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1
Gibbs, Samantha Jane. "Variability of Pliocene nannoplankton populations." Thesis, University of Cambridge, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.599385.
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Here I focus on the construction of high-resolution nannofossil records, in addition to carbonate preservation, isotope, and other environmental proxy records, for the equatorial Atlantic ODP Sites 662, 926 and 929, and the sub-equatorial Atlantic Site 659. This integrated study demonstrates the detailed character of he nannofossil populations (overall abundance, evolution and morphometric patterns). It also allows an assessment to be made of the stratigraphic and evolutionary importance of nannoplankton events during the mid Pliocene from 3.45-3.95 Ma. The mid Pliocene is demonstrated here to be an interval of subtle reorganisation characterised by the last occurrences of Sphenolithus sp. and Reticulofenestra pseudoumbilicus. The mid Pliocene lies in a wider interval of progressive extinctions of warm water, oligotrophic taxa associated with climatic deterioration from the Late Pliocene to Recent. Nannofossil sediment assemblages are controlled by both the initial production of the nannoplankton in the surface waters and dissolution (in the water column and pre- and post-burial). By the comparison of synchronous nannofossil and non-nannofossil records from Ceara Rise Sites 929 (4397 m water depth) with Site 926 (3598 m water depth), an ecologically dominated assemblage can be clearly distinguished from one that has experienced significant subsequent taphonomic overprinting by dissolution. The latter is differentiated by the number of co-varying relationships, the taxa that form those co-varying relationships, the coupling of dissolution indices with each other and with the co-varying nannofossil abundances, and the loss or reduction of dissolution-susceptible taxa. In non-dissolution influenced populations, two main signals are found to shape the downcore variability in nannofossil assemblages. The main signal is an evolutionary trend. To a lesser extent, the signal is dominated by strong cyclic abundance changes responding to orbitally forced climate changes. Only some of the variance observed in nannofossil abundance patterns can be explained by direct linear climatic forcing. This is to be expected given that in studies of seasonal coccolithophorid assemblages, only part of the variation observed can be explained by simple correlation with abiotic processes.
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Dolan, Aisling Margaret. "Modelling mid-Pliocene climate and ice sheets." Thesis, University of Leeds, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.590483.
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Given anthropogenic modification of the climate system, the future stability of Earth's major ice sheets and sea level is uncertain. One potential, lJ1ethod to investigate the behaviour of the Greenland and Antarctic ice sheets under a warmer-than-modern climate regime, is to look back at past warm periods of Earth history (for example the mid Pliocene Warm Period; 3.26 - 3.0 million years ago). The British Antarctic Survey Ice Sheet Model (BASISM) and the Hadley Centre Coupled Climate Model version 3 (HadCM3) allow the climate and ice sheets of the mid-Pliocene to be modelled, and their sensitivity to a range of uncertainties in forcing to be quantified. The ice sheets, particularly the Greenland Ice Sheet, are sensitive to changes in the Earth's orbital configuration and potential levels of atmospheric carbon dioxide (C02) during the mid-Pliocene. Exploring various orbital forcing scenarios in concert with a plausible Pliocene COz envelope (280 - 560 ppmv), enables models to generate Greenland ice sheet reconstructions that range from a 1.5% reduction from modern to an ice-free state. In contrast, on East Antarctica, significant ice sheet retreat is only simulated under warm Southern Hemisphere orbital conditions where C02 levels are at 400 ppmv or above. Maximum eustatic sea level rise corresponding to predicted ice sheet reductions is comparable with recent records suggesting mid-Pliocene sea level high-stands of 22 m greater than modern. However, ice sheet reconstructions are shown to be highly dependent on Q priori assumptions regarding the initial ice sheet configuration within the numerical modelling framework. Investigation of the dependency of ice sheet predictions on the models used, has demonstrated that results are sensitive to the modelled climatological forcing. Such dependency is most explicitly highlighted over Greenland, where Pliocene ice sheet predictions, given forcings from fifteen equivalently-configured climate models, range from no ice to a configuration that is larger than modern. These results underline the importance of considering mUltiple sources of uncertainty when predicting past ice sheets. v
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Hill, Daniel J. "Modelling earth's cryosphere during peak pliocene warmth." Thesis, University of Bristol, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.500436.
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Pope, James Owen. "Modelling Pliocene climate with perturbed physics ensembles." Thesis, University of Leeds, 2015. http://etheses.whiterose.ac.uk/10443/.
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Uncertainty in model simulations arises due to the construction of the model (structural uncertainty), the representation of sub-grid scale processes (parameter uncertainty) or the input of model boundary conditions. Perturbed physics ensembles (PPEs) produce an ensemble of simulations using a single climate model. A PPE produces different representations of climate by altering the tuning of parameterisations representing processes occurring on sub-grid scales, such as clouds and radiation. A PPE has been produced to investigate model parameter and boundary condition uncertainty for the mid-Pliocene Warm Period (3.264 to 3.025 Ma BP). Through the use of a PPE, 14 versions (13 perturbed members and the Standard version) of the UK Met Office atmosphere-ocean general circulation model HadCM3 were created. The full ensemble was re-run to assess the impact of simultaneously changing physical boundary conditions for orography, ice sheets and vegetation in combination with perturbed physics. Finally the effect of the potential range in reconstructed mid-Pliocene CO2 was investigated through a sub-ensemble of the PPE. Using data-model comparisons (DMCs), the ensemble members with higher than the Standard values of Charney sensitivity were better able to simulate the magnitude of high latitude mid-Pliocene warming. The strongest performing ensemble members for the DMCs displayed Charney sensitivities of 4.54°C, 4.62°C and 5.40°C, above the upper bound of the IPCC likely range (1.5 to 4.5°C). However, these warmer members with higher Charney sensitivities weakened the data-model comparison in the tropics. Ensemble members with lower than Standard values of Charney sensitivity, close to the lower bound of the IPCC likely range, better resolved temperature reconstructions in the tropics, but were unable to resolve high latitude warming. It is evident that the PPE is able to achieve the magnitude of mPWP warming but not the spatial distribution of the warming. The investigation into boundary condition uncertainty using the PPE reveals that the PRISM3D physical boundary conditions lead to improved simulations of the mPWP climate than the PRISM2 boundary conditions. For the range of atmospheric CO2 concentrations, the results from the sub-ensemble indicate that lower values of CO2 lead to reduced performance of the PPE members compared to the palaeo-data. The conclusion is that concentrations of CO2 below 350 ppmv for the mPWP would make simulating high latitude climates very difficult for climate models.
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Chapman, Mark Robert. "Late Pliocene planktonic foraminifera : palaeoceanography and faunal evolution." Thesis, University of East Anglia, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.332388.
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Haslett, Simon K. "Pliocene-Pleistocene radiolarian investigations of the Equatorial oceans." Thesis, University of South Wales, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.265674.
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Farquhar, Sarah Alice. "Lower Pliocene dinoflagellate cysts from the Mediterranean Sea." Thesis, University of Cambridge, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.612505.
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Daley, Gwen Marie. "Paleocommunities of the Yorktown Formation (Pliocene) of Virginia." Diss., Virginia Tech, 1999. http://hdl.handle.net/10919/39124.
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The fossiliferous Yorktown Formation (Pliocene) of Virginia was used as a natural laboratory for testing predictions of ecological and evolutionary theories. Specifically, coordinated stasis and ecological locking models have testable elements that can be analyzed using data from the Yorktown Formation. The ecological locking model requires that species within an ecosystem have strong interactions in order to stabilize morphologies of multiple lineages over millions of years. Species intereactions that are strong enough to do this should also be strong enough to be a major ordering force on the composition of paleocommunities.
Single and replicate samples were taken from 30 cm stratigraphic intervals within the Rushmere and Morgart's Beach Members at several localities. A total of 142 samples were collected from 5 localites, which yielded 29,000 specimens belonging to 140 species of bivalves, gastropods, and other taxonomic groups.
Principle components analysis, ANOVA, MANOVA, and other analyses were used to test the occurence and recurrence of local paleocommunities, paleocommunities, and paleocommunity types. Three paleocommunity types which occured under specific paleoenvironmental conditions were defined: rubbly bottom, transitional, and muddy bottom. Within a single locality samples from the same paleocommunity type yielded very similar faunal compositions, based on the relative abundance of the contained species. However, samples from the same paleocommunity type but different localities displayed low similarity values. This is consistant with local paleoenvironmental control of paleocommunity composition being more important than strong species interactions. The pattern predicted by the model of ecologic locking is absent from these Yorktown paleocommunities.
A guild analysis was performed on the data to test whether the same types of organisms recurred in a predictable fashion under similar paleoenvironmental conditions. While the guild structure of the rubbly bottom paleocommunity type did recur at several localities, the guild structure of the other paleocommunity types varied greatly from place to place.Ph. D.
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Howell, Fergus William. "Sea ice climate interactions in the Pliocene Arctic." Thesis, University of Leeds, 2015. http://etheses.whiterose.ac.uk/11692/.
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The mid-Pliocene Warm Period (mPWP, 3.264 to 3.025 Myr ago) has been extensively studied through the use of general circulation models (GCMs). Whilst the output from these simulations replicates closely many of the patterns of the climate of the interval indicated by proxy data, at northern high latitudes the reconstructed proxy data temperatures exceed the model temperatures by over 15˚C for some sites. This data-model discrepancy highlights the importance of focusing on model representation of processes that strongly affect the northern high latitude climates. Arctic sea ice exerts a strong influence on the Arctic climate, largely due to the ice-albedo feedback mechanism, and by creating an insulating layer between the ocean and the atmosphere. Interest in Arctic sea ice and its representation in climate models has been enhanced in recent years due to the rapid decline in the September minimum sea ice extent that has been observed since the advent of satellite observations in 1979. This thesis describes the results from simulations of the mPWP with the GCM HadCM3, focusing on the simulated Arctic temperatures and sea ice. A change to the parameterisation of sea ice albedo is implemented in the model, based on recent observations of changes in the albedo of Arctic sea ice. The results show mean annual surface air temperature (SAT) increases of up to 6˚C, and mean annual sea surface temperature (SST) increases of up to 2˚C, and the disappearance of Arctic sea ice in some summer months, but very small changes in the discrepancy between the model and proxy data temperatures. The sensitivity of simulated Arctic sea ice to orbital forcings and atmospheric CO2 in HadCM3 is also explored, with the results suggesting that changes in orbital forcing are sufficient to change the simulated mid-Pliocene Arctic from perennial to seasonal sea ice, unless combined with lower CO2 concentrations. Changes to orbits and CO2 are also combined with the alternative albedo parameterisation, and further data-model comparisons are performed, with the results continuing to show cooler model temperatures, but with a reduced gap. Also shown are the simulated Arctic sea ice outputs from eight different GCMs as part of the Pliocene Modelling Intercomparison Project (PlioMIP). The comparison demonstrates the model dependency on the simulation of Arctic sea ice, as only half of the models simulate perennial Arctic sea ice in the mid-Pliocene. The dominant influences on the sea ice simulation in the ensemble are also discussed.
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Korren, Caitlyn. "PALEOSEISMOLOGY OF A PLIOCENE EARTHQUAKE IN EASTERN TAIWAN." OpenSIUC, 2015. https://opensiuc.lib.siu.edu/theses/1639.
