Record of Early Toarcian carbon cycle perturbations in a nearshore environment: the Bascharage section (easternmost Paris Basin)
In order to understand the significance of the worldwide deposition of black shale facies in the Early Toarcian (~ 183 Ma), considerable attention has been drawn to this Early Jurassic sub-stage over the last 3 decades. The discovery of a pronounced negative carbon isotope excursion (CIE) within the...
| Main Authors: | , , , , , , |
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| Format: | Article |
| Language: | English |
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Copernicus Publications
2014-08-01
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| Series: | Solid Earth |
| Online Access: | http://www.solid-earth.net/5/793/2014/se-5-793-2014.pdf |
| _version_ | 1818325115727773696 |
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| author | M. Hermoso D. Delsate F. Baudin L. Le Callonnec F. Minoletti M. Renard A. Faber |
| author_facet | M. Hermoso D. Delsate F. Baudin L. Le Callonnec F. Minoletti M. Renard A. Faber |
| author_sort | M. Hermoso |
| collection | DOAJ |
| description | In order to understand the significance of the worldwide deposition of black
shale facies in the Early Toarcian (~ 183 Ma), considerable attention
has been drawn to this Early Jurassic sub-stage over the last 3 decades.
The discovery of a pronounced negative carbon isotope excursion (CIE) within
the black shales disrupting the generally positive trend in carbon isotopes
has stimulated many studies, particularly with a view to establish the local
versus global nature of this major geochemical phenomenon. Here we document
the sedimentological and chemostratigraphic evolution of a proximal
environment in the Luxembourgian sedimentary area. At Bascharage, Lower
Toarcian sediments record the isotopic signature of the Early Toarcian
oceanic anoxic event (OAE) by a pronounced positive trend that testifies for
widespread anoxia. The expression of the carbon isotope perturbation in this
section, however, is unusual compared to adjacent NW European sections. A
first −7‰ negative CIE, whose onset is recorded at the top of the
<i>tenuicostatum</i> zone, can be assigned to the well-documented and
potentially global Toarcian carbon isotope excursion (T-CIE) with confidence
using the well-constrained ammonite biostratigraphic framework for this
section. In this interval, facies contain only a limited amount of carbonate
as a result of intense detrital supply in such a proximal and shallow
environment. Stratigraphically higher in the section, the
<i>serpentinum</i> zone records a subsequent CIE (−6‰)
expressed as four negative steps, each being accompanied by positive shifts
in the oxygen isotopic composition of carbonate. The preservation state of
coccoliths and calcareous dinoflagellates in the second CIE is excellent and
comparable to that observed in under- and overlying strata, so this cannot be
an artefact of diagenesis. Considering the nature of this record, and the
lack of such a pronounced event in the <i>serpentinum</i> zone in coeval
sections in Europe, we hypothesise that this second CIE was caused by local
factors. The geochemical record of carbonate with a relatively light carbon
and relatively heavy oxygen isotopic composition is compatible with the
so-called Küspert model, by which a CIE can be explained by an influx of
<sup>12</sup>C-rich and cold waters due to upwelling bottom water masses. |
| first_indexed | 2024-12-13T11:39:21Z |
| format | Article |
| id | doaj.art-8b16886f7cd94a269fe7fcdefc6cf342 |
| institution | Directory Open Access Journal |
| issn | 1869-9510 1869-9529 |
| language | English |
| last_indexed | 2024-12-13T11:39:21Z |
| publishDate | 2014-08-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Solid Earth |
