9.17 Geochemistry of Evaporites and Evolution of Seawater M Ba˛Bel, University of Warsaw, Warszawa, Poland BC Schreiber, University of Washington, Seattle, WA, USA

Home , Aragonite sea, Evaporite, Sulfate mineral

9.17 Geochemistry of Evaporites and Evolution of Seawater M Ba˛bel, University of Warsaw, Warszawa, Poland BC Schreiber, University of Washington, Seattle, WA, USA

9.17.1 Introduction 484 9.17.2 Definition of Evaporites 484 9.17.3 Brines and Evaporites 484 9.17.4 Environment of Evaporite Deposition 485 9.17.4.1 Evaporation 486 9.17.4.2 Freezing 486 9.17.4.3 Brine (Evaporating Waters) 487 9.17.4.4 Salinity 487 9.17.4.5 Temperature 488 9.17.4.6 Heliothermal Effect 489 9.17.4.7 pH 489 9.17.5 Seawater as a Salt Source for Evaporites 489 9.17.6 Evaporite and Saline Minerals 490 9.17.7 Model of Marginal Marine Evaporite Basin 491 9.17.7.1 Conceptual Model of the Basin 492 9.17.7.2 Quantitative Model of the Basin 495 9.17.8 Mode of Evaporite Deposition 496 9.17.9 Primary and Secondary Evaporites 498 9.17.10 Evaporation of Seawater – Experimental Approach 499 9.17.11 Crystallization Sequence before K–Mg Salt Precipitation 499 9.17.11.1 Early Salinity Rise – Calcium Carbonate Precipitation 499 9.17.11.2 Gypsum Crystallization Field 501 9.17.11.3 Halite Crystallization Field 501 9.17.12 Crystallization Sequence of K–Mg Salts 503 9.17.12.1 Natural Crystallization 503 9.17.12.2 Theoretical Crystallization Paths 504 9.17.13 Isotopic Effects in Evaporating Seawater Brines and Evaporite Salts 505 9.17.14 Usiglio Sequence – A Summary 505 9.17.15 Principles and Record of Chemical Evolution of Evaporating Seawater 505 9.17.15.1 Principle of the Chemical Divide for Seawater 505 9.17.15.2 Ja¨necke Diagrams 507 9.17.15.3 Spencer Triangle 508 9.17.16 Evaporation of Seawater – Remarks on Theoretical Approaches 509 9.17.17 Sulfate Deficiency in Ancient K–Mg Evaporites 509 9.17.17.1 Sulfate Deficiency as the Secondary Feature 511 9.17.17.2 Sulfate Deficiency as a Record of Ancient Seawater Composition 513 9.17.18 Ancient Ocean Chemistry Interpreted from Evaporites 514 9.17.18.1 Implications from Evaporite Mineralogy and from Usiglio Sequence 514 9.17.18.2 Implications of Primary Evaporite Minerals (Excluding Implications from Fluid Inclusions) 516 9.17.19 Recognition of Ancient Marine Evaporites 516 9.17.19.1 Sedimentological Criteria 517 9.17.19.2 Mineralogical Criteria 517 9.17.19.3 Geochemical Criteria 517 9.17.20 Fluid Inclusions Reveal the Composition of Ancient Brines 518 9.17.20.1 Criteria for Seawater Recognition in Halite Fluid Inclusions 519 9.17.20.2 Reconstruction of Ancient Seawater Composition from Halite Fluid Inclusions 520 9.17.21 Ancient Ocean Chemistry from Halite Fluid Inclusions – Summary and Comments 523 9.17.22 Salinity of Ancient Oceans 530 9.17.23 Evaporite Deposition through Time 531 9.17.23.1 Late Ediacaran–Phanerozoic Marine Evaporites 532 9.17.23.2 Precambrian (Pre-Ediacaran) Marine Evaporites 536 9.17.23.3 Nonmarine Evaporites in Precambrian 544 9.17.23.4 Pseudomorphs after Evaporite Minerals in Precambrian 544

Treatise on Geochemistry 2nd Edition http://dx.doi.org/10.1016/B978-0-08-095975-7.00718-X 483 484 Geochemistry of Evaporites and Evolution of Seawater

9.17.24 Significance of Evaporites in the Earth History 546 9.17.24.1 Paleogeographic Indicators 546 9.17.24.2 Seals for Hydrocarbons and More (Evaporites and Hydrocarbons) 546 9.17.24.3 Halotectonics 547 9.17.24.4 Diagenesis and Metamorphism of Evaporites 547 9.17.25 Summary 547 Acknowledgments 548 References 548

9.17.1 Introduction Braitsch, 1971; Braitsch and Garrett, 1981). Some authors have suggested other names for salt rocks precipitated by mechanisms This chapter focuses almost exclusively on marine evaporites other than evaporation (e.g., Berkey, 1922; Debenedetti, 1976; and in particular on how the chemistry of seawater is reflected Warren, 1996; Wood et al., 2005); however, these names (‘reac- in the mineralogy and facies distribution of deposits in tionites,’ ‘precipitates,’ ‘thermalites,’ ‘replacementites’, etc.,) are geologic space and time. First, the deposits formed from evap- only rarely used in the geologic literature, or are not generally oration of modern seawater are characterized together with accepted. Nowadays, the term evaporites appears to be most their distinctive crystallization paths, and then, we show how commonly used in the very broad sense (cf. Twenhofel, 1950). the mineralogy and geochemistry of evaporites have been used Nevertheless, those evaporites strongly affected by diagenesis for the interpretation of the chemical evolution of the ocean with the primary features obliterated, as those occurring in salt through time. In order to fill in the background of the main diapirs, are more commonly described as salt deposits (e.g., salt theme, we attempt to supply more detailed and up-to-date diapirs, not evaporite diapirs; cf. Hudec and Jackson, 2007). The information on the geochemistry of evaporite environments name ‘salt deposits’ also can be applied to halite or calcium and evaporite deposits important or relevant to the problem of sulfate deposits precipitated from seawater in the zones of hydro- their current geochemical studies. thermal circulation in spreading zones of the oceanic crust (Berndt and Seyfried, 1997; Hansen and Wallmann, 2003; Hov- land et al., 2006; Petersen et al., 2000; Talbot, 2008). 9.17.2 Definition of Evaporites

The Latin word ‘evaporo’ means ‘to change into a vapor,’ and it 9.17.3 Brines and Evaporites is used to designate the type of rocks and salts that originate during evaporation of natural solutes on the Earth’s surface. In The common feature of all evaporites is that they are composed the nineteenth and the beginning of the twentieth century, these of salts easily soluble in water (Goldschmidt, 1937). Such deposits were simply termed ‘salt deposits’ and also, rarely, as soluble salts accumulate in natural water reservoirs and in evaporates (Goldschmidt, 1937; Grabau, 1920, p. 23). Although ocean waters in particular and are removed from these aqueous both terms, together with the term saline deposits, are in use solutions in significant quantity, only by evaporation of the today, the term evaporites (with modified spelling) introduced water. The essential feature of evaporites is that they precipitate by Berkey (1922) became the most popular and it is widely from concentrated watery solutions or brines (Sonnenfeld, accepted now. 1984, p. 1). Other inorganic chemical deposits usually contain Evaporites are difficult to define precisely. The broad defini- minerals that are only slightly soluble in water. These minerals tion was suggested by Twenhofel (1950, p. 486) who understood do not form as a result of evaporation of concentrated solu- the evaporites as a “group of sedimentary deposits whose origin is tions. The chemical behavior of such substances is commonly largely due to evaporation.” More exactly, he stated that “most relatively easy to predict and to study from solubility products evaporites result from evaporation of water of high concentra- and Eh–pH relations (Berner, 1971; Krauskopf, 1967). tion, but a few are formed by replacement, or freezing of concen- By contrast, the solubility of salts and their activity coeffi- trated waters” and added that “if subjected to heat and pressure, cients in brines vary widely and are not readily predictable as they the evaporites form new combinations” (Twenhofel, 1950, are dependent on concentrations of other ions, among other p. 487). He also included the deposits that “develop through factors (Karcz and Zak, 1987). In concentrated solutions, “the metamorphism of other evaporites” into this group (Twenhofel, water structure was shown to be completely destroyed,” and due 1950, p. 486). Evaporites are similarly defined in the current to ‘water deficiency,’ “the effects of ionic association and compe- edition of the Glossary of Geology but include “rocks with saline tition between oppositely charged ions for water molecules in minerals formed by other mechanisms, e.g., mixing of waters or their hydration shells are intensified” (Figure 1; Krumgalz, 1980, temperature change” (Neuendorf et al., 2005, p. 221). Evaporite p. 73; Kostenko, 1982). “Formation of ion pairs and triplets grains “reworked by wind or saline waters as clastic particles” are apparently is so extensive in highly saline sulfate and carbonate also considered as evaporites (Neuendorf et al., 2005, p. 221). brines that the true ionic strength may be less than half the value The latter evaporites are termed allochthonous by Hardie (1984). calculated from total molalities” (Berner, 1971, p. 48). The aver- Some authors restrict the term ‘evaporites’ for sediments age ionic strength of standard seawater is about 0.7, but salt formed exclusively by evaporation, and they use the name saline solutions with ionic strength greater than 1 may require more deposits or salt deposits for deposits formed not only by sophisticated models than those applied for seawater (Berner, evaporation but also by cooling and salting out (compare 1971). Evaporating seawater brines attain ionic strengths nearly Geochemistry of Evaporites and Evolution of Seawater 485

7 All ions in the solution Start of halite + 6 Na precipitation 2+ ) Mg

23 Cl− Start of gypsum Start of 5 2− 10 precipitation SO4 epsomite ϫ precipitation n 4

2 Number of ions ( 1

0 1 1.05 1.1 1.15 1.2 1.25 1.3 1.35 1.4 Density (g cm-3)

100

90 All H2O molecules Number of H2O molecules per one ion ) 80 23

10 70 ϫ

n 60 Start of Start of Start of gypsum 50 halite epsomite precipitation precipitation precipitation 40 30

Number of ions ( 20 10 0 1 1.05 1.1 1.15 1.2 1.25 1.3 1.35 1.4 Density (g cm-3) Figure 1 Numbers of molecules in the evaporating Black Sea water, after data by Il’insky (1948, cited by Kostenko, 1982), recalculated by Kostenko

(1982). Note ‘water deficiency’ – extreme deficiency in H2O molecules.

equal to 1, approximately at the onset of CaCO3 precipitation, basin in the ‘productive’ state, may be even more complex. Two and can attain ionic strengths as high as 12.8 (Figure 2; or more salts can crystallize simultaneously from the same McCaffrey et al., 1987) or even 17.40 close to the end of evapo- evaporating brine and can form complicated double salts and ration (Millero, 2009). For example the waters of the Great Salt many possible hydrates. During evaporation of highly saline Lake and the Dead Sea show ionic strengths of 6.4, and 7.9, brine, some hydrated precipitates can release water to the brine respectively (Millero, 2009), and the experimental brines from and can become dehydrated salt deposits (at ‘invariant points’). La Playa lake in Spain – up to 15.52 (Lopez and Mandado, 2007). The development of such points of dehydration is a very specific These brines and their salts thus require a quite different, more feature of evaporite systems (Gamazo et al., 2011; Ordo´n˜ez complex chemical theoretical approach and an ion-interaction et al., 1994; Sa´nchez-Moral et al., 1998). The extremely concen- model (Drever, 1997; Pitzer, 1973, 1995), which allows for the trated brines also show a lot of chemical and physical features calculation of mineral solubility in electrolyte solutions of high and phenomena absent in seawater and freshwater, some of ionic strengths. Ion-interaction models provide one of the best them still poorly understand (e.g., Buch et al., 1993; Karcz and approaches applicable for the modeling of salt crystallization Zak, 1987; Krumgalz, 1980; Sherwood et al., 1991; Sonnenfeld, from natural solutions (e.g., Brookins, 1988; Christov, 2011; 1984). Furthermore, the measurements of the chemical and Hamrouni and Dhahbi, 2001; Harvie and Weare, 1980; Krumgalz physical parameters in brines are not easy and require special et al., 1999; Millero, 2009; Ptacek and Blowes, 2000; Song and methods in extremely concentrated brines (e.g., Anati, 1999; Yao, 2003; Voigt, 2001). Pitzer’s model (Pitzer, 1973, 1995) is Tanweer, 1993). commonly applied to waters with ionic strength, I>0.72, whereas for waters with ionic strengths, I<0.72, Debye–Hu¨ckel or other theories are best applied (Dargam and Depetris, 1996; 9.17.4 Environment of Evaporite Deposition Drever, 1997; Langmuir, 1997; Ptacek and Blowes, 2000). The behavior of concentrated brines at saturation or super- Evaporite environments and brines are characterized by basic saturation with respect to one or more salts, as in an evaporite physicochemical features and parameters, such as salinity, 486 Geochemistry of Evaporites and Evolution of Seawater

14 Start of gypsum 12 precipitation

10 Start of kainite 8 precipi- ength tation Start of epsomite 6 precipitation Ionic str Start 4 Start of halite of carnallite precipitation precipitation 2

0 0 10 20 30 40 50 60 70 80 90 100 Degree of evaporation Figure 2 Ionic strength of the evaporating Caribbean seawater brines, based on data by McCaffrey et al. (1987). temperature, and pH, which fluctuate within some limits. well-understood process. The evaporation of concentrated brines The most important of these physical, geochemical, and sedi- is more complex. During evaporation from brines and bitterns, mentological features are reviewed (and some of them more the rate of evaporation slows with the rise of salinity. Evapora- clearly defined) in the following sections, beginning with the tion stops at some extremely high-salinity conditions, because process essential for deposition of evaporites – the evaporation. above a certain concentration, the brine becomes hygroscopic and adsorbs humidity from the air rather than drying, as shown, for example, by seminatural evaporation of the highly concen- 9.17.4.1 Evaporation trated Dead Sea brine (by Zilberman-Kron 2008, described in Katz and Starinsky, 2009). In the Dead Sea, the condensation of Evaporation is the most effective way to separate dissolved salts atmospheric humidity into the brine during the summer–fall from the water solute (i.e., promoting their precipitation). This transition reversed the brine level drop in the experimental con- term is widely used in the studies of evaporite deposits – instead tainers filled with brine (Yechieli and Wood, 2002). This prop- of vaporization – “to signify that under natural conditions evap- erty makes a seawater bittern a potentially good liquid desiccant oration occurs just so long as the atmosphere is not saturated (Lychnos et al., 2010). It was documented in the sabkha envi- with respect to H2O, and so long as no liquid (vapor) phase is ronment that the brine level in the ground rises during periods of present” (Braitsch, 1971, p. 84). Evaporation acts in two ways – elevated humidity, apparently due to the condensation of water first, it is able to bring the undersaturated solution (unable to from the air (Yechieli and Wood, 2002). The water from the precipitate the highly soluble salts) into the state of saturation sabkha surface can, however, evaporate to dryness during the and supersaturation, and then, secondly, it is able to promote daytime because its surface can attain very high temperatures more or less continuous precipitation of salts from such a solu- (up to 60 C). Here, solar heat contributes sufficient energy to tion in the evaporite basin, which is then in the ‘productive’ state. remove water by evaporation, and warm air over the sabkha Evaporation is the most important driving force in evaporite is able to absorb more water, which escapes from the system systems. The efficiency (rate) of evaporation is dependent on, or carried by the wind (Walton, 1978). limited by, such factors as temperature (both the brine and the In volcanic areas, thermal evaporation of the ground, heated air), humidity, air movement, salinity, and factors such as the from below, operates in a different way from solar evaporation as appearance of salt crust on the surface of brine, which inhibits it produces slightly different, commonly dehydrated evaporite the evaporation process (Groeneveld et al., 2010; Sonnenfeld, salt suites, stable in more elevated temperatures, and such evap- 1984). Evaporation “is of course greater where the relative oration commonly promotes acidity (Pulvirenti et al., 2009). humidity is low. Where however the temperature is also low, and therefore the total amount of water which the air can contain 9.17.4.2 Freezing is small, saturation is soon reached unless the dry air is constantly replaced. When the temperature is high, evaporation may be Freezing acts in a way similar to evaporation in its effect on brines – much greater even in stagnant air, but where this air is in motion it removes H2O from the solution in the form of ice and pro- it will be very rapid and extreme. Hence the importance of drying duces a residual, concentrated brine as well as the crystallization winds, i.e. winds of low relative humidity” (Grabau, 1920, of peculiar minerals (Stark et al., 2003). Freezing ends at an pp. 114–115). The quantitative data and models for rate of eutectic or cryohydric point when all compounds including brine evaporation are given by many authors, Walton (1978), H2O pass into the solid state (Mullin, 2001). The liquid brines Laborde (1985), Chen (1992), Steinhorn (1997), Oroud (1999, with eutectic temperature below 0 C are called cryobrines 2011), Krumgalz et al. (2000), Al-Shammiri (2002), Kampf et al. (Mo¨hlmann and Thomsen, 2011), and such brines probably (2005), and Gamazo et al. (2011), among others. exist on Mars as well as in our Earth’s polar regions (McEwen The evaporation of freshwater and normal salinity seawater et al., 2011). The minerals formed by freeze-drying are usually has been studied quantitatively for a long time and is a called cryogenic (e.g., Brasier, 2011). Some artificial calcium Geochemistry of Evaporites and Evolution of Seawater 487 chloride cryobrines have extremely low eutectic temperatures, total amount of salts dissolved in the water/brine, and brine, down to 210-215 K (Brass, 1980) and it is thought that some by definition, contains a lot of salt. It has been measured using other brines show even lower eutectic temperatures (199 K: many different units and in a number of ways. The absolute Faire´n, 2010, his Table 1; 201 K: Mo¨hlmann and Thomsen, salinity, S, as defined by Forschhammer (1865), is the mass of 2011, their Table 1). dissolved salts in seawater, brackish water, brine, or other During freezing of seawater, the eutectic temperature is saline solution per mass of that solution and is given in reached at 54 C when the freezing is according to the dimensionless units: g per kg, % (per mill), or ppt (parts per À Ringer–Nelson–Thompson pathway or at 36 C when it fol- thousand) (Anati, 1999; Gamsja¨ger et al., 2008): À lows the Gitterman pathway, which is thermodynamically sta- S mass dissolved salts =mass saline solution [1] ble pathway for freezing of seawater (Marion et al., 1999; Stark ¼ ð Þ ð Þ et al., 2003). Freezing of brines is modeled by numerical sim- This salinity is very rarely measured directly. Usually, it is ulations (e.g., Kargel et al., 2000). The most extreme natural evaluated by measuring some other physical parameter case, on Earth, is noted in the permanently unfrozen Don Juan (density, i.e., specific gravity, optical refraction index, electrical Pond in Dry Valley, Antarctica, containing one of the saltiest conductivity, etc.). It may also be measured by the concentra- 1 natural brines on Earth (salinity 388.9 gkgÀ ; Torii and tion (contents) of some conservative element (ions that do not Ossaka, 1965). Those brines can remain unfrozen down to participate in any of evaporitic precipitation and hence are 51 C (Marion, 1997). conserved in the solution) and accumulates in the brine during À its evaporation (such as Cl, Mg, K, Li, and Br; e.g., Brantley 9.17.4.3 Brine (Evaporating Waters) et al., 1984) for which a calibrated conversion scale is known. Conversion scales are however different for any particular The evaporation of water causes the amount of salt remaining in brine with its own chemical composition (e.g., Jellison et al., the water solution to rise – freshwater can become ‘brackish,’ 1999; Zinabu et al., 2002). Recently, several standard units for then saline, brine, and finally a bittern. ‘Freshwater’ is defined as the properties of seawater were introduced (Millero, 2010; sufficiently dilute to be potable, that is, containing less than Wright et al., 2011), of which the standard seawater composi- 1 1000 mg lÀ total dissolved solids (TDS; Drever, 1997), the tion reflecting the chemical composition of seawater is impor- value that is considered as close to a natural boundary of detec- tant for geochemical studies (Table 1; Millero et al., 2008). tion of human taste (Alekin, 1970; Hammer, 1986). The terms The recommended measure of salinity for seawater is given brackish, saline, and brine are not defined univocally and can be as a dimensionless, practical salinity ‘unit’ that is based on variously defined depending on the author and the country. conductivity measurements and is commonly designated as According to Drever (1997), brackish waters are too saline to ‘psu,’ which is not quite appropriate, because the practical be potable but are significantly less saline than seawater and salinity scale has no units (Millero, 1993, 2010; Millero et al., 1 containing between 1000 and 20000 mg lÀ TDS. In the older 2008). The seawater of average salinity is 35%, and in the literature, ‘brackish’ concerns the transitional zone between practical salinity scale, it has a salinity of 35.000. The other marine and freshwater and refers to those waters of intermediate commonly used dimensional measure of salinity is TDS 1 salinities being a mixture of freshwater and seawater (s. s.) (g lÀ ). It is the unit of total dissolved grams of solids per (Hammer, 1986). Saline waters have salinities similar to or liter of brine and has the dimension of density, and, as such, 1 greater than seawater (35000 mg lÀ TDS) (Drever, 1997). it is both temperature- and pressure-dependent, and therefore, In limnology, however, the boundary between freshwater and without the known temperature (at least), the information saline waters is set at 3% (Bayly, 1972; Bayly and Williams, about the absolute salinity is always incomplete (Anati, 1999). 1966), and the most-mineralized river waters were termed saline The unit recommended for monitoring the advance of by Meybeck (2003) when sum of ion concentrations is only over evaporation of seawater, and the associated processes includ- 1 1 24 meq lÀ , which is equivalent of 1.4 glÀ NaCl. Drever (1997) ing any salinity rise or fall, is the ‘evaporation ratio’ defined as also defined brines as waters significantly more saline than sea- the mass (weight) of H2O (not weight of brine) in the original water that usually contain much NaCl and are strongly salty in seawater divided by the mass (weight) of H2O in resulting taste. Bittern is the brine stripped of most of its sodium chloride evaporated brine (Garrett, 1980; Holser, 1979a). The other content and with the bitter taste of a magnesium chloride solu- similar unit is ‘volume ratio’ being described as ‘X seawater’ tion (Lychnos et al., 2010; Sonnenfeld, 1984). The residual, most that is the total volume of original seawater to total volume of concentrated evaporated bittern is commonly left to soak into brine (including dissolved salts; Holser, 1979a). Logan (1987) the precipitate and is called ‘mother liquor,’ although sometimes used ‘volume reduction ratio’ (Ver) defined as this term is also used alternatively with the bittern. Brines formed by evaporation can be called solar brines to Ver Vo Ve =Vo [2] distinguish them from the ascending subsurface hot brines ¼ ð À Þ called hydrothermal and supercritical brines (Talbot, 2008; where Vo is volume of original seawater and Ve is volume of note that the proper use of the genetic term hydrothermal evaporative outflow. The other recommended method of requires special caution; see Machel and Lonnee, 2002). monitoring the degree of evaporation (DE) of brine, particularly those trapped in halite fluid inclusions, is by the calculation of the degrees of evaporation for various elements (DE ) of 9.17.4.4 Salinity ELEMENTS brines related to modern seawater composition (Levy, 1977). Salinity is the most important parameter characterizing and Any conservative element not removed during the salt precipita- defining saline water, brine, or bittern. It is a measure of the tion can be used (McCaffrey et al., 1987; Raab and Spiro, 1991; 488 Geochemistry of Evaporites and Evolution of Seawater

Table 1 Major and other ions concentrations in seawater after various sources

Holland et al. (1986) Hay et al. (2006) Lowenstein and Hay et al. (2006) Millero et al. (2008); (from Holland, 1978), (after Gill, 1989)a; Risacher (2009) (after Gill, 1989)a; mi (mol kg –1) average concentration concentration % by (after Drever, 1988) molal concentration 1 1 in seawater of 35% weight ( g kgÀ ) (mmol kgÀ H2O) 1 ¼ salinity (mmol kgÀ )

2 Ca þ 10.2 0.41 11 0.0102 0.0106568 2 Mg þ 53.2 1.27 55 0.0524 0.0547421 Kþ 10.2 0.38 11 0.0097 0.0105797 Naþ 468.0 10.59 485 0.4608 0.4860597 2 SO4 À 28.2 2.67 29 0.0278 0.0292643 ClÀ 545 19.12 565 0.5394 0.5657647

HCO3À 2.4 0.12 2.4 0.0020 0.0017803 2 Sr þ nd 0.01 nd 0.0001 0.0000940 BrÀ 0.84 0.07 nd 0.0008 0.0008728 2 CO3 À nd 0.02 nd 0.0003 0.0002477 B(OH)4 nd nd nd nd 0.0001045 FÀ nd 0.03 nd 0.0015 0.0000708 OHÀ nd nd nd nd 0.0000082

B(OH)3 nd nd nd nd 0.0003258 CO2 nd nd nd nd 0.0000100 H2O nd 965.28 nd 17,389.8474 55.5084720 Other 0.02 nd nd nd Sum of halides 9.22 Sum of components 34.72 1.1605813 dissolved in water Sum of components 1000.00 56.6690534 dissolved in water, and water

1 mi, molality (mol kgÀ of solvent); nd, no data. aWith modifications to make chlorinity (Cl) of 19.2 equal to a salinity of 34.72% (after Hay et al., 2006)

Vogel et al., 2010; von Borstel et al., 2000). For example, the DE, measurement must be monitored with an accuracy of at least based on magnesium (DEMg), is calculated following the equa- 0.04 C (Anati, 1999). The particular problem is within super- tion (Zimmermann, 2000, 2001): saturated brine in state of salt precipitation. It is difficult to measure its properties accurately not only because of the pres- DE mmolMg=kgH O = mmolMg=kgH O ence of the invisible suspension of salt microcrystals (<4 mm) Mg ¼ ð 2 Þbrine ð 2 Þseawater [3] but also because the continued salt precipitation changes the chemical composition of brine that influences the other phys- During the K–Mg salt precipitation from evaporating ical parameters characterizing the brine and conversion scales seawater, Mg, K, Br, and Rb are removed from the brine, and (Anati, 1999; Stiller et al., 1997). only Li and B remain as conservative or relatively conservative The measured salinity of seawater brine may reach values of 1 elements (Vengosh et al., 1992), which more clearly indicate 504.8 (TDS, g lÀ ) at the beginning of the final bischofite the true DE (Zimmermann, 2001). The ratios of selected ions, crystallization stage (Fontes and Matray, 1993) and another 1 for example, (Na/Cl)eq, Mg/Cl, and Br/Cl, also reflect the DE, type of brine in some continental lakes over 500 g lÀ (e.g., 1 with some limitations (Holser, 1963; Levy, 1977). The evapo- 557 g lÀ , TDS), in one of the Wadi El Natrun alkaline lakes, ration of seawater brines can be traced on the diagrams com- Egypt (Taher, 1999). Boiling hot (110 C) Na–K–Mg–Cl brine paring the contents of some conservative components (e.g., Na from hydrothermal springs in Dallol salt diapir in Ethiopia 1 and Cl, Mg and Cl; Lowenstein et al., 2001) or the ratios of attains 420 gkgÀ (TDS; Hochstein and Browne, 2000). Sub- such components (e.g., Mg/Cl vs. Br/Cl; Holser, 1963). Con- surface brines can reach extremely high salinities such as 1 centration ratios for marine sabkha brine aquifers require spe- 643 glÀ recorded in Ca–Na–Cl-type brine from the Salina cial calculations (Wood et al., 2002). Formation in the Michigan Basin (Case, 1945). This brine 3 The recommended measures of concentration in brines are showed also one of the highest density, 1.458 gcmÀ , so far g/100 g H2O, g/100 g solution (%), and mol/1000 mol H2O measured in natural brines. (Braitsch, 1971, p. 28). The mutual comparison of various salinity units is 9.17.4.5 Temperature complicated, and in particular, such measurement requires the accompanying precise measurements of temperature. For The temperature variations in various Earth evaporite environ- a salinity accuracy of 0.02%, the temperature during salinity ments range from ca. minus 50 C to ca. plus 70 C, depending Geochemistry of Evaporites and Evolution of Seawater 489

on the climatic zone, and usually oscillate around 20–30 C in artificial heliothermal solar pans, a temperature above the the warm zone of Earth. However, temperatures on the sabkha boiling point of water was reached (109 C, in New Mexico, surface are up to 60 C (Kinsman, 1969) and in the algal mats up United States, Lodhi, 1996; the boiling point of seawater bit- to 60–80 C (Kinsman, 1966) and air temperature above the tern can reach 125 C in the bittern having a density 38 degrees sabkha may reach up to 50 C (Warren, 2000). The temperature Baume´; Buch et al., 1993). The heating of brine, to 50 C and of the gypsum surface at Tule Spring, in the Death Valley, United more, both due to input of heliothermal and solar heat States, reached 190 F ( 87.78 C; Hunt et al., 1966). The brine (insolation), apparently is limited to shallow water masses ¼ temperature in Salina Ometepec, Baja California, Mexico, (Schreiber and Walker, 1992; Sonnenfeld, 1984). attained 70 C (Casas and Lowenstein, 1989). Normally, however, the brine in shallow pans, including solar saltwork pans at 9.17.4.7 pH the stage of gypsum or halite crystallization, is no more than 30– 40 C (Benison and Goldstein, 1999). Many salt lakes and pH in saline lakes brine can be as low as 1.7 as recorded in the acid lagoons, for example, Kara Bogaz in Turkmenistan, experience lake Magic (Wave Rock 2), (240–280 ppt, TDS) in Western a temperature drop below 0 C in the winter, and temperatures Australia (Benison et al., 2007; Bowen and Benison, 2009) and below 55 C have been recorded from Antarctica salt lakes attains a pH 12.0, similar to the solar evaporation pans of the À (Marion, 1997). Hourly, diurnal, seasonal, and annual temper- Magadi Lake, Kenya (Grant, 2006; Grant et al., 1999). Evaporat- ature fluctuations are particularly important for precipitation of ing seawater brine commonly shows characteristic pH fluctua- salts from saturated solutions because temperature change in tions (Figure 3). The pH of evaporating seawater may rise from such a solution promotes supersaturation and precipitation the local values (e.g., 8.3 in Bocana de Virrila´, Peru) to 8.6 in the (e.g., Ganor and Katz, 1989; Sa´nchez-Moral et al., 2002). field of carbonate precipitation. It then drops rapidly to 7.3–7.5 at The relatively high temperatures of ancient evaporating the beginning halite saturation field and, further on, more slowly brines have been documented by fluid inclusion studies, par- to 7.0 within this field (Brantley et al., 1984; Des Marais et al., ticularly in ancient halite deposits. For example, the homoge- 1992; Dronkert, 1985; Landry and Jaccard, 1984; Levy, 1977; nization temperature of fluid inclusions in Permian halite McCaffrey et al., 1987; Nadler and Magaritz 1980; Pierre and from Kansas, United States, yielded original brine temperatures Ortlieb, 1981; Pierre et al., 1984a; Rieke and Chilingar, 1961; from 21 to 50 C (Benison and Goldstein, 1999) and from Vogel et al., 2010). Further drop to pH 5.7 is recorded in the 1 the Zechstein of Poland from 50 to 62 C (Vovnyuk and K–Mg salt precipitation field in brine of the density 1.327 gccÀ at Czapowski, 2007). Similarly, the minimum temperature of 30 C (Amdouni, 2000; Buch et al., 1993). The possible reasons halite crystallization in Oligocene Rhine Graben evaporites in for such pH fluctuations were listed by Levy (1977), Nadler and France was estimated as 63 C (Lowenstein and Spencer, 1990), Magaritz (1980), and McCaffrey et al. (1987) and discussed by and even higher temperatures (71 C on average) – for Permian Bodine (1976) and Krumgalz (1980). The similar pH values of Salado Formation in New Mexico (Lowenstein and Spencer, brine were recorded in fluid inclusions from ancient halites 1990). Studies of the Devonian sylvite and carnallite of the (Petrychenko, 1988; Petrychenko et al., 2005; Roedder, 1984), Pripyat Depression in Belorussia, interpreted as primary however Benison et al. (1998) found that pH could be as low as deposits, indicated brine temperatures 67–83 C, although 0-1 in some Permian halite lakes. Proper pH measurements ancient hydrothermal activity is recorded in this area (Hryniv of high-salinity brines require special techniques (Bowen and et al., 2007; Petrychenko and Peryt, 2004). Halite inclusions Benison, 2009; Sonnenfeld, 1984). from the Lower Cambrian Angara Suite on Siberian Platform showed brine temperatures from 60 to 86 C (Petrychenko et al., 2005). On the other hand, the ancient Silurian (Pridolian) 9.17.5 Seawater as a Salt Source for Evaporites halite of the Michigan Basin, United States, showed low temperatures (5–25 C) suggesting relatively cool climate during The mineralogy of evaporites depends on composition of salts deposition of these evaporites (Satterfield et al., 2005). dissolved in the evaporating water, and in particular on the proportions of specific dissolved ions. The source of salts for evaporite deposits are easily soluble chemical compounds (salts) 9.17.4.6 Heliothermal Effect dissolved in natural waters on Earth. There are many natural The capacity to store heat increases together with a rise in types of salt-containing waters in the Earth environments; salinity, and therefore, brine, when heated, cools more slowly however, the crucial source for most evaporites is the ocean – than the fresh- or seawater. In calm density-stratified brine the largest reservoir of saline water that contains the largest pools, heated by sun, the brine below a shallow pycnocline amount of the dissolved salts (Table 1). The hydrosphere con- can be heated by the sun’s rays due to a heliothermal effect to tains about 1386 million km3 of free (gravitational) water of extreme values – scalding unsuspecting bathers (Kirkland et al., which 96.5% (1338000 km3) is the ocean (Babkin et al., 21 1983; Sonnenfeld and Hudec, 1980). The brine in Lake 2003), containing 1.4 x 10 kg H2O (Le´cuyer et al., 1998; Pope Ursului, Romania, reached 69.5 C due to this effect, despite et al., 2012, Table S3). The volume of seawater may be up to 10% the fact it is in the temperate climatic zone (latitude 46350 N), larger when water stored in bottom ocean silts is added (refer- (Telegdi von Roth 1899, in Kirkland et al., 1983). Similar ences in Babkin et al., 2003). Lakes contain only 176400 km3 of heliothermal conditions cause temperatures of 60.5 C in water, that is, merely 0.013% of the hydrosphere. Among them, 3 Solar Lake, Sinai, Egypt (Cohen et al., 1977), and 67 C in freshwater lakes account about 91000 km and salt lakes only the bottom clays of the Tuzluchnoye Lake, at Iletsk, Forecas- 85400 km3, and 97% of their volume is found in one lake – the pian Depression, Russia (Dzens-Litovskiy, 1968). In some Caspian Sea (Babkin et al., 2003). The ocean contains 490 Geochemistry of Evaporites and Evolution of Seawater

Start of gypsum precipitation 8.5

Start of halite 8 precipitation

7.5 pH

6.5

6 0 5 10 15 20 25 30 35 40 Degree of evaporation Figure 3 pH changes during evaporation of Caribbean seawater, based on data by McCaffrey et al. (1987).

