes; 5) Widespread occurrence of BSRs provide substantial support for the presence of methane hydrates. Sulfate reduction rates are lowest along the main Amazon channel, with highest values distal of the main channel. Sedimentation rates are relatively low on the continental shelf and surrounding the main channel and highest toward the distal end of the main channel. Sulfate reduction rates provide key insights to the potential geographic variability of methanogenesis and methane hydrate formation. Given the tremendous influx of sediment from the Amazon River, this region is prone to massive sediment failures, subsequent release of methane hydrates, as well as significant potential for natural gas hydrates.
Dissertation
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Goldsmith, Yonaton A. "Trans-Asian Glacial - Interglacial Paleohydroclimate Reconstructed Using Lake Geomorphology and Organic and Inorganic Stable Isotopes." Thesis, 2017. https://doi.org/10.7916/D8F481HM.
Full textAbstract:
Earth’s climate can exist in many stable states that are vastly different from the modern climate state. Understanding modern and future climate requires a thorough understanding of the full range of possible climate states and the processes that trigger transitions between states. Quantitative reconstructions of past climate variables provide constrains on the magnitude, mechanisms and feedbacks involved in producing stable climate states. As such, they provide insights into past climate states unobservable today.
This thesis focuses on quantifying three metrics of past climate systems: (a) quantitative rainfall amount, which provides means for assessing how the spatial distribution of rainfall changed in the past, (b) the isotopic composition of past rainwater (δP ), which provides means for understand- ing how atmospheric circulation changed in the past, and (c) relative humidity, which provides estimates of evaporative processes and hydrospheric fluxes.
The regions studied are in the two far reaches of the Asian continent. In eastern Asia, changes in rainfall amount and δP over the past 125 ka were studied using geomorphological evidence from a closed basin lake in Inner Mongolia, China and compound-specific δDwax and δ13Cwax from organic molecules in lake sediments. In western Asia, the research focused on processes that govern modern δP and modern δDwax and δ13Cwax in soils. In addition the hydrological regime of the Eastern Mediterranean and the Levant during the Last Glacial Maximum were studied using evidence from speleothem δ18Oc and foraminifera δ18O.
These records provide empirical and quantitative information about rainfall amount, δP and relative humidity at singular locations, and as such provide the building blocks for producing coherent large-scale reconstruction of the migration of rain-belts in the past.
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Goldberg, Karin. "The paleoclimatic evolution of the Permian in the Paraná Basin in southern Brazil /." 2001. http://wwwlib.umi.com/dissertations/fullcit/3034466.
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Thesis (Ph. D.)--University of Chicago, Dept. of the Geophysical Sciences, December 2001.CD-Rom contains lithological and geophysical logs in Adobe PDF format. Includes bibliographical references. Also available on the Internet.
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Haynes, Laura. "The Influence of Paleo-Seawater Chemistry on Foraminifera Trace Element Proxies and their Application to Deep-Time Paleo-Reconstructions." Thesis, 2019. https://doi.org/10.7916/d8-x2x2-da06.
Full textAbstract:
The fossilized remains of the calcite shells of foraminifera comprise one of the most continuous and reliable records of the geologic evolution of climate and ocean chemistry. The trace elemental composition of foraminiferal shells has been shown to systematically respond to seawater properties, providing a way to reconstruct oceanic conditions throughout the last 170 million years. In particular, the boron/calcium ratio of foraminiferal calcite (B/Ca) is an emerging proxy for the seawater carbonate system, which plays a major role in regulating atmospheric CO2 and thus Earth’s climate. In planktic foraminifera, previous culture studies have shown that shell B/Ca increases with seawater pH, which is hypothesized to result from increased incorporation of borate ion (B(OH)4 -) at high pH; increasing pH increases the [B(OH)4 -] of seawater. However, further experiments showed that B/Ca responds to both pH and seawater dissolved inorganic carbon concentration (DIC), leading to the hypothesis that B/Ca is driven by the [B(OH)4 -/DIC] ratio of seawater. Because pH (and thus B(OH)4 -) can be determined via the δ11B composition of foraminiferal calcite, B/Ca therefore may provide an opportunity to determine seawater DIC in the geologic past.
The magnesium/calcium ratio (Mg/Ca) of foraminifer shells is a well-established proxy for seawater temperatures, where foraminiferal Mg/Ca increases at greater temperatures. However, foraminifera shell chemistry such as B/Ca and Mg/Ca ratios also depend on the major ion chemistry of seawater. For example, the seawater Mg/Ca ratio (Mg/Casw), which has increased significantly over the last 60 million years, is known to affect the sensitivity of the Mg/Ca proxy to temperature. In addition, the seawater boron concentration ([B]sw) has also increased across the Cenozoic. The dependence of B/Ca proxy relationships on Mg/Casw and [B]sw composition remains unknown.
