Two hundred and thirty six calcitic brachiopod shells, covering the entire Silurian Period ($\sim$30 Ma), were collected at high temporal resolution from stratotype sections on Anticosti Island (Canada), in Wales (UK), in the Oslo region (Norway), on Gotland (Sweden), and in Podolia (Ukraine), Estonia, Latvia and Lithuania. Data from petrography, scanning electron microscopy (SEM), cathodoluminescence, isotopes and trace elements all confirmed excellent preservation in most shells, thus ensuring retention of primary isotope signals. The only exceptions were samples from the Oslo region. The $\delta\sp $O and $\delta\sp $C values for the well preserved samples range from $-$3 to ${-}6.5\perthous$ and from -1 to 7.5$\perthous$ (PDB), respectively. In terms of temporal trends, oxygen- and carbon-isotopes vary in parallel, with an overall decrease with decreasing age of ${\sim}1\perthous,$ through the Silurian. Superimposed on these general trends are short-term variations that are negatively correlated with sea-level changes. Three successive positive $\delta\sp $O shifts in early Aeronian, latest Aeronian and early Wenlock correlate with sea-level lowstands and with glacial diamictite deposits in the Amazon Basin and in Africa. The $\sp‡$Sr/$\sp†$Sr values range from 0.707930 $\pm$ 0.000011 to 0.708792 $\pm$ 0.000017, increasing with decreasing age. This may indicate increasing riverine flux of radiogenic Sr into the ocean from weathering of continental sialic rocks due to progressive global warming. The Sr-isotope curve shows distinct inflexion points in the earliest Wenlock and in mid-Pridoli These can be used to correlate the Llandovery/Wenlock boundary in the U.K., on Gotland and in Lithuania and for the Kaugatuma/Ohesaare boundary in the Baltic states and Podolia. Partial linear regressions for Sr-isotope data form a pattern that climbs stepwise with decreasing age, with local drops around the Llandovery/Wenlock boundary and in the latest Ludlow. The slopes of the partial regression lines can be used for reliable age estimates with a resolution of about $\pm$2 biozones ($\sim$1.5 to 2 Ma).
| Identifer | oai:union.ndltd.org:uottawa.ca/oai:ruor.uottawa.ca:10393/10406 |
| Date | January 1997 |
| Creators | Azmy, Karem. |
| Contributors | Veizer, Jan, |
| Publisher | University of Ottawa (Canada) |
| Source Sets | Université d’Ottawa |
| Detected Language | English |
| Type | Thesis |
| Format | 195 p. |
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