Carbonate mud flows and other indicators of excess pore-fluid pressure in the Macumber Formation (Lower Carboniferous, Viséan) at Ingonish, Nova Scotia, Canada

Abstract

The Ingonish area of northern Nova Scotia offers the most extensive exposure of the Macumber Formation, the basal carbonate unit of the Lower Carboniferous (Middle Visean) Windsor Group of Nova Scotia and New Brunswick. The area also shows tectonic-free sedimentary characteristics of this unit. The formation consists of two principal lithologic units, a basal, black, earthy, carbonaceous limestone normally about 0.5 m thick and a thinly stratified, peloidal dolomudstone up to 17.5 m thick. At Burke Head, the dolomudstone is cut by at least 25 massive tufa mounds, elongated in cross-section and intersecting their surrounding strata by rising northeastward at angles of 15 to 25 degrees. At east Ingonish Island the basal unit is anomalous in being both dolomitized and thicker (5 m); there, both units are cut by at least 20 smaller massive tufa mounds. The mounds at both localities formed over deep-water hydrothermal vents, i.e., marine hot springs; the fossils of abundant chemosynthetic tubeworms surround the lower mounds on east Ingonish Island. The Macumber Formation overlies Horton Group braided-stream facies sandstones, and presumably underlies nearby, thick gypsum deposits of the Windsor Group.