During the Paleogene era (65-34 Ma), Earth’s climate was characterized by a number of rapid warming events termed ”hyperthermals”. Evidence from the sedimentary record suggests that hyperthermals were catalyzed by rapid carbon release and caused widespread ocean acidification and deep-sea deoxygenation. These hyperthermal events present the best geologic analog conditions to anthropogenic climate change, and their study can therefore help to illuminate how the Earth system responds to rapid carbon release and warming. Planktic foraminiferal B/Ca records from the largest hyperthermal event, the Paleocene-Eocene Thermal Maximum (PETM), show a large decrease, which agrees with the theory that ocean acidification should cause B/Ca to decline. However, the decrease is larger than can be reconciled from existing proxy calibrations conducted in modern seawater, begging the question of whether the low Mg/Casw of the Paleogene Ocean affected the sensitivity of B/Ca to the seawater carbonate system. Because there are also a number of outstanding uncertainties regarding the controls on B/Ca- including seawater [Ca] and shell growth rate, light intensity, and phosphate concentration- it is also possible that these factors contributed to the PETM B/Ca excursion. The influence of these additional parameters on B/Ca, as well as the influence of Mg/Casw, needs to be tested in controlled culture experiments.
To address these outstanding questions in proxy development, I conducted a series of culture experiments in three living planktic foraminifer species- Orbulina universa, Trilobatus sacculifer, and Globigerinoides ruber (pink). In order to refine our understanding of proxy controls on foraminiferal B/Ca, I investigated how foraminiferal B/Ca is affected by variable light intensity, growth rate (indirectly via seawater [Ca] manipulation), and seawater [B]. Subsequently I tested the influence of low seawater Mg/Ca, analogous to that of the Paleocene ocean, on B/Ca-carbonate chemistry relationships. In Chapters 2 and 3, I detail how my results support the notion that planktic foraminiferal B/Ca in these three symbiont-bearing species is driven by the B(OH)4 -/DIC ratio of seawater and is not compromised by growth rate effects. Furthermore, the sensitivity of B/Ca to B(OH)4 -/DIC is increased under low Mg/Casw in both O. universa and T. sacculifer. In Chapters 2 and 3, I hypothesize that this increased sensitivity is due to decreased cellular pH regulation under low Mg/Casw, leading to a greater sensitivity of the foraminiferal microenvironment’s carbon system to external forcing. I define new culture calibrations that can be applied to records from Paleocene seawater in Chapter 3, and use these calibrations to reconstruct surface ocean DIC and the overall size of the carbon system perturbation across the PETM in Chapter 4. Finally, in Chapter 5, I show how foraminiferal Mg/Ca responds to seawater Mg/Ca and the carbon system from these same experiments, with implications for accounting for carbon system influences on Mg/Ca from early Cenozoic proxy records.
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Peltier, Carly. "The precise timing and character of glaciations in Patagonia from MIS 6 to the Little Ice Age." Thesis, 2021. https://doi.org/10.7916/d8-46v3-qr64.
Full textAbstract:
By only considering records of climate and glaciers over the period that humans have been monitoring them, one might think that climate normally changes quite rapidly, and that glaciers have always been small. But in the not-so-distant past, an ice sheet covered the Southern Andes, flowing across the southern tip of the continent, and in some places, even terminating into the Atlantic Ocean. Glaciers rewrite the surfaces they inhabit, leaving behind indicators of their past behavior. By studying the landforms they create, we can reconstruct climates of the past. Here I present unique and novel glacier-climate reconstructions over southern and central Patagonia using a state-of-the-art dating approach tied to high resolution spatial mapping and glaciological modeling.
The main goal of this thesis is to constrain the precise timing and character of the past advances of three glaciers in Patagonia. To this end, I present new precise 10Be surface exposure datasets from two paleo outlet glacier lobes (at 45°S and 53°S), totaling 71 new moraine boulder ages. In these two valleys, I am able to reconstruct the last three major glaciations (MIS 6, 4, 2), as well as provide a constraint for the last two terminations (T1, T2). At a third site, I create a novel dataset to reconstruct the behavior of the Calluqueo glacier (48°S) from ~7,000 years ago to the present. All three sites are eastwards of the main Andes mountain range, spanning from southernmost Patagonia (53°S) to central Patagonia (45°S). To achieve my thesis objectives, I employed recent improvements in the 10Be exposure dating method, and tied the geochronological studies to new, high resolution maps of the glacial geomorphology created by the former glaciers and associated processes.
