EARLY SILURIAN PALEOLATITUDE OF THE SPRINGDALE GROUP REDBEDS OF CENTRAL NEWFOUNDLAND - A PALEOMAGNETIC DETERMINATION WITH A REMANENCE ANISOTROPY TEST FOR INCLINATION ERROR

We studied the palaeomagnetism of red fine-grained sandstones and coar se siltstones of the early Silurian Springdale Group of central Newfou ndland. At 10 sites, a high blocking temperature characteristic remane nce carried by haematite was isolated. This remanence is shown to pred ate probable early Devonian folding. Anti-parallel north- and south-di rected remanences through a 100 m section of redbeds and a positive co nglomerate test on haematite-bearing volcanic clasts suggest absence o f remagnetization. Inverting the south-directed sites and unfolding yi elds a characteristic remanence with a mean declination of 23.6-degree s and a mean inclination of -14.2-degrees (alpha95 = 7.3-degrees, k = 45.4). The inclination corresponds to a probable early Silurian palaeo latitude of 7-degrees-S +/- 4-degrees. We find no significant differen ce between early Silurian palaeolatitudes for central Newfoundland nor th 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 abou t 5-degrees by the early Silurian. This is consistent with palaeomagne tic results from Britain and Ireland that suggest no more than a narro w Iapetus at low palaeolatitude by the early Silurian. We also tested whether we have underestimated palaeolatitude because of sediment comp action reducing remanence inclination from that of the early Silurian field. We measured anisotropy of the isothermal remanence (IRM) acquis ition for one specimen from each stable site, finding that a field of 200 to 800 mT applied at 45-degrees to bedding produced an isothermal remanence oriented on average at 42-degrees to bedding. Theory then pr edicts that sediment compaction caused less than 2-degrees average inc lination shallowing in the Springdale Group redbeds, and less than a 1 -degrees underestimation of palaeolatitude.