Title: A provenance study to characterise the contribution of axial drainage systems to the deposition of lower Mesozoic sandstone reservoirs in the North Celtic Sea and St. Georges Channel Basins, offshore south east Ireland
Researchers: Odhran McCarthy and Dr Pat Meere
The North Celtic Sea Basin (NCSB) and Saint Georges Channel Basin (SGCB) are among a number of offshore sedimentary basins related to regional Mesozoic extension across northwest Europe. Their regional geology, water depth and distance from shore, combine to make these basins an attractive target for hydrocarbon exploration. With 83 exploration and appraisal wells drilled, there are 4 producing fields in the NCSB. Economically viable discoveries are hosted in Lower Cretaceous period sandstones but there is growing interest in the older hydrocarbon systems with reserves hosted in Permo-Triassic red bed lithologies. This is especially the case with the SGCB where there is a significant thickness of Permo-Triassic clastic sedimentary rocks. The provenance changes through these sediments are a proxy of changes in sediment sources, transport mechanisms, sea level change and tectonic activity. This study aims to understand changes in provenance and how it relates to both industry and academic questions. Understanding transport mechanisms confines the distribution of sediment packages within the basin’s and therefor, there potential for further exploration. Previous provenance work has been carried out by Tyrrell (2005) and Fairy (et al. 2017). These studies identified primary and secondary sources of sediment from onshore Ireland to these offshore rift basins throughout the Mesozoic. Utilising detrital geochronology, grain shape, heavy mineral and sedimentary petrographic analysis, this project aims to build on previous work and qualitatively characterise the contribution of sediments from Welsh, Irish, English and possibly French source regions.
1. During periods of marine regression, basin sediments will hold a spatial distinctive heavy mineral assemblage (HMA) and onshore source regions will be linked by axial drainage systems to the basin. 2. Periods of marine transgression allowed for a greater degree of sediment homogenisation and mixing source signals and possibly even introducing sediments derived from an unknown source region. 3. Tectonic activity during the Triassic may have influenced sediment infill and re-routing sediments from following their natural drainage patterns to a more E-W direction. 4. During the Triassic, the Budleighensis River fed sediment into the Wessex basin and some inland basins within the UK. It is possible that an offshoot of this major river system found its way into the NCSB or even the SGCB. 5. Paleocontinents Megumia, Avalonia and Laurentia will show a chemically distinct signatures which can be discriminated using HMA. 6. Temporal changes in provenance will be the result of the environment of deposition more than the source regional changes as source regions have not changed since the Mesozoic. 7. Carboniferous limestone’s overlying the onshore bedrock of Ireland during the Mesozoic may introduce unexpected source signals.
1. Determine the ultimate source of sediments in the Mesozoic fill of the NCSB and SGCB and the relative contribution of sediment derived from the north (southern ireland) or the south (remnant Variscan uplands) through transverse drainage systems to that derived from an axial drainage system from western Wales. 2. The project will also evaluate the temporal and spatial ecolution in sediment routing into the NCSB and SGCB from a number of distinct adjacent upland terranes over the course of the complete extentional history of these basins. 3. Using the proposed multidisciplinary approach the project will test the possibility of distinguishing the provenance of the sediment derived from two distinct Peri-Gondwanan terranes, i.e. Gandaria and Avalonia.