abstract: Climate and its influence on hydrology and weathering is a key driver of surface processes on Earth. Despite its clear importance to hazard generation, fluvial sediment transport and erosion, the drawdown of atmospheric CO₂ via the rock cycle, and feedbacks between climate and tectonics, quantifying climatic controls on long-term erosion rates has proven to be one of the grand problems in geomorphology. In fact, recent attempts addressing this problem using cosmogenic radionuclide (CRN) derived erosion rates suggest very weak climatic controls on millennial-scale erosion rates contrary to expectations. In this work, two challenges are addressed that may be impeding progress on this problem. The first challenge is choosing appropriate climate metrics that are closely tied to erosional processes. For example, in fluvial landscapes, most runoff events do little to no geomorphic work due to erosion thresholds, and event-scale variability dictates how frequently these thresholds are exceeded. By analyzing dense hydroclimatic datasets in the contiguous U.S. and Puerto Rico, we show that event-scale runoff variability is only loosely related to event-scale rainfall variability. Instead, aridity and fractional evapotranspiration (ET) losses are much better predictors of runoff variability. Importantly, simple hillslope-scale soil water balance models capture major aspects of the observed relation between runoff variability and fractional ET losses. Together, these results point to the role of vegetation water use as a potential key to relating mean hydrologic partitioning with runoff variability. The second challenge is that long-term erosion rates are expected to balance rock uplift rates as landscapes approach topographic steady state, regardless of hydroclimatic setting. This is illustrated with new data along the Main Gulf Escarpment, Baja, Mexico. Under this conceptual framework, climate is not expected to set the erosion rate, but rather the erosional efficiency of the system, or the steady-state relief required for erosion to keep up with tectonically driven uplift rates. To assess differences in erosional efficiency across landscapes experiencing different climatic regimes, we contrast new CRN data from tectonically active landscapes in Baja, Mexico and southern California (arid) with northern Honduras (very humid) alongside other published global data from similar hydroclimatic settings. This analysis shows how climate does, in fact, set functional relationships between topographic metrics like channel steepness and long-term erosion rates. However, we also show that relatively small differences in rock erodibility and incision thresholds can easily overprint hydroclimatic controls on erosional efficiency motivating the need for more field based constraints on these important variables. / Dissertation/Thesis / Doctoral Dissertation Geological Sciences 2014

This thesis reconstructs the landscape evolution of the Billy Big Spring site (24GL304, Glacier County, north-central Montana) from the last glacial maximum to present through the analysis of sediment and soil samples collected from a transect of auger tests that bisected the site and surrounding landforms. Interpretations were drawn from stratigraphy, pedologic data, sedimentologic analysis and radiocarbon dating. The site landscape came into being in the late-Pleistocene, after Wisconsin-age glaciers retreated. Glacial retreat left a meltdown depression on the land that filled with water to form a pond, which persisted through the early-Holocene. The onset of the mid-Holocene (Altithermal) occurred before ~8,415 cal. yrs. BP, when increasingly arid conditions caused the water level to drop. The first radiocarbon dated human occupation of this site occurred during the Altithermal, ~7,030 cal. yrs. BP, after the eruption of Mount Mazama (~7,633 cal. yrs. BP). Arid conditions continued until ~7,000 cal. yrs. BP, when pond water re-expanded across the basin, marking the transition to the cooler late-Holocene. Sometime before 2,100 cal. yrs. BP, dry conditions returned, and the extent of the pond water decreased again. Since this time, overland alluvial processes have deposited sediments in the basin. Many hypotheses on how the Altithermal impacted the people of the Northwestern Plains have been proposed since the 1950s, but little agreement has been reached. This is due to the fact that there was great variation in how the Altithermal expressed itself throughout the Northwestern Plains. The human reactions to this phenomena cannot be explained simplistically for the region as a whole. This study shows that the Billy Big Spring site experienced drying during the Altithermal, but despite this, people continued to occupy this site. This evidence adds to the argument that the Altithermal climate of the Northwestern Plains did not have severe enough impacts to impose much hardship on its occupants.

No description available.