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High seismicity coupled with high population density creates a recipe for high seismic risk in Taiwan. Taiwan is located at the convergences of the Eurasian and Philippine Sea plates. These convergences result in the development of an accretionary wedge. A basal decollemont bounds the NE-SW trending thrust packages. The most Eastern thrust package, the Central Range, experiences high erosion rates and exhumation rates which may induce high seismicity. Paleoseismic indicators improve the ancient seismic history and may aid in the constraint of geologic processes of an accretionary wedge. Pseudotachylytes, known as earthquake fossils, form by frictional melting during seismic slip. Cataclasites form by comminution during sliding. Frictional melts serve as a window to the fault plane. Pseudotachylytes may allow for the assessment of focal parameters through the utilization of fault plane geometry and slip surface properties. This study provides the first microstructural evidence for fault pseudotachylytes at the Hoping River locality in Eastern Taiwan. The 3.3 Ma Hoping River frictional melt evidences an ancient Mw 6.4 ±0.40 earthquake. This pseudotachylyte demonstrates an oblique fault with a reverse component which corresponds to the orientation of the thrust packages in the accretionary wedge. Sense of slip of both pseudotachylytes and cataclasites suggest a uniform stress field. Narrow fault cores suggest high strain localization. Coeval pseudotachylyte and quartz-calcite veins suggest shear heating as a mechanism, if a fluid reservoir along the basal decollemont in Taiwan exists.
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Chiotakis, Christina. "Pliocene crocodilians of chinchilla: Identification using dental morphometrics." Thesis, Queensland University of Technology, 2018. https://eprints.qut.edu.au/119219/1/Christina_Chiotakis_Thesis.pdf.
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The key research problem of this project was to identify Australian crocodilian species from isolated teeth, which make up the largest available fossil data set. Three-dimensional images of the teeth were created from computed tomography (CT) data and statistical comparisons allowed several extinct species to be distinguished from each other and from modern crocodiles. The research provides a new methodology for identifying crocodilian teeth, and potential for further usage of this methodology including identifying theropod dinosaurs and other species from isolated teeth.
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Bell, David Benjamin. "Onset of the Icehouse World : Atlantic deep-water circulation during the Pliocene and Pleistocene." Thesis, University of Edinburgh, 2014. http://hdl.handle.net/1842/16468.
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The transition from the warm, “greenhouse” conditions of the Pliocene to the cold, “icehouse” conditions of the Pleistocene marks a significant development in climate history. The deep-ocean is the largest dynamic reservoir of heat and carbon dioxide in the climate system that is accessible on timescales of Plio-Pleistocene climate change. Therefore, changes in the state of the deep-ocean may have played an important role in large scale Plio-Pleistocene climate change via variability in the meridional overturning circulation of the Atlantic (AMOC). In this thesis, paleoceanographic reconstructions of Plio-Pleistocene Atlantic deep-water circulation are presented from the perspective of Ocean Drilling Program Sites 1264 (2505m depth) & 1267 (4350m depth), situated at ~30oS in the Southeast Atlantic. Reconstructions are based on high-resolution (~<5,000 year time-step), down-core measurements of oxygen (δ18O) and carbon (δ13C) stable isotope ratios in benthic foraminifera. During the Pliocene, widespread high δ13C values in the Atlantic and at Sites 1264 & 1267 indicate low nutrient conditions and active deep-water renewal. The early Pliocene closure of the Central American Seaway (CAS) (~4.7-4.2 Ma) is considered to have been influential in establishing strong deep-water formation in the North Atlantic. Evaluation of δ13O and δ13C records from Site 1264 and throughout the North Atlantic, however, indicate that the CAS closure event had only a limited impact outside of the Caribbean Basin. Meanwhile, during the interval ~3.6-2.7 Ma, δ13C-gradients between Sites 1264-1267 are near zero and suggest strong North Atlantic Deep Water (NADW) prevalence in the Southeast Atlantic, similar to or stronger than the modern situation. The transition into Pleistocene style glacial-interglacial cycles at ~2.7 Ma is associated with a reduction of NADW prevalence in the Atlantic, particularly during glacials and at depth. At ~2.4 Ma, δ18O and δ13C records from Sites 1264 & 1267 reveal marked changes in deep-water circulation. Large (>0.5‰) δ18O-gradients emerge, with heaviest values seen at Sites 1264 & 1267 compared to records from the North Atlantic. At the same time, δ13C values increase at Sites 1264 & 1267. The combination of high δ18O and δ13C values at Sites 1264 & 1267 is consistent with enhanced export of a dense component of NADW that enters the Atlantic from the Nordic Seas by spilling over the Iceland-Scotland Ridge. Comparisons with other North Atlantic records suggest that the pathway of Iceland-Scotland Overflow Water (ISOW) was restricted, flowing along the abyssal East Atlantic and piling up at Walvis Ridge. Between ~2.0-1.5 Ma, maximum δ13C values and minimum δ13Cgradients within the North Atlantic and between the North Atlantic and Sites 1264 & 1267 indicate that the overall export of NADW was strongest for the Pleistocene. After ~1.5 Ma, Atlantic δ18O-gradients begin to reduce, along with δ13C values, although δ13C-gradients still imply strong NADW export. Starting at ~1.3 Ma and across the Mid Pleistocene Transition (MPT), Atlantic δ18O-gradients reduced markedly, as did North Atlantic-Pacific δ18O-gradients but to a lesser degree. After ~0.9 Ma, glacial reductions in NADW presence at depth are the most severe of the entire Plio-Pleistocene, while interglacial export of NADW into the Atlantic remained almost as high as pre MPT conditions. Changes in the strength of AMOC during the Plio-Pleistocene are inferred through comparisons of Atlantic deep-water history with records of sea surface temperature from the high latitude North Atlantic, South Atlantic and North Pacific. I propose that AMOC played an important role in the evolution of Pleistocene climate. Enhanced northward heat transport, due to an increase in the strength of AMOC at ~2.4 Ma, limited the growth of continental ice sheets and sea ice within the North Atlantic region. This may have been caused by increased equator-to-pole thermal gradients and decreased atmospheric moisture transport, increasing salinity, as the global climate cooled. A strengthening of AMOC at ~2.4 Ma is paralleled by significant deep-water changes recorded at Sites 1264 & 1267, implicating enhanced ISOW export into the Southeast Atlantic as an important component of AMOC at this time. A maximum in AMOC occurred between ~2.0-1.5 Ma, along with warming in the mid latitude North Atlantic. Scavenged heat from the South Atlantic promoted enhanced cooling of the Southern Hemisphere and the expansion of sea ice at ~1.5 Ma. Feedbacks originating in the Southern Ocean then acted to cool the globe and eventually pre-condition the climate for the MPT.
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Chepstow-Lusty, Alexander John. "Nannoplankton as indicators of climatic variability in the Upper Pliocene." Thesis, University of Cambridge, 1991. https://www.repository.cam.ac.uk/handle/1810/239128.
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Discoasters are the remains of an enigmatic group of nannoplankton, whose last representatives disappeared globally at 1.89 Ma. The one million years prior to their extinction has been analysed in high time resolution and a global database has been developed from ten sites in the Atlantic, Indian and Pacific Oceans. It has been shown that the variability in Discoaster abundance at low latitudes cannot be attributed solely to changes in sea-surface temperature; discoasters were demonstrated to be suppressed at upwelling sites. In combination with global satellite images of phytoplankton blooms (Lewis, 1989) and maps of modern sea-surface temperatures (CLIMAP, 1981), Discoaster abundance variations were interpreted in terms of the interplay between productivity pressure and sea-surface temperature. Discoasters thrived in the Indian Ocean at Site 709 (4°S) in warm waters with little productivity pressure, whereas Discoaster abundance was suppressed at Sites 677 (l°N) and 662 (l°S) in the Pacific and Atlantic, which although located in warm waters, were affected by upwelling. In addition to the reduced Discoaster abundances associated with upwelling, sea-surface temperature gradients are a significant factor when comparing high and low latitude sites. A marked drop in Discoaster abundance is apparent between 41°N and 56°N (i.e., between Sites 607 and 552). Relative abundances of species in the Discoaster assemblage revealed clearly their contrasting environmental preferences; D. brouweri was produced under a wide range of conditions, favouring warm, low productivity waters; D. asymmetricus and D. tamalis were produced in higher abundances relative to D. brouweri during cooler, low productivity episodes; D. pentaradiatus showed highest absolute abundance in warm, low productivity waters, although increasing in relative abundance at higher latitudes; D. surculus increased in relative abundance in high productivity regions and in cooler waters. At all sites, though most markedly at higher latitudes, Discoaster abundances declined after 2.4 Ma, when glaciation began in the North Atlantic.
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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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Kotilainen, Aarno Tapio. "Late Pliocene and Pleistocene sedimentation in the North Pacific Ocean." Thesis, University of Cambridge, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.621353.
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Zeng, Xian-Bin. "Evolution of the Mio-Pliocene submarine slope system : offshore Vietnam." Thesis, University of Manchester, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.527424.
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Prescott, Caroline Louise. "Orbital forcing and its importance in understanding the warm Pliocene." Thesis, University of Leeds, 2017. http://etheses.whiterose.ac.uk/19518/.
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The Pliocene is traditionally viewed as an epoch with a warm and stable climate. Data-Model comparisons for the mid-Pliocene (~3.3 – 3 Ma) have identified regions where models do not agree with geological proxies. Palaeoenvironmental syntheses used in these comparisons are time-averaged. It has been hypothesised that orbital cyclicity within the mid-Pliocene, not accounted for in previous model simulations or data syntheses, could contribute to data-model discord. Study of the Pleistocene (~11.7ka – 2.6 Ma) has established the importance of understanding climate variability and distinguishing the specific character of separate interglacial or glacial events. This thesis confirms such variability should be expected in the Pliocene. Using a climate model, two interglacials (MIS KM5c and K1) in the Pliocene are compared, and results demonstrate changes in the surface air temperatures (SATs) due to changes in orbital forcing can be substantial and differ between interglacials. A further two interglacials (G17 and KM3) are investigated, and changes in regional vegetation patterns and the summer Indian monsoon in response to orbital forcing over the four interglacial events are analysed. A notable vegetation response is seen in the continental interiors of North America and Eurasia, where forests are replaced by grassland and shrubland, and is most widespread for interglacials with the strongest orbital forcing (most different from present day). The Indian monsoon is slightly stronger than pre-industrial in KM5c (an interglacial with near-modern orbit), driven by higher CO2, and is significantly more intense in G17, K1 and KM3 than KM5c, due to orbital-driven increased seasonal SATs. Orbital forcing throughout Pliocene interglacials is found to have a significant effect on the simulation of regional climate, vegetation and the Indian monsoon system within the modelling framework used here. Time-averaged palaeoenvironmental synthesis therefore, cannot be expected to concur with climate model outputs using time specific orbital forcing.
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Mou, Yun. "Biochronology and magnetostratigraphy of the Pliocene Panaca Formation, southeast Nevada." Diss., The University of Arizona, 1999. http://hdl.handle.net/10150/284594.