We find in central Patagonia, the Ñirehuao glacier lobe was most extensive potentially during Marine Isotope Stage (MIS) 8, but certainly prior to MIS 6, followed by a major advance during MIS 6. This study presents one of the first directly dated records of a MIS 6 glacier expansion in Patagonia at 153±5.1 ka, where the glacier may have been in retreat at 137±4.2 ka. During the last glacial cycle, the glacier was most extensive during the middle of MIS 2, at 23.6±0.9 ka.
The southernmost section of the Ice Sheet, at Estrecho de Magallanes, was more extensive during Marine Isotope Stage 4 (MIS 4) than during MIS 2, representing the first direct dating of the MIS 4 glacier culmination in South America. Similar to the MIS 2 glacial maximum, within MIS 4 there were multiple advances that we date (6 samples) to between 67.5±2.1 and 62.1±2.0 ka. Inboard of the MIS 4 moraine complex, we date a sequence of geomorphically distinct MIS 2 moraines that represent separate major periods of glacial stability. The MIS 2 maximum extent occurred by 27.4±0.8 ka and was followed by at least four more full glacial culminations over a hundred miles beyond the Andes mountains. About 18 km inboard of the main MIS 2 landforms, the sequence is followed by smaller-scale recessional moraine crests that we date to 18.0±0.8 ka, indicating the glacier was in net retreat at this time.
In order to estimate the climate conditions necessary to drive the glacier advances that we date and map, we apply the University of Maine Ice Sheet Model to the Estrecho de Magallanes and Ñirehuao records. Tentative results suggest that the Magallanes lobe may have reached mapped inner and outer MIS 2 moraines with a climate that had approximately 4.5°C and 5.5°C cooler summers, respectively, assuming about 25% less annual precipitation relative to modern conditions.
A new record at Calluqueo, in central Patagonia, allows us to reconstruct Holocene (interglacial) glacier changes. Using 33 new 10Be ages with unprecedented precision, geomorphic mapping and historical imagery, we find that the Calluqueo glacier sat at its mid-Holocene maximum extent from ~6,900 until ~6,700 years before the present. Major moraine forming advances subsequently culminated at least seven more times, averaging every 500±31 years, between 5,620±203 and 3,120±106 years ago. A hiatus in moraine formation occurred from 3,120±106 until 1,160±50 years ago (860 CE). Major retreat occurred between 1600-1800 CE, followed by stability from 1800-1940 CE, and pronounced ongoing retreat since after 1940 CE. For the Holocene period, this record represents one of the first precise, directly-dated glacier histories from central Patagonia, and one of the few available for all of Patagonia. The timing of advances of the Calluqueo glacier has little in common with the glacial histories from the Northern Hemisphere, suggesting an inter-hemispheric asynchronicity. All together, we reconstruct the timing of glacial maxima at three sites in terrestrial Patagonia from 53°S to 45°S, with unprecedented precision, from pre-MIS 6 to the present day.
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Taylor, Brandon L. "A Speleothem-Based High Resolution Reconstruction of Climate in Southeastern Brazil Over the Past 4,100 Years." 2010. https://scholarworks.umass.edu/theses/390.
Full textAbstract:
Isotopic investigations of speleothem CR1 from Cristal Cave in southeastern Brazil have established a high-resolution record of climate change extending 4,100 years prior to sample collection in 2007. A total of 14 subsamples were collected from CR1 for U/Th age determination. ICP-MS analysis yielded very precise ages with analytical errors (2σ) averaging ± 13 years. An initial growth rate of .062 mm y-1 for the first 2860 years is followed by a rate of .08 mm y-1 for the remaining growth period allowing for sampling of δ18O at sub-decadal resolution. Stable isotope analyses show a large range of δ18O values between -7.5 ‰ to -4 ‰. The data show a trend of steadily decreasing values over the past 4,000 y BP. The exception to this trend is the last 150 years BP when some of the least negative and most variable values for the record are observed.
Variations in speleothem δ18O in southern Brazil have been shown to reflect changes in rainfall δ18O, which in turn indicate changes in rainfall source or rainfall amount (Cruz et al., 2006). In Southeastern Brazil, δ18O is controlled mainly by moisture source location, in particular South American monsoonal versus extratropical sources (Cruz et al., 2005). The relative contribution of monsoonal and extratropical moisture help to define the δ18O of regional precipitation via the mean location and southward extent of Hadley cell convective activity associated with the South American summer monsoon (Cruz et al., 2005). For example, decreases in precipitation δ18O are often interpreted as a decreased contribution of winter versus summer precipitation (Cruz et al., 2005). Assuming that the modern (observed) relationship between the seasonality and moisture source location effect occurring in southeastern Brazil have functioned for the past ~ 4,100 years, trends of more negative values towards modern day are likely due to increased summer precipitation and/or an overall increase in total yearly precipitation. The more enriched values of the past 100 years suggest a recent decrease in summer and/or total rainfall.
