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Analysis of the sedimentary fill of a foreland basin system can clarify the relative effect of tectonics, base-level fluctuations and climate during basin development. This study addresses the facies, architecture, planform, palaeocurrent andpalaeohydraulics of fluvial to estuarine deposits of the Early Cretaceous net-transgressive succession of the Western Interior Basin in the USAto better understand controls on deposition and preservation across foreland basin depozones through time. Outcrop data, virtual outcrop models and satellite imagery were used to develop facies and architectural schemes, delineate palaeotopographic highs, track downstream changes (laterally) and variation through time (vertically) for the Valanginian to Cenomanian Cedar Mountain and Naturita formations of east-central Utah. Fluvial channel bodies of the Cedar Mountain Formation share characteristics of modern-day sinuous single-thread distributive fluvial systems such aslateral channel migration that decreases downstream, a reduction in sinuosity,and a decrease in grain size. For the basal Cedar Mountain Formation, net sandstone to gross (100% to 38%) and degree of channel body amalgamation also decrease downstream. Channel bodies are arranged in multi-storeyand multilateral architectures with isolated channel bodies in the distal portion of the system. A meandering fluvial planform of varying sinuosities dominatesboth spatially and temporally. Palaeoflow was transverse or oblique to the basin axisand distributive fluvial systems terminated inan axial system near the eastern edge of Utah. Estuarine deposits of the Naturita Formation are tide-dominated deposits composed of tidally-influenced fluvial deposits at the base with overlying subtidal to intertidal deposits. Supratidal and coastal plain deposits are present in the uppermost portions of the outcrop and the succession is capped with localized beds of shells and pebbles and widespread deposits of marine mudstone of the Tununk Shale Member of the Mancos Shale. Estuarine deposits are limited in geographic extent by the presence of palaeotopography on the developing forebulge.

Pre-vegetation alluvium is unique; at the present day, plants affect multiple aspects of river functioning and deposition and so those rivers that operated before the evolution of land plants largely lack modern sedimentological analogue. However, such rivers were the norm for the first 90% of Earth history and so a better understanding of their sedimentary product enables insight into both the fundamental underlying mechanisms of river behaviour and the ways in which fluvial processes operated on ancient Earth and other rocky planets. This study presents five original fieldwork based case studies and an analysis of a holistic database of all of Earth’s pre-vegetation alluvium. Together these research strands offer perspectives on the sedimentological characteristics and stratigraphic trends of pre-vegetation alluvium and the behaviour and functioning of pre-vegetation rivers. Results show that, in pre-vegetation alluvial settings: 1) a variety of fluvial styles are represented, but diminished in comparison with syn-vegetation alluvium; 2) ‘sheet-braided’ architectures are common but may record a variety of fluvial planforms; 3) meandering planforms were less frequent, particularly in small- to moderate-sized river systems; 4) mudrock is on average 1.4 orders of magnitude less common than it is in syn-vegetation alluvium; and 5) microbial matgrounds were present, but had negligible effect on preserved architecture and facies. This thesis demonstrates that whilst the physical laws governing fluvial fluid-sediment interaction have not changed, the theatre in which they operated irrevocably evolved with the greening of the continents.

Red-bed alluvial systems are becoming increasingly important as hydrocarbon plays in the UK Northern North Sea. Commonly such ephemeral systems are hard to define in terms of reservoir architecture, due to the difficulty in correlating such diverse and palaeontologically-barren sequences. This project aims to improve understanding of one such system, the Late Jurassic Cormorant Formation, of the Northern North Sea, through detailed sedimentological study of two outcrop analogues. The whole-rock trace element geochemical correlation technique in a variety of settings. The Lower Old Red Sandstone Moor Cliffs Formation of the Anglo-Welsh Basin provides ideal conditions for testing the whole-rock trace element geochemical correlation technique. The Moor Cliffs Formation is a low net:gross alluvial red bed suite, which by virtue of Variscan deformation, outcrops in a well-exposed, easily accessible cliff section at Priests Nose, near Manorbier, Pembrokeshire. A 100m section was sampled to determine variables that may affect whole-rock trace element geochemical correlation. The results prove that whole-rock trace element geochemical correlation can be applied to alluvial successions, despite pedogenic modification and deep burial. The Late Triassic Blomidon Formation of the Fundy Basin, Nova Scotia, provided a second outcrop example of an alluvial red-bed sequence, which was deposited in similar palaeo-climatic and tectonic conditions to the Northem North Sea Triassic. The Blomidon Formation contained a range of fluvial styles from confined channels to unconfined sheetfloods. Three sections were studied along the hanging-wall margin of the Fundy Basin, separated by up to 150km along strike. Each section provided a contrasting basinal setting, allowing comparison of facies along strike and down depositional dip. Sections were measured in detail to quantify bed geometries and facies variants, facilitating architectural analysis. Specific attention was paid to features that may be diagnostic in sub-surface cored sections of the Northern North Sea Triassic. Correlation was possible on a number of scales, using laterally continuous ephemeral marker beds within the Blomidon Formation. Detailed facies evaluation has allowed the division of the Blomidon Formation into four distinctive facies packages that vary considerably in sandstone net:gross. Each facies assemblage is defined by variations in fluvial style and occurrence of evaporite rich, ephemeral lacustrine and rare aeolian sediments. It was possible to produce a broad, basin-wide correlation scheme for the Blomidon Formation, based on these four facies packages. Detailed facies analysis of three cores from the Cormorant Formation, Tem Field, Northern North Sea allowed definition of reservoir architecture, based on models derived from outcrop analogues. The results suggest that correlation based on individual horizons and facies packages is possible in alluvial red-bed sequences through detailed sedimentological study. The whole-rock trace element geochemical correlation technique can also provide additional datasets to enhance correlation in the subsurface.

