Climate and tectonic controls on stratigraphy in the Early Eocene Pyrenean foreland basin: new geochemical constraints

Thesis

Reference

Climate and tectonic controls on stratigraphy in the Early Eocene Pyrenean foreland basin: new geochemical constraints

HONEGGER, Louis

Abstract

On multi-millennial scales, sedimentary systems can be disturbed by external forcings such as tectonic uplift and climate change. These environmental changes affect sediment fluxes and sediment composition from the zone sediments are produced to their deposition zone.

Although we have a good understanding of how sedimentary systems react to forcings such as sea-level change, tectonic uplift or global warmings, major challenges remain concerning the record and unravelling of these signals in past sedimentary archives. These archives may hold key information for predictive models concerning actual and future environmental problems. To better understand how tectonic and climatic signals are recorded and are reflected in past sedimentary successions, an Eocene (33-56 Ma) sedimentary system in the south Pyrenean foreland basin was studied during a time-period rich in tectonic and climatic events.

HONEGGER, Louis. Climate and tectonic controls on stratigraphy in the Early Eocene Pyrenean foreland basin: new geochemical constraints. Thèse de doctorat : Univ.

Genève, 2020, no. Sc. 5478

DOI : 10.13097/archive-ouverte/unige:141608 URN : urn:nbn:ch:unige-1416080

Available at:

http://archive-ouverte.unige.ch/unige:141608

Disclaimer: layout of this document may differ from the published version.

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UNIVERSITY OF GENEVA FACULTY OF SCIENCES Department of Earth Sciences Professeur S´ebastien Castelltort

Climate and tectonic controls on stratigraphy in the Early Eocene

Pyrenean foreland basin: new geochemical constraints

by

Louis Honegger from

Genthod (Geneva), Switzerland

Thesis n ° 5478

May 2020

Thesis director

Dr. S´ebastien Castelltort Department of Earth sciences, University of Geneva, Switzerland

Jury Members

Dr. Thierry Adatte Institut of Earth Sciences,

University of Lausanne, Switzerland Dr. Julian Clark

Equinor Research Center, Austin, Texas, USA Dr. Andrea Fildani The Deep Time Institute, Austin, Texas, USA Dr. Brady Foreman Department of Geology,

Western Washington University, USA Dr. Laure Guerit

Geosciences Rennes,

University of Rennes 1, France Dr. Cai Puigdef`abregas

Department of Earth and Ocean Dynamics, University of Barcelona, Spain

Dr. Jorge Spangenberg

Institute of Earth Surface Dynamics, University of Lausanne, Switzerland

Abstract

On multi-millennial scales, sedimentary systems do not behave like a long and calm river, but can be disturbed by external forcings such as tectonic uplift and climate change. These environmental changes affect sediment fluxes and sediment composition on the scale of a source-to-sink system — from the zone sediments are produced to their deposition zone. Understanding how a sedimentary system reacts as a whole to a perturbation is crucial for human societies established along them in terms of flooding, rock fall, tourism, or natural resources, for instance. Although we have a good understanding of how sedimentary systems react to forcings such as sea-level change, tectonic uplift or global warmings, major challenges remain concerning the record and unravelling of these signals in past sedimentary archives, which may hold key information for predictive models concerning actual and future environmental problems. In this thesis, to better understand how tectonic and climatic signals are recorded and affected past sedimentary successions, I studied an Eocene source-to-sink system in the south Pyrenean foreland basin during a time-period rich in tectonic and climatic events.

Firstly, I assess the respective role of tectonic and climate in controlling the sediment flux to the Ainsa Basin where cyclic deposition under the form of sandy sediment gravity flows (SGF) separated by hemipelagic marls are observed. Using whole-rock carbon stable isotopes as a proxy for sea-level change I establish that, in line with sequence stratigraphic models, the majority of the SGF are linked to sea-level lowstands. However, one SGF corresponds to a sea-level highstand and is coeval with an increase in tectonic activity. These results put forward the nonuniqueness of the controls on clastic deposition.

Secondly, I explore the potential of fluvial environments to record small-scale global warming signals with a duration of 40 kyr and suggest hypotheses on the impact of these events on climate and soil dynamics. Using carbon isotopes on pedogenic carbonate nodules, I describe a negative carbon isotope excursion that I attribute to the hyperthermal event “U” occurring at ca. 50 Ma, and identified for the first time in continental deposits. This suggests that fluvial successions have the potential to record rapid climate change. In addition, an enrichment in immobile elements such as titanium, aluminium and zirconium, together with the presence or iron-oxide nodules, suggest an increase in weathering conditions during these

Thirdly, I evaluate the topographic growth of the Pyrenees during the Eocene.

Using whole-rock oxygen isotopes and the fact that δ¹⁸O values decrease with increasing altitude, I estimate the relative topographic growth of the Pyrenees by using the δ¹⁸O values to trace the input of freshwater in the system. A minimum in oxygen isotope values, coherent with tectonic constraints, suggest that the Pyrenees uplifted until ca. 49 Ma and stabilized afterwards. These results suggest that δ¹⁸O whole-rock data from foreland basins have the potential to faithfully record paleoenvironmental variations. These important limitations on the Pyrenean topography open the door to further constrain drainage areas and sediment flux to the basins.

All together these results highlight that tectonic and climatic signals are intricately intertwined in past geological archives. Yet they both have the potential to influence stratigraphic sequences and the potential to be recorded in an active foreland basins.

R´ esum´ e

A l’´echelle multimill´enaire, les syst`emes s´edimentaires ne se comportent pas comme` un long fleuve tranquille, mais peuvent au contraire ˆetre perturb´es par des for¸cages externes tels que le soul`evement tectonique et les changements climatiques. Ces changements environnementaux affectent les flux s´edimentaires et la composition des s´ediments `a l’´echelle d’un syst`eme source-to-sink — de la zone o`u les s´ediments sont produits `a leur zone de d´epˆot. Comprendre comment un syst`eme s´edimentaire r´eagit dans son ensemble `a une perturbation est crucial pour les soci´et´es hu- maines ´etablies le long de ce syst`eme en termes d’inondations, d’´eboulements, de tourisme ou de ressources naturelles, par exemple. Bien que nous ayons une bonne compr´ehension de la fa¸con dont les syst`emes s´edimentaires r´eagissent `a des for¸cages tels que les changements du niveau de la mer, le soul`evement tec- tonique ou des r´echauffements climatiques, des d´efis majeurs demeurent concernant l’enregistrement et le d´emˆelement de ces signaux dans les archives s´edimentaires pass´ees. Ces archives peuvent contenir des informations cl´es pour les mod`eles de pr´evision concernant les probl`emes environnementaux futurs. Dans cette th`ese, pour mieux comprendre comment les signaux tectoniques et climatiques sont en- registr´es dans les successions s´edimentaires pass´ees, nous avons ´etudi´e un syst`eme source-to-sink datant de l’´Eoc`ene dans le bassin d’avant-pays sud Pyr´en´een pendant une p´eriode riche en ´ev´enements tectoniques et climatiques.

Tout d’abord, nous avons ´evalu´e le rˆole respectif de la tectonique et du climat dans le contrˆole du flux s´edimentaire vers le bassin d’Ainsa o`u l’on observe des d´epˆots cycliques sous la forme de flux gravitaires de s´ediments sableux (FGS) s´epar´es par des marnes h´emip´elagiques. En utilisant les isotopes du carbone mesur´es sur les marnes comme indicateur du changement du niveau de la mer, nous avons ´etabli que, conform´ement aux mod`eles de stratigraphie s´equentielle, la majorit´e des FGS sont li´es aux bas niveaux eustatiques. Cependant, un FGS correspond `a un haut niveau eustatique et co¨ıncide avec une augmentation de l’activit´e tectonique. Ce r´esultat met en avant la non-unicit´e des contrˆoles sur les d´epˆots clastiques.