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About 2,500 specimens of small mammal fossils were collected from 10 localities in the Pliocene Panaca Formation in Meadow Valley, southeast Nevada. The most common taxa are cricetid and heteromyid rodents, and lagomorphs. Twenty-seven species, including five new species, were recognized from the fauna. A new genus of microtine rodent, Nevadomys, including three new species, N. fejfari, N. lindsayi, and N. downsi, is recognized. Nevadomys was probably derived from the Hemphillian Paramicrotoscoptes. Repomys minor n. sp. is another new species of high-crowned cricetid that was detected in the Panaca local fauna. With abundant upper and lower third molars of Repomys, it was possible to amend the diagnoses of genus Repomys. The fifth new species recognized from the fauna is a shrew, Paranotiosorex panacaensis n. gen. and sp. Enamel microstructure of molars of the microtine rodents Mimomys panacaensis and Nevadomys n. gen. from the fauna were examined under the scanning electronic microscope. Mimomys panacaensis shows the same schmelzmuster among different populations. Nevadomys has a more primitive schmelzmuster compared to Mimomys panacaensis. Both its leading and trailing edges are entirely composed of radial enamel. The assemblage of small mammal fossils suggests that the Panaca local fauna represents the early Blancan land mammal age. The first appearance datum of Mimomys panacaensis is suggested as the beginning of Blancan land mammal age, and the absolute age of the lowest stratigraphic datum of M. panacaensis in the Panaca Formation is interpolated from magnetostratigraphy and is considered as the age of the Hemphillian-Blancan boundary. The magnetostratigraphy of the Panaca Formation in Meadow Valley is established based on four sections in the basin. The ash in the Rodent Hill section was dated at 4.64 +/- 0.03 Ma, which constrains the correlation of the reversed polarity magnetozone in the Rodent Hill section to the C3n.2r in the Geomagnetic Polarity Time Scale (GPTS). The other three sections are correlated to the Rodent Hill section based on the ashes. The Panaca Formation in Meadow Valley was deposited from 4.50--5.30 Ma, and the Hemphillian-Blancan boundary is around 4.95 Ma, close to the termination of Thvera Subchron in the GPTS.
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Souron, Antoine. "Histoire évolutive du genre Kolpochoerus (Cetartiodactyla : Suidae) au Plio-Pléistocèneen Afrique orientale." Thesis, Poitiers, 2012. http://www.theses.fr/2012POIT2306/document.
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La sous-famille des Suinae est largement répandue en Afrique au Plio-Pléistocène et a été abondamment utilisée pour corréler biochronologiquement les sites à hominidés en se basant sur l'évolution morphologique rapide des troisièmes molaires dans différentes lignées. À partir d'un échantillon important de suinés africains actuels, les schémas de variation morphologique crânio-mandibulaire et dentaire sont quantifiés par morphométrie géométrique. Ce référentiel actuel sert à estimer la variabilité morphologique dans le registre fossile. La révision de la paléobiodiversité du genre Kolpochoerus (le suiné plio-pléistocène le plus abondant) dans les bassins du Turkana et de l'Awash s'appuie sur l'étude anatomique et morphométrique de matériels publié et inédit découverts dans la basse vallée de l'Omo (formation de Shungura) et dans la vallée moyenne de l'Awash en Éthiopie. Une nouvelle espèce fossile est décrite, les trajectoires évolutives au sein de chaque espèce sont quantifiées, et les interprétations biostratigraphiques sont révisées. Les liens de parenté au sein du genre Kolpochoerus sont décrits grâce à l'analyse cladistique. L'étude de la paléoécologie des suinés africains est basée sur l'anatomie comparée et la biogéochimie des isotopes stables (carbone et oxygène). Les suinés fossiles présentent une gamme de taille importante, ainsi que des régimes alimentaires et des habitats variés. Les nouvelles connaissances acquises sur leur biodiversité, leur phylogénie, et leur écologie permettent de proposer une histoire paléobiogéographique des Suinae en AfriqueThe subfamily Suinae is widespread in Plio-Pleistocene deposits in Africa, and was heavily used as a biochronological tool to correlate hominid-bearing sites based on the rapid morphological evolution of third molars in different lineages. A large sample of extant African suines enables to quantify patterns of variation in cranio-mandibular and dental morphology using geometric morphometrics. This modern referential is used to estimate the morphological variability in the fossil record. Revision of the paleobiodiversity of the genus Kolpochoerus (the most abundant Plio-Pleistocene suine) in Turkana and Awash basins is based on anatomical and morphometric studies of published and unpublished material discovered in the Lower Omo Valley (Shungura Formation) and in the Middle Awash Valley in Ethiopia. A new fossil species is described, evolutionary trajectories within each species are quantified, and biostratigraphic interpretations are revised. Phylogenetic relationships within the genus Kolpochoerus are described by the cladistic analysis. Paleoecological study of African suines is based on comparative anatomy and stable isotopic biogeochemistry (carbon and oxygen). Fossil suines display a wide range of body size, as well as various diets and habitats. The new results produced regarding their biodiversity, phylogeny, and ecology, enable to reconstruct a paleobiogeographic history of Suinae in Africa
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Sta, Ana Ma Corazon Victor. "Characterization of Miocene-Pliocene carbonate platforms, southern Southwest Palawan Basin, Philippines." [College Station, Tex. : Texas A&M University, 2006. http://hdl.handle.net/1969.1/ETD-TAMU-1796.
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Kemna, Hans A. Hemna Hans Axel. "Pliocene and Lower Pleistocene Stratigraphy in the Lower Rhine Embayment, Germany /." Köln : Institut für Geologie und Mineralogie der Universität zu Köln, 2005. http://opac.nebis.ch/cgi-bin/showAbstract.pl?u20=3934027172.
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Bonham, Sarah. "Dynamics of tropical climate and high-latitude teleconnections during the Pliocene." Thesis, University of Leeds, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.551228.
Full textAbstract:
The El Nino-Southern Oscillation (EN SO) in the tropical Pacific, is the most dominant mode of inter-annual variability in the climate system, with significant global impacts. It is therefore vital to understand how this phenomenon may respond to long-term changes in global mean temperature. One way to test this is to examine past warm climates such as the mid-Pliocene Warm Period (mPWP; ea. 3.26 to 3.0 Ma), when global mean temperature and atmospheric CO2 were higher than today, at levels similar to predictions for the late 21 st Century. MPWP proxy data suggest that the tropical Pacific was characterised by a reduced sea surface temperature (SST) gradient and permanent El Nino-like condition, which has implications for how ENSO may respond to anthropogenic forcing of the climate. ENSO dynamics during the mPWP were assessed through a series of model experiments using the Hadley Centre Coupled Climate Model. Tropical Pacific SST in the mPWP Control experiment was significantly warmer than the pre-industrial control with a low east-to-west gradient. Initial results showed that ENSO variability continued despite an El Nino-like mean state, with increased frequency and amplitude although fewer extreme events. The propagation of SST anomalies shifted towards the T-mode, similar to the pattern seen in the last 30 years of the instrumental record. Sensitivity experiments showed that the strongest contributors to changes in ENSO were lower orography over North and South America and higher CO2. In the extratropics, the presence of 'modern' teleconnection patterns in the mPWP simulation can be attributed to changes in boundary conditions, with large differences between modern and mPWP teleconnections. Finally, extending the control simulations by ~1,000 years, showed that these changes remain in the mid- Pliocene simulation, with reduced centennial variability compared to the pre-industrial control.
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Haywood, Alan M. "Evaluating general circulation climate model reliability with the Pliocene geological record." Thesis, University of Reading, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.271189.
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van, Galen Tika. "Relating early Human evolution to late Miocene - early Pliocene climate change." Thesis, Uppsala universitet, Institutionen för geovetenskaper, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-414361.
Full textAbstract:
Human evolution has been linked to climate change multiple times in the literature. One of the more well-known theories is the ‘savannah’ theory, which states that walking upright became an advantageous character when climate in Africa changed causing drier environments, changing woodlands to savannahs. Human ancestors could cross open fields more easily when walking upright, therefore it was thought that climate change could be a driving factor in the change to bipedal locomotion. Five hominin species were the basis of the study presented here, showing that change towards bipedal locomotion was a mosaic process with gradual change. A review of the relevant literature shows that the timing of change in fossils to bipedal locomotion and climate change do not coincide in the interval 6-3 Ma, therefore suggesting that climate change did not drive human evolution in this case. Changes towards open landscapes with C4 grass dominance peaked at the Pliocene-Pleistocene boundary (2.6 Ma), while the first hominin species already walked completely bipedally before 3.5 Ma.
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Boardman, Grant Stanley. "Salamanders of the Mio-Pliocene Gray Fossil Site, Washington County, Tennessee." Digital Commons @ East Tennessee State University, 2009. https://dc.etsu.edu/etd/1790.
Full textAbstract:
Screening efforts at the Gray Fossil Site, Washington County, Tennessee, have yielded a unique and diverse salamander fauna for the southern Appalachian Mio-Pliocene; including at least five taxa from three modern families (Ambystomatidae, Plethodontidae, and Salamandridae) supporting the woodland-pond interpretation of the site. All specimens represent the earliest record of their respective families in the Appalachian Mountains; with the Notophthalmus sp. vertebrae being the only Mio-Pliocene skeletal fossil known for the family Salamandridae in North America. Three types of plethodontid salamander are present, with one type representing the earliest known desmognathine. The desmognathine fossils lend credence to the 'Appalachian' origin of the clade in the Mio-Pliocene. The GFS salamander fauna is predominated by plethodontids; competition is inferred by the presence of several similarly large-sized taxa and is invoked to explain the presence of neotenic individuals in an otherwise amicable terrestrial environment.
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Schattauer, Sarah Ann. "Non-Ranid Anurans of the Mio-Pliocene Gray Fossil Site, Tennessee." Digital Commons @ East Tennessee State University, 2012. https://dc.etsu.edu/etd/1454.
Full textAbstract:
Researchers at the GFS, Washington County, Tennessee through the wet screening of nearly 100%of the sediment excavated at the site, recovered an extensive collection of anuran fossil elements. Until recently, these specimens have not been analyzed. The purpose here is the examination, description, and identification of all non-ranid anuran (frogsand toads) material using the following elements: ilium, urostyle, maxilla, frontoparietal, and last sacral vertebra. Anurans identified include Scaphiopus wardorum(extinct spadefoot toad), Bufo terrestris(southern toad), B. cf. B. marinus(giant neotropical toad), three morphotypes of Hyla(tree frogs), and Pseudacris cf. P. brachyphona(mountain chorus frog). Occurrence of these Anura support a paleoecological environment described as warm, moist, and wooded.
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Kerr, Steven Brent. "Petrology of Pliocene (?) Basalts of Curlew Valley (Box Elder Co.), Utah." DigitalCommons@USU, 1987. https://digitalcommons.usu.edu/etd/6688.
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Basalt outcrops in Curlew Valley consist of vii several flow remnants and eruptive centers situated along the valley margins. Basalt is also found in association with salic rocks that erupted in the central portion of The basalts are of probable Pliocene age and the valley. were erupted during a period of active extensional tectonics. Since their emplacement, and downfaulted. the basalts have been extensively eroded The present morphology reflects the erosional and depositional processes of prehistoric Lake Bonneville.
Twelve samples were analyzed chemically for major oxides, trace elements, and rare-earth elements. The basalts form a hypersthene normative series ranging from olivine tholeiite to tholeiite. Based on chemical data, the basalts form three distinct groups. Comparison of the major oxides shows two of the groups forming a differentiation sequence separate from the third group. Trace element and rare-earth element data indicate that the three chemical groups are related to a common source but that two batches of magma probably emanated from this source.
Pyrolite, spinel lherzolite, and garnet lherzolite were evaluated as hypothetical mantle materials from which a parent magma might be derived through partial melting. Based on rare-earth element profiles, garnet lherzolite appears to be the most likely source material for deriving the basalts. The trace element and rare-earth element data do not show any anomalies that would suggest contamination from crustal material.
Comparison of chemical data shows that the Curlew Valley basalts are genetically similar to basalts from the Kelton and Rozel Point-Black Mountain areas, southwest and southeast of the study area, respectively. The Curlew Valley basalts are chemically similar to olivine tholeiites from the Snake River Plain and Blackfoot Reservoir areas in Idaho, but they do not show much similarity to basalts near Snowville, Utah, northeast of the study area. The Curlew Valley basalts are generally more iron rich and less alkalic than other basaltic rocks from the eastern Basin and Range Province.
