Magnesium Supply Research Articles

Magnesium metabolism: basic aspects and implications of ciclosporine toxicity in rats.

In rapidly growing male Sprague-Dawley rats with an initial body weight of 100 +/- 10 g, we investigated how alimentary magnesium (Mg) supply, Mg metabolism and ciclosporine (Ci)-associated nephrotoxicity are interrelated. Food with 100 ppm Mg (1Mg) or 1,000 ppm Mg (stMg) or 10,000 ppm Mg (rMg), Ci 20 mg/kg body weight daily or olive oil were applied for 3 months (n = 10/group). Mg concentrations in various compartments were measured by atomic absorption spectrophotometry. Creatinine clearance (Jaffe), urinary N-acetyl-beta-D-glucosaminidase (NAG) activity (fluorometrically), urinary sodium excretion (flame photometry) and osmolality were measured. Histomorphological examination was done and renal renin expression was studied by monoclonal antibodies. Ci reduced the Mg concentration of the femur under 1Mg (72.6 +/- 9.7 vs. 112.6 +/- 14.3 mmol/kg dry substance, p < 0.05) and under stMg (150.6 +/- 16.6 vs. 194.1 +/- 10.2 mmol/kg dry substance, p < 0.05), thus indicating Ci-related Mg deficiency. This was due to a significant increase in Mg excretion in Ci treatment compared to dietary controls. Under rMg, there was no difference between Ci-treated and control animals. Ci treatment lowered creatinine clearance in 1Mg (1.42 +/- 0.05 vs. 3.02 +/- 0.58 ml/min) and in stMg (1.04 +/- 0.45 vs. 2.18 +/- 0.51 ml/min), NAG/creatinine and urinary sodium excretion were negatively affected by Ci under 1Mg and stMg. Histomorphology showed macrocalcifications due to Mg deficiency and Ci-specific findings, which were markedly enhanced in 1Mg and stMg. Animals with plentiful Mg supply had no functional alterations due to Ci and no or weakly expressed histomorphological lesions. Renin-positive stained cells were higher in Ci-treated animals. This seems to be functionally relevant under 1Mg and stMg, since it was associated with sodium retention and elevated relative heart weight, indicating hypertension. Alimentary or drug-induced Mg deficiency plays a relevant role in the pathophysiology of chronic Ci nephrotoxicity. Our data suggest that Mg supplementation is helpful to reduce Ci toxicity, even if there is 'normal' alimentary Mg intake.

Response of magnesium-deficient saplings in a young, open stand of Picea abies (L.) Karst. to elevated soil magnesium, nitrogen and carbon

A decline in a Picea abies L. (Karst.) stand in the Fichtelgebirge, NE-Bavaria, FRG has been attributed to a nutritional disharmony—a seasonal imbalance between a high supply of nitrogen, caused by high nitrogen deposition, and a low supply of soil magnesium, caused by soil acidification (Oren et al., 1988a). The nutritional disharmony hypothesis was tested on ten-year-old P. abies saplings in an adjacent stand growing on identical soil. The supply rate of magnesium relative to nitrogen was continuously increased or decreased during three successive growing seasons. Increasing the nitrogen or carbon supply resulted in a small increase in foliar nitrogen concentrations. Magnesium or carbon addition slightly raised the concentration of magnesium in the foliage. Reduction in crown leaf-area did not result in any appreciable changes in nutrient concentrations. Increased N supply decreased foliar Mg concentrations. In spite of the changes in the nutritional status of the needles, gas-exchange rates, pigment concentrations, needle characteristics and growth of twigs and stems did not differ among treatments. It appears that the growth of saplings was unimpaired at the foliar magnesium concentration at which the growth of adjacent mature trees was reduced. Moreover, it was not possible to promote nutritional disharmony in the saplings, including those receiving three times the annual nitrogen input. The study demonstrates that in young, relatively open stands of P. abies, much of the deposited nitrogen is not absorbed by the roots of saplings. Thus, the conceptual model of nutritional disharmony cannot explain forest decline if nitrogen uptake does not increase with deposition. Identifying the processes which control the uptake relative to the supply of all nutrients, and quantifying the rates of nutrient uptake are essential steps in using the conceptual model to explain specific decline symptoms.

