Discussion of “Geochemical signature of Ordovician Mn-rich sedimentary rocks on the Avalonian shelf”<sup>1</sup>Appears in Canadian Journal of Earth Sciences, 2011, <b>48</b>(4): 703–718 [doi: 10.1139/e10-092].

Romer and Kroner (2012) stated “the core of the Harlech Dome (i) in part is made up of Ordovician deposits and (ii) contains tectonic repetitions”. In their comment, Schofield et al. (this issue) distort this statement and state that (i) we claim the entire sedimentary sequence of the Harlech Dome is Ordovician and (ii) we misinterpreted their zircon data. We disagree. In our reply, we demonstrate that the argumentation of Schofield et al. (this issue) is driven by circular argumentation and that their use and interpretation of U–Pb zircon data is inadequate.

Reply to the discussion of the reply by R.L. Romer and U. Kroner on “Geochemical signature of Ordovician Mn-rich sedimentary rocks on the Avalonian shelf” ¹Appears in the Canadian Journal of Earth Sciences, 49(11): 1372–1377 [doi:10.1139/e2012-049].

Romer

Kroner

2012

Reply to the discussion by J.W.F. Waldron and C.E. White on “Geochemical signature of Ordovician Mn-rich sedimentary rocks on the Avalonian shelf”¹Appears in Canadian Journal of Earth Sciences, 2012, 49(6): 772–774 [doi: 10.1139/e2012-004].

Romer

Kroner

2012

In their comment, Waldron and White state that manganese-rich sedimentary rocks of Nova Scotia and Wales are Cambrian and were deposited in a deep-water turbidite basin called “Megumia” rather than on the Avalonian shelf. Available geochronological data are not in conflict with an Early Ordovician deposition age for manganese-rich sedimentary rocks north of the Rheic suture, including those of Nova Scotia and northern Wales. “Megumia” is part of the Avalonian plate, and the manganese-rich sediments were deposited on its shelf.

Discussion of the reply by R.L. Romer and U. Kroner on “Geochemical signature of Ordovician Mn-rich sedimentary rocks on the Avalonian shelf” ¹Appears in Canadian Journal of Earth Sciences, 49(6): 775–780, 10.1139/e2012-006.

Schofield

Waldron

White³

et al. 2012

In their article ‘Reply to the discussion by J.W.F. Waldron and C.E. White on “Geochemical signature of Ordovician Mn-rich sedimentary rocks on the Avalonian shelf”’, R.L. Romer and U. Kroner reinterpret geochronological data presented by J.W.F. Waldron, D.I. Schofield, C.E. White, and S.M. Barr to imply an Ordovician, not a Cambrian, depositional age for the succession of the Harlech Dome, North Wales, and Meguma Supergroup, Nova Scotia. However, an extensive history of biostratigraphic and geological survey data refutes this interpretation and shows that the rocks are unequivocally Cambrian. Waldron et al. used the U–Pb zircon laser-ablation – multicollector – inductively coupled plasma – mass spectrometry technique primarily to provide information on sediment provenance and not depositional age. Investigation of anomalously young 206Pb/238U ages showed evidence of Pb loss. These data provide little constraint on depositional age and cannot be used to infer that the Harlech Grits Group is Ordovician.