Deoxygenation and organic carbon sequestration in the Tethyan realm associated with the middle Eocene climatic optimum

The middle Eocene climatic optimum (ca. 40 Ma) stands out as a transient global warming phase of ~400 k.y. duration that interrupted long-term Eocene cooling; it has been associated with a rise in atmospheric CO2 concentrations that has been linked to a flare-up in Arabia-Eurasia continental arc volcanism. Increased organic carbon burial in the Tethys Ocean has been proposed as a carbon sequestration mechanism to bring the middle Eocene climatic optimum to an end. To further test these hypotheses, we assessed the sedimentary and geochemical expression of the middle Eocene climatic optimum in the northern Peri-Tethys, specifically, the organic-rich Kuma Formation of the Belaya River section, located on the edge of the Scythian Platform in the North Caucasus, Russia. We constructed an age-depth model using nannofossil chronobiostratigraphy. Throughout the studied middle Eocene interval (41.2–39.9 Ma), we documented sea-surface temperatures of 32–36 °C based on the tetraether index of tetraethers consisting of 86 carbons (TEX86), depending on proxy calibration, and during the early middle Eocene climatic optimum, we observed sea-surface warming of 2–3 °C. Despite the proximity of the section to the Arabia-Eurasia volcanic arc, the hypothesized source of volcanic CO2, we found no evidence for enhanced regional volcanism in sedimentary mercury concentrations. Sedimentary trace-element concentrations and iron speciation indicate reducing bottom waters throughout the middle Eocene, but the most reducing, even euxinic, conditions were reached during late middle Eocene climatic optimum cooling. This apparent regional decoupling between ocean warming and deoxygenation hints at a role for regional tectonics in causing basin restriction and anoxia. Associated excess organic carbon burial, extrapolated to the entire regional Kuma Formation, may have been ~8.1 Tg C yr–1, comprising ~450 Pg C over this ~55 k.y. interval. Combined with evidence for enhanced organic carbon drawdown in the western Peri-Tethys, this supports a quantitatively significant role for the basin in the termination of the middle Eocene climatic optimum by acting as a large organic carbon sink, and these results collectively illustrate that the closing Tethys Ocean might have affected global Paleogene climate

From Peri-Tethys to Paratethys : Basin restriction and anoxia in central Eurasia linked to volcanic belts in Iran

From the Alps in western Europe to the great steppes of Kazakhstan, the former Paratethys Sea once covered a vast area of our planet, of which the Black Sea, Caspian Sea and Aral lake are today’s remnants. The Paratethys formed as the Tethys ocean gradually closed, and was known as ‘Peri-Tethys’ until the late Eocene. The Peri-Tethys transformed into the Paratethys after it became an isolated basin from the Oligocene onwards. Initially, Laskarev (1924) coined the term Paratethys, describing the environment of Miocene sediments, containing peculiar fossils that developed in this isolated environment. Later, also Oligocene strata were included, which show the first isolation from the Tethys ocean. The birth of the Paratethys is characterised by a change in sedimentation reflecting well-oxygenated bottom waters during the Eocene, towards low-oxygen environments in the Oligocene (Maikop Series). In my thesis, we set out to unravel the roles of tectonic and eustatic mechanisms on the transition from Peri-Tethys to Paratethys and onset of oxygen-poor conditions. We focus on sections that show the change from the Eocene open configuration of the Peri-Tethys to the enclosed setting of the Paratethys, and on the progressively closing marine connections of the Paratethys. We investigate Maikop equivalent sediments in southern Germany (North Alpine Foreland basin; NAFB), and the Maikop and underlying sediments at its type section (Belaya river, Russia). My thesis covers millions of years, and a vast geographic area, to better understand the timing and paleogeographic changes in the basin. This large-scale approach has enabled us to shed light on many different aspects that were important for the evolution from Peri-Tethys to Paratethys. We show that the connection of the Paratethys trough the NAFB closes at 33.15 Ma, millions of years earlier than the previously estimated 28 Ma. In Russia, we show that oxygen-depleted episodes already occurred in the Kuma formation (middle Eocene) that coincide with the Middle Eocene Climatic Optimum (MECO; at 40.5 Ma). In Azerbaijan, we show that volcanism was active around 40.5 Ma, and that overlying sediments that are mapped as ‘Maikop Series’ are of Late Eocene age. We show that the geochemical signature of the volcanic rocks is that of a continental arc, which is in contrast to previous studies that interpreted them as back-arc basin volcanics. We suggest that there is one volcanic belt running from the Talysh in the south of Azerbaijan through Iran towards Bazman (southeast Iran). In the Alborz Mountains (Iran), we use vertical axis rotations derived from paleomagnetic data combined with literature data of the Pontides (Turkey) and the Lesser Caucasus (Georgia and Armenia) to calculate the amount of convergence that is taken up in the Greater Caucasus. We present new Ar-Ar ages of volcanic rocks in Azerbaijan and Iran, and compile ages of volcanic rocks throughout Iran from literature. We show that volcanism in Iran was very active around the MECO, and hypothesize that there is a relationship between the increase in arc volcanism and global climate