Deuxi`emement, nous avons explor´e le potentiel des environnements fluviaux `a enregistrer les signaux de r´echauffements climatiques d’une dur´ee de 40 ka puis nous avons sugg´er´e des hypoth`eses sur l’impact de ces ´ev´enements sur la dynamique des sols. En utilisant les isotopes du carbone mesur´es des nodules carbonat´es

identifi´e pour la premi`ere fois dans les d´epˆots continentaux. Cela sugg`ere que les successions fluviales ont le potentiel d’enregistrer un changement climatique rapide.

En outre, un enrichissement en ´el´ements immobiles tels que le titane, l’aluminium et le zirconium, ainsi que la pr´esence de nodules d’oxyde de fer, sugg`erent une augmentation des conditions d’alt´eration pendant ces ´ev´enements. Ces r´esultats pourraient impl´ement´es d’´eventuels mod`eles de pr´evision du changement climatique actuel.

Troisi`emement, nous ´evaluons la croissance topographique des Pyr´en´ees pendant l’´Eoc`ene en utilisant les isotopes d’oxyg`ene mesur´es sur la roche totale. Grˆace au fait que le δ<sup>18</sup>O diminue avec l’augmentation de l’altitude, nous estimons la croissance topographique relative des Pyr´en´ees en retra¸cant l’entr´ee dans le syst`eme d’eau douce avec une signature n´egative de δ¹⁸O. Un minimum en isotope oxyg`ene, coh´erent avec les contraintes tectoniques disponibles, sugg`ere que les Pyr´en´ees se sont soulev´ees jusqu’`a environ 49 Ma et se sont stabilis´ees par la suite. Ces r´esultats d´emontrent que les donn´ees de la roche totale δ<sup>18</sup>O provenant des bassins d’avant- pays ont le potentiel d’enregistrer fid`element les variations pal´eoenvironnementales.

Ces importantes contraintes sur la topographie pyr´en´eenne ouvrent la porte `a une nouvelle limitation des zones de drainage et du flux de s´ediments vers les bassins.

Tous ces r´esultats soulignent que les signaux tectoniques et climatiques sont

´etroitement li´es dans les archives g´eologiques pass´ees. Toutefois, les deux peuvent

`a la fois influencer les s´equences stratigraphiques et ˆetre enregistr´es dans un bassin d’avant-pays actif.

Remerciements

Tout d’abord, je voudrais remercier mon directeur de th`ese S´ebastien Castelltort pour l’opportunit´e qu’il m’a offerte de poursuivre ce projet apr`es ma th`ese de master. Merci pour le soutien, le point de vue critique qui m’a forc´e `a renforcer ma science, et ta capacit´e `a me remettre sur la piste quand je commen¸cais `a m’´eloigner.

Et merci pour les discussions non g´eologiques sur le terrain ou `a Gen`eve pendant ces cinq ann´ees!

Je tiens ´egalement `a remercier les personnes d’Equinor `a Austin, Julian Clark, Andrea Fildani et Mason Dykstra, qui ont soutenu ce projet scientifiquement et financi`erement depuis le d´ebut et ont rendu les missions sur le terrain beaucoup plus stimulantes sur le plan scientifique. Merci aux doctorants d’Austin, Margo Odlum et Kelly Thomson, pour l’initiation aux zircons et la visite de la 6e rue.

Merci ´egalement `a Cai Puigdef`abregas, qui a ajout´e un peu de tranquillit´e et de philosophie `a la g´eologie.

Je remercie ´egalement Thierry Adatte et Jorge Spangenberg de l’Universit´e de Lausanne, qui m’ont initi´e `a la g´eochimie et sans qui je serais beaucoup moins heureux de parler d’isotopes !

Et merci aussi `a tous mes co-auteurs, Jeremy K. Caves Rugenstein, Miquel Poyatos- Mor´e, Emmanuelle Chanvry, Damien Huyghe, Eric Verrechia, Kalin Kouzmanov, et Matthieu Harlaux, pour le travail de terrain, leurs commentaires, corrections, aide de laboratoire et suggestions.

Merci `a tous les ´etudiants genevois en master, Charlotte L¨auchli, Andres Nowak, Joshua Vernier et Teodoro Hunger, dont le travail de terrain et les donn´ees ont permis de d’enrichir mes r´efl´exions.

Merci `a l’´equipe technique et administrative de l’universit´e de Gen`eve, Elisabeth Lagut, Phine Romagnoli, Rolanda Ferreira de Freitas Lopes, Fr´ederic Arlaud, Fran¸cois Gischig, Jean-Marie Boccard, Nino Isabella, qui ont aid´e et facilit´e ma vie

`a l’universit´e depuis neuf ans ! Et merci `a Christine Lovis pour les moments qui ont permis `a de se sentir un peu comme `a la maison.

Merci au troisi`eme ´etage pour les bi`eres, les d´ejeuners et les caf´es, c’est l’une des raisons pour lesquelles venir au bureau a toujours ´et´e un plaisir.

ix

Merci `a Janelle et Stephen pour la relecture, les commentaires et les conseils de r´edaction !

Merci `a mes colocataires, Aline, Jess et Alexia qui m’ont soutenu durant toute ma th`ese et particuli`erement sur les derniers mois et avec qui j’ai pu de temps en temps penser `a autre chose.

Merci `a mes amis, `a ma famille et `a tous ceux qui ont soutenu ma grogne et mes discussions qui tournaient en boucle autour de ma th`ese au cours des derniers mois!

Et enfin, merci `a mon corps qui a su faire face `a 3 op´erations et `a une pand´emie.

Merci !

Contents

Abstract v

R´esum´e vii

Remerciements ix

List of Figures xv

List of Tables xvii

List of Abbreviations xix

1 Introduction 1

1.1 Environmental signals and source-to-sink

approach . . . 2

1.2 Field context . . . 7

1.2.1 Geological overview . . . 8

1.2.2 Climatic overview . . . 10

1.3 Thesis Objectives . . . 13

1.3.1 Detecting eustatic and tectonic signals with carbon isotopes in deep-marine strata, Eocene Ainsa Basin, Spanish Pyrenees 13 1.3.2 Alluvial record of an early Eocene hyperthermal within the Castissent Formation, South Pyrenees . . . 15

1.3.3 Eocene topographic evolution of the Pyrenees constrained by oxygen isotopes . . . 17

1.4 Research questions . . . 20

1.5 Thesis structure . . . 21

2 Detecting eustatic and tectonic signals with carbon isotopes in deep-marine strata, Eocene Ainsa Basin, Spanish Pyrenees 23 2.1 Introduction . . . 24

2.2 Data and methods . . . 26

2.3 Carbon isotopes, eustatic variations, and tectonic exhumation . . . 28

xi

2.4 Discussion: eustatic, tectonic, and climatic controls on clastic depo-

sition . . . 29

2.5 Conclusions . . . 32

3 Alluvial record of an early Eocene hyperthermal within the Castissent Formation, South Pyrenees 33 3.1 Introdution . . . 35

