Many studies have focused on hydrological and geochemical fluxes from land to the ocean via groundwater discharge, however few have assessed groundwater flow in deltaic settings. Hydrological budgets indicate that 1,000 to 5,000 m3s-1 of water flow from the Mississippi River (MR) to its delta (MRD) via subterranean pathways, however the spatial and geological controls on these processes are less known. This study suggests that deltaic lithofacies of paleoenvironments related to the delta cycle allow for groundwater to discharge out of the MR main channel and into the MRD through organic sediment-rich and silt-sand overbank and mouth bar facies. This study employs geophysical data, including chirp sonar subbottom profiling and continuous resistivity profiling (CRP), to detect the location of these sediments in Barataria Bay, a coastal bay located in the MRD. Chirp data indicate paleochannel features in the MRD, whereas CRP data indicate freshwater seepage into MRD embayments during high river stage events. Analyses of bulk properties of sediment cores are used to characterize delta facies sediments and determine variability in hydraulic conductivity values, which range from 10-7 to 10-2 ms-1. These geophysical and sediment core data show the potential for groundwater flux through deltaic sediments, and will contextualize geochemical tracer data collected by project collaborators. Results indicate that groundwater discharge in the MRD is directly controlled by the geological constraints of the delta region. These results illustrate the potential for substantial groundwater fluxes in other large river deltas, and present implications for urban and coastal infrastructure planning, as many large global deltas sustain significant populations. / 1 / Alexander M Breaux

No description available.

No description available.

Diagenesis is the sum of those processes whereby an originally sedimentary assemblage attempts to reach and maintain an equilibrium with its environment. Numerous factors influence and affect the diagenesis of sedimentary elastic assemblages - fundamentally unstable when deposited but never reaching equilibrium ith their environment. The interrelationship of these factors, however, precludes the identification of any single factor as wholly controlling the diagenesis of elastic sediments. The multifactorial nature of diagenesis is illustrated here by reference to the Middle Jurassic Dogger Formation and Ravenscar Group which outcrop on the North Yorkshire Moors and the Brent Group from Wells 3/3-1, -2, and -3 in the Ninian Field, and 210/15-2, also in the Northern North Sea.The Ravenscar Group is interpreted as being deposited in a fluvio-deltaic complex. Here, attempted equilibration of non-marine sediments with their pore waters resulted in a variety of diagenetic modifications. These are interpreted as being influenced strongly by bacterial degradation of organic matter, which lowered pH and then reduced Eh. This reduction of pH caused feldspar dissolution and muscovite neomorphosis to kandites throughout. Similarly, in the texturally and inineralogically mature sandbodies, quartz overgrowths and veriniform kandites precipitated from oxygenated pore waters, whilst chlorite and overgrowths formed in anoxic pore waters. This resulted in complete reduction of porosity in, and cementation of, finer and texturally less mature overbank sands. Conversely, channel sands were cemented into rigid but porous quartzose frameworks. In addition, soil horizons of sphaerosiderite developed as standing water on the floodplains stagnated. Bacterial ferric iron reduction throughout the water table then raised the pH and extensive siderite cements were precipitated. During burial, calcium carbonate saturated formation waters migrated into the remaining porous sandbodies and precipitated replacive ferroan calcite. In marine elastics, meanwhile, illite and potassium-feldspar overgrowths precipitated before in situ bacterial processes lowered pH here also. This resulted in dissolution of feldspars, muscovite neomorphism and precipitation of vermiform kandites. Subsequently, pH rose and ferroan calcite cementation occurred.It is suggested that "aggressive fluids" migrated into the larger connected sandbodies during burial. They dissolved the carbonate cements and precipitated dense pockets of blocky kandites. These sediments were little affected during continued burial. However, their Recent weathering may have dissolved carbonates and feldspars as well as neomorphosing chlorite to vermiculite.The reservoir rocks of the Ninian Field have formed from mature quartz-rich elastic sediments which accumulated in a transgressive sequence above Liassic mudrocks which was subsequently incised into by a fluvial system. Diagenetic modifications of the original sediments are similar to those of the Ravenscar Group, although neither chlorite nor soil horizons were observed in the wholly non-marine sediments. Porosity in marine sediments is occluded by extensive authigenic illite within a generally quartz framework. The effects of the fresh water table are also seen in the marine sediments over which the delta prograded. Then, during burial, ferroan calcite cementation and subsequent leaching and blocky kandite precipitation occurred here also. Hydrocarbon maturation and migration into the reservoir was preceded by alteration of pre-existing carbonates to ankerite, and. minor illitisation of blocky kandites. However, the only effort which can be related to oil emplacement is the widespread pyritisation around the oil-water contact.The sandstones from 210/15-2 are interpreted as formed from coarse elastic sediments which accumulated in a shallow-marine nearshore environment, possibly incised into by distributary channels. Initial marine connate water precipitated potassium-feldspar overgrowths before bacterial processes lowered pH and caused widespread kandite formation. Subsequently, these sediments were affected by ferroan calcite cementation, then leaching and blocky kandite precipitation. Although oil has migrated into these sediments, no other effects were observed.In addition to the factors which have been proposed previously as influencing diagenesis, I should like to propose that the climate of both the source area and of the depositional basin was of fundamental importance to diagenesis and many of the features observed in these rocks may be related to the original tropical climate. Moreover, as a result of the fundamental stability of the quartzose frameworks established during eogenesis, this climatic "finger print" may be recognised in all these sediments despite their subsequent diverse history.

