Ron Boyd

Bio: Ron Boyd is an academic researcher from University of Newcastle. The author has contributed to research in topics: Continental shelf & River delta. The author has an hindex of 30, co-authored 78 publications receiving 5361 citations. Previous affiliations of Ron Boyd include ConocoPhillips & Newcastle University.

Estuarine facies models; conceptual basis and stratigraphic implications

Abstract: The nature and organization of facies within incised-valley estuaries is controlled by the interplay between marine processes (waves and tides), which generally decrease in intensity up-estuary, and fluvial processes, which decrease in strength down-estuary. All estuaries ideally possess a three-fold (tripartite) structure: an outer, marine-dominated portion where the net bedload transport is headward; a relatively low-energy central zone where there is net bedload convergence; and an inner, river-dominated (but marine-influenced) part where the net transport is seaward. These three zones are not equally developed in all estuaries because of such factors as sediment availability, coastal zone gradient and the stage of estuary evolution. Two distinct but intergradational types of estuaries (wave- and tide-dominated) are recognized on the basis of the dominant marine process. Wave-dominated estuaries typically possess a well-defined tripartite zonation: a marine sand body comprised of barrier, washover, tidal inlet and tidal delta deposits; a fine-grained (generally muddy) central basin; and a bay-head delta that experiences tidal and/or salt-water influence. The marine sand body in tide-dominated estuaries consists of elongate sand bars and broad sand flats that pass headward into a low-sinuosity ("straight") single channel; net sand transport is headward in these areas. The equivalent of the central basin consists of a zone of tight meanders where bedload transport by flood-tidal and river currents is equal in the long term, while the inner, river-dominated zone has a single, low-sinuosity ("straight") channel. These facies models and their conceptual basis provide a practical means of highlighting the differences and similarities between estuaries. They also allow the predication of the stratigraphy of estuarine deposits within a sequence-stratigraphic context.

Transgressive Depositional Systems of the Mississippi Delta Plain: A Model for Barrier Shoreline and Shelf Sand Development

Abstract: Depositional sequences generated in the Mississippi River delta plain consist of a regressive and a transgressive component. The transgressive component has been considerably less studied but accounts for the majority of the surface area on the lower Mississippi River delta plain and up to 50 percent of the total sequence thickness in shallow-water deltas. The development and preservation of transgressive depositional systems in abandoned delta complexes follows the process of transgressive submergence in which the horizontal component of reworking occurs during shoreface retreat, combined with a vertical component of submergence acting to preserve the sequence. The evolution of transgressive depositional systems in each of the abandoned Holocene Mississippi River delta complex s can be summarized in a three-stage model beginning with stage 1, an erosional headland and flanking barriers. In this stage, regressive sand deposits contained within abandoned deltaic headlands are reworked by the eroding shoreface and dispersed longshore into contiguous flanking barriers enclosing restricted interdistributary bays. Submergence of the delta plain during relative sea-level rise generates an intradeltaic lagoon separating the former stage 1 sand body from the shoreline, forming stage 2, a transgressive barrier island arc. The landward-migrating barrier island arc is unable to keep pace with relative sea-level rise and the retreating mainland shoreline, resulting in submergence and the formation of stage 3, an inner-shelf shoal. Following submergence the former barrier island arc sand body continues to be reworked into a marine sand body on the inner continental shelf during stage 3. This sequence of coastal evolution provides direct evidence of barrier island formation, with each stage producing a distinctive stratigraphic signature. The current sea-level-rise models of shoreface retreat and in-place drowning developed for the U.S. Atlantic continental shelf do not adequately explain either the morphology or the stratigraphy of transgressive Mississippi River delta sand bodies. Current models of Mississippi deltaic stratigraphy emphasize the deep-water, artificially maintained Balize delta, which differs considerably from the shallow-water, shelf-phase delta complexes that are the primary depositional constituents of he Holocene Mississippi River delta plain.