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De, Kock Michiel Olivier. "Selected magnetostratigraphic studies in the main Karoo Basin (South Africa): implications for mass extinction events and the supercontinent of Pangea." Thesis, 2009. http://hdl.handle.net/10210/1953.
Full textAbstract:
M.Sc.The Late Carboniferous to early Jurassic Karoo Supergroup of South Africa witnessed two of the “big five” Phanerozoic mass extinction events, and the formation and subsequent break-up of the supercontinent Pangea. The closure of the Permian Period witnessed the greatest biotic crisis in the history of life. What is known about the Permian-Triassic boundary (hereafter referred to as the PTB) comes almost exclusively from marine successions in Europe and Asia. Although a major extinction event has been recognized in terrestrial successions, surprisingly little is known about its effects and timing. The exact placement of the PTB in the Karoo basin is not well constrained due to shortcomings of stratigraphic methods employed to date. This has made it extremely difficult to correlate the mass extinction events in the marine and non-marine environments; however, paleomagnetic studies could provide answers to both problems of absolute placement and correlation of the PTB in non-marine and marine successions. The PTB appears to lie within an interval of reversed polarity in many marine successions. A detailed magnetostratigraphic survey across the presumed PTB in the Karoo succession at localities in the north and south of the main Karoo Bain reveal two magnetic chrons, reversed followed by normal (with the boundary close to the reversal), which extends to slightly younger results from a previous study that identified an N/R pattern, thereby identifying a R/N/R pattern. The normal chron might correlate with the long basal Triassic normal polarity interval and the reversed polarity zones above and below it known from marine successions in the Alps, Russia, Pakistan and China. The PTB is thought to be situated coincident with the LAD of Dicynodon and the event bed of Ward et al. (2000), apparently above but not necessarily diachronous with a lithology change from predominantly green- to predominantly red mudstone. This placement falls within a normal polarity interval, but could conceivably have taken place at a time of reverse polarity due to delayed acquisition of magnetic remanence. The idea of an extraterrestrial impact as the cause of the end-Permian mass extinctions is strongly enhanced by a synchronous relationship between them. The configuration of the supercontinent Pangea during this time of earth history has been the matter of debate for the last three decades, with numerous alternative reconstructions to the classic Pangea A1 having been proposed for the time preceding the Jurassic. Paleomagnetic data from the Karoo allow for the definition of a new paleopole for West Gondwanaland, which prove a valuable tool for evaluating these various reconstructions. It is neither consistent with a Pangea B-type not C reconstruction for Pangea during this time interval, because of geological ambiguities. The most likely solution to the problem is that of a persistent non-dipole field contribution to the geomagnetic field during this time. Approximately 50 million years later Pangea was unambiguously in a classic Pangea A1 configuration, and life on earth suffered yet another set back. The end-Triassic mass extinction, which marks the sequence boundary between the Triassic and the Jurassic, has not received as much attention as the other four big Phanerozoic biotic disasters. In the Karoo a pronounced turnover in faunal assemblages from typical Triassic fauna to Jurassic Fauna (dinosaurs) is seen in the Elliot Formation. Magnetostratigraphic study of localities in the north and south of the Karoo Basin provided a magnetic zonation pattern for the Elliot Formation, a tool that has led to the constraining of the sequence boundary to the transition from the lower Elliot Formation to the middle Elliot and added to the hypothesis that the faunal turnover is globally synchronous. The determination of a paleolatitude for the Elliot Formation in combination with characteristically arid lithologies (eolian sandstones) provided the base for the evaluation of the paleoclimate that characterized Pangea during the Late Triassic to Early Jurassic. Key words: Karoo Basin, Magnetostratigraphy, Mass Extinction, Paleoclimate, Paleogeography, Paleomagnetism, Pangea, Permian-Triassic, Triassic-Jurassic
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Elmore, Aurora Cassandra. "Late Pleistocene changes in northern component water inferences from geochemical and sedimentological records from Gardar Drift /." 2009. http://hdl.rutgers.edu/1782.2/rucore10001600001.ETD.000051342.
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Rudloff, Owen M. "A 4600-year record of lake level and hydroclimate variability from an eastern Andean lake in Colombia." Thesis, 2016. http://hdl.handle.net/1805/10997.