Influence of changes in manganese and magnesium supply on some aspects of wheat physiology

Abstract Wheat (Triticum aestivum L.) cv. UP 2003 was grown in refined sand at three levels of manganese, 0.02 (deficient), 10 (adequate), and 200 (high) μM, each at three levels of magnesium, 0.02 (deficient), 2 (adequate), and 4 (excess) mM. In wheat magnesium deficiency aggravated the effects of low manganese supply namely decreases in dry weight, seed yield, chlorophyll content, Hill reaction activity, contents of DNA and RNA, and activities of ATPase and DNAse. On the other hand, the decrease in the activity of RNAse and increase in that of peroxidase were less pronounced in the combined deficiencies of manganese and magnesium than in manganese deficiency. Excess Mg accentuated the visible symptoms of Mn deficiency. Excess Mg also alleviated the effects of high manganese level by increasing the biomass, contents of chlorophyll, DNA, and RNA, Hill reaction activity, and activities of peroxidase and DNAse and by decreasing further leaf Mn content. It appeared that manganese could not replace the role o...

Photoinhibition and light-dependent turnover of the D1 reaction-centre polypeptide of photosystem II are enhanced by mineral-stress conditions

The function of photosystem II (PSII) and the turnover of its D1 reaction-center protein were studied in spinach (Spinacia oleracea L.) plants set under mineral stress. The mineral deficiencies were induced either by supplying the plants with an acidic nutrient solution or by strongly reducing the supply of magnesium alone or together with sulfur. After exposure for 8–10 weeks to the different media, the plants were characterized by a loss of chlorophyll and an increase in starch content, indicating a disturbance in the allocation of assimilates. Depending on the severity of the mineral deficiencies the plants lost their ability to adapt even to moderate iradiances of 400 μmol photons·m−2·s−1 and became photoinhibited, as indicated by the decrease in Fv/Fm (the ratio of yield of variable fluorescence to yield of maximal fluorescence when all reaction centers are closed). The loss of PSII function was induced by changes on the acceptor side of PSII. Fast fluorescence decay showed a loss of PSII centers with bound QB, the secondary quinone acceptor of PSII, and a fast reoxidation kinetic of q a - , the primary quinone acceptor of PSII, in the photoinactivated plants. No appreciable change could be observed in the amount of PSII centers with unbound QB and in QB-nonreducing PSII centers. Immunological studies showed that the contents of the D1 and D2 proteins of the PSII reaction center and of the 33-kDa protein of the water-splitting complex were diminished in the photoinhibited plants, and the occurrance of a new polypetide of 14 kDa that reacted with an antibody against the C-termius of the D1 protein. As shown by pulse-labelling experiments with [14C]leucine both degradation and synthesis of the D1 protein were enhanced in the mineral-deficient plants when compared to non-deficient plants. A stimulation of D1-protein turnover was also observed in pH 3-grown plants, which were not inhibited at growth-light conditions. Obviously, stimulation of D1-protein turnover prevented photoinhibition in these plants. However, in the Mg- and Mg/S-deficient plants even a further stimulation of D1-protein turnover could not counteract the increased rate of photoinactivation.

Partitioning of shoot and root dry matter and carbohydrates in bean plants suffering from phosphorus, potassium and magnesium deficiency

The influence of varied supply of phosphorus (10 and 250 mmol P m -3 ), potassium (50 and 2010 mmol K m -3 ) and magnesium (20 and 1000 mmol Mg m -3 ) on the partitioning of dry matter and carbohydrates (reducing sugars, sucrose and starch) between shoots and roots was studied in bean (Phaseolus vulgaris) plants grown in nutrient solution over a 12 d period. Shoot and root growth were quite differently affected by low supply of P, K, and Mg. The shoot/root dry weight ratios were 4.9 in the control (sufficient plants), 1.8 in P-deficient, 6.9 in K-deficient and 10.2 in Mg-deficient plants. In primary (source) leaves, but not in trifoliate leaves, concentrations of reducing sugars, sucrose and starch were also differently affected by low nutrient supply

Changes in phloem export of sucrose in leaves in response to phosphorus, potassium and magnesium deficiency in bean plants

The effect of varied phosphorus (10 and 250 mmol P m -3 ), potassium (50 and 2010 mmol K m -3 ) and magnesium (20 and 1000 mmol Mg m -3 ) supply on sucrose, reducing sugars, amino acids, P, K, and Mg in phloem exudate was studied in bean (Phaseolus vulgaris L.) plants over a 12 d growth period in nutrient solution. Phloem exudates were collected from detached primary leaves using the EDTA-promoted exudation technique. Compared with control nutrient-sufficient plants, sucrose export in the phloem exudate was drastically decreased by K deficiency and, particularly, by Mg deficiency, whereas P deficiency either had no effect or stimulated sucrose export. In Mg-deficient plants the rate of sucrose export was decreased to 10-20% of the control plants

Myocardial magnesium depletion during cyclosporine treatment, associated with reciprocal calcium overload, can be prevented by plentiful dietary magnesium supply.