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Sliko, Jennifer Leigh. "Nearshore Marine Paleoenvironmental Reconstruction of Southwest Florida during the Pliocene and Pleistocene." Scholar Commons, 2010. http://scholarcommons.usf.edu/etd/3587.
Full textAbstract:
Future climate change has been the subject of considerable speculation
with scientists called upon to predict timing, magnitude, and impact of these
changes.
The Pliocene Warm Period serves as the best-available, pre-modern
analog to predicted climate changes, and Pliocene climate anomalies are
examined as possible scenarios for future climate change. Comparing modern
conditions to the mean climate state of the Pliocene is essential for better
constrained predictions of future climate change, and seasonal
paleoenvironmental records provide a data set more analogous to instrumental
observations and thereby reducing the uncertainty in modeled climate changes.
This study first examines the potential of large gastropod shells as a
paleoclimate proxy. Specimens of Busycon sinistrum, active in winter, and
Fasciolaria tulipa , active in the summer, were collected alive from Tampa Bay
and St. Joseph Bay in the hope of establishing a multi-year record of seasonality.
The δ18O time series of each shell were compared with predicted δ18O, based on
local marine temperature variations, and both species cease shell growth during
the winter months, despite opposing seasons of feeding activity. As none of the
profiles provide information on winter environmental parameters, this
sclerochronological system was replaced by work on pristine specimens of the
scleractinian coral Siderastrea spp.
Seasonal δ18O and Sr/Ca time series from two Pliocene corals, collected
from the Lower Pinecrest Member of the Tamiami Formation in southwest
Florida, were used to calculate seawater δ18O variations. Inferred salinity in the
Pliocene has a reversed seasonal pattern from that of modern annual salinity
variations, and is interpreted to be a response to an increase in winter
precipitation, a teleconnection of the Pliocene “Super El Niño.” Concentrations of
variance in the typical ENSO frequency band are not apparent above the 95%
confidence interval, suggesting that the Pliocene was dominated by a perennial,
rather than an intermittent, El Niño-like state.
Further geochemical analyses from both Pliocene and Pleistocene
Siderastrea
spp. corals indicate a high nutrient nearshore marine environment in
south Florida. Marine phosphates, inferred from P/Ca analyses, were
significantly higher in the Pliocene Tamiami Fm. than in the Early Pleistocene
Caloosahatchee and Bermont Fms, and the decline in nutrients preceded local
extinction by > 0.5 Ma. Additionally, high-resolution P/Ca analyses of an
individual coral reveal no evidence of seasonality required by a previously
hypothesized upwelling-based nutrient delivery mechanism
The Pliocene nearshore marine environment in southwest Florida was
characterized by higher nutrients than in the Pleistocene and precipitation
patterns similar to modern El Niño teleconnections.
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Marlow, Jeremy Robert. "Application of U'Kâ†3â†7'' for long-term (Pliocene-Pleistocene) palaeoclimate reconstruction." Thesis, University of Newcastle Upon Tyne, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.366544.
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Everett, Nicholas S. "The La Paz Basin, northern Bolivian Andes : late Miocene - Pliocene continental sedimentation." Thesis, University of Aberdeen, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.287618.
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Dating from the late Miocene to c.2.7Ma in the Pliocene, the La Paz Formation is a poorly consolidated basin fill, extensively incised at La Paz but with poor exposure. This study is the first to incorporate detailed vertical logging (15 sections totalling >1400m), facies analysis and sedimentary analogues into speculative reconstruction of depositional systems. The Formation records deposition from multiple, coarse-grained Piedmont distributary fluvial systems, flowing Southwest from the Cordillera Real. A highly aggradational setting preserved evidence of vertical accretion from high-magnitude, highly concentrated gravel channel belt flooding, conditioned by a seasonal semi-arid climate and high sediment flux. Combined channel belt and floodplain successions (including immature alluvial palaeosols) record variations in the style of channel belt bifurcation, in channel stability and in the timescale of channel belt coexistence, identifying mainly medial and proximal distributary zones. Large-scale alluvial architecture was heavily determined by individual system flow and sediment flux, dependent on catchment size and lithology. There was little relationship between architecture and immediate basin-margin faulting (of uncertain nature); systems maintained their basin location, and a balance persisted between accommodation space and sediment influx. These findings suggest that the systems had antecedent drainages. Footwall-sources systems were only temporarily active after faulting. A new model is proposed in which creation of accommodation space was coupled to sediment flux because both were driven by differential uplift of the Cordillera. Tectonic and climatic controls are inextricably linked in the depositional record due to this uplift. Late Miocene basin opening is uncertain but may have involved strike-slip fault activation. Subsequently, the basin fill expanded outward, onlapping proximal and distal margins, possibly under decreasing climatic extremity. These changes suggest gently declining differential uplift superimposed on ongoing absolute uplift, which may have enhanced regional climatic trends.
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Wareham, Christopher Desmond. "Isotopic and geochemical studies of a Pliocene porphyry-mo system, Rico, Colorado." Thesis, University of Aberdeen, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.304968.
Full textAbstract:
The historic mining district of Rico in the southern Colorado Mineral Belt contains a Pliocene porphyry-Mo deposit and peripheral epithermal Pb-Zn-Ag deposits, and hot-springs. The porphyry-Mo mineralisation is confined almost exclusively to Precambrian greenstone. The epithermal mineralisation is hosted by a Palaeozoic and Mesozoic sequence dominated by carbonates, but containing evaporites. The system is geologically complex and focused on a resurgent dome which is cored by a horst of Precambrian strata, and cut by reactivated Precambrian basement shears. The shears have controlled the emplacement of the Laramide and Pliocene granitoids in area. The mineralisation is associated with more evolved members of the latter suite. Sr-Nd-Pb-O isotope and minor element data on the granitoid intrusions indicate that they are not simply differentiates of mantle magmas. However, Nd model ages indicate that they are not purely remelts of 1800Ma Precambrian crust. Realistically it is impossible to quantify the relative proportions of crust and mantle material involved in the genesis of the intrusions. Notwithstanding this, the Rico granitoids are isotopically distinct from those associated with Climax-type porphyry-Mo deposits in Colorado. Sr-Nd-Pb isotope and trace element data on a lamprophyre suite in the area suggest two episodes of mafic magmatism; a period whereby the source was predominantly subduction modified lithospheric mantle, and a period whereby the source was predominantly, OIB-type, asthenospheric mantle. δ-34S data and ore deposit paragenesis indicate that the sulphide S has an igneous origin and that the sulphate S was derived by mobilisation of Pennsylvanian evaporites. Modelling of the S isotopic data indicates a common S source for the epithermal and porphyry mineralisation. The sulphate and sulphide S reservoirs remained essentially decoupled during mineralisation. δ13C data are compatible with the hydrothermal C having been derived by the dissolution and re-precipitation of host sequence carbonate. Pb and Sr isotope analyses of ore and gangue minerals support the conclusions reached in the stable isotope study. The Sr isotope study indicates that the Sr isotopic composition of the hydrothermal fluids varies considerably. Pb isotope ratios measured on molybdenite, pyrite, and galena indicate that the mineralisation at Rico derived its Pb from source with a higher Th/U ratio than that involved in the genesis of Climax-type porphyry-Mo deposits. Sr and O isotope analyses of Laramide sills present throughout the Rico area indicate that the Sr isotopic composition of the hydrothermal fluids varied and that the Sr isotopic composition of altered sills is not solely a function of alteration temperature; the proportion of altered primary feldspar and the growth of Sr-rich secondary minerals is also important. REE data on these sills indicate that hydrothermal alteration mobilised and fractionated these elements, but that mobility is not simply a reflection of alteration temperature. [SO4]4- appears to have been an important REE complex in the near surface oxidising environment.
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Amezcua, Torres Natalia. "Stratigraphy and facies of the Pliocene Mayrán Lacustrine Basin System, Northeast México." Thesis, University of Manchester, 2012. https://www.research.manchester.ac.uk/portal/en/theses/stratigraphy-and-facies-of-the-pliocene-mayrn-lacustrine-basin-system-northeast-mexico(41ca84ca-a465-422e-a649-92ca28e4c274).html.
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Lake basins contain depositional systems whose stratigraphy and sedimentology are highly influenced by allogenic and authigenic processes. Identifying the relative roles of these controls is complicated in settings where both tectonic and climate influences control sediment inputs and accommodation availability. In order to identify how these controls may interact in carbonate lake basins the lacustrine Mayrán Formation, northeast México was investigated. The Mayrán Formation is well exposed and the strata geometries are well preserved. The necessary data needed to unravel these complexities was obtained using field based techniques (geological and structural mapping, sedimentary logging and sampling), combined with optical and electron optical microscopy, mineralogical (XRD), and geochemical (oxygen and carbon stable isotopes, total organic carbon [TOC], organic carbon isotopes, and U-Pb carbonate dating) techniques, to characterise the lake basins. These data reveal that the Mayrán Formation was deposited in four, northerly, down-stepping, broadly coeval, hydrologically linked, carbonate-dominated lake subbasins (the Mayrán Basin system), that formed at different elevations spanning ~500 m. Subbasin geomorphology was controlled by the inherited topography of the exhumed and eroded Parras foreland fold-and-thrust belt, as a result, the subbasins are compartmentalized by prominent sandstone ridges that form sills between subbasins. Sedimentary infill of the subbasins consists of a fluvio-lacustrine succession (carbonate and clastic) that overly an angular unconformity truncating the folded and faulted Cretaceous bedrock. Clastic sediments were preferentially trapped in the most proximal subbasin in the south, adjacent to the mountain front. In more distal settings to the north, carbonate production resulted in deposition of horizontally bedded lacustrine limestones with subordinated siliciclastics and evaporite minerals. Carbonate deposition occurred during overfilled to balance filled conditions. Prominent aggradational to progradational tufa clinoforms form at the spillover points between the subbasins, and interfinger up- and down-dip with the horizontally bedded lacustrine limestones. The tufas consist of steeply dipping clinoforms that prograde northwards. They formed by inorganic and biogenically mediated calcite precipitation as waters from the topographically upper lake overflowed the sill. U-Pb dating of speleothem cements formed in the tufas yield a Pliocene age (3.06 ± 0.2 Ma). The horizontally bedded limestones that predominantly fill the subbasins are composed of nine lithofacies. These are: ostracode mudstone-wackestone, clotted boundstone, gastropod wackestone-packstone, oncoid wackestone-packstone, stromatolite, charophyte wackestone-packstone, marlstones, crystalline carbonate and evaporite minerals. These lithofacies contain variable proportions of production-derived components, with subordinated detrital and diagenetic components. They overall contain inorganic and organic calcite (average 91%), organic matter (average 12.6 % TOC) and subordinated detrital quartz, feldspar and clay. Stable isotope conditions from stromatolite laminations (δ13C -6.3‰ and δ18O -8.0‰), and micritic matrix from samples in all the subbasins (δ13C -5.7‰ and δ18O -8.4‰), indicate that overall calcite deposition occurred in freshwater lakes, under predominantly oxic conditions. Carbonate particles deposited mainly by in situ disaggregation and by settling. Significant preservation of the organic matter likely occurred because of the fine grained carbonate matrix, and because of moderate rates of both carbonate sediment and organic matter production. Stacking patterns in the lake successions show an overall shallowing upward cyclicity. It is considered, that the effects of inherited basin geomorphology and climate, ultimately controlled facies variability and strata geometries in these subbasins.