The primary goal of this project is to develop a relative chronology of events in the geologic history of the Kentucky River, and to consider the geologic controls on those events. This study utilized published geologic and topographic data, as well as field observations and extensive compilation and comparison of digital data, to examine the fluvial record preserved in the Kentucky River valley in central Kentucky. Numerous fluvial features including abandoned paleovalleys, fluvial terraces and deposits, bedrock benches, and relict spillways between adjacent river valleys were identified during the course of the study. The morphology of the modern valley coincides with bedrock lithology and can be used to describe the distribution and preservation of modern and ancient fluvial deposits and features in the study area. Bedrock lithology is the dominant control on valley morphology and on the distribution and preservation of fluvial deposits and features in the study area. Some stream trends are inherited from the late Paleozoic drainage of the Alleghanian orogeny. More recent inheritance of valley morphology has resulted from the erosion of the river from one lithology down into another lithology with differing erosional susceptibility, thus superposing the meander patterns of the overlying valley style onto the underlying lithology. One major drainage reorganization related to a pre-Illinoisan glacial advance disrupted the northward flow of the Old Kentucky River toward the Teays River system and led to organization of the early Ohio River. This greatly reduced the distance to baselevel, and led to abrupt incision and a change in erosional style for the Kentucky River. The successful projection of valley morphologies on the basis of bedrock stratigraphy, the history of erosion suggested by fission track data and the results of this study, as well as soil thickness and development, all argue against the existence of a midto late-Tertiary, low-relief, regional erosional surface. This study instead hypothesizes that the apparent accordance of ridge-top elevations in the study area is a reflection of a fluvially downwasted late Paleozoic depositional surface.

Geography and the Environment / Studies of the Amazon drainage network have primarily focused on the Western Basin and the Amazon Cone, but they have neglected the integration between these areas. Data presents a time gap in the Amazon’s development and the forces responsible for the organization of the drainage network are poorly understood. A key element towards gaining an improved awareness of the Amazon is the Eastern Amazon River Valley. The focus of this study is an 80,000 km² portion of this area. An integrated method is adopted that combines terrain information derived from a digital elevation model with geologic data. The interpretation of DEM data is unique to this study. Seven distinct surfaces were identified, along with numerous erosional environments. This observation supports a geomorphologic record of numerous erosional events starting in the Miocene. This finding is significant as it rejects previous models for staircase-like terraces for the Amazon, and establishes a timeline for the development of geomorphologic landforms in the study area. In addition, neotectonics events provide an alternative explanation to the generation of topography in the study area. It was concluded that geomorphology in the study area is the result of physical and chemical weathering, and modified by neotectonics. These findings provide alternative means for Amazon landscape evolution. / text

Upland rivers control the large-scale topographic form of mountain belts, allow coupling of climate and tectonics at the earth’s surface and are responsible for large scale redistribution of sediment from source areas to sinks. However, the details of how these rivers behave when perturbed by changes to their boundary conditions are not well understood. I have used a combination of fieldwork, remotely sensed data, mathematical analysis and computer modelling to investigate the response of channels to well constrained changes in the forcings upon them, focussing in particular on the effects of glacial remoulding of the catchments draining the south flank of the Ladakh batholith, northwest Indian Himalaya. The last glacial maximum for these catchments is atypically old (~100 ka), and this allows investigation of the response to glaciation on a timescale not usually available. The geomorphology of the catchments is divided into three distinct domains on the basis of the behaviour of the trunk stream – an upper domain where the channel neither aggrades above or incises into the valley form previously carved by glacial abrasion, a middle domain where the channel incises a gorge down into glacial sediments which mantle the valley floor, and a lower domain where the channel aggrades above this postglacial sediment surface. This landscape provides a framework in which to analyze the processes and timescales of fluvial response to glacial modification. The dimensions of the gorge and the known dates of glacial retreat record a time averaged peak river incision rate of approximately 0.5 mm/y; the timescale for the river long profile to recover to a smooth, concave up form must exceed 1 Ma. These values are comparable with those from similarly sized catchments that have been transiently perturbed by changing tectonics, but have never been quoted for a glacially forced basin-scale response. I have also demonstrated that lowering of the upper reaches of the Ladakh channel long profiles by glacial processes can systematically and nonlinearly perturb the slope-area (concavity) scaling of the channel downstream of the resulting profile convexities, or knickzones. The concavity values are elevated significantly above the expected equilibrium values of 0.3-0.6, with the magnitude controlled by the relative position of the knickzone within the catchment, and thus also by the degree of glacial modification of the fluvial system. This work also documents the existence of very similar trends in measured concavities downstream of long profile convexities in other transiently responding river systems in different tectonoclimatic settings, including those responding to changes in relative channel uplift. This previously unrecognised unity of response across a wide variety of different environments argues that such a trend is an intrinsic property of river response to perturbation. Importantly, it is consistent with the scaling expected from variation in incision efficiency driven by evolving sediment flux downstream of knickzones. The pervasive nature of this altered scaling, and its implications for fluvial erosion laws in perturbed settings, have significant consequences for efforts to interpret past changes in forcings acting on river systems from modern topography. I follow this by examining in detail the channel hydraulics of the Ladakh streams as they incise in response to the glacial perturbation. I present a new framework under which the style of erosion of a natural channel can be characterized as either detachment- or transport-limited based upon comparison of the downstream distribution of shear stress with the resulting magnitude of incision. This framework also allows assessment of the importance of sediment flux driven effects in studied channels. This approach is then used to demonstrate that fluvial erosion and deposition in the Ladakh catchments is best modelled as a sediment flux dependent, thresholded, detachment-limited system. The exceptional quality of the incision record in this landscape enables an unprecedented calibration of the sediment flux function within this incision law for three different trunk streams. The resulting curves are not compatible with the theoretically-derived parabolic form of this relation, instead showing nonzero erosion rates at zero sediment flux, a rapid rise and peak at relative sediment fluxes of less than 0.5 and a quasi exponential decrease in erosional efficiency beyond this. The position of the erosional efficiency peak in relative sediment flux space and the magnitude of the curve are shown to be both variable between the catchments explored and also correlated with absolute sediment flux in the streams.