Myocardial magnesium depletion during cyclosporine treatment, associated with reciprocal calcium overload, can be prevented by plentiful dietary magnesium supply.

Effect of potassium, magnesium and nitrogen supply on grape juice composition of Riesling, Chardonnay and Cabernet Sauvignon vines

The effect of nitrogen (0 and 60 kg/ha), potassium (0 and 60 kg/ha) and magnesium (0 and 60 kg/ha) supply on grape juice composition was studied in a factorial block design on 3 varieties (Chardonnay, Cabernet Sauvignon and Riesling) grown in the Sunraysia (Karadoc, Nangiloc) (warm, irrigated), Coonawarra (moderately cool) and Mornington Peninsula (Dromana) (cool) districts of Victoria. Increased nitrogen supply appeared to be the most important nutritional factor, significantly increasing grape juice pH and malate concentration in all 3 varieties, citrate in 2 and tartrate and potassium concentrations in 1. Increased potassium supply increased juice pH significantly in only 1 variety, but malate and potassium concentrations in 2. Magnesium was the only fertiliser whose application led, at least in 1 variety, to a significant reduction of grape juice pH. Most treatment effects on grape juice composition were quite small, but nevertheless significant, indicating that particular fertiliser applications could be used as a management tool for the production of quality winegrapes.

Effects of a deficient magnesium supply during the dry period on bone turnover of dairy cows at parturition

The bone activity and bone mineral content in rib bones resected from 33 dairy cows between 3 and 8 h after parturition were measured, and the effects upon them of a deficient supply of dietary magnesium (Mg) during the last seven weeks of pregnancy were studied. The cows were fed a diet containing either 0.22% magnesium (low Mg) or 0.82% magnesium (high Mg) in the dry matter (DM), and the potassium content of both rations was increased to approximately 4.1% in the DM to reduce the absorption of magnesium. In the cows fed the low-Mg diet a fall in plasma Mg concentration was observed. In the low-Mg, low-parity cows the plasma Mg concentrations at parturition were higher than in the low-Mg, high-parity cows, i.e. 0.83 mmol/l and 0.54 mmol/l, respectively. After parturition four cows in the low-Mg, high-parity group showed clinical signs of hypocalcaemia but none of the other groups did so. The bone formation in low-parity cows was significantly (P less than 0.05) affected by Mg supply, with higher percentages of both trabecular surface covered by osteoid and osteoid volume in the low-Mg group. In the high-parity cows no significant differences in bone formation were found between the low- and high-Mg groups. An inadequate Mg supply resulted in a significantly (P less than 0.05) higher Ca content in the bone ash of low-parity cows and a significantly (P less than 0.05) higher bone ash percentage in the bone of high-parity cows.

Productivity and vitality of spruce stands: dynamic feedback simulation for responses to different annual and seasonal levels of magnesium supply from soil

Responses of Norway spruce stands to gradually decreased annual magnesium supply from soil, with two seasonal courses, are evaluated by computer simulation. At low supply, magnesium concentrations in the needles are reduced to levels inducing chlorosis, but annual growth of new needles remains at the same level as stands with adequate magnesium. Above-ground permanent biomass shows a decreased annual production with lower supply, mainly because of shorter net carbon gain caused by decreased assimilation which is due to magnesium deficiency in needles. An additional but less important reason is the magnesium deficiency in stem and branch cambium, which is most severe during summer at low magnesium supply rates. The interaction of magnesium and carbon balance is emphasized. Modeling and simulation are not used for prediction but to test the consistency of scientific hypotheses.

The Distribution of Mg, P and K in the Split Roots of Subterranean Clover

The aim of these experiments was to determine whether uninhibited root growth is possible in a soil lacking Mg, provided that the plant is adequately supplied with Mg from another region within the soil. Two experiments were undertaken using split root systems in free-draining sand or gravel irrigated daily with nutrient solution. Magnesium supply to one half of the root system was varied and root growth in the deficient part of the system was measured. Magnesium redistribution was compared to that of calcium, phosphorus and potassium.

