The Nullarbor Plain in southern Australia is an uplifted succession of Cenozoic marine carbonates whose surface has been exposed for ~14 m.y. This succession of limestones, particularly in the surfical middle Miocene Nullarbor Limestone, hosts a complex and prolonged record of meteoric diagenesis. Alteration took place through 3 broad phases of diagenesis encompassing 8 stages that are interpreted to have taken place over a dramatic regional climate change. Phase 1 diagenesis occurred under a humid middle Miocene climate and involved mineralogical equilibration with meteoric fluids, calcite cementation, widespread microkarst, and regional lacustrine and palustrine sedimentation producing copious amounts of ooids. These ooids are interpreted to have formed via microbial secretions and sediment aggradation over multiple seasons of changing rainfall and soil hydration states. Cortical laminations are proposed to represent microbial mucus envelopes during wet seasons alternating with dehydration during dry seasons and precipitation of fibrous clay minerals and CaCO3 that preserve the pre-existing microbial fabrics. Phase 2 alterations took place under a more temperate climate from the late Miocene to Pliocene with a later pronounced humid interlude. This phase encompassed ~8 m.y. and was dominated by karst process where deep cave dissolution occurred at depressed water tables related to globally low sea levels and later shallow caves developed during a Pliocene sea level highstand. Phase 3 has occurred since the late Pliocene and is indicative of the onset of modern semi-arid climatic conditions. This final phase involved the creation of subsoil hollows filled with blackened limestone lithoclasts, deep and shallow dolines, and indurated pedogenic calcrete that now forms much of the surface of the Nullarbor Plain. Blackened limestone clasts have been shown to form at the B-C boundary in soil profiles where roots have their cellular structures calcified and during this process incorporate trapped organics that ultimately produce the distinctive black colouration. The importance of this comprehensive diagenetic record is its direct applicability to the understanding of ancient subaerial exposure surfaces. / Thesis (Ph.D, Geological Sciences & Geological Engineering) -- Queen's University, 2012-07-16 12:09:35.842

<p> Millennial-scale variability in the Indian monsoon was temporally linked to changes in global ocean circulation during the last glacial period, as evidenced by planktic-benthic foraminiferal stable isotope and trace element results from an intermediate depth sediment core from the northwestern Bay of Bengal (Core NGHP-01-19B; 18&deg;58'N, 85&deg;39'E; 1,422 m). Paired planktic foraminiferal Mg/Ca and &delta;¹⁸O_c of <i> G. ruber</i> constrain sea surface temperatures and isolate millennial-scale variations in the &delta;¹⁸O of surface waters (&delta;¹⁸O_sw) which resulted from changes in river runoff in the northwestern Bay. Concurrently with low &delta;¹⁸O_sw events, benthic foraminiferal &delta;¹³C of <i>Cibicidoides </i> spp. decreased, suggesting an increased influence of an aged water mass at this intermediate depth site during the low salinity events. Benthic foraminiferal Cd/Ca of <i>H. elegans</i> supports the identification of this water mass as aged Glacial Antarctic Intermediate Water (GAAIW). Lagged correlation analysis (r= 0.41) indicates that changes in subsurface properties led changes in surface properties by an average of 380 years. The implication is that Southern Hemisphere climate exerted a controlling influence on the Indian monsoon during the last glacial period.</p>

<p> In southwestern United States, the North American monsoon (NAM) is the main driver of severe weather in the Southwest. How the monsoon has behaved in the past and how it will change in the future is a question of importance for natural resource management and infrastructural planning. In this dissertation, I present the results of three studies that have investigated NAM variability and change from the perspective of paleoclimate records, future climate change projections, and simulation of the low-frequency variability with the longest retrospective atmospheric reanalysis. </p><p> In the first study, a monsoon-sensitive network of tree-ring chronologies is evaluated within its ability to reproduce NAM variability during the past four centuries. The tree-ring chronologies can reasonable characterizes the dominant modes of NAM climate variability and reveal low-frequency climate variability at decadal and longer timescales that is beyond the ability of the instrumental record to temporally well resolve. This low-frequency climate variability seems to coincide with the occurrence of multiyear persistent droughts. </p><p> In the second study, we consider the modes of climate variability to assess the degree of physical uncertainty in climate change projections models used in the North American Regional Climate Change Assessment Program (NARCCAP). NARCCAP models are evaluated mainly on their ability to represent warm season driven by quasi-stationary Rossby wave trains and El Ni&ntilde;o Southern Oscillation &ndash; Pacific Decadal Variability (ENSO-PDV). Only one out of eight NARCCAP models has a reasonable representation of the seasonal cycle of monsoon precipitation and ENSO-driven variability in both the 20^th and 21^st centuries. No decadal variability was observed in any of the NARCCAP models. </p><p> In the third study, the low-frequency drought signal found with tree-ring chronologies is further explored within the framework of a regional climate modeling. The Twentieth-Century Reanalysis is dynamically downscaled (DD-20CR) and its statistic analysis suggests that low-frequency drought signal in the Southwest is driven by atmospheric circulation changes on global to continental scales that affect precipitation in Central American as well. Low-frequency climate variability is therefore likely responsible for the multiyear persistent droughts in the last four centuries, as independently evaluated from the tree-ring monsoon-sensitive network.</p>

