Lake Hayq is a closed, freshwater basin on the eastern margin of the north-central highlands, Ethiopia. Using a sediment core extracted from the northern basin, this thesis aims to provide a high-resolution, detailed palaeolimnological reconstruction of changes to the environment and climate in the region since the late Pleistocene. A multi-proxy approach was applied, utilising diatoms, photosynthetic pigments and X-ray fluorescence (XRF) spectrometry. Lithological and chronological analyses were also performed, as well as the development of a transfer function to model diatom-inferred conductivity, and other quantitative analyses. Between ~ 15.6 15.1 cal kyr BP, Lake Hayq experienced a lowstand, synchronous with the timing of Heinrich Event 1 and an intense drought across East Africa. At ~ 15.1 cal kyr BP a lake began to develop at the core site in response to wetter, more humid conditions, most likely caused by the reactivation of the African-Indian monsoonal circulation. This was abruptly ended however at ~ 14.7 cal kyr BP, as the climate shifted back towards aridity and Lake Hayq shallowed, in contrast to the majority of other East African lakes, which continued to refill. This most likely reflects changes to the Indian Ocean monsoon system caused by variability in the Atlantic Meridional Overturning Circulation at this time, in conjunction with site-specific mechanisms affecting the delivery of precipitation to Lake Hayq. At ~ 12.3 cal kyr BP the African Humid Period resumed over Lake Hayq and the lake refilled, reaching maximum water depth between ~ 12.0 10.0 cal kyr BP. The lake was dominated by planktonic diatom taxa and photosynthetic pigments indicate it was meromictic. Lake level gradually declined throughout the Holocene, culminating in the termination of the African Humid Period. A high-resolution study of the period tentatively suggests that climate flickering , in the form of oscillations between dominant diatom taxa, occurred in the build up to the major climatic shift. The termination spanned ~ 600 cal years between ~ 5.2 4.6 cal kyr BP. A lowstand occurred between ~ 3.9 2.2 cal kyr BP, during which the lake became occasionally subsaline. In the late Holocene, ~ 2.2 1.3 cal kyr BP, Lake Hayq became deep and fresh again, although there is evidence of lake level variability. The palaeo-record from Lake Hayq indicates that it broadly experienced the same high-latitude, glacial-interglacial dynamics and sub-millennial shifts in climate found in other palaeolimnological records from across East Africa. The precise timing and expression of these climatic events is not always synchronous between Lake Hayq and other East African waterbodies however, most likely caused by local, site-specific positive feedback mechanisms and variability in lake morphometry. This highlights the heterogeneous pattern of climate across the region and the significance of regional drivers. This palaeo-record, spanning the late Quaternary, will help bridge gaps in current knowledge and understanding of the underrepresented, climatically sensitive and vulnerable north Ethiopian highlands. This is vital for future climate change modelling and regional downscaling, and may also inform ethnographic-archaeological research in a region considered to be the cradle of humankind.

Dans ce travail de thèse, certaines étendues d’eaux continentales regroupant plusieurs types de système de dépôt comme les lacs, mers intérieures et lagunes ont été regroupées au sein d'un nouveau groupe de système sédimentaire mentionnés sous l'appellation de Wind-driven Water Body (WWB).Afin de caractériser l'évolution et l'enregistrement sédimentaire d'un exemple de WWB, une étude sédimentologique intégrée du bassin quaternaire du Lac Saint-Jean (Québec, Canada) a été menée à partir d'une approche intégrant géologie de terrain et imagerie géophysique très haute résolution (CHIRP 2D). A l'échelle du cortège sédimentaire, le régime glaciaire à paraglaciaire de la sédimentation et le rebond glacio-isostatique ont contrôlé au premier ordre, à la fois la succession lithologique et les architectures grandes échelles du bassin pour générer un Cortège de Régression Forcée (CRF) atypique. Au sein de ce cortège de régression forcée fini-glaciaire, une dynamique de système WWB s'est progressivement affirmée à partir de 8,5 cal. ka BP. Elle s'est exprimée par la mise en place d'une dynamique littorale importante occasionnellement associée à une circulation interne générant des courants de fonds lors d'épisodes de vents forts.Finalement, l'analyse sédimentologique du bassin du Lac Saint-Jean a permis de dégager plusieurs interprétations ayant attrait (1) à l'évolution des systèmes WWB et (2) aux séquences de déglaciation en domaine précédemment englacé. De plus, ce travail représente une contribution à l'échelle régionale pour les modalités de la dernière déglaciation du Sud-Est du Québec. / In this study, a certain number of continental enclosed basins including several depositional systems such as lakes, inland seas or lagoons have been grouped in a new sort of sedimentary system referred to as Wind driven Water Body. To characterize the sedimentary evolution and record of a WWB basin, an integrated sedimentological study has been carried out on the quaternary Saint-Jean basin (Québec, Canada) based on field onshore geology and offshore geophysics (CHIRP 2D).At the system-tract scale, the glacial to paraglacial sedimentation and the glacio-isostatic rebound controlled at first-order the lithofacies succession and large-scale architectures to generate an original Falling Stage System Tract (FSST). Within this FSST, since 8.5 cal. ka BP a WWB related sedimentary evolution overprinted the glacial to paraglacial evolution. This expressed in the form of the emplacement of an important coastal dynamics, occasionally accompanied by a lake-scale hydrodynamics at the origins of bottom currents during strong wind to storm events.Finally, the sedimentological analysis of the Saint-Jean basin brought numerous interpretations related to (1) the sedimentary evolution of WWB systems and (2) deglaciation sequences in previously glaciated domains. In addition, this work supplements the regional quaternary framework concerning the latest deglaciation evolution in southeast Quebec.