| spelling | doaj.art-8b16886f7cd94a269fe7fcdefc6cf3422022-12-21T23:47:42ZengCopernicus PublicationsSolid Earth1869-95101869-95292014-08-015279380410.5194/se-5-793-2014Record of Early Toarcian carbon cycle perturbations in a nearshore environment: the Bascharage section (easternmost Paris Basin)M. Hermoso0D. Delsate1F. Baudin2L. Le Callonnec3F. Minoletti4M. Renard5A. Faber6University of Oxford – Department of Earth Sciences, South Parks Road, Oxford OX1 3AN, UKMusée National d'Histoire Naturelle – Centre de Recherche Scientifique, 25 Rue Münster, 2160 Luxembourg, LuxembourgUPMC Université Paris 06 – UMR7193 ISTeP, 4 Place Jussieu, 75005 Paris, FranceUPMC Université Paris 06 – UMR7193 ISTeP, 4 Place Jussieu, 75005 Paris, FranceUPMC Université Paris 06 – UMR7193 ISTeP, 4 Place Jussieu, 75005 Paris, FranceUPMC Université Paris 06 – UMR7193 ISTeP, 4 Place Jussieu, 75005 Paris, FranceMusée National d'Histoire Naturelle – Centre de Recherche Scientifique, 25 Rue Münster, 2160 Luxembourg, LuxembourgIn order to understand the significance of the worldwide deposition of black shale facies in the Early Toarcian (~ 183 Ma), considerable attention has been drawn to this Early Jurassic sub-stage over the last 3 decades. The discovery of a pronounced negative carbon isotope excursion (CIE) within the black shales disrupting the generally positive trend in carbon isotopes has stimulated many studies, particularly with a view to establish the local versus global nature of this major geochemical phenomenon. Here we document the sedimentological and chemostratigraphic evolution of a proximal environment in the Luxembourgian sedimentary area. At Bascharage, Lower Toarcian sediments record the isotopic signature of the Early Toarcian oceanic anoxic event (OAE) by a pronounced positive trend that testifies for widespread anoxia. The expression of the carbon isotope perturbation in this section, however, is unusual compared to adjacent NW European sections. A first −7‰ negative CIE, whose onset is recorded at the top of the <i>tenuicostatum</i> zone, can be assigned to the well-documented and potentially global Toarcian carbon isotope excursion (T-CIE) with confidence using the well-constrained ammonite biostratigraphic framework for this section. In this interval, facies contain only a limited amount of carbonate as a result of intense detrital supply in such a proximal and shallow environment. Stratigraphically higher in the section, the <i>serpentinum</i> zone records a subsequent CIE (−6‰) expressed as four negative steps, each being accompanied by positive shifts in the oxygen isotopic composition of carbonate. The preservation state of coccoliths and calcareous dinoflagellates in the second CIE is excellent and comparable to that observed in under- and overlying strata, so this cannot be an artefact of diagenesis. Considering the nature of this record, and the lack of such a pronounced event in the <i>serpentinum</i> zone in coeval sections in Europe, we hypothesise that this second CIE was caused by local factors. The geochemical record of carbonate with a relatively light carbon and relatively heavy oxygen isotopic composition is compatible with the so-called Küspert model, by which a CIE can be explained by an influx of <sup>12</sup>C-rich and cold waters due to upwelling bottom water masses.http://www.solid-earth.net/5/793/2014/se-5-793-2014.pdf |
| spellingShingle | M. Hermoso D. Delsate F. Baudin L. Le Callonnec F. Minoletti M. Renard A. Faber Record of Early Toarcian carbon cycle perturbations in a nearshore environment: the Bascharage section (easternmost Paris Basin) Solid Earth |
| title | Record of Early Toarcian carbon cycle perturbations in a nearshore environment: the Bascharage section (easternmost Paris Basin) |
| title_full | Record of Early Toarcian carbon cycle perturbations in a nearshore environment: the Bascharage section (easternmost Paris Basin) |
| title_fullStr | Record of Early Toarcian carbon cycle perturbations in a nearshore environment: the Bascharage section (easternmost Paris Basin) |
| title_full_unstemmed | Record of Early Toarcian carbon cycle perturbations in a nearshore environment: the Bascharage section (easternmost Paris Basin) |
| title_short | Record of Early Toarcian carbon cycle perturbations in a nearshore environment: the Bascharage section (easternmost Paris Basin) |
| title_sort | record of early toarcian carbon cycle perturbations in a nearshore environment the bascharage section easternmost paris basin |
| url | http://www.solid-earth.net/5/793/2014/se-5-793-2014.pdf |
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