Full textAbstract:
Indiana University-Purdue University Indianapolis (IUPUI)Hydroclimatic variability in the eastern Colombian Andes is examined using a decadally-resolved, multiproxy lake sediment record from Laguna de Ubaque, Colombia. Hydroclimate trends are examined and compared to existing local, regional, and trans-Andean records to enhance existing knowledge of Late Holocene Colombian precipitation and assess potential hydroclimatic forcing mechanisms in tropical South America. Sedimentological analyses, including percent lithics, grain size, C:N and magnetic susceptibility are sensitive to hydroclimate and lake level while charcoal size and concentrations reflect fire variability. Results show that deep lacustrine conditions characterized by laminated deposits were not established until approximately 3500 cal yr B.P., prior to which, terrestrial C:N values and unstructured sediments indicate that drier, marsh-like conditions prevailed. Between 3500 and 2000 cal yr B.P., interrupted only by a 300-year arid interval from 2800 to 2500 cal yr B.P., greatly increased overall clastic deposition indicates a broad precipitation maximum while decreased sand deposition and the preservation of finely laminated sediment indicate deep lake conditions. After 2000 cal yr B.P., decreased clastic deposition suggests reduced precipitation, but the continued accumulation of laminated sediments indicates that conditions were wet enough to fill the basin continuously until the present day. These observations address two of the driving questions of Andean paleoclimate: were the northern and southern Andes in vi phase during the Holocene, or out of phase, and what are the main drivers of Holocene Andean climate? We find that the early part of Ubaque’s record more closely resembles southern Andean precipitation records until 2000 cal yr B.P., at which point it abruptly switches to resemble northern precipitation records. We attribute this to a combination of the southward migration of the intertropical convergence zone (ITCZ), and an increase in eastern Pacific sea surface temperatures (SST). In addition, we find that Colombian hydroclimate records exhibit a bimodal precipitation pattern, which we attribute to their location either on the Andean slopes or in the high interior Andes.
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Tian, Xiaochuan. "Structural and Climatic Effects of Large-Scale Basaltic Magmatism: Constraints and Insights from Geodynamic Models." Thesis, 2021. https://doi.org/10.7916/d8-2dvc-e762.
Full textAbstract:
This thesis concerns the causes and consequences of magma emplacement in the Earth’slithosphere during the formation of Large Igneous Provinces (LIPs) and continental rifts. Motivated by geological, geophysical, geochemical and paleoclimate data, I formulate geodynamic models to address the following questions: (1) How were the massive volumes of subaerially erupted lava, described in multi-channel seismic data as seaward-dipping reflectors (SDRs), formed and what can SDRs tell us about the rifting processes? (2) What thermal and rheological conditions are required to produce the contrast in topography of the two youngest LIPs: namely that the Columbia Plateau sits ~0.7 km lower than the surrounding region while the Ethiopian Plateau is ~1.5 km higher than its surroundings? (3) Why does significant global warming occur a few hundred-thousand years prior to the main phase of eruptions of the Columbia River Basalts and the Deccan Traps?
The major results of my thesis are: (1) The first two-dimensional thermo-mechanical treatment of SDR formation shows how the lithosphere thickness affects the deformation in response to magmatic loads during volcanic margin formation. I provide a quantitative mapping between the shape of SDRs and the strength of the lithosphere and this mapping reveals weak continental margin lithosphere during the initial continental breakup. (2) Cold and strong crust results in slow lower crustal flow and a persistent high plateau like the Ethiopian Plateau. In contrast, a combination of three things can produce a low plateau like the Columbia Plateau. First, hot and weak lower crust flows fast in response to topographic and magmatic loads. Second, a significant fraction of the magma intruded in the crust freezes onto and becomes part of the strong upper crust. Finally, the bulk of the intrusions occur before the main phase of extrusion to explain the geometry of the Columbia River Basalt lava flows. (3) I argue that the major eruptions of continental flood basalts may require densification of the crust by intrusion of larger volumes of magma than are extruded. Simple models show that magma crystallization and release of CO² from such intrusions could produce global warming before the main phase of flood basalt eruptions on the observed timescale.
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Sandstrom, Robert Michael. "Geochronology and reconstruction of Quaternary and Neogene sea-level highstands." Thesis, 2021. https://doi.org/10.7916/d8-1xn4-vb62.
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Understanding the past sensitivity of ice sheets and sea level rise in a warmer climate is essential to future coastal planning under the threat of climate change, as accurately modeling impending scenarios depends primarily on data from the past. Extreme warm events during the Quaternary and Neogene periods hold much of the information needed to predict future global climate conditions due to anthropogenic and natural forcings, and may provide unique glimpses of how much future sea level rise can be expected on both short- and long-term timescales. Constraining global mean sea level (GMSL) during past warm periods becomes increasingly difficult the further back in time one goes, especially as precise dating of globally distributed paleoshorelines, along with long-term vertical displacement rates, is essential for establishing GMSL and ice volume history. However, placing chronological constraints on shorelines beyond the limit of U-series radiometric dating (~600 kyr), or at high latitude sites lacking coral, has remained elusive. Even relatively recent warm periods, such as the Last Interglacial (~117-129 ka) has proved challenging for reconstructing GMSL, primarily due to uncertainties in long-term vertical deformation rates and timing of when the highstand occurred. The first two chapters of this thesis address the dating of carbonate shorelines older than ~500 kyr through refinement of the strontium isotope stratigraphy dating methodology. I apply these techniques to a well-known location with numerous uplifted fossil shorelines (Cape Range, Western Australia) to provide the first geochemically derived ages on three fossil shorelines spanning the Pleistocene to the Miocene. Accurate dating and mapping at this location allows correction of long-term vertical displacement. In the last chapter, I use these rates of uplift, in conjunction with twenty new 230Th/U-ages on corals from Western Australia, to refine the timing and peak elevation of the Last Interglacial sea level highstand.