Assessment of bone turnover in the dry period of dairy cows by measurement of plasma bone GLA protein, total plasma alkaline phosphatase activity and urinary hydroxyproline

Plasma osteocalcin, or plasma bone GLA protein (BGP), total plasma alkaline phosphatase activity and urinary hydroxyproline excretion of twenty-four pregnant dairy cows (thirteen in their first or second pregnancy, i.e. low parity, and eleven in their third or more pregnancies, i.e. high parity) were measured from 7 weeks before parturition until 1 week after parturition. Seven weeks before parturition the cows' ration was changed to one containing either 0.22% magnesium (low magnesium, LMg) or 0.82% magnesium (high magnesium, HMg) in the dry matter, and the potassium content of both rations was increased to approximately 4.1% in the dry matter to reduce the absorption of magnesium. Plasma BGP levels decreased significantly (P less than 0.01) as parturition approached while total plasma alkaline phosphatase activity and urinary hydroxyproline excretion did not. Magnesium supply and parity had no significant effect on this decrease. The overall plasma concentration of BGP, total plasma alkaline phosphatase activity and the urinary hydroxyproline/creatinine ratio in the prepartum period were affected by parity (P less than 0.05) with higher values in the lower parity cows. A significant positive correlation (r = 0.58, P less than 0.01) was found in all cows between plasma BGP level at parturition and the percentage of the bone surface covered with osteoblasts; however, plasma BGP was not correlated either with other histomorphometric variables or with total alkaline phosphatase activity during this time.

Effects of an inadequate dietary intake of magnesium on osteogenesis in dairy cows during the dry period

The osteogenic activity in the rib bones of 33 dairy cows (14 of parity 1 or 2, and 19 of parity 3 or more) during their last two months of pregnancy, and the effects upon it of a deficient supply of dietary magnesium, were studied by means of intravenous infusions of the fluorochromes oxytetracycline hydrochloride, calcein and chlortetracycline given nine weeks, five weeks and one week, respectively, before the expected time of parturition. Seven weeks before this date the cows' ration was changed to one containing either 0.22 per cent magnesium (LMg) or 0.82 per cent magnesium (HMg) in the dry matter, and the potassium content of both rations was increased to approximately 4.1 per cent in the dry matter to reduce the absorption of magnesium. Four of the 10 LMg-high parity cows showed signs of periparturient hypocalcaemia. A significant decrease in the number of labelled osteons towards parturition was demonstrated in both the low parity (P less than 0.05) and high parity cows (P less than 0.001). The mean bone apposition rate in high parity cows was significantly lower (P less than 0.001) than in low parity cows. The different levels of magnesium in the diets of the cows had no significant effects on the numbers of osteons which were labelled nine weeks, five weeks or one week before parturition, or on the numbers of osteons which took more than one label or on the bone apposition rate. These results show that in these cows the rate of bone remodelling decreased as parturition approached.

Performance of two Picea abies (L.) Karst. stands at different stages of decline : VII. Nutrient relations and growth.

A declining, closed-canopy Picea abies (L.) Karst. stand produced as much crown biomass as a healthy stand, although some trees were chlorotic due to magnesium deficiency. The production of wood per unit of leaf area in both stands was related to the foliar magnesium concentration. Although leaf area index and climate were similar at both sites, stemwood production was 35% lower in the declining than in the healthy stand. Nutritional disharmony, rather than a deficiency in a single element, was identified as the mechanism for reduced tree vigor. The role of nutrient stress in forest decline was detected by partitioning the season into three periods reflecting different phenological stages: a canopy growth period in spring, a stem growth period in summer, and a recharge period during the non-growing season. Needle growth was associated with nitrogen supply. Most of the magnesium supply required to meet the demand for foliage growth was retranslocated from mature needles. Magnesium retranslocation was related to concentration of nitrogen and magnesium in those needles before bud break. Retranslocation from mature needles during the phase of canopy production resulted in chlorosis in initially green needles if the magnesium concentration before bud break was low. Nitrogen concentration in 0-year-old needles generally remained constant with increasing supply, indicating that foliage growth was restricted by the supply of nitrogen. In contrast, magnesium concentration generally increased with supply, indicating that magnesium supply for needle growth was sufficient. Much of the magnesium required for wood production was taken up from the soil because stored magnesium was largely used for canopy growth. Uptake at the declining site was probably limited because of restricted root expansion and lower soil magnesium compared to the healthy site. For this reason only wood growth was reduced at the declining site. Because the recharge of magnesium during the non-growing period is dependent on uptake from the soil, it was more limited at the declining that at the healthy stand. However, as nitrogen uptake from the atmosphere may account for an appreciable proportion of the total uptake, and as its supply in the soil at both sites was similar, an unbalanced recharge of nitrogen and magnesium may have occurred at the declining site. If mature needles are unable to recharge with magnesium in proportion to the uptake of nitrogen, chlorosis is likely to occur during the next canopy growth period.

