Saline alkaline lake

To model the chemical effects of evaporation, we construct a reaction path in which H2O is removed from a solution, thereby progressively concentrating the solutes. We also must account in the model for the exchange of gases such as CO2 and O2 between fluid and atmosphere. In this chapter we construct simulations of this sort, modeling the chemical evolution of water from saline alkaline lakes and the reactions that occur as seawater evaporates to desiccation. 

Garrels and Mackenzie wanted to test whether simple evaporation of groundwater discharging from the mountains, which is the product of the reaction of rainwater and CO2 with igneous rocks, could produce the water compositions found in the saline alkaline lakes of the adjacent California desert. They began with the mean of... 

The reactions consume H+, driving the fluid toward alkaline pH, as shown in Figure 24.2. This effect explains the alkalinity of saline alkaline lakes. 

Figure 24.3 compares the calculated composition of the evaporated water, concentrated 100-fold and 1000-fold, with analyses of waters from six saline alkaline lakes (compiled by Garrels and Mackenzie, 1967). The field for the modeled water overlaps that for the analyzed waters, except that Ca++ and Mg++ are more depleted in the model than in the lake waters. This discrepancy might be explained if in nature the calcite and sepiolite begin to precipitate but remain supersaturated in the fluid. 

In a second example, we consider the changing chemistry of Mono Lake, a saline alkaline lake that occupies a closed desert basin in California, USA, and why... 

Mariner, R. H. Surdam, R. C. 1970. Alkalinity and formation of zeolites in saline alkaline lakes. Science, 170, 977-980. 

Analogous mechanistic studies of the formation of zeolite minerals have been reported. Kossowskaya (51), in this volume, considers the genetic associations of sedimentary zeolites and the dominant factors controlling their process of formation. An especially lucid and concise presentation of the mechanism of formation of sedimentary zeolites under low temperature conditions is given by Mariner and Surdam (52). In studies on the formation of zeolites in saline alkaline lakes, they show differential... 

Zeolites created in shallow sea sediments are also widespread. Other marine zeolites include analcime, merlinoite, chabazite, stilbite, and more rarely, erionite, mordenite, and laumontite. Figure 13 shows a schematic of the zoning patterns of autogenic zeolites and feldspars in tuffs of saline alkaline lakes, saline alkaline soils, deep-sea sediments, open hydrologic systems and burial diagenesis... 

Tuttle M. L. and Goldhaber M. B. (1993) Sedimentary sulfur geochemistry of the Paleogene Green River Formation, Western USA implications for interpreting depositional and diagenetic processes in saline alkaline lakes. Geochim. Cosmochim. Acta 57(13), 3023-3039. 

Sedimentary formations that contain significant amounts of zeolites are deposited in a number of relatively restricted geologic environments. The most important sedimentary zeolite minerals are analcime, clinoptilolite, heulandite, laumontite and phillipsite, and the dominant reaction is the alteration of volcanic tuff by alkaline solutions, whether in deep-sea deposits, saline, alkaline lake deposits and soils, or thicker, volcanic-rich sedimentary piles (Hay, 1966, 1978 Ikjima and Utada, 1966). Meteoric water moving downward through the last-named units typically forms smectite as an alteration mineral until solution salinity and pH have increased to the point where alteration is principally to zeolites. 

This system is represented by a closed basin, made of impermeable rocks and filled in the past by a saline alkaline lake. Water in this case could not permeate downwards but only evaporate, so the deposit develops horizontally, instead of vertically as in the previous occurrence. Here pH and salinity in the fluids tend to increase, giving rise to brines, c.g., basic, alkali-rich solutions. Concentric zones of authigenic minerals are so formed, from an outer and upper ring of little altered glass and clay minerals, to zeolites, analcime and a finally alkali-feldspars. A good example for this type of occurrence is Lake Tecopa, California, where the zeolitic ring is constituted by phillipsitc, clinoptilolite and erionite, followed by the central feldspar zone [36]. 

Phillipsite was found long ago in deposits on the sea floor (89). Since the discovery by Deffeyes (22) of phillipsite in lacustrine tuffs of Nevada, this zeolite has been reported commonly as a rock-forming constituent in tuffaceous rocks of the western United States (Table II, Figure 3). Phillipsite occurs in sedimentary rocks that range in age from Cretaceous to Holocene, but it is especially common in lacustrine deposits of late Cenozoic age, particularly those deposits of saline, alkaline lakes. Extensive and relatively pure beds of phillipsite are reported from southeastern Oregon, southeastern California, and Nevada. 

In a second example, we consider the changing chemistry of Mono Lake, a saline alkaline lake that occupies a closed desert basin in California, USA, and why gaylussite [CaNa2(CO3)2-5H2O], a rare hydrated carbonate mineral, has begun to form there. The lake has shrunk dramatically since 1941, when the Los Angeles Department of Water and Power began to divert tributary streams to supply water for southern California. 

Alkaliphile pH > 10.0 Saline-alkaline lakes and basaltic aquifers (4,5)... 

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