Precisely locating the Ordovician equator in Laurentia – Cover

Date: 2013-01-19

Reference number: OPUSeJ 201301162219POE



Title: Precisely locating the Ordovician equator in Laurentia

Authors: Jisuo Jin 1, David A.T. Harper 2, Robin M. Cocks 3, Phil J.A. McCausland 1, Christian M.Ø. Rasmussen 4 and Peter M. Sheehan 5

Abstract: The Late Ordovician equatorial zone, like the zone today, had few hurricane-grade storms within 10º of the equator, as emphasized by the preservation of massive-bedded Thalassinoides ichnofacies in a trans-Laurentian belt more than 6000 km long, from the southwestern United States to North Greenland. That belt also includes nonamalgamated shell beds dominated by the brachiopod Proconchidium, which would not have been preserved after hurricane-grade storms. The belt lacks such storm-related sedimentary features as rip-up clasts, hummocky cross-stratification, or large channels. In contrast, other contemporaneous Laurentian Thalassinoides facies and shell beds on either side of the belt have been disturbed by severe storms below fair-weather wave base. The position of the biofacies-defined equatorial belt coincides with the Late Ordovician equator deduced from paleomagnetic data from Laurentia, thus providing both a high-precision equatorial location and an independent test of the geocentric axial dipole hypothesis for that time.

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1 Department of Earth Sciences, Western University, London, Ontario N6A 5B7, Canada

2 Department of Earth Sciences, Durham University, Durham DH1 3LH, UK

3 Department of Earth Sciences, Natural History Museum, London SW7 5BD, UK

4 Natural History Museum of Denmark, University of Copenhagen, 1350 Copenhagen K, Denmark

5 Department of Geology, Milwaukee Public Museum, Milwaukee, Wisconsin 53233, USA.

Keywords: terms; separated; by; semi-colons N/A

Subject: Geology/ paleogeology

Language: English

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Citation: Jisuo Jin, J et al, 2012, “Precisely locating the Ordovician equator in Laurentia”, Geology online November 6, 2012, doi: 10.1130/G33688.1.

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