The early‑to‑middle Eocene (Ypresian to Bartonian) in the Paris Basin (France) and Mons Basin (Belgium): a record of hyperthermal events and climate impacts on sedimentary dynamics in coastal to continental environments

Started in november 2021

Funding: Bourgogne-Franche-Comté district, Mons University (Belgium), French geological survey

Supervisor: Pierre Pellenard (UBFC) ; cosupervisors: Jean-Marc Baele (Mons University, Belgium) & Florence Quesnel (French geological survey)

Defense the 19 june 2025

Abstract

In the Paris Basin, many socio-economic challenges are closely linked to the subsurface, particularly the Cenozoic cover. These challenges include water and mineral resources, as well as geotechnical risks. Tackling these issues requires a detailed understanding of the sedimentary record, involving studies with a high spatial and stratigraphic resolution. These studies help us better understand the geodynamic processes that control the formation, transport, deposition, and variability of sediments. Climate, in particular, plays a crucial role in regulating weathering and erosion processes, which lead to the production and transport of sediments. Therefore, understanding these climate processes is essential for deciphering the dynamics and infilling of sedimentary basins.

The Eocene epoch (56 to 34 million years ago) represents the warmest period of the Cenozoic, characterised by high atmospheric CO₂ levels and short, intense warming events (hyperthermal events), which are thought to be similar to modern climate warming. Despite the historical significance of the Paris and Belgian Basins in defining this period, they remain relatively poorly studied in terms of palaeoclimate. While some Eocene hyperthermal events have been identified in these basins, their potential impacts on sedimentation are still not well understood.

This study, which is part of the BRGM’s RGF Paris Basin project, aims to (1) document the record of Eocene hyperthermal events in the Paris Basin and the Mons Basin (Belgium), and (2) investigate how these events influenced sedimentation in coastal and continental environments, which are particularly sensitive to climate change. The main methods used include carbon isotope analysis of sedimentary organic matter to identify hyperthermal events, and clay mineralogy to reconstruct past weathering conditions.

The high-resolution study of five boreholes and six outcrops from the Paris Basin, as well as two boreholes (one drilled as part of this PhD) from the Mons Basin, allowed us to (1) clarify the PETM, EECO, and MECO records in the Paris Basin; (2) identify the LLTM for the first time in the Paris Basin and in a coastal setting; and (3) characterise the PETM, ETM2, and EECO in the Mons Basin. In a context where large‑scale tectonic deformations control major trends, isotopic and mineralogical data from this study indicate that intense weathering favours siliciclastic‑dominated sedimentation, while weaker weathering promotes carbonate to evaporite deposition.

The PETM, EECO, and MECO are linked to enhanced weathering and runoff conditions. The PETM, in particular, is marked by the transformation of smectite to kaolinite in weathering profiles that developed at the same time as sediment deposition. This suggests that the delay between clay formation in soils, its transport and preservation in coastal and continental environments is shorter than previously thought. In these proximal settings, factors such as palaeogeography, hydrodynamics, and neoformation processes can influence the distribution of clay assemblages, potentially introducing bias that could hinder the interpretation of the terrigenous signal in terms of climate. This has been observed here for the EECO. Low‑weathering periods, such as the LLTM, intensify complex processes of early dolomite and fibrous clay formation, driven by microbial activity and soil development in coastal environments.

Keywords

hyperthermal events, Eocene, continental weathering, clay minerals, organic carbon isotopes

Thesis advisory panel

Benjamin Brigaud, Paris-Saclay university
Nathalie Fagel, Liège university (Belgium)

Jury

AUBRY Marie-Pierre, Rutgers University, USA – reviewer
FRONTEAU Gilles, université de Reims Champagne-Ardenne – reviewer
FAGEL Nathalie, université de Liège – examiner
LE CALLONNEC Laurence, Sorbonne Université – examiner
VENNIN Emmanuelle, Université Bourgogne Europe – examiner
GODERNIAUX Pascal, université de Mons – examiner
PELLENARD Pierre, Université Bourgogne Europe – supervisor
BAELE Jean-Marc, université de Mons – supervisor
QUESNEL Florence, BRGM – invited (cosupervisor)

extrait:

lien_externe:

titre:

titre

date_de_debut_these:

novembre 2021

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Talon

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202111

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The early‑to‑middle Eocene (Ypresian to Bartonian) in the Paris Basin (France) and Mons Basin (Belgium): a record of hyperthermal events and climate impacts on sedimentary dynamics in coastal to continental environments