River incision into a widespread, upland low-relief landscape, and related patterns of exhumation recorded by low-temperature thermochronology, together underpin geodynamic interpretations for crustal thickening and uplift of the eastern Tibetan Plateau. We report results from a suite of 11 (U-Th-Sm)/He cooling-age samples. Eight samples comprise a 1.2 km relief section collected from elevations up to 4800 m in the Jiulong Shan, an elevated, rugged region located in the hinterland of the Yalong-Longmen Shan Thrust Belt, and surrounded on three sides by upland low-relief landscape surfaces. Zircon and apatite cooling ages record two episodes of rapid exhumation in the early Oligocene and late Miocene, that were separated by a period of stability from similar to 30 to 15 Ma. The first episode is consistent with a similar pulse evident from the Longmen Shan. The second episode is ongoing, and when integrated with adjacent cooling-age data sets, shows that doming of the Jiulong Shan has resulted in 2 to 4 km of differential exhumation of the plateau interior. We show from a compilation of glacial landform-mapping that the elevation of the plateau surface closely tracks global last glacial maximum equilibrium line altitude. We hypothesize that smoothing of highlands by efficient glacial and periglacial erosion, coupled with potential river captures and conveyance of sediments via external drainage, can yield an apparently continuous low-relief plateau landscape formed diachronously at high elevation. (C) 2016 Elsevier B.V. All rights reserved.

