Abstract. The early Cenozoic marine sedimentary record is punctuated by several brief episodes (<200 kyr) of abrupt global warming, called hyperthermals, that have disturbed ocean life and water physicochemistry. Moreover, recent studies of fluvial–deltaic systems, for instance at the Palaeocene–Eocene Thermal Maximum, revealed that these hyperthermals also impacted the hydrologic cycle, triggering an increase in erosion and sediment transport at the Earth's surface. Contrary to the early Cenozoic hyperthermals, the Middle Eocene Climatic Optimum (MECO), lasting from 40.5 to 40.0 Ma, constitutes an event of gradual warming that left a highly variable carbon isotope signature and for which little data exist about its impact on Earth surface systems. In the South Pyrenean foreland basin (SPFB), an episode of prominent deltaic progradation (Belsué–Atarés and Escanilla formations) in the middle Bartonian has been usually associated with increased Pyrenean tectonic activity, but recent magnetostratigraphic data suggest a possible coincidence between the progradation and the MECO warming period. To test this hypothesis, we measured the stable-isotope composition of carbonates (δ13Ccarb and δ18Ocarb) and organic matter (δ13Corg) of 257 samples in two sections of SPFB fluvial–deltaic successions covering the different phases of the MECO and already dated with magnetostratigraphy. We find a negative shift in δ18Ocarb and an unclear signal in δ13Ccarb around the transition from magnetic chron C18r to chron C17r (middle Bartonian). These results allow, by correlation with reference sections in the Atlantic and Tethys, the MECO to be identified and its coincident relationship with the Belsué–Atarès fluvial–deltaic progradation to be documented. Despite its long duration and a more gradual temperature rise, the MECO in the South Pyrenean foreland basin may have led, like lower Cenozoic hyperthermals, to an increase in erosion and sediment transport that is manifested in the sedimentary record. The new data support the hypothesis of a more important hydrological response to the MECO than previously thought in mid-latitude environments, including those around the Tethys.
<p>The Empord&#224; basin is located in NE Catalonia (Spain), overprinting the Eastern Pyrenees where this mountain belt reaches the Mediterranean Sea. The area offers an opportunity to study cycles of orogenic evolution, from mountain building to destruction, although with some peculiar features. Following Pyrenean contractional structures that ceased in the Oligocene, earlier than in the Central and Western Pyrenees finished during the lower Miocene, the extension that depressed the Empord&#224; basin seems to be a younger event (late Miocene-Pliocene) than the opening of the Western Mediterranean (Gulf of Lyon and Valencia trough; late Oligocene-Miocene). The regional NE-SW extensional fault systems that dominate from the Gulf of Lion to the Catalan Coastal Ranges and Valencia grabens contrast with the NW-SE normal faults in the Empord&#224; basin, which are also associated with alkali volcanism during the Neogene. This feature is still poorly understood, together with the absence of crustal root in the adjacent relict relief of the Pyrenees despite the relatively high elevation.</p> <p>To gain insights into these questions and into the detailed geochronology and mechanisms of the transition from convergence to extension, we have revisited the tectono-sedimentary record of the South-Pyrenean and Empord&#224; basins. First, the provenance of the clastic deposits from the Paleogene to the Neogene gives information about the evolution of the sedimentary systems, as well as the tectonic changes in the source regions. This data combined with low-temperature thermochronology of source reliefs and basin sedimentary units allows characterizing part of the geodynamic evolution from the NW Mediterranean realm. Complementary, new structural data from field observations and seismic profile interpretation provide us with inferences on a new structural model of the region.</p>
Abstract. The early Cenozoic marine sedimentary record is punctuated by several brief episodes (< 200 kyr) of abrupt global warming, called hyperthermals, that have disturbed ocean life and water physicochemistry. Moreover, recent studies of fluvial-deltaic systems, for instance at the Palaeocene-Eocene Thermal Maximum, revealed that these hyperthermals also impacted the hydrologic cycle, triggering an increase in erosion and sediment transport at the Earth’s surface. Contrary to the early Cenozoic hyperthermals, the Middle Eocene Climatic Optimum (MECO), lasting from 40.5 to 40.0 Ma, constitutes an event of gradual warming that left a highly variable carbon isotopic signature and for which little data exist about its impact on Earth surface systems. In the South-Pyrenean Foreland Basin (SPFB), an episode of prominent deltaic progradation (Belsué-Atarés and Escanilla formations) in the middle Bartonian has been usually associated with increased Pyrenean tectonic activity, but recent magnetostratigraphic data suggest a possible coincidence between the progradation and the MECO warming period. To test this hypothesis, we measured the stable isotope composition of carbonates and organic matter of 257 samples in two sections of SPFB fluvial-deltaic successions covering the different phases of the MECO and already dated with magnetostratigraphy. We find a negative shift in 𝛿 18Ocarb and an unclear signal in 𝛿13Ccarb around the transition from magnetic Chron C18r to Chron C17r (middle Bartonian). These results allow, by correlation with reference sections in the Atlantic and Tethys, to identify the MECO and document its coincident relationship with the Belsué-Atarès fluvial-deltaic progradation. Despite its long duration and a more gradual temperature rise, the MECO in the South Pyrenean Foreland Basin may have led, like lower Cenozoic hyperthermals, to an increase in erosion and sediment transport that is manifested in the sedimentary record. The new data support the hypothesis of a more important hydrological response to the MECO than previously thought in mid latitude environments, including those around the Tethys.
<p>Past sedimentary archives provide invaluable comparative insights to understand Earth&#8217;s surface reaction to climate shifts and perturbations. Foreland basins are particularly interesting settings for investigating the sedimentary record of ancient climate perturbations because their high-accommodation and high-sedimentation rates favour protracted and expanded records that complement more distal oceanic records. In addition, due to their proximity to source areas, they provide direct information on the land surface response to the regional impacts of global climate shifts.</p><p>However, besides climate signals, the stratigraphic record of foreland basins is subject to a broad range of other factors that make its interpretation challenging. Indeed, foreland basins are naturally sensitive to the influence of tectonics on sediment production and accommodation, either associated with the long-term tectonic evolution of the orogen-basin system, or with the more local and regional shorter-term structural dynamics and geodynamic perturbations. Moreover, if connected to oceanic domains, eustatic sea-level oscillations can also combine with the above factors in determining final stratigraphic patterns.</p><p>Over the last two decades, a large body of paleoclimate work has produced new and crucial data on global climate events that have affected our planet. In particular, a suite of global climate perturbations (warming, cooling) have been identified in the Paleogene, thanks to stable isotope of C and O, with some major global warming events such as the PETM, ETM2&3, the EECO, the MECO and others that have fundamental implications for the current global climate crisis.</p><p>This well-established climatic template provides a unique opportunity to test the impact of climate on surface systems in deep time, particularly during the Paleogene hothouse. Therefore, we here present our work on the Isabena section in the South Pyrenean Foreland basin, which is a uniquely continuous and well exposed succession encompassing from the upper Cretaceous to the upper Eocene. We sampled continuously at 1-10 meters intervals over the 4 km-thick succession, from the lower Eocene to the upper Eocene. This sampling results in a new and continuous magnetostratigraphy covering almost 30 Myr of stratigraphic evolution, and a new high-resolution stable isotope record of carbon and oxygen over the Paleogene. These results combined with sedimentological descriptions and stratigraphic analyses reveal the links between important sedimentation changes and global climate events. Preliminary results suggest that hyperthermal events are often associated with enhanced sediment transport and clastic deposition in the basin, while intervals comparatively cooler seem to be more prone to enhanced carbonate accumulation.</p>
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