<p> Lipids preserved in soils and sediments are important proxies in paleoclimate research. However, various growth conditions that affect the organisms synthesizing the lipids can in turn affect the abundance and stable isotopic compositions of the lipids themselves, and, consequently, can introduce significant errors in the paleoclimatic inferences drawn from them. This work examines how two climate proxies based on lipids, namely, glycerol dialkyl glycerol tetraether (GDGT)-based paleotemperature proxies in soils, and paleohydrological proxies based on hydrogen isotopic composition of lipids, respond to variability in environmental and other growth conditions (e.g., carbon source).</p><p> In order to evaluate the role of annual precipitation amount on the distribution of soil GDGTs and on GDGT-based temperature proxies in soils, we studied GDGT distribution in soils collected from two environmental transects in the USA&mdash;a dry, western transect covering six western states and a wet, east coast transect from Maine to Georgia. Our results indicate a significant impact of precipitation amount on soil GDGT distribution, which is related to soil aeration that in turn depends on precipitation amount, and also to soil pH. Our results also indicate that below an annual precipitation of 700-800 mm yr^&ndash;1 the MBT/CBT-temperature proxy based on soil GDGTs is not applicable. Furthermore, due to the distinct GDGT distributions in soils under arid conditions, soil input into lacustrine or marginal marine environments cannot be estimated using BIT index.</p><p> In order to estimate the effects of variability in environmental conditions and utilization of different substrates on D/H_lipid, we studied two heterotrophic organisms&mdash;<i>Haloarcula marismortui</i>, a halophilic archaeon and <i>Tetrahymena thermophila</i>, a ciliated protozoan, in pure cultures. Our results from experiments with <i>H. marismortui</i> indicate that metabolism of different substrates leads to formation of reducing agents (mainly nicotinamide adenine dinucleotide phosphate or NADPH) with distinct D/H signatures, which is reflected in the significant D/H variations in isoprenoidal lipids (ca. 100&permil;). Growth temperature affects growth rate as well as enzyme activities, and salinity of the growth media affects mainly growth rate of <i>H. marismortui</i>, and both cause similar variations in D/H_lipid (ca. 20-30&permil;) that are smaller compared to the substrate-effect. <i>T. thermophila </i>, on the other hand, responds to variations in growth temperature in a different manner. Isoprenoid and fatty acids synthesized by <i> T. thermophila</i> generally become more D-enriched with temperature increase. The isoprenoid ranges from being D-depleted to D-enriched relative to water with temperature increase, but the fatty acids do not display similar patterns. Our results from <i>T. thermophila</i> culture experiments indicate that temperature has a critical control on the D/H ratios of NADPH and possibly also intracellular water, due probably to temperature effects on processes that are related to growth and metabolism of <i>T. thermophila. </i></p>

