Geological Magazine

Original Articles

Geochronology of the Cambrian: a precise Middle Cambrian U–Pb zircon date from the German margin of West Gondwana

ED LANDINGa1 c1, GERD GEYERa2a3, ROBERT BUCHWALDTa4 and SAMUEL A. BOWRINGa4

a1 New York State Museum, 222 Madison Avenue, Albany, New York 12230, USA

a2 Institut für Geographie und Geologie, Lehrstuhl für Geodynamik und Geomaterialforschung, Bayerische Julius-Maximilians-Universität Würzburg, Am Hubland, 97074 Würzburg, Germany

a3 Department of Earth Sciences (Palaeobiology), Uppsala University, Villavägen 16, 752 36 Uppsala, Sweden

a4 Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA

Abstract

A volcanic tuff 1.0 m above the base of the Triebenreuth Formation in the Franconian Forest provides the first precise and biostratigraphically bracketed date within the traditional Middle Cambrian. The first illustration of fossils from the Triebenreuth Formation in this report and their discussion allow a more highly refined correlation within the Middle Cambrian. A weighted mean 206Pb–238U date of 503.14±0.13/0.25/0.59 Ma on zircons from this subaerial pyroclastic tuff was determined by U–Pb chemical abrasion isotope dilution mass spectrometry (CA-TIMS) techniques. At c. 6.0–7.0 Ma younger than the base of the traditional Middle Cambrian in Avalonia, the new West Gondwanan date from east-central Germany suggests that estimates of 500 Ma for the base of the traditional Upper Cambrian and 497 Ma on the base of the Furongian Series may prove to be too ‘old’. Biostratigraphically well-bracketed dates through most of the Middle Cambrian/Series 3 and below the upper Upper Cambrian/upper Furongian Series do not exist. An earlier determined 494.4±3.8 Ma date from the Southwell Group of Tasmania may actually prove to be a reasonable estimate for the age of the base of the traditional Upper Cambrian. Until high precision dates are determined on the base of the traditional Upper Cambrian and base of the Furongian Series, the rates of biotic replacements and geological developments and the durations of biotic zones in the Middle/Series 3 and Upper Cambrian/Furongian Series remain as ‘best guesses’.

(Received September 03 2013)

(Accepted February 12 2014)

Keywords:

  • Middle Cambrian;
  • U–Pb zircon date;
  • Germany;
  • Triebenreuth Formation

Correspondence

c1 Author for correspondence: elanding@mail.nysed.gov

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