Do extra-terrestrial impacts offer global stratigraphical markers?

Ice, marine and terrestrial sediment archives offer invaluable insights into Earth System processes. Precise tie-points between palaeorecords is essential to examin the phasing and drivers of inter-hemisphere climate variability. Globally, this can be done through the correlation of palaeomagnetic excursions/reversals. Regionally, volcanic ash (tephra) layers provide time-synchronous marker horizons and tephrochronology has been used to validate orbitally-tuned age models for marine records and to reveal time-transgressive climate changes on continental scales. Microscopic ejecta from extra-terrestrial impacts, microtektites, provide similarly instantaneous marker horizons to tephra, yet have the potential to correlate records over a greater area. Australasian impact (~780 ka) microtektites are used as stratigraphical markers in the Indian Ocean, yet their presence further afield is poorly constrained. This project is inspired by recently found candidates for Australasian impact microtektites in the South Atlantic. Well outside the currently defined strewn field for this impact we propose that certain impacts may provide globally synchronous marker horizons.

Microtektites are glassy spheroids <1 mm in diameter formed by vaporisation of the earth’s crust with the high temperatures and pressures of extra-terrestrial impacts. These molten silicate droplets cool rapidly and fall back to earth. Due to their near-instantaneous deposition, microtektite-rich horizons from known impact events are invaluable stratigraphical markers in marine sediments. However, the geographical range of specific microtektite strewn fields remain poorly constrained in the marine realm and largely unstudied within the lacustrine and cryosphere. This project will investigate the spatial distribution of microtektite horizons associated with a number of extra-terrestrial impact events. The ultimate outcome of this project will be a novel microtektite-based chronology for the Quaternary that bridges marine, terrestrial and cryosphere environments.

Working between BAS, the Departments of Geography and Earth Sciences the student will select well-dated extra-terrestrial impact events and work systematically to extend known microtektite strewn fields. The student will interrogate stratigraphic information (including paleomagnetics, biostratigraphy, stable isotope stratigraphy) to select sampling intervals within candidate cores from the DSDP/ODP/IODP, ICDP and other collections as appropriate. They will develop novel morphological and geochemical approaches to characterise impact-specific microtektite horizons. The student will add progressively more distal cores until the geographical limit of each strewn field is determined (zero microtekties). In addition, the student may consider spatial analysis of microtektite morphology and geochemistry to better constrain the site of the impact in cases where a crater has not been identified. The student will be encouraged to evolve and direct the project themselves.