Effects of Magnesium Deficiency on Carbohydrates in Phaseolus vulgaris

AbstractPhaseolus vulgaris ‘Saxa’ was cultivated in quartz sand under natural light conditions in an open‐top‐chamber and supplied with either complete (1.3 mM Mg) or magnesium‐free nutrient solution. 57 days old plants showed interveinal chloroses of older leaves, decreased magnesium and increased potassium tissue concentrations in leaves and pods.Plants with magnesium supply exhibited typical diurnal changes of hexoses, sucrose and starch in trifoliate leaves. Magnesium deficiency caused retarded sucrose formation and pronounced starch accumulation in trifoliate leaves throughout the day.Soluble sugars and starch were decreased in pods of plants without Mg‐supply.The results are discussed with regard to diurnal changes of carbohydrate metabolism.

Effect of the Supply of Potassium, Calcium, and Magnesium on the Absorption, Translocation, and Assimilation of Ammonium- and Nitrate-Nitrogen in Wheat Plants

Forty-two-day-old wheat (Triticum aestivum L. var. Asakazekomugi) plants were treated with complete, K-free (—K), Ca-limited (—Ca), and Mg-free (—Mg) nutrient solutions for 10 days using 2 mM NH4NO3 as the nitrogen source, which was replaced with 4 mM 15 NH4C1 or Na15NO3 for the subsequent 2 days to investigate the absorption, translocation, and assimilation of inorganic nitrogen in relation to the mineral supply. In another experiment plants were grown on NO3 −, NH4 +, NH4N03, and K-free and Ca-limited NH4N03 nutrient solutions for 10 days, and then in the latter three treatments the nitrogen source was replaced with NO3 − and half of the —K plants received K for 6 days to examine the changes in the nitrate reductase activity (NRA). Wheat plants absorbed NH4 −N and NO3-N at a similar rate. Influence of K on the absorption of N03-N was stronger than that on the absorption of NH4-N in wheat plants. The supply of K to the —K plants increased the absorption of NO3-N, while the absorption of NH4-N still remai...

Effects of calcium and magnesium intakes and feeding level during the dry period on bone resorption in dairy cows at parturition

A study was made of the influence of low and high calcium intakes at two feeding levels (experiments 1 and 2), and of different magnesium intakes (experiment 3) during the dry period, on the cellular resorptive activity in bone of dairy cows at parturition. In experiment 1 (26 cows) the feed intake was 1.12 times maintenance and the calcium intake was either 13.0 g d-1 or 83.5 g d-1. In experiment 2 (33 cows) the feed intake was 1.9 times maintenance and the calcium intake was either 26.4 g d-1 or 87.2 g d-1. In experiment 3 the cows feed intake was 1.4 times maintenance, the calcium intake was 71 to 72 g d-1 and the magnesium intake was either 16.6 g d-1 or 71.0 g d-1. Bone biopsies were taken from the tuber coxae between three and eight hours after parturition. In experiment 1 the cellular resorptive activity in bone from older cows was higher in the cows receiving the low calcium diet. In experiment 2 the differences between the bone resorptive activities of the two groups were small. In experiment 3 the bone resorptive activity was lower in the cows with a deficient supply of magnesium. There were significant relationships in young cows, but not in older cows, between the cellular resorptive activity in bone and the rate of calcium mobilisation measured biochemically. These results suggest that in older dairy cows bone resorption makes only a minor contribution to the total rate of calcium mobilisation at parturition and is therefore of minor importance for the prevention of periparturient hypocalcaemia.

