| Title | Sedimentology and stratigraphy of the Kettle Point Formation: implications for widespread marine anoxia and the extensive deposition of Upper Devonian black shales in eastern North America |
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| Author | Bingham-Koslowski, N ; Jin, J; Tsujita, C; Azmy, K |
| Source | Atlantic Geoscience Society, Special Publication (2017), 2017 p. 18-19  Open Access |
| Links | Online - En ligne
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| Image |  |
| Year | 2017 |
| Alt Series | Natural Resources Canada, Contribution Series 20170241 |
| Publisher | Atlantic Geoscience Society |
| Meeting | 43rd AGS Colloquium and Annual Meeting; Fredericton; CA; February 10-11, 2017 |
| Document | book |
| Lang. | English |
| Media | paper; on-line; digital |
| File format | pdf |
| Province | Ontario |
| Subjects | sedimentology; sulphur isotope ratios; isotopic studies; mudstones; black shales; deposition; depositional environment; depositional history; organic residues; lithofacies; Kettle Point Formation;
Devonian |
| Program | GEM2: Geo-mapping for Energy and Minerals Baffin Region Atlas |
| Released | 2017 01 01 |
| Abstract | The Upper Devonian Kettle Point Formation of southwestern Ontario is characterized by intervals of organic-rich interlaminated black shale interbedded with organic-poor greyish green mudstones and rare
red beds, separated by metre-scale sequences of non-interlaminated black shale. The formation shows a largely consistent background value for the black shales around -20(permil)
d34S, punctuated by a substantial positive excursion of ~32(permil)
(up to +12.87(permil)) coincident with a significant section of greyish green mudstone and red beds. Organic content, in conjunction with the sulphur isotope data, indicate that the black shales were deposited during periods of anoxia with thick
intervals of non-interlaminated black shales representing the acme of anoxic conditions. Greyish green mudstones, with their lack of organic-content, increased bioturbation, and higher, more-positive, sulphur isotope values, therefore record
deposition in more oxygenated environments. A new 4-stage, 2 cycle depositional model for the Kettle Point Formation is proposed with relative water depth interpreted as the key control on the vertical diffusion of oxygen in the water column, and
therefore on the distribution of the Kettle Point lithofacies. Interbedded black shales and greyish green mudstones were deposited in relatively shallow waters where minor, short-lived falls in relative sea level promoted dysoxic to oxic conditions
and the deposition of organic-poor lithologies. Non-interlaminated black shales are indicative of substantial rises in relative sea level, resulting in widespread anoxia and the deposition of thicker and more laterally extensive packages of
organic-rich sediment. The sedimentology and stratigraphy of the Kettle Point Formation and other syndepositional black shales, suggests that the extensive deposition of organic-rich sediment across eastern North America during the Late Devonian was
a product of widespread anoxia related to fluctuating water depth and restricted circulation in intracratonic and foreland basin depositional centers. |
| Summary | (Plain Language Summary, not published)
The Upper Devonian (380-360 mya) Kettle Point Formation in southwestern Ontario is composed of alternating layers of black and green mudrocks. The
change in colour reflects the presence (black) or absence (green) of organic material within the rocks. The preservation of organic material in shales is primarily controlled by oxygen content in the water column, as oxygen breaks down organic
matter and therefore black shales represent deposition in an oxygen-free (anoxic) environment. The main factors influencing water column oxygen levels during the deposition of the Kettle Point Formation were determined to be fluctuating water depths
and the development of restricted circulation. Upper Devonian black shales are not limited to southwestern Ontario and the presence of extensive, similar-aged, organic-rich deposits throughout eastern North America suggests that the conditions
responsible for the deposition of the Kettle Point shales (anoxia, restricted circulation) were widespread. |
| GEOSCAN ID | 306097 |
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