Authors: MacDonald, D.E.
Freshwater marl and tufa deposits in Alberta were surveyed and evaluated as possible sources of calcium carbonate for use in treating acidic agricultural soils. Fieldwork was concentrated in the Peace River-Grande Prairie and central regions of Alberta. The total marl and tufa resources of these two areas, based on this study, are estimated to be 10 million cubic meters. Few deposits are present in the Peace River-Grande Prairie area and only three of these exceed 50 000 cubic meters in size. Deposits in central Alberta are confined to two areas: west of the 5th meridian, and north of latitude 53 degrees 30''. Tufa deposits are concentrated in the western region and are numerous; few, however, exceed 10 000 cubic meters in volume. Nine marl deposits in central Alberta exceed 50 000 cubic meters, five of which exceed one-half million. Most of the calcareous deposits examined contain greater than 50 percent Calcium Carbonate Equivalence (C.C.E.), which is the quality cut off used in this report to define marl. The marl is mainly fossiliferous micrite with calcareous algae (Characeae) present in various amounts. Contaminants include organic detritus and quartz. Clay minerals generally constitute less than 5 weight percent of the marl.
Tufa usually contains greater than 80 percent C.C.E., is well indurated, and consists of micrite and coarser calcite.
The formation of the marl and tufa deposits requires a source of calcium carbonate within the glacial drift or bedrock. The deposition process is manifest through leaching of this carbonate by percolating acidic groundwater, transportation of calcium bicarbonate ions in an aquifer, discharge at the surface, and precipitation of calcium carbonate due to the removal of CO2 from the water. Ideal conditions for marl deposition include a cool, moderately humid climate with a spruce forest vegetation. Under these conditions, a maximum amount of leaching occurs. Presence of high topographic relief to promote groundwater flow through short, local groundwater systems favours marl deposition. Marl generally forms at ponded discharge sites and tufa forms at well-drained sites.
Eight major classes of deposits, based on mode of formation and geological and hydrogeological setting, have been established.
Hillside-spring deposits are tufa and marls deposited where springs discharge on a hillside. Spring mound marl deposits are centered around springs discharging onto flat glaciolacustrine terrains. Spring fed lake marl deposits occur in lakes currently or at one time fed by springs discharging from bedrock. Shoreline fringe marl deposits occur as belts along shorelines of large lakes.
Abandoned channel marl deposits are present in Recent ox-bow lakes or postglacial abandoned channels; none are currently precipitating marl. Seepage ponded marl deposits occur in ponds, swamps, and small lakes that are fed by short, local groundwater systems confined to glacial drift. Hillside-seepage marl deposits form in areas of diffuse groundwater seepage along hillsides. Miscellaneous includes preglacial marl beds, deposits in Recent back swamps along streams, alkali flat deposits and calcareous sediments of Recent age. None of these deposits are of commercial potential.