Chemostratigraphy (CaCO3, TOC, delta C-13(org)) of Sinemurian (Lower Jurassic) black shales from the Wessex Basin, Dorset and palaeoenvironmental implications
The Shales-with-'Beef' and Black Ven Marls of the Charmouth Mudstone Formation (Sinemurian) exposed on the Dorset Coast in southern England (Wessex Basin) show stratigraphic variation in carbonate, organic carbon and organic-carbon isotopes. Little environmental significance is attached to...
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| Format: | Journal article |
| Language: | English |
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2013
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| _version_ | 1826342844200124416 |
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| author | Jenkyns, H Weedon, G |
| author_facet | Jenkyns, H Weedon, G |
| author_sort | Jenkyns, H |
| collection | OXFORD |
| description | The Shales-with-'Beef' and Black Ven Marls of the Charmouth Mudstone Formation (Sinemurian) exposed on the Dorset Coast in southern England (Wessex Basin) show stratigraphic variation in carbonate, organic carbon and organic-carbon isotopes. Little environmental significance is attached to the variation of carbonate except in the case of the tabular and nodular limestones interrupting the sequence that probably record stratigraphic condensation and/or sedimentary stillstands that, in an extreme case, were accompanied by sea-floor erosion to produce the bored and encrusted ?Coinstone'. Relatively high total organiccarbon (TOC) contents are present in the laminated mudstones of the lower turneri Zone (upper brooki and lower birch Subzones) and the obtusum Zone (obtusum and stellare Subzones). Basin stratification related to fresh-water influx was the most likely aid to deoxygenation and enhanced preservation of organic matter. The organic-carbon isotope curve (δ13Corg), which shows positive excursions in the upper turneri Zone (upper birchi Subzone) and highest obtusum-raricostatum Zones (highest stellare Subzone, densinodulum and lower raricostatoides Subzones), does not correlate with the TOC stratigraphy and was clearly not controlled by local patterns of organic-matter burial. Long-term (hundreds-of-thousands of years) variations in the carbonisotope (δ13Corg) curve are interpreted as reflecting changing seawater isotopic composition and, in the case of the stratigraphically higher interval, may be related to marine organic-carbon burial on the margins of the proto-Atlantic, as exemplified by the Lusitanian Basin in Portugal. Correlation of the carbon-isotope profile with putative sea-level curves is problematic in detail, although significant local transgressive pulses in the turneri and late raricostatum Zones are approximately coincident with positive δ13Corg excursions.© 2013 Gebrüder Borntraeger, Stuttgart, Germany. |
| first_indexed | 2024-03-07T05:51:00Z |
| format | Journal article |
| id | oxford-uuid:e8e008c2-27e1-462f-ae3c-135790a1d273 |
| institution | University of Oxford |
| language | English |
| last_indexed | 2024-03-07T05:51:00Z |
| publishDate | 2013 |
| record_format | dspace |
| spelling | oxford-uuid:e8e008c2-27e1-462f-ae3c-135790a1d2732022-03-27T10:50:00ZChemostratigraphy (CaCO3, TOC, delta C-13(org)) of Sinemurian (Lower Jurassic) black shales from the Wessex Basin, Dorset and palaeoenvironmental implicationsJournal articlehttp://purl.org/coar/resource_type/c_dcae04bcuuid:e8e008c2-27e1-462f-ae3c-135790a1d273EnglishSymplectic Elements at Oxford2013Jenkyns, HWeedon, GThe Shales-with-'Beef' and Black Ven Marls of the Charmouth Mudstone Formation (Sinemurian) exposed on the Dorset Coast in southern England (Wessex Basin) show stratigraphic variation in carbonate, organic carbon and organic-carbon isotopes. Little environmental significance is attached to the variation of carbonate except in the case of the tabular and nodular limestones interrupting the sequence that probably record stratigraphic condensation and/or sedimentary stillstands that, in an extreme case, were accompanied by sea-floor erosion to produce the bored and encrusted ?Coinstone'. Relatively high total organiccarbon (TOC) contents are present in the laminated mudstones of the lower turneri Zone (upper brooki and lower birch Subzones) and the obtusum Zone (obtusum and stellare Subzones). Basin stratification related to fresh-water influx was the most likely aid to deoxygenation and enhanced preservation of organic matter. The organic-carbon isotope curve (δ13Corg), which shows positive excursions in the upper turneri Zone (upper birchi Subzone) and highest obtusum-raricostatum Zones (highest stellare Subzone, densinodulum and lower raricostatoides Subzones), does not correlate with the TOC stratigraphy and was clearly not controlled by local patterns of organic-matter burial. Long-term (hundreds-of-thousands of years) variations in the carbonisotope (δ13Corg) curve are interpreted as reflecting changing seawater isotopic composition and, in the case of the stratigraphically higher interval, may be related to marine organic-carbon burial on the margins of the proto-Atlantic, as exemplified by the Lusitanian Basin in Portugal. Correlation of the carbon-isotope profile with putative sea-level curves is problematic in detail, although significant local transgressive pulses in the turneri and late raricostatum Zones are approximately coincident with positive δ13Corg excursions.© 2013 Gebrüder Borntraeger, Stuttgart, Germany. |
| spellingShingle | Jenkyns, H Weedon, G Chemostratigraphy (CaCO3, TOC, delta C-13(org)) of Sinemurian (Lower Jurassic) black shales from the Wessex Basin, Dorset and palaeoenvironmental implications |
| title | Chemostratigraphy (CaCO3, TOC, delta C-13(org)) of Sinemurian (Lower Jurassic) black shales from the Wessex Basin, Dorset and palaeoenvironmental implications |
| title_full | Chemostratigraphy (CaCO3, TOC, delta C-13(org)) of Sinemurian (Lower Jurassic) black shales from the Wessex Basin, Dorset and palaeoenvironmental implications |
| title_fullStr | Chemostratigraphy (CaCO3, TOC, delta C-13(org)) of Sinemurian (Lower Jurassic) black shales from the Wessex Basin, Dorset and palaeoenvironmental implications |
| title_full_unstemmed | Chemostratigraphy (CaCO3, TOC, delta C-13(org)) of Sinemurian (Lower Jurassic) black shales from the Wessex Basin, Dorset and palaeoenvironmental implications |
| title_short | Chemostratigraphy (CaCO3, TOC, delta C-13(org)) of Sinemurian (Lower Jurassic) black shales from the Wessex Basin, Dorset and palaeoenvironmental implications |
| title_sort | chemostratigraphy caco3 toc delta c 13 org of sinemurian lower jurassic black shales from the wessex basin dorset and palaeoenvironmental implications |
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