EARLY SILURIAN PALEOLATITUDE OF THE SPRINGDALE GROUP REDBEDS OF CENTRAL NEWFOUNDLAND - A PALEOMAGNETIC DETERMINATION WITH A REMANENCE ANISOTROPY TEST FOR INCLINATION ERROR
Jp. Hodych et Kl. Buchan, EARLY SILURIAN PALEOLATITUDE OF THE SPRINGDALE GROUP REDBEDS OF CENTRAL NEWFOUNDLAND - A PALEOMAGNETIC DETERMINATION WITH A REMANENCE ANISOTROPY TEST FOR INCLINATION ERROR, Geophysical journal international, 117(3), 1994, pp. 640-652
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.