During the Pleistocene the Great Basin was filled by endorheic lakes that receded greatly during the Holocene. Several proxy records provide extensive evidence that the basin has gone through periods ...of amelioration from low precipitation followed by a return to dry conditions through the Holocene. Relative to the Pleistocene/Holocene transition and middle Holocene, aside from the Medieval Climate Anomaly, study of the late Holocene has received less attention. In recent years evidence has emerged for a ca. millennial length drought termed the Late Holocene Dry Period (LHDP), between about 2800 and 1800 years ago. The LHDP has been proposed to follow a dipole climatic pattern associated with changes in precipitation linked to the Southern Oscillation Index (SOI) and described as a dry southwest and wet northwest in the United States. Here I present a 4000-year pollen record from northwestern Nevada, investigating the potential for the Late Holocene Dry Period to conform to the modeled dipole pattern in this part of the region. This site is located near a zone of ambiguity between wet and dry conditions in order to identify more definitively where the modeled dipole pattern is centered.
Bu çalışma, İç Anadolu'nun önemli havzalarından biri olan Çankırı-Çorum havzasında, Orta Eosen yaşlı Kocaçay Formasyonu'na ait birimlerin Mollusk (Gastropoda ve Bivalvia) faunasının sistematiğini ve ...biyostratigrafisini ortaya koymayı amaçlamaktadır. Bu kapsamda Çorum Bayat ve Sungurlu, Kırıkkale Sulakyurt ve Kırşehir Çiçekdağı olmak üzere dört alt alanda arazi çalışmaları gerçekleştirilmiş, her bir alt alanda en az ikişer olmak üzere toplam 11 adet ölçülü stratigrafik kesit alınmıştır. Formasyonda Mollusca şubesine ait 2 cins ve 59 tür olmak üzere toplam 61 adet fosilin detaylı sistematik tanımlaması yapılmıştır. Tanımlanan Gastropoda sınıfına ait 1 cins (Turritella sp.) ve 34 adet tür; Tectus mitratus, Velates perversus, Jponsia cuvieri, Tympanotonos (Eutympanotonos) conulus, Turritella (Haustator) imbricataria, Mesalia fasciata, Campanile giganteum, C. incomptum, C. leymeriei, C. cf. parisiense, Cernina sphaerica, Amauropsella spirata, Cepatia cepacea, Euspirocrommium oweni, Globularia sigaretina, G. vulcani, Pachycrommium scalariformis, Gisortia cf. murchisoni, Sinum karamassensis, Euspira achatensis, Tornus (Adeorbis) tenuistriatus, Seraphs olivaceus, Seraphs sopitus, Xenophora cf. agglutinans, X.cf. patellata, Amaea (Acrilla) essomiensis, Clavilithes (Clavellofusus) clavellatus, C.cf. maximus, C.pinus, Fusinus zafiranboliensis, Gibberula ovulata, Eoconus diversiformis, Syrnola conulus ile Bivalvia sınıfına ait 1 cins (Nucula sp.) ve 25 adet tür Ostrea multicostata, O. roncaensis, Pycnodonte brongniarti, P. cymbiola, P. gigantica, Pecten tchihatcheffi, Chlamys subdiscors, Palliolum solea, Mimachlamys plebeia, Anomia tenuistriata, Spondylus asiaticus, S. eocenus, S. radula, Lima cf. spatulata, Miltha gigantea, Saxolucina saxorum, Crassatella (Pachythaerus) gibbosula, C. gigantica, C. tumida, C. subtumida, Venericar planicosta, Trapezium parisiensis, Cardium nummuliticum, Trachycardium gratum, Tellina cf. granconensistürleri saptanmıştır.Faunanın paleocoğrafik ve stratigrafik yayılımı incelendiğinde Kocaçay Formasyonu'nun Lütesiyen-Bartoniyen çağlarında çökeliminin gerçekleştiği sonucuna varılmıştır. Tanımlanan faunanın paleoekolojik özellikleri formasyonun kuzey kesimde deltaik sığ denizel; ortada lagüner, sığ denizel ve güneyde sığ denizel özellikte olduğu tespit edilmiştir. Çalışılan alanlarda Ostrea roncaensis, Velates perversus, Miltha gigantea ve Pycnodonte gigantica Bolluk biyozonları ile Ostrea roncaensis ve Campanile incomptum, Pycnodonte gigantica ve Crassatella gigantica, Amauropsella spirata ve Globularia sigaretinaTopluluk biyozonları tanımlanmıştır.