The Cambrian clastic sediments of northwest Scotland crop-out along the line of the Moine Thrust Zone between Skye in the south and Loch Eriboll in the north and form the basal 250m of a broadly transgressive Cambro-Ordovician sequence of clastic and carbonate sediments. These sediments were deposited on the passive western margin of the lapetus Ocean. The clastic stratigraphy consists of four members; the Lower Member, Pipe Rock, Fucoid Beds and Salterella Grit. The Lower Member consists of 100-125m of mature, cross-bedded quartzarenites which have been subdivided into three facies associations. The lowest association is a 10m thick series of cross-bedded channel sands interpreted as mesotidal barrier inlet deposits. This association is erosively overlain by 10m of thinly bedded, cross-bedded and parallel laminated sands interpreted as lower shoreface sediments. The remainder of the Lower Member comprises compound cross-bedded cosets 1-10m thick interpreted as tidal sandwave deposits. The sudden appearance of numerous Skolithos burrows at the Lower Member-Pipe Rock boundary is interpreted as an evolutionary event representing the colonisation of the Cambrian shelf by suspension feeding annelids. The Pipe Rock is an 85-100m thick sequence of mature, highly burrowed quartzarenites considered to have been deposited in a tidal shelf to outer shelf tempestite setting. The Fucoid Beds consists of 20m of a mixed clastic-carbonate sequence of thinly bedded wave rippled tempestites interbedded with fairweather echinoderm grainstones. The Salterella Grit is a 0-15m thick coarsening upwards sequence of muds and quartzarenites interpreted as having been deposited as tidal sandridges which went through active and moribund stages of development before being buried under carbonate platform sediments. The dominant controls on the facies developed in this sequence were thermal subsidence, eustatic sea level rise and tidal resonant effects. Two rapid shallowing events, in the middle of the Pipe Rock and at the top of the Fucoid Beds, may have been produced by variations in the spreading rate of the lapetus Ocean.

No description available.