From Peri-Tethys to Paratethys : Basin restriction and anoxia in central Eurasia linked to volcanic belts in Iran

From the Alps in western Europe to the great steppes of Kazakhstan, the former Paratethys Sea once covered a vast area of our planet, of which the Black Sea, Caspian Sea and Aral lake are today’s remnants. The Paratethys formed as the Tethys ocean gradually closed, and was known as ‘Peri-Tethys’ until the late Eocene. The Peri-Tethys transformed into the Paratethys after it became an isolated basin from the Oligocene onwards. Initially, Laskarev (1924) coined the term Paratethys, describing the environment of Miocene sediments, containing peculiar fossils that developed in this isolated environment. Later, also Oligocene strata were included, which show the first isolation from the Tethys ocean. The birth of the Paratethys is characterised by a change in sedimentation reflecting well-oxygenated bottom waters during the Eocene, towards low-oxygen environments in the Oligocene (Maikop Series). In my thesis, we set out to unravel the roles of tectonic and eustatic mechanisms on the transition from Peri-Tethys to Paratethys and onset of oxygen-poor conditions. We focus on sections that show the change from the Eocene open configuration of the Peri-Tethys to the enclosed setting of the Paratethys, and on the progressively closing marine connections of the Paratethys. We investigate Maikop equivalent sediments in southern Germany (North Alpine Foreland basin; NAFB), and the Maikop and underlying sediments at its type section (Belaya river, Russia). My thesis covers millions of years, and a vast geographic area, to better understand the timing and paleogeographic changes in the basin. This large-scale approach has enabled us to shed light on many different aspects that were important for the evolution from Peri-Tethys to Paratethys. We show that the connection of the Paratethys trough the NAFB closes at 33.15 Ma, millions of years earlier than the previously estimated 28 Ma. In Russia, we show that oxygen-depleted episodes already occurred in the Kuma formation (middle Eocene) that coincide with the Middle Eocene Climatic Optimum (MECO; at 40.5 Ma). In Azerbaijan, we show that volcanism was active around 40.5 Ma, and that overlying sediments that are mapped as ‘Maikop Series’ are of Late Eocene age. We show that the geochemical signature of the volcanic rocks is that of a continental arc, which is in contrast to previous studies that interpreted them as back-arc basin volcanics. We suggest that there is one volcanic belt running from the Talysh in the south of Azerbaijan through Iran towards Bazman (southeast Iran). In the Alborz Mountains (Iran), we use vertical axis rotations derived from paleomagnetic data combined with literature data of the Pontides (Turkey) and the Lesser Caucasus (Georgia and Armenia) to calculate the amount of convergence that is taken up in the Greater Caucasus. We present new Ar-Ar ages of volcanic rocks in Azerbaijan and Iran, and compile ages of volcanic rocks throughout Iran from literature. We show that volcanism in Iran was very active around the MECO, and hypothesize that there is a relationship between the increase in arc volcanism and global climate

