About This Item

Share This Item

The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 57 (1973)

Issue: 4. (April)

First Page: 779

Last Page: 779

Title: Petrology and Sedimentation of Early Paleozoic Island-Arc Deposits, Newfoundland: ABSTRACT

Author(s): S. G. Franks, J. Helwig

Article Type: Meeting abstract


The Cambro-Ordovician New Bay Formation (2,000 m) of the Newfoundland Appalachians is a southward-thickening prism of conglomeratic, volcanogenic turbidites interbedded with sandstone and black argillite. Abundant sedimentary structures include tool and scour marks, cross-lamination, normal and multiple graded bedding, slump folds, and channels. The top of the formation is mostly agglomerate interbedded with red-and-green laminated silty argillite. Trails and burrows are the only fossils.

The sandstones are lithic-feldspathic arenites and basaltic wackes composed of fresh, angular unstable mineral grains and little quartz. The conglomerates have volcanic and sedimentary clasts enclosed in an ashy matrix altered to chlorite. Volcanic clasts are basalt, andesite, and dacite porphyry. Sedimentary clasts include green cherty siltite, fine-grained feldspathic arenite, abundant rip-up clasts of argillite, and rare jasper.

Analysis of Bouma sequences, amalgamated contacts, and trace fossils indicates abrupt regression late in New Bay deposition. Sole marks, slump folds, and channel axes indicate marginal sediment supply from turbidity currents and slumping down an east-facing submarine slope.

On the northwest the formation thins and apparently passes into marine and subaerial pyroclastic strata of the Wild Bight Group. On the east it is in sedimentary and tectonic contact with the Dunnage melange which has been interpreted as an ocean trench deposit. The petrology and sedimentology of the New Bay Formation compares closely with certain Miocene volcanic arc deposits described from Malekula Island, New Hebrides. Therefore the New Bay is interpreted as a volcanogenic "apron" deposited in the arc-trench gap of a Cambro-Ordovician island arc.

End_of_Article - Last_Page 779------------

Copyright 1997 American Association of Petroleum Geologists