3.2 Geological setting . . . 37

3.3 Material and methods . . . 40

3.3.1 Sampling . . . 40

3.3.2 Carbon and oxygen stable isotopes . . . 40

3.3.3 Major and trace element composition . . . 41

3.3.4 Mean annual precipitation . . . 41

3.3.5 Grain-size estimation . . . 42

3.3.6 Correlation with target curves . . . 42

3.4 Results . . . 43

3.4.1 Sedimentology of the Castissent Formation at Chiriveta . . . 43

3.4.2 Stable isotope record . . . 45

3.4.3 Major and trace elements . . . 45

3.5 Discussion . . . 46

3.5.1 Carbon and oxygen isotope record . . . 46

3.5.1.1 Identifying the CIE . . . 46

3.5.1.2 Mechanisms causing the CIE . . . 50

3.5.2 Geochemical signature of hyperthermal events . . . 52

3.5.3 High-resolution hyperthermal signal . . . 53

3.5.4 Possible implication for the preservation potential of hyper- thermals in continental sections . . . 54

3.6 Conclusions . . . 55

4 Eocene topographic evolution of the Pyrenees constrained by oxygen isotopes 57 4.1 Introduction . . . 58

4.2 Pyrenean tectonic and climatic framework . . . 60

4.2.1 Tectonic evolution . . . 60

4.2.2 Global and regional climate . . . 62

4.3 Material and Methods . . . 64

4.3.1 Sampling . . . 64

4.3.2 Stable isotopes . . . 64

4.3.3 Organic matter . . . 65

4.3.4 Comparison with global record . . . 65

4.4 Results and discussion . . . 66

4.4.1 Absolute values and diagenetic overprint . . . 66

4.4.2 Oxygen isotope evolution . . . 67

4.4.3 Carbon stable isotope evolution . . . 72

4.5 Conclusions . . . 72

Contents xiii

4.6 Paleocene tectonic quiescence . . . 74

5 Investigating the potential of small hyperthermals as stratigraphic correlation tools in fluvial environments 77 5.1 Introduction . . . 77

5.2 Limitations . . . 81

5.3 Material . . . 81

5.4 Results . . . 83

5.4.1 Sedimentology of the Castissent Formation at La Roca . . . 83

5.4.2 Stable isotope record . . . 84

5.4.3 Automated petrography (QEMSCAN) . . . 84

5.5 Discussion . . . 85

5.5.1 Hyperthermal U record in La Roca . . . 85

5.5.2 Influence of hyperthermal U on fluvial architecture . . . 87

5.6 Conclusion . . . 89

6 On the signature of orogenic development and early Eocene climate in the elemental and mineralogical composition of foreland hemipelagic marls and sandstones 91 6.1 Introduction . . . 91

6.2 Material and methods . . . 93

6.2.1 Sampling . . . 94

6.2.2 Marlstone major and trace element composition . . . 95

6.2.3 Sandstone mineral composition and mineral index of alteration 95 6.2.4 Fluvial input . . . 95

6.3 Results . . . 96

6.4 Discussion . . . 96

6.4.1 Untangling climatic and tectonic signals . . . 96

6.5 Conclusion . . . 99

7 Conclusion 101 7.1 Summary of key findings . . . 101

7.2 Emerging research questions . . . 105

A Appendix Figures 109 A.1 Supplementary figures Chapter 2 . . . 109

A.2 Supplementary figures Chapter 3 . . . 112

A.3 Supplementary figures Chapter 4 . . . 116

B Appendix Tables 121 B.1 Tables chapter 2 . . . 121

B.2 Tables chapter 3 . . . 125

B.3 Tables chapter 4 . . . 130

B.4 Tables chapter 5 . . . 149

B.5 Tables chapter 6 . . . 151 B.6 Thesis playlist . . . 157

C Conferences 159

D CV 161

Bibliography 165

List of Figures

1.1 Examples of cyclic signals . . . 3

1.2 Source-to-sink system . . . 5

1.3 Geological and paleogeographical map of the Pyrenees . . . 8

1.4 Chrono-litho-stratigraphic diagrams of the Tremp-Graus and Ainsa Basins during the Paleocene-Eocene times . . . 10

1.5 Eocene climatic overview . . . 12

1.6 Factors controlling the stratigraphic record . . . 14

1.7 Earth surface feedback to a hyperthermal event . . . 16

2.1 Paleogeography of the Ainsa Basin (Pyrenees, Spain) lower Eocene 25 2.2 Stratigraphy of canyon-axis sediment gravity flow (SGF) formations, and Pueyo composite section (Pyrenees, Spain) . . . 27

2.3 The δ¹³Ccarb record in the Ainsa Basin (Pyrenees, Spain) versus Pyrenean tectonics, global sea level, and isotopic records . . . 30

3.1 Late Palaeocene and early Eocene benthic carbon isotope record . . 36

3.2 Simplified situation and geological map of the study area . . . 38

3.3 Time constraints on the Castissent Formation . . . 39

3.4 Field images of the Chiriveta section . . . 45

3.5 Isotope and geochemical data from the Chiriveta section . . . 46

3.6 Continental δ¹³C and δ¹⁸O values from the early Eocene . . . 48

3.7 Scaling of the Chiriveta isotope section with deep-sea record . . . . 49

3.8 Components influencing the δ¹³C values of pedogenic carbonate nodules . . . 51

4.1 Simplified situation and geological map of the Ainsa and Tremp- Graus sub-basins and chrono-litho-stratigraphic diagram . . . 61

4.2 Global climatic and Pyrenean tectonic signals of the past 80 Ma. . . 63

4.3 Hi v. Tmax and Hi v. OI and plots of the Roda and El Pueyo sections. 67 4.4 South Pyrenean oxygen and carbon isotopic record. . . 67

4.5 Comparison between South Pyrenean, global and North Iberian continental margin δ¹⁸O records. . . 69

4.6 Paleotopography evolution of the Pyrenees. . . 72

4.7 Geographical and geological position of the Ar´en section . . . 74

4.8 δ¹⁸O record from the Ar´en section . . . 75

5.1 Eocene time-interval with no change in magnetozone or biozone . . 79 xv

5.2 Correlation between continental and marine sections using the PETM negative δ¹³C excursion as a marker . . . 81 5.3 Geological map and transect of the Castissent Formation . . . 82 5.4 Isotope data from the Chiriveta and La Roca sections . . . 83 5.5 QUEMSCAN^® image of the iron-barite nodule from La Roca section 85 5.6 Influence of hyperthermal ”U” on high-frequency stacking sequence

of the Castissent A member . . . 88 6.1 Alteration indices from the Paleocene to Oligocene Gulf of Mexico . 93 6.2 Tectonic vs. climate signal propagation . . . 94 6.3 Al, Fe, Ti, and Ca concentrations and respective Pearson correlation

coefficients of the Eocene marine south Pyrenean foreland basin. . . 97 6.4 Oxygen isotope, Aluminium (Al) and mineral index of alteration

(MIA) records from the south Pyrenean foreland basin. . . 98 A.1 Geological map of the study area in the Ainsa basin with location

of samples . . . 109 A.2 Oxygen and carbon isotopes data cross-plot from the Ainsa basin . 110 A.3 HI-Tmax cross-plot from Ainsa basin samples . . . 111 A.4 Macroscopic view of pedogenic nodules from the Chiriveta section . 112 A.5 Correlation options between Chiriveta and global δ¹³C records . . . 113 A.6 CIE amplitudes from I1, I2, H2, ETM2 and PETM in continental

and marine environments after (Abels et al. (2016) . . . 114 A.7 Grain-size proxies in the Chirivetta section . . . 115 A.8 Pyrenean, global (Cramer et al. (2009)), and smoothed and normal-

ized δ¹⁸O records . . . 116 A.9 Pyrenean, global (Cramer et al. (2009)), and smoothed and normal-

ized δ¹⁸O records . . . 117 A.10 Cramer et al. (2009) and the South Pyrenean δ¹⁸O records with depth118 A.11δ¹³C v. δ¹⁸O plots of the Roda, Camp and El Pueyo sections from

the south Pyrenean basins . . . 119

List of Tables

B.1 Pueyo section stable isotope on bulk carbonate results and Rockeval results . . . 121 B.2 D50values for 14 samples of the Chiriveta section using a Bettersizer

