IAP-25-094

Tectonics, Topography, and Transport: Sediment routing systems and sinks of the Strathclyde Group, Midland Valley Scotland.

The Intergovernmental Panel on Climate Change (IPCC), the International Energy Agency (IEA) and the UK’s Committee on Climate Change (CCC) agree that carbon capture and storage (CCS) represents a component of the solution to the climate crisis. The Midland Valley is a key target for CCS because it represents the most extensive unmetamorphosed onshore sedimentary basin in Scotland (i.e. containing successions with significant potential matrix permeability) (Heinemann et al., 2019; Smith et al., 2024).

The Midland Valley Basin (MVB) is a late Palaeozoic basin bounded by the SW-NE-striking Highland Boundary and Southern Upland faults. It is filled with a largely Devonian to Carboniferous siliciclastic succession largely northerly provenance, and includes intrusive and extrusive volcanics (Monaghan et al. 2024). The MVB is generally interpreted as having formed through sinistral crustal transtension from the latest Silurian, followed by Carboniferous (Visean-Westphalian) dextral transpression and contraction, based largely on the occurrence of SSW-NNE-striking intrabasinal open folds that are unequivocally coeval to sediments of that age (Underhill et al., 2008). These folds partitioned the MVB into synclinal depocentres with distinct subsidence histories and facies distributions (Underhill et al., 2008).

The Lower Carboniferous (Visean, c. 347-330 Ma) fluvio-deltaic Strathclyde Group is the major target for CCS, with proven reservoir, seal and trap configurations (Monaghan et al., 2012; 2017; Heinemann et al., 2019), particularly in fluvial channel-fills and delta-front (mouth bar) strata. The outstanding exposures along the Fife Coast offer an extraordinary window of detail to resolve the tectonostratigraphy of the Strathclyde Group and the MVB more generally, at a sub-seismic scale. Here, growth-strata defining half-graben geometries, fluvial channel clustering and major units displaying soft-sediment deformation imply the existence of long-lived extensional faults that can be interpreted to reflect Visean intrabasinal transtension (Model 1) or gravitational failure into the axes of growing transpressional structures (Model 2) (Underhill et al., 2008). Irrespective of the driving mechanism for extension, these half-grabens represented distinct sediment routing systems and sinks.

This project will combine observations of the geometries and sediment routing fairways of syn-tectonic strata in the Strathclyde Group of East Fife with structural observations in order to (1) explain the genesis of extensional structures in a purportedly transpressional basin, (2) refine or revise models of the Carboniferous tectonostratigraphy of the MVB, and (3) develop models predicting the loci of sedimentary routing systems and sinks (i.e. reservoirs) in the MVB. Linking routing systems and sediment sinks to transtensional structures (Model 1) versus gravitational failure into the axes of growing transpressional synclines (Model 2) will have significant implications about where reservoir units will be projected in the subsurface of the MVB and where the thickest potential CCS repositories would be located.

The Strathclyde Group in East Fife has an in-place litho-, bio- and chronos-stratigraphy (Owens et al., 2005; Monaghan et al., 2024), that has not been fully integrated into the greater MVB. Though growth-strata indicative of extension are known, the geometry, and orientation of these structures as well as their placement in time and space remain undescribed. Similarly, the geometries of growth strata, the loci and axes of fluvial channel belts with respect to extensional structures are uncertain.

Project aims will therefore be achieved through extensive field data collection of structural data, including geometries and relationships with strata that can be used to differentiated between structures coeval with deposition, and those that post date it. Field data will also focus on describing sedimentary facies, geometries and paleocurrents in order to reconstruct paleogeographic time-slices mapped alongside active structures. The results of the study will be integrated into the existing stratigraphic and correlation framework for the Strathclyde Group in east Fife, as well as regional legacy borehole and seismic data and tectonostratigraphic models of the MVB.

Year 1

Literature review, training, data collection (Fieldwork and desk based study of legacy datasets)

Year 2

Additional data collection, data analysis. Drafting of first chapter/manuscript and presentation at national conference: Control of extensional structures on sediment routing and deposition.

Year 3

Data analysis, Drafting of second chapter/manuscript and presentation at international conference: Genesis of extensional structures in an otherwise transpressional basin.

Year 3.5

Third chapter/manuscript: Predictive model of Visean fluvio-deltaic CCS reservoirs in the MVB. Completion of thesis and submission

Training will be provided in advanced physical sedimentology and stratigraphy of continental and nearshore systems, structural geology, subsurface data analysis and integration techniques, and Geographical Information Systems by experts in syn-tectonic and soft sediment deformation (e.g. Ayckbourne et al., 2023, 2024), fluvio-deltaic systems (Jerrett et al., 2017, 2018; Owen et al., 2015, 2019) and the geology of the Midland Valley (Owens et al., 2005, Prave et al., 2010). The student will benefit from experience of presenting at national and international conferences, training and support offered by the University of St Andrew’s Academic Skills Project led by the Centre for Educational Enhancement and Development team (alongside training provided by the Iapetus DTP). The training will provide the basis for a future career in Earth and Environmental science, in the industrial, government or academic sectors.