No description available.

The Amazon River is the largest by discharge and basin area globally, annually it delivers large volumes of water to the oceans through a mono modal flood cycle. During this cycle an unknown quantity of water is exchanged with the adjacent floodplain. The volume and duration of this exchange plays an important natural function for sedimentological, biogeochemical and ecological processes. It is known that hydraulic processes within the floodplain, including water depths, flow discharges and inundation timings, influence this exchange of water between the Amazon River and its floodplain. Hence the overall aim of this thesis was to investigate how water was routed through the Amazon floodplain and the hydraulic processes behind this routing. Floodplain water routing and hydraulics are influenced by three key aspects in the Amazon: 1) the volume of water, 2) the pathways along which this volume is routed, and 3) the influence oflocal water sources in the floodplain upon water derived from the Amazon River. Addressing these aspects led to three key scientific questions around which this thesis was structured: 1) What volume of water was exchanged between the Amazon River and its floodplain? 2) Along what flow pathways does this exchange occur? and 3) How does water from local hydrological sources influence the floodplain hydraulic processes? Investigations in this thesis were focussed upon a 30,000 km2 study site situated in the middle reach of the floodplain, ~250 km upstream of Manaus, Brazil. Within this area a two-dimensional hydraulic model was constructed from and tested against data from insitu gauges, satellite data and field work observations. The model was then used to address each of the above scientific questions. Before investigating the first question, it was necessary to develop a method to minimise the vegetation canopy distortion errors which had degraded the accuracy of the Digital Elevation Model (OEM), used by the model to represent floodplain topography. After this method, volumetric exchanges between the river and the floodplain were quantified by assessing the volume of water which filled and drained annually from the floodplain. Then the volume of flow routed through the floodplain as a proportion of the total flow was assessed by identifying cross sectional flow differences from simulations with and without floodplain storage components. Between 1995 - 1997 the floodplain filled during rising water by 93 - 113 km3 , whilst during falling water the floodplain drained 75 - 113 km3. Annual flows through the floodplain represented 6.4% - 10.7% of the total flow via the Amazon River, this increased to 9.0% - 18.8% at high water and decreased to 1.3%- 2.3% at low water. The role of floodplain channels as preferential flow pathways for water entering and exiting the floodplain was investigated by incorporating their geometry into the hydraulic model using a subgrid methodology. The overall effect of all these channels was to increase the duration of connection between the Amazon River and the floodplain. Consequently floodplain inundation volume increased by 7.3% - 11.3% at high water, and decreased at low water by 4.0% - 16.6%. These floodplain channels tended to function in networks, whereby smaller channels delivered flow into the floodplain, these collected into larger channels which then drained back into the main river. In total, these networks served as a net drainage mechanism taking flow from the floodplain back to the main river. The influence of local hydrological water inputs from terrafirme catchments which bounded the floodplain, were represented from simulated outflows from a hydrological rainfall-runoff model. Over the entire domain floodplain hydraulics were insensitive to these additional inputs, however a more significant influence could be observed int the areas surrounding the input locations. Temporally, the most significant influence was during falling and low water, when some areas witnessed flow increases of 15% - 400%. During this time, water in the floodplain could be composed of up to 10% - 15% from these local water sources. In answering the thesis aim, the work that will be presented shows that the Amazon floodplain routes a large proportion of the total flow within the study domain. This large exchange of water is aided by the existence of flow pathways, afforded from floodplain channel features, which play an important role in connecting the river and floodplain during early rising water and late falling water. Floodplain hydraulic processes are subtly influenced by local water inputs, which can be important in sustaining flows during falling and low water.

No description available.

Existing facies models of rift basin evolution are biased towards humid climatic regimes. This study uses geomorphic and sedimentologic observations from the actively extending, arid to semi-arid Basin and Range Province, Western U.S.A., to critically assess the applicability of the existing models to dryland regions. This was achieved by documenting the range of landscape responses to extensional tectonism in drylands, with the subsequent development of a revised, dryland specific, extensional basin facies evolution model. The geomorphic and sedimentologic character of six representative modern basins was mapped, and their facies proportions calculated. Key observations are the rarity of well-integrated exogenic fluvial systems and the resulting dominance of sediments issuing out of transverse catchments. The landscape maturity of the basins was quantified in order to compare their facies distributions within an evolutionary framework, serving as a proxy for rift phase. Syn to post rift facies evolution is characterised by: 1) a progression with drainage evolution from mixed debris and stream flow to stream flow dominated processes in marginally derived alluvium; 2) the inundation of playa facies as marginal facies prograde into increasingly central positions; 3) the resultant loss of facies asymmetry; 4) increasingly homogenised basinal facies, as longer sediment residence times at the surface allow for greater potential reworking; 5) a reduction in marginal catchment relief. Observations from the modern basins were tested against the Miocene to Recent post rift basin fill of the Virgin River Depression. Existing models suggest the dominance of axial fluvial sedimentation throughout the life of extensional basins. Findings of this study show that longitudinal fluvial sedimentation in dryland basins is, however, limited and if present, more likely to be restricted to the later, post rift stages of basin evolution.