Long-term perspectives on the evolution of river deltas have provided useful knowledge capable of responding to pending questions related to the ongoing climate and environmental changes. Increasing utilization pressure on delta environments has necessitated increased attention to protect the socio-economic and ecological values. As a result, multiple local initiatives have been designed, aimed at mitigating environmental deterioration and implementing adaptive measures, but many such initiatives have shown limited success. This thesis uses a case study of Save River delta in Mozambique to explore the relation between geomorphological evolution and socio-ecological system dynamics in delta environments. In addition, key environmental variables that concern the society today are highlighted and discussed in a management perspective. The results of the study show the development of Save River delta from the mid-Holocene to the present. The geomorphological settings of the delta suggest a faulted coastline over which subsequent deposition of fluvial sediments has formed a protruding delta front. Between c. 3000 and 1300 years ago, fine-grained sediments accumulated on top of the delta-front in the proximal part of the delta. This type of material was deposited under intertidal conditions and supported the formation of mangrove habitat. The geographical distribution of the mangrove deposit was driven by successive stages of back-barrier swamp formation and sea-level change as the delta evolved. From c. 1300 years ago, the river delta started to receive fluvial sediments from pulses of floods forming an alluvial floodplain. These sediments have accumulated mainly on the fine-grained mangrove wetland deposit. All the geomorphological features have evolved in a shoreward-shifting pattern over time. Centennial to decadal changes observed in the delta have followed a predictable geomorphological pattern, which is also part of the millennial evolution. The mangrove system, the base for the socio-economic system, is consequently strongly affected by the geomorphological development of the area. An increasing sensitivity of socio-ecological systems to environmental stressors, e.g. floods, cyclones and erosion, has motivated multiple initiatives to work towards a sustainable management of delta environments. This thesis highlights the need for interplay between geomorphology and ecology, considering both long- and short-term dynamics of delta environments. Hitherto, management initiatives have been concentrated on fragmented interventions of controlling water flow, which have disrupted the natural dynamics by obstructing the sedimentation-erosion cycle. To change this trend, coastal planners need to consider the significance of natural processes, e.g. cyclones, floods, erosion and accretion, for the long-term ecological and social sustainability of delta environments. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 1: Manuscript. Paper 2. Manuscript. Paper 3: Manuscript. Paper 4: Manuscript.</p>

In this dissertation, we have examined mineral assemblages and geomorphologic features in the Sisyphi Planum region of Mars, as well as examined the mineral assemblage of palagonite in Iceland. Chapter 2 is focused on the mineral assemblages detected on possible glaciovolcanic edifices in the Sisyphi Planum region of Mars. Minerals were identified utilizing visible/near-infrared orbital spectra from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM). Analysis of eleven CRISM images located on the volcanic edifices revealed three distinct spectral classes in the region which are interpreted to be: gypsum-dominated, smectite-zeolite- iron oxide-dominated (possibly palagonite), and polyhydrated sulfate-dominated material. The possible palagonite detections on the volcanic edifices, the geomorphology of the region, and the analogous terrestrial mineralogy of subglacial eruptions strongly suggests the formation of these minerals during subglacial eruptions or associated hydrothermal systems. This implies that thick water ice sheets were present in this region in the late Noachian or early Hesperian, and that the subglacial hydrothermal systems could have supported habitable environments with excellent biosignature preservation potential. Chapter 3 is focused on evaluating the variability of the composition and crystallinity of palagonite on Earth in order to inform efforts to identify it on Mars. We hypothesized that variability in palagonite composition and crystallinity could occur due to differences in environmental conditions during formation. Palagonite samples were collected in Iceland at subglacial volcanic sites around Reykjavík in the Western Volcanic Zone, on the southern coast in the Eastern Volcanic Zone, and from the Herðubreið tuya and Askja volcano in the Northern Volcanic Zone. Visible/near-infrared reflectance spectroscopy, thermal-infrared emission spectroscopy, and quantitative XRD were used to assess the bulk mineralogy, crystallinity, and clay composition of all samples. Results show the sampled palagonites contain partially devitrified glass, unaltered glass, and secondary minerals including clay minerals, poorly crystalline ferric oxides, and zeolites. However, one sample (SCoast01) shows a vastly different mineral assemblage in all sample techniques, including well-crystalline Fe/Mg-clays as opposed to the poorly-crystalline Al-clays observed in our other samples. Based on previous studies of subaqueous palagonites and the location this sample was collected from, we hypothesize that the SCoast01 sample was formed in a submarine environment rather than subglacial. This suggests that it may be possible to differentiate submarine vs. subglacial palagonite on Earth based on composition and from remote sensing observations on Mars. Chapter 4 is a geomorphologic study of the Sisyphi Planum region of Mars where we identified and classified the tops of the Sisyphi Montes as well as geomorphologically mapped the Sisyphi Planum region. Here, we address an overarching question: What is the relationship between the Sisyphi Montes and the ice in this region? To do this, we identified 106 edifices in the region and classified them into five categories: 1) flat topped, 2) rounded tops, 3) sharp peaks, 4) cratered peaks, and 5) height less than 300 meters – a “catch-all” category for all features below the specified height, which exhibit less distinctive morphologies in MOLA topography. While many of the edifices could be sub-glacial in origin, we find that the only morphologic class that exhibits uniquely subglacial morphologies are the flat-topped edifices. These edifices are similar to terrestrial tuyas, which form when a subglacial volcano breaches an ice sheet and erupts a plateau of sub-aerial lavas. Based on the geomorphologic map and topographic data, we have shown that flat-topped edifices are all located outside of regions that we map as the Mantled Unit, which we infer to be related to the Dorsa Argentina Formation. The combination of the flat topped edifices and their location outside of the mapped ice-related regions strongly suggests that the ice in the region was once more extensive than what is currently observed. While this has been proposed in the past, it has not been documented how far the ice sheet could have extended. Here we show that the ice must have extended to at least as far as the flat topped edifices in the region. The combination of these chapters using both mineralogy and morphology suggest that the Sisyphi Planum region of Mars was subglacial in origin. <br><br>