Magnetic to the Core – communicating palaeomagnetism with hands-on activities

Abstract. Palaeomagnetism is a relatively unknown part of Earth sciences that is not well integrated into the school curriculum in the UK. Throughout recent years, there has been a decline in the number of Earth science students in the UK. In 2018 and 2019, we developed outreach activities and resources to introduce the scientifically engaged general public to palaeomagnetism and raise awareness of how geomagnetism affects society today, thus putting palaeomagnetism, and Earth sciences, in the spotlight. We tested our ideas at local events that were visited mostly by families with small children, with tens to hundreds of participants. Our project culminated in the Magnetic to the Core stand at the Royal Society Summer Science Exhibition in 2019, which is visited by members of the general public, students and teachers, scientists, policymakers and the media. At this event, we communicated the fundamentals of palaeomagnetism through hands-on activities and presented our recent research advances in a fun and family- friendly way. To test the impact of our exhibit on knowledge of palaeomagnetism and Earth's magnetic field on visitors, we designed an interactive quiz and collected results from 382 participants over 8 d. The results show a significant increase in median quiz score of 22.2 % between those who had not yet visited the stand and those who had visited for more than 10 min. The results from school-aged respondents alone show a larger increase in the median score of 33.5 % between those who had not yet visited and those who had spent more than 10 min at the stand. These findings demonstrate that this outreach event was successful in impacting visitors' learning. We hope our Magnetic to the Core project can serve as an inspiration for other Earth science laboratories looking to engage a wide audience and measure the success and impact of their outreach activities. </jats:p

Exploring a link between the Middle Eocene Climatic Optimum and Neotethys continental arc flare-up

The Middle Eocene Climatic Optimum (MECO), a ~ 500 kyr episode of global warming that initiated at ~40.5 Ma, is postulated to be driven by a net increase in volcanic carbon input, but a direct source has not been identified. Here we show, based on new and previously published radiometric ages of volcanic rocks, that the interval spanning the MECO corresponds to a massive increase in continental arc volcanism in Iran and Azerbaijan. Ages of Eocene igneous rocks in all volcanic provinces of Iran cluster around 40 Ma, very close to the peak warming phase of the MECO. Based on the spatial extent and volume of the volcanic rocks as well as the carbonaceous lithology in which they are emplaced, we estimate the total amount of CO2 that could have been released at this time corresponds to between 1052 and 12 565 Pg carbon. This is compatible with the estimated carbon release during the MECO. Although the uncertainty in both individual ages, and the spread in the compilation of ages, is larger than the duration of the MECO, a flare-up in Neotethys subduction zone volcanism represents a plausible excess carbon source responsible for MECO warming

Exploring a link between the Middle Eocene Climatic Optimum and Neotethys continental arc flare-up

The Middle Eocene Climatic Optimum (MECO), a ~ 500 kyr episode of global warming that initiated at ~40.5 Ma, is postulated to be driven by a net increase in volcanic carbon input, but a direct source has not been identified. Here we show, based on new and previously published radiometric ages of volcanic rocks, that the interval spanning the MECO corresponds to a massive increase in continental arc volcanism in Iran and Azerbaijan. Ages of Eocene igneous rocks in all volcanic provinces of Iran cluster around 40 Ma, very close to the peak warming phase of the MECO. Based on the spatial extent and volume of the volcanic rocks as well as the carbonaceous lithology in which they are emplaced, we estimate the total amount of CO2 that could have been released at this time corresponds to between 1052 and 12 565 Pg carbon. This is compatible with the estimated carbon release during the MECO. Although the uncertainty in both individual ages, and the spread in the compilation of ages, is larger than the duration of the MECO, a flare-up in Neotethys subduction zone volcanism represents a plausible excess carbon source responsible for MECO warming

Exploring a link between the Middle Eocene Climatic Optimum and Neotethys continental arc flare-up