<p> The increased surface melting of the outlet glaciers of the Vatnaj&ouml;kull Ice Cap has a profound affect on the dynamics of the ice-bed couple and landform genesis. Soft-bedded glaciers are largely inaccessible, which creates a problem. One challenge is to understand the complex interactions of the glacier bed and its resultant depositional and deformational landform systems. This study investigates an outlet glacier from the Vatnaj&ouml;kull Ice Cap, described herein as the Fl&aacute;aj&ouml;kull glacier system. To circumvent some of these problems, three separate projects were conducted in this dissertation: (1) magnetic fabric study of effective pressure (difference between the ice-overburden pressure and pore-water pressure) and shear rate (glacier velocity) using a laboratory ring-shear device; (2) glaciological analysis of magnetic fabrics and c-axis orientations of dirty ice veins; and (3) investigation of drumlin formation using magnetic till fabrics and field relationships. Several hypotheses were addressed for each of these studies, which include: (1) to determine if fabric strength is independent of shear rate and effective pressure. This hypothesis was tested and the results confirmed that the fabric strength (S1 eigenvalue) was independent of shear rate and effective pressure. Based on these results, effective pressure and shear rate cannot be interpreted from fabric strength evidence from glacial deposits; (2) in the glaciological study, I hypothesized that the dirty ice veins were sub-vertically sheared from the bed near the ice front, but then moderately deformed. Results from the magnetic fabrics indicate that the maximum K1 susceptibility axis (77&deg; plunge) is approximately parallel to the vein margins verify that the injection was sub-vertical. The long axes of the recrystallized ice grains (parallel to foliation plane defined by K₁ &ndash; K₂) appeared to show a good correlation with the plunge of the maximum K₁ susceptibility. Also, the eigenvector plunge of the c-axes was approximately normal to the shear plane, which supports previous theory that c-axes rotate away from the shear plane toward the vertical. Multi-maximum girdle fabrics from the c-axes and associated textures from thin sections (e.g. nucleated grains, bulging of grain boundaries and slips band) suggest that some deformation likely occurred after emplacement; and (3) the Boulton hypothesis was tested using magnetic till fabrics and field relationships. According to this idea, drumlins form due to hydrologic heterogeneity (permeability differences in granular materials) causing a solid nucleus to form in the bed where sediment is accreted and sheared in the direction of ice flow. At Fl&aacute;aj&ouml;kull, the magnetic fabrics from sites B and C mimicked the glacier flow direction with the longitudinal flow plane (K₁ &ndash; K₃) approximately parallel to the NNW-SSE drumlin long axis. The drumlin cores consisted of outwash sand and gravels which likely acted as rigid obstacles in the bed. Ice overriding resulted in heterogeneous deformation of the drumlin cores following the deposition of the upper basal till carapace. These results support the Boulton hypothesis. </p><p> These studies demonstrate significant progress toward understanding fabric strength development of soft-bedded glaciers. In linking studies (1) and (3) the ring-shear device was used to provide insights into fabric strength development upon shear rate and effective pressure. In the third study previous ring-shear experiments, magnetic till fabrics and field relationships were used to understand modern drumlin genesis.</p>

<p> The age of the Ruby Ranch Member (RRM) of the Cedar Mountain Formation in East-Central Utah was recently constrained using carbon isotope chemostratigraphy to span known excursions associated with the late Aptian. The RRM is characterized by calcrete horizons that are thought to occur across the C10 carbon isotope excursion. Along with carbonate stable isotope analyses and the region&rsquo;s paleo-position in a depositional basin on the leeward rain shadow of the Sevier Orogenic belt, this interval is hypothesized to coincide with an aridification event. Our research objective is to quantify the extent of this aridity using clumped isotope paleothermometry (<i>n</i> = 7) and paleoprecipitation proxies (n = 51) for samples collected across the C10 chemostratigraphic interval. Two weathering indices, CIA-K and CALMAG, were applied to data obtained using X-ray fluorescence spectrometry. Using these proxies, we determined mean annual precipitation across the RRM at its type section. Precipitation values (<i> n</i> = 27) obtained through CIA-K for identified paleosol horizons ranged between 795 and 1275 mm/year, and through CALMAG ranged between 735 and 1042 mm/year. Precipitation values decreased through the C10 interval which may indicate increased aridity. Clumped isotopes provided ?47 values ranging from 0.647 to 0.693&permil;. Paleotemperature measurements (n = 4) from accepted carbonate samples were between 27.9 and 46.3 &deg;C. Isotopic compositions of water calculated from carbonates ranged between -4.4&permil; and -1.9&permil; VSMOW. Precipitation values and temperatures were not lowest during the C10 interval. Temperatures peaked at the end of the C10 interval and decreased afterward, indicating a potential for cooler, more arid conditions. These results suggest that carbon cycle changes during the mid-Cretaceous may have influenced paleoclimate conditions experienced in terrestrial settings.</p><p>