47.578 1018 kg of salts (for an average salinity of 34.72%; then documented, in more detail, by Forschhammer (1865) and Â 2 Hay et al., 2006). The eight major seawater ions, ClÀ, SO4 À, is variously known as Marcet’s principle, Forchhammer’s princi- 2 2 HCO3À, BrÀ, Naþ, Mg þ, Ca þ, and Kþ, comprise 99.76% by ple, the principle of constant proportions (Horne, 1969; Millero weight of the dissolved salts, and the most abundant ClÀ and Naþ et al., 2008; Schopf, 1980), or simply the first law of chemical ions make up 85.59% by weight of the salt in the seawater (Hay oceanography (Dana Kester in Millero, 2010). et al., 2006). The total amount of the salts dissolved in the ocean That principle permits a calculation of the value of salinity is enough to form a continent “three times the size of Europe as it from the known concentration of one component of given appears above the sea level” (Grabau, 1920, p. 50). seawater. In such a way from the known concentration of all The ocean was the main source of salts for the largest halogens, which is easy to measure and is defined as chlorinity ancient evaporite deposits popularized by Hsu¨ (1972) under (Cl in %), the salinity (S in %) is calculated according to the the name the ‘saline giants’ (called also basin-center or basin- well-known Knudsen’s law (Millero, 2010): wide evaporites; Kendall, 1992; Warren, 2006). The compo- S % 0:030 1:805Cl % [4] nents of seawater are therefore the most important for ð Þ ¼ þ ð Þ evaporite deposition. From many elements dissolved in seawa- Due to continued mixing, the isotopic composition of ter and eight major ions listed earlier, only seven of them create many components is fairly constant in the present-day ocean, stable and volumetrically significant salts being the product of including H2O not contaminated by glacial melt or river waters seawater evaporation (proportion of total salts by weight, in %, (Holser, 1992; Knauth and Beeunas, 1986; Le´cuyer et al., 2 is given in brackets): Naþ (30.51), ClÀ (55.08), SO4 À (7.69), 1998), and also recently recognized the isotopic composition 2 2 Mg þ (3.67), Ca þ (1.17), Kþ (1.10), and HCO3À (0.35) (Hay of boron, magnesium, and presumably also chlorine (Argento et al., 2006). All these are also common in the other natural et al., 2010; Foster et al., 2010; Ling et al., 2011). This is water reservoirs on Earth (lakes, rivers, rainwater, and the basis for the construction of many isotopic curves for groundwater); however, in different combinations and vari- ancient seawater, crucial for geochemical analysis of Earth sed- able proportions, both are similar and quite different than imentary record as well as widely used for stratigraphic studies those of seawater. These seven ions are able to create a dozen (Boschetti et al., 2011a; Holland, 2003; Holser, 1979b; Veizer of various evaporite minerals, which are more or less common. et al., 1999). Not only the composition of soluble salts (major ions) present in seawater and their volume but also the molar proportions of particular ions in this water decide the mineralogy of marine 9.17.6 Evaporite and Saline Minerals evaporite deposits. The molar proportions of major ions are 2 2 constant in today’s ocean (Naþ >Mg þ >Ca þ Kþ and ClÀ > Braitsch and Garrett (1981) distinguished the evaporite min- 2 SO4 À >HCO3À), and this fact is of the crucial importance and erals “that have crystallized during the solar evaporation of is the basis of the global geochemical investigation. The ocean is aqueous solutions, predominantly solutions of strong currently in a nonstratified state and its water masses mix mainly electrolytes” from saline minerals “consisting of soluble salts, due to continuing thermohaline circulation leading to homoge- the formation of which includes not only evaporation but also neity of its composition including semiclosed continental seas. cooling and ” (Braitsch and Garrett, 1981, The near constant ratios of seawater constituents (irrespective of p. 451). The main mineral components of evaporites are pre- the seawater salinity) were first noted by Marcet (1819). It was sent in surface and subsurface waters on Earth in the form of Geochemistry of Evaporites and Evolution of Seawater 491

2 easily soluble salts. They include four cations (Naþ, Kþ, Mg þ, carbonate minerals, such as trona, nahcolite, and shortite; 2 2 and Ca þ) and three anions (ClÀ, SO4 À, and HCO3À); the last (2) Na silicate minerals, such as magadiite and kenyaite; and 2 is present in the water in association with CO3 À depending on (3) Na or Ca borate minerals (Smoot and Lowenstein, 1991). pH. The anion BrÀ is also common; however, it is not able to The first assemblage of minerals is expected to form from the create its own solid compounds during evaporation but dia- evaporation of the hypothetical Archean–Proterozoic soda dochically replaces ClÀ in the crystal lattice of chlorine salts in ocean water (Kempe and Degens, 1985). Furthermore, the small quantities (halite, carnallite, sylvite, etc.). The other borates that occur in some Permian evaporite deposits are con- much less common anions occurring locally in continental sidered as marine in origin (Helvaci, 2005; Stewart, 1963). 2 environments include B4O7 À, NO3À, and IÀ. In some areas, Sodium sulfates, such as mirabilite (Na2SO4 • 10H2O), are also rare anions like FÀ, or chromates, also appear. A number of encountered in marine evaporites. Mirabilite precipitates from 2 2 3 other cations, like Sr þ, Fe þ, and Al þ, are also components of almost any sulfate brine, including seawater brine, during freez- some more or less rare evaporite or saline (soluble) minerals, or ing (Garrett, 1970; Valyashko, 1962). For example, it precipitates minerals associated with evaporites, and some such minerals are in winter in the Great Salt Lake that contains brine very similar to less soluble (a list of such recognized rare minerals is growing seawater brine (Hardie, 1985). Glauberite, which appears to be a with time; Łaszkiewicz, 1967; Pueyo, 1991; Sonnenfeld, 1984). typical continental evaporite mineral (Salvany et al., 2007), is Major rock-forming evaporite salts are thus chlorides, sul- theoretically a predicted product of evaporite precipitation from fates, and carbonates of calcium, sodium, potassium, and mag- seawater (Holland, 1984). Hardie (1985) included glauberite nesium, commonly creating hydrated compounds as well as into his listing of components of marine evaporites as well. The double, triple, and more complex salts (Table 2). typical marine evaporite minerals, excluding those formed dur- Borates, nitrates, iodates, fluorides, and chromates are ing freezing of seawater and seawater brine, include more than encountered in continental environments and originate from 30 soluble minerals (Sonnenfeld, 1984; Stewart, 1963). specific types of waters. Common evaporite minerals include High solubility is the essential feature of saline minerals, more than 80 minerals (Braitsch, 1971; Sonnenfeld, 1984; reflecting the nature of evaporite deposits, that is, formed from Stewart, 1963), and the majority of them are relatively rarely the most soluble components (Goldschmidt, 1937), although observed. The list of evaporite minerals is even longer when the there are some exceptions (Table 4; Braitsch and Garrett, 1981). minerals formed in extremely cold environments are concerned. Many of these minerals are encountered in other, nonevaporite environments precipitating from fluids of the similar composition to the evaporating brines. 9.17.7 Model of Marginal Marine Evaporite Basin Only three evaporite minerals make up the major rock- forming and volumetrically most important deposits, and Chemical models for an evaporite basin are critical in under- these are gypsum (CaSO4 • 2H2O) and anhydrite (CaSO4), and standing the sedimentology of evaporites, and a working less commonly halite (NaCl), all together estimated to form model for a marine evaporite basin is particularly important. more than 90–95% of modern and ancient precipitates There is no functioning marine-sourced basin on the Earth

(Warren, 2006, p. 564). Very commonly, dolomite (CaCO3 • today able to produce evaporites on the scale of ancient saline MgCO3) and magnesite (MgCO3) are associated with giants. This is perhaps due to the effect of sea-level rise and evaporites; however, generally, they are not treated as typical flooding of the coastlines related to ice-caps melting during evaporite minerals. From these listed three minerals, gypsum decline of the last Pleistocene glaciation (Glennie, 1987). Addi- is certainly the most common at the surface and in shallow tionally, there is no active K–Mg salt-forming basin of marine subsurface. K–Mg salts are much rarer and include the following origin today. Small, short-lived halite basins can serve only as a most common minerals: sylvite (KCl), carnallite (KCl • MgCl2 • partial analog of the ancient evaporite sedimentation that took 6H2O), langbeinite (K2SO4 • 2MgSO4), kainite (4KCl • 4MgSO4 • place in the past, over areas comparable to continent sizes. 11H2O), and polyhalite (K2SO4 • MgSO4 • 2CaSO4 • 2H2O) Hence, without a substantial working model, there are difficul- (Borchert and Muir, 1964; Stewart, 1963). Together with calcite ties in establishing a fully operative estimate of the hydrolog-

(CaCO3), dolomite (CaMg(CO3)2), and magnesite (MgCO3), ical, sedimentological, and geochemical processes that may they constitute the 12 major minerals encountered in evaporite operate in such a basin, particularly during the deposition of rocks (Table 3; Stewart, 1963). K–Mg salts, and many attempts have been made to build a An important genetic classification of saline minerals may reasonable model of the function of such a basin (Ba˛bel, 2007; be made according to the source of salts in the brine of evap- Dronkert, 1985; Sonnenfeld, 1984). Some large saline lake orite basin, that is, seawater and continental water. Accord- basins, like the Dead Sea, can help in creating a match but ingly, the saline minerals can be divided into (1) minerals of cannot give answers to all the questions. the marine or marginal marine evaporites and (2) minerals of As pointed out by Hardie (1984), what is understood by the continental or nonmarine evaporites (Braitsch and Garrett, term ‘marine’ evaporite basin is ‘at best’ a ‘marginal marine’ 1981). Because many the same minerals occur in both groups, basin, surrounded by land and thus being always under some univocal distinction between the marine and nonmarine evap- influence of nonmarine sources of water. Such a basin, orite minerals is commonly impossible or difficult. Many min- depending on the degree of isolation from the sea, can evolve erals precipitated from seawater also occur in continental lakes into a ‘nonmarine’ basin with the brine being the mixture of with water very similar in composition to seawater. many types of waters inflowing into the basin from the land Some ancient mineral assemblages cannot be crystallized and/or from subsurface, with the water of the ancient ocean. from recent seawater without major modification. Today, those The model of such a basin is of the crucial importance for assemblages only occur in saline lake environments: (1) Na the understanding of the geochemical evolution of the ancient 492 Geochemistry of Evaporites and Evolution of Seawater

Table 2 Significant evaporite and salt minerals (after various Table 2 (Continued) sources, abbreviations for some minerals after Eugster et al., 1980; lg Langbeinite K SO 2MgSO c Usdowski and Dietzel, 1998) 2 4 Á 4 le Leonite K SO MgSO 4H O r 2 4 Á 4 Á 2 Chloride pc Picromerite Simple salts ( schoenite, K2SO4 MgSO4 6H2O r ¼ Á Á ha Halite NaCl vc scho¨nite) sy Sylvite KCl c Gl Glauberite Na2SO4 CaSO4 c Á hh Hydrohalite NaCl 2H O r, S Syn Syngenite K2SO4 CaSO4 H2O r Á 2 Á Á bi Bischofite MgCl 6H O r ( kalushite) 2 Á 2 ¼ Ant Antarcticite CaCl 6H O vr Triple salt 2 Á 2 Double salts Po Polyhalite K2SO4 MgSO4 2CaSO4 2H2O c Á Á Á ca Carnallite KCl MgCl 6H O c Chloro- Á 2 Á 2 Tc Tachyhydrite CaCl 2MgCl 12H O r carbonate 2 Á 2 Á 2 Triple salt Triple salt Rhinneite FeCl 3KCl NaCl r Northupite Na2CO3 MgCO3 NaCl r 2 Á Á Á Á Sulphato- Sulpho- chlorides carbonate Double salt Double salt ka Kainite 4KCl 4MgSO 11H O c Burkeite Na2CO3 MgSO4 r Á 4 Á 2 Á Triple salt Triple salt da D’ansite MgSO 3NaCl 9Na SO r Tychite 2Na2CO3 2MgCO3 Na2SO4 r 4 Á Á 2 4 Á Á Carbonate Sulpho-chloro- Simple salts carbonate

A Aragonite, calcite CaCO3 vc Triple salt Thermonatrite Na CO H O c Hanksite 9Na2SO4 2Na2CO3 KCl r 2 3 Á 2 Á Á Natron (natural Na CO 10H O c Iodates 2 3 Á 2 soda) (exemplary)

Nahcolite NaHCO3 c Lautarite Ca(IO3)2 vr Double salts Nitrates and Dolomite CaCO MgCO vca sulphato- 3 Á 3 Huntite 3MgCO CaCO r nitrates 3 Á 3 Trona NaHCO Na CO 2H O c (exemplary) 3 Á 2 3 Á 2 Shortite 2CaCO Na CO c Niter KNO3 r 3 Á 2 3 Pierssonite CaCO Na CO 2H O c Nitratine NaNO3 r 3 Á 2 3 Á 2 Gaylussite CaCO Na CO 5H O c Darapskite Na2SO4 NaNO3 H2O r 3 Á 2 3 Á 2 Á Á ( natrocalcite) Borates ¼ Sulfate (exemplary) Simple salts Simple salt A Anhydrite CaSO vc Kernite Na2B4O7 4H2O r 4 Á Bassanite CaSO 0.5H O r Borax Na2B4O7 10H2O r 4 Á 2 Á (hemihydrate) Colemanite Ca2B6O11 5H2O r Á G Gypsum CaSO 2H O vc Double salt 4 Á 2 ks Ki Kieserite MgSO H O c Ulexite NaCaB5O9 8H2O r 4 Á 2 Á Sanderite MgSO 2H O r Chromates 4 Á 2 Leonhardtite MgSO 4H O r Tarapacaite K2CrO4 vr 4 Á 2 Pentahydrite Lopezite K2Cr2O7 vr ( pentahydrate, MgSO 5H O vr ¼ 4 Á 2 allenite) Components of evaporite rocks: vc, very common (typically rock-forming); c, common hx Hexahydrite MgSO 6H O r and relatively common; r, rare; vr, very rare; S, seasonal mineral, precipitates from 4 Á 2 ( sakiite) cooled or frozen brine, and dissolves in warmer brine. ¼ a ep Epsomite Ideal stoichiometric composition, the chemical formulae of natural dolomite varies ( reichardtite, MgSO 7H O c from calcian to magnesian dolomite, Ca(1 x)Mg(1 x)(CO3)2, and documented ¼ 4 Á 2 þ À bitter salt) composition ranges from Ca1.16Mg0.94(CO3)2 to Ca0.96Mg1.04(CO3)2 (Warren, 2000). th Thenardite Na2SO4 c mi Mirabilite Na SO 10H O c, S 2 4 Á 2 evaporite deposits and for quantitative geochemical studies. ( Glauber’s ¼ The ‘universal’ conceptual and quantitative model of the evolv- salt) ing marginal marine evaporite basin developed during the stud- Celestite SrSO c 4 ies of evaporites is briefly outlined in the succeeding text. Double salts gs Ap Glaserite Na SO 3K SO r 2 4 Á 2 4 ( aphthitalite) ¼ 9.17.7.1 Conceptual Model of the Basin vh Vanthoffite 3Na SO MgSO vr 2 4 Á 4 bl Bloedite, blo¨dite Na SO MgSO 4H O c The marginal marine evaporite basin is commonly considered as 2 4 Á 4 Á 2 ( astrakhanite) a depression separated from the sea by a topographic barrier, ¼ lw Loeweite, lo¨weite 2Na SO 2MgSO 5H O r 2 4 Á 4 Á 2 which can drown or emerge, and with sporadically restricted (Continued) open water connections between the basin area and the open Geochemistry of Evaporites and Evolution of Seawater 493 ocean. The former basin type was termed a salina, the latter is Both basin types can eventually pass into a saline lake when the considered a salt lagoon (Figure 4(a) and 4(b)), and one basin influx of seawater to the basin is entirely arrested (Figure 4(c)). type can pass into the other during the course of geologic The salina model of the basin has many well-recognized modern evolution, such as has been observed in the Kara Bogaz (Dzens- and subfossil analogs (Ba˛bel, 2007; Logan, 1987; Nunn and Litovskij and Vasil’ev, 1962; Grabau, 1920; Kosarev et al., 2009). Harris, 2007) and until now was considered as the most important or even the only one reasonable model for ancient saline Table 3 Major minerals encountered in evaporite rocks, excluding giants (e.g., Rouchy and Caruso, 2006; Warren, 2010). The salt siliciclastic components (Borchert and Muir, 1964; Garret, 1970; Stewart, lagoon model (Dronkert, 1985; Sonnenfeld, 1984) was criticized 1963) as hydrologically unsound and unrealistic (Kendall, 1988, 2010; Kendall and Harwood, 1996; Shaw, 1977; Warren, 2000); Anhydrite CaSO 4 however, the recent evaporite deposition and refluxing bottom Calcite CaCO3 Carnallite KCl MgCl 6H O brine currently recorded in the Kara Bogaz (Kosarev et al., 2009) Á 2 Á 2 Dolomite CaCO MgCO (ideal stoichiometric suggest that this model (Figure 4(a)) is functional in some 3 Á 3 composition) instances. Gypsum CaSO 2H O The crucial element in creating an evaporite basin is the 4 Á 2 Halite NaCl requirement of a negative water balance. The outflow of water Kainite 4KCl 4MgSO 11H O Á 4 Á 2 (brine) from the system (via evaporation, seepage, or a return Kieserite MgSO H O 4 Á 2 current) should be greater than inflow of the waters of any kind Langbeinite K SO 2MgSO 2 4 Á 4 (seawater plus meteoric water). This implies the presence of Magnesite MgCO 3 a number of climatic factors that accelerate the rate of evapo- Polyhalite K SO MgSO 2CaSO 2H O 2 4 Á 4 Á 4 Á 2 Sylvite KCl ration, which should exceed precipitation at least during some part of the year (Schmalz, 1971).

Table 4 Solubility in water of evaporite salts and some other minerals

1 Mineral Chemical formula Solubility (g lÀ ) Temperature (C) References

Barite BaSO4 0.0025 25 1 Davis and Collins (1971) a Æ Calcite CaCO3 0.012 25 Pia (1933) in Hutchinson (1975, p. 661) b c d 0.06 , 0.4 25 Freeze and Cherry (1979) a Aragonite CaCO3 0.014 25 Pia (1933) in Hutchinson (1975, p. 661) b c d Dolomite CaMg(CO3)2 0.05 , 0.3 25 Freeze and Cherry (1979) Celestite SrSO4 0.114 25 1 Davis and Collins (1971) e Æ Gypsum CaSO4 ·2H2O 0.207 25 Bock (1961) 2.0 20 Borchert and Muir (1964) 2.4 25d Freeze and Cherry (1979) f Anhydrite CaSO4 0.20 18 Smith (1918); Grabau (1920, p. 21) 0.275g 25 Bock (1961) 2.98 20 Sonnenfeld (1984)

Glaserite (aphtithalite) Na2SO4 ·3K2SO4 145 20 Borchert and Muir (1964) e Epsomite (reichardtite, bitter salt) MgSO4 ·7H2O 38.5 25 Grabau (1920, p. 22); Seidell (1940) 262 20 Borchert and Muir (1964)

Hexahydrite (sakiite) MgSO4 ·6H2O 308 20 Borchert and Muir (1964) Sylvite KCl 32.95f 18 Smith (1918); Grabau (1920, p. 21) 35.5g 25 Grabau (1920, p. 22); Seidell (1940) 340 20 Borchert and Muir (1964) Halite NaCl 35.86f 18 Smith (1918); Grabau (1920, p. 21) 36.12g 25 Grabau (1920, p. 22); Seidell (1940) 360 25d Freeze and Cherry (1979) f Thenardite Na2SO4 16.83 18 Smith (1918); Grabau (1920, p. 21) 388 40 Borchert and Muir (1964) e Mirabilite (Glauber’s salt) Na2SO4 ·10H2O 5.0 0 Grabau (1920, p. 22); Seidell (1940) 28.0e 25 Grabau (1920, p. 22); Seidell (1940) 448 20 Borchert and Muir (1964) e Bischofite MgCl2 ·6H2O 56.7 25 Grabau (1920, p. 22); Seidell (1940) 2635 20 Borchert and Muir (1964)

Antarcticite CaCl2 ·6H2O 5360 20 Sonnenfeld (1984) a Solubility in supposedly CO2-free water, solubility is higher in water containing much dissolved CO2. b 3 At partial pressure PCO2 = 10À bar. c 1 At partial pressure P 10À bar. CO2 ¼ dAnd at 1 bar (105 Pa) pressure. e Amount of pure compound without water of crystallization, in g/100 g H2O. f 3 In g/100 cm H2O. g In g/100 g H2O. 494 Geochemistry of Evaporites and Evolution of Seawater

Lagoon basin 3. If a salt is formed, evaporation is the driving force that leads to the precipitation of this salt (Mullin, 2001). The removal of water to the atmosphere by evaporation raises the concentration of particular ionic components of this salt which is necessary for its crystallization. Sea level rm p e sc In the zones of high evaporation, waters in hydrologically closed and semiclosed basins, due to a negative water balance, oc sr evolve slowly toward a state of saturation and supersaturation of soluble salts. According to Valyashko (1962), the life of such sc - Surface inflow current p - Precipitation basins can be divided into earlier ‘preparatory’ and later a ‘self- oc - Bottom outflow current e - Evaporation sr - Seepage reflux precipitating’ stage, beginning from the time when the state of (a) rm - Run-off meteoric water saturation and supersaturation of the first soluble salt is reached in the water body, and this salt is precipitating in the Salina basin basin. The dominating mechanisms of deposition in ‘self-precipitating’ basins are the processes of crystallization, dissolution, and transformation (early diagenesis) of salts. Therefore, these are crucial concepts for understanding the Sea level sedimentary record of such basins and principles of their rm p Basin water level su development. e d Evaporation, however, is not the only driving force of the salt se precipitation in such a productive basin. The salts can also sr crystallize due to temperature changes of the saturated solution se - Seepage influx d - Range of evaporite (Sloss, 1969), mixing of brines known as salting out or salination su - Surface inflow drawdown (Raup, 1970, 1982; Sonnenfeld, 1984), and also brine freezing p - Precipitation sr - Seepage reflux or freeze-drying may occur in areas of very cold climates (Marion rm - Run-off meteoric water (b) e - Evaporation et al., 1999; Sonnenfeld, 1984; Strakhov, 1962). These cold climate salts are the most ephemeral deposits on Earth. Saline lake Water is the main carrier of salts. The water flowing into the No any seawater evaporite basin transports dissolved salts into the areas of inflow through the barrier deposition. The largest mass and volume of such salts normally come from the sea because the seawater contains much more salt than any kind of meteoric water inflowing into a basin. Sea level rm p Basin water level Most meteoric waters observed on continents (waters derived e 1 from rain or snow) contain much less than 1 g kgÀ of dis- 2 X solved solids. The ‘salinity’ or content of dissolved salts (Ca þ, sr 2 2 Mg þ, Naþ, Kþ, CIÀ, SO4 À, HCO3À, NO3À, and dissolved SiO2) rm - Surface run-off p - Precipitation in large rivers all over the world ranges from a few milligrams 1 (c) sr - Seepage reflux e - Evaporation per liter to 1000 mg lÀ (Meybeck, 1976), and the average total concentration of dissolved solids in the large world rivers was Figure 4 Principal models of evaporite basins: the marginal marine 1 estimated as 89.2 mg lÀ (Meybeck, 1979). The river waters evaporite basin of the lagoon (a) and the salina type (b) and the marginal flowing into an evaporite basin would be thus at least 35 saline lake basin (c). times less saline than seawater but generally are much less saline. This means that the influx of such freshwater to the saline water, even in large volume, is not able to substantially Evaporation is a crucial factor in such a basin playing three influence the ionic proportions (ratios) of the dissolved salts fundamental roles: within it. Furthermore, fresh nonmarine, meteoric, or river 1. It lowers the basin water level (depressed water level defines waters would be able to modify the ionic proportions in the the range of the evaporite ‘drawdown’ during the emer- basinal brines only if the ionic proportions in that nonmarine gence of the barrier separating the basin from the sea; Figure water were significantly different than that in the seawater or 4(b)) and builds the hydraulic head that forces the marine the seawater brines in the basin. The influence of nonmarine water to flow or seep into the evaporite basin utilizing waters would be negligible when these differences are small. a permeable barrier, thus promoting the transport of Therefore, even though the basin is supplied with extremely dissolved seawater salts to a depositional site. This mecha- large amounts of meteoric water, which otherwise is difficult to nism explains the great thicknesses of ancient evaporite expect in arid evaporite environments, marine salt composi- deposits. tion very likely dominates the mixture of these nonmarine 2. It raises the salinity of the basinal water and produces a meteoric water and seawater. Rigaudier et al. (2011) calculated, brine; the concentrations of particular ions in the brine from the isotopic composition of water trapped in fluid inclu- increase together with the increase in salinity in a process sions in Messinian halite, that the crystals grew in the mixture known as evaporitic concentration. of seawater and meteoric waters dominated by the latter Geochemistry of Evaporites and Evolution of Seawater 495

(50–75%). The proportion of the ionic components in basinal 9.17.7.2 Quantitative Model of the Basin waters should not be significantly different than in seawater or The marginal marine evaporite basin model (Figure 4) was ‘pure’ seawater brines especially in the early stages of evaporite developed quantitatively and subjected to numerical simula- basin evolution, unless some significant influx of highly saline tions (e.g., Logan, 1987; Nunn and Harris, 2007). The crucial waters, like hydrothermal brines, enters the basin (Hardie, idea, developed by Valiaev (1970), that the salinity evolution 1990; Lowenstein and Risacher, 2009). in the basin depends on the ratio of inflow to outflow was Brine partially escapes from the system by seepage reflux, as in supplemented by Kopnin (1977) and Holser (1979a). It was the McLeod salina, Australia (Logan, 1987), and by outflow later explored by Sonnenfeld (1980, 1984) and then fully bottom current, when the barrier separating the basin from the developed by Sanford and Wood (1991) and Ayora et al. sea is below the sea level – as in the Kara Bogaz (Kosarev et al., (1994) who integrated it with the model of evaporite precipi- 2009; Sonnenfeld, 1984). The presence of a brine reflux by tation of salts from seawater and related brines by Harvie et al. underground seepage in case of a salina basin, and additionally (1980). also by return bottom current – in a lagoon basin, is the impor- For the purpose of numerical modeling, the basin was tant feature of the model basin. Together with this brine, some of assumed to evolve with a constant (conservative) water volume the dissolved salts are removed from the basin. The assumed (this volume can also vary in some alternate models; Ayora brine reflux is the best and the simplest explanation for the et al., 1995). Thus, the evaporated and refluxing volume of ‘escape of salts’ from the system, which is a necessary condition water may be replaced by an equal volume of influx water that for the deposition of ancient evaporite sequences that always was made up of seawater, other water, or a mixture of the two seem to have different proportions of salts from those expected (Figure 5). The inflowing water is presumed to be completely by complete evaporation of seawater in the hydrologically closed mixed with the basinal water. Atmospheric precipitation and system (Hite, 1970; King, 1947; Klein-BenDavid et al., 2004). evaporation were omitted in salt balance calculations because Long-term chemical evolution of the brine in some mar- they usually do not carry any substantial amount of salts. The ginal marine basins can lead to brines having nonmarine salts ‘escape’ from the system carried by refluxing water or characteristics (Klein-BenDavid et al., 2004). When inflowing being precipitated on the basin floor. The steady state of the continental or other nonmarine waters show ionic composi- basin – its constant volume – and the evolving salinity of tion and/or ionic proportions extremely different from those basinal brines were considered as the basic condition for the of marine water for a sufficiently long time, or show relatively accumulation of the particular sequences of evaporite min- high salinity, mixing can change the initial marine proportions erals. The changes from one evaporite mineral sequence to of ions and produce a mixed brine (Hardie, 1984, 1990). The another were controlled by the particular parameter called ionic composition of a basinal brine changes with time prin- ‘degree of restriction’ or ‘restriction index’ (Cendo´ n et al., cipally because of the precipitation of successive evaporite minerals and various back and early diagenetic reactions with chemical sediments. During advancing evaporation, all these CW MP E processes selectively remove particular ions from the parent brine (Valyashko, 1962). The other causes of chemical changes are dissolution and reprecipitation (recycling) of earlier or older SW salts (Holser, 1979a). In the case of variations in bottom relief, OC the brine can evolve in different ways in each subbasin or parts of SP the basin. The refreshment of brine is possible due to increased influx of both marine water and meteoric water (Holser, 1979a). SR In relatively wetter climates, brackish subbasins can develop on the landward side of a large evaporite basin, perhaps showing the MP - Meteoric precipitation peculiar chemical composition of the waters. They also can E - Evaporation appear in the final stages of evolution of the basin, when the SW - Seawater inflow current water level in the basin is at sea level and the influx of marine water is minimal (Kendall and Harwood, 1996). OC - Basinal water outflow current In summary, a marginal marine basin can show various SR - Seepage outflow types of brines depending on place and stage of basin evolu- CW - Continental water inflow tion – from strictly marine to nonmarine, mixed, and even SP - Salt precipitates brackish, in the case of an interval of wetter climate. Many ancient evaporite basins commonly show sediments having Atmospheric water, negligible % of salts both marine and nonmarine physical features, contain both Seawater, 3.5% of salts rare marine and nonmarine fossils, and reveal geochemical characteristics of salts pointing to both marine and nonmarine Continental water <<0.1% of salts derivation of the brine. As shown by Kirkland et al. (1995, Basinal water or brine, mixture of seawater, 2000) and Denison et al. (1998), these contradictions are continental and atmospheric water relatively simple to resolve, assuming that the basin was of a Figure 5 Qualitative model of marginal marine evaporite basin used marginal marine type and the brine was neither exclusively for numerical modeling of evaporite salt sequences, dependent on marine nor exclusively nonmarine but was a mixture of marine restriction index of the basin; after Sanford and Wood (1991) and Ayora and various nonmarine waters. et al. (1994). 496 Geochemistry of Evaporites and Evolution of Seawater

2003; Fanlo and Ayora, 1998) formerly described as the leak- on the course of evaporitic precipitation in great detail. They age ratio (Sanford and Wood, 1991). It is the value of water assumed that in marine basins, QSW (seawater inflow in liters outflow relative to the total inflow or, in short, the ‘leakage’ to per time) is higher than QRW (continental water inflow, i.e., ‘inflow’ QL/QI, where QL is the outflow due to direct reflux to rivers and groundwater) and that cSW (the concentration, in the sea by bottom current and leakage (seepage) to aquifers moles per liter of solution, of the particular solutes in seawater) and QI is the total inflow (Ayora et al., 1994, 1995; Cendo´ n is one order of magnitude higher than cRW (the concentration of et al., 2008; Sanford and Wood, 1991). The restriction index the solutes in continental waters), and therefore, the mass of the

