Carbonate and evaporite sedimentation at Clinton Lake, British Columbia, Canada

Clinton Lake is a small ephemeral lake lying in a glacial paleomeltwater channel near Clinton, Interior British Columbia. The lake is a Mg-Na-S0 (sub 4) brine (>300 g l (super -1) TDS), similar to those at Basque, 50 km to the south. Like the Basque Lakes, Clinton Lake has permanent deposits of epsomite. There are six main depositional subenvironments: (1) hillslopes, (2) springs, (3) carbonate playa, (4) hummocky carbonate mudflats, (5) saline mudflats, and (6) ephemeral lake or saline pan. There is no channelled inflow, and Clinton Lake is fed mainly by groundwater, direct precipitation, and diffuse runoff. About 120 m north of the lake, at slightly higher elevation, lies a small carbonate playa. called Clinton Pond. This is fed by a series of small springs and seepages. Other springs issue from the basin margins, but most seep into the ground or evaporate before reaching the lake. Shallow brine covers Clinton Lake during spring and early summer, but most of the surface is salt encrusted by late summer and autumn. Preliminary analyses of the basin waters and sediment mineralogy suggest that Clinton Lake may be fed by at least two distinct groundwater sources. The first type has a very high Na/Cl ratio (>15); the second type is less evolved, less saline, and has a lower Na/Cl ratio (<12). Both types of groundwaters have very high Mg/Ca ratios, resulting from contact with Mg-rich bedrock and early precipitation of calcite cements in soils. Aragonite and Mg-calcite are precipitated at the spring orifices, further depleting the waters in calcium. Some spring waters flow into Clinton Pond, where aragonite and hydromagnesite precipitate. Pond waters, augmented by other springs, may seep below hummocky carbonate mudflats toward Clinton Lake. At Clinton Lake, these waters mix with other shallow, dilute seepage and possibly, artesian groundwaters discharging through the lake floor. Cores and surficial muds from the saline mudflat contain hydromagnesite, aragonite, dolomite, and magnesite, and gypsum. Most calcium and much of the carbonate are precipitated in the outer mudflat, leaving a Mg-Na-S0 (sub 4) brine. Clinton Lake is a "spotted lake," consisting of more than 100 brine pools separated by rims of Mg-carbonate and gypsum muds. In summer, clear epsomite crystallizes in the pools as rafts and bottom-nucleated crystals. Mirabilite forms from residual brine in the autumn. Permanent epsomite deposits, showing evidence for repeated dissolution and recrystallization, underlie the pools. Clinton Lake is the successor to an earlier Mg-carbonate marl lake. Historical records suggest that evaporite precipitation could be very recent.