Abstract
The 2012 geologic time scale for the Ordovician and Silurian systems; advances and challenges
Abstracts with programs - Geological Society of America, Vol.44(7), p.588
Geological Society of America, 2012 annual meeting
11/2012
Abstract
The 2012 geologic time scale for the Ordovician and Silurian systems has been produced using the constrained optimization software CONOP9. The optimizing algorithms developed to automate biostratigraphic correlation are used to build a composite sequence of biostratigraphic range-end events, mainly using graptolites. The resulting scaled composite is converted to a relative geological time scale by identifying stage and zone boundaries within the sequence of graptolite events. The present Ordovician-Silurian scale differs from GTS2004 for several reasons. The radiogenic isotope database has been considerably revised. Several dated samples used in the previous time scales have been excluded because they do not meet the analytical standards and protocols adopted for the present scale, and eight new high-precision age determinations have been added. In addition, the age determinations for all dated ash beds have been recalculated to standardize for decay systems, decay constants, and tracer/standard error, resulting in changes to several of the dates, of from 1 to 3 m.y. The biostratigraphic ages of several of the dated samples have also been revised. In addition, the CONOP biostratigraphic database has been expanded from 256 sections and 1400 taxa to 512 sections and 2000 taxa. In the 2012 time scale, the age of the base of the Ordovician System is 485.4 + or - 1.9 Ma, the base of Silurian is 443.8 + or - 1.5 Ma and the base of the Devonian is 419.2 + or - 3.2 Ma. The average stage durations for the Ordovician and Silurian are 5.9 Myr and 3.0 Myr, respectively. The mean uncertainty on stage durations for the study interval is 1.19 Myr. Areas of greatest uncertainty, and where improved radiometric control is needed, are near each of the system boundaries--base Ordovician, base Silurian and base Devonian. In addition, integration of data from a wider range of fossil groups will improve the resolution and correlation potential of the Ordovician-Silurian composite.
Details
- Title: Subtitle
- The 2012 geologic time scale for the Ordovician and Silurian systems; advances and challenges
- Creators
- Michael Melchin - Xavier UniversityPeter SadlerRoger A CooperBradley D Cramer
- Resource Type
- Abstract
- Publication Details
- Abstracts with programs - Geological Society of America, Vol.44(7), p.588
- Conference
- Geological Society of America, 2012 annual meeting
- Publisher
- Geological Society of America (GSA)
- ISSN
- 0016-7592
- Alternative title
- Geological Society of America, 2012 annual meeting
- Language
- English
- Date published
- 11/2012
- Academic Unit
- Earth and Environmental Sciences; International Programs; Office Of The Provost
- Record Identifier
- 9984240802302771
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