Late Quaternary Depositional Processes in Orphan Basin, Northeast Continental Margin of Newfoundland

Efthymios K. Tripsanas, David J.W. Piper, Kimberley A. Jenner, and Calvin D. Campbell
Geological Survey of Canada (Atlantic), Dartmouth, NS

Orphan Basin is located on the glaciated southeast continental margin of Canada, northeast of Newfoundland. The west and southwest shelf edge and slope of Orphan Basin are deeply incised by numerous canyons and gullies. The canyons extend to the basin floor as channel systems. Most of the channel systems have formed on top of debris flow deposits and are estimated to be older than 45 ky.

Interpretation of sediment cores indicates three discrete depositional intervals during the last 45 ky. The first interval occurred prior to 30 ky B.P. and consists of moderately bioturbated silty-clay with common IRD. The second interval occurred between 30 ky B.P. and 14 ky B.P., and consists of moderately bioturbated silty-clay with common to abundant IRD interbedded with abundant thin bedded sand-mud turbidites. The fine grain-size of the turbidites implies that their origin was probably from hyperpycnal flows produced by glacier melt-water plumes, suggesting that during this time interval, the glaciers extended to the shelf edge. The third depositional interval occurred during the last 14 ky and consists of moderately bioturbated silty-clay with rare IRD. The dominance of hemipelagic sediments during this period indicates that glaciers had significantly retreated and there was no direct terrigenous supply to the slope of Orphan Basin. However, cores from channels reveal the existence of debris-flows, diamictons, and sorted gravel and sand in this inteval. The widespread and contemporary occurrence of these mass-transport deposits indicate that these events probably originated from large sediment failures produced by earthquakes.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005