Carbon Cycle and Ecosystem Response to the Jenkyns Event in the Early Toarcian (Jurassic)
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The Toarcian Oceanic Anoxic Event, also known as the Jenkyns Event, was a hyperthermal episode which occurred during the early Toarcian (c. 183 Ma; Early Jurassic) and resulted in numerous collateral effects including global warming, enhanced weathering, sea-level change, carbonate crisis, marine anoxia–dysoxia, and a second-order mass extinction. This volume presents the last advances for understanding early Toarcian environmental changes through different disciplines: biostratigraphy, micropalaeontology, palaeontology, ichnology, palaeoecology, sedimentology, integrated stratigraphy, inorganic, organic and isotopic geochemistry, and cyclostratigraphy. The study of this abrupt climate change is critical for predicting future global changes, and for understanding the complex biogeochemical interactions through time between geosphere, atmosphere, hydrosphere and biosphere.
Primary v. carbonate production in the Toarcian, a case study from the Llanbedr (Mochras Farm) borehole, Wales Available to Purchase
Correspondence: [email protected]
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Published:November 03, 2021
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CiteCitation
Alessandro Menini, Emanuela Mattioli, Stephen P. Hesselbo, Micha Ruhl, Guillaume Suan, 2021. "Primary v. carbonate production in the Toarcian, a case study from the Llanbedr (Mochras Farm) borehole, Wales", Carbon Cycle and Ecosystem Response to the Jenkyns Event in the Early Toarcian (Jurassic), M. Reolid, L. V. Duarte, E. Mattioli, W. Ruebsam
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Abstract
The leading hypothesis for the Toarcian oceanic anoxic event (T-OAE; c. 183 Ma) and the associated negative C-isotope excursion is the massive release of 12C favouring greenhouse conditions and continental weathering. The nutrient delivery to shallow basins supported productivity and, because of O2 consumption by organic-matter respiration, anoxia development. However, several studies have shown that calcareous nannoplankton experienced a decrease during the T-OAE. Nannofossil fluxes measured in the Llanbedr (Mochras Farm) borehole, Wales, UK, were the highest prior to the negative C-isotope excursion, along with high amounts of taxa indicative of nutrient-rich environments (Biscutaceae). Such conditions attest to high productivity. Fluxes show the lowest values in the core of the event, along with a size decrease of Schizosphaerella and a peak in Calyculaceae. The recovery of nannofossil fluxes and Schizosphaerella size occurred concomitant with the return of C-isotopes to more positive values. Concomitantly, deep dwellers (Crepidolithus crassus) dominated, indicating a recovery of the photic-zone productivity. These observations demonstrate that the cascade of environmental responses to the initial perturbation was more complex than previously considered. In spite of elevated nutrient delivery to epicontinental basins in the early Toarcian, carbonate and primary productions of nannoplankton were depressed in the core the T-OAE, probably because of prolonged thermohaline seawater stratification.
- anaerobic environment
- assemblages
- biostratigraphy
- boreholes
- C-13/C-12
- carbon
- carbonates
- Cardigan Bay
- case studies
- Europe
- Great Britain
- greenhouse effect
- isotope ratios
- isotopes
- Jurassic
- Lower Jurassic
- lower Toarcian
- Mesozoic
- microfossils
- nannofossils
- nutrients
- oceanic anoxic events
- organic compounds
- pelagic environment
- Pliensbachian
- respiration
- size
- stable isotopes
- Toarcian
- United Kingdom
- Wales
- Western Europe
- Schizosphaerella
- Cardigan Bay Basin