Incised-valley systems : origin and sedimentary sequences

Abstract: Incised-Valley Systems: Origin and Sedimentary Sequences - Incised valleys were not widely recognized prior to the 1980?s. Most early workers forced the isolated, incised-valley deposits along an uncomformity into a single continuous unit, ignored them by including them within larger stratigraphic units, or interpreted them as deltaic distributaries or non-incised fluvial channels. In the last decade, intense interest in the influence that changes in accommodation space have on stratigraphic organization has focused attention on incised-valley systems, because they are one of the most visible records of major decreases in accommodation. In practical terms, they are also a significant key to the identification of sequence-bounding uncomformities. As a result, many successions have been re-examined and incised-valley fills are being found in rapidly growing numbers. This volume is an outgrowth of this widespread interest in incised-valley sedimentation. Many of the papers were initially presented at the Special Session on ?Recognition and Facies of Incised Valley Fills? held at the AAPG-SEPM Annual Meeting (Calgary) in June, 1992.

Fluvial responses to climate and sea‐level change: a review and look forward

Abstract: Summary Fluvial landforms and deposits provide one of the most readily studied Quaternary continental records, and alluvial strata represent an important component in most ancient continental interior and continental margin successions. Moreover, studies of the long-term dynamics of fluvial systems and their responses to external or ‘allogenic' controls, can play important roles in research concerning both global change and sequence-stratigraphy, as well as in studies of the dynamic interactions between tectonic activity and surface processes. These themes were energized in the final decades of the twentieth century, and may become increasingly important in the first decades of this millennium. This review paper provides a historical perspective on the development of ideas in the fields of geomorphology/Quaternary geology vs. sedimentary geology, and then summarizes key processes that operate to produce alluvial stratigraphic records over time-scales of 103−106 years. Of particular interest are changes in discharge regimes, sediment supply and sediment storage en route from source terrains to sedimentary basins, as well as changes in sea-level and the concept of accommodation. Late Quaternary stratigraphic records from the Loire (France), Mississippi (USA), Colorado (Texas, USA) and Rhine–Meuse (The Netherlands) Rivers are used to illustrate the influences of climate change on continental interior rivers, as well as the influence of interacting climate and sea-level change on continental margin systems. The paper concludes with a look forward to a bright future for studies of fluvial response to climate and sea-level change. At present, empirical field-based research on fluvial response to climate and sea-level change lags behind: (a) the global change community's understanding of the magnitude and frequency of climate and sea-level change; (b) the sequence-stratigraphic community's desire to interpret climate and, especially, sea-level change as forcing mechanisms; and (c) the modelling community's ability to generate numerical and physical models of surface processes and their stratigraphic results. A major challenge for the future is to catch up, which will require the development of more detailed and sophisticated Quaternary stratigraphic, sedimentological and geochronological frameworks in a variety of continental interior and continental margin settings. There is a particular need for studies that seek to document fluvial responses to allogenic forcing over both shorter (102−103 years) and longer (104−106 years) time-scales than has commonly been the case to date, as well as in larger river systems, from source to sink. Studies of Quaternary systems in depositional basin settings are especially critical because they can provide realistic analogues for interpretation of the pre-Quaternary rock record.

Spatial patterns of plastic debris along Estuarine shorelines.

Abstract: The human population generates vast quantities of waste material. Macro (>1 mm) and microscopic (<1 mm) fragments of plastic debris represent a substantial contamination problem. Here, we test hypotheses about the influence of wind and depositional regime on spatial patterns of micro- and macro-plastic debris within the Tamar Estuary, UK. Debris was identified to the type of polymer using Fourier-transform infrared spectroscopy (FT-IR) and categorized according to density. In terms of abundance, microplastic accounted for 65% of debris recorded and mainly comprised polyvinylchloride, polyester, and polyamide. Generally, there were greater quantities of plastic at downwind sites. For macroplastic, there were clear patterns of distribution for less dense items, while for microplastic debris, clear patterns were for denser material. Small particles of sediment and plastic are both likely to settle slowly from the water-column and are likely to be transported by the flow of water and be deposited in areas whe...

Drowning of the Mississippi Delta due to insufficient sediment supply and global sea-level rise

Abstract: Global sea-level rise, reduced sediment supply and subsidence threaten the stability of the Mississippi Delta. Calculations of riverine sediment load and storage indicate that 10,000–13,500 km2 of the delta could be submerged by AD 2100.