QL/QI ranges from zero in a completely closed basin to one solutes precipitated from continental waters can be neglected for the open ocean. The predicted sequence and thickness of in calculations. For example, Ayora et al. (1995) noted that the evaporite mineral facies were related to the number of the concentration of sulfate ions in river water is one order of ‘evaporated basins’ (see Ayora et al., 1994, 1995; Sanford and magnitude lower than that of seawater and therefore its influence Wood, 1991; Sonnenfeld, 1980, 1984 for detailed equations on isotopic composition (O, S) of basinal ‘marine’ water is not and explanations). significant and can be neglected (see Claypool et al., 1980; In the basin model, the accumulation of a great thickness of Kirkland et al., 1995; Denison et al., 1998, for similar an evaporite salt is possible when the basin is under a steady calculations). state regime, that is, preserving both a constant basin volume The influence of CaCl-rich hydrothermal brine influx on and solute concentration of the basinal brine (Ayora et al., deposition in basins leading to precipitation of KCl-type evap- 2001; Sanford and Wood, 1991). A steady state develops after orites was modeled by Cendoń et al. (2003) and Garcıá-Veigas some time for a given QL/QI ratio (the degree of restriction). et al. (2009). The influence of recycling processes on the Numerical models showed that the QL/QI ratio influences the sequence of crystallization in this basin type was further mod- type of salts precipitated (paragenesis) and the thickness of the eled by Cendόn et al. (2004). Cendoń et al. (1998) explored particular mineral formed, while the chemical composition the same model of the basin to predict the salt deposition in and proportion of the inflow waters influence the relative two interconnected subbasins containing the halite and potash amount of solutes, and to a lesser extent, the paragenesis of deposits. salts (Ayora et al., 1994). Highly limited outflow or a com- The loss of salt components from the basin via the pletely restricted basin (Q /Q 0) causes an unrealistically atmosphere in the form of salt-bearing aerosols or via aeolian L I ¼ low amount of the each salt to precipitate previous to the transport of salts (by salt storms) is usually neglected in the next soluble salt (Ayora et al., 1995). The numerical model models, although in nature they are well documented and may thus developed has been used successfully to interpret the be quantitatively significant (Risacher et al., 2006; Wood and sequences of ancient halite and K–Mg evaporites in terms of Sanford, 2007). the evolving basinal brines in marginal marine basins, being a The basin model has some unrealistic features and one of mixture of marine and some nonmarine waters. them is the assumption of the complete mixture of waters In the marginal marine basin, the main source of salts is inflowing into it. In reality, the separation of brine bodies seawater, and therefore, both brine and evaporite salts should within the same basin is a typical feature of many evaporite generally show the marine geochemical characters that are basins. Shallow basins, such as Kara Bogaz or Bocana de observed in recent coastal salinas (Logan, 1987). Salinity rise Virrila´, show horizontal salinity gradients; deep basins, such should lead to the deposition of evaporite salts following the as the Dead Sea, are commonly permanently stratified. The Usiglio sequence (Stewart, 1963). Modeling, supported by influx of seawater, flood, or river water into deep basins com- field observations from the MacLeod basin, however, revealed monly leads to the establishment of a pycnocline and to spe- that this model pathway depends on the inflow/outflow rate cific depositional processes occurring in between the brine (seepage reflux in a salina basin; Figure 4(b)), which controls bodies (Ba˛bel and Bogucki, 2007; Holser, 1979a; Torfstein the maximum salinity level in the basin and thus limits the et al., 2005). possibility of the precipitation of higher salts (Logan, 1987; As with any model that is an extreme simplification of reality – Sonnenfeld, 1984; Valiaev, 1970; Wood and Sanford, 1990). the numerical models thus far introduced and described earlier Changes in the inflow/outflow rate influence the order of the do not cover all the environmental processes observed acting in precipitated salts and, for example, gypsum can be deposited real basins, such as sulfate reduction, or interaction of the after halite, as documented in the MacLeod salina (Kendall precipitated minerals with the solution, such as dehydration. and Harwood, 1996; Kendall and Warren, 1988, Figure 2.35; Some of these are covered by models of closed (lake) basins Logan, 1987). (Sańchez-Moral et al., 2002; Yan et al., 2002). The inflow/outflow rate also controls the thickness of deposited evaporite salts, and sometimes, there is only a small accumulation of gypsum before halite (Sanford and 9.17.8 Mode of Evaporite Deposition Wood, 1991). In the case of limited outflow, the Naþ, Kþ, 2 Mg þ, and ClÀ ions are not involved in the initial Ca carbonate When an evaporating brine becomes supersaturated with respect 2 and Ca sulfate precipitation, and the SO4 À, not fully used for to a particular salt, it can precipitate in any portion of the brine Ca sulfate precipitation, can accumulate in the brine, and the body. Some areas, however, are most favorable, particularly the basin then has a great potential for the deposition of NaCl and bottom of the basin and the brine–air interface. Shoals and basin K–Mg salts (see Hite, 1970). margins (bays and evaporite flats) are particularly advantageous. Ayora and coworkers (Ayora et al., 2001) considered the The shallow water has a smaller volume and thus warms more influence of the chemistry of meteoric (nonmarine) water influx easily than the greater volume of deep water. Because of the Geochemistry of Evaporites and Evolution of Seawater 497 higher temperature, the evaporation rate is more rapid on the twinned crystals from the Messinian of the Cyprus and Sicily shoals. Secondly, there is more surface area per unit of water and 3.5-m-long gypsum crystals from the Badenian of Poland volume in the shallows in comparison with the deep parts of the (Ba˛bel et al., 2010, with references; see a comment in Lugli basin, and hence, even the same evaporation rate leads to faster et al., 2010, p. 94). Similar sizes can also be reached in second- salinity rise in these shallow areas of the basin (in small bays, ary (diagenetic) salt crystals (halite and gypsum) growing in evaporite flats, etc.). Thus, the salinity and concentration of ions some synsedimentary karst cavities within evaporite sediments are higher in shallow zones, leading to more rapid precipitation (Dıáz et al., 1999). Gypsum crystals commonly form twins and of salts (Corneé et al., 1992). are able to create complicated crystalline structures, showing Salt may precipitate (1) at the brine/air interface; (2) within different morphology within each sedimentary subfacies, and the brine column, particularly at the pycnocline; (3) directly on are specific for each environment within any one basin the floor of the evaporite basin; and (4) in brine-soaked sedi- (Aylloń-Quevedo et al., 2007; Ba˛bel et al., 2010; Lugli et al., ments or brine-soaked organic mats as displacive crystals or 2010; Ortı´, 2011; Rodrı´guez-Aranda et al., 1995). Many mor- pore-filling cements (Logan, 1987; Schreiber, 1978). The accu- phologies and sedimentary sequences, however, seem to be mulations of such crystals can create several more or less repeated from basin to basin and are recognizable even when distinct genetic groups of deposits: (1) subaqueous crystal moving from primary gypsum morphologies to subsurface cumulates, (2) subaqueous bottom precipitates (bottom- anhydrite. grown crystals and crystal crusts), (3) intrasediment precipitates One of the most significant factors, which control gypsum (incorporative, displacive, and replacive crystals and nodular morphology and facies distribution, appears to be the presence aggregates), and (4) clastic accumulations (Figure 6; see of microbial communities and the organic compounds they Hanford, 1991; Kendall, 1992, 2010; Logan, 1987; Lowenstein, produce in the basinal brine (Oren, 2010). Additionally, some 1982; Schreiber et al., 1976; Smoot and Lowenstein, 1991). evidence indicates that the bottom-grown selenite crystals may These genetic groups are best known from gypsum and halite grow in a regionally oriented manner under the influence of precipitates. brine currents (Ba˛bel and Becker, 2006; Ba˛bel and Bogucki, Bottom precipitates are commonly formed as firmly cemen- 2007; Lugli et al., 2010). Such region-wide currents may even ted, interlocking, orderly crystal crusts. The specific feature of shape the selenite–gypsum microbialite domes in some areas gypsum deposits is the growth of extremely large selenite crys- (Ba˛bel et al., 2011) similar to the elongated elliptical halite tals in such layers. The examples include 4.5-m-long gypsum ridges growing in more saline brine currents, as in the Dead Sea

Clastic halite Floating rafts Bottom-grown halite

Gypsum microbialites HALITE Microbialites Crystal rafts Selenite domes

Clastic Sabkha Bottom grown intrasediment Cumulates crystals precipitates GYPSUM

Selenite crust

Figure 6 Modes of evaporite deposition, the idea for the diagram borrowed from Kendall (2010). 498 Geochemistry of Evaporites and Evolution of Seawater

(Karcz and Zak, 1987). Such domal structures may range in exhumation, and weathering (Jowett et al., 1993; Testa and size from a few centimeter–decimeter to several meters and are Lugli, 2000). The most common mode of cementation of an common in selenite crusts (Ortı´ et al., 1984a; Warren, 1982), evaporite sediment is via the formation of syntaxial over- but oriented growth forms also are noted in some halite growths that may blur the distinction of the grain from the deposits (Talbot et al., 1996). cement. Halite crystals growing in bottom crusts commonly show The reconstruction of the diagenetic evolution of most millimeter-scale zoning arranged into chevron-like pattern evaporite rocks, which have undergone the burial–exhumation reflecting the upward cyclic accretion of the faces of cube. Some cycle, is therefore difficult. The basic problem is the proper of the growth zones are diurnal and several growth zones can pathway for the reconstruction of the sequence and time(s) form in 1 day (Roberts and Spencer, 1995). These rapidly grow- of the petrological, mineralogical, and textural–structural ing cube faces typically trap the brine inclusions that commonly changes and to find the criteria for recognition of the primary are the target of geochemical studies (Figure 15). feature of the evaporite rock. The precipitation of salts at the brine–air interface results Dronkert (1985, p. 94) following Ingerson (1968), in the development of floating crystals or crystal rafts. The defined that the primary evaporite minerals are those that most characteristic and common are halite ‘boat-like’ or ‘hop- “precipitated directly from the solution” whereas secondary per’ crystals (Arthurton, 1973; Hanford, 1991; Valyashko, minerals “formed later than the primary ones and at least in 1951). Because of their rapid growth rate, they are able to large part from them” and suggested 17 geochemical and trap copious amounts of fluid inclusions (Roberts and Spen- structural criteria for their distinction. It is well known that cer, 1995). Similar rafts are known from carnallite as well as many evaporite sediments can be transformed very early gypsum crystals (Chivas, 2007; Ortı´ et al., 1984a; Talbot (replaced by more stable mineral association), just after they et al., 1996). Floating single crystals coalesce and form rafts. are formed in the basin, and therefore the term primary Sunken crystals and rafts create specific deposits known as should be understood in the broader way – it should include cumulates (Lowenstein, 1982; Lowenstein and Hardie, 1985; depositional as well as postdepositional but preburial pro- Shearman, 1978). cesses (Hardie et al., 1985). The synsedimentary alteration of Halite commonly grows faster in the near surface zone epsomite to bloedite in the Quero Lake (Spain) is one clear of brine mainly due to night cooling effect of the NaCl- example (Sa´nchez-Moral et al., 1998). Indeed, Braitsch saturated brine heated during solar evaporite concentration (1971) defined the term ‘primary precipitation’ in an in the daytime (but sometimes also due to heating; Karcz and extremely extended way including “the (early) diagenetic Zak, 1987). Because of accelerated growth in this zone, the alterations of metastable to stable precipitates” (Braitsch, specific crystalline, mounded structures may form (salt mush- 1971, p. 92). He justified that “from the standpoint of the rooms, e.g., Ganor and Katz, 1989). Similarly, salt umbrellas conditions of formation,” “no changes are necessary in the form when the crystal growth is associated with water level parameters such as temperature, concentration etc. for the onset fall (Mu¨ller, 1969). Sometimes, pillar- or atoll-like structures of stable equilibria” except of “the adjustment of the activation several meters in size are formed (Talbot et al., 1996). energy necessary for the onset of stable equilibria” (Braitsch, The other spectacular but rare form of salt mineral crystalli- 1971, p. 92). zation is in high-energy environments as growth of accretion- Thus, depending on the time of formation, the minerals ary (coated) grains that are termed pisoids or ooids when they and fabric (including fluid inclusions) of evaporite deposits are more rounded in shape. Mirabilite, halite, and gypsum can be subdivided into three main groupings (Hardie et al., ooids and pisoids are known from both modern and ancient 1985, p. 12): deposits (Ba˛bel and Kasprzyk, 1990; Castanier et al., 1999; Tekin et al., 2007, 2008; Weiler et al., 1974). Evaporite deposits, and particularly gypsum, commonly 1. “Depositional, i.e., formed at the time of deposition of a form in the presence of microbial (cyanobacterial) mats. They sedimentation unit or deposited in its existing form.” create microbialite domal structures (analogous to carbonate 2. “Post-depositional but pre-burial, i.e., formed diageneti- microbialites) that, however, are complex hybrid structures cally soon after deposition by processes controlled by the presumably more inorganic (chemical) than organic (micro- existing depositional environment.” bial) in origin (Ba˛bel et al., 2011; Petrash et al., 2012; Riding, This second stage of formation is equivalent of the 2008; Rouchy and Monty, 1981, 2000; Vogel et al., 2010). ‘eogenetic stage’ distinguished and defined by Choquette and Pray (1970, p. 219) as “the time interval between final deposition and burial of the newly deposited sedi- 9.17.9 Primary and Secondary Evaporites ment or rock below the depth of significant influence by processes that either operate from the surface or depend The high solubility of evaporite salts and their halokinetic for their effectiveness on proximity to the surface.” The properties made them chemically and physically very mobile lower limit of the eogenetic zone was defined at “that material both in the sedimentary environment and particu- point at which surface recharged meteoric waters, or larly during diagenesis and burial. They are easily dissolved, normal (or evaporated) marine waters, cease to actively and rather easily ‘recrystallized,’ as well as able to easily circulate by gravity or convection” (Moore, 1989, p. 25). replace one another forming new minerals during burial 3. Post-burial, i.e., formed by late diagenetic or metamorphic- history. The hydrous salts can be commonly dehydrated and metasomatic processes controlled by the subsurface burial rehydrated in the sedimentary environment, during burial, environment” (Hardie et al., 1985, p. 12). Geochemistry of Evaporites and Evolution of Seawater 499

The criteria for syndepositional features include “(1) me- 1990; Rahimpour-Bonab et al., 2007). Both ancient sylvite and chanical sedimentary structures and detrital textures and fab- carnallite crystals show structures typical of the growth on the rics produced during traction and suspension load deposition bottom of evaporite basin (Kendall, 2010; Wardlaw, 1972a,b). of chemical sediment particles; (2) crystalline textures and fabrics produced as chemically precipitated minerals grew in place on and within bottom sediment; and (3) features 9.17.10 Evaporation of Seawater – Experimental indicative of contemporaneous cementation, dissolution and Approach reprecipitation of salts. Additional criteria come from fluid inclusions and mineral stability ranges” (Hardie et al., 1985, The crucial concept for an understanding of the geochemistry p. 13). These and other criteria for distinguishing the primary of marine evaporites is an understanding of the process of and secondary crystals in evaporites are listed elsewhere (Ba˛bel evaporation of seawater leading to salinity increase and evap- and Becker, 2006; Hardie, 1984; Holser, 1966; Spencer, 2000). oritic concentration of particular ions, followed by the ordered Some criteria for the primary nature of crystals growing on the precipitation of particular salts. The first reported experiment substrate in nonevaporite environments are also useful for of complete evaporation of seawater using a marine water evaporites (Dejonghe, 1990; Kendall and Iannace, 2001; Sum- sample, taken on the French coast of the Mediterranean, was ner and Grotzinger, 2000). Extraordinary preservation of layer- by Usiglio (1849a,b). This water sample had a 38.45% salinity, ing may indicate the primary origin of salts (Braitsch, 1971); with an associated air temperature of 40 C. Usiglio described however, secondary structures present in deformed evaporites the process and order of salts precipitated in a quantitative way commonly mimic primary features, making distinction of pri- and this order is now called the Usiglio sequence (see, e.g., mary from secondary evaporites very difficult (Schreiber and Logan, 1987). The experiment was repeated by Bassegio Helman, 2005; Warren, 2006). (1974) and McCaffrey et al. (1987), among others. The early Hardie (1984, p. 201) further subdivided the evaporites stages of evaporation leading to gypsum and halite precipita- into the following types: tion are particularly well known and are observed in many 1. The ‘primary’ evaporites or ‘modified primary evaporites’ – marine solar saltworks (Busson et al., 1982; Geisler-Cussey, which are “not sufficiently altered by burial metamorphism 1986; Herrmann et al., 1973; Ortı´ and Busson, 1984). All or metasomatism to hide the identity of the primary these empirical observations were made in slightly different ( syndepositional) mineral assemblages” and fluctuating temperature (air and brine), but all showed ¼ 2. The ‘secondary’ evaporites – “so altered after burial that the coincident results, particularly during the early stages of evap- primary minerals cannot be unambiguously identified” oration (Table 5). Some differences and inconsistencies, mainly related to the influence of temperature differences, For geochemical studies, the crucial theme of this chapter, appear in the later stages of the precipitation of K–Mg salts only the primary autochthonous evaporites that are precipi- from highly concentrated brine (Garrett, 1970). The final tated in place can give reliable information about the chemistry stages of evaporation and precipitation of K–Mg salts are of the evaporite basin water (Hardie, 1984). known mainly from experiments and theoretical calculations Evaporites can occur both as primary and secondary min- (for a review of the experiments, see Braitsch, 1971). erals in ancient deposits, although some of them are more typical as primary, the others more common as secondary. Of the common potash minerals, sylvite (KCl), the most common component of the marine K–Mg salts (Dean, 1978; Garrett, 9.17.11 Crystallization Sequence before K–Mg 1970; Holser, 1979a; Stewart, 1963), was commonly inter- Salt Precipitation preted as the product of replacement or incongruent dissolu- The sequence of crystallization up to saturation with K–Mg tion of primary carnallite (KCl • MgCl2 • 6H2O), which could take place syndepositionary (e.g., El Tabakh et al., 1999a; salts is well known from solar saltworks, where seawater passes Richter-Bernburg, 1972) or during exhumation (retrograde through three stages or fields characterized by precipitation of diagenesis; Harville and Fritz, 1986). The following reaction calcium carbonate, calcium sulfate, and sodium chloride of incongruent dissolution of carnallite (after Hardie, 1984) is (Figure 7). considered as the most important in diagenesis of potash evaporites • (Braitsch, 1971): 9.17.11.1 Early Salinity Rise – Calcium Carbonate Precipitation 2 KCl MgCl2 6H2O s KCl s Mg þaq 2ClÀ aq ð Þ ! ð Þ þ ð Þ þ ð Þ The calcium carbonate field is the first field of elevated salinity 6H2O l [5] 3 þ ð Þ (>35%, seawater density: 1.0258 gcmÀ at 12 C) up to the salinity characterizing the first precipitation of gypsum (i.e., (where s solid, aq aqueous, or soluble in water, and 140–200%, seawater brine density: 1.11–1.13). Logan ¼ ¼ l liquid). (1987), similar to Usiglio (1849a), established that aragonite ¼ By utilizing a similar reaction, sylvite is produced commer- started to precipitate at the volume reduction ratio V 0.5. er ¼ cially from carnallite by dissolution in water (Fokker et al., Usiglio recorded the end of CaCO3 precipitation within 2000). Recently, an increasing number of reports revealed the the field of gypsum. A common phenomenon within the primary, synsedimentary nature of ancient sylvite and carnall- Ca carbonate field is the appearance of thick microbial (cyano- 1 ite deposits (e.g., Cendo´n et al., 1998; Lowenstein and Spencer, bacterial) mats at salinities greater than 110% (S 110 g kgÀ ¼ 500 Geochemistry

Table 5 Evolution of evaporating modern seawater brines, based on data from semi-natural (saltworks), natural, and experimental evaporation, compiled and averaged data from many sources repeated after of

Fontes and Matray (1993) Evaporites

Stages and brine types Volumetric TDS Cl SO4 Na Mg Ca K Mg Br 1 1 1 1 1 1 1 1 1 mass (density, (g lÀ ) (mg lÀ ) (mg lÀ ) (mg lÀ ) (mg lÀ ) (mg lÀ ) (mg lÀ ) (mg lÀ ) (mg lÀ ) 3 1 1 1 1 1 1 1 1 kg mÀ (mmol kgÀ ) (mmol kgÀ ) (mmol kgÀ ) (mmol kgÀ ) (mmol kgÀ ) (mmol kgÀ ) (mmol kgÀ ) (mmol kgÀ ) and

0.0 1.022 35.8 19780 2770 11 000 1320 420 408 1320 68 Evolution Seawater 565.7 29.2 485.2 55.1 10.6 10.6 55.1 0.86 1.0 1.084 124.7 69000 10100 37800 4530 1540 1470 4530 234 Gypsum beginning 2029 110 1714 194 40.1 39.2 194 3.05

2.0 1.204 307.9 175600 19100 95100 13400 450 3600 13400 578 of

Halite beginning 5527 222 4616 615 12.5 103 615 8.07 Seawater 2.1 1.220 334.4 188200 28900 89000 20900 237 5300 20 900 950 Halite 5994 339 4371 971 6.68 153 971 13.4 2.2 1.247 332.0 185200 36400 65600 35500 170 7730 35500 1327 Halite 5709 414 3119 1596 4.64 216 1596 18.2 2.3 1.238 383.8 189900 65400 63000 50500 96 12900 50500 1830 Halite 6271 797 3200 2432 2.81 386 2432 26.8 3.0 1.286 400.2 190500 82200 48200 56120 tr 17680 56120 2970 Epsomite beginning 6066 966 2367 2607 510 2607 41.9 4.0 1.290 410.3 223900 56100 22100 72900 tr 25900 72900 4770 Sylvite beginning 7179 664 1093 3410 753 3410 67.9 5.0 1.305 418.2 257600 35400 15000 85700 – 17000 85700 5300 Carnallite beginning 8194 416 723 3976 490 3976 74.8 5.1 1.325 462.6 304600 27100 8150 108800 – 860 108800 7380 Carnallite 9953 327 412 5186 25.5 5186 107 6.0 1.364 504.8 337300 34900 1680 122 000 60 860 122 000 7530 Bischofite beginning 11 074 423 85 5841 1.74 25.6 5841 110 tr, traces; ‘-‘, no data. Geochemistry of Evaporites and Evolution of Seawater 501

35‰–(140-200)‰ (140-200)‰–(290-325)‰ (290-325)‰–375‰

1.03–(1.10-1.13) g cm−3 (1.10-1.13)–(1.20-1.26) g cm−3 (1.20-1.26)–(1.32) g cm−3

Salinity, density

Halite Initial Gypsum pans pans Seawater Seawater evaporation pans brine 35‰ >370‰

CaCO3 CaSO4·2H2O NaCl

2- Remaining SO4 -rich brine

35‰ Sea 1.0258 g cm−3 (at temp. 12 °C)

2 Figure 7 Scheme of the marine saltwork pan after Ortı´ et al., 1984a,b, modified. Remaining SO4 À-rich brine flows back to the ocean or, in some saltworks, back to the concentration pans to promote more precipitation of gypsum, which crystallizes due to a mixture of brines (Raup, 1982).

3 and density 1.087 g cmÀ ; Segal et al., 2006) that dominate In the lower end of the gypsum field, the first gypsum usually until 150% or even higher, where they cease with the onset of is a fine-grained precipitate; in more concentrated waters, it the precipitation of gypsum (references in Ba˛bel, 2004a). forms firm coarser-crystalline crusts commonly displaying the The photosynthetic activity of cyanobacteria raises the content centimeter-to-decimeter large domal structures. When crystals of dissolved oxygen that shows daily fluctuations (up to show sizes larger than 2 mm, they are commonly called sele- 1 7.8 mg lÀ , 131% supersaturation), particularly in the zones nite (Warren, 1982). The interesting feature of the ‘selenite’ where accumulations of O2-rich bubbles are seen on the surface field is that mat-creating cyanobacterial communities do not of the mats (Corne´e et al., 1992). The greatest level of calcium only inhabit the sediment/water interface but actually also carbonate productivity was observed in salinities between 50 live within the selenite crust. They grow and remain within 1 and 70 g lÀ and the mineral formed was Mg calcite, with the photic zone, where transparent selenite crystals play a minor additions of calcite and aragonite (Ortı´ et al., 1984a). role comparable to light channels, forming endoevaporitic

The amount of CaCO3 precipitated during evaporative concen- microbial mats (Canfield et al., 2004). The presence of a com- tration is negligible in comparison with the ensuing salts (gyp- plex, living microbial community, particularly cyanobacteria, sum, halite, and K–Mg salts). In natural environments, except within gypsum sediments profoundly influences the geochem- for calcium carbonate precipitation that is induced by evapora- ical microenvironment, leading, for example, to increased tion, several other nonevaporite driving mechanisms for CaCO3 amounts of photosynthetically produced oxygen (up to con- deposition commonly operate within the basin. These mecha- centration equal four times air saturation during the day), but nisms can be more important and can deposit a large amount of that oxygen remains within the interstitial brine. carbonate when the basin stays within the field of carbonate salinity for a long period of time while being constantly supplied with inflowing seawater (see, e.g., Decima et al., 1988). 9.17.11.3 Halite Crystallization Field At the beginning of the halite crystallization, small amounts of gypsum still form, usually as tiny needlelike crystals, intermixed 9.17.11.2 Gypsum Crystallization Field with minuscule halite cubes. Halite begins to crystallize when the This field ranges from the start of gypsum crystallization with standard seawater is evaporated to 0.09–0.1 of the original vol- the volume reduction in total water having a ratio V 0.2 ume, that is, at a volume reduction ratio V 0.09 (Logan, 1987) er ¼ er ¼ (Logan, 1987) or 0.19 (Usiglio, 1849b), beginning at 150% or 0.095 (Usiglio, 1849b). Halite, unlike almost all other com- and continuing up to beginning of the halite crystallization at mon sedimentary minerals, requires relatively low degree of salinity 290–320% (seawater brine density 1.20–1.26). supersaturation to begin precipitation (Berner, 1971). For exam- Minor amounts of gypsum form within the lower portion of ple, in the Adriatic solar saltworks, nearly twofold supersatura- the halite field because the fields of crystallization overlap. tion was necessary for the first gypsum to precipitate and only 502 Geochemistry of Evaporites and Evolution of Seawater

1.3 times supersaturation for the initial halite (Herrmann et al., During seawater evaporation extending up to this stage, the 1973). The halite crystallization continues up to very high salin- concentrations of major ions systematically change in a pre- ities, passing the point where the first magnesium sulfate dictable way – well known from geochemical studies in solar crystallizes (together with the halite) at salinity 375% and saltworks and experimental evaporation of seawater (Figure 8; brine density 1.32. e.g., Geisler-Cussey, 1997; Levy, 1977).

8000 100 Start of Start of gypsum Ca2+ precipitation - epsomite

O) Br

2 precipitation 90 Li+ -H O)

1 Start 2 − of halite precipitation -H

kg 80 1 − 6000 kg (mMol

70 - - 2 Cl Start 4 (mMol + of carnallite Na +

, SO 2- precipitation 60 - SO4 2+

, Cl Mg , and Li - 2+ 4000 K+ 50 , Br , Mg 2+ + 40 , Na + Start of kainite 30 2000 precipitation 20 Concentration of Ca 10 Concentration of K

0 0 0 10 20 30 40 50 60 70 80 90 100 Degree of evaporation

1400 Start of Start of Start of epsomite kainite 1350 gypsum precipitation precipitation precipitation

1300 Start of halite precipitation )

3 1250 − cm 1200 Start

Density (g 1150 of carnallite precipitation

1100

1050

1000 0 10 20 30 40 50 60 70 80 90 100 Degree of evaporation Figure 8 Major and minor ion concentrations and density rise in evaporating Caribbean seawater, after McCaffrey et al. (1987) and Warren (2006), 2 modified. Degree of evaporation based on Mg þ and Liþ, after McCaffrey et al. (1987). Geochemistry of Evaporites and Evolution of Seawater 503

9.17.12 Crystallization Sequence of K–Mg Salts seawater precipitates, because of its great similarity to halite – both minerals crystallize together. The sequence of evaporite crystallization of marine K–Mg salts The Crimean lake Saki, where the crystallization experiments is known from empirical observations of the evaporating sea- were conducted, was supplied with seawater by seepage through water brines and from laboratory and theoretical chemical the sandy bar and was slightly impoverished with respect to Kþ studies of saline solutions. in relation to the Black Sea water (Valyashko, 1962). The brackish Black Sea water ( 17% in the surface waters) is also slightly 2 depleted in Kþ and enriched in Ca þ in relation to the open 9.17.12.1 Natural Crystallization ocean water (Carpenter, 1978). Therefore, these results are not Complete natural evaporation of seawater was rarely monitored exactly representative of the evaporation of standard oceanic to total dryness and/or with a necessary level of precision. The water (McCaffrey et al., 1987, their Figures 3-8). crystallization sequence strongly depends on many environ- The evaporating Mediterranean bitterns from saltworks of mental factors, and the main ones are the temperature (both France gave the following sequence of K–Mg salts at a natural of the brine and the air) and its variations, fluctuations in range of changing temperatures 28–35 C: epsomite alone, humidity, rate of evaporation, rate of precipitation, depth of then epsomite and kainite, then kainite, and, finally, kainite water, and even small deviations from standard chemical com- in association with bischofite and/or carnallite (Charuit and position of the inflowing seawater brines recorded in particular Genty, 1980). Krauskopf (1967) suggested that kainite (and regions (Garrett, 1970, 1996; Jadhav, 1985; Krauskopf, 1967; kieserite) forms only when the rate of evaporation is suffi- Valyashko, 1962). The natural crystallization is always polyther- ciently slow and the brine and precipitating salts stand together mal. The temperature of bitterns in saltworks is most commonly for a long time. These and associated sulfate salts (e.g., leonite) between 18 and 35 C but can reach 50 C in the most concen- were found to crystallize from supersaturated solutions slowly trated bitterns and may drop to 5 C, as recorded in the winter in and with difficulty (Bergman and Luzhnaya, 1951; Hadzeriga, France (Charuit and Genty, 1980; Jadhav, 1985). The natural 1967; Hardie, 1984, p. 207). Kainite crystallization from the crystallization in saltworks follows the so-called equilibrium Black Sea bittern was recorded only in one experiment, during mode crystallization (Bea et al., 2010), in which bitterns remain a period of very slow evaporation (Il’insky 1948 in Valyashko, in permanent contact with all previously precipitated solids. 1962), and it was considered as a secondary salt by Valyashko During fractional crystallization (Harvie et al., 1980), mostly (1962). On the other hand, in the Indian saltworks, kainite joins known from theoretical models and laboratory studies, all the the crystallization of epsomite, sakiite, and halite before the start precipitates are assumed to be removed from the bittern, of carnallite precipitation and is present volumetrically as the although in fact they are also in contact with this bittern at the most significant precipitate at that interval of the crystallization moment of their formation. path (Chitnis and Sanghavi, 1993; Garrett, 1970). As documented in seawater evaporation processes in coastal In the Indian saltworks, carnallite crystallizes in the density saltwork pans around the world, the next salt, which appears in interval 1.29–1.33 (sp. gr.) and with bischofite, being the final the course of crystallization, is invariably epsomite (Cohen-Adad product of the seawater crystallization path, in the interval et al., 2002; Ortı´ et al., 1984a; Valyashko, 1962), although mir- 1.33–1.37 (sp. gr.) (Jadhav, 1985). In the French Mediterra- abilite may precede crystallization of that mineral, during winter nean saltworks, bischofite begins to crystallize from brine of or throughout evening cooling of the brine (Garrett, 1970). the density 1.364 (Fontes and Matray, 1993). Kieserite was Interestingly, some of the detailed studies of salinas along the found crystallizing together with bischofite at the final desic- Mediterranean (in Spain and France) do not report mirabilite cation stage of seawater in India (Chitnis and Sanghavi, 1993). (Geisler, 1982; Ort´ı et al., 1984a,b) although the study by Copious crystallization of bischofite was recorded as the mass Charuit and Genty (1980) does. During further evaporation, of floating feather- and needlelike crystals in the density inter- water studied from evaporating ponds along the Black Sea, epso- val 1.370–1.377 (sp. gr.) at temperature 38–43.5 C (Jadhav, mite was transformed into sakiite (hexahydrite), which also 1985). Further concentration of the dense brine by solar evap- crystallized in the primary form (Valyashko, 1962). Sakiite oration, above the 1.377 specific gravity, was not possible due crystallization together with epsomite and halite was also to the high viscosity of the bittern and absorption of atmo- recorded in India (Chitnis and Sanghavi, 1993). spheric moisture (Jadhav, 1985). The bischofite began to dis- During further evaporation of the Black Sea water, the solve when the bittern was heated over 44 C and disappeared carnallite crystallization was joined to the crystallizing salts, at 50 C. In India, night temperature drops down to 10 C led and finally bischofite was crystallized together with these salts, to precipitation of epsomite from the bitterns that at 30 C are up to the end of evaporation (Valyashko, 1962). During exper- unsaturated with this salt, showing solubility strongly depen- imental evaporation of the Black Sea water at 25 C, Valyashko dent on temperature (Chitnis and Sanghavi, 1993). Winter (1962, p. 160) observed that sylvite started to crystallize nearly cooling of seawater bitterns is utilized for commercial produc- simultaneously with sakiite, and it continued the crystalli- tion of epsomite in France. K–Mg salt crystallization is accom- zation up to the start of carnallite precipitation. This result panied by halite, which ceases to precipitate when Na ions appears to support the early finding by van’t Hoff and became exhausted from the bittern before final precipitation Meyerhoffer (1899, cited by Balarew, 1993), later abandoned, of bischofite (Amdouni, 2000). that sylvite, instead of kainite, is obtained during seawater By heating, cooling, and freezing of the brine, the mixing of evaporation. Valyashko (1962) noted also that sylvite crystalli- bittern from various evaporation stages, addition of bittern to zed during cooling of the bittern (see also Garrett, 1970). formerly precipitated salts, dilution of the bittern by seawater, Valyashko (1962) warned that sylvite may be unnoticed in and other seminatural operations, a number of other salts can 504 Geochemistry of Evaporites and Evolution of Seawater precipitate in solar saltworks, including mirabilite and glauber- natural sequence described earlier), some steps are lacking. ite (Garrett, 1980, 1996; Hardie, 1985). The mixing of seawater The complete set of steps is the following (also see Table 6): brines leads also to precipitation of gypsum, halite (Ortı´ et al., (1) Precipitation before saturation with respect of salts of the 1984a; Raup, 1970, 1982), and sylvite and tachyhydrite (Wali, five-component system, which encloses Ca carbonate, Ca 2000). The maximum recorded density of evaporating seawa- sulfate, and Na chloride stages of crystallization ter brine was 1.377 (sp. gr.) at 30 C (Buch et al., 1993; Jadhav, (2) Precipitation of Mg or Na–Mg sulfates without K salts 1985), and a similar artificial seawater solution – 1.339 – was (without sylvite and carnallite) created in experiments by Lychnos et al. (2010). In the highest (3) Precipitation of K–Mg salts (particularly sylvite), without salinity pans, the complete segregation of solids from liquid is carnallite practically impossible, and all the apparently solid phases (4) Precipitation of carnallite should be considered as containing 10–20% of mother (5) Terminal precipitation with bischofite liquor (Hadzeriga, 1964). The natural sequences, particularly those from the coast of These stages are known also as the halite-, bloedite/epso- the Black Sea, are simpler than the sequences predicted by mite-, kainite-, carnallite-, and bischofite-dominant stages, theoretical studies of mineral solubilities and numerical simu- respectively (Eggenkamp et al., 1995). lations (Braitsch, 1971; Eugster et al., 1980; Valyashko, 1962). During experimental precipitation of seawater salts, the first Mg sulfates at the A–B boundary begin to crystallize when the brine is 70 times more concentrated than seawater, K-bearing 9.17.12.2 Theoretical Crystallization Paths salts (the B–C boundary) when it reaches 90 times the initial concentration (McCaffrey et al., 1987). The theoretical sequences of crystallization of marine K–Mg Evaporation to dryness leads to the final point, “where the salts were established from solubility studies and determina- solution evaporates at a constant composition” (Usdowski and tion of saturation points of these salts developed by Jacobus Dietzel, 1998, p. 70) and is simultaneously saturated with Henricus vant’Hoff (the first Nobel prize winner in chemistry respect to all (at least two or more) dissolved solutes. This in 1901), and his students, as well as from numerical calcula- final point or state is called eutonic or drying-up (Borchert tions based mainly on the Pitzer ion-interaction model and Muir, 1964; Mullin, 2001; Sonnenfeld, 1984; Usdowski (Al-Droubi et al., 1980; Eugster, 1971; Harvie et al., 1980; see and Dietzel, 1998; Valyashko, 1962). The term eutonic coined review by Bea et al., 2010). The sequences strongly depend not by Kurnakov and Zhemchuzhnii in 1920 (Gamsja¨ger et al., only on temperature but also on the kinetic factors of nucle- 2008; Kurnakow and Zˇ emcˇuzˇny, 1924), is used not only to ation and crystallization (in particular, whether stable or unsta- describe the point at saturation diagrams where the evapora- ble mineral equilibria prevail) and on whether the reactions tion to dryness ends at the given invariant temperature and between evolving brine and earlier formed salts actually took pressure (Figures 10-12) but also, less formally, to describe the place. Therefore, several alternative models and paths of evap- final processes of crystallization or final composition of the orative crystallization must be considered and at least several naturally evaporating solutions. theoretical sequences are possible. Theoretical sequences are The described crystallization path concerns the present-day usually calculated for isothermal evaporation. A simulation of seawater, which evaporates in closed system without the contin- polythermal evaporation, for Quero Lake (Spain), was made uous addition of fresh seawater. Such an addition, if present, by Sa´nchez-Moral et al. (1998). could introduce calcium into the system, equally as the other The theoretical stratigraphic columns showing both order ions, and this could certainly lead to precipitation of the other and thickness of the various sequences of marine salts pre- modified mineral suites. The predicted minerals crystallizing dicted for isothermal evaporation have been calculated and together with halite, and as the next solids formed after halite, drawn by Braitsch (1971) and then by Braitsch and Kinsman would be polyhalite and glauberite (Holser, 1979a). The crystalli- (1978). Usually, the temperature sequence for 25 C is used for zation path of evaporated seawater, which includes the original comparison with the natural sequences. All the crystallization presence of calcium, was successfully modeled by computer paths, including the natural sequence produced during tem- program written by Harvie et al. (1980). In this program (applied perature fluctuations typical of the Crimean coast of the Black widely for studies of brines from halite inclusions), polyhalite is Sea described earlier, can be subdivided into five steps or stages the expected mineral phase on the crystallization path that runs (Braitsch, 1971). In some theoretical sequences (as in the differently than the path predicted by solubility studies of five-

