Structure Cylindrique Verticale dans un Dépôt Meuble Quaternaire, au Nord de Montréal, Québec

Abstract

A vertical cylindrical structure, with concentric layers, occurs in a thick sand and silt Quaternary deposit north of Montreal. The cylinder transects horizontally-layered fine, medium, and coarse stratified sand; beds are 2–4 cm or 8–10 cm in thickness, and many are characterized by cross stratification. The cylinder has a total height (observed) of 152.5 cm and a diameter of 34 cm at the top and 24 cm at the base. A horizontal section at the top shows internal structure characterized by concentric layers of medium sand, fine sand, and silt in the center; the vertical section exhibits cone-in-cone structure. Micro-faults occur in proximal surrounding layers and within the structure itself. It is suggested that this vertical, cylindrical structure resulted from the action of a whirlpool eroding a deep cylindrical hole in unconsolidated sediments. Refilling of the hole by particles previously sucked off by the whirlpool immediately followed the erosional phase. The concentric arrangement of layers results from the settling of particles under whirlpool motion. Another possible origin of the structure is a spring rising through unconsolidated sands.