Extensive research has been conducted at Lake Tanganyika with the aim of understanding its vulnerability to both warming climate and fishing pressure. However, much of this work has been restricted ...to the more accessible northern basin. Studies from a limited geographic region of the lake are insufficient to explain whole-lake dynamics of the world’s longest lake, that stretches ~670 km (3.4–8.9°S), across several bathymetric basins. While strong evidence suggests that lake warming has played a critical role in decreasing fish abundance in Lake Tanganyika, limnological changes associated with warming have not been shown to be a lake- wide phenomenon. Paleolimnological methods can be used to compare the trajectories of environmental change among regions. This study examines southern Lake Tanganyika to provide insight into whether paleo-environmental changes observed in the northern basin are, in fact, representative of lake-wide phenomena, and in the process help to improve fisheries management. Here, we present new paleoecological analyses from two deep-water sediment cores from the southern basin of Lake Tanganyika. Fossil diatom assemblages show a shift in dominance towards lightly-silicified taxa (Nitzschia spp.) after ~200 YBP, with fewer heavily- silicified taxa. These results are indicative of a relative reduction in convective lake mixing but are not always coincident with temperature trends, suggesting local windiness may also be important for stratification history. A general decrease in diatom concentration in the late Holocene is probably reflective of a decrease in net primary productivity in response to the inferred decrease in convective mixing. In contrast, the episodic presence of deep benthic invertebrates (ostracodes and molluscs) at these deep sites, which also co-occur with high Mn, indicates infrequent and short-lived pulses of much deeper ventilation of the southern basin than has been recognized previously. The coincident presence of periphytic diatom species and benthic invertebrates during periods of strong stratification suggests that the lake bottom was periodically ventilated by descending denser (cooler or more sediment-rich) influent waters along the steep slopes of the coastline. Fish fossil abundance also is correlated with the dominance of heavily-silicified diatom taxa, which itself requires stronger wave activity and upwelling of deep, nutrient-rich water. Thus, changes in lake productivity in the southern basin appear to be climate-mediated, but in ways not previously documented in the northern part of the lake.
A paleoecological evaluation was undertaken on an exposure of the Comanche Peak Limestone Formation in Oglesby, Texas. The Comanche Peak Limestone Formation is part of the Early Cretaceous-aged ...Fredericksburg Group, a sequence of carbonate rocks recording the encroachment of the Western Interior Seaway during the Middle Albian. Named and described by R. T. Hill in the late 1800’s, the Comanche Peak Limestone Formation has not gathered as many studies as the overlying Edwards Limestone Formation. The Edwards Limestone Formation is dominated by rudistid grainstone (Dunham, 1962) and contains natural gas and petroleum reservoirs, in addition to being a major aquifer of Texas. While the Comanche Peak Limestone Formation lacks these economic resources, it has a scientifically valuable record of the Early Cretaceous paleoecology of Central Texas. The Paleoecological study found that the site was dominated by bivalve and gastropod groups, consistent with carbonate shelf environments. Interpretations of the fossil data utilizing PAST software suggests evidence of at least 4 distinct paleoenvironments and associated faunal assemblages. Analyses of these paleoenvironments were complicated by the coarse recrystallization of the Comanche Peak fauna and the diminishing quantity of fossils moving up through the outcrop, and reconstructions are tenuous without further study.
Phytolith analysis has high potential for reconstructing past vegetation with higher spatial resolution compared other high-resolution proxies, such as pollen and spores. Phytolith assemblages are ...used in paleoecology to reconstruct changes in vegetation structure through time. In addition, spatial variability of the phytolith signal (across samples collected along a single stratigraphic level) is interpreted as indicative of habitat heterogeneity based on the notion that phytolith assemblages are derived from vegetation that died and decayed in place and therefore hold a local signal. However, this and other assumptions have not yet been tested directly in modern environments; current data are insufficient to establish modern calibrations for the deep time phytolith record, and thus understand the fossil phytolith records in different vegetation types.In Chapter 1 and 2 of this dissertation I aim at helping bridging this gap, by 1) defining an appropriate methodology to sample phytolith for modern analogue studies that is applicable to the deep-time phytolith record; 2) and by providing a modern reference study of soil phytolith along transects in two Neotropical vegetation types in Costa Rica: a rainforest and a dry forest. I investigate the following questions: 1) how many samples and from which part of the (phytolith-rich) soil A-horizon are needed to reflect accurately the standing vegetation? (Chapter 1); 2) are gradients in vegetation structure, composition, and diversity recorded in phytolith assemblages across transects in rainforest and dry forest soils? (Chapter 2); and 3) can we use one or more phytolith assemblages to characterize these two vegetation types, and distinguish them in the fossil record? (Chapter 2).In Chapter 3, I apply the lessons learned from Chapter 1 and 2 to the study of vegetation heterogeneity and vegetation change in Patagonia, at the onset of the Middle Miocene Climatic Optimum (MMCO)–the last global warming event taking place on Earth before the current one, between ~17 and 14.5 Ma. The MMCO is poorly documented in the Southern Hemisphere and at high latitudes. The Santa Cruz Formation (SCF), in southern Patagonia, is an exception, preserving one of the most diverse and well-preserved fauna assemblages on Earth. Fauna and stable isotope data from the SCF suggest that global warming associated with increased aridity favored heterogeneous habitats characterized by many ecological niches which were able to support abnormally high fauna diversity. The phytolith record of SCF has been so far poorly studied but constitute the best line of evidence for high resolution reconstruction of vegetation change through time as well as of spatial patterns of vegetation variability (heterogeneity). Using phytolith assemblages from the SCF I investigate the following questions: 1) How did vegetation structure change in response to the initial warming pulse of the MMCO? 2) How did grass community composition change in response to warmer and drier conditions at the onset of the MMCO? 3)Was the remarkably high diversity of the Santa Cruz fauna supported by habitats characterized by vegetation heterogeneity (i.e., a mix of forested and open vegetation areas) throughout the onset of the MMCO as would be predicted based on modern ecology and SCF faunal data?In Chapter 1 phytolith from modern soil assemblages from two Neotropical forests in Costa Rica (a dry forest and a rainforest) are studied to determine a sample strategy for future modern analogue studies that is applicable to the phytolith deep-time record. Results suggest that the typical approach in deep-time paleoecology of taking point samples from the lower A-horizon of paleosols is justifiable (at least for paleosols reflecting rainforest and dry forest soils), and should therefore be implemented in future phytolith modern analogues studies that aim at improving interpretations of the deep-time phytolith record. Thus, the results of Chapter 1 constitute the basis upon which the modern analogue study described in Chapter 2 was conductedIn Chapter 2, additional soil phytolith assemblages collected along vegetation transects are used to investigate whether and how soil phytoliths reflect gradients in vegetation structure, composition and diversity across the two habitat types (dry forest and rainforest). In all, our results demonstrate that phytolith assemblages can definitely distinguish dry and wet forest habitats. In addition, our results also suggest that phytolith assemblage characteristics within vegetation types do not capture all aspect of environmental and plant community gradients. However, overall higher environmental heterogeneity of the dry forest results in higher heterogeneity of the phytolith assemblages. This result suggest that overall, spatial sampling (along a transect) and the analysis of phytolith assemblage composition allow to reconstruct some structural, and compositional aspects of habitat heterogeneity, and that that phytolith assemblage heterogeneity within a habitat might be indicative of habitat heterogeneity.In Chapter 3, phytolith assemblages from The Santa Cruz Formation (Patagonia) spanning the onset of the Middle Miocene Climatic Optimum (MMCO) are analyzed to reconstruct vegetation response to the climatic event as well as to reconstruct vegetation heterogeneity across two stratigraphic layers, representing two snapshots of the SCF vegetation at two different times. Results show that before the onset of the MMCO southeastern Patagonia was characterized by heterogeneous habitats with abundant pooid C3 grasses and a woody component represented by conifers, dicots, as well as palms in varying abundance. This habitat corresponded to woodland or open woodland/shrubland, including palm shrubland. In the upper SCF, at the onset of the MMCO (inferred from isotopic data to be drier), grass abundance decreased, and phytolith assemblages indicate that the landscape was dominated by a woody component of the vegetation. In addition, grass communities were dominated by C3 pooid grasses whereas grasses of the tropical PACMAD clade (which includes both C3 and C4 grasses) were only a minor component of grass communities. We interpret these trends as reflecting the expansion of dry-adapted woody vegetation in response to MMCO climate change, and to the detriment of a C3 grass community which was not adapted to dry conditions. Further, we suggest that PACAMD grasses at the SCF were likely primarily C3, and the expansion of dry-adapted C4 grasses and grass-dominated open habitats did not take place in Patagonia until after the early middle Miocene.