Table 6 Subdivision of the crystallization sequence of the evaporating seawater into geochemical zones after various authors, increase in degree of evaporation and concentration is from 1 to 5

Van’ t Hoff school as summarized by Braitsch (1962, in 1971 edition) Zones after Valyashko (1972b) Zones after Hardie (1984)

5 E – terminal precipitation with bischofite Bischofite zone MgCl2 4 D – precipitation of carnallite Carnallite zone KCl 3 C – precipitation of KMg-salts, without carnallite Sylvite zone KCl

2 B – precipitation of NaMg or Mg sulfates without K-salts Magnesium sulfate zone MgSO4 1 A – precipitation before saturation with respect of salts of the Zone of halite and zone of gypsum- CaSO4 five-component system anhydrite Geochemistry of Evaporites and Evolution of Seawater 505 component system of K–Mg salts described earlier (Hardie, Commonly, brines are permanently stratified, which can 1984). This program is flexible and permits analysis of crystalli- lead to separate isotopic composition of particular brine bod- zation paths of modified marine waters of various compositions, ies. The isotopic signals of evaporite deposits are complicated including ancient seawaters, which showed crystallization paths by this stratification effect and require a special approach to different from the path of modern seawater described earlier. resolve some isotopic imbalance problems (e.g., ‘sulfur pump’ mechanism proposed by Torfstein et al., 2005).

9.17.14 Usiglio Sequence – A Summary 9.17.13 Isotopic Effects in Evaporating Seawater Brines and Evaporite Salts During the evaporation of seawater, the salinity and density of water increases as well as the concentration of particular ions, During evaporation, more of the light water molecules (16O as leading to saturation, supersaturation, and precipitation of par- compared to the 18O) are selectively removed from the liquid, ticular compounds. The general rule is that first compounds that passing into vapor, leading to enrichment of the remaining precipitate are less soluble, that is, calcium carbonate (calcite liquid water in heavier isotopes (18O and 2H – deuterium: D). and aragonite), calcium sulfate dihydrate (gypsum), and During evaporation of seawater to the stage of halite crystalli- sodium chloride (halite), so the order of precipitation reflects zation, parallel to this process, oxygen in sulfate ions is enriched the rise in solubility (Table 4). The composition of brine in 18O (Pierre, 1985; Pierre et al., 1984b). Evaporation can also becomes simpler evolving from the initial seven-component cause enrichment in heavier 13C (in relation to 12C) isotope system toward the five-component system in the field of K–Mg (Potter et al., 2004; Stiller et al., 1985; Valero-Garce´s et al., salt precipitation (Table 5 and Figure 14(b) and 14(c)). 1999). However, further evaporation of seawater brine from the start of halite precipitation leads to reverse effect, that is, depletion of heavier isotopes in the water (Valyashko et al., 1977), reflected 9.17.15 Principles and Record of Chemical in characteristic ‘evaporite loop’ on the dD–d18O plot (Holser, Evolution of Evaporating Seawater 1979b, 1992. The reverse effect is caused by rising salinity causing a progressive decrease in activity of water molecules in evaporat- Evaporating seawater brine changes its composition together ing saline solutions and hydration of ions (Pierre, 1988, 1989). with the precipitation of the sequence of evaporite minerals The paths of particular evaporite loops (for a given water reser- according to laws reflected by crystallization paths on the voir) depend on the humidity, the isotope ratios of D and O in the graphic diagrams. Some of them are particularly important air, and the cation composition of the basinal brine, which for the study of the evolution of evaporating brines. reduces the activity of H2O and its isotopic components (Sofer and Gat, 1975 ; Horita, 2005). Water molecules are used for the 9.17.15.1 Principle of the Chemical Divide for Seawater hydration of ions present in the brine, which introduces additional fractionation effects in the water, specific to each ionic The precipitation of simple salts induced by and proceeding species (Gat, 2010; Pierre, 1988). Evaporated seawater brines during evaporite concentration leads to specific changes in the mixed with meteoric or other waters may have biased dD and concentration of ions involved in precipitation. This is the 18 d O values due to mixture of H2O with different isotopic char- consequence of the fact that during the equilibrium precipita- acteristic (Duane et al., 2004) and can be studied in fluid inclu- tion, two conditions must be obeyed simultaneously (Eugster sions in evaporite minerals (e.g., halite; Knauth and Beeunas, and Hardie, 1978; Eugster and Jones, 1979; Hardie and 1986; Knauth and Roberts, 1991). H and O in water molecules Eugster, 1970; Hardie and Lowenstein, 2003): in hydrated salts precipitated from these waters (such as gypsum) 1. The ion activity product of the solution must remain con- are subjected to isotopic fractionation and can be used for the stant at constant pressure and temperature. interpretation of the origin of the basinal and other waters when 2. The ions are removed from the solution in strictly appropriate the range of fractionation is known from experiments (Holser, molar proportions (usually in equal proportions in case of 1979b; Koehler and Kyser, 1996). The same isotopic effects are common evaporite minerals: gypsum (CaSO4 2H2O) and recorded in evaporated nonmarine brines (e.g., Cartwright et al., 2 2 Á halite (NaCl), Ca þ:SO À 1:1, and Naþ:ClÀ 1:1, respec- 2009). Gypsum, which is most common among hydrated marine 4 ¼ ¼ tively; see Hardie and Eugster, 1970; and Drever, 1982, for salts, is potentially an excellent marker recording the derivation of more detailed explanation of that process and Hina and H O in brines (Buck and Van Hoesen, 2005; Farpoor et al., 2004, 2 Nancollas, 2000, for explanation of the role of concentra- 2011; Hodell et al., 2012). However, special laboratory tech- tions, supersaturation, and stoichiometry in the crystal nucle- niques to exclude ‘nonhydration’ water (moisture and adsorbed ation and growth, as well as for their relation to the ion water) from the analysis without any loss of hydration water are activity product). required to obtain the proper results (Playa` et al., 2005; Rohrssen et al., 2008). Condition 1 specifies that the concentration of particular 2 2 Isotopic processes in brines are specific and can influence the ions of the given binary evaporite salts (e.g., Ca þ and CO3 À 2 2 isotopic signal leading to erroneous interpretations (Schreiber in the case of calcite and Ca þ and SO4 À in the case of and El Tabakh, 2000). In saline waters and brines, at salinity and gypsum) must vary antithetically, thus the rise of concentration concentrations exceeding those of seawater, the isotopic fraction- of one ion is accompanied with the fall of the concentration of ation processes are influenced by ‘salinity effects’ (Gat, 1995, the other (Drever, 1997, Figure 15-2; Hardie and Eugster, 2010; Horita, 2005, 2009; Koehler and Kyser, 1996). 1970). Condition 2 requires that the molar ratio of the 506 Geochemistry of Evaporites and Evolution of Seawater

component ions of precipitated salt must change, unless it is Evaporite concentration exactly equal to one at the beginning. Molar proportions of all the considered ions in the modern seawater are different than one and were likely different than one in the ancient seawater. The Therefore, the ion with the lower concentration at the onset of CaCO3 Precipitation of divide evaporitic precipitation will progressively decrease in concen- CaCO3 tration, whereas the other ion showing initially higher concen- 2+ - - 2+ Ca > HCO3 HCO3 > Ca tration will increase in concentration, although relatively more slowly than before the onset of precipitation. The Precipitation Alkaline brine The continued precipitation of the salt will lead to a drop in gypsum Na-K-Mg of gypsum the concentration of the ion showing lower concentration up divide Cl-SO -CO CaSO4·2H2O 4 3 to the limit of the detection and practically to its selective elimination from the brine, when the precipitation of the 2+ 2- 2- 2+ Ca > SO4 SO4 > Ca given salt ceases. The brine irreversibly changes its composition in the strictly predicted way. Usually, from the modern seawater, at the beginning of evaporative concentration, calcite pre- CaCl2 brine MgSO4 brine Na-K-Mg-Ca Na-K-Mg cipitation enriches the residual solution in the more abundant ionic component and depletes it in the other. Cl Cl-SO4 Calcite precipitation induced by evaporation of seawater (a) eliminates all HCO3À ions from the solution according to the I. Water with SO4 > Ca reaction (Holland et al., 1996): Start of gypsum precipitation Mg 2 Ca þ aq 2HCO3À aq CaCO3 s H2O l CO2 g [6] ð Þ þ ð Þ ! ð Þ þ ð Þ þ ð Þ

SO4 (where aq aqueous, or soluble in water, s solid, l liquid, ¼ ¼ ¼ and g gas). ¼ The greater the initial disparity between the two ionic com- Mg/Ca ponents, the faster is the enrichment–depletion process. In this way, “calcite precipitation acts as a branching point or chemical divide in the sense that seawaters that are initially carbonate- Concentration rich will experience a further relative enrichment of carbonate and depletion of calcium and vice versa” (Eugster, 1980, p. 44). Ca Presently seawater is calcium-rich and hence the seawater brine is relatively enriched in calcium and depleted of carbonate after Salinity calcite precipitation (Figure 9). However, in the hypothetic soda ocean water of the Archean–Proterozoic, the carbonate II. Water with Ca > SO 4 ion is more abundant than calcium (Kempe and Degens, 1985), and therefore, evaporation should lead to elimination Mg of calcium within it and to evolution of such waters along the carbonate-rich path of chemical divide and precipitation of Ca-free minerals typical of the soda lakes. Ca The next common evaporite mineral precipitating from modern seawater after calcite – gypsum – “provides a chemical divide with respect to calcium and sulfate in the same manner Start of gypsum as calcite provided a chemical divide between calcium and precipitation carbonates” (Figure 9(b) I; Eugster, 1980, pp. 44, 46). SO4 Thus, each precipitation step acts as “a chemical divide, Concentration Mg/Ca separating brine evaporation paths depending upon their composition prior to saturation” (Harvie et al., 1982, p. 1615). This was called ‘fractionation by mineral precipitation’ (Eugster, 1980; Eugster and Jones, 1979) or principle of (b) Salinity chemical divide as described by Drever (1982) and is now Figure 9 (a) Chemical divides and chemical evolution of major types of popularized under the name of ‘chemical divide.’ waters during evaporative concentration of surface inflow waters (after The end of precipitation of a given salt, here CaCO3, is thus Hardie and Lowenstein, 2003). (b) Hypothetical passage of the chloride interpreted as the exhaustion of the calcium ion, which origi- ‘nonalkaline’ brines through the gypsum chemical divide: leading to an nally is present in the evaporating water in a relatively small increase in SO /Ca ratio, and hence the Mg/Ca ratio in case of evaporation 4 amount. The evolution of the chemical composition of the of seawater type of brine with SO4>Ca (I), and to an increase in Ca/SO4 ratio and consequently to (II) little change in Mg/Ca ratio in case of evaporation of waters undergoing the evaporation can be interpreted as a calcium chloride brine with Ca>SO4 (after Hardie, 1987, modified). succession of chemical divides. Geochemistry of Evaporites and Evolution of Seawater 507

During evaporite concentration and precipitation of succes- basins, although, of course, it is not the only mechanism sive salts, the modern seawater passes through the sequence of which influences the hydrochemistry of such basins (Herczeg points – ‘chemical divides’ – in a strictly predictable way that and Lyons, 1991; Yan et al., 2002). The important limitation of depends on mutual molar proportions of particular ions in the the chemical divide model is the inability to add constituents seawater. Because in the seawater, as in almost all natural to the solution (Dargam and Depetris, 1996). waters, the first mineral that precipitates is calcite, it is the cause of the first chemical divide, and then the gypsum precip- 9.17.15.2 Ja¨necke Diagrams itation is the cause of the next divide. Because in modern sea- 2 2 water Ca þ >CO3 À (in molar values), the CaCO3 ceases to The useful diagram showing the crystallization paths of seawater 2 precipitate when nearly the entire amount of CO3 À ions in brines for the five-component system was invented by Ernst 2 2 the brine is exhausted. Because Ca þ Mg þ > Ca þ > ratios of different ions or salts, but not their concentrations in 2 2 Kþ/ClÀ >SO4 À >CO3 À) at the end of Ca carbonate precipi- the solution. The diagram permits one to trace the relative 2 2 2 2 2 tation passes into (Naþ >Mg þ >Ca þ >Kþ/ClÀ >SO4 À) changes of Kþ, Mg þ, and SO4 À proportions along the crystalli- within the gypsum precipitation field, and then into zation paths to the drying-up or eutonic point at a given con- 2 2 (Naþ >Mg þ >Kþ/ClÀ >SO4 À) at the end of gypsum precip- stant temperature (Figure 11). The stability fields of the salt itation and within halite precipitation field. This latter halite minerals along the crystallization path permit prediction of the brine contains only five major components (plus conservative expected sequence of crystallization at a given temperature. The BrÀ), in comparison with seven main components in the initial diagram does not show the evolving changes in the concentra- seawater, and it is this brine from which K–Mg salts are precip- tion of Naþ and ClÀ as well as changing water content (H2O) in itated from modern seawater. Such five-component system of the system. ions was and is the most intensively studied portion of the It is assumed that the system is always saturated with basic chemical system from which oceanic K–Mg salts are and NaCl. The important feature of the diagram is that the position were precipitated today and in the past. of modern seawater remains unchanged during halite crystalli- Seawater brines of high salinity show ratios of some ions zation after the precipitation of Ca carbonates and Ca sulfates, that are different than ratios in modern seawater. During evap- until the actual onset of precipitation of K- and MgSO4- oritic concentration of seawater, ionic proportions remain bearing salts (Horita et al., 2002). For ancient seawaters defi- constant only up to the start of Ca carbonate precipitation. cient in sulfates, the other Mg–Ca–2K type of diagram is used Then, some of these proportions gradually change in the pre- (Figure 14). 2 dicted way, starting with the proportions in between Ca þ and The Ja¨necke diagram was prepared from laboratory solu- 2 CO3 À as well as between them and the remaining ions. Dur- bility studies of salts at the constant temperature. Some ing evaporative crystallization of seawater salts, the concentra- authors adopted the Ja¨necke diagram to show the real com- tion of some ions rises, attains a maximum, and then gradually position of halite seawater brines undergoing natural, that is, drops in a strictly predicted way (Figure 8; Table 5). For polythermal evaporation with accompanying precipitation of example, in the middle of the halite precipitation field (DE K–Mg salts (Garrett, 1980). The ‘crystallization paths’ were 2 45), the concentration of Mg þ ions (ppm) equals the con- represented by dispersed streams of points on such diagrams centration of Naþ ions and then becomes higher (McCaffrey (Valyashko, 1962) and were used to draw some average lines et al., 1987). The evolving seawater brine thus not only has a separating the ‘stability’ fields of the precipitating salts chemical composition simpler from seawater of normal salin- (Valyashko, 1962). Such a diagram for naturally evaporating ity but also is different from seawater, as far as the ratios of ions seawater, much simpler than Ja¨necke diagram for 25 C, was are concerned; however all these differences can be predicted. drawn by Kurankov and supplemented by Valyashko (1962) The evolution of seawater brine evaporating to dryness within and is known as the solar diagram (Figure 12; Holser, 1979a; the field of K–Mg salt precipitation is more difficult to predict, Valyashko, 1972a,b). Kainite is not present on the solar dia- mainly because of the strong influence of temperature fluctu- gram because this salt was not observed during evaporation ations on the kind of precipitated salts and other phenomena of the Black Sea water. Valyashko (1962) enlarged the field of typical of high-salinity brines (Braitsch, 1971). The predicted sylvite on the diagram based on the data from experimental pathways of chemical changes of evaporating brines and asso- evaporation of especially prepared solutions from which the ciated evaporitic precipitates are commonly traced on the var- sylvite was crystallized in the course of evaporation as well as ious diagrams along lines that are called the ‘evaporation the Black Sea water. Farther on, Valyashko (1972b) used the paths’ or ‘crystallization paths.’ These paths end in the final same solar diagram to show the predicted path of crystalli- drying or eutonic point. zation and sequences of K–Mg salts precipitated from hypo- The principle of chemical divide is successfully used to thetical ancient seawater impoverished with respect to sulfate explain the chemical evolution of waters in many closed (Figure 12). Crystallization paths omitted the epsomite field 508 Geochemistry of Evaporites and Evolution of Seawater

Thenardite primary sylvite crystallization from brine similar to present seawater, except for the extremely low content of Mg sulfate.

9.17.15.3 Spencer Triangle The principle of the chemical divide permits the prediction of the Modern seawater chemical evolution of natural waters undergoing evaporation depending on the initial chemical composition of the water Sylvite solute (inflow waters). The ‘Spencer triangle’ (Lowenstein et al., 1989; Spencer, 2000; Spencer et al., 1990) is the best graphic technique for the prediction of the evolutionary pathways of the water solutes during evaporation (Figure 13). They are intended Glaserite to show how inflow waters change, by evaporative concentration and precipitation of calcite and gypsum, into specified type of brine (Jones et al., 2009; Lowenstein and Risacher, 2009; Smoot and Lowenstein, 1991; see also Chapter 7.13). The triangle is a

ternary phase diagram for the system Ca–SO4–(CO3 HCO3).

Increasing concentration 2 2 2 þ The basic components, Ca þ, SO À, and (CO À HCO À), 4 3 þ 3 are expressed in equivalents, as units of charge concentration, and are placed at corners of the diagram (Figure 13(a) and Bloedite 13(b)). The calcite (CaCO3) compositional point is placed sw halfway between the Ca and (CO3 HCO3) corners, because . þ there are equal equivalents of Ca and (CO3 HCO3) in calcite. K2Cl2 Na2SO4 þ z Similarly, the gypsum–anhydrite compositional point is placed halfway between the Ca and SO4 corners. Calcite is stable and can crystallize across the entire field of the triangle (similarly as Mg calcite and aragonite). Gypsum–anhydrite crystallizes along the Ca–SO side of the diagram. All waters may precipitate MgCl 4 (a) 2 halite and other K or Mg salts at some point, particularly on later stages of evolution. There are two chemical divides on the

SO4 diagram: lines from calcite point to SO4 corner and from calcite K2 to gypsum–anhydrite point, which separate inflow waters into Thenardite three types, which evolve into relative specified types of brine, Glaserite depending on the initial water compositions expressed as Sylvite equivalents of Ca, HCO3 plus CO3, and SO4. These are alkaline (or Na–HCO3–SO4) waters or brines, neutral (Cl–SO4) brines, and calcium chloride (CaCl) brines (Spencer, 2000). Inflow Picromerite Bloedite sw waters can be plotted on the diagram, and their chemical evo- Leonite Epsomite lution, during evaporation and calcite and gypsum precipita- Kainite Sakiite tion, evolves into an explicit brine type that can be specifically (hexahydrite) traced. The initial water represented by specific point on the Carnallite z Kieserite Mg diagram will precipitate calcite and move directly away from the Bischofite calcite compositional point. Continued evaporative concentration and calcite crystalli- Crystallization path zation will result in migration of the water composition to the

sw - Modern seawater brine join between (HCO3 CO3) and SO4 corners, or the join z - Drying-up or eutonic point þ (b) between Ca and SO4 corners, depending on initial water composition. Ca-poor Na–HCO3–SO4 (or Ca-poor Na–HCO3– Figure 10 (a) 3D phase diagram for Mg, Na, K, Cl, and SO at 4 SO –Cl) brines form from waters with equivalents of increasing concentration at temperature 25 C. During evaporite 4 HCO CO SO >Ca that evolve directly away from the concentration, the composition of seawater follows line marked by 3 þ 3 þ 4 arrows. (b) 2D diagram known as Ja¨necke triangle (a projection of the 3D CaCO3 composition during precipitation of calcite. These diagram shown in (a)). Crystallization path of seawater is marked by waters are not able to precipitate gypsum but precipitate arrows (after Ja¨necke, 1929 in Dronkert, 1985, Figure 1.1; Łaszkiewicz, sodium sulfate and sodium carbonate salts. 1967; Krauskopf, 1967). Soda lakes and hypothetic soda ocean water belong to this

type (Kempe and Kazmierczak, 2011). Waters in the Cl–SO4 field, and started with sylvite as the first K–Mg salt after halite, such as present-day seawater, form Ca-poor, Na–Cl–SO4-rich exactly as in ancient sequences of marine K–Mg salts, and brines following the precipitation of calcite and gypsum. Waters similarly to those noted during evaporation of the Bonneville in the Ca–Cl field, with Ca equivalents >HCO CO SO 3 þ 3 þ 4 salt flat brines, Utah, USA (Hadzeriga, 1964, 1966, 1967). (which implies that some Ca is balanced by Cl), evolve into

These can be treated as the rare present-day example of massive Ca–Cl brines devoid of SO4 and HCO3 following the Geochemistry of Evaporites and Evolution of Seawater 509

Mg Mg Mg Bischofite Bischofite Bischofite z z z Kieserite Kieserite Carnallite Kieserite Carnallite Carnallite K2 K2 K2

Sylvite Sylvite Sylvite

Kainite Kainite Epsomite Sakiite

Kainite Epsomite SO4 SO4 (b) 15 °C 25 °C 35 °C

Mg Carnallite Mg Carnallite MgCarnallite Bischofite Bischofite Bischofite Kainite Kieserite Kieserite Kieserite Kainite 0.8 Leonite Kainite Sakiite Sakiite Epso- 0.2 Sylvite mite 0.6 Epsomite Sylvite Sylvite 0.4 Picromerite Leonite sw sw sw 0.4 Bloedite 0.2 Picromerite Bloedite Bloedite Glaserite K Glaserite Glaserite 2 0.6

0.8 Thenardite Thenardite Thenardite 0.6 0.8 Mirabilite 0.4 Crystallization path 0.2 0.2 0.2 z - Drying-up or eutonic point SO4 15 °C SO4 25 °C SO4 35 °C sw - Seawater brine (a)

Figure 11 (a) Solid-solution equilibria in quinary system Na2Cl2–K2Cl2–MgCl2–Na2SO4–K2SO4–MgSO4–H2O for 15 C, 25 C, and 35 C, shown on Ja¨necke diagrams, redrawn from Usdowski and Dietzel (1998), all stability fields saturated with NaCl, (b) enlarged Mg apices of the triangles shown in (a). precipitation of calcite and gypsum. The three types of brines can constant temperature) and added that “it seems highly produce the three predictable distinct assemblages of evaporite improbable that actual conditions existing in nature can be minerals (Spencer, 2000; Spencer et al., 1990). adequately represented by one of these models” (Braitsch, 1971, p. 84). Nevertheless, he stated “the comparison of different models with natural salt series is the only direct way of 9.17.16 Evaporation of Seawater – Remarks on approaching the actual composition of the solutions and the Theoretical Approaches conditions under which they existed” (Braitsch, 1971, p. 84).

The numerous modeling approaches to predict the order the evaporative crystallization of salts and the associated quantita- 9.17.17 Sulfate Deficiency in Ancient K–Mg tive aspects of this process are unsatisfactory (Hardie, 1984). Evaporites Usdowski and Dietzel (1998) made such a general comment to existing solubility data of marine salts; “a good many of the In many ancient marginal marine evaporite basins, the vertical data are not reliable,” usually “due to the fact that equilibrium sequence of facies follows the Usiglio sequence, that is, in is difficult to attain experimentally and that metastable states ascending order, the Ca carbonate Ca sulfate Na chloride ! ! prevail” (Usdowski and Dietzel, 1998, p. 12). Braitsch (1971) facies. However, K–Mg portions (if preserved) are always sig- commented that the models based on solubility data are nificantly different in many aspects. Some salts predicted by strongly dependent on assumed ideal conditions (such as theory (bloedite, kieserite, and reichardtite) are rare or absent, 510 Geochemistry of Evaporites and Evolution of Seawater

Figure 12 (a) Kurnakov-Valyashko solar diagram (Mg corner) and crystallization paths of seawater and seawater depleted with respect to sulfate to different degrees; the direction of change of the seawater composition is from sw to 1, 2, 3, 4, and 5. (b) corresponding columns of evaporite deposits precipitated from seawater and seawater depleted with sulfate to different degrees after Valyashko, 1972b, modified). other salts (vanthoffite, loewite, and langbeinite) are more ‘epsomite facies,’ that is, step B in the sequence of K–Mg salts common than expected, and some unexpected salts appear (Table 6; Braitsch, 1971). The ancient K–Mg sequences com- during the evaporation of seawater (polyhalite and anhydrite) monly start with sylvite, instead of epsomite, and are fol- (Stewart, 1963; Valyashko, 1962). lowed by carnallite-dominated salts and show significantly The lack of the bloedite crystallization during the evapora- smaller amounts of sulfates in B-E part of the sequence tion of seawater at 25 C can be, at least partly, explained by (Tables 6 and 10). What is more striking is that the deposits the extremely difficult and slow experimental nucleation and that contain primary halite, sylvite, and carnallite are usually crystallization of this salt (the appearance of first bloedite entirely free from the primary Mg sulfate salts. Such deposits crystals in a supersaturated solution required as much as make up more than 60% of ancient potash deposits (Table 10; 2 months of waiting; Bergman and Luzhnaya, 1951). Hardie, 1990). Of the many discrepancies between real From the geochemical point of view, one particular crystallization sequences and the theoretical predictions, the difference is the most significant – the apparent lack of an most remarkable feature is the deficiency of Na–Mg, Mg, and Geochemistry of Evaporites and Evolution of Seawater 511

Ca2+

Na+ Cl- Calcium (456.6) (536.0) 2- K-Mg-Ca chloridessulfates SO4 (38.5) Calcium chloride Gypsum Ca-Cl anhydrite Calcite Ca2+ (17.7) Neutral Cl-SO4 (20.0)

- HCO3 (2.3) Calcium K-Mg sulfates sulfates 2+ Mg Neutral HCO3-SO4 (111.1) 2+ 2- Ca SO4 (20.0) (56.2) - Sodium - K+ HCO SO 2- Sodium HCO3 3 4 sulfates (9.7) (2.3) carbonates + 2- (a) (b) CO3

Figure 13 (a) The major ions in seawater; in miliequivalents per liter (redrawn from Hite RJ (1985) The sulfate problem in marine evaporites. In: Schreiber BC and Harner HR (eds.) 6th International Symposium on Salt, Toronto, Ontario, Canada, May 24–28, 1983, vol. 1, pp. 217–230. Alexandria, VA: The Salt Institute). (b) Spencer triangle – ternary phase diagram illustrating how inflow waters evolve into brines following the principle of chemical divides. Two chemical divides 2 (lines connecting calcite and SO4 À, and calcite and gypsum–anhydrite) separate waters that will evolve (following arrows) during evaporation and precipitation of calcite and gypsum into Ca–Cl brines, Ca–SO4 brines, and Ca–HCO3–SO4 brines (redrawn from Smoot JP and Lowenstein TK (1991) Depositional environments of non-marine evaporates. In: Melvin JL (ed.) Evaporites, Petroleum and Mineral Resources. Developments in Sedimentology, vol. 50, pp. 189–347. Amsterdam: Elsevier). The divides are based on the relation of equivalents of calcium to equivalents of SO4 and HCO3 in the inflow water. The relations of these equivalents in seawater are shown on (a).