S3 Plus. . . 125 B.3 Clay minerals results from sample MO2 to MO7 in the top of the

Castissent Formation Member A. . . 125 B.4 Aluminium (Al), titanium (Ti), zirconium (Zr), mean annual pre-

cipitation (MAP) values, and age model of the Chiriveta section. . . 125 B.5 δ¹³C andδ¹⁸O values and age model of the Chiriveta section. . . 126 B.6 Correlation pointers between age of ODP site 1263 and Chiriveta’s

section height. . . 129 B.7 δ¹³C andδ¹⁸O values and age model of the south Pyrenean Basins . 130 B.8 Total organic carbon data of the south Pyrenean Basins . . . 142 B.9 δ¹³C andδ¹⁸O values of the La Roca section. . . 149 B.10 Aluminium content and age model from the south Pyrenean Basins 151 B.11 Mineral index of alteration from sandstones and age model from the

south Pyrenean Basins . . . 156

xvii

List of Abbreviations

A accommodation

Al aluminium

BSE back-scattered electrons

Ca calcium

CIE carbon isotopic excursion DOC dissolved organic carbon

EECO early-Eocene climatic optimum ETM Eocene thermal maximum

Fe iron

Fm. Formation

Gt giga ton

GTS2012 Geological Time-Scale version 2012

HC hydrocarbons

HI hydrogen index

kyr kilo years

Ma million years

MAP mean annual precipitation MIA mineral index of alteration

OI oxygen index

OM organic matter

PETM Paleocene-Eocene thermal maximum pCO2 partial pressure of carbon dioxide (CO2) psu practical salinity unit

Q10 Q10 temperature coefficient, indicates the rate of change of a biological or chemical system as a consequence of a 10 degrees increase in

temperature

QEMSCAN quantitative evaluation of materials by scanning electron microscopy xix

r Pearson correlation coefficient

S sediment flux

SD standard deviation

Si silicon

Tc compensation time scale

Ti titanium

TOC total organic carbon

VPDB Vienna Pee Dee Belemnite standard wt.% weight percent

XRD X-Ray diffraction XRF X-Ray fluorescence

Zr zirconium

Chapter 1 Introduction

The main objective of Earth sciences is to deduce the history of Earth from the geological record. Earth’s rock archives hold the only accessible clue to phenomena extending far beyond our time-scale. Earth’s rocks record, for instance, mountain building, past climate changes, resources formation, and storage, which are outside the reach of our direct monitoring. Much like historical studies, geological reasoning ambition is to narrate particular events that occurred at a given location (Frodeman (1995)) in order to apprehend our direct environment with its future changes and evolution. Studying Earth archives can potentially lead to laws/rules that can be applied globally, which in turn are building stone of predictive models. For instance, geological studies that have brought to light tectonic-plates motion opened the door to past and future plate position, putting forward hypothesis on past biogeography or potential earthquakes zones (e.g., Molnar (1987), Harland (1969)). Studying Earth’s geological record is of fundamental importance because by living on the surface of this planet, we are tied to its internal dynamics.

Many human societies are established next to mountains, rivers, lakes, and seas and are deeply dependent on what these environments provide for industry, energy, housing or tourism. All these physical environments have evolved through time and their modifications can be preserved in the sedimentary record. This history of past environmental signals provides the background for our understanding of today and future environmental problems. For instance, in view of the current climate change, addressing how water discharge in rivers changed during past climate warming events has important implications today for constructions built along them. The study of past phenomenon, including their frequency and amplitude, and how they

1

marked the sedimentary record can be clues to better apprehend natural events, and can even be eye-openers for natural hazard such as lake tsunamis (Kremer et al. (2012)). Studying how each of these environments and the sedimentary systems as a whole behaved in response to past environmental changes is essential to addressing future anthropological challenges.

1.1 Environmental signals and source-to-sink approach

In this work, to explore the response of sedimentary systems to external drivers, I focus on tracing past environmental signals recorded in sedimentary successions.

As a starting point, I define a signal as:

a function that conveys information about the behaviour of a system or attributes of some phenomenon.

Priemer (1990)

Applied to natural sciences and to the rock record, environmental signals are described as:

changes in sediment production, transport, or deposition that originate from perturbations of environmental variables such as precipitation, sea level, rock uplift, subsidence, and human modifications.

Romans et al. (2016)

The sediments are thus the function which carries precious information about Earth’s past behaviour. An environmental signal studied in the field under the form of sediment type, sedimentary structures, macro and micro-fossils, geochemical data. . . contains information about past climatic, tectonic and/or biotic events.

For example, varves in lake sediments are tracers of seasonal (summer-winter) variations and are therefore, besides being high-resolution dating deposits, direct recorders of climatic and environmental phenomenon occurring at the time of their deposition (Zolitschka et al. (2015), Figure 1.1). Other signals, far beyond our historical, observable time-scale, can be recorded in sediments: for example, Milankovich climatic cycles linked to the cyclical astronomical variation of Earth

Introduction 3 rotation with a duration of 2×10⁴ to 4×10⁵ years , icehouse vs. greenhouse cycles (ca. 10⁸ years) or super-continent cycles (10⁸ to 10⁹ years) (Romans et al. (2016),

Figure 1.1).

10⁸ 10⁷ 10⁶ 10⁵ 10⁴ 10³ 10² 10¹ 10⁰ 10^-1 10^-2 10^-3 10^-4

10^-5 10⁹

temporal scale

Signals

months

floods, storms, etc.

earthquakes tides

annual (e.g., varves)

decadal climate

(e.g., ENSO) Milankovitch orogenic cycles supercontinent

cycles centennial-millennial

climate (e.g., monsoonal)

precessionobliquity eccentricity

year kyr Myr Gyr

New Hampshire, 500 yr old varve

Milankovitch cyclicity linked deposits Scala dei Turchi, Sicily, Italy Centennial flood, Arve River, Geneva, 2015

NAGV Project Keyston / Laurent Gillieron

Figure 1.1: Examples of cyclic signals after Romans et al. (2016).

By studying past environmental signals, one is inevitably confronted to the question of their preservation in the stratigraphic record. Because the stratigraphic record is made of the accumulation with time of distinct particles, deposition and thus the record of environmental signal is inherently discontinuous (Sadler (1981)). The sedimentary record completeness conundrum is a long-standing debate in Earth sciences (e.g., Barrell (1917), Straub et al. (2020)) and is a critical limiting factor when studying past environmental signals.

The signal record can be hindered in three main ways (after Straub et al. (2020)):

i. The signal can be buffered by the sedimentary system. It can be the case if the system’s scale and response time to an external forcing is significantly larger than the signal duration. In that respect, large sedimentary systems (longer than 300 km) will buffer high-frequency (shorter than 100 kyr) signals (Castelltort and Van Den Driessche (2003)).

ii. The signal can be incomplete or missing because of a partial preservation of the stratigraphic record due to the internal dynamics of a system or extended

periods of erosion. Sedimentary systems can also be neither depositing nor eroding causing the signals to be condensed in a surface hence causing gaps in the sedimentary records (Straub and Foreman (2018)).

iii. Finally, the internal dynamics of a sedimentary system through chaotic transport can distort the environmental signal until it is no longer recognizable in the sedimentary archives (Jerolmack and Paola (2010)).

