Earth Sciences Research Collection

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Now showing 1 - 5 of 112
  • Publication
    Flow transformations, Mud Partitioning, and the Variable Stratigraphic Architecture of Basin-Floor Fan Fringes
    Highly efficient sediment gravity flows can bypass mid-fan channels and lobes and deposit significant volumes of sand, mud, and particulate organic matter in outer-fan and basin-plain settings. The Serpukhovian to Bashkirian fill in the Shannon Basin, western Ireland, includes deep-water fan deposits (Ross Sandstone Fm) that gradationally overlie basin-floor shales (Clare Shale Fm). As part of a broader progradational succession, the upward transition from muddy basin floor to sandy fan preserves the stacked deposits of settings present prior to, and outboard of, mid-fan channels and lobes. Three fully cored boreholes and associated wireline data constrain the facies tracts in an 18-km-long panel oriented oblique to original depositional dip. Two distal successions dominated by hybrid event beds (HEBs) are recognized, separated by a prominent condensed section. The lower Cos-heen system includes m-thick, tabular HEBs with prominent linked debrites that pass down dip into much thinner sandstones overlain by sand-speckled mudstone caps that thicken distally before thinning. The latter are interpreted as secondary mudflows released following reconstitution of more thoroughly mixed sections of the up-dip linked debrites. Significant bypass and accumulation of mud by this mechanism helped heal local topography and maintain a relatively flat sea floor, promoting an overall tabular geometry for the deposits of larger volume hybrid flows reaching the distal sector of the basin. The overlying distal Ross system fringe is characterized by very fine- to fine-grained sandstones and is lateral to compensationally stacked lobes farther to the west. It has a progradational (at least initially) stacking pattern, facies transitions developed over shorter length scales, and includes outsized event beds, but these are thinner than those in the Cosheen system. Common banding and evidence for turbulence suppression by dispersed clay rather than entrained mud clasts indicate that these were transitional flows. In this case, event beds are inferred to taper distally, with significant mud emplaced by plug flow retained as caps to sandy event beds rather than bypassing down-dip. Different flow transformation mechanisms thus impacted how mud was partitioned across the fringe of the two systems, and this influenced bed geometries, larger scale bed stacking patterns, and stratigraphy. Whereas the flow-efficiency concept stresses the ability of flows to carry sand in a basinward direction, it is also imperative to consider the variable efficiency of mud transport given the operation of clay-induced flow transformations. These can either promote bypass or trigger premature fallout of mud, with implications for how systems fill accommodation, bed-scale facies transitions, and the burial and preservation of particulate organic carbon fractionated along with the clay in deep-water system fringes.
  • Publication
    Examples of fault steps controlling event migration in seismic swarms
    (Society of Exploration Geophysicists, 2022) ; ;
    This study provides spatiotemporal constraints on seismicity within fault zones and identifies key links between fault step and event migration. We show that event distributions in seismic swarms can image stepping geometries reminiscent of relay zones commonly observed along fault zones. Earthquake migration can propagate across steps, indicating a transfer of deformation, but can be obstructed by others. Preliminary quantitative results show that whether a step transfers or blocks deformation depends on the separation between the bounding segments relative to the maximum magnitude of the events. These findings support the importance of understanding the role of internal fault geometry on seismicity and show that high accuracy event locations provide a critical understanding of seismicity.
  • Publication
    An Overview of Deep Geothermal Energy and Its Potential on the Island of Ireland
    This paper provides a short overview of geothermal energy, including a discussion on the key geological controls on heat distribution in the subsurface, and on the different types of geothermal resource and their potential uses. We then discuss the island of Ireland as an example of the role that geothermal energy can play in decarbonising the heat sector in a region characterised by relatively low-enthalpy (temperature) resources. Significant shallow geothermal potential exists across the island via the deployment of ground source heat pumps. The geology of onshore Ireland provides relatively limited potential for deep hydrothermal aquifers with primary porosity and permeability. Therefore, deep geothermal exploration on the island is likely to be focused on fractured carbonate reservoirs of Carboniferous age, with recorded groundwater temperatures reaching 38°C at 1 km depth, or on lower permeability petrothermal reservoirs developed as Enhanced or Advanced Geothermal Systems. The exception to this occurs within Mesozoic basins in Northern Ireland where porous and permeable Permo-Triassic sandstones are preserved beneath Paleogene basalts. Geothermal potential also exists in equivalent basins immediately offshore Ireland. For example, Triassic sandstones within the Kish Bank Basin, a few kilometres off the coast of Dublin, have estimated reservoir temperatures of 20–120°C across the basin.
      126Scopus© Citations 2
  • Publication
    The Stratigraphic Nomenclature of the Irish Offshore Basins
    (Department of the Environment, Climate and Communications, 2021-07-14) ; ;
    Over 50 years of research and exploration in the Irish offshore have provided a vast archive of geological and geophysical information from which the geological evolution of the region has been pieced together. A total of 161 exploration and appraisal wells, a significant number of development wells and a small number of important shallower boreholes have been drilled, while a very large volume of 2D and 3D seismic data has been acquired across the Irish offshore. In addition, a number of important regional wide-angle seismic reflection and refraction profiles have helped constrain the deep crustal structure and controls on the main basins. The history of exploration has been summarised in various publications, including Naylor & Shannon (2011) and Shannon (2018).
  • Publication
    The Standard Stratigraphic Nomenclature of Offshore Ireland
    (Government of Ireland, 2018-11-23)
    A 4 year project with the objective to create an updated, consistent and official stratigraphic framework for offshore Ireland ranging from the Palaeozoic to Quaternary. Ireland’s offshore stratigraphic nomenclature is currently informal, a unified scheme has never been published, one of the few countries with O&G activity without such scheme; as a result industry/academia are left to devise their own names. The project was initiated, steered and funded by the Irish Shelf Petroleum Studies Group (ISPSG) consisting of members of the Petroleum Infrastructure Programme (PIP) who hold offshore Atlantic acreage.