K–Mg sulfates. The sulfate salts, epsomite, kieserite, and kai- The localized lack of the epsomite facies can be explained nite, predicted to precipitate from modern seawater, and by sedimentological processes acting in an open system, such others, such as langbeinite, are rare or entirely lacking in as nondeposition, erosion (synsedimentary dissolution), brine many ancient marine evaporite deposits (Borchert, 1969). reflux, changes in temperature, or brine stratification (Ayora Ancient deposits show generally a much smaller than expected et al., 1994). Recently, Krupp (2005) presented the concept of amount of K- and Mg-bearing sulfate minerals than should large-scale KCl-rich deposition of marine salts similar to the result from the evaporation of present-day seawater. This is idea of mineral ‘fractionation mechanism’ (Eugster, 1980). known as the ‘sulfate deficiency.’ This deficiency has been This mechanism operates during natural recycling processes long known and has been a central problem discussed in the on the emerged margins of evaporite basin, where more solu- geochemistry of evaporites. ble salts are carried by meteoric waters to the basin center and The ancient sequences lacking the epsomite facies are increase the solute load, particularly the NaCl content, in this easy to obtain from the crystallization of modified seawater. zone (Borchert, 1969, with references). In a similar way, Krupp

This seawater is impoverished with respect to MgSO4 and is (2005) suggested that the selective leaching of K–Mg sulfate CaCl2-enriched, as was proven by both theoretical calcula- marine salts on the basin margin, combined with various syn- tions and experiments (Herrmann, 1991). In particular, diagenetic reactions and transformations during transport of Valyashko (1972a,b) presented interpretation of possible the solutes down to the basin center, could lead to entirely paths of crystallization of K–Mg salts depending on the chloride-type potash deposition there. amount of SO4 removed from the solution (Figure 12). The explanation of sulfate deficiency in ancient evaporites splits into three main possibilities, which all can be true 9.17.17.1 Sulfate Deficiency as the Secondary Feature depending on the particular case: During the last century, most investigators, with a few excep- 1. The chemical composition of ancient ocean was different tions, believed in the near-constancy of the seawater composi- than today. tion at least since the Cambrian, and they mostly ignored the

2. The deficiency is the effect of the modification of the chem- possibility of primary crystallization of MgSO4-poor salts ical composition of marine brine in evaporite basins. directly from ancient seawater (possibility 1, mentioned ear- 3. The deficiency is a secondary effect of the burial and diagenetic lier). The argument in favor of such a view is the fact that some alteration of ‘normal’ evaporite sequences (Borchert, 1969; K–Mg salts or brines from primary halite fluid inclusions of the Braitsch, 1971; Dean, 1978; Harville and Fritz, 1986; same or nearly the same age from different subbasins show Petrychenko, 1989). various degree of sulfate depletion and that the intensity of 512 Geochemistry of Evaporites and Evolution of Seawater sulfate depletion can vary strongly within the same basin (Ayora 5. The polyhalitization of the previously deposited gypsum or et al., 2001; Garc´ıa-Veigas et al., 1995). A number of hypotheses anhydrite (Braitsch, 1971; Hardie, 1984; Harville and Fritz, were suggested to explain the Mg sulfate deficiency by modifi- 1986; Hite, 1985). cation of seawater brine in the evaporite environment, that is, The polyhalite (2CaSO4 • MgSO4 • K2SO4 • 2H2O) can form assuming that MgSO4-poor salts represent only nonmarine-fed from gypsum (CaSO • 2H O) according to the reaction evaporites (Garrett, 1996; Hardie, 1984). 4 2 (Hardie, 1984): Two of the simplest ways are considered here to produce 2 MgSO4-poor brine from seawater. First is to remove SO4 À, 2 2 2CaSO 2H O 2Kþ Mg þ 2SO À 2 4 2 s aq aq 4 aq and the second is to add Ca þ, which should lead to the ð Þ þ ð Þ þ ð Þ þ ð Þ 2CaSO MgSO K SO 2H O 2H O [12] 2 4 4 2 4 2 s 2 l • ð Þ ð Þ additional removal of SO4 À trapped in the gypsum (CaSO4 ! þ 2H2O) crystallizing before K–Mg salts. The following major or from anhydrite (CaSO4) according to the reaction (Braitsch processes were suggested as responsible for such sulfate and Kinsman, 1978): depletion: 2 2 2CaSO4 s 2Kþ aq Mg þ aq 2SO4 À aq 2H2O l ð Þ þ ð Þ þ ð Þ þ ð Þþ ð Þ 1. The bacterial sulfate reduction and escape of S in the form 2CaSO4 MgSO4 K2SO4 2H2O s [13] ! ð Þ of H2S to the atmosphere (Sonnenfeld, 1984). 2. The addition of Ca from the nonmarine sources external to This process should remove not only sulfate but also mag- the basin such as: nesium and potassium ions from the brine. Hardie (1984) (a) calcium bicarbonate-rich river water (Valyashko, suggested that polyhalite crystallization should precede the 1972b) or deposition of the five-component system and successfully modeled the sulfate-deficient crystallization path under such (b) CaCl2-rich hydrothermal waters, particularly in rift zones (Hardie, 1990). an assumption (see Harvie et al., 1980). 3. The additional flux of seawater directly to halite brine The presented hypotheses were questioned in the following (Hite, 1985), which according to Holser (1979a), can lead ways: Sulfate reduction was criticized as unrealistic because to precipitation of polyhalite (2CaSO4 • MgSO4 • K2SO4 • the rate was too low for this process and a great volume of 2H2O). 2 organic matter would be required as the energy source for the 4. The addition of Ca þ via dolomitization of the previously deposited Ca carbonate (Hite, 1985; Kendall, 1989, 2005; activity of sulfate-reducing bacteria (Hardie, 1985; Hite, 1985). Levy, 1977; Schoenherr et al., 2008) (note that primary Sulfate reduction commonly takes place in pore waters and 2 does not affect the equilibrium concentration in the brine direct precipitation of dolomite would only remove Ca þ 2 above the sediments. Similar to dolomitization (discussed and Mg þ from the brine). in the succeeding text), it is a postdepositional process unable The dolomitization of calcite or aragonite (CaCO3) pro- 2 to influence the crystallization path of evaporating basinal duces dolomite (CaMg(CO3)2) and liberates Ca þ ions following the ideal reaction: brines (Hardie, 1985). Furthermore, Petrychenko (1989, p. 12) noted that H2S is lacking among gases present in inclu- 2 2 Mg þ aq 2CaCO3 s CaMg CO3 2 s Ca þ aq [7] sions in diagenetic halites suggesting the lack of any bacterial ð Þ þ ð Þ ! ð Þ ð Þ þ ð Þ 2 sulfate reduction processes in pore waters (see also Kovalevych These Ca þ ions combine with sulfate ions to precipitate et al., 2006a; Petrychenko et al., 2005; Siemann and more gypsum (CaSO4 • 2H2O) or anhydrite (CaSO4) and Ellendorff, 2001). thus lower the content of sulfate in the brine: The influx of calcium bicarbonate-dominated river waters 2 2 Ca þ aq SO4 À aq CaSO4 s [8] to evaporite basins is an expected process. In about 90% of ð Þ þ ð Þ ! ð Þ 2 2 2 major rivers on Earth, Ca þ and HCO3À are the most abundant Ca þ aq SO4 À aq 2H2O l CaSO4 2H2O s [9] 2 ð Þ þ ð Þ þ ð Þ ! ð Þ ions; in the remaining rivers, Naþ, CIÀ, or SO4 À are dominant All together, the process should lead to a decrease in (Meybeck, 1976). It requires improbably large amounts of 2 2 2 both Mg þ and SO4 À and an increase in Ca þ ions in the such waters to supply enough calcium, because meteoric brine (e.g., Hardie, 1987). According to other authors, the waters are highly diluted (the contents of dissolved solids 1 dolomitization is also represented by the supplementary commonly range from 10 to 1000 mg lÀ ; Meybeck, 1976, reaction (Machel, 2004, with references), which does not 2003), and therefore, it seems unrealistic (Garrett, 1970; Hite, 2 liberate Ca þ ions: 1985). The influx of river waters would add not only calcium

2 2 and carbonate but sometimes also sulfate ions. Mg þ aq CO3 À aq CaCO3 s CaMg CO3 2 s [10] ð Þ þ ð Þ þ ð Þ ! ð Þ ð Þ The influence of Ca from outside of the depositional basin and the reactions [7] and [10] can be written together as appears to be more realistic in case of smaller basins with follows: limited inflow of seawater or when Ca is supplied by high-

2 2 salinity hydrothermal sources (Hardie, 1990). In several recent Mg þ aq 2 x CO3 À aq xCaCO3 s ð Þ þ ð À Þ ð Þ þ 2 ð Þ pluvial evaporite basins, supplied with meteoric waters CaMg CO3 2 s 1 x Ca þ aq [11] ! ð Þ ð Þ þ ð À Þ ð Þ together with the addition of CaCl2 saline waters from deep According to Machel (2004), reaction [11] more realis- hydrothermal sources, they were shown to cause the brine 2 tically expresses how much Ca þ is exported during modification toward the Ca–Cl field (Lowenstein and

dolomitization, which depends on particular case Risacher, 2009). Also, the CaCl2 brines can be carried to the characterized by parameter x. surface by convective circulation promoted by thermal Geochemistry of Evaporites and Evolution of Seawater 513 subsurface source or by topographically driven circulation the dolomitization hypothesis (e.g., Kovalevych and Vovnyuk, (Hardie, 1990). In this case, however, the effect of the higher 2010). salinity of the source waters is apparently opposite from that of Except for the topographically driven flow, the other more marginal marine basins (much more salts are carried in by realistic mechanism for supplying the mineralized water mod- hydrothermal sources than by meteoric waters). ifying the chemistry of the host water in the basin is thermal Polyhalitization was criticized by Hite (1985) who believed convection, driven by subsurface heat sources, commonly that polyhalite is found in most evaporites, with a few excep- transporting Ca–Cl-rich hydrothermal brine up to the surface tions, in amounts too small to be responsible for effective (as documented by Lowenstein and Risacher, 2009). modification of the basinal brine composition. Although Stewart (1963) considered polyhalite as the third most abun- 9.17.17.2 Sulfate Deficiency as a Record of Ancient dant sulfate in marine evaporites, after gypsum and anhydrite, Seawater Composition and Garrett (1970), together with kainite, as the third most For the past few decades, a growing amount of evidence has abundant salt mineral containing potash, after sylvite and clearly suggested that the sulfate deficiency is not merely the result carnallite, Hite (1985) believed that the polyhalite is mostly a of secondary changes or deposition from nonmarine brine but late diagenetic product and that the host brine layer remained the primary feature inherited from the host chemistry of ancient relatively unaffected by such polyhalitization. seawaters. The justified supposition – that the chemistry of Paleo- Dolomitization appears to be the best explanation for zoic and Mesozoic oceans was quite different than today – has sulfate deficiency favored by some authors (Hite, 1985; emerged in the late 1970s and 1980s from studies of carbonates. Holland, 1978; Kendall, 2005). Hardie (1998) pointed out In 1975, Sandberg proved that aragonite ooids with radial struc- on several difficulties in this explanation: ture from the Great Salt Lake are primary forms, thus also proving that the common ancient radial calcite ooids are primary as well, 1. Laboratory dolomitization of calcite or aragonite has not not secondary (from ‘recrystallization’ of aragonite) as it was been achieved at normal surface temperatures (however, a thought before. Consequently, it appears that the distribution of heliothermal effect can facilitate the dolomitization; primary calcite and aragonite ooids in geologic time is apparently Aharon et al., 1977). regular (Figure 17(f)) and this realization was the basis for dis- 2. The dolomitization in marine environments also precedes tinction of ‘aragonite’ and ‘calcite’ seas, the former precipitating with difficulty, and usually, it produces calcian dolomites aragonite, the latter calcite as the commonest mineral (Hardie, mostly precipitated as cements and not being a replacement 1996; Lowenstein et al., 2003; Sandberg, 1983; Wilkinson et al., product (Hardie, 1987; Pierre et al., 1984a). 1985). 3. This modern ‘dolomitization’ has not produced CaCl 2 Further studies showed that the main factor that presumably brines (Hardie, 1987; but see Levy, 1977; Wood et al., promoted the basic difference in Ca carbonate mineralogy in 2002, 2005). the ancient oceans was the changing molar proportions of 4. To be effective in sulfate ‘elimination,’ dolomitization 2 2 Mg þ/Ca þ ions in the evolving seawater, oscillating between should precede the gypsum precipitation (Holland et al., 1 and 5 (Figure 17(e); Steuber and Rauch, 2005). Both 1996). Hardie (1998) noted, however, that in hypersaline experimental and observed geochemical data from various sedi- marine environment of the Persian Gulf sabkhas, calcian mentary environments strongly suggest that when the molar dolomite forms from hypersaline MgSO4-rich seawater 2 2 Mg þ/Ca þ ratio in seawater was high (>2) – the preferred min- brines only after Ca sulfate has been precipitated (see eralogy was aragonite (and high-Mg calcite), and when low ( 2) – also Levy, 1977; Pierre et al., 1984a). In the same way, calcite (Hardie, 1996, 2003; Lowenstein et al., 2001; Stanley and during seepage reflux of such brines, dolomite forms in Hardie, 1998, 1999). Some other factors, such as concentration of the bottom sediments of the Solar Lake in Sinai (Aharon 2 SO À (Bots et al., 2011), however, could also control the et al., 1977). Gypsum precipitation “raises the Mg/Ca ratio 4 aragonite–calcite mineralogy (Holland et al., 1996; Ries, 2010; well above that of modern seawater, which in turn promotes Zhuravlev and Wood, 2009). A growing amount of evidence the formation of a dolomite-like phase” (Hardie, 1998, suggests that evolving seawater Mg/Ca ratio strongly influenced p. 91). and also controlled the carbonate mineralogy of skeletal organ- 5. The next problem with dolomitization is how the pore isms in Phanerozoic supporting the concept of secular fluctua- waters modified by dolomitization can be supplied from tions of Mg/Ca ratio in seawater (Porter, 2010; Ries, 2009, 2010; the subsurface up to the evaporite basin waters. Kendall Ries et al., 2008; Stanley, 2006; Stanley et al., 2002). (1989) suggested the reasonable model of such a process, The mineralogy of ancient marine K–Mg salts shows that based on topographically driven hydrological mechanism, the KCl-rich (sulfate-deficient) evaporites and the MgSO -rich where deep formation waters ascending into evaporite 4 evaporites are also regularly distributed in time, apparently basin of the salina type (Figure 4(b)), with a deeply coinciding or overlapping with calcite and aragonite sea time depressed water level, are able to dolomitize the carbonates intervals. It seems that during the aragonite seas, as today, in the subsurface, and then inflow into the basin from MgSO salts (such as polyhalite and kieserite) were the main artesian sources. Due to the mixing of these modified 4 potash minerals, while MgSO -poor KCl-rich potash salts were waters with basinal waters or brines, gypsum can be 4 dominant in time of calcite seas. The appearance of KCl evap- precipitated. orites coincides with the global high-sea-level periods in the The lack of any volumetrically significant dolomites in Cretaceous and some earlier parts of the Phanerozoic (Hardie, many sulfate-deficient evaporite basins casts serious doubt in 1996). Two currently discussed and tested hypotheses explain 514 Geochemistry of Evaporites and Evolution of Seawater this coincidence, suggesting that the major driving forces of the 1977; Holser et al., 1989, p. 31). Marginal marine evaporites compositional changes of seawater were would be supplied with water from the upper portion only and in such a case the restoration of the chemical composition of 1. fluctuations in spreading rate and rate of influx/sequestration the ocean from the evaporites would concern the upper box of Mg and Ca during the hydrothermal circulation in mid- only. Recently, Garcı´a-Veigas et al. (2011), investigating the ocean ridges (Hardie, 1996; Spencer and Hardie, 1990) and geochemistry of Zechstein cyclothems, suggested that the Z2 2. increased dolomitization of carbonate platforms during salts were deposited from upwelling of anoxic bottom seawa- sea-level highstands (Holland, 2005; see, e.g., Steuber and ters during overturn event of the stratified anoxic Panthalassa Rauch, 2005, for further comments and information). ocean (circum-Pangean ocean), and the result of their work coincides with conclusions by Luo et al. (2010). The essential problem currently studied is how much Mg is The restoration of the ancient seawater chemistry can able to ‘escape’ from ocean water due to its hydrothermal reac- be made indirectly from (1) the mineralogy of marine evapo- tion with the basaltic crust, in comparison with the amount of rites, (2) the observed vertical sequence of salt minerals in a Mg that is consumed via dolomitization of ocean sediments section, (3) the geochemistry of primary evaporite minerals (Arvidson et al., 2011; Elderfield and Schultz, 1996). The other (trace, minor, and REE elements and isotopic composition of problem is geochemical evolution of sulfates in the seawater; for these minerals) and also ‘fossil’ pore fluids, and (4) more example, Canfield and Farquhar (2009) suggested recently that it directly and precisely from the analysis of chemical composi- was bioturbation, which appeared in the Phanerozoic, which tion and other geochemical features of fluid inclusions in caused a severalfold increase in seawater sulfate concentration, primary salt minerals. contributing to appearance of sulfate marine evaporites. The crucial element in the validation of the new emerging ideas is the reconstruction of the chemistry of ancient oceans 9.17.18.1 Implications from Evaporite Mineralogy from the available sedimentological record, and in this respect, and from Usiglio Sequence the evaporites became a target of the very intensive studies over the past few decades. The calculation of the possible limits in the concentration of major seawater ions implied from the mineralogy of evaporites and from the preservation of the Usiglio sequence of crystallization (Ca carbonate Ca sulfate Na chloride facies) was ! ! 9.17.18 Ancient Ocean Chemistry Interpreted from attempted by Holland (1972, 1984) and Kovalevych (1990) Evaporites based on chemical characteristics of modern seawater. The lack of sodium carbonates (trona) and bicarbonates, in Evaporites themselves supply the crucial, most significant, and all known Phanerozoic marine evaporites, implies that during direct information on the chemistry of ancient oceans (Berner, the early stages of evaporation nearly all of the HCO3À has 2004; Hardie, 1984). For example, owing to the fact that been removed by CaCO3 precipitation (Holland, 1984). In isotopic fractionation of sulfur during precipitation of gypsum other words, the evaporite precipitation after calcite precipita- and anhydrite is negligible (Claypool et al., 1980; Hansen and tion did not pass along the chemical divide containing carbon- Wallmann, 2003; Holser, 1979b; Seal et al., 2000), except in ate minerals but followed the sulfate branch (Figures 10(a) the later stages of evaporite crystallization within the halite and and 14). This would imply that in the Phanerozoic seawater,

K–Mg sulfate fields (Strauss, 1997), the isotopic composition mCa 2 has always exceeded mHCO3 /2 (Holland, 1984). If the 2 þ À 2 of sulfur in marine sulfate evaporites has been used to trace the Ca þ concentration ever fell below half that of HCO3À, Ca þ isotopic evolution of sulfur in the Phanerozoic seawater would be exhausted during CaCO3 deposition. “If evaporating (Kampschulte and Strauss, 2004, with references). Based on seawater is to precipitate first calcium carbonate and then this fact, it can be assumed that marine evaporites record the calcium sulfate then the calcium ion concentration must sulfur isotopic composition of ancient seawater very well exceed one half the bicarbonate ion concentration. If this (Hansen and Wallmann, 2003). were not the case, precipitation of calcium carbonate would Before the discussion of the use of evaporites in interpreting exhaust the calcium ions in seawater leaving none to enter the chemistry of ancient oceans, it is necessary to pay some gypsum” (Walker, 1983, p. 520). 2 attention to the ocean itself. The upper limit for Ca þ concentration in seawater is set by The first assumption was that the ancient oceans (no the solubility of gypsum and the fact that seawater is undersat- matter what their composition) had a constant uniform com- urated with respect to this mineral (Holland, 1972). According 2 position worldwide and that they obeyed Marcet’s principle to Holland (1972), a threefold increase in the Ca þ concentra- (Forschhammer, 1865), behaving much like today’s ocean, tion of the modern seawater is enough to produce an ocean, which is a consequence of its continuous mixing. The idea which is saturated with gypsum, in which case the gypsum that ancient oceans were not fully mixed but permanently would be an equally common marine mineral as calcite. Fossil stratified however is commonly applied and accepted in record indicates, however, that gypsum deposition always modeling of the Archean, Proterozoic, and Phanerozoic oceans required some degree of seawater evaporation, so this upper 2 (e.g., Huston and Logan, 2004; Strauss, 1997). Stratification of limit for Ca þ concentration was never reached in any ancient ancient oceans was more than likely (Reddy and Evans, 2009). seawater comparable with the modern one. In a similar way, Geochemical modeling of the stratified oceans requires a two the concentration of Na and Cl in ancient oceans would be part, stratified ocean model with chemical (and isotopic) com- much higher than in the present ocean because of the high position different within each part (‘a two-box model’; Holser, solubility of NaCl and high concentrations required for its Geochemistry of Evaporites and Evolution of Seawater 515

Bischofite Mg Tachyhydrite Bischofite Ca II III

Sakiite (hexahydrite)Epsomite Carnallite I Kainite

Leonite

Bloedite Sylvite Sylvite

Picromerite

Glaserite Thenardite

K SO 4 2 (a)

g l-1 g l-1 20 200

16 160

12 120

6 60 2.77

21.0 1.33 -

2 15.5 104.1 11.03 - 0.15

4 191.2 19.83

2 2+ traces 0.40

+ + -

4 - - 2+ 3 - + 0.42 3

3.3 SO traces Na Cl Cl K Mg Na

4 SO + Mg 2+ 2+ K HCO Ca HCO Ca 0 0 (b) (c)

g l-1 g l-1 200 200

160 160

120 120

60 60 104.1 15.5 104.1

traces 191.2

191.2

traces + traces 15.5 -

- 2+

10.0 traces - 3

- 3.3 Cl Na 2 traces 2+

Cl Na 40 -

40 3

4 + 2+ 2 Mg 3.3

4 2+ K + Mg SO HCO Ca K HCO SO Ca 0 0 (d) (e)

Figure 14 (a) K–Mg–SO4 and Mg–Ca–2K type of Ja¨necke diagrams, and three hypothetical standard seawater brines: modern, sulfate one (I), intermediate (II), and chloride one (III); after Kovalevych (1990). (b) Ionic composition of modern seawater; (c) ionic composition of evaporating modern seawater brine at the start of the halite precipitation, representing standard sulfate brine (I); (d) ionic composition of evaporating hypothetical intermediate seawater brine at the start of the halite precipitation (II); and (e) ionic composition of evaporating hypothetical chloride seawater brine at the start of the halite precipitation (III). Redrawn from Kovalevych VM (1990) Salt Deposition and Chemical Evolution of the Ocean in Phanerozoic. 155 pp. Kyiv: Naukova dumka (in Russian), based on data from Valyashko (1962). 516 Geochemistry of Evaporites and Evolution of Seawater saturation state. The oceans would be far from saturation with 9.17.18.2 Implications of Primary Evaporite Minerals NaCl even if all known halite deposits on Earth were dissolved (Excluding Implications from Fluid Inclusions) (Holland, 1978, 1984), in which case it would result only in a The original composition of the water, salinity and its fluctua- doubled salinity ( 70%, Knauth, 2011), whereas halite satu- tions, can be interpreted to some extent from minor and trace ration of the modern evaporating seawater is at 320%. Salin- element content both in ‘fossil’ brine (e.g., Vengosh et al., 2000; ity of 70% is not enough for the precipitation of halite in the Boschetti et al., 2011b) and in common primary evaporite min- ocean and such copious precipitation was not recorded. 2 erals (gypsum, anhydrite, and halite). In the latter, more common The lower limit for Ca þ concentration in seawater can be case, the interpretation is based on known distribution coeffi- established from the fact that the precipitation of gypsum always cients (Dean and Tung, 1974; Holser, 1979b; Kushnir, 1980, precedes halite in modern and ancient marine evaporites 2 1982a; Lu et al., 2001, 2002; Ort´ı et al., 1984a; Rosell et al., (Holland, 1972). If Ca þ concentration in modern seawater 1998), particularly for Sr, Na, K, and Mg in case of Ca sulfates were reduced by a factor of 30 (thirty), this water would become (Playa` et al., 2007), and Br in case of halite (Holser, 1979b; saturated simultaneously with gypsum and halite during evapo- Valyashko, 1956; Zherebtsova and Volkova, 1966a,b). An rite concentration. If this factor were larger (>30), then halite attempt at restoration of the chemical composition of Messinian would start to crystallize before gypsum during evaporite con- brine, based on trace element concentration in gypsum and centration (Holland, 1972), that is, in a way different than pre- anhydrite, was made by Kushnir (1982b) (see comments by Lu dicted by the Usiglio sequence. On the other hand, “the et al., 1997) and Mesoproterozoic seawater by Kah et al. (2001). precipitation of gypsum before halite requires a minimum sul- 2 Geochemical data, and in particular REE content and iso- fate concentration of 2.5 mM at a present day Ca þ concentra- topic composition of minerals, can help to distinguish the tion of 10 mM (to reach the solubility product of gypsum of marine from nonmarine evaporites and are discussed in 25 mM” (Holland, 1984; Reuschel et al., 2012, p. 85). Section 9.17.19.3 (in the succeeding text). The other limits can be established from the fact that evaporite gypsum deposition nearly ceases near the start of halite 2 crystallization because the Ca þ ions necessary for gypsum 2 precipitation are nearly exhausted at just that time. If the Ca þ 9.17.19 Recognition of Ancient Marine Evaporites 2 concentration in seawater ever exceeds the sum of SO4 À concentration and half of HCO3À concentration, the late salts The crucial point in the interpretation of the ancient evaporites 2 2 would be enriched in Ca þ and depleted in SO4 À (Holland, and the ancient seawater chemistry (composition) from these 1972). Holland (1972) also claimed that the presence of pri- evaporite deposits is to properly reveal the marine geochemical mary dolomite in marine carbonates implies that the ratio of signal preserved in the marine marginal evaporite basin, 2 2 Mg þ concentration to Ca þ concentration has never been less which, as previously discussed, can be always modified by than one in seawater. influx of some nonmarine waters. How to define, understand, The methodology outlined by Holland (1972) was used by and recognize ‘marine’ features in ancient evaporite deposits is, Walker (1983) and discussed by Grotzinger and Kasting (1993) however, not an easy task. to establish ranges of seawater composition in the Precambrian. Braitsch and Kinsman (1978) distinguished the ‘normal Holland et al. (1986) summarized many previous estimates, marine’ and the ‘modified marine’ evaporites among the pri- including works by Eugster and Jones (1979), Eugster et al. mary marine evaporite deposits, with transitional types known (1980), and Harvie et al. (1980), and claimed that the concen- only from a few cases. Normal marine evaporites were defined tration of nearly all of the major seawater ions could have varied as those “with magnesium sulfates and complex salts such as by a factor of 2 to 3 (in either direction) without a modification polyhalite, kainite, langbeinite, but without primary sylvite,” of the Usiglio sequence of crystallization. Kovalevych (1990) whereas the modified marine evaporites are “without summarized and supplemented these data (Table 7). these minerals but with primary sylvite.” As already mentioned, the ongoing studies of the saline giants and the geo- Table 7 The permissible ranges of concentrations of equivalents of chemistry of ancient seawater led to the current opinion that 1 major ions in ocean water during Phanerozoic (in mol kgÀ ) (after the ‘modified marine’ evaporites were likely precipitated from Holland, 1974, interpreted and supplemented by Kovalevych, 1990) ancient, unaltered seawaters that were different than today’s seawater. Ion Ancient ocean Present ocean One of the problems faced in geochemical studies of evap-

Naþ (0.230)–0.950 0.468 orites lies in distinguishing the marine (originated from sea- ClÀ (0.270)–1.100 0.546 water) from continental evaporites derived from the waters 2 Mg þ 0.01–(0.4) 0.107 similar to seawater in composition, which give the same struc- Kþ (0.005)–(0.02) 0.01 ture and order of precipitated minerals as seawater. The best 2 Ca þ 0.002–0.06 0.02 example is the Great Salt Lake in Utah, United States, with [0.02–0.06] brine of continental derivation, very similar to seawater 2 SO4 À 0.04–0.6 0.056 brine. Ancient marine and similar continental evaporites can [0.02–0.056] be identical in mineralogy and facies distribution. HCO À 0.001–0.02 0.002 3 In attempting to clarify the problem, Hardie (1984, p. 203) 0.002–0.006 defined the autochthonous marine evaporite as “a sedimentary In parentheses () – very approximate data. saline mineral deposit formed in situ in a marine or marginal In square brackets [ ] – according to interpretation by Kovalevych (1990). marine depositional environment by evaporation of ocean water Geochemistry of Evaporites and Evolution of Seawater 517 with the composition of average modern seawater, or at least with borate minerals (note however that tachyhydrite is expected the composition similar enough to modern seawater to give the to precipitate from Cretaceous seawater brines extremely same mineral sequence on evaporation.” This definition was enriched in Ca; Timofeeff et al., 2006); and (8) absence of chosen to serve for “the purpose of revealing, quantitatively, minerals that normally crystallize from SO4-rich brines (such important differences between modern and ancient ocean as seawater) but not from Ca–Cl brines (Hardie, 1990; Low- water chemistry” (Hardie, 1984, p. 204). Hardie (1984) further enstein and Risacher, 2009; Lowenstein et al., 1989). Based on suggested the following sedimentological, mineralogical, and these criteria, Hardie (1990) pointed out several ancient chemical criteria, which can help to distinguish the marine (as ‘marine’ evaporite basins as representing deposition from he defined them) and nonmarine evaporites: extremely modified seawater, unsuitable for geochemical studies of ancient ocean chemistry (Table 10). 1. The nature of the associated nonevaporite facies 2. Kinds of fossils (if present) 3. Kinds of primary saline minerals 9.17.19.2 Mineralogical Criteria 4. The association and vertical succession of such minerals Smoot and Lowenstein (1991) pointed out that distinguishing (sequence of crystallization) marine from nonmarine evaporites according to mineralogical 5. Geochemical characteristics of such minerals: trace ele- criteria is, in practice, nearly impossible. The ideal sequence of ments, isotope geochemistry, and fluid inclusions crystallization expected for seawater cannot be produced in real environments because of reasons such as (1) the changing supply of seawater and syndepositional reactions brine–min- 9.17.19.1 Sedimentological Criteria erals, (2) the change in chemistry of seawater by mixing with Sedimentological and faunal criteria are not always univocal. other waters, and (3) the ancient seawater “may not have Sedimentological criteria indicating the nonmarine evaporites always had the same composition” (Smoot and Lowenstein, include the geographic setting, the surrounding and intercalat- 1991, p. 304). ing of evaporites exclusively with continental facies, and the Mineralogical criteria commonly cannot be helpful because presence of nonmarine fossils. However, the reverse, that is, the most common marine evaporite minerals – gypsum and that evaporite deposits intercalated with marine sediments are halite – are also the most common in nonmarine evaporites also marine, is not necessarily valid – this is clear from the (Hardie, 1984; Smoot and Lowenstein, 1991). Furthermore, nature of every marginal evaporite basin (Hardie, 1984). some minerals considered as typical of the continental brines In marine evaporites, during the complete desiccation and also precipitate from seawater brine and in marine environments, isolation from the sea, continental evaporite facies can develop for example, mirabilite or glauberite (Hardie, 1985). In particular, in the same area immediately under/overlying marine facies such minerals as glauberite (CaSO4 • Na2SO4), polyhalite (Smoot and Lowenstein, 1991). Naturally, mixed water evap- (K2SO4 • MgSO4 • 2CaSO4 • 2H2O), epsomite (MgSO4 • 7H2O), orites are easy to imagine in these settings. bloedite (Na2SO4 • MgSO4 • 4H2O), sylvite (KCl), and tachyhy- Many sedimentary marine and continental evaporite facies drite (CaCl2 • 2MgCl2 • 12H2O) are not diagnostic for marine/non- are very similar and difficult to differentiate. One of the rare marine settings (Eugster, 1980). There are, however, a few mineral processes and facies not expected in continental lake sediments assemblages that cannot crystallize from recent seawater without is tidal fluctuations and related deposits (Smoot and major modification by specific nonmarine inflow and that today Lowenstein, 1991). However, the lack of evidence of tidal occur in saline lake environments only: (1) Na carbonate mine- deposits does not exclude the marine character of the basin, rals, such as trona, nahcolite, and shortite; (2) Na silicate min- which can be surprisingly similar to that in lakes (in fact, many erals, such as magadiite and kenyaite; and (3) Na or Ca borate ‘marine’ basins are just lakes supplied with seawater entering minerals (Smoot and Lowenstein, 1991). The first assemblage of the depression through a barrier; Figure 4(b); Ba˛bel, 2004b). minerals is however expected to form from the evaporation of the In the case of ancient continental evaporite basins, by def- hypothetical Archean–Proterozoic soda ocean water (Kempe and inition supplied with meteoric waters, the possible influx of Degens, 1985). Eugster (1980) listed the following carbonate hydrothermal Ca–Cl waters can be detected by the following minerals exclusive to continental evaporites: trona (NaH observations: (1) evidences of the volcanism and faulting con- CO3 • Na2CO3 • 2H2O), gaylussite (CaCO3 • Na2CO3 • 5H2O), bur- temporaneous with sedimentation in evaporite basin; (2) pres- keite (Na2CO3 • 2Na2SO4), northupite (Na2CO3 • MgCO3 • NaCl), ence of intruded plutonic rocks below the evaporites; hanksite (9NaSO4 • 2Na2CO3 • KCl), and dawsonite (NaAl (3) presence of metamorphic rocks suggesting the regional (OH)2CO3). hydrothermal heating (as in case of the Salton Sea, USA); (4) the hydrothermal Fe–Mn–Cu–Pb–Zn–Ba mineralization in 9.17.19.3 Geochemical Criteria fractures suggesting the circulation of hydrothermal fluids near the surface; (5) elevated concentrations of Ca–Cl in fluid Geochemical criteria useful for establishing the distinction inclusions of primary evaporite minerals; (6) the relatively between marine and nonmarine evaporites include the trace high concentrations of trace elements, such as Fe, Mn, Cu, elements (e.g., Br and Rb contents in chloride minerals – Pb, Zn, and Ba, both within the crystals and in the fluid halite, sylvite, and carnallite), isotope (d18O, d34S, or inclusions of evaporite minerals – calcite, dolomite, gypsum/ 87Sr/86Sr and 34S/32S ratios in sulfate salts, 37Cl/35Cl and d11B anhydrite, and halite, sylvite, and carnallite; (7) presence of in chlorides), and fluid inclusion studies (e.g., Boschetti et al., minerals typical of Ca–Cl brines – tachyhydrite (CaCl2 • 2011a; Chaudhuri and Clauer, 1992; Chivas, 2007; Denison MgCl2 • 12H2O) and antarcticite (CaCl2 • 6H2O), or Ca–Na and Peryt, 2009; Denison et al., 1998; Eastoe and Peryt, 1999; 518 Geochemistry of Evaporites and Evolution of Seawater

