Analysis Of Microtextures On Quartz Sand Grains Of Triassic Age, From The Minas Basin - Cobequid Bay Area (Bay of Fundy), Nova Scotia

Abstract

<p> Triassic sandstones form rapidly eroding cliffs around much of the Minas Basin, Nova Scotia. The sand eroded from these cliffs is one major source of the modern intertidal sands. Wave erosion of the cliffs locally produces a small sand beach at the high tide level. </p> <p> Eight samples were examined using the Scanning Electron Microscope: two from the Triassic sandstones, and six from the high-tide beach below the cliffs. All samples contained rounded, as well as subrounded and subangular, quartz grains in the 0.5 - 1.00 mm size fraction. As the samples originated in the cliffs, abrasion by strong tidal currents cannot account for the rounded grain shape. </p> <p> All grains studied had suffered some degree of diagenesis in the form of a precipitation coat. This was generally thicker on the rounded grains than on the more angular ones. The Triassic sandstone grains generally illustrated upturned plates, semiparallel steps, conchoidal breaks and a fine V-shaped pattern. The high beach grains illustrated upturned plates, V-shaped patterns, conchoidal breaks, greater rounding of featu res present and arc-shaped steps. Wehrfritz (1973) studied quartz grains from intertidal sand bars in the Minas Basin. He concluded that grains were considerably rounded by intertidal processes, and the frequency of V-shapes increased with grain roundness. </p> <p> Although some rounding of the beach sands was inherited, wave and tidal action aided in rounding the features further. The initial rounding of the sand grains within the sandstones may have occurred during periods in the Triassic when they were exposed to wind or reworked in the lakes. </p>