The city of Tikal, in northeastern Guatemala, was a major Maya polity for many centuries until the site core was abandoned within a 50-year span during the Terminal Classic period (A.D. 850 – 950). ...The inhabitants relied upon freshwater stored in their reservoirs, especially during the dry seasons. Diatoms, because of their well-preserved siliceous frustule, can be used as a proxy to determine water quality through time. Our results indicate that the water of at least one of their major reservoirs was contaminated during the Late Classic period, just prior to the abandonment of the site core of the city. Here we present a chronological change of Tikal reservoir water quality from Early Classic through Post Classic times as indicated by diatom content in radiocarbon dated layers of reservoir sediment pits. Within the Early Classic Period and Late Classic Period contexts, Lindavia radiosa and L. bodanica were the dominant diatom species, suggesting that water quality was within today’s Environmental Protection Agency’s (EPA) standards for safe drinking water. When we examine the end of the Late Classic period data, however, Cyclotella meneghiniana in the Palace Reservoir indicated the water developed eutrophic characteristics. Analysis of Tikal’s Palace reservoir sediment indicates deteriorating water quality and severe eutrophication near the end of the Maya occupation of the city.
Cultural eutrophication, the addition of excess nutrients to an aquatic system, is a significant water quality concern that often promotes excess algal growth and deep-water oxygen depletion. ...Deep-water oxygen also influences internal nutrient loading and is an important parameter used to assess cold-water fish habitat, though long-term data are often unavailable. Chironomid (Diptera: Chironomidae) assemblages have been shown to change with deep-water oxygen concentrations and can therefore be used to reconstruct these missing data sets. This thesis used paleolimnological techniques to analyze inferred whole-lake primary production, sedimentary chironomid assemblages, and inferred volume-weighted hypolimnetic oxygen to determine how cold-water fish habitat has changed through time. I will also examine whether biological recovery after nutrient-targeting remediation was introduced was evident in sedimentary chironomid assemblages. I focused on two lakes with increasing inferred whole-lake primary production (Muskrat and Stoco lakes, Ontario) and one lake with decreasing inferred primary production (Lac Duhamel, near Mont Tremblant, Québec) over time. The majority of change in response to elevated inferred whole-lake primary production is evident in littoral taxa and head capsule concentrations, though oxy-conforming profundal taxa (e.g. Micropsectra) did respond to increased whole-lake primary production. Overall, deep-water oxygen recovery after nutrient-targeting remediation was not evident in the sedimentary chironomid assemblages and that there were generally only subtle responses to elevated whole-lake primary production. Many of our lakes had historically low deep-water oxygen concentrations that were suboptimal for cold-water fish throughout their sedimentary records, with two lakes experiencing modest declines after there were increases in whole-lake primary production. These paleolimnological data can be used to set realistic mitigation targets for deep-water oxygen conditions and cold-water fish habitat restoration.
Fire is an important earth-system process, which is impacted by climate, and in turn shapes plant communities and drives biogeochemical cycling. Long-term perspectives on fire history are valuable in ...understanding the historical role of fire in maintaining plant communities, and paleoenvironmental methods are a primary source for this information. Great Lakes barren communities, characterized by pines and other fire-adapted plants growing in sandy, well-drained soils, are a regionally unique ecosystem type that is likely fire dependent. However, long-term perspectives on fire history are needed to inform management. In this study, I quantify multiple size-fractions of charcoal throughout a peat core to compare burning at different spatial-scales through time, comparing and contrasting fire history in the Great Lakes barren community with that of the broader island and regional mixed-deciduous forest. I compare these fire history records with a surface-moisture reconstruction developed through testate amoeba analyses to assess hydrological controls on burning, and use my data to discuss the utility of peatland fire history records and make brief management recommendations. Macroscopic charcoal influx was high throughout most of the ~6000-year record, with particularly high levels indicating periods of increased local burning 4.1-3.6 ka, 2.6-2.1 ka, and over the last ~400 years prior to fire suppression. Microscopic charcoal influx showed little correlation with the macroscopic record (r=0.17), indicating mostly distinct signals from regional and local fires respectively. However, nine instances of simultaneous local and regional fire episodes were identified, likely representing occurrences of major, widespread fires. All simultaneous regional and local fire events occurred when bog moisture was drier than average, and regional fire history was weakly correlated with bog hydrology for the past 2500 years. Results indicate that the sand barren landscape has a history of persistent local burning with an average fire return interval of about 55 years, and fire history was unrelated to local bog hydrology, although increased large fires during the Medieval Climate Anomaly and decrease large fires during the LIA suggest a possible relationship with temperature or seasonal moisture changes. Controlled burning of Great Lakes barren communities that is broadly consistent with the observed historical fire frequency of the past 400 years is most likely to maintain this rare and unique community. Finally, my results highlight the value of peatland records of fire history, which have been underutilized in paleoenvironmental studies even though these depositional systems provide some advantages over lakes.