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Novello, Alice. "Les phytolithes, marqueurs des environnements mio-pliocènes du Tchad. Reconstitution à partir du signal environnemental des phytolithes dans l'Afrique subsaharienne actuelle." Thesis, Poitiers, 2012. http://www.theses.fr/2012POIT2303/document.
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Ce mémoire présente l'étude du signal phytolithique de sédiments mio-pliocènes du Tchad(Afrique Centrale) datés entre 7-2 Ma, et contemporains des Homininés anciens Sahelanthropustchadensis et Australopithecus bahrelghazali. Une calibration de la relation plantes-phytolithes-solspour l'Afrique tropicale subsaharienne actuelle a d'abord été réalisée pour apprécier la signatureenvironnementale des phytolithes dans le registre fossile. L'analyse des assemblages phytolithiques de98 espèces de graminées (Poaceae) a permis d'élaborer trois nouveaux indices phytolithiques à partirde 43 types propres aux Poaceae. Testés sur une base de 57 sols/sédiments modernes du Tchad, cesindices permettent de tracer les associations graminéennes aquatiques du Lac Tchad, les associationsmésophytiques des milieux humides soudaniens, et les associations xérophytiques des milieux secssahéliens. L'analyse des assemblages phytolithiques des sols/sédiments actuels considérés dans leurensemble a permis d'évaluer le potentiel de ce proxy à caractériser la physionomie des formationssoudano-sahéliennes modernes. La calibration a été appliquée à l'étude d'un enregistrementsédimentaire discontinu du Lac Tchad (6-2 Ma) (forage de Bol, 13°N/14°E) et à celle de 18 niveauxpaléontologiques du Djourab (7-3.5 Ma) (16°N/17°E). Les résultats indiquent la présence de savanesintermédiaires à fermées et de zones de végétation aquatique dominantes à 7 Ma dans le Djourab, puisde savanes plus ouvertes et sèches à 3.5 Ma. Une phase de bas niveau lacustre est enregistrée entre3.6-2.8 Ma à Bol, et un pic d'aridité à 3.2 Ma. Enfin, les résultats montrent l'existence de graminéesen C4 au Tchad depuis 7 MaThis thesis dissertation is dedicated to the study of the phytolith signal of Mio-Pliocenesediments from Chad (Central Africa) dated between 7-2 Ma, and contemporary to the early Homininspecies Sahelanthropus tchadensis and Australopithecus bahrelghazali. A calibration work studyingthe relationship plants-phytoliths-soils in modern sub-Saharan tropical Africa was carried out in orderto assess the environmental significance of the phytolith signal in the fossil record. Phytolithassemblages produced by 98 sub-Saharan grass species (Poaceae) were analyzed and the results led tothe development of three new phytolith indices defined from 43 types specific to Poaceae. Tested on adatabase of 57 modern soil/sediment samples from Chad, these indices allow drawing aquatic grassassociations of Lake Chad, mesophytic grass associations of wetlands from the Sudanian domain, andxerophytic grass associations of drylands from the Sahelian domain. The analysis of modern soilphytolith assemblages (total assemblages) was used to assess the potential of this proxy to characterizethe physiognomy of the Sudano-Sahelian vegetation types. The calibration had been applied to thestudy of a discontinuous sedimentary record from Lake Chad (6-2 Ma) (Bol core, 13°N/14°E) and of18 paleontological levels from the Djourab (7-3.5 Ma) (16°N/17°E). The results indicate thedominance of intermediate to closed savannas and areas of aquatic vegetation at 7 Ma in the Djourab,and more open and dry savannas at 3.5 Ma. A limited lacustrine stage is recorded between 3.6-2.8 Maat Bol, and a shift of aridity at 3.2 Ma. Finally, the results show the existence of C4 grasses in Chadsince 7 Ma
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Csank, Adam. "DECIPHERING ARCTIC CLIMATE IN A PAST GREENHOUSE WORLD: MULTI-PROXY RECONSTRUCTIONS OF PLIOCENE CLIMATE." Diss., The University of Arizona, 2011. http://hdl.handle.net/10150/145445.
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The high sensitivity of high latitudes to global climate changes is the stimulus for the study of ancient Arctic ecosystems under greenhouse conditions. With an increasing number of studies, including the most recent Intergovernmental Panel on Climate Change (IPCC) report highlighting Pliocene climate as key example for the study of Earth system sensitivity to higher levels of atmospheric CO₂, the need for accurate proxy records for this period is crucial. In order to investigate Pliocene climate, I used stable isotopic studies of fossil molluscs, moss and wood from two fossil forest deposits in the Canadian High Arctic. Temperatures were determined for an Early Pliocene (4-5 Ma) fossil forest site located on Ellesmere Island using 'clumped' and stable isotopic analysis of mollusc shells and stable isotope values of fossil wood. Mollusc inferred growing season (May-Sept) temperatures derived using two independent techniques were estimated to be 11-16° C warmer than present (1950-1990) Ellesmere Island temperatures. Tree ring inferred growing season (June-July) temperatures (JJ) were 10-16° C and mean annual temperatures (MAT) were 18-20° C warmer than present (1950-1990). Mean annual and growing season (JJ) temperatures were also determined using fossil wood from a younger (2.4-2.8 Ma) late Pliocene-early Pleistocene site on Bylot Island. This deposit represents the remains of a flora that grew during an interglacial warm period during the transition to large-scale Northern Hemisphere glaciation that occurred between 2.5 to 3 million years ago. Mean annual temperatures were ~12° C and growing season temperatures were ~13° C warmer than present (1923-2010). The interglacial setting of the Bylot Island site and the warm temperatures suggests that prior to using such sites as true analogues of future conditions we may need to consider how close the feedbacks operating then were to the feedbacks we might expect in the future. However, that temperatures so much warmer than present existed in the high Arctic during a period when levels of atmospheric CO₂ were at nearpresent levels indicates that we may be moving beyond our ability to use the Pliocene as an example of the future.
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Moody, Louise Dawn. "Indonesian climate investigations using stable isotopic data from modern, Holocene and Pliocene corals." Thesis, University of Canterbury. Geological Sciences, 2012. http://hdl.handle.net/10092/6729.
Full textAbstract:
Earth’s climate system has experienced significant changes throughout its history. Tropical, glacial and interglacial conditions have persisted across the globe during the Tertiary, and the present interglacial period with strong seasonality and episodes of warming and cooling has existed for the last several thousand years. However, rapid warming during the last century has highlighted the importance of understanding past climate behaviour, in order to predict the likely effects of such warming on our future climate. This has led to the use of proxies, such as sediment cores, tree rings, ice and carbonates, which provide high resolution palaeoclimate archives. Studies using a variety of proxies from around the globe have developed a network of site specific climate information, offering insights of climate fluctuations on a millennial scale, and identifying changing oceanic conditions as a major influence on global climate change. Coral skeletons are particularly sensitive recorders of ambient seawater conditions as they record fluctuations of oxygen and carbon in their aragonitic skeletons, which are caused by perturbations of sea surface temperature (SST) and sea surface salinity (SSS). Therefore, tropical oceans themselves provide a crucial record of climate change. Many of the coupled atmospheric-oceanographic processes that drive the global climate system occur in the Indo-Pacific, making it a particularly important region for data collection. Porites corals from the Indo-Pacific have been studied in detail and have revealed high resolution SST and SSS records, yet comprehensive investigations using other coral species are minimal. This study expands upon the current understanding of coral proxies by investigating three coral species of different ages, and provides new insights into the palaeoclimate history of the Indo-Pacific.
Goniastrea retiformis, Platygyra pini and Platygyra lamellina corals have been retrieved from Timor Leste in the Indo-Pacific, and analysed using stable and radiogenic isotopic techniques. Sclerochronology was used to determine that the 4.5 year old, modern G. retiformis coral was living from 2006-mid 2010. Uranium-thorium (U/Th) analysis provided a mid Holocene age of 4.5 ± 0.092 (2σ) ka for the fossil P. pini. Uranium-lead (U/Pb) techniques were used to obtain a 2.7 ± 0.34 (2σ) Ma age for the fossil P. lamellina. A rigorous diagenetic screening process of X-ray diffraction (XRD), petrographic analysis of thin sections, and scanning electron microscopy (SEM) has been carried out to ascertain the extent of preservation in each coral. X-ray images allow annual density bands to be located and unique micromilling paths were developed for the three samples. This enabled us to obtain the first δ¹⁸O and δ¹³C stable isotope results for a G. retiformis coral, and the first fossil coral results for the Platygyra genus. Cross spectral analysis has been used to verify the periodicity of seasonal fluctuations visible in the data, and confirmed that these coral species are suitable for use as climate proxies.
G. retiformis is an abundant reef coral distributed throughout the tropical Pacific, and has a robust skeletal configuration making it suitable for use as a climate proxy. The 4.5 year long record has revealed that δ¹⁸O and δ¹³C values range from -4.62‰ ± 0.03‰ (2σ) to -6.11‰ ± 0.02‰ (2σ), and 1.57‰ to -2.53‰, with means of -5.35‰ and -1.02‰, respectively. These values are in agreement with the average δ¹⁸O range of -5.1 to -5.6‰ in modern corals throughout the Indo-Pacific, predominantly of the Porites genus. Statistical analysis of the isotopic data has revealed a quasi-biennial signal in G. retiformis, typical of the temporal interaction between El Niño Southern Oscillation (ENSO) and the South Asian monsoon. Results have also been compared to the Southern Oscillation Index (SOI) in order to assess potential relationships between coral isotopes and ENSO. This has shown an accurate record of El Niño and La Niña events for the first half of the ~ 4.5 year record, from 2006 to mid 2008. Climate processes such as local rainfall and the Indian Ocean Dipole (IOD) are also reflected in the record, to varying extents.
The use of Platygyra corals as climate proxies is limited to three investigations using modern samples, despite the fact that this genus has a much broader latitudinal range than the extensively studied Porites genus. This thesis provides the first examination of fossil samples, and provides analysis of both pristine and altered specimens. The 4.5 ka P. pini coral has allowed investigation of the palaeoclimate record in a sample that has been exposed to diagenesis. XRD, petrographic and SEM analyses have revealed widespread secondary aragonite growth, dissolution and secondary calcite within the coral, which would have occurred due to marine and freshwater diagenesis. However, primary growth textures have been retained in some areas of the coral. δ¹⁸O and δ¹³C values range from -3.47‰ ± 0.03‰ (2σ) to -5.45‰ ± 0.02‰ (2σ), and 3.43‰ to -0.49‰, with means of -4.82‰ and 1.12‰, respectively. These values are significantly more positive that the mean δ¹⁸O of four Platygyra corals from the Pacific region, which range from -4.82‰ to -5.10‰. There are two reasonable explanations for this. Secondary aragonite, which is detected throughout the milled section of coral, causes positive shifts in coral δ¹⁸O, an effect which is likely to have altered the geochemical record of this particular coral. But the fact that SST in the southern Indo Pacific Warm Pool (IPWP) during the mid Holocene were 1.2° C cooler than present must also be acknowledged, as cooler temperatures also impart a shift toward higher δ¹⁸O, due to equilibrium fractionation processes. SST reconstruction using the temperature dependence equation from a modern Platygyra coral reveals an SST range of 18.5-27.6° C, and mean of 24.7° C. The present day mean annual SST of 28° C suggests that mid Holocene temperatures less than 26.8° C are unrealistically cool, highlighting the fact that isotopic fractionation during diagenesis has affected coral chemistry. However, the presence of interannual periodicity indicates that ENSO was operating, and the magnitude of isotopic fluctuation through the 10 year record is similar to that found in modern and other Holocene corals. We suggest that although absolute isotopic and SST values are unreliable, prohibiting the extraction of high resolution climate records, insights into the behaviour of broad scale, seasonal and interannual climate processes may still be obtained.
