Paleohydraulic Reconstructions, Geochemical Signals and Intermittency Estimates from the Middle Eocene Escanilla Formation, Spain

The Earth’s surface undergoes changes over time due to various factors such as changes in climatic processes, sea level, and tectonic activity. These changes occur gradually and often go unnoticed to the human eye but are left behind as evidence in the form of sedimentary layers and erosional patterns that can be studied over geological time periods. For instance, ancient fluvial deposits are important archives of past changes and investigating their different aspects has implications for understanding past climate and landscape evolution. This doctoral thesis is focussed on the Middle Eocene (∼40 Ma) aged Escanilla Formation in the south-central Pyrenees, Spain, and is a compilation of 4 different studies. The first study documents how ancient riverbed systematically evolved from lower slopes in coarser-grained high amalgamation (HA) intervals, and higher slopes in finer-grained low amalgamation (LA) intervals. These changes were primarily driven by climate-controlled water discharge variations rather than base level changes. The second study presents a comprehensive geochemical record of the Middle Eocene Climatic Optimum (MECO), a global warming event that occurred at ∼40 Ma, using a suite of sampled paleosols, fluvial stromatolites, and pedogenic nodules. Geochemical proxies include carbon and oxygen stable isotopes, weathering indices, mean annual precipitation, clumped isotope temperature and clay mineralogy. Based on the regional preservation of the MECO and the climate, this study highlights fluvial sedimentary successions as interesting terrestrial archives of past changes in global climate. The third study explores a relationship between water discharge, sediment flux variability, and changing fluvial stratigraphic architecture with results indicating that HA intervals were most likely deposited under more intermittent and short-lived, intense precipitation events, while LA intervals were the result of less intermittent flows throughout the year. These estimates are consistent with values from modern ephemeral rivers typically found in arid to semi-arid climatic conditions, and highlight the connection between hydroclimate, river morphodynamics, and landscape evolution. Finally, the fourth study, explores a potential relationship between the MECO and a continental arc flare-up as a source of pCO2. An increase in mercury content relative to the MECO likely suggests a link between the two. Collectively, these studies provide new insights into the complex dynamics of past climate and landscape evolution, and have implications for interpreting ancient sedimentary deposits such as changes in fluvial stacking patterns, highlighting the importance of fluvial sedimentary successions as key archives of past global climate evolution and perturbations.