The Scarborough Formation is the youngest marine horizon of formation status within the dominantly deltaic Aalenian - Bajocian Ravenscar Group, Cleveland Basin, northeast England. Sedimentary facies analysis has been performed on the three conformable lithostratigraphic units which make up the bulk of the Scarborough Formation outcrop: Blea Wyke, Byland Limestone and Crinoid Grit Members. This form of analysis was performed in an effort to determine the depositional environments of the members. The information derived from the study enables one to trace the palaeogeographic evolution of the Cleveland Basin throughout much of Scarborough Formation times.The clastic Blea Wyke Member [6 facies] is attributed to deposition in a shallow [<4m], essentially microtidal,delta-destructive marine embayment. This embayment formed through non-eustatic marine transgression initiated by the compactional subsidence of an abandoned [Gristhorpe Member] delta lobe. Open to the east, the embayment covered some 2000km2 of the Cleveland Basin when fully established. A range of sand bodies evolved on the silty embayment floor in response to spatial and temporal changes in the wind-forced wave and current regime. These sand bodies included subtidal shoals, laterally extensive storm-emplaced sand blankets, and a classic delta-destructive sheet sand formed through the landward translation of a low-profile barrier bar.Under sustained rate-of-subsidence controlled marine transgression, clastic input to the Blea Wyke Member embayment eventually waned. In response, the overlying Byland Limestone Member [6 facies] was deposited in the western part of the Cleveland Basin in the form of a carbonate-dominated lagoon-barrier-inner shelf complex. The barrier component of the complex evolved through transgressive upward-shoaling under the influence of wind-forced wave and current activity. Composed of pellet lime grainstones, it protected a lagoon within which the dominant deposits were pellet lime mudstones, wackestones and packstones. Lithological and faunal similarities between the lagoon and inner shelf suggest that much of the shelf region may have comprised former back-barrier lagoon-fills exhumed during transgression.Byland Limestone Member times were terminated by an acceleration in the rate of marine transgression followed by tectonic uplift and subsequent geomorphic decay of the major landmass to the north [Mid North Sea High]. Transgression generated an east-west orientated epeiric seaway connecting the Sole Pit Trough with an areally restricted Pennine Massif. Within this seaway, clastic sediment derived chiefly from the Mid North Sea High was deposited in the form of a progradational, regional-scale composite sheet sand body: the Crinoid Grit Member [8 facies]. Deposition occurred under the combined influence of tidal currents, wind-forced currents and wave activity. Three main facies belts are recognised: paralic tidal sandwave complex, storm-dominated inner shelf and sandy middle shelf. The presence of a tidal sandwave complex is particularly interesting; it indicates that the forging of a marine connection to the west of the Cleveland Basin was necessary before tidal cyclicity could become prominent within the basin.

This thesis is an attempt to combine a number of different approaches as part of a wider attempt to re-interpret the late Quaternary history of the Vale of Pickering and Northern Wolds in Yorkshire. This involved the critical analysis of part evidence together with the collation and interpretation of data from a variety of sources, some published, some unpublished but mostly from field work.The course of the research followed a number of different lines. The first of these was to study the sedimentary data from glacial and pro-glacial deposits in the Vale of Pickering to assess their age and environment of deposition. The sediments were mapped in the field and analysed in the laboratory. A glacial outwash rather than lake-beach origin was proved for an important group of these sediments. The sedimentary data from the Vale of Pickering showed that ice had undoubtedly advanced further into the area than had been envisaged by Kendall at the turn of the century. - this was supported independently by geomorphological evidence and more sedimentary data from the northern Yorkshire Wolds escarpment. In the western end of the Vale, a thicker lobe of ice than that supposed by Kendall seems to have advanced into the area from the Vale of York, but its furthest limits cannot be shown from data available at the moment.On the Yorkshire Wolds an attempt was made to delineate the advance of the Late Quaternary ice, but unfortunately the data was so poor that no firm limits could be drawn. Glacial outwash sediments were found at several scattered sites and compared with those found in the Vale, some similarity was proved, suggesting that meltwater from late Quaternary glaciers had flowed across the Wolds and that ice from the Vale had overtopped the Wolds scarp along much of its length. The soils were analysed and found to have a higher blown sand content than suspected previously. The blown sand content increased towards the northwest, suggesting a probable glacial outwash source.The dry valleys were studied and new light shed on the processes which may have contributed to their formation. In addition evidence of periglacial evidence from the whole region was collected, described and assessed. Finally it was found that the structural lines of disturbance which traverse the chalk of the northern Wolds could easily be mapped from aerial photographs. These were mapped and included in the thesis as a small contribution to the solid geology of the area, even though they only impinge indirectly upon the main scope of this study.