<p> Multi-proxy comparative analyses of sediment from Eagle Lake, including TOC, &delta;13C and &delta;15N composition of bulk organic material, n-alkane distribution, and biogenic silica, was used to document hydroclimatic changes during the early and late Holocene. Eagle Lake is currently located near the transition zone of the North American Precipitation Dipole, with the timing of precipitation showing a winter-wet scenario common to the Pacific Northwest, but overall precipitation (e.g. aridity) showing a Pacific Southwest pattern. The width and position of this transition is poorly constrained during the Holocene and is hypothesized to have migrated, particularly in response to the North American Monsoon. Eagle Lake is thus ideal in providing insights to the past positions of the dipole. Multi-proxy analyses results in differences between the early and late Holocene at Eagle Lake. TOC is lower in the early Holocene, however C:N ratios are much more variable indicating a transition from algal source material to terrestrial and back to algal material prior to the Mazama ash. There are also greater fluctuations of biogenic silica during the early Holocene, suggesting rapid changes in productivity. </p><p> To place these Holocene changes within the context of known climatic and anthropogenic conditions of the 20th century, a ~100 year record of hydrologic change is compared to drought and lake-level drops induced by the formation of the Bly Tunnel. Importantly, the effects of the tunnel on lake level is superimposed on the 1930s drought, making it difficult to disentangle the two impacts. However, the TOC and C:N ratios clearly mirror variations in lake level suggesting that they are effective indicators of Holocene variations. </p><p>

Studies of large herbivorous mammal (ungulate) communities have revealed an association between increased tooth crown height (hypsodonty) and a shift to more arid environments over the Cenozoic. Ecometric analyses have also been used to examine the relationship between current climate conditions and crown height of these communities, and very successfully used to estimate past precipitation. Small herbivorous mammals (rodents and lagomorphs) have been shown to similarly adapt to changing habitats over the Cenozoic, but did so millions of years earlier than larger mammals. Here, we have utilized ecometric methods to examine the relationships between rodent and lagomorph crown height and diversity with current climate conditions, finding strong correlations of community structure parameters with climate, particularly mean annual temperature, maximum temperature of the warmest month, and minimum temperature of the coldest month. We applied the resultant regression equations to well-sampled fossil localities from North America, spanning over 37 million years, allowing estimation of climate conditions in deep time. As expected, estimates show a general pattern of decrease in both precipitation and temperature across North America from 37 Ma to the present. Overall, these findings provide a new broadly-applicable proxy for estimation of Cenozoic climate conditions at a local scale.

No description available.

Recent successful drilling operations at Lake El'gygytgyn, NE Russia have recovered sediment cores back to 3.6Ma, representing the longest time-continuous sediment record of past climate change in the terrestrial Arctic. Analysis of the hydrogen isotopic ratio (δD) of specific organic biomarkers allows reconstruction of past hydrological conditions, thereby providing a powerful tool for reconstructing past Arctic climate changes. Compound specific isotopic analysis of sedimentary lipids from this remote basin provides new insights into the climate evolution of the Arctic, capturing the mechanisms and dynamics of the last two glacial-interglacial transitions, potentially enhancing the accuracy of modeled future climate change projections and presenting an opportunity to estimate past polar amplification of climate change. The results of this research document the first continuous, high fidelity continental record of reconstructed δD in precipitation from terrestrial plant leaf waxes in the High Arctic spanning the last 120 ka. The hydrogen isotopic composition of lipid biomarkers were determined from previously obtained Lake El'gygytgyn sediment cores and compared with other multi-proxy evidence of past climate change within the lake basin. The modern isotope hydrology and controls on the δD lipid signal were first established within the El'gygytgyn Basin from modern precipitation, stream and lake waters, ice cover as well as modern vegetation, water column and lake bottom surface sediments in order to provide a modern context to properly constrain and interpret paleoclimatic proxy data. Reconstructed δD records of paleoprecipitation and temperature at Lake El'gygytgyn lead other northern hemisphere climate records (e.g. North Greenland Ice Core Project, NGRIP δ18O records) and are in phase with other continental and Antarctic climate records, suggesting early high northern latitude continental warming prior to established glacial-interglacial transitions. The data set generated here leads to multiple avenues of future work and provides critical insights into Arctic paleoclimate and paleohydrology, contributing to our understanding of high latitude environmental change over geological timescales. Collectively, the results of this dissertation research will provide a context for paleoclimate reconstructions and future organic geochemical and stable isotope analysis. Future application of compound-specific H isotope analyses to long drill cores (recovered in 2009; ∼315m of sediment) will potentially provide a quantitative high-resolution record of paleoclimatic and paleoenvironmental changes spanning the last 3.6 Ma.