Started in november 2021

Funding: Bourgogne-Franche-Comté district, Mons University (Belgium), French geological survey

Supervisor: Pierre Pellenard (UBFC) ; cosupervisors: Jean-Marc Baele (Mons University, Belgium) & Florence Quesnel (French geological survey)

Defense the 19 june 2025

 

Abstract

In the Paris Basin, many socio-economic challenges are closely linked to the subsurface, particularly the Cenozoic cover. These challenges include water and mineral resources, as well as geotechnical risks. Tackling these issues requires a detailed understanding of the sedimentary record, involving studies with a high spatial and stratigraphic resolution. These studies help us better understand the geodynamic processes that control the formation, transport, deposition, and variability of sediments. Climate, in particular, plays a crucial role in regulating weathering and erosion processes, which lead to the production and transport of sediments. Therefore, understanding these climate processes is essential for deciphering the dynamics and infilling of sedimentary basins.

The Eocene epoch (56 to 34 million years ago) represents the warmest period of the Cenozoic, characterised by high atmospheric CO₂ levels and short, intense warming events (hyperthermal events), which are thought to be similar to modern climate warming. Despite the historical significance of the Paris and Belgian Basins in defining this period, they remain relatively poorly studied in terms of palaeoclimate. While some Eocene hyperthermal events have been identified in these basins, their potential impacts on sedimentation are still not well understood.

This study, which is part of the BRGM's RGF Paris Basin project, aims to (1) document the record of Eocene hyperthermal events in the Paris Basin and the Mons Basin (Belgium), and (2) investigate how these events influenced sedimentation in coastal and continental environments, which are particularly sensitive to climate change. The main methods used include carbon isotope analysis of sedimentary organic matter to identify hyperthermal events, and clay mineralogy to reconstruct past weathering conditions.

The high-resolution study of five boreholes and six outcrops from the Paris Basin, as well as two boreholes (one drilled as part of this PhD) from the Mons Basin, allowed us to (1) clarify the PETM, EECO, and MECO records in the Paris Basin; (2) identify the LLTM for the first time in the Paris Basin and in a coastal setting; and (3) characterise the PETM, ETM2, and EECO in the Mons Basin. In a context where large‑scale tectonic deformations control major trends, isotopic and mineralogical data from this study indicate that intense weathering favours siliciclastic‑dominated sedimentation, while weaker weathering promotes carbonate to evaporite deposition.

The PETM, EECO, and MECO are linked to enhanced weathering and runoff conditions. The PETM, in particular, is marked by the transformation of smectite to kaolinite in weathering profiles that developed at the same time as sediment deposition. This suggests that the delay between clay formation in soils, its transport and preservation in coastal and continental environments is shorter than previously thought. In these proximal settings, factors such as palaeogeography, hydrodynamics, and neoformation processes can influence the distribution of clay assemblages, potentially introducing bias that could hinder the interpretation of the terrigenous signal in terms of climate. This has been observed here for the EECO. Low‑weathering periods, such as the LLTM, intensify complex processes of early dolomite and fibrous clay formation, driven by microbial activity and soil development in coastal environments.

 

Keywords

hyperthermal events, Eocene, continental weathering, clay minerals, organic carbon isotopes

 

Thesis advisory panel

Benjamin Brigaud, Paris-Saclay university
Nathalie Fagel, Liège university (Belgium)

 

Jury

AUBRY Marie-Pierre, Rutgers University, USA - reviewer
FRONTEAU Gilles, université de Reims Champagne-Ardenne - reviewer
FAGEL Nathalie, université de Liège - examiner
LE CALLONNEC Laurence, Sorbonne Université - examiner
VENNIN Emmanuelle, Université Bourgogne Europe - examiner
GODERNIAUX Pascal, université de Mons - examiner
PELLENARD Pierre, Université Bourgogne Europe - supervisor
BAELE Jean-Marc, université de Mons - supervisor
QUESNEL Florence, BRGM - invited (cosupervisor)