Title: Sand delivery to passive margin basins – towards quantitative source to sink analysis
Researchers: Martin Nauton-Forteu and Dr Shane Tyrrell
This research is part of the Sediment Tracking targeted project, within the Energy Security challenge of iCRAG. Within National University of Ireland, Galway (NUIG), the project operates within the Sediment Origins Research Team (SORT), led by Dr. Shane Tyrrell, comprising one post-doctoral research and three PhD students. This group aims at better understanding the generation, history and provenance of sediments and sedimentary rocks, by developing new tools and approaches, with the ultimate objective of constraining environmental change on the earth’s surface. This has clear applied aspects, and can allow for improved prediction of reservoir distribution and/or quality in the subsurface.
The specific aim of this PhD project is to investigate and constrain the factors which control and modify detrital mineralogy prior to final deposition in passive margin sedimentary basins – with specific focus on assessing and constraining hinterland (lower drainage basin) storage and mixing and its impact on reservoir sandstone quality in basins offshore western Ireland. Processes such as weathering, mixing or sorting can occur during erosion, transport, intermediate storage and burial. The longer the sediment stays in the sedimentary system, the more it will be prone to changes in its composition. Heavy minerals have been proven useful to investigate sedimentary provenance (Mange and Wright, 2007). Morton and Hallsworth (1994, 1999) have used heavy mineral indices to recognise that lowstand and highstand facies have different heavy mineral signatures. The apatite-tourmaline index (ATi) is believed to be controlled by the residence-time in the sedimentary system. Apatite and tourmaline both have similar hydrodynamic properties and thus won’t be preferentially impacted by mixing or sorting. Moreover they are not impacted by diagenesis (Morton and Hallsworth 2007). Apatite being less stable than tourmaline, it will be more easily weathered. The longer the sediment stays stored in the system, the more apatite will be dissolved compared to tourmaline. A low ATi is thus representative of a relatively longer residence-time in the system than a higher index – hence this signal can be sensitive to sea level fluctuations which will vary the time it takes sediment to flush through the system.
This project seeks to test these ideas by using a multi-proxy sedimentary provenance approach. The mineralogy of both framework and heavy mineral components is investigated and single grain techniques such as U-Pb geochronology on zircon and apatite and, when possible, Pb isotopes in K-feldspars, are employed to recognise variations in provenance and distinguish these from compositional variations caused by storage. The well-studied sequences of the mid-Carboniferous Clare Basin are used as an ideal test case. During the Serpukhovian-Bashkirian (330-315Ma), a siliciclastic infill occurred under the influence of glacio-eustatic sea-level fluctuations. The sedimentary successions thus might have recorded variations in composition which could potentially be linked with a pre-depositional history of the sediment such as an intermediate storage phase. The shallow-water Tullig deltaic cyclothem and the deep-water turbidites of the Ross Formation are being investigated. This project will then apply the learnings from the Clare Basin to sandstones in basins offshore western Ireland which are far less constrained in terms of their provenance and the controls on reservoir distribution and quality.