Jin, Jisuo6; Harper, David A.T.3; Cocks, L. Robin M.4; McCausland, Phil J.A.6; Rasmussen, Christian M. Ø.7; Sheehan, Peter M.5
1 Natural History Museum of Denmark, Natural History Museum of Denmark, Faculty of Science, Københavns Universitet2 Western University3 Durham University4 Natural History Museum5 Milwaukee Public Museum6 Western University7 Natural History Museum of Denmark, Natural History Museum of Denmark, Faculty of Science, Københavns Universitet
The Late Ordovician equatorial zone, like the zone today, had few hurricane-grade storms within 100 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.
Geology (boulder), 2013, Vol 41, Issue 2, p. 107-110