Lessons from our ancient Frozen Planet: towards an unified theory for glacial sequence stratigraphy – SeqStrat-Ice

The project revolves around two main case studies : a sedimentary archive of the last deglaciation in Québec that goes back in time 15 000 years; a much older archive (Ordovician) that constitutes the record of the growth, the cyclic waxing & waning and the final demise of a large ice sheet centred upon present-day Africa, which was once at southern polar latitude (Gondwana palaeo-continent). Both the archives were investigated in terms of depositional environments (fluvioglacial, coastal or turbiditic sands, glacimarine or offshore muds, …), stratigraphic architectures (palaeovalleys, delta progradations, raised beaches, …) and chronology (radiocarbon dating in Québec, micropalaeontology in Morocco). From the continent to the sea, none of the individual sedimentary systems and resulting strata can offer a comprehensive view of the entirety of the paleoclimatic evolution, each of them only contributing to the record of specific events. As geological data sets are in essence fragmentary, numerical and analogical modelling can provide additional insights, and models were re-designed to accommodate the specifics of a glacial context (effects of the postglacial isostatic rebound; incision cycles of subglacial valleys).

Glaciations in the deep time have left behind a sedimentary record that is more complex, but also richer than was generally envisioned. The team’s efforts in unravelling the ancient archives demonstrated a number of analogies with the development of much younger glaciations. Only in juxtaposing in time and space the pieces of the puzzle, distributed at the scale of a sedimentary basin (> 100 x 500 km), the full strength of our unique archive become clear, and it can be used to accurately link glaciation & deglaciation with episodes of past, extreme, climate changes. Our emerging revised interpretation of the Ordovician glaciations rejects claims of this being an aberrantly unique episode in geological time, but instead draws parallels with much better known glaciations in the Cenozoic.

Dietrich P., Ghienne J.-F., Lajeunesse P., Normandeau A., Deschamps R. & Razin P. in press – Deglacial sequences and glacio-isostatic adjustement: Quaternary compared with Ordovician glaciations. In: Glaciated Margins: The Sedimentary and Geophysical Archive, Le Heron, D. P. et al. (eds), Geological Society, London, Special Publications, 475, DOI : 10.1144/SP475.9

Lelandais T., Ravier E., Pochat S., Bourgeois O., Clark C., Mourgues R., Strzerzynski P., 2018 – Modelled subglacial floods and tunnel valleys control the life cycle of transfers ice streams. The Cryosphere, 12, 2759-2772. DOI : 10.5194/tc-12-2759-2018

Ghienne J.-F., Benvenuti A., El Houicha M., Girard F., Kali E., Khoukhi Y., Langbour C., Magna T., Míková J., Moscariello A., Schulmann K. 2018 – The impact of the end-Ordovician glaciation on sediment routing systems: A case study from the Meseta (northern Morocco). Gondwana Research, 63, 169-178. DOI : 10.1016/j.gr.2018.07.001
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Ghienne J.-F., Desrochers A., Vandenbroucke T., Achab A., Asselin E., Dabard M.-P., Farley C., Loi A., Paris F., Wickson S., Veizer J., 2014 – A Cenozoic-style scenario for the end-Ordovician glaciation. Nature Communications, 5:4485. DOI: 10.1038/ncomms5485

Dietrich P., Ghienne J.-F., Normandeau A., Lajeunesse P. 2017 – Reconstructing ice-margin retreat using delta morphostratigraphy. Scientific Reports 7: 16936. DOI:10.1038/s41598-017-16763-x

At the end of the project, 23 papers in international scientific journals are published. Amongst them, 9 papers directly and entirely result from data acquired since project launch; SEQSTRAT-ICE significantly contributing to the 14 other papers having thematics in line with the project. In addition, the SEQSTRAT-ICE findings have been presented to the scientific community owing to presentations in French (9) and international (33) meetings. The bonds forged and data collected during the project will enable the team to deliver many more products over the years to come, witness e.g., 2 papers in the pipeline of production and 7 other to be submitted in 2018 or 2019.

This project revolves around the sequence stratigraphy of the glaciogenic sedimentary record, our only direct archive of ancient glaciations. Understanding this archive is of fundamental importance when modelling past (and predicting future!) climate change and for the study of biogeochemical signals throughout Earth’s history. There also is a socio-economic incentive for studying glaciogenic successions as they include reservoir structures for petroleum as well as for groundwater. Understanding Earth systems dynamics during glaciations is crucial to intelligently tackle three of the main challenges facing society in the 21st century: climate change and its environmental impacts, energy diversification, and water resource management. Unfortunately, and in flagrant contrast to conventional depositional systems, there currently is no general model that can assist geoscientists to unravel the glaciogenic archives. Existing models are fundamentally flawed as they ignore the variety of depositional conditions that inherently characterise glaciogenic systems.
The overarching aim of this project is to develop unified sequence stratigraphic concepts that will provide a robust framework for the investigation of the glaciogenic records through space and time. The project is organized around three scientific pillars, encompassing the full spectrum of spatial and temporal scales:
• The numerical modelling of glaciation-related depositional systems: the challenge is to link a stratigraphic modelling tool (Dionisos, developed at the IFP-EN) and an ice-sheet model (e.g. Sicopolis) that drives advancing/retreating ice fronts. Tests and validation will be based on Quaternary case studies and on geological datasets.
• An in-depth study of the Late Ordovician glacial record, arguably the best-known example of a pre-Quaternary glaciogenic record: we postulate that the Ordovician glaciation is one of two end members in a series of glacial concepts: this end member comprises glaciations on shallow continental platforms, in contrast to the other, well-known, Cenozoic-style end member where ice sheets extended over deep shelves. This hypothesis will be tested using old and new data from our natural laboratory in the Upper Ordovician strata in Morocco. A comparison with far-field signals will differentiate global events from local ones and will allow accurate time calibration, permitting in turn a stratigraphic modelling.
• Finally, the integration of the results in an evolving unified conceptual framework, with the two end-members as discussed above (data for the Cenozoic-style end member will be taken from the literature), but also using other cases studies as found throughout the evolution of Earth. Our result will be an original, universal sequence stratigraphic model for glaciogenic successions.
We designed an in-depth survey of glacial sedimentary systems, valorising skills that we have developed over the last decade through numerous industrial research contracts, but few academic projects (e.g. ECLIPSE, CNRS). In this ANR proposal we develop a fundamental research project, functioning autonomously from industrial stakes. The team includes 4 academic partners: 3 academic research groups or 'UMRs' (the Institut de Physique du Globe de Strasbourg; Biogéosciences, Dijon; Géosystèmes, Lille) and the IFP-Energies Nouvelles. Researchers from other universities also integrate the wide network (Bordeaux, Cergy Pontoise, Rennes), as well as a number of experts (LSCE, international collaborators). Some of the tasks are linked to a full-time PhD project, to be funded through this ANR project. An additional 18-months post-doctoral position and a third PhD project (educational allocation, MENRT) are expected to complete the collaboration. Undergraduate students will be significantly involved for modelling and fieldwork, including masters and training stages of engineering schools (ENSEGID, Bordeaux; EOPG, Strasbourg, LaSalle, Beauvais).