Overview

Project Highlights:

  • Field-based research in a stunning coastal setting, Assynt Scotland
  • Part of Leicester’s new impact-cratering research group
  • Hands-on expert training in clastic sedimentology and structural geology

Overview:

When asteroids collide with Earth they cause catastrophic air blasts, heat generation, earthquakes and tsunami that devastate the environment and biota. Such hypervelocity collisions are a fundamental process of planetary evolution, and arguably represent the greatest known natural hazard. Yet surprisingly, several aspects of what happens during an impact event are not understood. To properly understand their wider effects on Earth, we need to better understand the processes of cratering and associated ejecta emplacement near source. A principle source of information lies in the geological record, but well-preserved, well-exposed impact-ejecta blankets on Earth are rare.

This project will take advantage of exceptional exposure of an impact ejecta blanket, known as suevite, and its relationship to enclosing, well-exposed sedimentary strata along a 50 km stretch of Scottish coastline. The aim will be to learn what happens during a major impact and how the regional environment is affected. The Proterozoic Stac Fada impact ejecta blanket is of particular interest because it is thought to have been emplaced subaerially in a continental environment that has suffered minimal subsequent deformation: this means that the emplacement mechanisms can be deduced in ways that would not be possible elsewhere, where marine reworking and tectonism mask the primary emplacement processes.

The project will suit a student who likes independent fieldwork in remote terrain and has a keen interest and facility for clastic sedimentology and structural geology. Facies analysis will be undertaken to reconstruct the paleo-environments and drainage before, and after, the Stac Fada impact event, to better understand how ejecta emplacement changes a landscape.

Figure 1: A billion years ago, a large asteroid hit Scotland, but what were the processes involved and how did the catastrophy affect the landscape?

Methodology

Detailed geological fieldwork at several sites along the coast of NW Scotland will have three inter-related strands. (1) Characterisation of the suevite sheet, by logging and quantitative textural analysis of impact-melt particles and aggregates to shed light on fragmentation and emplacement mechanisms. (2) An investigation of enclosing breccias, sandstones and siltstones below and above the suevite sheet to compare the paleoenvironments before and after the impact-event. (3) Structural analysis of deformation features in the suevite and enclosing strata to determine the kinematics and timing of deformation in relation to suevite emplacement, including fracture-filling, brittle and soft-state deformation.

The student will join an exciting new research group investigating impact-ejecta blankets worldwide, with instructive opportunities for direct comparisons with other impact-sites, including impact-deformation at Ries (Germany), and new data sets on impact-melt shapes from Ries, Chicxulub (Mexico) and Manicouagan (Canada) generated by the group.

Training and Skills

The student will receive hands-on field training in clastic sedimentology, involving construction of detailed graphic logs, fence diagrams, with correlation and interpretation of lithofacies and unconformity surfaces. Training will also be provided in Scotland and Germany in structural analysis, involving detailed structural mapping onto drone-generated 3D images, sterio-plotting, and kinematic interpretation of brittle and semi-brittle deformation structures. Laboratory training will be provided on Leicester’s new SEM, and on quantitative characterisation and interpretation of clast shape and morphology. There will be opportunities to present within lab groups and seminars at Leicester and to national and international meetings (TSG, BSRG, meteoritics meetings). Training will be provided on science writing for international publications.

Timeline

Year 1: Fieldwork (field training, structural mapping, sedimentary logging) in NW Scotland. Field visit to deformation structures at Ries impact crater, Bavaria. Drawing-up logs and manipulating drone data to produce 3-D structural maps. Sample preparation and optical microscopy. Departmental presentation.

Year 2: Fieldwork (structural mapping, sedimentary logging) in NW Scotland followed by synthesis of data, correlation, interpretation of sedimentary environments. SEM and digitisation of clast shapes. Meetings with impact-cratering group. Presentation at national meetings

Year 3: Final fieldwork, followed by structural and sedimentological interpretations of sedimentary environments, construction of palaeogeographies and emplacement model for publication. Interpretation of clast shape populations. Presentation at international meteoritics meeting. Thesis writing.

Partners and collaboration (including CASE)

A strength of the project is that the student will benefit from working within a new impact-cratering research group that has international expertise (6 international colleagues from USA, Germany, Russia and Canada) in several aspects of impact cratering. The project will have links with the impact group at University of Frieburg, Germany, and also with the NW Highlands Geopark. The student will be involved in outreach activities in association with collaborators at the NW Highland Geopark and the Ries Geopark in Bavaria.

Further Details

Please contact Professor Mike Branney, University of Leicester (mjb26@le.ac.uk).

See: https://www2.le.ac.uk/departments/geology/research/vtmrg