A strong annual periodicity has been detected when analysing the stable isotopic values recorded in the 2.7 Ma P. lamellina coral. This indicates that seasonal SST fluctuations were the dominant influence on this coral. Ranges of -4.67‰ ± 0.03‰ (2σ) to -5.48‰ ± 0.02‰ (2σ) and 0.88‰ to -1.12‰ for δ¹⁸O and δ¹³C, respectively, are similar to modern Platygyra coral results, suggesting that this coral has been preserved in pristine condition. Palaeo-SSTs have been reconstructed using a modern Platygyra temperature dependence equation, providing a range of 24-27.7° C and a mean of 25.9° C. Foraminiferal data from sediment cores in the greater Indo-Pacific suggest that mean annual SSTs at this time were ~ 2-3° C cooler than present. The coral record I present supports this statement, providing new insights into our understanding of tropical palaeoclimates. This coral has been entrained within a turbidite deposit on the sea floor that has subsequently been uplifted during the emergence of Timor, with U/Pb dating allowing further constraints of the stratigraphic age of the deposit. Tectonic narrowing is postulated to have caused major changes to the Indonesian Throughflow (ITF) from 4-2 Ma, and been a driver of major global climate change beginning in the late Pliocene. This means that fossil Platygyra corals Timor Leste could provide unique time slices of information about this important time in global climate history.
This study confirms that G. retiformis, P. pini and P. lamellina corals are excellent candidates for further, detailed investigations. They provide the opportunity to develop new coral proxies which are both abundant throughout the tropics and distributed over a wide latitudinal range. Their prevalence in both modern and fossil reefs means that once modern samples of each species have been calibrated against modern SST and SSS, these corals will provide reliable, quantitative palaeoclimate proxies, with potential for data capture throughout the Indo-Pacific and mid latitudes. Geochemical coral archives are a crucial tool in the study of climate processes, and we believe that these species are ideally suited to enhancing and refining our current understanding of earth’s climate system.
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Bolton, Clara Thérèse. "Orbital and suborbital climate variability during the Pliocene intensification of northern hemisphere glaciation." Thesis, University of Southampton, 2010. https://eprints.soton.ac.uk/168995/.
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The late Pliocene is marked by the end of an interval of warm, relatively stable global climate and a secular shift into a bipolar glaciated world. The intensification of northern hemisphere glaciation (iNHG) central to this climatic transition was accompanied by a decrease in atmospheric carbon dioxide concentrations and commenced around 3.5 million years ago. The climate forcing and response mechanisms involved in the iNHG are subjects of ongoing debate in the palaeoclimate literature. In this thesis, I reconstruct palaeoproductivity and suborbital climate fluctuations during this important interval, with particular focus on the first three consecutive, large, obliquity-paced glacial-interglacial cycles (marine isotope stages, MIS, 101-95), using proxy methods applied to deep-sea sediments in the equatorial oceans and the North Atlantic. In this way, I evaluate the forcing mechanisms, biogeochemical cycles and climate implications during the late Pliocene. In Chapter 2, palaeoproductivity is reconstructed in the western and eastern equatorial Pacific Ocean. Data reveal that productivity fluctuations are in phase between east and west and are obliquity-paced. This implicates high-latitude rather than local forcing of export productivity and no apparent role for east-west thermocline tilting on these timescales, as previously proposed. In Chapter 3, multi-proxy palaeoproductivity reconstructions in the eastern equatorial Pacific and Atlantic Ocean upwelling zones are considered in terms of proxy applicability and export productivity. Results suggest that alkenone accumulation may be a useful indicator of export productivity and that the late Pliocene biological pump was stronger during glacials than interglacials. In Chapter 4, an inferred secular productivity shift is investigated using calcareous nannofossil assemblages. Assemblage shifts at an equatorial Pacific and a North Atlantic Ocean site support the interpretation of an increase and a decrease in export productivity, respectively. Implications of a strengthened tropical biological pump at this time are considered. In Chapter 5, high-resolution climate records are used to investigate suborbital variability at North Atlantic Integrated Ocean Drilling Program Site U1313. Data indicate that only smallamplitude suborbital variability occurs during the late Pliocene, with no amplification within the boundary conditions and inferred ice-volume variations of MIS 103 to 95.
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Petrick, Benjamin Fredericks. "Pliocene-Pleistocene evolution of Benguela upwelling and Agulhas Leakage in the SE Atlantic." Thesis, University of Newcastle upon Tyne, 2014. http://hdl.handle.net/10443/2728.
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Understanding the impacts of the transition from the warmth of the middle Pliocene to the large amplitude, 100 ka glacial-interglacial cycles of the late Pleistocene helps us to better interpret both the local forcings and global impacts of possible future climate changes. In this thesis, changes in ocean circulation over the last 3.5 million years (Ma) are investigated using a marine sediment core recovered from the SE Atlantic Ocean, a region often described as an ocean gateway because it includes the transfer of heat and salt from the Indian to the Atlantic Ocean between Antarctica and South Africa (the “Agulhas Leakage”). However, the response of this region to Pliocene-Pleistocene climate evolution remains unclear. This thesis analyses the climate information recorded at Ocean Drilling Program (ODP) Site 1087 (31º28’S, 15º19’E, 1374m water depth) to investigate the history of Agulhas Leakage and associated ocean circulation changes including the Antarctic Circumpolar Current to the south, and the productive Benguela upwelling system to the north. This thesis presents the results generated using several organic geochemistry proxies and foraminiferal analyses to reconstruct the climate history at ODP 1087. These include the UK37’ index (for sea surface temperatures, SSTs), the TEX86 index (for ocean temperatures and an upwelling indicator), pigment analysis (for productivity changes), foraminifera assemblages (as water mass indicators), and dinoflagellate assemblages (for SSTs and water mass indicators). During the Pliocene and early Pleistocene, ODP 1087 was dominated by the Benguela Upwelling system, which had shifted south relative to today, and three prominent cold periods punctuate the overall warmth (during the M2 and KM2 stages, and at 2.8 Ma). From 2.2 Ma a longer term cooling trend begins, and further cooling occurs at 1.6 Ma, both of which are interpreted to represent periods of intensification of the Benguela Upwelling. The start of modern Agulhas Leakage occurs at ~0.9 Ma, marked by the start of early warming at the site ahead of the terminations. Finally, from 0.6 Ma there is an intensification of Agulhas Leakage which has led to an overall warming of SSTs which span both glacial and interglacial stages. Overall, the ODP 1087 record shows that this region is more reactive to southern hemisphere and local forcings such as changes in the southern wind field and ice expansion around Antarctica, rather than to northern hemisphere forcing.
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SUGIYAMA, Kazuhiro, Takami NOBUHARA, and Keisuke INOUE. "Preliminary report on Pliocene radiolarians from the Nobori Formation, Tonohama Group, Shikoku, Southwest Japan." Dept. of Earth and Planetary Sciences, Nagoya University, 1992. http://hdl.handle.net/2237/2811.
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Crudeli, Daniela. "Early pliocene evolution of coccolithophores in the Caribbean Sea taxonomy, biostratigraphy, paleoecology and paleoceanography /." [S.l.] : [s.n.], 2005. http://e-diss.uni-kiel.de/diss_1760/d1760.pdf.
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Marchant, David R. "Miocene-Pliocene-Pleistocene paleoclimate and glacial history of the western Dry Valleys region, Antarctica." Thesis, University of Edinburgh, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.538081.
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A case is made for the stability of the polar East Antarctic Ice Sheet since middle-Miocene time from landscape development and surficial sediments in the western Dry Valleys region, southern Victoria Land. The alternate hypothesis that calls for repeated Miocene and Pliocene growth and decay of wet-based ice sheets across East Antarctica requires atmospheric temperatures 20"C above present values and late Pliocene ice-sheet overriding of the Transantarctic Mountains. The geomorphological and sedimentological results suggest that these conditions were not met in the western Dry Valleys. Rather, mean annual atmospheric temperatures during the last 13.6 Ma were at most only 3° to SoC above present values; ice-sheet overriding occurred in middle Miocene time (> 13.6 Ma); and Pliocene glacier expansion was limited. These conclusions are based on field studies in the western Asgard Range and in the Quartermain Mountains. The chronology comes from 4OAr/39 Ar laser fusion analyses on individual volcanic crystals and glass shards removed from in-situ volcanic ashes that occur in stratigraphic association with unconsolidated diamictons in the western Dry Valleys region. The combined geomorphological and sedimentological evidence indicates that slope evolution in the western Dry Valleys was severely restricted since at least the middle Miocene. The implication is that most of the landscape is relict and that it reflects ancient erosion under semi-arid climate conditions prior to middle-Miocene time.
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Franz-Odendaal, Tamara. "Analysis of dental pathologies in the Pliocene herbivores of Langebaanweg and their palaeoenvironmental implications." Doctoral thesis, University of Cape Town, 2002. http://hdl.handle.net/11427/4172.
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Bibliography: leaves 228-243.This study evaluates the extent of dental pathologies in several ungulate species from the Pelletal Phosphate Member (PPM) at Langebaanweg, and uses this analysis, along with stable isotope analyses, to obtain fresh insight into the local palaeoenvironment during the Early Pliocene.
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White, Helena Elizabeth. "Establishing the chronostratigraphy and Miocene-Pliocene palaeoenvironmental history of the Fazzan Basin, Libyan Sahara." Thesis, University of Leicester, 2017. http://hdl.handle.net/2381/39907.
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The vastness of the Sahara Desert makes it a key region for the study of global climate change. Large and important gaps remain, however, in our understanding of the palaeoenvironmental history of the Sahara due to limited terrestrial evidence. The Fazzan Basin, south-west Libya, is one of a few regions to document North Africa’s palaeohydrological history in the form of lake shorelines and sedimentary deposits. The most extensive of these belongs to the Al Mahruqah Formation, recently upgraded to Group status, which is believed to have been deposited by Lake Megafazzan. Previous dating using OSL/U-series has revealed the deposits to be of Quaternary age. However, the origin and age of the deposits are still subject to ongoing debate with the chronological and palaeoenvironmental framework of Miocene-Pliocene units severely lacking. In order to develop and extend the knowledge of the basin during the Neogene, geochemical and sedimentological analyses have been conducted on deposits from six stratigraphic sections from across the northern Fazzan Basin. Palaeomagnetic dating, which is able to date beyond the range of previous dating techniques, has also been completed. This research provides what is believed to be the only low resolution, long-term palaeoenvironmental record of the central Sahara. Magnetostratigraphic and geochemical assessments question the previously proposed ages of the Al Mahruqah Group revealing that several humid intervals leading to several phases of lake development not only occurred in the Quaternary, but throughout the Miocene and early Pliocene. It is therefore proposed that the main drainage networks of the Fazzan basin were established in the early Miocene and hence ideas originally thought about the geomorphological history of the basin need to be redeveloped. It is hoped this research will not only help to fill the palaeoclimatic void of this important region but also potentially contribute to the understanding of the wider Saharan palaeoclimate.
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O'Connell, Brennan. "Sedimentology and depositional history of the Miocene-Pliocene southern Bouse Formation, Arizona and California." Thesis, University of Oregon, 2017. http://hdl.handle.net/1794/22300.
