Mechanisms for exceptional preservation in the Fezouata Lagerstätte (Early Ordovician, Morocco) Farid Saleh To cite this version: Farid Saleh. Mechanisms for exceptional preservation in the Fezouata Lagerstätte (Early Ordovician, Morocco). Earth Sciences. Université de Lyon, 2020. English. NNT : 2020LYSE1126. tel-03328479 HAL Id: tel-03328479 https://tel.archives-ouvertes.fr/tel-03328479 Submitted on 30 Aug 2021 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. N°d’ordre NNT : xxx THESE de DOCTORAT DE L’UNIVERSITE DE LYON opérée au sein de l’Université Claude Bernard Lyon 1 Ecole Doctorale N° ED 341 (Évolution, Écosystèmes, Microbiologie, Modélisation) Spécialité de doctorat : Sciences de la Terre/Earth Sciences Discipline : Taphonomie/Taphonomy Soutenue publiquement le 16/07/2020, par : Farid SALEH Mechanisms for exceptional preservation in the Fezouata Lagerstätte (Early Ordovician, Morocco) Devant le jury composé de : Daniel, Isabelle Pr Univ. Lyon 1 Présidente Mangano, Gabriela Pr Univ. Saskatchewan Rapporteure Ma, Xiaoya Pr Yunnan Univ. Rapporteure Daley, Allison Pr Univ. Lausanne Examinatrice Harper, David Pr Durham Univ. Examinateur Lefebvre, Bertrand CR CNRS Directeur de thèse Pittet, Bernard MCF Univ. Lyon 1 Co-directeur Perrillat, Jean-Philippe MCF Univ. Lyon 1 Co-directeur TABLE OF CONTENT ACKNOWLEDGMENTS ABSTRACT RÉSUMÉ 1. INTRODUCTION 2. GENERAL BACKGROUND 3. MATERIAL AND METHODS 4. BURIAL BY STORM DEPOSITS 5. DECAY AND MINERALIZATION 6. FOSSIL MATURATION AND WEATHERING 8. TAPHONOMIC BIAS IN THE FEZOUATA SHALE 9. CONCLUSION AND OUTLOOK REFERENCES ACKNOWLEDGMENTS A lot can happen in a few years. Back in 2012, I was studying aiming to be a physician. Here, I am now writing the acknowledgments of my Ph.D. in Earth Sciences. I would take this opportunity not only to thank the people that supported me during the last 30 months but also to thank those who were by my side in each and every step during this long bumpy, yet exciting journey. I cannot express enough gratitude to Bertrand Lefebvre, and Bernard Pittet, my supervisors since my Master’s internship. They both helped me gain the knowledge I currently have. I couldn’t do any of the work without their presence. They were all the time here, by my side, encouraging me when I had one of those crazy ideas you’ll be reading in the upcoming chapters. But also, bringing me down to Earth when I went in my interpretation too far or too fast. You both taught me how a researcher should be. I will be remembering your remarks each and every single time I write a paper in the future, for the rest of my academic career. Many thanks to Jean Philippe Perrillat, my co-director, whose curiosity brought us to work together. His rigorous comments helped me concretize two (3 in total) of what I think are the most exciting projects of my Ph.D. Allison Daley is the superwoman of my Ph.D. She was here, whenever I needed to talk with someone either on a scientific topic or just on my daily life problems. The Ph.D. would have been a tougher journey without her presence. This thesis also benefited from the positive environment provided by the LGLTPE, and the extreme kindness and support of Emanuela Mattioli, in addition to numerous collaborations with talented researcher: Jonathan Antcliffe, Muriel Vidal, Martina Nohejlová, Francesc Perez Peris, Lukas Laibl, Lorenzo Lustri, Pierre Gueriau, David Harper, Yves Candela, Aaron Hunter, Pierre Sansjofre, Stefan Lalonde, Khadija El Hariri, Marika Polechová, and Khaoula Kouraiss. In addition to fruitful discussions with colleagues: Isabelle Daniel, Gilles Escarguel, Vincent Perrier, Claude Colombié, Guillaume Suan, Frédéric Quillévéré, Vincent Grossi, Ingrid Antheaume, and passionate amateurs: Eric Monceret, and Daniel Vizcaïno. I would also like to thank Gabriella Mángano, and Xiaoya Ma for agreeing to evaluate my work and write their reports. I am sure that many collaborations will emerge with you in the future. To the friends that I met in France: Nevena, Genia, Bea, Raimon, Auguste, Pauline, Lorenza, Ophélie, and Claire, I really appreciate you guys for supporting me during the day at the university and during the night at the “LookBar”. To my Lebanese friends Antonia, Sylia, Moukbel, Joe, Leba, Wael, and Yorgo, thank you for being able to deal with all my “philosophical” thinking over the last twenty years. Noura and Rawan M., you wrote most of my memories in the streets of Hamra. You are a main part of the happy moments during the last two years. Doph you are a cornerstone in my life. Thank