These concepts are essential to bear in mind when studying past environmental signals.

In this project, I investigate past environmental signals using a source-to-sink approach, which aims to take the sedimentary system as a whole from the sediment production zone to its deposition zone (Figure 1.2). Its ambition is to quantify the influence and propagation of environmental signals on sediment fluxes over different time-scales and interconnect the production, transport and deposition zones of sediments (Walsh et al. (2016)). Rather than a specific instrument, source-to-sink research is more similar to an intellectual and technical toolbox where the geologist chooses between a range of methods (i.e., geochemistry, palaeontology, (sequence) stratigraphy, biology, physical, numerical and analogical modelling. . . ) to come up with a solution to his or her questionings (Frodeman (1995)).

A source-to-sink system consists of three different zones; the erosion, the transfer and the deposition zone (Castelltort and Van Den Driessche (2003), Schumm (1981), Figure 1.2). In general terms, the erosion zone is the main sediment feeder through rivers and channels incising positive topography and transferring sediment downstream (Castelltort and Van Den Driessche (2003)). The transfer zone links the erosion and deposition zones and is a zone of sediment bypass and/or storage.

Finally, the deposition zone stores the upstream sediment flux. All the zones are influenced by tectonic uplift and subsidence, and climate under the form of rainfall and temperature as well as base level changes (Castelltort and Van Den Driessche (2003)).

Recent source-to-sink studies have led to an integrated approach of Earth’s surface response to external forcings. Examples include: how sedimentary system propagate sedimentary signal from observable to deep-time time-scale (Romans et al. (2016)), which sedimentary system buffers or propagates increase of sediment supply on 10-100 kyr times-scale (Castelltort and Van Den Driessche (2003)), empirical

Introduction 5 link between quantifiable source-to-sink system features such as drainage area, channel length, gradient, shelf and basin floor fans, for predictive models (Sømme et al. (2009), Milliman and Syvitski (1992)), the role of river transport and thus potential record in marine sediments of multi-millennial climatic cycles (Simpson and Castelltort (2012)) or the propagation of a 56 My old rapid climatic perturbation through a source-to-sink system (Duller et al. (2019)). The source-to-sink approach aims to obtain more predictive global stratigraphic models for resources and geological interpretations, in the same way that, 30 years ago, sequence stratigraphy enabled prediction of potential resource location of near-shore sedimentary systems based on sea-level variations (Walsh et al. (2016)). Moreover, in the light of today’s anthropological influence on source-to-sink systems though damns, construction activity, river channelization, contaminants, and climate change it is essential to have a broader understanding of how the system react as a whole under changing conditions (Turner et al. (2015), Walsh et al. (2016)).

time time

time

erosion sedimentation

transfer

CLIMATE CLIMATE

TECTONICS

SED. FLUX

TECTONICS

base level

source sink

Source-to-sink system

Signal propagation

sediment supply signal at exit of erosion zone

Qs Qs

Qs

Figure 1.2: Source-to-sink system showing the three subsystems: erosion, transfer and sedimentation and a schematic propagation through the system of a sediment supply increase (Modified from Castelltort and Van Den Driessche (2003), Romans et al. (2016)) However, there are still major unknowns about how a source-to-sink system stores and propagates past climatic and tectonic signals, and understanding this is

fundamental to deducing Earth’s history. For instance, on a multi-millennial time scale, both climatic and tectonic signals influence the stratigraphic record and can therefore be challenging to untangle (Romans et al. (2016), Figure 1.1). It makes the identification and the assessment of the origin of stratigraphic sequences challenging (Zhang et al. (2019), Schwarzacher (2007), Simpson and Castelltort (2012), Castelltort and Van Den Driessche (2003)). In relation to climatic signals, major long-term climatic records come mostly from deep-marine cores (e.g., Zachos et al. (2001)) but the extent to which fluvial successions can provide complete and faithful archives of past climatic events is still largely unknown (Foreman and Straub (2017), Straub and Foreman (2018), Trampush et al. (2017)). The need for greater understanding of this phenomenon is critical for studies aiming to trace the propagation of such signals in both continental and marine environments.

Furthermore, in order to apprehend the sediment production from the source zone, the evolution of drainage systems and their impact on the rest of the sedimentary system, tracing of the past topographic evolution of mountain ranges is crucial but still poorly constrained (Chamberlain and Poage (2000), Poage and Chamberlain (2001), Garzione et al. (2000), Botsyun et al. (2019)).

In this thesis, by investigating a source-to-sink system in reverse — from the sink to the source zone, based on field work and geochemical analysis from the South Eocene Pyrenean basin, I address these challenges.

1. In the sink zone, I compare global and local geochemical records to assess the origin of stratigraphic cycles in marine settings (chapter 2).

2. In the transfer zone, I investigate the geochemical record of floodplain deposits in order to measure the potential of such an environment to record short-lived climatic event known as ”hyperthermals” (chapter 3).

3. Finally, I evaluate the early Eocene uplift timing of the Pyrenees (source zone) by combining a large set of geochemical data from the sink zone (chapter 4).

I next give a brief geological and climatic context of the the South Eocene Pyrenean basin in section 1.2. I follow with a more detailed background to the research questions addressed in the chapters of this work in sections 1.3.1 to 1.3.3.

Introduction 7

1.2 Field context

The south Eocene Pyrenean Basins present a particularly suitable geological and climatic context to discuss and explore the preservation of climatic and tectonic signals.

The Pyrenees comprise a east-west 430 km-long mountain range separating Spain and France and culminating at 3404 m. It is bounded on the north by the Aquitaine retro-foreland basin and on the south by the Pyrenean pro-foreland basin comprising Cretaceous to Oligocene deposits (S´eguret (1972)). The good outcrop conditions, the accessibility, the vicinity of various depositional environments as well as the field analogues for hydrocarbon exploration (e.g., Falivene et al. (2006), Ard´evol et al. (2000), Nijman and Nio (1975), Mutti et al. (1985)), have made the south Pyrenean foreland basin the subject of numerous studies since the late sixties.

Thanks to these studies, we know that the south Pyrenean foreland basin has a strong stratigraphical and tectonical framework (e.g, Puigdef`abregas and Souquet (1986), Verg´es et al. (2002), Macchiavelli et al. (2017), Chanvry et al. (2018)) and important bio- and magnetostratigraphical constraints (e.g., Bentham and Burbank (1996), Payros et al. (2009), Poyatos-Mor´e (2014), Schaub (1981), Tosquella et al.

(1998)). Moreover, the south Pyrenean foreland basin fill encompasses the Paleocene to Eocene period which corresponds to a green-house epoch (i.e., global warm conditions, with no ice at the poles) which reached a maximum during the Early Eocene Climatic Optimum (EECO) (Westerhold and R¨ohl (2009), Hyland and Sheldon (2013)). In addition, pronounced warming events of relative short duration (40 to 200 kyrs) known as a ”hyperthermal events” punctuate this globally warm

epoch.

Good age-controls, active tectonic setting and a global context of strong and well known climatic events at various amplitude and duration make the Eocene south Pyrenean basin an ideal place to study, trace and confront climatic and tectonic signals at short and long time-scales.

The following sections include a brief overview of the geological and climatic context of this work. More specific details regarding each study location are given in the corresponding chapters.

43°N

42°30’N Sierras Interiores

Sierras Exteriores

Pyrenean Axial

Zone

Bóixols thrust Serres Marginals t.

Montsec t.