Understanding hydraulic connectivity and groundwater mixing is vital to the preservation of global groundwater resources and the long-term sustainability of groundwater systems. The globally expanding unconventional gas industry has resulted in concerns regarding the occurrence of methane (CH4) in groundwater and its impact on overall groundwater quality. Globally, much of the concern regarding the impact of gas production on neighbouring and overlying aquifers used to supply groundwater to other industry involves the upward migration of CH4 from underlying formations targeted for gas extraction. Using an integrated biogeochemical and environmental tracer approach this thesis aims to constrain CH4 source attribution, map migration pathways and characterise groundwater mixing in two economically important alluvial aquifers that provide groundwater to multiple industries in eastern Australia. The Condamine Catchment in south-east Queensland (Qld) and the Lower Namoi Catchment in north-west New South Wales (NSW) are both stressed alluvial aquifers that are used extensively to supply water for irrigated agriculture, stock and domestic use. In addition, both catchments are in varying stages of coal seam gas (CSG) development and production, which has introduced uncertainty regarding the potential impact of this development on adjacent and underlying groundwater resources. Major ion chemistry, radioactive isotopic tracers and microbiological community analyses are used with CH4 concentration and isotopic results to constrain the source of CH4 in both study areas and illustrate the utility of using an integrated approach for assessing groundwater mixing. The results presented in this thesis show that the presence of CH4 in groundwater is highly variable and dependent on the biogeochemical conditions, making source attribution using CH4 data alone difficult. The major ion and isotopic tracer data elucidate groundwater movement and mixing, whilst the microbiological analyses offer robust evidence for or against the in situ production of CH4. Thus, the biogeochemical results from both catchments significantly enhance the ability to constrain the source of CH4 in the alluvial groundwater and the impact of production, degradation and migration processes on its occurrence.

Numerous studies suggest that denitrification in riparian zones removes nitrogen from groundwater as it moves from terrestrial to aquatic ecosystems. However, removal rates vary widely among sites complicating the incorporation of riparian zones into models of nitrogen movement across landscapes. Because denitrification in the riparian subsurface is often limited by the supply of microbially-available carbon, explaining how and why carbon supply varies among riparian zones using mappable landscape attributes holds practical and theoretical appeal. First principles suggest three carbon sources for subsurface microbes: (1) dissolved organic carbon leached from surface soils; (2) deep plant roots; and (3) buried, carbon-rich soil horizons deposited long ago. Working in Rhode Island USA at riparian zones mapped as outwash and alluvium, I investigated the relative importance of different carbon sources to 3 meters depth. Field and laboratory experiments showed that both roots and buried horizons can supply carbon in the shallow subsurface (40-75 cm), but that buried horizons dominate below 75 cm. Radiocarbon dates and results from ingrowth cores showed that roots 40-75 centimeters deep grow and decompose on decadal time scales and form patches of organic matter that may influence nitrogen removal from groundwater. However, in both alluvial and outwash profiles, most roots below 80 cm are relics (usually > 140 years old) and therefore do not act as direct carbon conduits between the surface and deep subsurface. Laboratory incubations of buried soils from many sites demonstrated that high rates of carbon mineralization associated with these soils are common. In-situ groundwater incubations and 14C dating demonstrated that metabolism of ancient carbon constitutes at least 31% of total carbon mineralization >2 meters below the surface at some sites. My results suggest that: (1) the depth of the biologically active zone extends as deep as buried horizons; (2) on outwash and alluvium the riparian surface and subsurface are largely decoupled on time scales of months to years; (3) functional classifications of riparian zones intended to support management need to include buried horizons and recognize the limited influence of surface vegetation on subsurface biogeochemistry over short time frames.

Terrace deposits along a 40 mile segment of the Colorado River between Austin and Bastrop, Texas, are mapped in detail. The following deposits have been delineated (lowest to highest): Floodplain, Sixth Street Terrace, Montopolis Terrace, Capitol Terrace, Hornsby Terrace, Asylum Terrace, and Delaney Terrace. The Hornsby Terrace deposits and the Montopolis Terrace deposits were previously unrecognized. A program of mechanical analysis was conducted on samples taken from the terrace deposits and the floodplain. Cumulative frequency curves of grain size from five samples collected up to 15 miles apart from the Asylum Terrace gravel, are distinctively grouped--different from all other samples. Cumulative frequency curves from five samples from the Hornsby Terrace gravel also plot in a close grouping distinct from other samples. Over short distances where abrasion is not a dominant factor it seems that grain size distribution may be useful as a means of correlation of terrace remnants. Analysis of the lithologies of these samples indicate that the Hornsby, Asylum and Delaney Terrace gravels are practically without limestone clasts, in a drainage basin that is, presently, composed dominantly of limestone. This suggests that the Commanche Series in the Edwards Plateau region was not extensively exposed but was covered by the Gulf Series at the time of the formation of these terraces. The Manor lag gravel, an upland gravel in the thesis area, is thought to be the remnant of a high terrace deposit of the Colorado River. All terrace gravels except the Capitol and Montopolis Terrace gravels are thought to be the result of lateral planation by a stream at or near grade. The Montopolis and Capitol Terrace gravels are thought to be the result of a lengthy episode of lateral planation by the Colorado River accompanied by slow degradation.