Early Silurian palaeolatitude of the Springdale Group redbeds of central Newfoundland: a palaeomagnetic determination with a remanence anisotropy test for inclination error

Abstract

We studied the palaeomagnetism of red fine-grained sandstones and coarse siltstones of the early Silurian Springdale Group of central Newfoundland. At 10 sites, a high blocking temperature characteristic remanence carried by haematite was isolated. This remanence is shown to predate probable early Devonian folding. Anti-parallel north- and south-directed remanences through a 100 m section of redbeds and a positive conglomerate test on haematite-bearing volcanic clasts suggest absence of remagnetization. Inverting the south-directed sites and unfolding yields a characteristic remanence with a mean declination of 23.6 and a mean inclination of - 14.2 (myg5= 7.3, k = 45.4). The inclination corresponds to a probable early Silurian palaeolatitude of 7s f 4. We find no significant difference between early Silurian palaeolatitudes for central Newfoundland north and south of the Red Indian Line suture, and conclude that the part of the Iapetus Ocean across the suture had narrowed to less than about 5 by the early Silurian. This is consistent with palaeomagnetic results from Britain and Ireland that suggest no more than a narrow Iapetus at low palaeolatitude by the early Silurian. We also tested whether we have underestimated palaeolatitude because of sediment compaction reducing remanence inclination from that of the early Silurian field. We measured anisotropy of the isothermal remanence (IRM) acquisition for one specimen from each stable site, finding that a field of 200 to 800 rnT applied at 45 to bedding produced an isothermal remanence oriented on average at 42 to bedding. Theory then predicts that sediment compaction caused less than 2 average inclination shallowing in the Springdale Group redbeds, and less than a 1 underestimation of palaeolatitude.