No description available.

Speleothem trace elements are an important and effective tool for palaeoenvironmental reconstruction. They can be used to reconstruct a plethora of climate variables, and are a vital tool for improving our understanding of the climate system. This is particularly important given the on-going challenges of comprehending and tackling anthropogenic climate change. Only by thoroughly understanding controls on climate variability can we attempt to predict future change. This thesis presents a broad study of current speleothem trace element proxies. In addition to reviewing the current state of knowledge, this thesis presents several additions and developments to the speleothem trace element toolkit. The 22 year ATM-7 trace element record from Belize has a greater than seasonal resolution, and a highly precise chronology. As a result of this exceptional chronology, combined with extremely high resolution LA-ICP-MS analysis, it is possible to detect the geochemical indicators of volcanic ash deposition. Principal Component Analysis identifies a clear signal of a multi-elemental input of trace elements at the beginning of the wet season following volcanic eruptions with ash reaching the cave site. U/Ca variability in aragonitic speleothems is strongly influenced by the occurrence of Prior Aragonite Precipitation. The U/Ca record in Belizean stalagmite YOK-G strongly suggests that modern drying has occurred in Belize, primarily caused by a reduction in wet season rainfall. This is consistent with published stable isotope data from YOK-G, previously interpreted as the result of southward ITCZ displacement. These results strongly suggest that U/Ca values in aragonitic speleothems are excellent proxies for rainfall variability. This new tool, combined with the exceptional chronological control characteristic of aragonitic stalagmites and the high spatial resolution afforded by modern microanalytical techniques, should facilitate the construction of new exquisitely resolved rainfall records, providing rare insights into seasonality changes as well as long-term changes in local recharge conditions. In the Bermudan stalagmite BER-SWI-13, magnesium concentrations record, via varying prior calcite precipitation, changes in local rainfall which appear to correspond to variation in the North Atlantic Oscillation (NAO). Through a different mechanism, phosphorous also correlates with changes in the NAO. We infer that local effective rainfall changes, influenced by NAO state, influence bioproductivity above the cave and thus the amount of phosphorous in dripwaters. Surprisingly, for a location such as Bermuda, we see no evidence of clear direct anthropogenic influence on speleothem chemistry. These results V suggest that Bermudan speleothems are well situated to record basin scale climate changes in the North Atlantic. Together, these three separate studies demonstrate the strength and versatility of high- resolution trace element analysis of speleothems. They establish new techniques of data analysis, new proxies, and the applications of existing proxies in new contexts to reconstruct palaeoenvironmental variables. Looking forward, these discoveries demonstrate that speleothem trace elements continue to have a great deal to offer to the field of palaeoclimate reconstruction, and that there are still new techniques and applications to be developed.

Quantifying the geometries of evaporite deposits at a <1 km scale is critical in our understanding of similar ancient depositional systems, but is challenging given evaporite mineral dissolution at surface conditions. Two high-resolution stratigraphic studies in mines provide insight into the geometries, dimensions, and spatial distributions of sedimentary bodies in 3-D at a <1-km scale in evaporites. A field mapping study was conducted in Brightling (Purbeck Group) and Boulby (Zechstein Group) mines, in southeast and northeast England, respectively. This is integrated with XRD, petrography, and δ13C and δ18O isotope analyses. The evolution and conditions of sedimentation during the Tithonian in the Weald Basin is also evaluated. A newly defined megasequence boundary at the base of the Purbeck Group is suggested to mark the onset of rifting of the Bay of Biscay and to the north of the Charlie-Gibbs Fracture Zone, which implies an earlier rifting phase than previously proposed. Basal Purbeck lateral facies changes are influenced by the position in the Weald Basin, normal fault systems, and relative sea level changes. In Brightling Mine, the basal Purbeck exhibits carbonate-evaporite shoaling upward cycles, likely controlled by localized high-frequency relative sea level changes and/or sabkha hydrology. The dynamic process of evaporite deposition led to subtle stratigraphic heterogeneities and changes in bed thicknesses, but largely continuous lateral bedding. Boulby Mine offers a unique opportunity to study early deformation structures in ancient polyhalite that formed in playa conditions. The controlling mechanism that formed these syndepositional polyhalite tepees is attributed to soft sediment deformation via polyhalite dewatering coupled with penecontemporaneous precipitation of halite during fluid escape. This study offers new insight into the types of heterogeneity observed in ancient evaporites formed in marginal playa and sabkha environments at a < 1 km-scale, which can include a variety of compositions and morphologies at a range of scales.