The paucity of polliniferous deposits on the British chalklands has left something of a vacuum in the known vegetational history of the British Isles. Conflicting ideas of the past landscape of the chalklands have been presented by archaeologists (e.g. Clark, 1936) and botanists (e.g. Tansley, 1939; Pigott and Walters, 1954). The Tansleyan view, i.e. that the chalklands were forested until the Bronze Age, has held sway. Tansley suggested that the dominant species were Quercus and Fraxinus. This was challenged by the view that Tilia may have been a dominant on basic soils (Merton, 1970). Such palaeoecological evidence as exists would suggest that woodlands covered the southern chalklands prior to Bronze Age disturbance, thus vindicating the Tansleyan school.In this thesis data from a site lying on the Yorkshire Wolds are presented. For the first time a broad spectrum of palaeoecological information is presented from a British Flandrian chalkland deposit. Pollen, bryophytes, plant propagules and macrofossil remains, mollusc and insect data form the basis for an environmental reconstruction of the major water catchment area of the Yorkshire Wolds.This is complemented by a study of modern analogue sites where a vegetation survey had been undertaken. Plant propagules, molluscs and bryophytes from the surface soil and modern pollen rain (trapped over a one year period) were collected from each site. These data were incorporated into statistical analyses to compare the changes in the fossil data with the range of known analogue habitats (after Lamb, 1984).Willow Garth, an ancient carr woodland in the Great Wold Valley, yielded fossil-rich deposits from the late-glacial and Flandrian periods. Although the sedimentary history of this site would appear to be incomplete, an exceptionally detailed image of the palaeoecological history of this valley emerges. The transition from the late-glacial fen and tundra to the Pre-Boreal forest occurred at c. 9200 B.P.. However, the progression towards the mixed woodland of the Boreal forests appears to have been interrupted by the activities of Mesolithic man. It is suggested that Mesolithic hunter-gatherers were 'managing' the woodlands to maximise the carrying capacity of their game. One consequence of this activity was to prevent the forest canopy from closing over the chalk grassland. Calcicolous grassland species were present throughout this period suggesting that the local chalk grassland may never have been totally shaded out. If this was the case the chalk grasslands around the Great Wold Valley would be of considerably greater antiquity than is generally supposed.During the late-Neolithic and the Bronze Age there is abundant evidence of anthropogenic disturbance with the presence of agricultural weed taxa and pollen of Cerealia. Chalk grassland species are also represented in both the faunal and floral records from this period. Cattle probably grazed the fen and the local wetland flora reached a peak of diversity. In early Saxon times the fen started to dry out and it is suggested that its land use may have changed from a grazed fen to an osier bed at c. 1200 B.P.

The Penrith Sandstone and brockrams (breccio-conglomerates) are continental red-beds of Lower Permian and Permo-Triassic ages respectively. The brockrams are predominantly the deposits of coalescing alluvial fans which accumulated as the products of subaerial sheetflood, transitional debris flow and braided river processes at the margins of desert basins bordering the upstanding Lake District. The fans were deposited on an irregular topography which is demonstrated to have a probable minimum preburial relief of 250 to 300 metres in west Cumbria. The cross-stratified Penrith Sandstone of the Eden Valley accumulated as the foresets of large scale (up to 100 metres width) aeolian dunes orientated in response to a uniform east-south-easterly palaeowind. Dune-bedding within these deposits indicates a crescentic-downwind (barchanoid) configuration for the dune slipfaces. The stratigraphic unit termed the 'Upper Brockram' is believed to represent the deposits of ephemeral streams (arroyos) which flowed through and reworked part of the aeolian sand sea of the Penrith Sandstone. Nodular carbonate profiles occurring within sandstone/siltstone horizons intercalated with distal alluvial fan deposits in west Cumbria are interpreted as immature caliche soil horizons and represent periods of surface stability (non-deposition) of indeterminate length. Petrographic evidence indicates the most important process of formation to have been that of replacement of the detrital quartz component by microcrystalline non-ferroan calcite. Extensive post-depositional (diagenetic) modification to the mineralogy and texture of the brockrams of west Cumbria has resulted from the mechanical infiltration of clay, the dissolution of the less stable detrital components (primarily volcanic clasts), replacement by secondary clay and the precipitation of interstitial and void-filling authigenic clay, a hydrated haematite precursor mineral, ferroan and non-ferroan calcite and gypsum. Most reactions are considered to have occurred as stages within an evolving diagenetic sequence.