The Middle Eocene Climatic Optimum (MECO), a ~ 500 kyr episode of global warming that initiated at ~40.5 Ma, is postulated to be driven by a net increase in volcanic carbon input, but a direct source has not been identified. Here we show, based on new and previously published radiometric ages of volcanic rocks, that the interval spanning the MECO corresponds to a massive increase in continental arc volcanism in Iran and Azerbaijan. Ages of Eocene igneous rocks in all volcanic provinces of Iran cluster around 40 Ma, very close to the peak warming phase of the MECO. Based on the spatial extent and volume of the volcanic rocks as well as the carbonaceous lithology in which they are emplaced, we estimate the total amount of CO2 that could have been released at this time corresponds to between 1052 and 12 565 Pg carbon. This is compatible with the estimated carbon release during the MECO. Although the uncertainty in both individual ages, and the spread in the compilation of ages, is larger than the duration of the MECO, a flare-up in Neotethys subduction zone volcanism represents a plausible excess carbon source responsible for MECO warming

Exploring a link between the Middle Eocene Climatic Optimum and Neotethys continental arc flare-up

The Middle Eocene Climatic Optimum (MECO), a ~ 500 kyr episode of global warming that initiated at ~40.5 Ma, is postulated to be driven by a net increase in volcanic carbon input, but a direct source has not been identified. Here we show, based on new and previously published radiometric ages of volcanic rocks, that the interval spanning the MECO corresponds to a massive increase in continental arc volcanism in Iran and Azerbaijan. Ages of Eocene igneous rocks in all volcanic provinces of Iran cluster around 40 Ma, very close to the peak warming phase of the MECO. Based on the spatial extent and volume of the volcanic rocks as well as the carbonaceous lithology in which they are emplaced, we estimate the total amount of CO2 that could have been released at this time corresponds to between 1052 and 12 565 Pg carbon. This is compatible with the estimated carbon release during the MECO. Although the uncertainty in both individual ages, and the spread in the compilation of ages, is larger than the duration of the MECO, a flare-up in Neotethys subduction zone volcanism represents a plausible excess carbon source responsible for MECO warming

A persistent non-uniformitarian paleomagnetic field in the Devonian?

The Devonian has long been a problematic period for paleomagnetism. Devonian paleomagnetic data are generally difficult to interpret and have complex partial or full overprints– problems that arise in data obtained from both sedimentary and igneous rocks. As a result, the reconstruction of tectonic plate motions, largely performed using apparent polar wander paths, has large uncertainty. Similarly, the Devonian geomagnetic polarity time scale is very poorly constrained. Paleointensity studies from volcanic units suggest that the field was much weaker than the modern field, and it has been hypothesised that this was accompanied by many polarity reversals (a hyperreversing field). We sampled Middle to Upper Devonian sections in Germany, Poland and Canada which show low conodont alteration indices, implying low thermal maturity. We show that there are significant issues with these data, which are not straightforward to interpret, even though no significant heating or remineralisation appears to have caused overprinting. We compare our data to other magnetostratigraphic studies from the Devonian and review the polarity pattern as presented in the Geologic Time Scale. Combined with estimates for the strength of the magnetic field, we suggest that the field during the Devonian might have been so weak, and in part non-dipolar, that obtaining reliable primary paleomagnetic data from Devonian rocks is challenging. Careful examination of all data, no matter how unusual, is the best way to push forward our understanding of the Devonian magnetic field. Paleointensity studies show that the field during the Devonian had a similar low strength to the Ediacaran. Independent evidence from malformed spores around the Devonian-Carboniferous boundary suggests that the terrestrial extinction connected to the Hangenberg event was caused by increased UV-B radiation, supporting the weak field hypothesis. A fundamentally weak and possibly non-dipolar field during the Devonian could have been produced, in part, by true polar wander acting to maximise core-mantle heat flow in the equatorial region. It may also have influenced evolution and extinctions in this time period. There are a large number of paleobiological crises in the Devonian, and we pose the question, did the Earth’s magnetic field influence these crises