This thesis is primarily concerned with geomorphological aspects of caves - karst hydrology, speleogenesis and the origin of speleothems. Cave exploration was a necessaiy prerequisite for such studies and its progress is traced from prehistoric times to the systematic regional investigations of the 17th century and later, The first extensive work was in Slovenia, stimulated by the practical importance there of karst hydrology for water supply and flood control. Large karst springs had long attracted attention and several hypotheses had been advanced previously; according to some they were supplied by water raised from the sea, others explained them by condensation and finally their source as rainfall was accepted. The study of intermittent karst lakes led eventually to the postulation of what amounted to a water-table. A true understanding of speleogenesis and the origin of speleothems depended on a knowledge of the chemistry of limestone solution, which in its turn depended on the rejection of phlogiston at the end of the 18th century. Before that time only mechanical erosion was normally conceived as a means of removing particles of solid rock and subsequently redepositig them to form speleothems although a few people earlier in the century had involved an unspecified "aerial acid". There were also several more primitive theories including the formation of caves by tectonic "catastrophes", by erosion as the water of Noah's Flood drained back underground, and the inflation of cavities in still soft limestone by decomposition gases. For many years speleothems were thought to possess a low form of life, growing like plants rather than by accretion. After the action of carbon dioxide in speleogenesis was appreciated a new question arose - whether caves could be formed in the saturated zone or whether they were due solely to vadose water. For many years the problem was not recognized but violent controversy was taking place over it by the end of the 19th century.

No description available.

Low enthalpy geothermal resources located within deep Permian and post-Permian sedimentary basins across the UK are estimated to contain at least 300 EJ (x1018 J) of heat, sufficient if fully developed to supply all heating needs in the UK for the next century. The geothermal heat estimate is based on data held within the Geothermal Catalogue (Busby, 2010). A source of deep well data not included in the Geothermal Catalogue is held by the oil and gas industry; access to this data has allowed new geothermal research to be undertaken to re-evaluate and constrain an existing geothermal resource (the Cheshire Basin), and to evaluate a previously un-quantified resource (the East Midlands). These areas were determined based on the availability of oil and gas well data. Data relating to the East Midlands indicate the total available extractable heat from produced oil and co-produced water located in Carboniferous sediments totals 2.64 MWt. In the Welton Field water from non-oil bearing horizons are factored in; the extractable heat increases from 0.91 MWt to 1.6 MWt. The Cheshire Basin uses the offshore East Irish Sea Basin as an analogue to better constrain the aquifer properties of the Triassic Sherwood Sandstone Group (SSG) and Permian Collyhurst Sandstone Group (CS). It also assesses the connectivity of these Groups across the basin. The Helsby Sandstone Formation (part of the SSG) will likely exhibit a minimum transmissivity of 4.26 D m alone. Data for the CS were inconclusive due to diverging porosity trends between the basins; transmissivity could be on average 0.13 D m or 3.85 D m with resulting flow rates of 47.7 m3 d-1 or 1431 m3 d-1. Factoring in reservoir stimulation is deemed necessary if the CS is to be targeted. The connectivity of the basin is restricted by large N-S orientated largely cemented faults, restricting flow in an E W orientation. In addition the connectivity is further affected by facies heterogeneity and diagenesis; this increases tortuosity that may be advantageous in a geothermal context. The work is pertinent given the UK’s commitment to the Kyoto Protocol and Renewable Energy Directive. Geothermal technologies are low CO2 emitters, are non-intermittent, unobtrusive, do not attract large emission-based taxes, have long (~25 year) lifespans and have minimal post-use clean up costs. The uptake of geothermal resource within the UK still remains low, however, indicating barriers to uptake exist. Technical barriers (i.e. those relating to drilling of the well, geology, flow rates and temperature) are not limiting uptake. Non-technical barriers relating to lack of risk insurance schemes and longer payback times owing to the relative value of hot water versus petroleum are identified as restricting factors to the uptake of geothermal resources. Geothermal energy development in the UK is still in its infancy and work such as this only strengthens the case for investment. The potential for geothermal resource exploitation to offset the conventional energy consumed to produce heat is sizeable; no other renewable technology has the capacity to deliver heat that low enthalpy geothermal offers.