Bedrock and Sediments of Kouchibouguac Bay, New Brunswick

Abstract

On the basis of bottom samples and echograms from Kouchibouguac Bay and Northumberland Strait, the bottom topography, bottom lithology, and sediment distribution of the area are described and conclusions drawn regarding the composition of the underlying bedrock and the history of the sediments. A series of maps drawn after hydrographic charts dating back to 1839 show a buildup of the offshore barriers and underwater bars southeastward in the direction of long shore currents. Comparisons between maps illustrating bottom topography and bottom sediments show areas of topographic highs to be composed of bedrock and gravel whereas the topographic depressions consist chiefly of sand. Studies of the petrological composition of bedrock fragments and the gravel fraction reveal that green sandstone is the most common rock type in the samples from the inner part of Kouchibouguac Bay and probably underlies much of the area. On the basis of the abundant reddish-brown rocks in the samples from the outer part of the bay and the central area of Northumberland Strait it is concluded that the Scouduc Formation forms the bedrock in this area, whereas the red sandstone in samples near the coast of Prince Edward Island have been derived from the formations that form this island. Sediment colour and heavy mineral composition of the samples resemble that of the local sedimentary formations and indicate that the sand is derived from these rocks.The gravel in the area consists of glacial material, more or less reworked by wave action. The sand in the bay also appears to be relict material. This is concluded from the occurrence of sand deposits interpreted on the basis of sedimentary parameters, relation to topography, and association with present-day river mouths, as former river deposits. In a 1–2 mile-wide zone along the offshore barrier, wave action controls the deposition and distribution as shown by both normal decrease of mean diameter seaward and negative skewness values in the sediments.