Exploring the links between climate, weathering, and dynamic topography during the Late Cretaceous in Southern Africa: a geochemical and mineralogical approach within a source-to-sink system

Started in october 2020

Funding: EU program Marie Curie Actions, Université Bourgogne Franche-Comté (UBFC) and université de Bourgogne (uB)

Supervisors: Emmanuelle Pucéat and Pierre Pellenard

Defended the 31 may 2024

Abstract

The major uplift phase encountered by southern Africa during the late Cretaceous led to a drastic increase in denudation rates. This event provides a unique opportunity to explore the long-term response of chemical weathering and erosion to intense tectonic uplift within the greenhouse climate context of the late Cretaceous. The respective importance of these two processes in the evolution and distribution of detrital fluxes and in the formation of reservoirs is a key question that still remains to be elucidated. The aim of this PhD is to apply a novel geochemical approach, combining clay mineralogical analyses with Hf-Nd isotopic analyses (∆εHf) on clay fractions to (1) decipher the respective evolution of chemical weathering and erosion during the late Cretaceous uplift of southern Africa, (2) explore the links between erosion and weathering processes and the evolution and distribution of detrital fluxes in this tectonic setting, and (3) explore the potential impact of this uplift on late Cretaceous climate evolution, through CO₂ consumption by silicate weathering reactions.

Three sites (DSDP core 361, borehole O-A1, borehole P-A1) located in a proximal-distal transect along the Cape Basin were targeted to track the evolution of denudation processes by applying a source-to-sink approach. The obtained record shows consistent sediment provenance for the sites, including units from southwestern-central areas of the South African Plateau during the late Cretaceous. The clay mineralogy and the (∆εHf(80)) indicate an increase in chemical weathering along the late Cretaceous starting around the Cenomanian-Turonian (ca. 95 Ma), while an increase in physical erosion is observed between the Campanian – Danian (ca. 77-62 Ma). This enhancement in denudation occurs while the global climate is under a cooling trend that started around the Turonian (ca. 93 Ma), which is not favourable to enhanced denudation episodes. This tectonically-driven enhancement in denudation during the late Cretaceous, particularly in chemical weathering, appears to be one of the main mechanisms responsible for the triggering of the global climate cooling trend during the late Cretaceous, not only by the drawdown of CO₂ through mineral reactions, but also by potentially enhancing marine productivity through sustained input of continental nutrients into basins adjacent to the southern African margin.

Keywords

geochemistry, Cretaceous, paleoclimate, clay minerals, tectonics, weathering

Jury

Nathalie Fagel, université de Liège – reviewer
Guillaume Suan, université Claude-Bernard Lyon – reviewer
Marion Garçon, université Clermont-Auvergne – examinaner
Aaron Bufe, université Ludwig Maximilian, Munich – examinaner
Marc De Rafelis, université Paul Sabatier, Toulouse – examinaner
Emmanuelle Pucéat, université de Bourgogne – supervisor
Pierre Pellenard, université de Bourgogne – cosupervisor
François Guillocheau, université de Rennes 1 – cosupervisor

extrait:

lien_externe:

titre:

Explorer les liens entre le climat, la météorisation et la topographie dynamique au cours de la crétacé supérieur : une approche géochimique et minéralogique dans un système source-puits

date_de_debut_these:

octobre 2020

nom:

Gaitan

date_de_debut_these_numerique:

202010

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kc_raw_content:

Exploring the links between climate, weathering, and dynamic topography during the Late Cretaceous in Southern Africa: a geochemical and mineralogical approach within a source-to-sink system

Started in october 2020

Funding: EU program Marie Curie Actions, Université Bourgogne Franche-Comté (UBFC) and université de Bourgogne (uB)

Supervisors: Emmanuelle Pucéat and Pierre Pellenard

Defended the 31 may 2024

 

Abstract

The major uplift phase encountered by southern Africa during the late Cretaceous led to a drastic increase in denudation rates. This event provides a unique opportunity to explore the long-term response of chemical weathering and erosion to intense tectonic uplift within the greenhouse climate context of the late Cretaceous. The respective importance of these two processes in the evolution and distribution of detrital fluxes and in the formation of reservoirs is a key question that still remains to be elucidated. The aim of this PhD is to apply a novel geochemical approach, combining clay mineralogical analyses with Hf-Nd isotopic analyses (∆εHf) on clay fractions to (1) decipher the respective evolution of chemical weathering and erosion during the late Cretaceous uplift of southern Africa, (2) explore the links between erosion and weathering processes and the evolution and distribution of detrital fluxes in this tectonic setting, and (3) explore the potential impact of this uplift on late Cretaceous climate evolution, through CO₂ consumption by silicate weathering reactions.

Three sites (DSDP core 361, borehole O-A1, borehole P-A1) located in a proximal-distal transect along the Cape Basin were targeted to track the evolution of denudation processes by applying a source-to-sink approach. The obtained record shows consistent sediment provenance for the sites, including units from southwestern-central areas of the South African Plateau during the late Cretaceous. The clay mineralogy and the (∆εHf(80)) indicate an increase in chemical weathering along the late Cretaceous starting around the Cenomanian-Turonian (ca. 95 Ma), while an increase in physical erosion is observed between the Campanian – Danian (ca. 77-62 Ma). This enhancement in denudation occurs while the global climate is under a cooling trend that started around the Turonian (ca. 93 Ma), which is not favourable to enhanced denudation episodes. This tectonically-driven enhancement in denudation during the late Cretaceous, particularly in chemical weathering, appears to be one of the main mechanisms responsible for the triggering of the global climate cooling trend during the late Cretaceous, not only by the drawdown of CO₂ through mineral reactions, but also by potentially enhancing marine productivity through sustained input of continental nutrients into basins adjacent to the southern African margin.

 

Keywords

geochemistry, Cretaceous, paleoclimate, clay minerals, tectonics, weathering

 

Jury

Nathalie Fagel, université de Liège - reviewer
Guillaume Suan, université Claude-Bernard Lyon - reviewer
Marion Garçon, université Clermont-Auvergne - examinaner
Aaron Bufe, université Ludwig Maximilian, Munich - examinaner
Marc De Rafelis, université Paul Sabatier, Toulouse - examinaner
Emmanuelle Pucéat, université de Bourgogne - supervisor
Pierre Pellenard, université de Bourgogne - cosupervisor
François Guillocheau, université de Rennes 1 - cosupervisor