Eastoe et al., 2007; Eggenkamp et al., 1995; Flecker and Ellam, the chemistry of the evaporating ancient brines, and halite 2006; Flecker et al., 2002; Holser, 1979b, 1992; Kirkland et al., appears to be the best mineral for such a study. Ancient halite 1995, 2000; Kloppmann et al., 2001; Lu and Meyers, 2003; Lu is much better preserved than the other common marine evap- et al., 1997; Matano et al., 2005; Palmer et al., 2004; Paris et al., orite mineral – gypsum, which becomes altered to anhydrite by 2010; Pierre, 1988; Pierre et al., 1984a; Playa` et al., 2000; Raab dehydration during burial (Jowett et al., 1993). Inclusion stud- and Spiro, 1991; Raup and Hite, 1996; Schreiber and El ies, in gypsum, are rare and were made only in primary Tertiary Tabakh, 2000; Seal et al., 2000; Taberner et al., 2000; selenites. Thus far, analyses from the gypsum of marginal Toulkeridis et al., 1998; Toulkeridis et al., 1998; Utrilla et al., marine evaporite basins showed very low values of salinity, 1992; Vengosh et al., 1992). The isotopic composition of all are actually outside of the value range for gypsum crystalli- ‘evaporative’ or associated carbonates can be helpful to some zing from seawater brine, and much lower than the standard degree (Magaritz, 1987; Schreiber and El Tabakh, 2000), and 35% seawater salinity (e.g., Attia et al., 1995; Kulchitskaya, 40Ca/42Ca isotope ratios in gypsum can be used for recognition 1982; Peryt, 2001; Petrychenko et al., 1997). In contrast to of the source of inflowing water (Nelson and McCulloch, ancient crystals, fluid inclusion analyses in modern marine 1989). evaporitic gypsum yielded proper salinity values, typical of Trace elements are useful but not unequivocal indicators of salinity range for the precipitation of that mineral from seawa- marine evaporites. It is well known that the quantitative range ter (Sabouraud-Rosset, 1972). of the trace element Br, found both in today’s seawater brines Holser (1963, 1979a) was one of the first who began the and the marine halite, may overlap ranges present in non- study of brines from fluid inclusions in ancient halite and marine brines and halites (Hardie, 1984, 1985; Warren, showed that Mg/Cl and Br/Cl ratios of inclusion brines from 2006). Because of that, and in particular, the values identical the Permian halite are similar to those of modern seawater. or similar to recent marine halites found in ancient halites Later, very detailed studies revealed many features of basinal cannot be used as indicators of marine origin of such halite. halite brines such as pH, Eh, temperature, and composition of The values that are much lower or higher than those present in gases trapped in these brines (Kovalevych, 1990; Petrychenko, today’s halites can only suggest but not prove nonmarine or a 1988). What was more significant is that they proved, without recycled origin of salts (developed from crystallization from any doubt, that the chemical composition of many basinal nonmarine brine or from brine developed from dissolution of waters of marginal marine evaporites preserved in primary marine salts) (for comparison, see Schoenherr et al., 2008). halite inclusions was indeed different from recent seawater Not only bromine but also the other trace elements in solid brine (at the stage of halite saturation). Further advance of solutions within evaporite salts can be misleading in dis- modern analytical techniques has enabled collection of even tinguishing of marine from the nonmarine evaporites more detailed and precise data from many basins, which con- (Hardie, 1984). A similar overlap in range exists, for example, firmed these results. From these studies, a clear picture for marine and nonmarine 34S/32S ratios (Smoot and emerged in late 1980s that the brines in ancient marginal Lowenstein, 1991). REE patterns of concentration in marine halite basins (well before the start of K–Mg salt precip- braitschite (Ca, Na2)O • REE2 • O3 • 12B2O3 • 6H2O) and gypsum itation) were more commonly Na–K–Mg–Ca–Cl type, not were used in order to distinguish the marine from continental Na–K–Mg–Cl–SO4 type as expected for the evaporation of source of brines in evaporite deposits by Raup (1968), Toulkeridis modern seawater to halite precipitation field (see Das et al., et al. (1998) and Playa` et al. (2007). 1990, and summaries in Horita et al., 1996, 2002; Kovalevych High-quality trace element studies, however, require special et al., 1998a,b; Horita and Holland, 1998; Holland, 2003). laboratory techniques to remove contamination coming Additional studies of halite inclusion brines have supplied from fluid inclusions dispersed within the crystals (Lu et al., more and more data confirming this picture (Khmelevska 1997; Moretto, 1988; Playa` and Rosell, 2005; Raup and Hite, et al., 2000; Kovalevych et al., 2006a,b; Petrychenko et al., 1996; Schro¨der et al., 2003). 2005, 2012; Timofeeff et al., 2006). It also appears that many From the listed studies, only the fluid inclusion analysis halite basins lacking K–Mg salts follow the same general trends gives direct information about the brine chemistry and tem- and most commonly evidence a Na–K–Mg–Ca–Cl type of perature at the time of crystal growth (Holser, 1979a; Knauth brine in primary halite fluid inclusions, not Mg sulfate brine and Beeunas, 1986; Knauth and Roberts, 1991; Roedder, 1984; similar to modern seawater brine, as it was expected earlier Siemann and Ellendorff, 2001; Smoot and Lowenstein, 1991; (e.g., Hite, 1985). This was a new and important fact. The Timofeeff et al., 2001). The specific criteria for recognition of simplest explanation of that observation is that the composi- the marine character of brines in ancient halite fluid inclusions tion of the ocean evolved with time, and such an interpretation are described further in the text. was early accepted by Petrychenko (1988) and Kovalevych (1990), among others. All these studies clearly showed that the ancient Mg sulfate-poor evaporites were not the product of 9.17.20 Fluid Inclusions Reveal the Composition secondary postdepositional replacement processes, and the of Ancient Brines halite brines in many ancient evaporite basins were already Mg sulfate-deficient at the beginning of halite precipitation, Analyses of primary fluid inclusions supply the best, reliable, which excludes the possibility of postdepositional replace- and direct information about the chemical composition of ments. The problem then appeared as how to illuminate brine from which the salt crystallized (Hardie, 1984; Holser, the chemical composition of the ancient seawater more pre- 1979a). The advance of the modern analytical techniques has cisely from the studies of halite fluid inclusions. The next target enabled considerable progress in gaining new information on and challenge in the study of fluid inclusions in ‘marine’ halite Geochemistry of Evaporites and Evolution of Seawater 519 is how to recognize the composition of the ancient seawater from the chemical composition of brine trapped in the fluid inclusions. One of the first attempts, before the use of numerical modeling described in the succeeding text, was made by Kovalevych (1990) who introduced the concept of ‘standard’ seawater and ‘standard’ seawater brines. Following the lead of some earlier investigators (Valyashko, 1962, and others), he suggested that ancient Phanerozoic seawater evolved in between three basic and ultimate types called sulfate, intermediate, and chloro-calcium waters and established the composition of major ions in these seawaters (except for the sulfate type, which contained the same array of ions as in modern seawater). He assumed, partly because of the very high residence time of some ions and also because there was no evidence concerning the scale of their variations through time, 2 that the concentrations of major ions ClÀ, Naþ, Kþ, and Mg þ are the same in all three standard seawaters. We now know that 2 the concentration of Mg þ surely can vary through time because this ion is readily removed from seawater during hydrothermal circulation of seawater through mid-ocean ridges. However, at the same time, confusing the issue, the 2 2 concentrations of the remaining SO4 À, Ca þ, and HCO3À varied systematically. Kovalevych then calculated the composition of the seawater brines of the three particular seawater types at the beginning of each halite precipitation stage and drew the points of the three hypothetical standard seawater brines on the Ja¨necke type of diagrams (Figure 14; see also Kovalevych et al., 1998b).

Figure 15 Primary growth zoning of the halite cube faces, created by 9.17.20.1 Criteria for Seawater Recognition in Halite bands of fluid inclusions, Bochnia Salt Mine, upper Zuber deposits Fluid Inclusions (corridor Tesch, level V), the Badenian of the Carpathian Foredeep, Poland, length of the crystal 65 mm, photos courtesy Krzysztof Fluid inclusions in primary halite were used for the identification ¼ of the marine evaporites based on the following test criteria Bukowski. (Horita et al., 2002; Timofeeff et al., 2001; Zimmermann, 2000): show remarkable chemical evolution related to many pro- 1. Sampling of the earliest (first) halite in a precipitation cesses including recycling of salts (see also Petrychenko sequence, that appears just above the last Ca sulfates et al., 2012, for similar interpretation). (gypsum and anhydrite), well before the start of potash 2. Sampling the halites from deposits with features diagnostic salt precipitation, and from the earliest salt cyclothem in a of perennial subaqueous depositional conditions to mini- sequence (Kovalevych, 1990; Kovalevych et al., 1998b). mize the possibilities of syndepositional recycling (Smoot These earliest halites are assumed to have been precipitated and Lowenstein, 1991; Timofeeff et al., 2001). Most com- from the least modified seawater brine in a marine mar- monly fluid inclusions from the first developed ‘chevron’ ginal evaporite basin. Such a halite also eliminates the structures, representing primary growth bands (growth zon- complications of a back reaction of early formed salts with ing) of crystals, are analyzed (Figure 15). The recycling evolved brines and its influence on brine chemistry, which process, that is, dissolution of earlier precipitated salts, may bias the marine signal (Timofeeff et al., 2001). The increases the proportion of the ions derived from the dis- early halite can be additionally recognized by relatively low solution of these salt (e.g., Naþ and ClÀ from halite, Kþ, 2 Br content or other geochemical data (Horita et al., 1996). Mg þ, and ClÀ from carnallite) in the seawater, which then Sampling within the tectonically stable basins that are will have a modified composition. Recycling is so common devoid of carbonate platforms, without an influx of clastic (e.g., Logan, 1987) that it is impossible to exclude it in any deposits, and is close to the seawater inlet into an evaporite marginal marine evaporite basin. The recycling (dissolu- basin is required (Horita et al., 2002). This criterion is tion) of halite (NaCl) and sylvite (KCl) causes the ions crucial in a true recognition of marine signal in ancient Na, Cl, K, and Cl to be added to basinal brines in equal evaporite deposits, and it was proved by Garcı´a-Veigas molar proportions (1:1:1:1) changing the Na/Cl and K/Cl et al. (2011) and Cendo´n et al. (2008) that in the late ratios in these brines. For example, brines in the Qaidam Permian Zechstein basin and Oligocene Mulhouse basin Basin has an elevated concentration of K, up to several in France, only the earliest halites bear relatively unchanged hundred milimolal above the value predicted by the evap- marine brines, whereas the upper parts of each section oration of parent waters, because the dissolution of 520 Geochemistry of Evaporites and Evolution of Seawater

carnallite added K to these basinal brines (Spencer et al., 2002, p. 3734). Additionally, the statistically significant 1990). High Kþ concentration in halite fluid inclusions can number of samples should be analyzed to confirm the result. reflect recycling and syndepositional dissolution of potas- 6. To be sure that the sample and results really, or in the best sium salts. Such inclusions should not be used for the way, reflect the ancient seawater composition, the composi- reconstruction of ancient seawater chemistry (Lowenstein tional changes of the basinal brine should be ruled out by et al., 2005). “Evaporative concentration of such altered complex systematic sedimentological and geochemical stud- seawater will produce brines with a different chemical com- ies within the whole section and basin area. This very rigor- position from brines evolved from pristine seawater” and ous criterion was suggested by a group of authors who halite crystallized from such significantly altered brines proved that in many basins, including those that were sam- “cannot be used for study of ancient seawater chemistry” pled for ancient halite brine analysis and gave ‘positive’ (Timofeeff et al., 2006, p. 1982). However, Timofeeff et al. results, such changes are particularly common phenomena (2006, p. 1982) noted that “the great mass of dissolved salt (Ayora et al., 1994, 1995; Cendo´n et al., 2008; Garc´ıa-Veigas in large brine bodies makes modification of the major-ion et al., 1995). They pointed out that “the detection of brine- chemistry by syndepositional recycling processes or non- rock reactions is not possible by analyzing isolated samples. marine inflow waters less likely than in shallow/ephemeral Reaction detection is only possible when the brine evolution systems.” Nevertheless, commonly analyzed macroscopi- is reconstructed in detail by using systematic fluid-inclusion cally visible chevron structures, with primary fluid inclu- analyses throughout complete sequences and numerical sim- sion bands in halite, are created only in shallow brine ulation of evaporation scenarios. Moreover, this methodol- (Holser, 1979a) but are absent in primary coarse crystalline ogy distinguishes which parts of the evaporite sequences, and clear halite cubes growing at depth down to 250 m in apparently deposited in a marine setting, are in fact formed the Dead Sea (Herut et al., 1998). Timofeeff et al. (2006) by recycling previous evaporites in an endorheic basin” used the additional nonpetrographic criterium to exclude (Ayora et al., 2001, p. 251). Zimmermann (2000) applied the possibility of recycling, which can be used after the fluid other factors that discredited the validity of some analyses inclusion analyses (no. 3 in the succeeding text). and did an exemplary ‘screening’ of the various data 3. “The major ion chemistry of an individual fluid inclusion obtained for Tertiary salt deposits. Horita et al. (2002, p. must lie on the evaporation curve defined by the entire suite 3732) frankly commented that if one follows the criteria of fluid inclusions from the same deposit. Individual fluid listed earlier, “it is difficult, if not impossible, to identify inclusions whose chemical compositions do not fall on the evaporite deposits that meet all these requirements.” Their defined evaporation curve must have formed from screening method included comparison of the halite of the chemically-modified parent seawaters” (Timofeeff et al., same or similar geologic age from different evaporite basins 2006, p. 1982). Such inclusions should be excluded from to determine whether the composition of inclusion brines the calculations of seawater chemistry. The large degree of bears global (i.e., seawater) or rather local or regional signal. scatter in data from halite fluid inclusions suggests that they are not primary in origin (Horita et al., 2002, p. 3737). Zimmermann (2000, 2001) described the other calculations 9.17.20.2 Reconstruction of Ancient Seawater and graphic methods for distinguishing the evaporated sea- Composition from Halite Fluid Inclusions water from other types of brines met in halite inclusions. The reconstruction of the ancient seawater compositions from 4. The comparison of major ion chemistry of halite fluid inclu- 2 2 the composition of brines in fluid inclusions trapped in pri- sions on plots (Naþ, Kþ, and SO À against Mg þ and ClÀ) 4 mary evaporite mineral (halite) requires three distinct study from several geographically separated evaporite basins of the steps (Timofeeff et al., 2001): same age, utilizing a significant number of analyses, will permit the tracking of the evaporation paths in separate 1. An accurate technique for the chemical analysis of basins. If these plots (a) fall along the same distinctive evap- fluid inclusions must be utilized. The methods used for oration path and if (b) the paths for the various basins of the precise halite inclusions investigation were described by same age overlap one another, this will imply that the parent Timofeeff et al. (2000) and reviewed by Vovnyuk and Kova- water had a uniform chemical composition and thus repre- levych (2007) and Kovalevych and Vovnyuk (2010). The sents the true ancient seawater. The overlapping evaporation concentrations of Na and Cl in some halite fluid inclusions paths clearly indicate minimal influence of nonmarine must be calculated (adjusted) with the help of the computer inflow and syndepositional recycling (Lowenstein et al., program by Harvie et al. (1984) (see Timofeeff et al., 2001). 2001; Timofeeff et al., 2001). The criterion of consistency is 2. The establishment, by the use of the rigorous criteria crucial for testing the reliability of the results and it is similar (described in the previous sections), that the fluid inclu- to criterion introduced earlier by Nielsen (1989) for testing sions really contain evaporated seawater, uncontaminated the sulfur isotopic age curve, based on analyses of Ca sulfates by nonmarine inflow and/or syndepositional recycling. from different evaporite basins (Strauss, 1997). 3. The utilization of the method for the backcalculation of 5. The analysis of fluid inclusions requires the use of clearly the chemical composition of seawater from the composi- defined criteria for primary inclusions (Vovnyuk and tion of fluid inclusion brines that have undergone evapo- Kovalevych, 2007). “Primary, single-phase brine inclusions rative concentration and have been modified by the with negative crystal shapes in primary halite in which hop- precipitation of evaporite minerals (such as calcite and pers and chevrons are outlined by alternating bands of gypsum in case of ancient seawaters similar to modern inclusion-rich and -free zones are preferable” (Horita et al., seawater). Geochemistry of Evaporites and Evolution of Seawater 521

This third point is the most difficult test to pass, because EDS and extraction-IC techniques), which required special the reconstruction of original composition of seawater from adjustment with the help of computer modeling calculations halite seawater brine requires the solution of two basic (Timofeeff et al., 2001). difficulties: Lowenstein et al. (2001) analyzed fluid inclusions from late (3a) “Assumptions must be made in defining the degree Precambrian (543–544 Ma, Ara Group, Oman; Schro¨der et al., of evaporation (DE)—that is, the ratio of the concentration 2003; Schoenherr et al., 2008); Early Cambrian (520–540 Ma, of a conservative element in brines to that in the initial Angarskaya Fm., Siberia); Silurian (418–440 Ma, Salina Group, seawater” (see eqn [3]; von Borstel et al., 2000); Michigan, United States, and Carribuddy Group, Western Aus- (3b) “Uncertainties are introduced by the precipitation tralia); Permian (251–258 Ma, Salado Fm., New Mexico, United of mineral phases (carbonates, gypsum/anhydrite, and States); Early Cretaceous (112–124 Ma, Muribeca Fm., Brazil, halite) before and during halite precipitation” (Horita and Loeme Fm., Congo); Late Cretaceous (94–112 Ma, Maha et al., 2002, p. 3734). The modern analytical techniques Sarakham Fm., Laos–Thailand); and some Tertiary evaporite permit detection of the concentration of Br in halite inclu- basins, as well as modern marine halites. All these basins were sion brine. This concentration was used to calculate the DE interpreted as marine in origin, based on geologic criterion. The of the fluid inclusion, under reasonable assumption that Br concentrations of Mg and Na against Cl from fluid inclusions concentration in seawater has not changed during Phaner- were traced on the diagrams, which revealed distinct evaporation ozoic, because Br has residence time in the ocean 100 My paths of the basinal waters (Figure 16). Late Precambrian, Perm- (Horita et al., 2002, but see Leri et al., 2010). Furthermore, ian, and Tertiary paths nearly coincided, and the same feature the data from fluid inclusions suggest that similarly, the showed the Cambrian, Silurian, and Cretaceous paths grouped concentration of K did not change significantly during together differently. These two pathway clusters reflect higher Phanerozoic (Horita et al., 2002) and therefore K concen- amounts of Mg in the evaporating water of the former group tration can also be used as a measure of DE in some cases. than in the latter. What was the most significant – the evapora- The backcalculation is made by a simple trial-and-error tion paths from geographically separate basins of the same age fitting method with the application of the numerical computer overlapped, which was taken as the crucial evidence for the modeling program for evaporating seawater type of brines shared marine derivation of the analyzed basinal brines. All of devised by Harvie et al. (1984). The diagrams produced from the ancient brines showed relatively lower concentrations of Mg geochemical data collected from halite fluid inclusions are than the modern seawater brine, with the late Precambrian and visually compared with those calculated by computer program Permian fluid inclusions closest to modern concentrations under some trial assumptions and the best-fit diagrams are (Lowenstein et al., 2001). found that are chosen to represent the original composition Lowenstein et al. (2001) also established the Mg/Ca ratios of ancient seawater. This methodology was successfully tested (maximum and minimum values for each time interval) of on the recent marine halite deposits (Timofeeff et al., 2001). palaeoseawaters by using both the measured concentrations One of the first breakthrough papers on the use of fluid of brines from the fluid inclusions (all the major ions) and the inclusion studies to recognize and follow oscillations in seawater complicated but logical series of assumptions and restorations. chemistry was published by Lowenstein et al. (2001). Essential in For the Cambrian, the Silurian, and the Cretaceous, the maxi- this and following interpretations is the fact that the marine halite mum values of Mg/Ca were taken directly from the measure- precipitation field is broad (Figure 8). In recent evaporating ments of Mg and Ca concentrations in fluid inclusions. In these seawater, halite begins precipitation from c.290–320% and con- measurements, the concentration of Ca was interpreted as tinues crystallization until the start of epsomite precipitation at lower in relation to Mg (that is the conservative ion) due to

375%. At that time, in the ideal closed system, no other salts loss of the Ca ion in the earlier precipitation of CaCO3 and precipitate from the brine except for some gypsum at the begin- CaSO4. The minimum value of Ca concentration was calcu- ning of halite crystallization field, so the majority of ions show lated using the appropriate backtracing procedure. The mea- conservative behavior within this field. When the salinity rises, sured values of concentrations of the other major ions (Na, K, the concentration of Mg and K ions in the halite brine also rises Ca, and Cl) were plotted versus the concentration of the Mg proportionally, and the molal ratios of these conservative ions are ion, which was interpreted as being the measure of the evapo- preserved, some of them reflecting or still preserving the ratios rite concentration until the first Mg salt precipitation. Then by present in original ancient seawater. The Na and Cl ions will using a computer program developed to monitor the changes however change their proportions and concentrations because in concentration of major ions during evaporite concentration of the chemical divide principle (Cl>Na in seawater). The brine of given water (Harvie et al., 1984) and by using the trial-and- (of different salinity) trapped in fluid inclusions in halites that error fitting method, the chemical composition of paleosea- crystallized along the crystallization paths within the halite field water was determined (the best fit to the data). The succession will thus record these constant ratios or the gradual changes of of salts formed by the evaporation of modeled paleoseawater ion concentrations. Thus, it is possible to relate these ratios and matched the observed sequence in ancient evaporites (Usiglio changes to changes in salinity and restore the original propor- sequence). “All modeling was done using a present-day ClÀ of 2 tions of salts in the original ancient seawater. The start of halite 548 mmol and assuming that SO4 À was 14 mmol; present- 2 crystallization on the evaporation path of recent seawater is day SO4 À is 28 mmol” (Lowenstein et al., 2001). 2 recorded by a drop in Naþ and an accelerated increase of Mg þ The fluid inclusions in the halite of Precambrian and Perm- concentration at about 6000 mmol of ClÀ. One of the main ian evaporites did not contain measurable Ca. Apparently, the difficulties was however the determination of concentration of ancient brines were similar to modern evaporating seawater

Na and Cl in small halite inclusions (investigated by ESEM X-ray brine, the evaporation and precipitation of CaCO3 and CaSO4 522 Geochemistry of Evaporites and Evolution of Seawater

6000

5000 Primary fluid inclusions in halite

Modern 4000 O)

2 Late Cretaceous -H

1 Early Cretaceous -

kg 3000 Permian Silurian Cambrian

Na (mmol 2000 Precambrian Seawater evaporation

1000

0 3000 4000 5000 6000 7000 8000 9000 10 000 11 000 -1 Cl (mmol kg -H2O)

5000 Evaporating modern seawater brine up to K-Mg-salts precipitation (data after McCaffrey et al. 1987) 4000 Evaporating modern seawater brine during K-Mg-salts precipitation O)

2 (data after McCaffrey et al. 1987)

-H 3000 1 -

kg Primary fluid inclusions in halite 2000 Modern Late Cretaceous Mg (mmol Early Cretaceous Permian 1000 Silurian Cambrian Precambrian Seawater evaporation 0 3000 4000 5000 6000 7000 8000 9000 10 000 11 000 -1 Cl (mmol kg -H2O)

2 Figure 16 Measured concentrations of Naþ (A), and Mg þ (B), versus ClÀ, in primary fluid inclusions present in modern and ancient halite (after Lowenstein et al., 2001; Timofeeff et al., 2001; von Borstel et al., 2000) and in evaporating Caribbean seawater during fractional crystallization in saltwork pans and laboratory (based on data by McCaffrey et al., 1987), and compositional path of evaporation of modern seawater calculated by computer program written by Harvie et al. (1984). Naþ and ClÀ molalities from all fluid inclusions were adjusted with the help of the same program under assumption of NaCl saturation. Diagrams reproduced from Lowenstein et al. (2001), modified and supplemented.

2 2 2 consumed virtually all Ca þ from the brines, leaving SO4 À in for Tertiary seawaters based on Mg þ concentrations determined excess during further evaporite concentration, that is, during from fluid inclusions for these waters by other authors. The halite precipitation. The Mg/Ca ratios for these waters were results were presented on the diagram supplemented with the 2 calculated similarly as described earlier. Ca þ concentration curve showing predicted modeled variations of Mg/Ca ratio in 2 equals 10 mmol (which is Ca þ concentration in modern sea- time previously calculated by Hardie (1996). 2 2 water giving the maximum Mg þ/Ca þ ratio on the diagram) The final point of their discussion is the restoration of the 2 was used for maximum value of the Mg/Ca ratio, and a Ca þ of composition of ancient seawater from inclusions accepted as 15 mmol, that is, 1.5 times modern seawater – for minimum representing seawater brine, that is, from established coinci- 2 2 Mg þ/Ca þ ratio. A similar procedure of calculations was used dent and overlapping evaporation path taken from fluid Geochemistry of Evaporites and Evolution of Seawater 523

inclusions from separate basins of the same age. It is done by During the Early Cretaceous, the concentration of Naþ at using the HMV computer program simulating evaporation the given concentration of ClÀ in primary fluid inclusions in paths of some assumed seawater. “The calculated evaporation halite was higher than today, than in Permian, and in latest pathways are plotted and compared with the measured inclu- Neoproterozoic (Lowenstein et al., 2001). The Cretaceous sea- sion brines. The parent seawater chemistry is then adjusted in water showed very high calcium concentrations, which gives 2 2 an iterative process to best fit the fluid inclusion data” the lowest Mg þ/Ca þ ratios ( 1) documented in Phanerozoic (Timofeeff et al., 2001, p. 2299). seawater from halite fluid inclusions (Lowenstein et al., 2003, In the ensuing papers, increasingly detailed restorations of 2005; Timofeeff et al., 2006). Such low ratio favored the pre- seawater chemistry were presented basing on the same meth- cipitation of calcite from seawater rather than aragonite or 2 odology and number of the same or similar interrelated high-Mg calcite. Elevated Ca þ concentrations leading to the 2 2 assumptions (Brennan and Lowenstein, 2002, 2004; Lowenstein relation Ca þ >SO4 À at the point of gypsum saturation per- et al., 2005). mitted the Cretaceous seawater to evolve into Mg–Ca–Na–K– 2 The calculations of the chemical composition of Permian Cl brines devoid of measurable SO4 À and able to precipitate seawater from halite fluid inclusions were made under the rare calcium-containing evaporite mineral tachyhydrite assumptions proposed by Lowenstein et al. (2005): (CaCl2 • 2MgCl2 • 12H2O) at the end of evaporation path (Figures 8, 14, and 18; Wardlaw, 1972a). Since the Early 1. Salinity and concentration of ClÀ, that is, chlorinity, of Cretaceous, seawater evolution has been unidirectional – the Permian seawater were the same as in the modern seawater. 2 2 concentration of Mg þ and SO4 À increased and concentration 2. HCO3À can be ignored in the modeling because in the recent 2 1 of Ca þ decreased (Holland, 2005). Kump (2008) noted an seawater, the concentration of this ion (2.5 mmol kgÀ 2 2 1 intriguing rule that the concentration of Mg þ and Ca þ was H2O) is negligible in comparison with ClÀ (565 mmol kgÀ 2 inversely related when the concentration of Ca þ was less than H O) and with other major ions (Table 1). 2 20 milimol and positively related when it was above this 3. The milimolal concentration of Kþ in Permian seawater was concentration. assumed to be equal 10, similarly as supposedly in the 2 2 It seems that variations in concentrations of Ca þ and SO À entire Phanerozoic (Horita et al., 2002). This assumption 4 in Phanerozoic seawaters were synchronous and inversely pro- results from the fact that the recorded K/Br ratio in Phaner- portional (Demicco et al., 2005; Hansen and Wallmann, 2003; ozoic halite fluid inclusions has been relatively constant Kovalevych, 1990; Kovalevych and Vovnyuk, 2010; Stanley and (Horita et al., 2002) and that Br concentration in Phanero- Hardie, 1998; Figure 17(b) and 17(c)). Potassium showed a zoic seawater presumably did not change significantly, consistent low stable concentration in all studied Phanerozoic because the residence time of this element in seawater is 2 time intervals, and its (assumed) constant level permitted the estimated at 100 Ma. The Mg þ concentrations were calcu- 2 calculation for concentrations of other ions. Cl variations over lated from Mg þ/Kþ ratio recorded in fluid inclusions. The 2 time, hence also paleosalinity of seawater, were not determined ratios of Kþ/SO4 À in brine inclusions were used to calcu- 2 from the halite fluid inclusion studies (Knauth, 2005, p. 60) late the SO À concentrations in Permian seawater. The 4 and, similar to K concentration, was assumed to be constant. concentration of Naþ was calculated from charge balance, 2 The interpreted concentrations (particularly Naþ) were after the concentrations of all the other ions (ClÀ, SO4 À, 2 2 ‘adjusted’ to paleosalinity (chlorinity or concentration of Cl) Ca þ, Mg þ, and Kþ) were estimated. of the same level as today. The assumed constant concentration of Br in ancient seawaters served as a base of determination for the DE, as well as 9.17.21 Ancient Ocean Chemistry from Halite Fluid the base of the calculations of the concentration of other ions Inclusions – Summary and Comments in ancient seawaters. The concept of a bromine constant is now doubtful in the light of investigation by Channer et al. (1997) At present, nearly all major time intervals containing Phaner- and Gutzmer et al. (2003) and because Leri et al. (2010) ozoic saline giants are covered by the analyses and reconstruc- showed that Br is likely not the conservative element in ancient tions of seawater chemistry from halite fluid inclusions seawater. Furthermore, some recent studies showed non- (Table 8; Figures 17 and 18) and are used for testing the conservative behavior of bromine in both the ocean and salt geochemical models of seawater evolution (e.g., Berner, pan environments (Berndt and Seyfried, 1997; Martin, 1999; 2004; Hansen and Wallmann, 2003; Holland, 2005). The Risacher et al., 2006; Wood and Sanford, 2007). main results of these restorations are the following: The partition coefficient of Br in halite depends on the Permian seawater was chemically similar to modern chemical composition of seawater and can be both experimen- 2 seawater; however, it was slightly depleted in SO4 À and tally and theoretically predicted for seawater of various com- 2 enriched in Ca þ in relation to present-day seawater, although positions (Siemann and Schramm, 2000). The Br content in 2 1 the Ca þ concentration close to modern 11 mmol kgÀ H2O first marine halites from various stratigraphic intervals appears cannot be excluded (Garcı´a-Veigas et al., 2011; Lowenstein to vary exactly following the interpreted changes in Phanero- 2 2 et al., 2005). The Mg þ/Ca þ ratio was >2 that was favorable zoic seawater chemistry as predicted by Hardie (1996), this for the precipitation of aragonite and Mg calcite as ooids and being the first independent test for his model of seawater cements. Fluctuations in Mg/Ca ratio and fluctuations of Ca evolution (Siemann, 2003). and Mg concentrations in time, as detected from halite fluid The causes of these compositional changes and the chemi- inclusions, are well supported by numerous geochemical stud- cal evolution of the ocean are the subject of the current ongo- ies of carbonates (Steuber and Rauch, 2005). ing scientific debate and numerical modeling. The various 524 Geochemistry of Evaporites and 1 Table 8 Major-ion chemistry of ancient seawater (mmol kgÀ H2O) interpreted from chemical composition of fluid inclusions in marine halite; selected results of recent investigation Evolution 2 2 2 2 2 Time Age (Ma) m(ClÀ) m(SO4 À) m(HCO3À) m(Naþ) m(Mg þ) m(Ca þ) m(Kþ) m(Mg þ)/m(Ca þ) References

