CGRG Bibliography of Canadian Geomorphology
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Author : Boespflung, A.; Long, B.F.N.; and Occhietti, S.
Date : 1995
Title : CAT-scan in marine stratigraphy: a quantitative application
Publication : Marine Geology
Issue : 122(4):
Page(s) : 281-301
Abstract
Computed axial tomography (CAT-scan) gives a pseudo-3D representation of sedimentary cores. Sediments may be described and numerically processed from digitized high resolution images. A 150 m long borehole was drilled and sampled at Ile-aux-Coudres, middle estuary of the St. Lawrence, Quebec, and analysed by a tomodensitometer (CAT-scanner). This borehole represents mainly the Illinoian-Sangamonian transition series (isotopic stage 5e, 130-80 kyr B.P.) of a post-glacial glacioisostatic marine invasion and the subsequent regressive prodelta. Four representative samples, 900 mm long, were chosen for analysis from a transition zone between glacial and prodeltaic sediments. They have been described from tomographic longitudinal and transversal sections, from CT number series, and also from classical analysis such as grain size, organic matter and carbonates. CT numbers reflect sedimentary characteristics and are closely linked to grain size and to organic matter. Carbonates are only weakly correlated, probably because of its low concentration. Bed thickness and numerical processing of CT number series are used to characterize lamina, and allow for depicting sub-annual, annual and longer periodicities. Clay facies, fine and thick rhythmites, and isolated diamicton beds were identified. From bottom to top, the first sample contains homogeneous clay rhythmites, typical of a distal environment; the second is composed of diamictons and thin, alternating light-dark annual lamina sets; in the third sample, annual light-dark rhythmites are slightly thicker and display subtle semi-annual cyclicities; in the fourth sample, annual rhythmites are several centimetres in thickness and contain preserved sub-annual events, of possible seasonal cyclicity. This succession of facies and associated stratal periodicities may be typical of transgressive sedimentation in a basin such as the St. Lawrence estuary during the transition from glacial to non-glacial conditions.
Bibliography of Canadian Geomorphology