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Primary v. carbonate production in the Toarcian, a case study from the Llanbedr (Mochras Farm) Borehole, Wales

Alessandro Menini, Emanuela Mattioli, Stephen P. Hesselbo, Micha Ruhl and Guillaume Suan
Primary v. carbonate production in the Toarcian, a case study from the Llanbedr (Mochras Farm) Borehole, Wales (in Carbon cycle and ecosystem response to the Jenkyns event in the early Toarcian (Jurassic), M. Reolid (editor), L. V. Duarte (editor), E. Mattioli (editor) and W. Ruebsam (editor))
Special Publication - Geological Society of London (September 2021) 514 (1): 59-81

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 (super 12) C favouring greenhouse conditions and continental weathering. The nutrient delivery to shallow basins supported productivity and, because of O (sub 2) 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.


ISSN: 0305-8719
Coden: GSLSBW
Serial Title: Special Publication - Geological Society of London
Serial Volume: 514
Serial Issue: 1
Title: Primary v. carbonate production in the Toarcian, a case study from the Llanbedr (Mochras Farm) Borehole, Wales
Title: Carbon cycle and ecosystem response to the Jenkyns event in the early Toarcian (Jurassic)
Author(s): Menini, AlessandroMattioli, EmanuelaHesselbo, Stephen P.Ruhl, MichaSuan, Guillaume
Author(s): Reolid, M.editor
Author(s): Duarte, L. V.editor
Author(s): Mattioli, E.editor
Author(s): Ruebsam, W.editor
Affiliation: Universite de Lyon, Villeurbanne, France
Affiliation: University of Jaen, Spain
Pages: 59-81
Published: 20210922
Text Language: English
Publisher: Geological Society of London, London, United Kingdom
References: 144
Accession Number: 2021-075099
Categories: Isotope geochemistryStratigraphy
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus.
N52°49'00" - N52°49'00", W04°05'60" - W04°05'60"
Secondary Affiliation: Institut Universitaire de France, Paris, FRA, FranceUniversity of Exeter, Penryn, GBR, United KingdomUniversity of Dublin, Dublin, IRL, Ireland
Country of Publication: United Kingdom
Secondary Affiliation: GeoRef, Copyright 2022, American Geosciences Institute.
Update Code: 202152
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