Modern seawater 0 565 29 2.5 485 55 11 11 5.2 Timofeeff et al. (2006); Lowenstein and Timofeeff (2008, with references) of Cretaceous (Albian– 112.2–93.5 565 14 (8–16) 462 34 26 (20–28) 11 1.3 (1.2–1.7) Timofeeff et al. (2006) Seawater Cenomanian) Cretaceous (Aptian) 121.0–112.2 565 8.5 (5–12) 416 42 35.5 (32–39) 11 1.2 (1.1–1.3) Timofeeff et al. (2006); Lowenstein and Timofeeff (2008, with references) Permian (Tatarian) 258–251 565 23 (18–26) Ignored 469 52 14 (9–17) 10 3.7 (3.1–5.8) Lowenstein et al. (2005) Permian (Artinskian– 283–274 565 19 (13–22) Ignored 439 60 17 (11–20) 10 3.5 (3.0–5.5) Lowenstein et al. (2005); Lowenstein Kungurian) and Timofeeff (2008, with references) Permian (Asselian–Sakmarian) 296–283 565 20 (15–24) Ignored 461 52 15 (10–19) 10 3.5 (2.7–5.2) Lowenstein et al. (2005) Late Silurian 423–419 565 10 420 45 33 11 1.4–2 Brennan and Lowenstein, 2002; Lowenstein and Timofeeff (2008, with references)

1 1 The values were calculated under assumptions that: m(ClÀ) was equal to modern seawater; m(Kþ) was equal 10 mmol kgÀ H2O for the Permian seawater, and 11 mmol kgÀ H2O for the Cretaceous and Silurian seawater; for the other assumptions, see references. Geochemistry of Evaporites and Evolution of Seawater 525

70 Mg

O) 60 2 H 1

- 50

30 ) (mmol kg Mg/Ca 2+ 20 6 i 10 ) m(Mg

2+ 5 0 0 100 200 300 400 500 600 Ma 4 (a) /m(Ca i )

Ca 2+ 3 50

O) 2 2 m.(Mg H

1 40 - 1

30 0 (e) 0 100 200 300 400 500 600 Ma ) (mmol kg 20 2+

10 m(Ca Calcite (b) 0 Aragonite 0 100 200 300 400 500 600 Ma 20

SO4 ences 15 O) 2 ) - H 20 2 1 4 -

SO 10

m( 10 (mmol kg Number of occurr (c) 0 5 0 100 200 300 400 500 600 Ma O)

2 20 K (f) T Cr J T P P M D S O Cm H ) 1 + -

K 10 m(

(mmol kg 0 100 200 300 400 500 600 Ma Solid circle - value from analyses, (d) open circle - assumed value

2 2 2 Figure 17 (a–d) concentrations of major ions (Mg þ, Ca þ, SO4 À, and Kþ) in the Phanerozoic seawater restored from halite fluid inclusions, after Horita et al., 1991 (in orange), Zimmermann, 2000 (in yellow), Brennan and Lowenstein, 2002 (in pink), Horita et al., 2002 (in blue), and (e) diagram showing oscillations of calculated Mg/Ca ratio in Phanerozoic calcite and aragonite seas, after Lowenstein et al., 2001 (in red), Horita et al., 2002 (in blue), and Timofeeff et al., 2006 (in green), with references. Circles, triangles, and thick-thin vertical bars in figures (a-e) are based on the assumption of 2 2 different values for m(Ca þ)I · m(SO4 À)i, (f) occurrence of marine calcite and aragonite ooids in Phanerozoic, after Wilkinson et al., 1985, time scale modified after Ogg et al., 2008. models are tested and compared with the chemical restorations such as karst solution basins on the coast of the Mediterranean of seawater chemistry from halite fluid inclusions. However, so (Nadler and Magaritz, 1980). On the other hand, seawater far, the reliable reconstructions from such inclusions are lim- seeping through the barrier into one of the largest marginal ited only to several ‘points’ on the stratigraphic scale, the large marine basins – MacLeod basin (Australia) – is nearly the intervals in between them remain without any certain data same in composition as the open Indian Ocean water (Logan, from halite brine inclusions (Figure 17). 1987, his Table 5). The evaporating seawater brines at various The basic assumption of the described interpretational strat- stages of concentration within this basin (up to halite satura- egies was that seawater in the marginal marine evaporite basins tion) are similar in composition (but not exactly the same) as reached the stage of halite crystallization strictly preserving its the original Indian seawater brines (Figure 19; Logan, 1987). marine character. In modern marine evaporite environments, Some ions in the basinal seawater brines commonly show slight we can find examples that support this idea, but there also are deviations from the expected values for these components, some that do not support that view. Marine halite brine is easily presumably due to salt recycling, particularly in case of Na modified in its composition in small peripheral evaporite pans and Cl (Logan, 1987, his Table 5). Similar deviations are 526 Geochemistry of Evaporites and Evolution of Seawater

Figure 18 (a–d) Evolution of the composition of Phanerozoic evaporating seawater brine at the halite precipitation stage (mol%) estimated from primary fluid inclusions in marine halite shown on the Mg–2K–SO4 and Mg–Ca–2K Ja¨necke diagrams at 25 C, (a) for 0–150 Ma, (b) for 150–250 Ma, (c) for 250–390/410(/530)Ma, and (d) for 390/410 (/530)–550 Ma (redrawn, with corrected Badenian age, from Horita J, Zimmermann H, and Holland HD (2002) Chemical evolution of seawater during the Phanerozoic: Implications from the record of marine evaporates. Geochimica et Cosmochimica

Acta 66: 3733–3756), mSW-modern seawater brine at the halite precipitation stage. (e–f) Mg, SO4, and Ca concentrations in modern seawater of SO4- rich type (e) and in ancient seawater of Ca-rich type (f), representing two extreme types of seawater in the Phanerozoic (redrawn from Kovalevych VM and Vovnyuk S (2010) Fluid inclusions in halite from marine salt deposits: Are they real micro-droplets of ancient seawater? Geological Quarterly 54: 401–410 and references cited therein). Modern seawater in (e) after Holland (1984). Ca-rich seawater in (f) calculated (based on data in Kovalevych et al., 1998a; Horita et al., 2002; Lowenstein et al., 2001, 2003) under assumption that Na and Cl contents (which made up about 90% of total ion content in modern and ancient seawater types) did not change significantly. K content was constant. recorded in lagoon-type basins – Bocana de Virrila´ in Peru shows very remarkable deviations from expected concentrations (Figure 20; Brantley et al., 1984) and Ojo de Liebre in Mexico (Geisler-Cussey, 1997; Herrmann et al., 1973; Nadler and (Geisler-Cussey, 1997; Pierre et al., 1984a). Similarly, in Medi- Magaritz, 1980), and is early lost during evaporation presumably 2 terranean saltworks, Naþ, ClÀ, and SO4 À, unlike conservative through ion exchange with clay minerals (Hardie and Eugster, 2 Mg þ, show remarkable deviations in concentrations in more 1970, p. 288). However, as it was already mentioned, Timofeeff saline brine, that is, they do not create perfectly coincident et al. (2006) strongly believed that “the great mass of dissolved crystallization paths. In some modern basins, potassium salt in large brine bodies,” that is, in saline giants, “make Geochemistry of Evaporites and Evolution of Seawater 527

7000 Na+ Cl- 6000 Mg2+ MacLeod 2- SO4 Ca2+ -

O) 5000 Br 2 -

-H Cl 1 - Na+

kg 2- 4000 SO4 Ca2+ Start of halite Mg2+ + precipitation 3000 K Br-

Concentration (mMol 2000 Start of gypsum precipitation 1000

0 0 5 10 15 Degree of evaporation

300

250 O) 2 -H

1 200 - Start of gypsum Start of halite kg precipitation precipitation

150

100 Concentration (mMol

0 0 5 10 15 Degree of evaporation Figure 19 Comparison of the crystallization paths of the Caribbean seawater based on data by McCaffrey et al., 1987 with the geochemical characteristic of the basinal brines of the MacLeod basin (after Logan, 1987). modification of the major-ion chemistry by syndepositional In spite of the fact that the criteria for the seawater signal in recycling processes or nonmarine inflow waters less likely than halite inclusions are numerous and rigorous in the majority of in shallow/ephemeral systems” (Timofeeff et al., 2006, p. 1982). the important papers with apparent successful interpretation These authors introduced the special criterium, described earlier of the chemistry of ancient seawater (see extensive sections (Section 9.17.20.1), for exclusion of data representing the sup- earlier), these criteria, particularly concerning actual sampled posed modified parent seawater from the ‘true’ seawater brine. sections and geology of the halite basins, are not discussed. The The other problem is the use the complete set of criteria for ‘screening’ procedure for the selection of the samples was the proper recognition seawater brine in halite inclusions. sometimes described very poorly or was omitted. Some 528 Geochemistry of Evaporites and Evolution of Seawater

7000 Cl- Na+ 2- 6000 SO4 Ca2+ Mg2+ K+

O) 5000 2 Br- -H

1 2+

- Mg 2- kg SO 4000 4 Cl- Bocana de Na+ Virrilá Ca2+ Start of halite 3000 K+ precipitation

Concentration (mMol 2000

Start of gypsum 1000 precipitation

0 0 5 10 15 Degree of evaporation

300

250 O) 2

-H 200 1 Start of gypsum Start of halite - precipitation

kg precipitation

150

100 Concentration (mMol

0 0 5 10 15 Degree of evaporation Figure 20 Comparison of the crystallization paths of the Caribbean seawater (based on data by McCaffrey et al., 1987) with the geochemical characteristic of the basinal brines of the Bocana de Virrila´ (after Brantley et al., 1984).

restorations were made without showing overlapping crystalli- Horita et al. (2002) found it very difficult (and in fact impos- zation paths from basins of the same age considered as crucial sible) to identify the evaporite deposits that meet all the criteria criterion for proper recognition of seawater derivation of brine for primary seawater trapped in halite inclusions, as listed in in fluid inclusions. In fact, attempting to synthesize all the the earlier sections. Therefore, they “only consider halite from available data on halite fluid inclusions with seawater brine, evaporite deposits whose Sr and S isotope signature indicates Geochemistry of Evaporites and Evolution of Seawater 529 unequivocally that they are marine in origin” (Horita et al., geochemical analysis of the evolution of the basinal waters to 2002, p. 3734). Many authors described the Br contents in halite show that the signal in the sample is exclusively from uncon- as the main argument in favor of the marine origin of salt. Such taminated seawater (point 6 discussed earlier; Ayora et al., solutions were earlier criticized by several authors who have 1994, 1995). shown that isotope and trace element data are inconclusive in Ayora et al. (2001) were able to restore the chemical evolu- this respect (Hardie, 1984; Schreiber and El Tabakh, 2000; tion of brine in several Mesozoic and particularly in Tertiary Warren, 2006). The exclusively marine derivation of many evap- evaporite basins based on the analysis of mineral associations, orites sampled for marine brine in halite inclusions still remains primary fluid inclusion analysis in halite, and numerical sim- controversial (compare, e.g., Brennan and Lowenstein, 2004; ulation of the model marginal marine evaporite basin Lowenstein et al., 2001; Schoenherr et al., 2008). (described in Section 9.17.7.2). They explained the chemical The weak point of all these restorations is that they require composition of brine trapped in halite exclusively by processes too many uncertain assumptions concerning the ‘starting’ of alteration of the marine water of the present-day composi- composition of the ancient seawater. As noted by Steuber and tion, that is, by sulfate depletion related to dolomitization or

Rauch (2005, p. 200), “experimental data on major ion com- addition of CaCl2-rich brine to basinal waters, or other pro- position of palaeo-seawater are still scarce, have a coarse tem- cesses. They noted that sulfate depletion observed in brine poral distribution, and require assumptions on the from fluid inclusions varied in intensity in basins of the same composition of evaporating brines, resulting in some uncer- age, as well as throughout the evolution of the same basin. tainty for the reported values.” The restorations of the concen- The studied basins were relatively small in comparison with tration of Mg and Ca ions in paleoseawater were based on a the largest saline giants. However, recently, the same features great number of uncertain assumptions, so Tyrrell and Zeebe were documented in the giant sequence of Permian Zechstein (2004) called these restorations ‘best guess’ rather than proved, cyclothems (Garcıá-Veigas et al., 2011). although they emphasized that they are well supported by Some of these variations cannot be explained by global and many other facts from the associated nonevaporite record. ‘secular’ variations in ocean chemistry, the variations are too The empirical data were compared with the numerical sharp and the time spans too short to achieve global mixing of models of the evaporating seawater evolution in the ideal sys- the oceans. Also young or subfossil sequences of the marginal tem. These numerical models were successfully tested on data marine basins show deviations from the sequence expected from from fluid inclusions in the modern Inagua saltworks and in a evaporation of present-day seawater, like the potash evaporites salt pan on the supratidal sabkha (Timofeeff et al., 2001). from Dallol, Danakil Depression, whose lower part is made up McCaffrey et al. (1987, p. 937) stated that “the sequence of of sulfate and contains kainite, whereas the upper part is primar- mineral formation and the evaporation path of seawater defined ily chloride and composed of sylvite (Hardie, 1990; Holwerda by the Inagua brines largely corresponds to the theoretical frac- and Hutchinson, 1968). Cendόn et al. (2004) pointed out that tional crystallization path of seawater described by Eugster et al. “evaporitic successions have to be proven marine before they can (1980) and Harvie et al. (1980),” which was confirmed by be confidently used to deduce seawater palaeochemistry,” and Timofeeff et al. (2001). The model, however, was not tested in Ayora et al. (2001, p. 251) concluded that “the solute proportion a basin on the scale of an ancient saline giant. Saltworks cannot recorded in the fluid inclusions can be explained by the evapo- be exactly compared with such a basin. The important difference ration of present day seawater as a major recharge” and therefore is that halite pans in solar saltworks are supplied by gypsum the “changes in potash mineralogy and sulfate depletion in fluid brine already stripped of calcium, that is, having composition inclusions are not conclusive arguments in favor of secular var- different than seawater (McCaffrey et al., 1987; Timofeeff et al., iations in the composition of the ocean.” Cendoń et al. (2008) 2001), whereas the ‘realistic’ halite basin is expected to be sup- stated that results of their own work in Mulhouse basin proved plied directly by seawater (Figures 4(a) and 4(b) and 5), as in that the chemical changes within the basinal waters were differ- the scenario considered by Holser (1979a). ent within the individual subbasins of the similar age. These Finally, there is always a danger that the ancient halite changes were also too rapid to be explained by any global secular inclusions analyzed simply do not represent the evaporated variations of the ocean chemistry. They again stated that this seawater or basinal water (Vovnyuk and Kovalevych, 2007). “precludes the use of isolated fluid inclusions samples as a Von Borstel et al. (2000) recognized that several ‘network’ proxy of ancient ocean composition” and in particular “it pre- fluid inclusions from modern marine halite from solar salt- cludes the use of fluid inclusions in isolated samples to recon- works showed highly variable chemistry and higher concentra- struct the composition of the Oligocene ocean” (Cendoń et al., tion that the brine from which they crystallized. These authors 2008, p. 111), because two halite samples from Mulhouse basin explained that such inclusions evaporated after sampling were used previously to back calculate the chemistry of Oligo- (Timofeeff et al., 2001). Some ‘anomalous’ modern halite cene oceanic water from fluid inclusions by some other authors. fluid inclusions from Baja California deviate from the evapo- On the other hand, in the modeling of the Mulhouse basinal ration paths predicted by computer programs, and many water evolution during evaporation, these authors, agreeing that others show more or less broad scatter (Timofeeff et al., 2001). “identifying potential end-member water chemistry in an ancient Ayora and other authors who are specialized in restoration evaporite basin is difficult,” just used the modern seawater of the chemical evolution of the basinal waters in marginal for modeling “as there is no experimental and independent marine evaporite basins are warned about the uncritical accep- (non-evaporite based) data for Oligocene seawater composition tance of the halite fluid inclusion data, particularly from single available” (Cendoń et al., 2008, p. 116). A similar integrated samples, as the evidence of clear uncontaminated record of approach of restoration of the chemical evolution of the basinal ancient ocean chemistry. The essence of their criticism is the water and seawater signal in it was recently made for the Polish requirement of complete and holistic sedimentological and Permian basin by Garc´ıa-Veigas et al. (2011). 530 Geochemistry of Evaporites and Evolution of Seawater

However, the following evidences can be found in favor of process of albitization of plagioclases (Cowen, 2000; also see secular variations of the chemical composition of seawater Chapter 8.7). ClÀ however remains relatively unchanged during (Kovalevych et al., 2006a): this circulation – it is therefore particularly conservative element in seawater, and its concentration was probably relatively stable 1. The major compositional changes of brines in fluid inclu- or changed very slowly through geologic time (cf. Holland et al., sions in ‘marine’ halites show clear stratigraphic control, 1986). All these factors suggest that the ocean was remarkably irrespective of paleogeographic position of the basin (see salty, that is, contained a great deal of Cl in the Phanerozoic and summary by Kovalevych et al., 1998a,b). perhaps since the beginning of ocean creation. 2. The halite brines of the marine Neogene basins show such The opposite position to this view is the vanished soda stratigraphic control and are of the SO -rich type (the same as 4 ocean hypothesis (Kazmierczak et al., 2004; Kempe and present-day seawater halite brine), because in Neogene time, Degens, 1985; Kempe and Kaz´mierczak, 1994, 2011) that seawater was unambiguously of the same type as today. assumes the existence of high amounts of CO in the oldest 3. The uniform trend of changes in composition of brine was 2 atmosphere and that implies the carbonic acid weathering of detected in marine Neogene halite inclusions showing that 2 silicates on the early Earth, according the Urey reaction. during last 40 My, the concentration of oceanic Mg þ was Consequently, there was the production of huge amounts of rising (Horita et al., 2002; Zimmermann, 2000), although carbonate and bicarbonate anions in seawater some data from that time interval can be questioned 2 2 (HCO À CO À >ClÀ SO À) causing an oceanic pH as (Cendoń et al., 2008). 3 þ 3 þ 4 high as 11. According to this hypothesis, the main driving 4. The changes in the major element chemistry of ancient force for the transition of the presumed soda ocean into the seawater coincide or overlap in time with major variations present-day halite ocean during Proterozoic was the subduc- in the mineralogies of marine nonskeletal carbonates tion of seawater (as pore water) together with oceanic crust and (ooids and cements) and also mineralogy of potash evapo- sediments in subduction zones (e.g., Lećuyer et al., 1998; Pope rites, changes of isotopic composition of some elements, et al., 2012), and the subsequent formation of continental and other geologic processes in the Phanerozoic crust with accumulated carbonates and organic carbon (Kovalevych, 1990). In particular, the variations of carbon- (Kempe and Kaz´mierczak, 1994). The concept implies a slowly ate and potash salts mineralogies apparently had the same but continuously growing content of ClÀ beginning with the shared causative reasons and tied to the fluctuations in Mg/ lowest values in the Hadean to today’s values and with a Ca ratio in seawater. substantial amount of Na in the vanished early ocean 5. The apparent lack of extensive contemporaneous dolomite 2 2 (Naþ Kþ >Ca þ Mg þ; Kempe and Kazmierczak, 2011). in many evaporite basins speaks against the importance of þ þ Kempe and Kaz´mierczak (1994) suggested that calcium con- dolomitization for changes in basinal brine composition. centration could rise in early ocean attaining some critical level 6. The variations in brine composition and especially intensity that induced skeletogenesis in marine animals in Cambrian, in of sulfate depletion in separate basins of the similar age (as 2 response to increased Ca þ ‘stress.’ Morse and Mackenzie recorded by Garcıá-Veigas et al., 1995; Ayora et al., 2001) (1998) agreed with the concept of gradual calcium concentra- can be explained by the influence of local factors, such as tion rise in the early ocean; however, they believed that the water–rock interactions and inflow of nonmarine water. ocean was always NaCl-dominated, as today, and that pH was

lower than now due to a higher amount of CO2 in the early atmosphere. Unfortunately, a scarce Precambrian evaporite 9.17.22 Salinity of Ancient Oceans record and the lack of unquestionable marine evaporite deposits in the earliest rocks do not permit recognition of the Na and Cl are the most abundant elements in the seawater true chemistry of the earliest ocean. Based on the other evi- responsible for its salinity. NaCl is responsible for the salty taste dence and theoretical models, currently most authors believe of marine and other waters. Early geochemical calculations that the chloride was dominant anion in seawater that was as (Goldschmidt, 1937; Rubey, 1951, 1955) suggested that the salty (or saltier) as today since the Archean (Foriel et al., 2004; amount of Cl in the seawater is so large that it “cannot be assumed Hardie, 2003; Holland and Kasting, 1992; Knauth, 2011). to be derived entirely from weathered igneous rocks” but was Many authors, modeling the history of the ocean chemistry, already present in primitive atmosphere of the early Earth assume that the volume of the ocean was more or less constant (Goldschmidt, 1954, p. 66). Cl is an incompatible element that or that it continuously grew since the time of its creation (see presumably was outgassed as HCl together with H2O during the Mason, 1958; Pinti, 2006; Rozanov, 2010; Schopf, 1980, and earliest Earth history (Holland, 1984; Knauth, 2005). Most references in these publications). However, the hypotheses that probably, the entire inventory of Cl was present in the ionic the ocean volume decreased or oscillated with time are recently form in the early ocean, until the time of deposition of huge also accepted (Ingebritsen and Manning, 2003; Knauth, 2011; evaporite formations on accreting continents in the Paleoproter- Le´cuyer et al., 1998; Pope et al., 2012). The volume of ocean has ozoic (Knauth, 1998). ClÀ has the longest residence time among oscillated slightly due to global glaciations. During Quaternary, major elements present in seawater – estimated as 2.27 108 year 2% of the seawater volume was incorporated in the ice sheets Â ( 227 My) by Land (1995), comparable with Br (100 My: (Hay et al., 2006) and could have caused an average salinity rise ¼ Holland et al., 1986; Br is considered by Holland et al., 1996, as in the ocean from 35% up to 36–37.6% (Hay et al., 2006). showing constant concentration in Phanerozoic seawater). Naþ, According to Stevens (1977), Pleistocene salinity variations did however, is lost continuously during hydrothermal circulation not exceed 1.5%. of seawater through the basaltic cover of the mid-ocean ridges, The volume of the preserved marine evaporite deposits also being sequestered in the newly formed crust mainly in the was used for the calculation of the salinity of ancient ocean Geochemistry of Evaporites and Evolution of Seawater 531

2 under assumption that the ocean volume was constant since should lead first to lowering of SO4 À concentration in the the beginning. If we agree with this assumption and accept that ocean, because this ion is always sequestered in the deposited all the evaporite minerals found today in sedimentary rocks gypsum before halite precipitation. Apparently, however, were present in dissolved form in the ocean, from its inception this sequestration does not always take place. Hansen and (with the volume comparable to today), we can calculate that Wallmann (2003) suggested this as the cause of the lowered the salinity of early ocean was about twice today’s salinity, that concentration of seawater sulfate and calcium 20 Ma. is, 70% (Knauth, 1998, 2005, 2011). Wortmann and Chernyavsky (2007) also recognized the influ- Holland (1984, p. 461) roughly estimated that the average ence of such diminution, caused by the substantial Ca sulfate salinity of the Phanerozoic seawater was no more than 30% evaporite deposition in the Early Cretaceous (Aptian), on the higher than today, that is, it was less than 45.4%. Based on the global geochemical S and C cycling in that period. Deposition amount of evaporitic deposits in the geologic record, Hay et al. of the 1.125–1.6875 106 km3 of salts during the Messinian Â (2006) calculated that the salinity of the Phanerozoic ocean salinity crisis (Ryan, 2008), 5% of salt content of the ocean varied between 35% and 47%, and only in the Cretaceous (Ryan, 2009), could also depress the average salinity of the period could it have dropped to 32–33%. They presented the ocean. Holser (1984) estimated that salinity dropped rapidly model of salinity changes since Cambrian. The fluid inclusions four or five times between the Permian and the Cretaceous by in late Cambrian–early Ordovician carbonate cements show 1–4% due to evaporite deposition (mainly NaCl). salinity within the range 31–47% (Johnson and Goldstein, Stein et al. (2000) calculated that global acmes of evaporite 1993), which overlap and generally coincide with the range deposition could disturb the isotope 87Sr/86Sr ratios in seawater predicted by this model (Figure 21). Knauth (2011) suggested by refluxing brine flowing out from the largest saline giants, such that the estimates by Hay et al. (2006) are probably too high as the late Permian Zechstein basin, the Callovian Louann salts and that “the idea that Paleozoic life could thrive at such high in the Gulf of Mexico, and the Messinian Mediterranean basin. inferred salinity is likely to be resisted by marine biologists and paleontologists” (Knauth, 2011, p. 771). The extremely large volume of evaporites in Neoproterozoic 9.17.23 Evaporite Deposition through Time and Permian possibly could temporarily lower the salinity of the ocean for several per mill (%) during those time intervals The largest saline giants are preserved in deposits formed from (Fischer, 1964; Holser, 1984; Vickers Rich, 2007). Stevens late Ediacaran through the Cenozoic (Table 9). According to (1977) calculated the volume of Permian halites known at available data, there are only four basinal areas with the volume that time as nearly 1.6 106 km3 and estimated that the Perm- of salts over 1100000 km3 recorded in that time interval, and the Â ian salinity dropped to 31.5%, that is, about 10%. Sulfate in Gulf of Mexico basin (160 Ma) is the largest one containing Zechstein sediments is also equal to 10% of the sulfate 2400000 km3 of salt (Evans, 2006). The next in size appears to content of the present ocean (Schaffer 1971 cited by Holland, be the Messinian evaporites of the Mediterranean and Red Sea 1972). Luo et al. (2010), based on the compilation of data by region (Rouchy and Caruso, 2006) estimated on 1400000 km3 Hay et al. (2006), estimated that late Permian deposition of Ca in volume (mean calculated from data by Ryan, 2008). Among 2 sulfate could lower the concentration of SO4 À in the ocean the pre-Ediacaran saline giants, the largest volume of recorded about 6 mM. Holser (1984) and Holland et al. (1996) sug- salts is found in Centralian Superbasin in Australia ( 800– gested that the increased evaporite deposition in some periods 830 Ma; the Bitter Spring Fm. and its equivalents; Lindsay,

Range of salinity 50 from various models 50

40 40

Salinity from 30 30 fluid inclusions Recent average in marine calcite salinity 34.7‰ 20 20 Mean salinity of ocean in ‰ 10 10

0 0 pCm Cm O S D C P T J Cr P N Neopro- terozoic Paleozoic Mesozoic Cenozoic 600 500 400 300 200 100 0 Age (Ma) Figure 21 Reconstruction of the mean salinity of the ocean during the Phanerozoic according to Hay et al. (2006). Salinity of Cambrian–Ordovician seawater from fluid inclusions after Johnson and Goldstein (1993). 532 Geochemistry of Evaporites and Evolution of Seawater

Table 9 The world’s largest evaporite basins; compilation based on Table 9 (Continued) various sources, repeated after Evans (2006), and supplemented after Ryan (2008) Precambrian (pre-Ediacaran; >600 Ma)

3 Cenozoic–Mesozoic (0–250 Ma) Evaporite basin Age in Ma Volume in km

e Evaporite basin Age in Ma Volume in km3 2b Minto Inlet, Canada ca. 800 90000 3 Duruchaus, Namibiaf ca. 800 15000 1 Messiniana 5 2250000a 4 Copperbelt, Central ca. 830? 25000 2 Red Sea 10 900000 Africag 3 SW Iran 20 300000 5 Centralian, Australiah ca. 800 140000 4 S Mozambique 20 27000 6 Borden, Canada ca. 1200 15000 5 E China 40 20000 7 Char/Douik, W Africa ca. 1200? 8000 6 Rus, Arabia 50 200000 8 Belt basin, N America 1460 10000 7 N Sahara 90 32000 9 Discovery, W Australia ca. 1500 2800 8 Indochina 100 50000 10a Balbirini, N Australia 1610 2500 9 S Atlantic 120 35000 10b Lynott, N Australia 1635 3000 10 Hith, Arabia 150 360000 10c Myrtle, N Australia 1645 13000 11 Central Asia 150 250000 10d Mallapunyah, N Australia 1660 5000 12 Andes 160 40000 10e Corella, N Australia 1740 2000 13 Gulf of Mexico 160 2400000 11 Stark, Canada ca. 1870 30000 14 Alan, Arabia 180 20000 12 Rocknest, Canada ca. 1950 1000 15 Tanzania 200 150000 13 Juderina, W Australia ca. 2100 1000 16 N Sahara 200 710000 14 Tulomozero ca. 2100 1000 17 Keuper 225 50000 15 Chocolay-Gordon Lake ca. 2250 4500 18 Jilh, Arabia 230 120000 succession, Superior 19 S China 230 80000 craton, Canada–USA

Permian–Carboniferous (250–360 Ma) Remarks to some pre-Ediacaran basins after Evans (2006), see Table 11 for further information. Lack of or highly controversial data are marked by “?”. 3 Evaporite basin Age in Ma Volume in km aAfter Ryan (2008). bBedded magnesite, ca. 500 m in thickness, in rift. 1 Zechstein 250 200000 cAbundant pseudomorphs after anhydrite, halite, and shortite, up to 1 km in thickness 2 Khuff, Arabia 260 75000 over an area of ca. 50 000 km2, in the same rift. 3 E European 270 1100000 dca. 100 m in thickness over an area of 300 000 km2. 4 Peru–Bolivia 270 62000 eEvaporites attain a thickness of ca. 300 m across an interpolated depositional area of 5 Midcontinental USA 270 81000 300 000 km2. 6 Amazon 300 25000 fca. 500 m thick and about 30 000 km2 evaporite succession. 7 Sverdrup 315 120000 gBasin-scale evaporite solution megabreccias, inferred thickness of the evaporites ca. 8 Canadian Maritime 340 46000 500 m, over an area of 50 000 km2. hThe most extensive pre-Ediacaran gypsum, anhydrite, and halite deposits, with a Devonian-late Ediacaran (360–600 Ma) typical thickness ca. 800 m, covering an aggregate area of ca. 140 000 km2. Evaporite basin Age in Ma Volume in km3

1 E European 370 1100000 1987; Stewart, 1979) that contain 140000 km3 of evaporites 2 Taimyr 370 18000 3 W Canada 390 86000 (Evans, 2006). The lake evaporites attain smaller but remarkable 4 Morsovo 400 81000 volumes, as, for example, 2.5 km thick halite deposits of the 3 5 Michigan 420 29000 Hualapai basin, Arizona, United States, with 200 km volume 6 Canning 440 26000 of salt (Faulds et al., 1997), the other examples are the Dead Sea 7 Canadian Arctic 460 19000 or central Andean basins. 8 Mackenzie 500 110000 Large accumulations of K–Mg salts are rare and marine evap- 9 Morocco–Iberia 520 50000 orites containing volumetrically important K–Mg salts occur in 10 Siberia 520 800000 only about 40 Phanerozoic basins (Table 10; Goncharenko, 11 Persian Gulf 545 500000 2006; Vysotskii et al., 1988; Warren, 2010). Precambrian evapo- 12 Salt Range 550 240000 rites are thought not to contain K–Mg salts (Muir, 1987). Glau- Precambrian (pre-Ediacaran; >600 Ma) berite occurs with halite in Sinian (late Neoproterozoic) evaporites in Sichuan, China (XiaoSong, 1987). Evaporite basin Age in Ma Volume in km3

1a Skillogalee, S Australiab ca. 770 25000 9.17.23.1 Late Ediacaran–Phanerozoic Marine Evaporites 1b Curdimurka, S Australiac ca. 785 50000 2a Kilian-Redstone River, ca. 770 30000 The marine evaporite record from late Ediacaran to Recent Canadad time shows a characteristic pattern of changes. From Cambrian to the lower half of the Permian (including Artinskian), the (Continued) potash deposits were only of the chloride type, with sylvite Table 10 Major evaporite basins with potash salts deposits, their volume and chemical character, compilation of various sources, repeated after Hardie (1990), and Vysotskii et al. (1986), and supplemented (after Hardie, 1996; Harville and Fritz, 1986; Hryniv et al., 2007; Land et al., 1995; Lowenstein and Spencer, 1990; Petrychenko et al., 2005, 2012; Rahimpour-Bonab et al., 2007; Talbot et al., 2009b; Timofeeff et al., 2006; Valyashko, 1962; Warren, 2006)

Location Formation Age Volume of potash Mineralogy Chemical character deposit (all deposits contain halite)

Qaidam Basin, China Holocene >60 km3 ca, (sy), (mi), (Po) KCl 3 3 Danakil Depression, Ethiopia Houston Formation with Sylvinite Pleistocene (< 1 Ma) >40 km (>30 km ka, ca, sy, ks, (Po), (rh), (bi) MgSO4–KCl Member of sylvinite) Kaidak basin, Kazakhstan Late Pliocene? ? ca, mi, bi MgSO4-KCl Dead Sea basin Sedom Formation Late Pliocene to early Pleistocene Minor (sy), (ca) KCl 3 Sicily, Italy Solfifera series Late Miocene (Messinian) ca. 50 km ka, ca, sy, ks, Po, Bi, lg MgSO4 Mediterranean Sea Late Miocene (Messinian) ? Po, ka MgSO4 Erevan basin, Armenia Middle Miocene ? ca, sy KCl Carpathian Foredeep, Ukraine–Romania Vorotyshcha and Kalush formations Early and middle? Miocene ? ka, lg, sy, ks, Po, (ca), (gs), MgSO4 (Ukraine) (Eggenburgian/Badenian?) (bl), (lw), (mi) Great Kavir Basin, Iran Upper Red Formation Middle Miocene ? sy, ca, Po, (lg), (gs) KCl Iran Lower Fars Formation Early Miocene ? (Po) MgSO4 Rhine Graben, Germany, Mulhouse Zone Salifere Early Oligocene ca. 22 km3 sy, (ca) KCl basin, France Navarra Basin (Ebro Basin), Spain Late Eocene ? ca, sy KCl Geochemistry Catalan Basin (Ebro Basin), Spain Late Eocene >80 km3 ca, sy, (Po) KCl 6 3 Khorat Plateau (Khorat and Sakon Maha Sarakham Formation Late Cretaceous >1.5 10 km ca, sy, Tc, (B) KCl–CaCl2 2MgCl2 12H2O Â Á Á Nakhon basins), Thailand Congo Basin, West Africa Salt beds between Chela Series and Early Cretaceous (Aptian) ca. 5 106 km3 of ca, sy, Tc, bi KCl-CaCl 2MgCl 12H O Â 2 Á 2 Á 2

Mavuma Beds K-bearing salts of

Gabon Basin, West Africa Salt beds between Cocobeach and Early Cretaceous (Aptian) ? ca, Tc, bi KCl–CaCl2 2MgCl2 12H2O Evaporites Á Á Madiela formations Sergipe-Alagoas basin, Brazil Ibura Member, Muribeca Formation Early Cretaceous (Aptian) 50–200 km3 of ca, Tc, sy KCl–CaCl 2MgCl 12H O 2 Á 2 Á 2 carnallite

Forecaucasian (Ciscaucasian) Basin Late Jurassic (Tithonian, ? sy, (Po) KCl and Kimmeridgian?)