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The Miocene to Pliocene southern Bouse Formation preserves a record of depositional environments immediately prior to and during integration of the Colorado River to the Gulf of California. Uncertainty over Bouse paleoenvironments obscures our understanding of the timing and magnitude of regional uplift, as well as the conditions and processes that were active during integration and early evolution of the Colorado River. Prior studies over the past 20 years have concluded that the southern Bouse Formation accumulated in chain of lakes isolated from the ocean. Sedimentologic analyses presented here aid interpretation of depositional environments and provide evidence for a strong tidal influence on deposition, consistent with a marine interpretation of other prior studies. This interpretation places a critical constrain on the elevation of these deposits at ca. 5 Ma, and suggests post-Miocene uplift of the Lower Colorado River corridor.
This thesis includes previously published coauthored material.
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Le, Guevel Goulwen. "Étude de la réponse isotopique des coccolithophoridés à des changements de pCO2 en culture pour des applications paléoclimatiques au Pliocène." Electronic Thesis or Diss., Sorbonne université, 2024. http://www.theses.fr/2024SORUS111.
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L'étude du climat et des relations entre les enveloppes impliquées dans son fonctionnement (hydrosphère, atmosphère, lithosphère et biosphère) représente un enjeu majeur. La reconstitution des paléoenvironnements permet en outre d'étayer les modélisations numériques du climat futur. Plusieurs proxies biogéochimiques permettent de reconstruire des paléo-températures de surface océaniques (SSTs) et des paléo-pCO2 (UK'37, δ18O, εp alk et δ11B par exemple). Afin de compléter et préciser les reconstitutions effectuées à partir de ces marqueurs, un nouveau proxy de pCO2 est développé et est utilisé depuis quelques années : il s'agit de la différence entre les rapports isotopiques en carbone (Δδ13C) de coccolithes - des plaques calcaires produites par les coccolithophoridés - de différentes tailles. L'écart isotopique entre des coccolithes de différentes tailles est dicté par les flux de carbone à travers la membrane des cellules et par le rapport photosynthèse versus calcification. Quand la pCO2 diminue et le pH augmente, c'est-à-dire lorsque la biodisponibilité ambiante du carbone diminue, le δ13Ccoccolithe des grosses cellules diminue alors que celui des petites cellules n'est pas modifié. Ainsi, le Δδ13C est d'autant plus grand que la pCO2 est faible : cela constitue le fondement du nouveau paléo-baromètre que nous développons. Ce travail de thèse est basé sur une double approche biogéochimique en culture et sur des analyses de sédiments avec pour objectif d'améliorer la précision de la calibration entre le Δδ13C et la pCO2 en vue d'applications paléoclimatiques , en particulier au Pliocène.Pour ce faire, nous avons réalisé une campagne de cultures de coccolithophoridés sous des pCO2 comprises entre 200 et 1400 ppmv et des pH compris entre 8,3 et 7,6 (spectres de pCO2 et de pH caractéristiques du Cénozoïque). Les quatre souches étudiées (RCC1256 Emiliania huxleyi, RCC1314 Gephyrocapsa oceanica, RCC1323 Helicosphaera carteri et RCC1200 Coccolithus braarudii) présentent une diversité de tailles et appartiennent à une diversité de taxons qui sont représentatifs de ceux dont les coccolithes sont retrouvés dans les archives carbonatées du Cénozoïque. Ces travaux de culture nous ont permis de proposer de nouvelles équations de transfert entre le Δδ13C et la pCO2 (δ13C des petits coccolithes - Noelaerhabdaceae - qui reste stable et δ13C des gros coccolithes - C. braarudii - qui augmente avec l'augmentation de la pCO2 et la diminution du pH). De plus, l'étude combinée du δ13C de la matière organique et du δ13C des coccolithes a permis de montrer que les variations de δ13Ccoccolithe de C. braarudii, qui sont à l'origine des variations de Δδ13C, sont la conséquence d'un changement d'intensité du fractionnement entre le CO2 du milieu et la matière organique produite par les algues entre 200 et 500 ppmv.Nous avons utilisé les équations de transfert issues des travaux de cultures sur des sédiments du Pliocène (5,3 - 2,6 Ma, période analogue au scénario SSP2-4.5 du GIEC) provenant de l'Atlantique sud (site 516) et équatorial (site 999A). Les équations de transfert Δδ13C-pCO2 issues de nos travaux de cultures permettent de reconstruire des pCO2 de l'ordre de grandeur de celles publiées par d'autres proxies, avec notamment une diminution des concentrations en CO2 entre le milieu et la fin du Pliocène. De plus, l'étude du δ18O des coccolithes dans les sédiments nous a permis de réévaluer à la baisse les SST précédemment reconstruites pour le site 516 jusqu'à des valeurs cohérentes avec celles proposées par les modélisations numériques du climat, et de discuter de la paléocéanographie du Pliocène dans l'océan Atlantique au regard des données des sites 516 et 999A. L'augmentation des SST entre 4,8 et 3,8 Ma au site 999A marque la fin de la fermeture du CAS alors que la diminution des pCO2 à partir de 3,3 Ma est en lien avec l'intensification de la mise en glace dans l'hémisphère nordThe study of climate and the interactions among the Earth system components involved in its operation (hydrosphere, atmosphere, lithosphere, and biosphere) represents a major challenge. Additionally, reconstructing paleoenvironments supports numerical modelling of future climate. Several biogeochemical proxies enable the reconstruction of paleo-sea surface temperatures (SSTs) and paleo-pCO2 levels (e.g., UK'37, δ18O, εp alk, and δ11B). In order to complement and refine the reconstructions based on these markers, a new pCO2 proxy has been developed and utilized in recent years: the difference between carbon isotopic ratios (Δδ13C) of coccoliths - calcareous plates produced by coccolithophores - of different sizes. The isotopic difference between coccoliths of different sizes is governed by carbon fluxes across cell membranes and the photosynthesis versus calcification ratio. When pCO2 decreases and pH increases, indicating reduced ambient carbon availability, the δ13Ccoccolith of larger cells decreases while that of smaller cells remains constant. Thus, Δδ13C is greater with lower pCO2 levels, forming the basis of the new paleo-barometer being developed. This thesis work employs a dual biogeochemical approach involving culture experiments and sediment analyses with the aim of improving the precision of the calibration between Δδ13C and pCO2 for paleoclimatic applications, particularly targeting the Pliocene epoch.To achieve this, we conducted a coccolithophore culture campaign under pCO2 from 200 to 1400 ppmv and pH from 8.3 to 7.6 (characteristic pCO2 and pH spectra of the Cenozoic). The four strains studied (RCC1256 Emiliania huxleyi, RCC1314 Gephyrocapsa oceanica, RCC1323 Helicosphaera carteri, and RCC1200 Coccolithus braarudii) produced coccoliths of various sizes and belong to diverse taxa representative of those whose coccoliths are found in Cenozoic carbonate archives. These culture studies enabled us to propose new transfer equations between Δδ13C and pCO2 (δ13C of small coccoliths - Noelaerhabdaceae - remaining stable, and δ13C of large coccoliths - C. braarudii - increasing with rising pCO2 and decreasing pH). Furthermore, the combined study of δ13C of organic matter and δ13C of coccolith demonstrated that variations in C. braarudii δ13Ccoccolith, that drive Δδ13C variations, result from changes in the fractionation rate between aqueous CO2 in the environment and organic matter produced by algae between 200 and 500 ppmv.We employed our transfer equations derived from coccolithophore culture studies on Pliocene sediments (5.3 - 2.6 Ma, analogous to the SSP2-4.5 scenario of the IPCC) from the South Atlantic (site 516) and equatorial (site 999A) regions. The Δδ13C-pCO2 transfer equations enable the reconstruction of absolute pCO2 similar with those published by other studies, notably indicating a decrease in CO2 concentrations between the middle and the end of the Pliocene. Additionally, the analysis of coccolith δ18O in sediments allowed us to downwardly revise previously reconstructed SSTs for site 516 to values consistent with those proposed by climate numerical models, and to discuss Pliocene paleoceanography in the Atlantic Ocean based on data from sites 516 and 999A. The increase in SSTs between 4.8 and 3.8 Ma at site 999A marks the end of the closure of the Central American Seaway (CAS), while the decrease in pCO2 from 3.3 Ma onwards is linked to the intensification of the Northern Hemisphere glaciation
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Dennison-Budak, Cordelia W. "Ostracodes as indicators of the Paleoenvironment in the Pliocene Glenns Ferry Formation, Glenns Ferry Lake, Idaho." Kent State University / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=kent1271442702.
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Peryam, Thomas, and Thomas Peryam. "Sedimentation, Climate Change and Tectonics: Dynamic Stratigraphy of the Pliocene-Pleistocene Fish Creek-Vallecito Basin, California." Thesis, University of Oregon, 2012. http://hdl.handle.net/1794/12519.
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In order to better understand the interactions between climate change, landscape erosion and sedimentation, a detailed study was conducted on Plio-Pleistocene non-marine deposits of the Palm Spring Group in the Fish Creek-Vallecito basin, California, USA. Three inter-related studies focused on (1) local response to global climate change in late Pliocene-early Pleistocene time, (2) large-scale evolution of lithofacies architecture, and (3) climate modulation of late Pliocene sediment flux on Milankovitch time scales.
Stable isotopes and paleosol classification reveal that between ~4.0 and 0.75 Ma, aridity increased in the study area concurrent with a shift towards a less intense and more winter-dominated precipitation regime. These changes are interpreted to reflect the long-term waning of summer monsoon precipitation in southern California.
A dramatic and enigmatic reorganization of basin strata occurred at 2.9 Ma. Detailed basin analysis shows that locally-derived sediment was supplied by the predecessors of two modern drainages, Vallecito and Carrizo creeks. Initial progradation of alluvial deposits from these two sources across the Colorado River delta plain began between 4.0-3.4 Ma. At 2.9 Ma, rapid progradation of these two deposystems was coeval with emplacement of a megabreccia and transgression of Borrego Lake. My data indicate that tectonic realignments at both local and regional scales drove this reorganization.
Time series analysis of rock magnetic data from a densely-sampled stratigraphic section of the lacustrine Tapiado Formation reveals that between 2.9 and ~2.75 Ma landscape denudation in the Carrizo Creek catchment was partly modulated by orbital obliquity. Peaks in landscape denudation implied by my data correspond to obliquity highs. More frequent high intensity precipitation events (i.e. monsoons and tropical storms) probably drove increased erosion during these time periods relative to obliquity lows. The breakdown of this relationship at around 2.75 Ma corresponds to a dramatic increase in northern hemisphere glaciation and may reveal a reduction in monsoonal influence in southern California.
A geologic map of the Fish Creek-Vallecito basin is included as a supplemental file to this dissertation.
This dissertation contains previously published and unpublished coauthored material.
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Valentine, Annemarie Mitzy. "An investigation into the seasonality of the Pliocene southern North Sea Basin : a sclerochronological approach." Thesis, University of Derby, 2014. http://hdl.handle.net/10545/314169.
