Occurrence and Significance of Iron, Manganese, and Titanium in Glacial Marine Sediments from the Estuary of the St. Lawrence River

Abstract

In glacial marine sediments from the St. Lawrence estuary, iron varies between 1.32 and 5.42%, manganese between 0.043 and 0.28%, and titanium between 0.31 and 0.64%. The regional distributions of these elements are related to sediment texture. Analyses of individual sediment size-fractions show that Fe, Mn, and Ti concentrations generally increase with decreasing grain size. Variations in elemental ratios between the different grades suggests that not all of the Fe and Mn is located in detrital silicate minerals. Dithionite extraction of selected sediments resulted in preferential dissolution of 3–16% of the total iron, presumably that derived from amorphous and crystalline iron oxides and from sorbed material.Hydroxylamine–hydrochloride removed 5–60% of the total manganese, presumably that derived from exchangeable Mn, easily reducible Mn oxides, and sorbed Mn material. The soluble fraction is highest in freshly deposited pelites from the center of the estuary. Soluble Fe and Mn occur as oxide films on the particles deposited from suspension, and the amount held depends on rate of deposition and on the physicochemical conditions in the waters and in the sediments. In contrast, Ti occurs in detrital minerals and accumulates at the same rate as detrital sedimentary material. It is unaffected by environmental changes. This investigation shows that, despite the derivation of the sedimentary material from the Canadian Shield predominantly by nonchemical erosional processes, small but significant chemical modification of iron- and manganese-bearing material is taking place in response to present physicochemical conditions.