Chapter 1 re-evaluates strontium isotope stratigraphy dating techniques for chronologically constraining fossil shorelines from ~0.5 to >30 Ma. Using marine terraces from South Africa, Western Australia, and the Eastern United States as examples, this chapter presents a refined sampling and dating methodology to overcome limitations on diagenetically altered samples, which are ubiquitous in older carbonate shorelines. Discussion on best practices for constraining maximum or minimum ages includes a novel scoring methodology for alteration and a sequential leaching procedure that is specifically suited for shallow-water biogenic carbonate fauna.
In Chapter 2, I apply the revised strontium isotope stratigraphy dating methodology to three previously unknown aged terraces in Cape Range, Western Australia. The results obtained show Late-Miocene, Late-Pliocene and Mid-Pleistocene shorelines, which I then use to reconstruct the vertical uplift history of the anticlinal structure and relative rates of deformation. This study is the first to directly date the three terraces, and provides the deformation history necessary for constraining Last Interglacial sea level at Cape Range. In addition, we are able to place maximum relative sea level constraints on all three of these older shorelines.
Chapter 3 builds upon the previous chapter by focusing on the Last Interglacial sea level history along ~300 km of coastline in Western Australia (Cape Range and Quobba). This chapter presents new U-series ages on multiple coral heads that are among the highest in-situ corals ever dated in Western Australia, with ages spanning from ~125.3 – 122.6 ka. Detailed geomorphic analysis, particularly at Cape Range, constrains the relative sea level highstand to 6.9 ± 0.4 m. When glacial isostatic adjustment models are applied to the age and elevation data, the resulting Eemian GMSL highstand occurred between 125.5-123.0 ka and reached an elevation between 4.9 and 6.7 m. This is later in the Interglacial and lower in elevation than many recent studies suggest.
This dissertation focuses on refining sea level highstands from the Last Interglacial to the Late Miocene in a relatively small (but historically important) region of Western Australia. However, the methodologies presented here provide a powerful multi-proxy dating and mapping approach, which, when applied to regions with multiple marine terraces, can greatly improve the reliability of younger shoreline elevations by reducing neotectonic and dynamic topography uncertainties. The carbonate screening techniques and 87Sr/86Sr stratigraphy dating described here are applicable to a wide range of marine carbonates, with the ability to place accurate chronologic constraints on shorelines from 0.5 to >30 Ma. As I show in chapter 3, when combined with 230Th/U-dating on Late Pleistocene coral in places where multiple marine terraces exist, valuable long-term vertical deformation constraints can allow for far more accurate analysis of sea level in younger paleo shorelines (i.e. Last Interglacial).
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Henderson, Samuel Straker. "Tracking deep-water flow on Eirik drift over the past 160 kyr linking deep-water changes to freshwater fluxes /." 2009. http://hdl.rutgers.edu/1782.2/rucore10001600001.ETD.000051018.
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Ali, Guleed. "Late Glacial and Deglacial Fluctuations of Mono Lake, California." Thesis, 2018. https://doi.org/10.7916/D8CC2BNN.
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Anthropogenic climate change risks significant changes in the global distribution of precipitation. Across the western United States, modelling studies show significant reductions in wetness that imply weighty societal and ecological impacts. But the validity of the model projections need to be ground-truthed. Paleo-hydroclimate data are useful reference points to assess a model’s ability to hindcast past hydroclimate. If the hindcast matches the paleodata, it brings confidence to a model’s ability to predict future hydroclimatic change.
The foremost metric of hydroclimate in the geologic record is the surface area of lakes in hydrologically closed basins. In such basins, a lake’s surface area is determined by the balance between precipitation and evaporation. The lake will expand when the balance is positive, and it will contract when the balance is negative.
In this dissertation, I develop a 25-9 ka record of lake fluctuation from the Mono Basin, a hydrologically closed basin in east-central California. I deduced the fluctuations using three pieces of evidence: stratigraphy; geomorphology; and geochronology. These pieces of evidence were determined from a study of the Mono Basin’s Late Pleistocene lithostratigraphic unit: the Wilson Creek Formation.