Bu çalışma, Batı Karadeniz Bölgesi Bartın ili Amasra ilçesi Bostanlar mevkiinde Karadon ve Kozlu Formasyon'larında (Karbonifer) gerçekleştirilmiştir. Türkiye'nin ekonomik önem taşıyan taşkömürü ...sahalarından biri olan havzadan, Hattat Enerji ve Maden Tic. A.Ş. şirketine ait 9 karotlu sondajın (toplam 336 örnek) kömürlü birimden örnekleme yapılmıştır. Karbonifer'in Vestfaliyen yaşlı kömür örnekleri laboratuvarda hazırlanarak, içerisindeki sporomorfların (palinolojik açıdan) incelenmesi yöntemiyle yaşlandırılmıştır. Yaşlandırma, sporomorfların varlık, bolluk veya biraradalıkları gibi stratigrafik özellikleri dikkate alınarak yapılmıştır. Sporomorfların bileşimi sadece yaşlandırmada değil aynı zamanda korelasyonda da stratigrafik öneme sahiptir. Havza tektonizma etkisiyle kıvrımlı ve faylı bir yapıdadır. Tektonizmanın etkili olduğu bu gibi kömür havzalarındaki en önemli jeolojik sorun çalışılmakta olan stratigrafik düzeyin saptanmasıdır. Bu nedenle kömür damarlarında palinolojik korelasyon denemesi yapılmıştır. Korelasyon denemesi öncelikle kalın (ara kesmeleri ile beraber 0,90 m ve üzeri kalınlık gösteren) damarlarda ve daha sonra kalınlıklara bakılmaksızın tüm damarlarda sporomorfların oransal bolluklarına göre yapılmış ve benzer sporomorf özelliğine sahip kılavuz olabilecek düzeyler belirlenmiştir. İncelemeler sonucunda paralik kömür havzalarında beklenildiği gibi yatay yönde kömür damarlarının kalınlıklarında farklılıklar olduğu gözlemlenmiştir. Ayrıca incelenen örnekler Kuzey Yarıküre (Lavrasya) kömür kuşağındaki kömürlerle palinolojik ve paleoekolojik olarak benzerlik sunmaktadır. İncelemeler sonucunda Vestfaliyen A-B ve Vestfaliyen C-D olmak üzere iki palinolojik zon belirlenebilmiştir. Önceki çalışmalar ışığında çalışma alanı için belirlenen zonların sporomorf bolluklarına göre bitki vejetasyonu (paleoekolojik) yorumlanmıştır. Sonuç olarak Türkiye'nin karasal Karbonifer'de palinoloji, paleoekoloji ve palinostratigrafik bir çalışma gerçekleştirilmiştir. Palinolojinin kömür işletmeciliğinde karşılaşılan problemlerin çözümlerinden biri olarak kullanılabileceği belirlenmiştir.
La tordeuse des bourgeons de l’épinette (Choristoneura fumiferana), ou TBE, est l’insecte perturbateur le plus important des forêts de conifères du nord-est de l’Amérique du Nord. Depuis le début du ...20e siècle, on observe en forêt boréale un changement majeur de la dynamique des épidémies de la TBE au nord de sa distribution. Elles sont notamment plus sévères et plus fréquentes que celles des siècles précédents. On constate également que l’épidémie ayant débuté en 2006 dans la région de la Côte-Nord est d’une intensité inhabituellement élevée. Alors que plusieurs études documentent l’historique des épidémies du centre et du sud du Québec, très peu s’attardent à celles au nord de la distribution. Pourtant la Côte-Nord est une région dominée par l’épinette noire (Picaea Mariana), une essence prisée par l’industrie forestière du Québec, mais également un hôte secondaire de la TBE. La présente étude vise à combler ce manque de connaissance en établissant une longue chronologie des épidémies de la TBE pour la région de la Côte-Nord. Alors que la dendrochronologie sur arbres vivants nous permet d’établir des chronologies d’un maximum de 300 ans, les méthodes dites paléoécologiques présentent un potentiel beaucoup plus grand. Dans le cadre de ce projet, des centaines d’arbres subfossiles ont été extraits de la zone littorale du lac Dionne situé dans la région de Baie-Comeau. Près de 800 arbres ont ensuite été interdatés à l’aide des méthodes classiques de dendrochronologie. Cela a permis d’établir la plus longue chronologie des épidémies de la TBE : plus de 700 ans. Cette dernière met également en évidence la présence des épidémies pour la période climatique dite chaude du début du 20e siècle à aujourd’hui. Toutefois, on ne distingue aucune épidémie pour la période climatique précédente (AD 1550-1850), où le climat est historiquement plus froid. En effet, la dernière épidémie identifiée correspond à celle des années 80. Ces résultats concordent avec les observations déjà réalisées dans cette région.
