HR: 0800h
AN: GP11D-0876    [Abstracts]
TI: Palaeomagnetism of the Late Neoproterozoic of Ella O, North-East Greenland
AU: * Kilner, B
EM: benk@earth.ox.ac.uk
AF: Deparment of Earth Sciences, University of Oxford, Parks Road, Oxford, OX13PR United Kingdom
AU: Mac Niocaill, C
EM: coanllm@earth.ox.ac.uk
AF: Deparment of Earth Sciences, University of Oxford, Parks Road, Oxford, OX13PR United Kingdom
AU: Stouge, S
EM: ss@geus.dk
AF: Geological Museum, University of Copenhagen, O Voldgade 5-7, Copenhagen, 1350 K Denmark
AU: Harper, D
EM: dharper@savik.geomus.ku.dk
AF: Geological Museum, University of Copenhagen, O Voldgade 5-7, Copenhagen, 1350 K Denmark
AB: Neoproterozoic to lower Ordovician sediments outcrop in a N-S trending band in the fjord region of North-East Greenland. The sequence comprises, in ascending order, the Eleonore Bay Group, the Tillite Group and the Canyon and Spiral Creek Formations. The Eleonore Bay Group is thought to be Upper Riphean in age and consists of cherty limestone and dolomite capped by red siltstone. The overlying Tillite Group contains two tillite packages separated by an intertillite which comprises marine siltstone and sandstone. The Canyon and Spiral Creek Formation consist of evaporitic red siltstone, with chert-rich horizons and some dolomite. The Spiral Creek Formation is overlain by a basal Cambrian quartzite. 500 samples were collected from the late Precambrian succession on the island of Ella O in Kong Oscars Fjord. Sampling was aimed in particular at red beds and other likely magnetic targets. The specimens were demagnetised using progressive alternating frequency and thermal techniques and typically revealed a multi-component remanence structure. A majority of the specimens carry a low stability (generally $<$ 20mt, $<$ 250$\deg$) component, directed north and steeply down. This closely resembles present Earth's field. Demagnetisation of the Eleonore Bay Group reveals a high stability component directed south and shallow down, with an opposing component north and up. After tilt correction the mean direction yields a palaeolatitude of 4$\deg$. This component passes field tests, and is interpreted as primary. Magnetic characteristics in the Tillite Group are distinct from those of the Eleonore Bay Group. The Lower Tillite Formation carries an east directed shallow down component. The palaeolatitude derived from this direction indicates low latitude deposition for the glacial rocks above the Eleonore Bay Group. The Upper Tillite Formation carries a high stability component directed steeply upwards. Specimens from a limited pilot study pass reversal and fold tests, but further experiments are required to verify the result. If confirmed, this would indicate a hiatus between the lower and upper tillites. It also suggests that the Upper Tillite, which potentially correlates with the 630Ma 'snowball' Earth event, was deposited at high latitude. This would be the first confirmation that the late Neoproterozoic Marinoan glaciation extended over a broad range of latitudes.
DE: 9315 Arctic region
DE: 9619 Precambrian
DE: 1500 GEOMAGNETISM AND PALEOMAGNETISM
DE: 1520 Magnetostratigraphy
DE: 1525 Paleomagnetism applied to tectonics (regional, global)
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2004 AGU Fall Meeting