The study area extends from west of the Great Divide to the Broken Hill and Tibooburra regions of far western New South Wales, encompassing several important mining districts that not only include the famous Broken Hill lodes (Pb-Zn-Ag), but also Parkes (Cu-Au), Peak Hill (Au), Cobar (Cu-Au-Zn) and White Cliffs (opal). The area is generally semi-arid to arid undulating to flat terrain covered by sparse vegetation. ¶ During the Cretaceous, an extensive sea retreated across vast plains, with rivers draining from the south and east. After the uplift of the Great Divide associated with opening of the Tasman Sea in the Late Cretaceous, drainage swung to the west, cutting across the Darling River Lineament. The Murray-Darling Basin depression developed as a depocentre during the Paleogene. Climates also underwent dramatic change during the Cenozoic, from warm-humid to cooler, more seasonal climates, to the arid conditions prevalent today. Up until now, there has been very little temporal constraint on the development of this landscape over this time period. This study seeks to address the timing of various weathering and landscape evolution events in northwestern New South Wales. ¶ The application of various regolith dating methods was undertaken. Palaeomagnetic dating, clay δ18O dating, (U+Th)/He and U-Pb dating were all investigated. Palaeomagnetic and clay dating methods have been well established in Australian regolith studies for the last 30 years. More recently, (U+Th)/He dating has been successfully trialled both overseas and in Australia. U-Pb dating of regolith materials has not been undertaken. Each method dates different regolith forming processes and materials. Palaeomagnetic and clay dating were both successfully carried out for sites across northwestern New South Wales, providing a multi-technique approach to resolving the timing of weathering events. Although (U+Th)/He dating was unsuccessful, there is scope for further refinement of the technique, and its application to regolith dating. U-Pb dating was also unsuccessfully applied to late-stage anatase, which is a cement in many Australian silcretes. ¶ Results from this study indicate that the landscape evolution and weathering history of northwestern New South Wales dates back at least 60 million years, probably 100 million years, and perhaps even as far back as 180 million years. The results imply that northwestern New South Wales was continuously sub-aerially exposed for the last 100 Ma, indicating that marine sedimentation in the Murray-Darling and Eromanga-Surat Basins was separated by this exposed region. The ages also provide further evidence for episodic deep chemical weathering under certain climatic conditions across the region, and add to the data from across Australia for similar events. In particular, the palaeomagnetic ages, which cluster at ~60 ± 10 Ma and 15 ± 10 Ma, are recorded in other palaeomagnetic dating studies of Australian regolith. The clay ages are more continuous across the field area, but show older clays in the Eromanga Basin sediments at White Cliffs and Lightning Ridge, Eocene clays in the Cobar region, and Oligocene – Miocene clays in the Broken Hill region, indicating progressively younger clay formation from east to west across northwestern New South Wales, in broad agreement with previously published clay weathering ages from around Australia. ¶ These weathering ages can be reconciled with reconstructions of Australian climates from previously published work, which show a cooling trend over the last 40 Ma, following an extended period of high mean annual temperatures in the Paleocene and Eocene. In conjunction with this cooling, total precipitation decreased, and rainfall became more seasonal. The weathering ages fall within periods of wetness (clay formation), the onset of seasonal climate (clay formation and palaeomagnetic weathering ages) and the initiation of aridity in the late Miocene (palaeomagnetic weathering ages). ¶ This study provides initial weathering ages for northwestern New South Wales, and, a broad geochronology for the development of the landscape of the region. Building on the results of this study, there is much scope for further geochronological work in the region.