TREMP-GRAUS BASIN AINSA

BASIN BASINJACA

EBRO FORELAND

BASIN AQUITAINE

BASIN Variscan basement

Pyrenean Mesozoic and Cenozoic

Cenozoic in forelands

France

Spain Atlantic Ocean

Pyrenees

study area study area

N

1° 2°E

SPCU SPCU

500km

Iberia

Eurasia

(a) (b)

(c)

Figure 1.3: (a) - Structural sketch showing the main structural units of the central Pyrenees. (b) - Geographical position of the study area. (c) - Paleogeographical reconstruction of the Pyrenees during Eocene times (ca. 50 Ma). SPCU - South

Pyrenean Central Unit. Modified from Mu˜noz et al. (2013)

1.2.1 Geological overview

The Pyrenees is an orogen that developed from the upper Cretaceous to Miocene times from the convergence between the Iberian and European plate (Mu˜noz (1992), Puigdefabregas et al. (1992)). The motion of the Iberian micro-continent can be divided in two main phases (Macchiavelli et al. (2017)). The first phase corresponds with the opening of the Atlantic Ocean during the Jurassic-Cretaceous (154-83 Ma), where Iberia rotated anti-clockwise opening the Bay of Biscay. The second phase is associated with the convergence of Africa and Europe (83-0 Ma). The Pyrenees relief has been built mainly during two major phases of growth at ca. 52 and 35 Ma. Both phases are associated with an increased convergence rate between Iberia and Europe, and increased shortening rates and increased exhumation rates (Macchiavelli et al. (2017), Rosenbaum et al. (2002), Whitchurch et al. (2011), Fitzgerald et al. (1999), Verg´es et al. (2002), Grool et al. (2018)). The time-span of the present work concerns the late Paleocene to Eocene period (60-40 Ma).

Introduction 9 Among the sedimentary successions of the south Pyrenean basin, I focus on the Eocene succession of the Tremp-Graus and Ainsa basins. These basins are part of the South Pyrenean Central Unit (SPCU), a set of three major south-propagating thrust (Boixols, Montsec and Sierras Marginales) and their associated basins, bounded north by the axial zone and south by the orogenic front (Mutti et al.

(1988), S´eguret (1972), Figure 1.3). During Eocene times, the Tremp-Graus and Ainsa basins were elongated basins, parallel to the Pyrenean orogen and open west towards the Bay of Biscay (Puigdef`abregas and Souquet (1986), Figure 1.3b).

Consequently, sedimentation evolved from shelf and continental deposits in the eastern Tremp-Graus basin to more distal deep-marine turbidites deposits in the Ainsa and Jaca basins (Nijman and Nio (1975), Munoz et al. (1994)).

The Tremp-Graus basin is a piggyback basin positioned on top of the Montsec nappe (Marzo et al. (1988)) limited by the Boixols fault in the north and the Montsec thrust in the south Figure (1.3a). The Tremp-Graus basin is filled by approximately 7 km of syn-orogenic sediment covering the Cretaceous to the Oligocene periods.

The Paleocene to Eocene succession (i.e., focus of this work) is divided in four main groups (Chanvry et al. (2018), Figure 1.4). (1) The Paleocene Tremp Group, characterized by redbeds and alluvial conglomeratic deposits (Schmitz and Pujalte (2003), Puigdef`abregas and Souquet (1986)). (2) The lower Ypresian Alveolina Limestone, characterized by a large-scale marine transgression (Plaziat (1981), Puigdef`abregas and Souquet (1986)). (3) The Illerdian-Cuisian shallow water Figols Group (Torricelli et al. (2006)). (4) The Cuisian to Lutetian Monta˜nana Group, which encompasses the major fluvial progradation of the Castissent Formation (Nijman and Nio (1975), Nijman (1998), Marzo et al. (1988)). In the Ainsa basin, the distal time-equivalent of the Monta˜nana Group, is the Hecho Group (slope facies)(Nijman (1998)).

The Tremp-Graus basin passes to the Ainsa basin in the area of the Foradada fault, a northwest to southeast strike-slip fault connecting the major Montsec and Pe˜na Monta˜nesa thrusts (S´eguret (1972), Farrell et al. (1987)). Both basins are connected by submarine canyons systems (Millington and Clark (1995), Mutti et al. (1988)).

The Ainsa basin in filled with approximately 4 km of deep-marine deposits of the Hecho Group covering the middle Cuisian to Lutetian period (Gupta and Pickering (2008), Fontana et al. (1989), Mutti (1977), Figure 1.4). The Hecho Group is composed of 7-8 sandy turbiditic systems containing each 2 to 8 sand bodies (Fosado, Molinos, Arro, Gerbe, Banast´on, Ainsa, Morillo and Guaso systems).

46 Ma 47 48 49 50 51 52 53 54 55 56 57 58 59

PaleoceneEocene ThanetianYpresianLutetian Illerdian

Ainsa

sub-basin Graus-Tremp

sub-basin

y h p a r g it a r t

S E

W

Sis-Gurp paleo-valleys

Boltana Fm.

Morillo Ch.

Ainsa Ch. Gerbe

Banaston Ch.

Campanue Fm.

Perarrua Fm.

Castissent Fm.

Castigaleu Fm.

Morillo Lmst.

La Puebla Lmst.

Riguala Marl Alveolina Lmst.

Claret Cglm.

Navarri Fm.

Tremp Fm.

Up. Detritic Complex

Roda Sdt.

Arro Ch.

Fosado Ch.

San Esteban

Fm. Montllobat Fm.

Capella Fm.

Charo-Lascorz

Atiart Pocino Guaso Ch.

Guaso Ch.

Cuisian

Hecho Gp.

Hecho Gp.

Figure 1.4: Chrono-litho-stratigraphic diagrams of the Tremp-Graus and Ainsa Basins during the Paleocene-Eocene times. From Chanvry et al. (2018)

.

These sand bodies, interbedded with intervals of hemipelagic marls, occur with a cylicity of about 400 kyr (Pickering and Bayliss (2009)).

1.2.2 Climatic overview

The Tremp-Graus and Ainsa basins record successions from the Paleocene to the Eocene period which is a time-period rich in climatic changes.

Global deep-sea climatic record characterizes the Paleocene to the Eocene period with a climate about 12^◦C warmer than today and without ice at the poles (Zachos et al. (2001)). This warm period culminated during the EECO during ca. 4 Ma after which the climate began to cool (∼Eocene-Oligocene transition, Zachos et al.

(2008)) towards today’s ice-house period (i.e., with permanent ice at the poles).

A long-term negative shift in oxygen isotopes marks the EECO in the deep-sea

Introduction 11 global climatic records (e.g., Cramer et al. (2009), Figure 1.5). The EECO period is also marked by an increase in terrigenous supply towards the sea, presumably linked to a higher continental runoff enhanced by an accelerated hydrological cycle and a higher seasonality (i.e., more rain in a shorter amount of time) (Payros et al.

(2015), Slotnick et al. (2012)).

Coeval with this warm period, the global climatic record shows transient warming events known as ”hyperthermal events” (e.g., Lauretano et al. (2015)). The Palaeocene-Eocene Thermal Maximum (PETM; 56 Ma, duration about 170 kyr) was the first of these hyperthermal events to be identified globally because of its notable magnitude and preservation in both marine and continental deposits (Koch et al. (1992), Figure 1.5). The PETM represents a global warming of 5 to 9^◦C induced by a release of approximately 1500 to 4500 gigatons of carbon to the ocean and atmosphere (Bowen et al. (2006)). The PETM has been widely studied because of its similarity with today’s global warming (e.g., Bowen et al. (2015)). The study of the PETM opened the door to the identification of other hyperthermal events of lower magnitude (warming of 1 to 3^◦C) and lower duration (40 kyr) and to date, a total of 39 hyperthermal events are identified for the late Palaeocene to early Eocene period (Westerhold et al. (2018), Figure 1.5). In the deep-marine records, these events are defined by paired negative excursions in carbon and oxygen isotope data above background variability (Cramer et al. (2003), Nicolo et al. (2007), Zachos et al. (2008), Sluijs and Dickens (2012), Lauretano et al. (2016)). The isotope excursions are considered as hyperthermal events typically if the amplitude of both stable isotope excursions are greater than one standard deviation (SD) of pre-hyperthermal background values (Kirtland-Turner et al. (2014)). Similarly to the EECO, in coastal marine sections, hyperthermal events trigger an enhanced flux of continental material towards the sea (Schmitz et al. (2001), Bowen et al.