you for being here in all my ups and downs. Many thanks to all my family members especially my uncles: Bassam and Houssam for all the socio-political challenging and motivating conversations we had when I was taking a break from research. And lots of appreciations go to my cousin and my academic mentor Dane. Without your help, I wouldn’t be in France now. Many hugs to my little cousins: Lynn, Cérine, and George. You give me loads of inspiration and emotional support with every smile you put on your faces. Last but not least, I would like to express my gratitude towards my parents Leila, and Nassim. Thank you for loving me, believing in me, and doing everything for me to succeed. I know you are my biggest fans and please know that I am yours too. I love you so much. 1 ABSTRACT The Fezouata Shale is the most diverse Lower Ordovician unit with exceptional fossil preservation. Fossils from this formation altered our understanding of early metazoan communities at the transition between the Cambrian Explosion and the Ordovician Radiation. The paleontology and the general sedimentological context of the Fezouata Shale are well established. However, little was done to understand the interaction between both, and studies regarding fossil preservation remain scarce. In this thesis, we investigate the general conditions and mechanisms responsible for soft-tissue preservation in the Fezouata Shale. Comparing brachiopod, bivalve, and trilobite size fluctuations between sites allowed us to constrain burial rates in this formation. This permitted the discovery of a relative post-mortem burial tardiness in sites where exceptional fossil preservation occurred. Moreover, mineralogical investigations showed a correlation between particular chlorite phases (i.e. chamosite/berthierine) and preserved soft parts. This mineralogy may have slowed down oxic decay and its deposition was most probably due to periods with high seasonality. Furthermore, we hypothesized for the first time, a possible implication of biomolecules (i.e. ferritin) in the preservation of soft parts. This, if confirmed, would resolve the observed discrepancies between the fossil record preserving nervous systems to the exclusion to everything else, and decay experiments showing that nervous tissues are among the first structures to decay and disappear in laboratory conditions. Additionally, we show that metamorphism was not operational in the Fezouata Shale. However, modern weathering leached organic material from surface sediments and transformed pyrite into iron oxides. This finding infers that the original mode of preservation of the Fezouata Shale comprises both carbonaceous compressions and accessory authigenic pyritization. The direct implication of this work was shown through a comparison of enigmatic patterns preserved in three groups of echinoderms. It appears that some of these patterns in eocrinoids and somasteroids do not reflect original anatomies and are preservation artifacts. However, it is certain that the structures preserved in stylophorans are real, closing a long-standing debate on the affinity of this animal group. Finally, a general comparison between the Fezouata Shale and Cambrian Lagerstätten allowed us to decipher the implication of the suggested taphonomic pathway on fossil preservation. It appears that the Fezouata Shale mechanism for preservation failed to preserve completely cellular organisms (e.g. chordates, ctenophores, medusoids) implying a possible underestimation of the original Fezouata Biota and confirming that the Cambrian Explosion and the Ordovician Radiation are one single episode of anatomical innovation. Thus, all these results have implications on understanding ecosystems, and evolution at the dawn of animal life and may contribute in the future to the development of a predictive approach for the discovery of exceptionally preserved biotas. 2 RÉSUMÉ La Formation des Fezouata a livré les assemblages à préservation exceptionnelle les plus diversifiés de l'Ordovicien inférieur. Les fossiles de cette unité ont bouleversé notre compréhension des premières communautés animales à la transition entre l'explosion cambrienne et la diversification ordovicienne. La paléontologie et le contexte sédimentologique général de la Formation des Fezouata sont bien établis. Cependant, l'interaction entre les deux demeurait peu connue, et les études concernant la préservation des fossiles étaient rares. Dans cette thèse, nous étudions les conditions et les mécanismes qui ont abouti de la préservation