Abstract
The early Eocene experienced a series of short-lived global warming events, known as hyperthermals, associated with negative carbon isotope excursions (CIE). The Paleocene-Eocene Thermal Maximum (PETM or ETM-1) and Eocene Thermal Maximum 2 (ETM-2) are the two main events of this Epoch, both marked by massive sea-floor carbonate dissolution. Their timing, amplitude and impacts are rather well documented, but CIEs with lower amplitudes also associated with carbonate dissolution are still poorly studied (e.g. events E1 to H1), especially in the terrestrial realm where hiatus/disconformities and various sedimentary rates in a single succession may complicate the assignation to global isotopic events. Here we present a new high-resolution multi-proxy study on the terrestrial, lagoonal and shallow marine late Paleocene-early Eocene succession from two sites of the Cap d’Ailly area in the Dieppe-Hampshire Basin (Normandy, France). Carbon isotope data (δ13C) on bulk organic matter and higher-plant derived n-alkanes, and K-Ar ages on authigenic glauconite were determined to provide a stratigraphic framework. Palynofacies, distribution and hydrogen isotope values (δ2H) of higher-plant derived n-alkanes allowed us to unravel paleoenvironmental and paleoclimatic changes. In coastal sediments of the Cap d’Ailly area, δ13C values revealed two main negative CIEs, from base to top CIE1 and CIE2, and 3 less pronounced negative excursions older than the NP11 nannofossil biozone. While the CIE1 is clearly linked with the PETM initiation, the CIE2 could either correspond to 1) a second excursion within the PETM interval caused by strong local environmental changes or 2) a global carbon isotopic event that occurred between the PETM and ETM-2. Paleoenvironmental data indicated that both main CIEs were associated with dramatic changes such as eutrophication, algal and/or dinoflagellate blooms along with paleohydrological variations and an increase in seasonality. They revealed that the intervals immediately below these CIEs are also marked by environmental and climatic changes. Thus, this study shows either 1) a PETM marked by at least two distinct intervals of strong environmental and climatic changes or 2) at least one “minor” CIE: E1, E2, F or G, was associated with strong environmental and climatic changes similar to those that occurred during the PETM.
Highlights
The late Paleocene and early Eocene were marked by a series of extreme and fast transient global hyperthermal events (Cramer et al, 2003; Lourens et al, 2005; Coccioni et al, 2012; Westerhold et al, 2018)
The Cap d’Ailly area in northern France (Fig. 1) displays a series of expanded late Paleocene-early Eocene sedimentary sections corresponding to terrestrial and lagoonal environments that outcrop on top of the Cap d’Ailly cliffs (Dupuis et al, 1998; Magioncalda et al, 2001). These Paleogene sediments are divided into three Formations (Fig. 2; Dupuis et al, 1998): (i) the Mortemer Fm is best known for its uppermost lacustrine-palustrine Member, the “Calcaire du Cap d’Ailly” (CCA) Mb; (ii) the Soissonnais Fm begins with the lagoonal “Sables et Argiles à Ostracodes et Mollusques” (SAOM) Mb that is overlain by the marine clay of the Craquelins Mb (Fig. 2); (iii) the transgressive Varengeville Fm first displays three glauconitic clayey sand units (FV1 to FV3) that are overlain by two clay units (FV4 and FV5) separated from each other by a glauconitic and bioclastic sand bed
Our results show five negative carbon isotope excursions (CIE), the main ones being CIE1 and CIE2, within terrestrial and coastal sediments of the Sparnacian Mortemer and Soissonnais Formations, which are older than the NP11 nannofossil biozone
Summary
The late Paleocene and early Eocene were marked by a series of extreme and fast transient global hyperthermal events (Cramer et al, 2003; Lourens et al, 2005; Coccioni et al, 2012; Westerhold et al, 2018). Cramer et al (2003) showed that four events, “E1”, “E2”, “F” and “G”, still poorly studied, occurred between PETM and ETM-2, respectively 250, 350, 750 and 940 ka after the PETM (Westerhold et al, 2017) Their CIE magnitudes are much smaller than that of the PETM, even though the “E1” CIE magnitude can reach half of that of the PETM in Italy (Coccioni et al, 2012). Our integrated data unravel climatic and environmental changes at other time intervals than the one occurring at the Paleocene-Eocene boundary and their possible link with carbon isotopic events in this mid-latitude coastal environment
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