(2004), Nicolo et al. (2007), Dunkley Jones et al. (2018)).

Palynological data from the south Pyrenean foreland basin suggest a climate evolv- ing from subtropical in the Paleocene, tropical during the EECO, and decreasing afterwards during the Eocene accompanied by monsoonal climate (Haseldonckx (1973), Figure 1.5). The EECO is interpreted as a time of increased rainfall, runoff and weathering (Payros et al. (2015)) and the PETM as a time of important increase of water discharge, which triggered an important terrigenous material flux towards the ocean plausibly helped by a regional vegetation decline (Chen et al.

(2018)).

Kominz et al. 2008

Miller et al. 2005

sea level (m) above present

50 100 15075 125

25 5554535251504948

Lutetian

55545352515049484756 4756

Stage

Magneto-stratigaphy EoceneEpoch 585745 Ma46

PaleoceneYpresianThanetian

C24n.3nC24n.1nC24n.2n C23n.2rC23n.2nC23n.1n C22nC21rC21nC24rC22rC25nC25rC20r

585745 Ma46 PETMH1/ETM2H2X/ETM3

E1 F I1I2JLMNOPQRST UV WE2

1.5

δ¹³Ccarb benthic (‰)

1.0 0.5 0.0 -0.5 -1.0 -1.5

EECO ODP 1263 ODP 1265ODP 1262

C22nH4 C22nH5

C21rH1 C21rH2 C21rH3

C21rH4 C21rH5

C22nH3

C21n.H1

ODP 1209

δ¹⁸Ocarb benthic (‰)

-2-1.5-1-0.500.5 TropicalSub-tropical

South-Pyrenean long-term climate

Towards ice-house Earth

Green-house Earth hyperthermal event

Figure1.5:Eoceneclimaticoverview.RevisedmagnetostratigraphyfromWesterholdetal.(2017).Ypresiansouth-PyreneanclimatefromHaseldonckx(1973)basedonpalynologicaldata.Compiledδ 13Candδ 18OdataonbenthicsfromWesterholdetal.(2017)andhyperthermalnamesfromLauretanoetal.(2016)andCrameretal.(2003).EarlyEoceneClimaticOptimum(EECO)timingbasedonWesterholdetal.(2018).

Introduction 13

1.3 Thesis Objectives

Hereafter, I articulate the specific scientific background to the research questions addressed in this work.

1.3.1 Detecting eustatic and tectonic signals with carbon isotopes in deep-marine strata, Eocene Ainsa Basin, Spanish Pyrenees

Cyclic sedimentation refers to the organised repetition of distinctive lithological units (Duff et al. (1967)). These units are found in a large range of depositional environments and with a wide order of amplitude and time-scale (Einsele et al.

(1992), Figure 1.1). This observed periodicity suggests a specific mechanism capable of creating the cyclicity (Schwarzacher (2007)) but this mechanism can be difficult to assess (Castelltort and Van Den Driessche (2003), Schwarzacher (2007), Simpson and Castelltort (2012)). Indeed, sedimentary systems are complex environments where climate, tectonics and the biosphere interact creating numerous possibilities to create cyclicity (Schwarzacher (2007)). Apart from the influence of Milankovitch cycles — change of Earth’s rotation around its axis and around the sun influencing Earth’s climate — which are predictable and calculated back in time (Laskar et al.

(2011)), these cyclicities with periods of a thousand to a million years, occur over longer time-scale than what we are able to observe making direct comparison with recent deposits difficult (Schwarzacher (2007), Romans et al. (2016)).

The potential of stratigraphic cycles to be recorded in the sedimentary record, is a function of accommodation (i.e., space available for the deposition of sediments) and sediment supply (Cross (1988), Gardner (1995), Mitchum et al. (1977), Posamentier and Vail (1988), Catuneanu et al. (2009), Figure 1.6). However, virtually all possible driving factors able to influence the amplitude of sediment supply and/or accommodation space with different magnitudes and frequency are able to generate such cycles (Castelltort and Van Den Driessche (2003), Schwarzacher (2007)).

Accommodation on one hand is controlled by rise and fall of the sea level as well as subsidence, i.e., the gradual downward settling of Earth’s surface. Sediment supply on the other hand is controlled by topography (tectonics) and climate (Figure 1.2). For instance, an increase in uplift rates, affecting the topographic relief will provide more sediment to the system (e.g., Burbank et al. (2003)). Climate

change such as the one occurring during the EECO will increase precipitation favouring erosion and transport of sediment towards the basin (e.g., Slotnick et al.

(2012)), creating a similar signal in the stratigraphic record than a increase in uplift. Moreover, climate and tectonic forcings can occur on similare time-scale making them difficult to untangle (Romans et al. (2016), Figure 1.1). Despite the increase in geochemical tools to analyse the sedimentary record (i.e., clumped isotopes (Eiler (2007), cosmogenic nuclide (Covault et al. (2011)), defining the origin of stratigraphic cycles is still a challenge. Answering this question is central for geology because when sediments get lithified and become part of the geological record; direct observation and quantification of the driving factors are not available any more. Therefore, by understanding the processes taking place at intermediate time-scales, one can try to predict Earth’s surface responses to long-term changes.

EUSTATISM

SUBSIDENCE

SEDIMENT FLUX

available accommodation space

Figure 1.6: Factors controlling the stratigraphic record. From Lafont (1994).

In the Ainsa basin, in the South Pyrenean foreland basin, cyclic deposition is observed under the form of sandy sediment gravity systems separated by important thickness of hemipelagic marls. The origin of the cyclic deposition of these sediment gravity flow systems from the Hecho Group is a long standing question (e.g., Mutti et al. (1988), Heard et al. (2008), Cantalejo and Pickering (2014, 2015), Weltje and Van Ansen (1996), Nijman (1998), Pickering and Bayliss (2009), Payros et al.

(2009)). The controls put forward to explain this repetitive deposition pattern are either upstream driven (i.e., tectonic or climatic) or dowstream driven (i.e., sea-level fluctuations).

To understand the origin of cyclicity in the Ainsa basin, the following question need to be addressed: What is the respective role of tectonics and climate in controlling the sediment flux to the Ainsa basin? What proxy can be used to confront the sediment gravity flow occurrence to tectonic/- climatic forcings?

Introduction 15

1.3.2 Alluvial record of an early Eocene hyperthermal within the Castissent Formation, South Pyrenees

We know that climate has varied through time at different time-scale and amplitude.

For instance in more recent times, the last ice age which started 2.5 million years ago is characterized by extensive ice sheet in the northern hemisphere (Lorens et al. (2004)). The glaciers have been advancing and retreating during this ice age during periods known as glacial-interglacial cycles with a periodicity paced with Milankovitch cycles of 100, 41 and 23 kyr (Sigman and Boyle (2000), Hays et al. (1976)). Past climatic events have shaped today’s landscapes by carving mountains and lakes such as the Geneva lake (Wildi et al. (1999)). Moreover, they have influenced today’s living organisms evolution and distribution (Hewitt (2000)) and are therefore important focus points of past-climate studies.