Influence of a deficient supply of magnesium during the dry period on the rate of calcium mobilisation by dairy cows at parturition

The influence of a deficient magnesium supply during the dry period on the ability of dairy cows to mobilise calcium at parturition was investigated. The daily rations pre-partum consisted of 6 kg grass hay, and 4 kg concentrates containing either 1.58 per cent magnesium (HMg) or 0.22 per cent magnesium (LMg). Nine cows of parity one to six received the LMg diet and 10 cows of parity one to seven the HMg diet. Both rations provided 1.40 times maintenance on an energy basis and contained 4 per cent potassium in the dry matter. Throughout the dry period the mean concentration of magnesium in the plasma of the LMg group was significantly lower than in the HMg group and at parturition the mean plasma concentrations were 0.65 mmol litre-1 and 1.16 mmol litre-1, respectively. After parturition two cows in the LMg group showed clinical signs of hypocalcaemia but none of the HMg group did so. Cows of the LMg group had a lower mean rate of calcium mobilisation (0.27 mmol min-1) than those of the HMg group (0.34 mmol min-1) but the difference could not be explained by differences in bone turnover as reflected by urinary hydroxyproline excretion. Such a reduced rate of calcium mobilisation may be a contributory factor in the high incidence of milk fever in some herds fed inadequate magnesium in the dry period.

Supply and uptake of potassium, calcium and magnesium of spray carnations (Dianthus caryophyllus) grown in rockwool

In two experiments with carnations grown in rockwool the effects of different cation ratios in the nutrient solution were studied. The results showed that carnations need a high calcium supply. The crop did not appear to be sensitive to different potassium-magnesium ratios in the nutrient solution. In the nutrient solution added mole ratios K∶Ca∶Mg=55∶35∶10 seemed to be optimal. Such ratios in addition led to ratios of 55∶30∶15 in the root environment. Tissue analysis showed that in younger leaves of peduncles harvested a potassium content of 900 mmol per kg dry matter was optimal. For calcium a content of 350 and for magnesium 100–150 mmol per kg was needed. Analytical data of plant-sap analyses were closely correlated with data gained by digestion of dried material. For potassium and magnesium the relationships were linear. However, for calcium a curvilinear relationship was found. In the experiments indications were obtained that a sufficient calcium supply suppressed foot rot in carnations.

Chemistry and Environments of Dolomitization —A Reappraisal

Dolomitization of calcium carbonate can best be expressed by mass transfer reactions that allow for volume gain, preservation, or loss during the replacement process. Experimental data, as well as textures and porosities of natural dolomites, indicate that these reactions must include CO 3 2− and/or HCO 3 − supplied by the solution to the reaction site. Since dolomite formation is thermodynamically favoured in solutions of (a) low Ca 2+/Mg 2+ ratios, (b) low Ca 2+/CO 3 2− (or Ca 2+/HCO 3 −) ratios, and (c) high temperatures, the thermodynamic stability for the system calcite-dolomite-water is best represented in a diagram with these three parameters as axes. Kinetic considerations favour dolomitization under the same conditions, and additionally at low as well as at high salinities. If thermodynamic and kinetic considerations are combined, the following conditions and environments are considered chemically conducive to dolomitization: (1) environments of any salinity above thermodynamic and kinetic saturation with respect to dolomite (i.e. freshwater/seawater mixing zones, normal saline to hypersaline subtidal environments, hypersaline supratidal environments, schizohaline environments); (2) alkaline environments (i.e. those under the influence of bacterial reduction and/or fermentation processes, or with high input of alkaline continental groundwaters); and (3) many environments with temperatures greater than about 50°C (subsurface and hydrothermal environments). Whether or not massive, replacive dolostones are formed in these environments depends on a sufficient supply of magnesium, and thus on hydrologic parameters. Most massive dolostones, particularly those consisting of shallowing-upward cycles and capped by regional unconformities, have been interpreted to be formed according to either the freshwater/seawater mixing model or the sabkha with reflux model. However, close examination of natural mixing zones and exposed evaporitic environments reveals that the amounts of dolomite formed are small and texturally different from the massive, replacive dolostones commonly inferred to have been formed in these environments. Many shallowing-upward sequences are devoid of dolomite. It is therefore suggested that massive, replacive dolomitization during exposure is rare, if not impossible. Rather, only small quantities of dolomite (cement or replacement) are formed which may act as nuclei for later subsurface dolomitization. Alternatively, large-scale dolomitization may take place in shallow subtidal environments of moderate to strong hypersalinity. The integration of stratigraphic, petrographic, geochemical, and hydrological parameters suggests that the only environments capable of forming massive, replacive dolostones on a large scale are shallow, hypersaline subtidal environments and certain subsurface environments.