Summary
A reassessment of published age determinations, including some recent dates on Middle Devonian, Late Silurian, basal Caradoc and middle Arenig rocks, enables the construction of a more precise time-scale. The most accurate points on our scale are: basal Frasnian, 368 ± 8 Ma; early Ludlow, 421 ± 2 Ma; end of early Llandovery, 431 ± 6 Ma; early Caradoc, 450 ± 7; middle Arenig, 482 ± 5 Ma. Interpolations from these data indicate that the base of the Devonian is 412 ± 5 Ma, and the base of the Silurian is 435 ± 7 Ma. The end of the Devonian is less precise, we estimated it to be at 354 + 10, -5 Ma (depending on stratigraphic and sedimentological estimates for the duration of the Frasnian and Famennian stages). The base of the Tremadoc is perhaps 513 ± 10 Ma. Dating by K/Ar, 40Ar/39Ar, U/Pb and Sm/Nd all show good agreement, but some Rb/Sr isochrons on acid volcanic rocks lie off our time-scale line. Most fission track dates on zircons from bentonites have very large errors; a few with the smallest errors are shown on our graph, but none of them have been precise enough to use in the construction of the time-scale.
- © 1985 The Geological Society. Authorization to photocopy items for internal or personal use, or the internal or personal use of specific clients, is granted by The Geological Society for libraries and other users registered with the Copyright Clearance Center (CCC) Transactional Reporting Service, provided that a base fee of $02.00 per copy is paid directly to CCC, 21 Congress Street, Salem, MA 01970, USA.
Please note that if you are logged into the Lyell Collection and attempt to access content that is outside of your subscription entitlement you will be presented with a new login screen. You have the option to pay to view this content if you choose. Please see the relevant links below for further assistance.
INDIVIDUALS
Log in using your username and password
Purchase access
LIBRARY USERS
Log in through your institution
The Ordovician, Silurian and Devonian periods
