Evaporites geologic variations

Holland, H.D., Horita, J. and Seyfried, W.E. Jr. (1996) On the seawater variations in the composition of Phanerozoic marine potash evaporites. Geology, 24, 993-996. 

Evaporitic sulfur has a range of sulfur isotopic composition from +10%o to +30%o, while sedimentary sulfur is depleted in the heavy isotope and has a range of isotopic composition of about —40%o to +10%o. Most of this variation reflects systematic changes with geological age. The source fractions of a river water can be estimated from an isotopic mass balance ... 

Hardie LA (1996) Secular variation in seawater chemistry An explanation for the coupled secular variation in the mineralogies of marine limestones and potash evaporites over the past 600 m.y. Geology 24 279-283... 

The lowest observed 5 B-values of around -30%c are for certain tonrma-lines (Chaussidon and Albarede 1992) and some non-marine evaporite seqnences (Swihart et al. 1986), whereas the most enriched HB-reservoir is given by brines from Australia and Israel (Dead Sea) which have 5 B-valnes of np to 60%c (Vengosh et al. 1991a, b). A very characteristic feature of boron geochemistry is the isotopic composition of ocean water with a constant 5 B-valne of 39.5%c (Spivack and Edmond 1987), which is abont 50%c heavier than average continental crnst value of -10 2%o (Chaussidon and Albarede 1992). Isotope variations of boron in some geological reservoirs are shown in Fig. 2.7. 

Rubey (1950) formulated questions concerning the history of the ocean, and Holland (1972) has attempted to solve the problem of ocean development, which is fundamental. Conway (1942,1943,1945) discussed whether the ocean had from its very beginning in the Precambrian the same volume and composition as today. Holland (1972) examined the geological records provided by evaporite deposits and affirmed that the composition of the ocean never was fundamentally different. Holland s calculations set definite limits for variations in pH, C02 pressure and related CO3 and HCO3 concentration, and Mg++, Ca++ and sulfate concentrations and ratios to each other, but do not give the total amount of sea water present at each geological age. 

Holland H. D. and Zimmermann H. (1998) On the secular variations in the composition of Phanerozoic marine potash evaporites Comment and reply. Geology 26, 91-92. 

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