There are 19 tephra intercalated in the Wilson Creek tephra. They are named by their reverse depositional order (Ash 19 is the oldest and Ash 1 is the youngest). Uncertainty on their ages cause confusion as to the paleo-hydroclimate record of the Mono Basin. The age of Ash 19, for example, is important because its deposition marks the onset of relatively high lake levels that occurred during the last glaciation. There are two principal interpretations of Ash 19’s age: 40 ka, which is based on lacustrine macrofossil 14C data; and 66 ka, which is underpinned by paleomagnetic intensity data. In chapter 2, I tested these end-member interpretations. I used the U/Th method to date carbonate deposits that underlie and cut across Ash 19. The U/Th data show that Ash 19 must have been deposited between these two dates: 66.8 ± 2.8 ka; and 65.4 ± 0.3 ka. These dates are, therefore, more consistent with the 66 ka interpretation of Ash 19’s age. Thus the onset of relatively high lake levels in the Mono Basin corresponds with the rapid drawdown of atmospheric CO2 during Marine Isotope Stage 4. The coincidence between the drop in atmospheric CO2 and lake level rise is suggestive of a causal link.
In chapter 3, I determined Mono Lake's fluctuations 25-9 ka. This time encompasses three climatic intervals: the coolest time of the last glaciation, termed the Last Glacial Maximum (LGM); the period corresponding to the rapid termination of the last glaciation, termed the deglaciation; and the early Holocene, a period of inordinate warmth that immediately followed the last glaciation’s termination. In this study, I used stratigraphic and geomorphic evidence in conjunction with 14C and U/Th dates. I measured the 14C dates on bird bones and charcoal. And I measured the U/Th dates on carbonates. Together the data showed that the lake's rises and falls concurred with North Atlantic climate. Periods of aberrant warmth in the North Atlantic concurred with low stands of Mono Lake. On the other hand, extreme cooling in the North Atlantic correlated with Mono Lake high stands. The timing of these lake fluctuations also corresponds with variations in other tropical and mid-latitude hydroclimatic records. The global harmony in the hydroclimatic records suggests a unifying conductor. I hypothesize that the conductor is tropical atmospheric circulation.
In chapter 4, I present evidence on the peculiar case of an extreme low stand of Mono Lake. The low stand is dubbed the “Big Low”. The principal evidence underpinning the Big Low derives from a sedimentary sequence exposed along the canyon walls of Mill Creek. The strata show that the lake fell below 1,982 m between the deposition of Ashes 5 and 4—making this low stand the lowest recognized level of Mono Lake during the Wilson Creek Formation. Observations from dispersed sequences corroborate this interpretation. And three data constrain the age of the Big Low to be between ~24.4-20.5 ka: a carbonate U/Th date on a littoral conglomerate associated with the Big Low; a carbonate U/Th date that underlies Ash 4; and a carbonate U/Th date that cuts across Ash 5. Thus the interval that the Big Low must occur within encompasses the LGM. The timing of this low stand, therefore, corresponds with summer temperature minima, suggesting that the fall was due not to an increase in evaporation but due to a decrease in precipitation. This finding is counter to conventional wisdom: that the LGM was a relatively wet interval. In addition, both the documentation of a low stand during glacial maximum conditions and the inference that precipitation must have been reduced are contrary to previous published interpretations from model and paleoclimatic data. These discrepancies raise significant questions about our understanding of the regional expression and forcing of hydroclimate across the western United States during the LGM. Because of this period’s importance to ground-truthing climatic models, additional evidence on the geographic extent of this unexpected result is essential.
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Brown, Kenneth M. "The bench deposits at Berger Bluff : Early Holocene-Late Pleistocene depositional and climatic history." 2006. http://hdl.handle.net/2152/13061.
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Mullin, Michelle R. D. "Stable isotope record of soil carbonates from the Eocene-Oligocene transition, Badlands National Park, South Dakota, USA." 2010. http://liblink.bsu.edu/uhtbin/catkey/1632468.
Full textAbstract:
Sections in and around Badlands National Park, Custer County, South Dakota contain a wealth of faunal and floral data within the White River Group. The Chadronian and Orellan North American Land Mammal Ages define the Eocene-Oligocene boundary here. Faunal and floral changes associated with the Chadronian-Orellan interval have long been attributed to the global Greenhouse-Icehouse climatic transition. Stable isotopes were obtained from paleosol carbonates across the Chadronian-Orellan boundary at three locations in Badlands National Park. Results show wide fluctuations of oxygen isotopes in the uppermost Chadronian and lower Orellan, while carbon isotopes remain relatively stable. The records provide an opportunity to compare the continental response to global change with a near-shore marine system response (Gulf Coastal Plain, USA); and to the world at large. Results indicate a decoupling of the terrestrial response to the Oi-1 glacial event from the marine response. Local conditions appear to play an important role in controlling the record of stable isotopes in paleosol carbonates in the region.Geologic history of the Eocene-Oligocene -- Climate records -- Causes of climate change -- Climate change across the Eocene-Oligocene -- Current findings -- Discussion.
