Late Quaternary sedimentology and sediment instability of a small area on the Scotian Slope

Mosher, David Cole (1987) Late Quaternary sedimentology and sediment instability of a small area on the Scotian Slope. Masters thesis, Memorial University of Newfoundland.

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Abstract

The Late Quaternary stratigraphy and sedimentation of a small, morphologically smooth region on the Scotian Slope, known as the Verrill Canyon area, has been investigated using high-resolution seismic profiles and piston cores. -- The acoustic stratigraphy in the area has been established with the use of high resolution seismic profiles. Most of the study area is underlain by evenly stratified, coherent reflectors which thin downslope. These reflectors are rooted in outer shelf/upper slope tills and till-like tongues which extend over the shelf break and interfinger with upper slope sediments. Gullies cut the upper slope and a few extend downslope as erosional valleys. Widespread sediment failure has resulted in detachment scarps, slumps, and acoustically-defined disturbed zones. -- Piston cores from undisturbed and erosional zones within the study area provide a composite stratigraphic section over 20 m thick which extends into the Mid-Wisconsinan (approx. 32,000 yBP). Five lithofacies are identified: (1) bioturbated, mottled mud; (2) homogeneous mud; (3) laminated mud; (4) thin-bedded sand; and (5) poorly sorted mud. Hemipelagic, or "no-event" lithofacies comprise about 50% of total sediment cored. Mass-transported sediment, or "event" lithofacies, including fine-grained turbidites and debris flows, comprise the remaining cored material. Synsedimentary deformation features were observed in cores taken from the acoustically identified disturbed zones. -- Wisconsinan sedimentation on the Scotian Slope has been largely affected by glacial events. Processes related to ice margins and lower sea levels served to transport material to the slope. High sedimentation rates and vigorous environmental conditions resulted in abundant sediment failures, producing the event lithofacies. During non-active sedimentation periods, background depositional processes resulted in hemipelagic deposition with abundant bioturbation. The entire study area is covered by a are to two metre drape of fine-grained, bioturbated, Holocene sediment. -- The aocustically-deJfined disturbed zones record the occurrence of a large scale sediment fMlure. Sediment deformation in cores frtxn these failed zones indicates they are ocqposed of a ocrplgx arrangement of slide blocks, vAiich transform'at the distal margins of -the disturbed zones into debrites. Erosionad. scours downslope of "the dlsturbeckt zones^^uggest the^ this sediment failure developed into a large xurbidity current. This failure event was likely seisraically triggered.

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