Full textAbstract:
The Pliocene world c.5.3 Ma to c.2.58 Ma exhibited a relatively stable climate with a warmer global mean surface temperature than present-day by ~2 °C to 3 °C, and palaeoclimate analysis from this interval is used to understand climate drivers in ‘warmer world’. Previous oxygen isotope thermometry investigations of Pliocene southern North Sea Basin (SNSB) Aequipecten opercularis from the Coralline Crag Formation in Suffolk, UK repeatedly reveal evidence of a cold-temperate climate regime. Contrastingly, other biological proxies record a warm-temperate/sub-tropical regime. This investigation concentrated on oxygen, carbon and microgrowth increment widths (MIWS) of fossil shell material from Pliocene SNSB spanning an interval of~4.4 Ma to ~2.5 Ma. The study sites included shallow marine Pliocene formations from the western and eastern SNSB, the Ramsholt Member of the Coralline Crag Formation, Suffolk UK, and the Luchtbal Sands and Oorderen Sands Members of the Lillo Formation, Belgium, and the Oosterhout Formation in the Netherlands. Oxygen isotopic palaeotemperature results showed cooler summer temperatures than presently in the SNSB, which were reflective of a cool-temperate regime. There was no evidence of warm-temperate or sub-tropical summer palaeotemperatures in the Pliocene SNSB as suggested by other planktonic proxies. This investigation discussed the possible causal factors for the cooler – than- expected winter and summer palaeotemperatures in the ‘warmer’ Pliocene world as recorded by this proxy. Discrepancies between the cool summer benthic palaeotemperatures from the bivalves and the warmer sub-tropical or warm-temperate summer palaeotemperature estimations from planktonic biological proxies was rectified by the application of a theoretical summer stratification factor (SSF). However, rectifying the discrepancies between cooler (cold-temperate) benthic winter palaeotemperatures and the warmer winter palaeotemperatures from other proxies was difficult because stratification does not occur during the winter. Dormancy behaviours in the warm- temperate –sub-tropical organisms was proposed as a suitable mechanism to allow their coexistence with the cool-tolerant bivalves, which were able to grow and feed underneath the thermocline during the summer months. Therefore, the investigation showed how the Pliocene SNSB exhibited a greater seasonality than occurs presently in the SNSB. The driver for the cooler winter temperatures in the Pliocene SNSB was not identified. Localised explanations including continental wind effects, interannual variations in MOC strength, and increased storm activity in the winter bringing cooler water into the SNSB were all suggested as potential drivers. Global features of climate including interglacial/glacial cycles and orbital forcing effects were factors also proposed for the overall mixed palaeotemperature signal in the Pliocene SNSB.
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Darcy, Hannah E. "Additional Research and Taxonomic Resolution of Salamanders (Amphibia: Caudata) from the Mio-Pliocene Gray Fossil Site, TN." Digital Commons @ East Tennessee State University, 2015. https://dc.etsu.edu/etd/2527.
Full textAbstract:
The Gray Fossil Site (GFS), a Mio-Pliocene (4.5–7 Ma) locality in the southern Appalachians, boasts the most diverse pre-Pleistocene salamander fauna in North America: Desmognathus sp., Plethodon sp., Notophthalmus sp., a Spelerpinae-type plethodontid, and Ambystoma sp. Because greater taxonomic resolution can result in more precise paleobiological interpretations, additional specimens were studied here. ETMNH 8045, a nearly complete articulated ambystomatid, appears most like Ambystoma maculatum in dentition and vertebral proportions. ETMNH 18219, an isolated vomer, is consistent with modern Pseudotriton and Gyrinophilus in possessing a postdentigerous process and a similar dentigerous row morphology. If these taxa, or species of similar ecological preferences, occurred around the GFS, it seems unlikely they co-inhabited the sinkhole lake. Aquatic stages of Pseudotriton and terrestrial Gyrinophilus last multiple years; their presence could further support a perennial lake interpretation. Modern A. maculatum preferentially breed in vernal pools; confirmed identification could suggest local seasonal wetlands.
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Adroit, Benjamin. "Structures des paléoforêts européennes de la fin du Cénozoïque : apport des interactions plante-insecte." Thesis, Montpellier, 2018. http://www.theses.fr/2018MONTG008/document.
Full textAbstract:
Les plantes et les insectes forment l’un des principaux niveaux trophiques des écosystèmes au cours des 325 derniers millions d’années. Aujourd’hui, l’augmentation rapide et continuelle de la température principalement causée par l’activité humaine depuis les derniers siècles, perturbe la balance des écosystèmes sur Terre. En conséquence, comprendre le rôle des interactions entre les plantes et les insectes, à travers le temps mais aussi les réseaux trophiques, est essentiel. Le registre fossile est une opportunité exceptionnelle d’examiner les réponses aux interactions plante-insecte lors de longues variations climatiques et à travers des traces de réaction de la plante sachant que la Terre a déjà été soumise à de nombreux changements climatiques. Durant les derniers 3 millions d’années, des oscillations entre de longues périodes froides et de courtes périodes chaudes ont eu lieu. Les écosystèmes Européens ont particulièrement été impactés par ces oscillations. Le Langerstätte de Willershausen (Allemagne) a été particulièrement étudié. C’est un gisement contenant plus de 8000 feuilles fossiles. Ces feuilles relatent d’une paléoforêt ayant existé il y a 3- 2,6 Ma dans un climat plus chaud qu’aujourd’hui (ca.+5°C). Dans ces conditions climatiques, de nombreuses espèces d’écosystèmes Méditerranéens étaient présentes, telles que l’Érable de Montpellier ou l’Olivier. En comparaison, d’autres paléoforêts ont été prise en compte : Berga (du même âge et proche de Willershausen) et Bernasso (plus jeune que Willershausen (2,16 — 1,96 Ma) localisée dans le sud de la France près de la Méditerranée. Ces forêts sont comparables notamment du fait des nombreux taxons communs qu’elles partagent. En outre, certaines de ces espèces sont aujourd’hui endémiques de la région du Caucase, telles que le Parrotie de Perse ou encore l’orme du Caucase. Le but de cette étude a été de déterminer en quoi les différences climatiques peuvent être impliquées dans les changements des interactions plante-insecte au sein des paléoforêts Européennes de la fin du Pliocène - début du Pléistocène. Les résultats obtenus ont permis de mettre en évidence les impacts de la saisonnalité des températures et précipitations facteurs impactants les interactions plante-insecte des paléoforêts Européennes. Il est apparu que les écosystèmes sujets à d’intenses saisonnalités hydriques ont pu engendrer une plus grande spécialisation des interactions plante-insecte déduite d’un fort taux d’interactions spécialistes observées. En parallèle, les températures les plus froides durant l’année semble être un facteur important dans la faible diversité de dégâts, probablement dû à un faible métabolisme de la majorité des insectes. L’absence de corrélation convergente entre la richesse des plantes et la richesse des interactions pourrait suggérer que l’influence des facteurs climatiques surpasse l’impact potentiel des interactions biotiques locales. Pour l’ensemble de ces paramètres qui ont pu avoir un impact sur les interactions plante-insecte, nos connaissances actuelles sont encore insuffisantes. Il serait intéressant de focaliser davantage d’études sur les forêts modernes avec les méthodes appliquées dans le fossile. C’est dans cette intention qu’une partie de cette étude a étudié une espèce de plante (Parrotia persica) actuellement endémique de la forêt Hyrcanienne (Iran). Cette forêt est supposée être une forêt analogue des paléoforêts Européennes étudiées dans cette thèse. Pour le moment, les observations qui ont été faites en Iran semblent corroborer notre interprétation. Au final, les études sur les interactions plante-insecte des forêts anciennes et actuelles, combinés avec les études de changements climatiques, pourraient nous permettre de mieux caractériser les relations entre les insectes et les plantes au sein d’une forêtInsects are the most diverse animals on Earth, and neatly associated with plants they represent two of the major groups of organisms both in species diversity and biomass quantity. The majority of their interactions involves insect feeding and insect parasitism mostly on leaves. Plant and insect compose one of the main trophic levels in ecosystems over the 325 million years. Today, the continuous and fast rising of temperature mostly due to human activities since the last century is disturbing the balance of ecosystems on Earth. Consequently, to understand the role of plant and insect interactions, through time but also trophic networks, becomes crucial. The fossil record is an exceptional opportunity to survey responses of plant-insect interaction to climate variations over long time interval through traces of plants reactions caused by interaction with insects, as Earth has already experienced many climate changes. For the last 3 million years, oscillations between long cold periods and short warm periods have occurred. Europe ecosystems has been particularly impacted. The Lagerstätte of Willershausen (Germany) was specifically study. It is an exceptional fossil outcrop that contains ca. 8000 collected fossil leaves. These leaves testify a paleoforest developed there around 3—2.6 Ma ago in a climate warmer than today (ca. +5°C). Under these conditions, many plant species typical of the Mediterranean ecosystems were settled there, such as Montpellier maple or Olive tree. For comparison, other paleoforests were studied: Berga (similar in age and geographically close to Willershausen) and Bernasso (younger than Willershausen (2.16—1.96 Ma) and located in southern France close to Mediterranean. These forests were compared as many common plant taxa were similar between each other. Furthermore, some species today endemic to the Caucasian region, such as Persian ironwood or Caucasian elm, were also present in these outcrops. The aim of this study is to determine how far the climate differences could be involved in the changes of plant-insect interactions in European paleoforests of the late Pliocene – early Pleistocene. Results highlighted the impacts of both hydric and temperature seasonality, hitherto underestimated in the fossil record, on the patterns of plant-insect interaction in the European paleoforests. It appeared that ecosystems subject to intense hydric seasonality could led to higher specialization of plant-insect interaction inferred by higher rate of observed damages due to ‘specialists insects’. In parallel, the coolest temperature during the year seems to be a major factor in the low diversity of damage in paleoforest, presumably due to lower insect metabolism. Absence of convergent correlations between plant richness and damage richness could suggested that influence of climatic factors override impact of these local biotic factors. In order to understand the whole parameters that could have an impact on plant-insect interactions, our current knowledges are still insufficient. It would be wise to make more investigations on modern forests with the methods as applied in fossil record community structure studies. These investigations could help to understand the factors potentially involved in the establishment of a pattern of plant-insect interactions. It is in this perspective that a part of this study was precisely focused on one plant species (Parrotia persica) currently endemic to the Hyrcanian forest (Iran). This forest is supposed to be an analogue forest of the European paleoforests as those studied in this thesis. For now, observations made in Iran tend to corroborate our interpretation. Finally, the studies on plant-insect interactions in past and extant ecosystems, combined with the study of climatic changes, should permit us to better characterize the relations between plants and insects in forests through time
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Lee, Richard A. "Late Pliocene-Pleistocene evolution of the Little Pine fault and its function on the control of sedimentation during basin formation| An examination of the Late Pliocene-Pleistocene Paso Robles Formation, Santa Maria Basin, California." Thesis, California State University, Long Beach, 2014. http://pqdtopen.proquest.com/#viewpdf?dispub=1526922.
Full textAbstract:
New stratigraphic and geomorphic data from the Santa Maria Basin, California, suggests that the major basin-bounding Little Pine fault system has been acting in a primarily reverse offset fashion since the late Pleistocene. A series of stratigraphic columns in the Plio-Pleistocene Paso Robles Formation measured along the Little Pine fault indicate that there was episodic uplift during the latest Pleistocene. A 20-40% increase in the percent composition of resistive, Franciscan Complex-derived cherts within active drainages indicate that uplift of the San Rafael Mountain front increased rapidly since the deposition of older sediments. The shape of stream profiles created along the Little Pine fault suggest ongoing uplift associated with the central and southeastern segments of the fault, with a lesser amount of uplift occurring further northwest along the Little Pine fault. A number of ridgeline profiles were also created which exhibit significant jumps in topography near, or just northeast of the Little Pine fault, suggesting that recent uplift is responsible. The ridgeline profiles also suggest an increased rate of uplift adjacent to the central and southeastern segments of the Little Pine fault zone, in agreement with the along-strike variations in uplift suggested by the stream profiles. Stream traces were also examined for deflections as they flowed across the Little Pine fault, but most show no significant lateral offset.