The Eocene is considered as a green-house period, where ice caps are not present or only ephemeral (e.g., Zachos et al. (2001), Pekar et al. (2005)). However, other orbitally paced climatic events know as ”hyperthermal events” occur during the Paleocene and Eocene periods (e.g., Lauretano et al. (2016), Figure 1.5).

Hyperthermal events are defined in marine settings and measured on whole-rock as well as foraminifera by a carbon and oxygen isotope excursion larger than one standard deviation together with an increase in iron (Fe) content in the whole- rock (Kirtland-Turner et al. (2014)). These hyperthermals represent rapid global warming events of 1 to 3 degrees (Stap et al. (2010)). Their origin is still debated but these events are caused by a rapid injection of isotropically light carbon (i.e., depleted in ¹³C, giving a negative δ¹³C signal, see δ¹³C inset) potentially linked to changes in ocean ventilation and oxidation of organic matter in abyssal oceans (Sexton et al. (2011)). These Eocene hyperthermal events can show similar features (after Foster et al. (2018), Figure 1.7):

∗ A rapid warming episode with a duration of about 40 kyr (and 200 kyr for the PETM).

∗ A reduction in oceanic oxygen content which can lead to ocean anoxia and increase carbon burial

∗ A increase in atmospheric CO2 and ocean acidification leading to carbonate dissolution in marine environments

∗ An increased hydrological cycle and increase seasonality

∗ An increase of continental erosion/weathering rates

release of isotopically light

CO₂ (CIE)

increase pCO₂ & T°

increase evaporation

accelerated hydrological cycle

increase runoff

& continental erosion sea level

CCD

enhanced seasonal precipitation

shallowing of the CCD Fe and clay layer in deep-sea cores

reduced vegetation

Figure 1.7: Earth surface feedback to a hyperthermal event. CIE: Carbon isotope excursion. CCD: carbonate compensation depth

Studying hyperthermal events is important in several ways. Because these events happen at a global scale, they can be useful correlation points and critical fea- tures for studies addressing environmental signal propagation in source-to-sink systems (e.g., Duller et al. (2019)). Moreover, studying Earth’s behaviour to past hyperthermal events is one of the only ways to test and to provide fundamental information to climatic models modelling today’s climate change (Foster et al.

(2018)). Finally, hyperthermal events, and particularly important ones such as the PETM, are important moments of mammalian turnover and have the potential to influence the evolution of life (Gingerich (2006), Chew (2009)). These knowledge gains and today’s climatic circumstances, explain why hyperthermal studies have flourished since 30 years with more than 600 scientific paper on the PETM alone (McInerney and Wing (2011)).

Major events such as the PETM event have proven to be detectable in both marine and continental environments (e.g.; Abels et al., 2016; Koch et al., 1992) but the signal preservation potential of smaller scale climatic events in continental environments is less straightforward (Foreman and Straub (2017)).

Since the first studies that applied sequence stratigraphy concepts to continental deposits, the preservation of environmental signals in the continental stratigraphic record has been considered incomplete, especially during falling sea-level (Shanley and McCabe (1994), Wright and Marriott (1993)). Floodplain deposits are consid- ered as discontinuous in nature due to non-continuous flood, avulsion, and channel migration sedimentation processes and the irregular depositional thickness relative

Introduction 17 to the position of the channel (Turner et al. (2015)). This potential incompleteness of the sedimentary record (Barrell (1917), Sadler (1981)) and the capacity of a sedimentary section to document a continuous paleoclimatic signal have probably led many workers to prefer the deep-marine records for paleo-climatic studies.

Yet, continental strata, which form in direct contact to environmental conditions occurring at the time of their formation, might preserve important clues to the way the Earth system reacted to abrupt warming (Sheldon and Tabor (2009)).

However, the extent to which fluvial successions can provide complete and faithful archives of past climatic events, especially those with the smallest magnitudes, is still largely unknown (Foreman and Straub (2017), Trampush et al. (2017), Straub and Foreman (2018)).

The South Pyrenean foreland basin deposits in the Tremp-Graus basin encompass the Eocene period where numerous hyperthermal events occur. Among the South Pyrenean successions, the Castissent fluvial Formation is an important depositional event occurring at ca. 50 Ma which deposited, besides thick coarse sand channels, lateral important paleosol successions. Moreover, several studies give important time-constraints over this period, allowing a good calibration with global climatic records.

From this setup arise the following questions: Can the continental environment record small-scale hyperthermal events? If yes, is it possible to point out which hyperthermal event is recorded? What is the geochemical signature and climatic impact of a small-scale hyperthermal event in a continental environment?

1.3.3 Eocene topographic evolution of the Pyrenees con- strained by oxygen isotopes

Convergent tectonic plates lead to crustal deformation and to the creation of positive topography (e.g., Willett (1999)). The development of a mountain range occurs over 10 Ma to 100 Ma time scale (Figure 1.1), and is thus far beyond direct observation. Moreover it develops in a non-linear way, with periods of rapid growth succeeding periods with a more moderate topographic growth (e.g., Curry et al. (2019)). However, past topographic evolution is important to define for several reasons. Topographic relief, through enhanced precipitation and erosion,

Carbon isotopes (δ¹³C)

Carbon has two stable isotopes, from light to heavy: ¹²C and ¹³C.

The isotope ratio R is defined as:

R =

13C

12C

By convention, because natural frac- tionations are small, carbon isotope ratios are calculated as deviation re- garding a standard substance:

δ¹³C = R_sample−R_standard R_standard

If the δ¹³C is negative, the sample is depleted in the heavy isotope relative to the standard.

δ¹³C varies through time in function of primary productivity and carbon burial.

When important volumes of carbon with a negative δ¹³C signature are re- leased into the carbon system through i.e., release of volcanic gases (δ¹³C = -6 h), oxidation of organic matter (δ¹³C = -26h), or release of methane clathrate (δ¹³C = -60 h), the global δ¹³C record shifts towards negative val- ues. Hyperthermal events are marked by such shifts in δ¹³C.

In contrast, a global increase in carbon burial will shift theδ¹³C towards more positive values.

After Hoefs (2019).

provides sediment to the sedimentary system (Willett (1999)) and is therefore important to constrain in order to apprehend a source-to-sink system as a whole.

Moreover, mountains are key features regarding atmospheric circulation and climate.

Because moutain range act as a barrier, defining when and at which altitude were orogens in the past is crucial to develop past atmospheric circulation models as well vegetation and fauna distribution paleomaps (Suc and Fauquette (2012), Mulch (2016), Hewitt (2000)). Topographic evolution is the final result of the interaction between tectonics, mantle dynamics and climate and are therefore essential to decipher these signals. For instance, the topographic evolution and important orographic barrier of the Himalayas are thought to be in part responsible for the long-term transition from the Eocene green-house to today’s ice-house period (e.g., Molnar and England (1990), M.E.Raymo and W.F.Ruddiman (1992))

Approaches to constrain paleo-topography can either give quantitative results such as flexural models (Mill´an et al. (1995)) or palynology studies (Suc and Fauquette (2012)). Others provide relative topographic growth change by using indirect increase or decrease of proxies such as the measure of sediment flux and provenance to the basin (France-Lanord et al. (1993)), thermochronology tracing exhumation rates (Garver et al. (1999)), convergence rates (Rosenbaum et al.

(2002)), and oxygen isotopes (Rowley et al. (2001)). This last approach is based on the fact that when an air mass comes across a topographic relief, it rises