Department of Geology
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Fawcett, Peter J. "Simulation of climate-sedimentary evolution a comparison of climate model results to the geologic record for India and Australia /." 1994. http://catalog.hathitrust.org/api/volumes/oclc/33920205.html.
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Abell, Jordan Tyler. "Earth, Wind, and Water: Plio-Pleistocene Climate Evolution in East Asia and the North Pacific." Thesis, 2021. https://doi.org/10.7916/d8-4b42-t424.
Full textAbstract:
The Pliocene, a geologic epoch spanning ~2.6-5.3 million years ago (Ma), was a period in Earth’s history where temperatures were several degrees warmer than today and atmospheric CO2 was close to modern levels, making it an analogue for future climate change. Following this interval, the planet’s climate shifted to the familiar glacial-interglacial cycles of the Pleistocene (~0-2.6 Ma), beginning with the development of extensive Northern Hemisphere ice sheets at ~2.7 Ma. In response to these changes through the Plio-Pleistocene, several components of the Earth System, particularly related to East Asia and the North Pacific Ocean, varied both temporally and spatially, further modifying regional and global climate through various feedbacks. In this thesis, I utilize a combination of geochemical proxies derived from North Pacific marine sediments as well as a regional climate model to better understand the evolution of the westerly winds, North Pacific Ocean circulation, and East Asian desert landscapes, across the last five million years.
In Chapter 1, I reconstruct Pliocene dust fluxes at two different sites in the North Pacific using the constant flux proxy extraterrestrial 3He (3HeET), the first of such records in the Pliocene. Along with 3HeET-derived export productivity fluxes and sea surface temperatures from the westernmost core, I show that the Northern Hemisphere westerly winds, were shifted poleward and weaker during much of the warm Pliocene. Coinciding with the intensification of Northern Hemisphere Glaciation, the westerlies shifted equatorward and strengthened at ~2.7 Ma, and during subsequent glacial periods thereafter. Combining my dust flux record with others from different ocean basin, I find that these changes in the westerly winds were globally synchronous.
Chapter 2, entitled “Pliocene Variability of Active Pacific Meridional Overturning Circulation: Reevaluating North Pacific Productivity and Redox Conditions from ~2.5-6 Ma”, presents additional 3HeET-based export productivity flux data, as well as redox element concentrations, from the central subarctic North Pacific through the Pliocene. The new records suggest elevated North Pacific export production during the interval spanning ~4-5.5 Ma, followed by a decrease in the mid-Pliocene (~3.5-4 Ma). Combining this new data with previously published records and modeling output, I provide additional evidence for an active Pacific meridional overturning circulation during the warmer-than-present Pliocene, and add constraints on its variability under various climatic conditions.
In Chapter 3, I bring together two constant flux proxy-derived dust flux datasets from the same core in the western North Pacific Ocean to provide novel insight into Quaternary dust dynamics in East Asia. By utilizing constant flux proxies, and accounting for inputs of volcanic material, I show for the first time that dust input to the North Pacific decreased over the last ~2.7 Myr, particularly during glacial periods. While quite different from other previously published dust datasets, this finding is consistent with our current understanding of East Asian dust production mechanisms, and acts as a strong impetus to perform more comprehensive studies of dust fluxes to the North Pacific and other depositional areas downwind of arid regions.
Chapter 4 transitions to a terrestrial setting, in which I investigate the impacts of shifting arid region surface albedo on the atmospheric boundary layer using the Hami Basin, China, as a test location. Combining new simulations from the Weather Research and Forecasting base model and available geologic data, I report a previously undescribed “wind-albedo-wind” feedback process. Specifically, I propose that wind erosion, in conjunction with surficial sediments of various albedos, leads to altered wind speeds, and eventually fluctuations in erosion itself. In Chapter 5, I expand upon the work in the preceding chapter by coupling the Weather Research and Forecasting model with a chemistry component to simulate dust emissions. In addition, along with albedo, I characterize previously interpreted surface changes through time to reflect shifts in erodibility and surface roughness.
I conclude that although albedo does ultimately influence near-surface wind speeds and dust emissions as predicted in my earlier study, the effects of variable surface roughness and erodibility dominate. Integrating these results with an updated interpretation of the geologic evolution of the Hami Basin, we find that during various periods of the last ~700 ky, the Hami Basin, and likely the greater stony Gobi Desert, could have been much more important dust sources than today.