Middle Asian Basin, Turkmenistan– Late Jurassic ? ca, sy, (rh) KCl Evolution Uzbekistan–Tajikistan Gulf of Mexico, USA Louann formation salt Middle Jurassic (Callovian) ? sy KCl Aquitanian basin, France Late Triassic (Keuper) ? ca, sy, Po, ks KCl–MgSO4 Northern Sahara Salt Basin, Algeria Trias a evaporites (salina d’Ourgla) Late Triassic (Carnian-Norian) ? sy KCl of Moroccan Meseta basins Late Triassic (Carnian-Norian to ? ca, sy, rh, (ks), (bi), KCl Seawater perhaps early Jurassic)

(Continued) 533 534

Table 10 (Continued) Geochemistry

Location Formation Age Volume of potash Mineralogy Chemical character deposit (all deposits contain halite)

English Zechstein basin Teesside group (Z3, Leine), and Late Permian (early and late ? sy, (ca), (rh) KCl Staintondale group (Z4, Aller) Tatarian) of

3 Evaporites N.W. European Basin Zechstein (Z1, Werra; Z2, Stassfurt, Z3, Late Permian (Kazanian to 2000 km ca, sy, Po, ks, lg, ka, bl, gs, MgSO4 Leine; Z4, Aller) Tatarian) lw, (rh) 3 Delaware Basin, New Mexico and Texas, Salado Formation Late Permian (Tatarian) 500 km sy, lg, Po, ks, ca, ka, bl, le, KCl–MgSO4 USA lw, gs

Pericaspian Basin, Russia, Kazakhstan Iren horizon Early Permian (Kungurian) ? ca, Po, sy, bi, ka, lg, ks, gs, KCl–MgSO4 and bl, lw, (B) Evolution Upper Kama Basin (Solikamsk, Cis-Ural Iren horizon, Berezniki Formation Early Permian (Kungurian) 119 km3 sy, ca KCl trough), Russia Upper Petschora basin, Russia Iren horizon Early Permian (Kungurian) ? sy, ca KCl 3

Supai Basin, Arizona, USA Supai Formation (Upper) Early Permian 0.1 km sy KCl of

(Leonardian Artinskian) Seawater ¼ Pripyat trough, Belarus K-bearing deposits correlated with Early Permian ? sy, ca, ks, (bi) MgSO4–KCl Kramators’k Formation 3 Dnipro-Donets depression, Ukraine Kramators’k Formation Early Permian (Sakmarian) 7.35 km ca, ks, Po, sy, bi, B, (lg) MgSO4–KCl Amazon basin, Brazil Nova Olinda Formation Early Carboniferous to early ? sy KCl Permian Eagle basin, Colorado, USA Eagle Valley Evaporite Carboniferous, middle to late 0.1 km3 sy, ca KCl Pennsylvanian (Desmoinesian– early Virgilian) Paradox basin, Colorado and Utah, USA Paradox Formation (Hermosa Group) Carboniferous, middle 450 km3 sy, ca, Po, (ks), (Rh), (B) KCl Pennsylvanian (Desmoinesian) Canadian Maritimes (Moncton Basin), Cassidy Formation, Windsor Group Carboniferous, early 30 km3 sy, ca, (rh), (Po), (B) KCl Canada Mississippian (early Visean) Adavale Basin, Queensland, Australia Boree Salt Member, Etonvale Formation Middle Devonian ? sy KCl West Canadian basin (Elk Point basin), Prairie Evaporite Middle Devonian (Givetian) 3000 km3 sy, ca KCl Canada–USA Pripyat trough and Dnipro-Donets Lower and upper salt units Late Devonian (Frasnian– 6000 km3 sy, ca KCl depression, Belarus–Ukraine Fammenian) Morsovo basin, Moscow syneclise, Morsovo Salt Member Middle Devonian (Eifelian) 0.02 km3 sy, (ca) KCl Russia Tuwa basin, South Siberia, Russia Ikhedushiihgol Formation Middle Devonian (late Eifelian– ? sy, (rh) KCl early Givetian) Michigan Basin, USA–Canada Salina Group Middle to late Silurian (Wenlock– 1000 km3 sy, (ca), (Po), (B) KCl Pridoli) East Siberia, Russia Angara Formation Early Cambrian 25 km3 ca, sy KCl East Siberia, Russia Usolye Formation, and other formations Early Cambrian 15 km3 ca, sy, (rh) KCl Sar Pohl, Iran Hormoz Salt Neoproterozoic to Middle ? sy, rh KCl Cambrian (Cambrian?) Salt Range Basin, Pakistan Salt Range Formation Late Neoproterozoic to early lg, ka, (sy), (Po), (ks) MgSO4 Cambrian

Lack of or highly controversial data are marked by “?”. Mineral abbreviations: B – borate minerals; bi – bischofite, MgCl2 6H2O; Á bl – bloedite, Na2SO4 MgSO4 4H2O; Á Á ca – carnallite, KCl MgCl2 6H2O; Á Á gs – glaserite, Na2SO4 3K2SO4; Á ka – kainite, 4KCl 4MgSO4 11H2O; Á Á ks – kieserite, MgSO4 H2O; Á le – leonite, K2SO4 MgSO4 4H2O; Á Á lg – langbeinite, K2SO4 2MgSO4; Á lw - loeweite, 2Na2SO4 2MgSO4 5H2O; Á Á mi – mirabilite, Na2SO4 10H2O; Á Po – polyhalite, K2SO4 MgSO4 2CaSO4 2H2O; Á Á Á rh – rhinneite, FeCl2 3KCl NaCl; Á Á sy – sylvite, KCl;

Tc – tachyhydrite, CaCl2 2MgCl2 12H2O; Geochemistry Á Á (sy) – within parentheses, mineral aggregates; sy – without parentheses, rock-forming mineral; sy – in bold, economically significant minerals. Chemical character of the deposits: MgSO4 – rich in magnesium sulfate; of MgSO4-KCl – mixed or intermediate character, sulfates dominate; Evaporites KCl–MgSO4 – mixed or intermediate character, chlorides dominate; KCl – poor in magnesium sulfate; KCl–CaCl2 2MgCl2 12H2O – poor in magnesium sulfate, and containing tachyhydrite. Á Á and Evolution of Seawater 535 536 Geochemistry of Evaporites and Evolution of Seawater and carnallite as the major components (Table 10; Zharkov Hanseran Evaporite Group in Rajasthan, and Mg sulfates et al., 1978). In the upper half of Permian, that is, from occur in Salt Range evaporites in Pakistan (Horita et al., Kungurian to Tatarian, the chloride sedimentation was accom- 2002, with references). These are probably the oldest known panied by sulfate deposition (Zharkov, 1981). The Mesozoic volumetrically significant K–Mg salt deposits, except for the potash evaporites are again dominantly of the chloride type, Ara Formation that contains ash beds dated radiometrically at whereas in Neogene, the K–Mg sulfate salts appeared again 542.0 0.3 Ma and 542.6 0.3 Ma (Schro¨der et al., 2004); the Æ Æ in the geologic record together with the chloride type age of these formations is, however, poorly constrained.

(Sonnenfeld, 1984). Thus, the MgSO4-rich evaporites are con- From the known record of the marine and marine-related fined only to the Permian, the Miocene, and the Quaternary evaporites in Earth history (i.e., saline giants), it is evident that (Hardie, 1990). the mineralogical and chemical composition of evaporites The distribution of marine K–Mg salts in time appears to was surprisingly stable. In particular, the K–Mg evaporites reflect two Phanerozoic megacycles: the Paleozoic megacycle present since the Cambrian evidence both chloride chemistry and Mesozoic–Cainozoic megacycle that both began from (Salt Range Formation, Pakistan) and sulfate type of chemistry long-lasting chloride type of evaporite deposition and abruptly (Usolye Formation, Russia). That is the same chemistry that is end with deposition of chloride–sulfate evaporites in Permian known in majority of K–Mg deposits from the Cambrian until and from Neogene to today, respectively (Kovalevych, 1990, today (Strakhov, 1962; Vysotskii et al., 1988). Based on these with references). The Neogene K–Mg sulfate salts contain more observations, it was interpreted that from the end of the Pre- sulfate minerals (kieserite, langbeinite, polyhalite, and kainite) cambrian time onward, both the chemical composition of the than do the Permian salts (Kovalevych, 1990). ocean and possibly the salinity of the ocean was established In some periods of time, an enormous amount of salts was and was similar or remained nearly the same as today. There is accumulated and these phases of deposition appear to have no record of the irreversible evolution of evaporite composi- been spread across much of the planet (Table 9). The geologic tion in Phanerozoic (Strakhov, 1962); however, the record of record suggests at least two main intervals of increased evapo- fluctuation is recognizable both in the K–Mg facies and brine rite deposition in Earth history: 180–250 Ma and 500–700 Ma composition in halite fluid inclusions. (Holser, 1984; Knauth, 2005). Evans (2007) suggested two Two periods that lasted 40 My were recognized in the acmes of deposition for the Precambrian-to-Cambrian interval: Phanerozoic, lacking any record of marine saline giants: in at 800 Ma (in Cryogenian), which produced 350000 km3 Ordovician (Zharkov, 1981) and between the Upper Conia- of evaporites, mainly Ca sulfates, and in late Ediacaran to Early cian and the end of Paleocene (Sonnenfeld, 2000). Ordovician Cambrian time, resulted in 1.5 million km3 of mixed Ca sul- is the only Phanerozoic system without recognized potash fate and Na chloride salts. In Phanerozoic, about 40% of all evaporites (Goncharenko, 2006). salts were sequestered in the Permian–Triassic interval (Knauth, 2005), and according to Trappe (2000), these evap- 9.17.23.2 Precambrian (Pre-Ediacaran) Marine Evaporites orites together contain 35% of the world’s evaporite resources. It seems that these evaporite-rich intervals are apparently asso- Precambrian evaporites (marine and nonmarine) are mostly ciated with the paleogeographic configurations that developed represented by pseudomorphs after gypsum, anhydrite, and during and after the breakup of the two supercontinents: Rodi- halite (Zharkov, 2005). Evans (2007) counted about 100 docu- nia – in late Proterozoic (Neoproterozoic) (Knauth, 2005), mented examples, including ten from the Archean (Table 11). and Pangea – in Phanerozoic interval (Gordon, 1975). These About 20 deposits have total preserved or estimated salt vol- periods were favorable for evaporite deposition because of the umes attaining 1000 km3, and all of them occur in the Protero- appearance of many enclosed, rapidly subsiding basins in equa- zoic era (Table 9). torial and circum-equatorial settings (Knauth, 2005; Trappe, The scarcity and lack of evaporites before 2 Ga was 2000). explained as the result of selective removal (Gordon, 1975; Hay (personal information in Hansen and Wallmann, Hardie, 2003, among others), related at least partly to their 2003) calculated that the average global rate of evaporite very high solubility – they did not survive the metamorphic deposition in Cretaceous and Cenozoic reached maximum conditions that have affected these very old rocks. Additional 18 1 in 150–140 Ma (2.315 10 kg 10À My) and 20–10 Ma reasons could be following: (1) the lack of extensive platforms 18 1 Â (3.459 10 kg 10À My) and minimum in 70–60 Ma time at the margins of emerging continents, necessary for large-scale Â 18 1 interval (0.071 10 kg 10À My). The Messinian evaporites evaporite deposition (Strakhov, 1962), and (2) the fact that Â ( 5.96–5.33 Ma) are one of the greatest evaporite events on there were only a few continents in the Archean and they were Earth considering that their volume, at least 2.25 106 km3, relatively small and apparently did not create a supercontinent Â was deposited in a relatively short time interval – 640 ky – in (Knauth, 2005; Walker, 1985). Note, this view is only a much shorter time than recognized in any other saline giants hypothesis (see Armstrong, 1991; Lenardie, 2006) and other (Rouchy and Caruso, 2006; Ryan, 2008). authors argue for vey rapid growth of continental crust in that Late Neoproterozoic evaporites occupying Pangea spread same span of time (Lowe and Tice, 2007). The acceptance of from the Indian subcontinent (Rajasthan, Salt Range in the slow gradual accretion of continents means that the chem- Pakistan), Oman (Ara Formation), and Saudi Arabia–Iran istry of the early oceans (<2 Ga) was driven mainly by mantle (Hormoz, formerly Hirmuz or Hormuz, series) (Horita et al., processes with increasing influence of the input from the rivers 2002; Schoenherr et al., 2008; Talbot et al., 2009). Potash salts on emerging lands only in later Precambrian and continuing up of both sulfate and chloride type, with polyhalite, kainite, to today (Godderis and Veizer, 2000; Reddy and Evans, 2009). langbeinite, and sylvite and carnallite, are known from the The other consequence is that the assumed high salinity of the Table 11 Inferred and direct evidence of earliest evaporites in Archean through early Mesoproterozoic rocks, based on the compilation by Pope and Grotzinger (2003), Bekker et al. (2006), Schro¨der et al. (2008), and sources given by these authors, and some additional references cited below

Location Age (Ga) Units Evaporite evidence Thickness Notes References

43 Canada 0.7–1.2 Minto Inlet and Kilian Gy Multiple gypsum beds up Marine Pope and Grotzinger (2003) formations, Shaler Group to 30 m thick 42 Mauritania ca. 1.1 Oued Tarioufet Formation, Atar Ca-Evp, ca. 50 m (?) SGa (?), marine Kah et al. (2012) Group, Gouamir and Ca-ps-Gy or Ar, Tenoumer formations, El ps-Ha, Mreiti Group, Taoudeni Basin sc-breccias, chicken-wire texture 41 Mauritania, ca. 1.2 Char Group, Mauritania, Douik ps-Ha ca. 50 m SGb, marine, possibly correlate Evans (2006) Algeria Group, Algeria with evaporites in Atar and El Mreiti Groups (above) 40 Canada 1.2 Society Cliffs Formation, Victor Gy, Multiple beds a few cm’s SGc, restricted marine Kah et al. (2001), Evans Bay Group, Borden Basin ps-Ha, to meter’s thick, (2006) sc-breccias >100 m 39 USA 1.15–1.3 Upper Marble, Grenville Series An, as lenses and beds Beds (or lenses) >40 m Metamorphosed evaporites Whelan et al. (1990) thick 38 USA, 1.46 Waterton, Altyn, Prichard, and ps-Evp, 100 m SGd, marine, two evaporite Evans (2006) Canada Wallace formations, Belt ps-Gy, horizons Supergroup ps-An, ps-Ha, Geochemistry length-slow chalcedony, chicken-wire textures, scapolite 37 Australia ca. 1.5 Discovery Formation, Edmund ps-Gy, or 70 m SGe, marine, several evaporite Evans (2006)

Group, Bangemall ps-An horizons of

Supergroup, Bangemall basin Evaporites 36e Australia 1.61 Balbirini Formation, McArthur- ps-Ha, ? SGf, alkaline lake suggested by Walker et al. (1977), Evans Mt Isa basins pseudomorphs after sulfates, shortite (2006) ps-Sh, cauliflower cherts and 36d Australia 1.635 Lynott Formation, McArthur-Mt ps-Gy, ca. 300 m SGf, marine sabkha Walker et al. (1977), Evans

Isa basins ps-Ha, (2006) Evolution cauliflower cherts 36c Australia 1.645 Myrtle, Emmerugga, and other ps-Gy, ca. 200 m SGf Walker et al. (1977), Evans formations, McArthur-Mt Isa ps-Ha (2006) basins of 36b Australia 1.66 Mallapunyah, Paradise Creek, ps-Gy, >10 m SGf, marine sebkha Walker et al. (1977), Evans Seawater Esperanza, Staveley ps-Ha, (2006) formations McArthur-Mt Isa botryoidal quartz nodules basins after anhydrite, massive replacement by gypsum 537 (Continued) 538

Table 11 (Continued) Geochemistry

Location Age (Ga) Units Evaporite evidence Thickness Notes References

36a Australia 1.74 (1.54–1.74) Corella Formation, McArthur-Mt ps-Sh, ca. 500 m SGg, alkaline lake suggested by Walker et al. (1977), Muir Isa basins ps-Gy (?), shortite (1987), Evans (2006)

quartz-replacing anhydrite of

nodules Evaporites 35 India >1.7 Vempalle Formation, Papaghni ps-Ha, ? Marine, associated with lava Pope and Grotzinger (2003) Group ps-Gy flows 34 Canada 1.8 Cowles Lake Formation ps-Ha, >200 m Marine to non-marine, halite Pope and Grotzinger (2003)

ps-Gy, >>gypsum and sc-breccias 33 Canada 1.8 Brown Sound Formation ps-Ha, ca. 300 m Marine to non-marine, halite Pope and Grotzinger (2003) Evolution ps-Gy, >>gypsum sc-breccias 32 Russia 1.8–1.9 ps-Gy, ? Associated with barite, sabkha Pope and Grotzinger (2003) of ps-An Seawater 31 Canada 1.82–1.91 Tavani Formation, Hurwitz Q-ps-Gy, ? Coastal pans, marine-to-non- Aspler and Chiarenzelli Group Dol-ps-Gy, marine (2002) halite moulds 30 Canada ca. 1.87 Stark and Hearne formations, ps-Ha, 200–600 m, SGh, marine to non-marine, Pope and Grotzinger Great Slave Lake Supergroup silicified hopper casts, and reconstructed halite >>gypsum (2003), Evans (2006) pagoda halite, thickness of ps-Gy, evaporites ca. 100 m ¼ sc-megabreccia 29 Canada 1.8–2.0 Kasegalik and Mc-Leary ps-Gy, ca. 150 m Marine Pope and Grotzinger (2003) formations, Belcher Group ps-Ha 28 Canada ca. 1.95 Rocknest Formation, Dol-ps-Gy, Traces of evaporites SGi (?), Evans (2006) Coronation Supergroup, Slave ps-An, dispersed within marine, lagoon on inner shelf, craton ps-Ha carbonates passive margin 27 S Africa 2.06 Dewaras Group Gy (?) Lacustrine environment in rift Pope and Grotzinger (2003) 26 Russia ca. 2.09 Tulomozero Formation, Upper Ca-ps-Gy, Multiple units >20 m, SG j, passive margin, playa lake, Melezhik et al. (2005), Jatulian Group Dol-ps-Gy, within ca. 500 m of marine sabkha, intertidal flats Brasier et al. (2011), Si-ps-Gy, total thickness Reuschel et al. (2012) An (relics), pseudomorphs after anhydrite and gypsum crystals and nodules, ps-Ha, sc-breccias, enterolithic and chicken wire structures 25 Russia ca. 2.1 Fedorovka (Fedorov) Formation An, as layers and veins ? Passive margin Zharkov (2005), Bekker (Aldan Shield) et al. (2006) 24 Zimbabwe ca. 2.15 Norah Formation, Deweras An, as layers ? Intracratonic rift basin Bekker et al. (2006) Group 23 Gabon ca. 2.0–2.2 Francevillian C Formation, Ca-ps-An, ? Marine, supratidal-sabkha Pre´at et al. (2011) Francevillian Group Ca-ps-Gy environment 22 USA ca. 2.15 Lower part of the Nash Fork Molds after anhydrite nodules ? Passive margin Bekker et al. (2006) Formation, Snowy Pass and gypsum crystals Supergroup 21 Canada ca. 2.15 Laparre Formation, Peribonca Dol-ps-Gy, ? Passive margin Bekker et al. (2006) Group, Otish Supergroup Dol-ps-An (after crystals and nodules) 20 S Africa ca. 2.15 Lucknow Formation, Q-ps-Gy, ? Marine, passive margin Bekker et al. (2006), (2.10–2.20) Olifantshoek Group and Q-ps-An, Schro¨der et al. (2008) Transvaal Supergroup molds after gypsum and anhydrite 19 Australia ca. 2.15 (2.2)? Bubble Well Member, Juderina Si-Evp, ca. 100 m SGk, Marine or marginal El-Tabakh et al. (1999a) Formation, Yerrida Group Q-ps-Gy, marine, associated with Q-ps-An volcanics 18 S Africa 2.2 Pretoria Group ps-Mir <2 m Sodic lake deposits in a playa Pope and Grotzinger (2003) setting 17 Australia ca. 2.2 Bartle Member, Killara Si-ps-An, ? Playa lake (alkaline?) Pirajno and Gray (2002) Formation, Yerrida Group Si-ps-Gy,

Kao-ps-Gy or An, An (relics), Geochemistry ps-Sh?, ps-Tro? 16 USA ca. 2.22–2.3 Kona Dolomite, Chocolay Group Si-ps-Gy, 30–1000 m SGl, marine, associated with Bekker et al. (2006) Si-ps-An, volcanics, intracratonic basin, ps-Ha (moulds), open to passive margin, of

sc-breccias correlated with Gordon Lake Evaporites Formation 15 Canada ca. 2.22–2.3 Gordon Lake Formation, Ba (as beds), silicified and Multiple horizons in SGl, marine? passive margin, Cameron (1983), Bekker Huronian Supergroup pristine anhydrite and >300 m supratidal and sabkha zone, et al. (2006) gypsum nodules and layers, correlated with Chocolay and Si-tr-An; Group

beds of anhydrite nodules Evolution 14 S Africa 2.52–2.56 Campbellrand-Malmani Si-ps-Ha, >500 m Marine Sumner and Grotzinger carbonate platform, Transvaal Ca-ps-Gy (?), (2004), Gandin et al. Supergroup sc-breccias (2005) of

(Continued) Seawater 539 540 Geochemistry

Table 11 (Continued)

Location Age (Ga) Units Evaporite evidence Thickness Notes References of

13 S Africa ca. 2.58 Black Reef and Oaktree ps-Ha (moulds), ? Supratidal flat or sabkha Eriksson et al. (2005) Evaporites formations, Transvaal Ca-ps-Ar Supergroup 12 Australia 2.4–2.8 (2.6) Carawine Formation (Carawine Dol-ps-Gy, <20 m Marine, considered as the Simonson et al. (1993),

Dolomite), Hamersley Group Si-ps-Gy, or earliest undoubtful selenite Sumner and Grotzinger and Dol-ps-Ar (?), deposits (2000) ps-Ha Evolution 11 Australia 2.6–2.7 Black Flag Beds Ank-ps-Gy, 40 m Tidal flats (?) associated with Pope and Grotzinger (2003) Ank-ps-An (?) volcanics 10 Canada 2.7 Steeprock Group Ca-ps-Ar, or Pseudomorphs Marine, carbonate platform with Grotzinger (1989), Sumner of Ca-ps-Gy (?), dispersed within stromatolites, supposedly and Grotzinger (2000), Seawater Si-tr-Gy, carbonates non-evaporite carbonate (Ar) Hardie (2003) Si-tr-An (?) deposits 9 Zimbabwe 2.7 Cheshire Formation, Belingwe Ca-ps-Ar, or 10 m Marine, carbonate platform with Grotzinger (1989), Hardie Greenstone Belt Ca-ps-Gy (?) stromatolites, supposedly (2003) non-evaporite carbonate (Ar) deposits 8 Australia 2.7 Tumbiana Formation, Fortescue ps-Ha ca. 320 m Lacustrine or marine Buick (1992), Awramik and Group Buchheim (2009) 7 S Africa 2.8 Ventersdorp Supergroup ps-Nat ? Lacustrine Pope and Grotzinger (2003) 6 Australia 2.97–3.19 Ga Farrel Quartzite, George Creek ps-Evp, Several horizons Continental margin Sugitani et al. (2003, 2007) Group Si-ps-Nah 5 Australia 3.3–3.5 Rocklea Dome ps-Ha, <20 m Boulter and Glover (1986) ps-Gy 4 S Africa 3.4 Witkop Formation, Nondweni Ba-ps-Gy <1.5 m Associated with volcanics Wilson and Versfeld (1994), Greenstone Belt Hofmann and Wilson (2007) 3 S Africa 3.4 Buck Reef Chert, Kromberg Ba, 5–40 m Byerly and Palmer (1991), Formation, Onverwacht Ba-ps-Gy (?), Lowe and Worrell (1999), Group, Barberton Greenstone ps-Nah, Lowe and Byerly (2007) Belt Si-Evp, molds, silicified sc-breccias 2 Australia ca. 3.4 (3.35– Strelley Pool Chert (Strelley Ba, Multiple beds, <10 to Associated with volcanics, Lindsay et al. (2005), 3.43), or Pool Formation), Kelly Group Ba-ps-Gy, 25 m interpreted as marine Warren (2006), Allwood (3.346–3.459) Si-ps-Nah (?), et al. (2007, 2009), Van Si-ps-Ba (?), Kranendonk (2007) ps-Ha, Si-ps-Ar (?) 1 Australia ca. 3.49 (3.447– Dresser Formation (North Pole Ba (as beds), Multiple beds, <10 to Associated with volcanics, Lambert et al. (1978), Lowe 3.496) Chert), Warrawoona Group Ba-ps-Gy, 25 m considered as non-marine (1983), Buick and Dunlop Si-ps-Gy (crystal rosettes), (1990), Shen and Buick ps-Ha (2004), Runnegar et al. (2001), Allwood et al. (2007), Lowe (1983), Grotzinger (1989), Warren (2006), Van Kranendonk (2007)

Saline giants (SG), with volume 1000 km3, are distinguished and shortly described (in footnotes) after Evans (2006), except of the Mesoproterozoic Taudeni Basin (see Table 9). An, anhydrite; Ank-ps-Gy, ankerite pseudomorphs after gypsum; Ba, barite; Ba-ps-Gy, barite pseudomorphs after gypsum; Ca-Evp, calcitized evaporites; Ca-ps-Ar, carbonate pseudomorphs after aragonite; Ca-ps-An, carbonate pseudomorphs after anhydrite; Ca-ps-Gy, carbonate pseudomorphs after gypsum; Ca-ps-Gy or -Ar, carbonate pseudomorphs after gypsum or aragonite; Dol-ps-An, dolomite pseudomorphs after anhydrite; Dol-ps-Gy, dolomite pseudomorphs after gypsum; Gy, gypsum; Kao-ps-Gy or An, kaolinite pseudomorphs after gypsum or anhydrite; ps-An, pseudomorphs after anhydrite; ps-Evp, pseudomorphs after evaporites; ps-Gy, pseudomorphs after gypsum; ps-Mir, pseudomorphs after mirabilite; ps-Nah, pseudomorphs after nahcolite; ps-Nat, pseudomorphs after natron; ps-Ha, pseudomorphs after halite; ps-Sh, pseudomorphs after shortite; ps-Tro, pseudomorphs after trona; Q-ps-An, quartz pseudomorphs after anhydrite; Q-ps-Gy, quartz pseudomorphs after gypsum; sc-breccias, solution collapse breccias; Si–Evp, silicified evaporites; Si-ps-An, silicified pseudomorphs after anhydrite; Si-ps-Ar, silicified pseudomorphs after aragonite; Si-ps-Gy, silicified pseudomorphs after gypsum; Si-ps-Nah, silicified pseudomorphs after nahcolite; Si-tr-An, quartz filled traces after anhydrite; Si-tr-Gy, quartz filled traces after gypsum. Lack of or highly controversial data are marked by “?”.

Notes to saline giants (SG): Geochemistry aTraces of calcitized evaporites within a few tens of m thick stratigraphic interval traced at the distance >1500 km. bThe basin area 800 200 km. Â cThe basin area ca. 140 000 km2. dTwo intervals of vanished or metamorphosed evaporites on an area of 300 200 km; restoration of tectonic shortening suggests a basin ca. 100 000 km2 in size. Â eThe basin area ca. 40 000 km2. of fThe basin area at least 5000 km2. Evaporites gScapolite-albite-tourmaline association, total ca. 500 m thickness across an area of 200 20 km. Â hThe basin area ca. 300 000 km2. iTraces of evaporites within ca half of the thickness of a carbonate facies, which spans an area of about 250 50 km, and in a lagoon zone about 200 km wide. Â jRelict evaporitic textures within ca. 500 m of the dolomitic section. kThe basin area 100 100 km. and Â lPseudomorphs in ca. 100 m of the section over a ca. 400 100 km in Chocolay Group (USA); a 40 m thick basal part of the Gordon Lake Formation (Canada) contains anhydrite nodules and breccias, interpreted as a sabkha environment. Â Evolution of Seawater 541 542 Geochemistry of Evaporites and Evolution of Seawater initial ocean began to decrease due to the accumulation of et al., 2004). The predicted concentration of sulfate in Meso- evaporites on continental shelves not earlier than 2.5 Ga proterozoic was presumably as low as 2.7–4.5 mM (Kah et al., (Knauth, 2005). 2004). At that time, the availability of Ca was apparently Probably, the oldest known record of marine evaporites is limited by excess precipitation of calcium carbonate resulting represented by silicified pseudomorphs after beds of some from elevated carbonate saturation, and therefore, a great DE unknown bottom-grown evaporite crystals occurring in would be required to attain gypsum saturation (Kah et al., 3.43 billion-year-old Strelley Pool Chert, in Pilbara Craton, 2004, with references). In the presence of high amounts of Cl Australia (Table 11 and Figure 22). These beds show traces of and Na in the Mesoproterozoic seawater, halite would precip- synsedimentary dissolution, and of syntaxial growth over disso- itate before gypsum during evaporation, which is consistent lution surfaces, and are associated with stromatolitic structures with the scarce geologic record. It seems likely that very low and solution–collapse breccias. Lowe (1983) suggested gypsum concentration of sulfate ions before Mesoproterozoic or aragonite, and Lowe and Tice (2004) – nahcolite, as the (Reuschel et al., 2012), even though the concentration of original mineralogy. Lindsay et al. (2005) recognized post- calcium ions could be high (Rouchon et al., 2009), resulted evaporite ‘chicken-wire’ textures formed by quartz aggregates in lack or very sparse deposition of Ca sulfates during the early and described 30-cm-long quartz pseudomorphs after supposed time of Earth history (Eriksson et al., 2005; Foriel et al., 2004; barite and also aragonite crystals. However, Allwood et al. Kah et al., 2004; Zentmyer et al., 2011). It is estimated that the (2007), who recently restudied these outcrops, did not specify concentration of sulfate ions was less than 200 mM in the what evaporite mineral crystallized in the early Archean envi- Archean, and it rose to over 1 mM in the early Paleoproterozoic ronment, although in later work, they agreed that it was and to more than 2.5 mM in the mid-Paleoproterozoic “probably originally aragonite” (Allwood et al., 2009, p. (Reuschel et al., 2012, with references), 9548), as it was also suggested by van Kranendonk (2006). Grotzinger (1989), Grotzinger and Kasting (1993), Grotzinger Allwood et al. interpreted the environment as “an isolated, and Knoll (1995), Sumner and Grotzinger (2000), and Pope partially restricted, peritidal marine carbonate platform, or and Grotzinger (2003) questioned the occurrence of marine reef, where there is virtually no trace of hydrothermal or terrig- bottom-grown gypsum crystals and massive evaporite deposi- enous clastic input” (Allwood et al., 2007, p. 198). Marine tion in the Archean and Paleoproterozoic and challenged the environment of these deposits was earlier proved by geochem- earlier interpretation that the chemistry of the ocean was likely ical studies (van Kranendonk et al., 2003). the same as today since the (late) Archean (Hardie, 2003; The traces of evaporites (pseudomorphs) from marine Walker, 1983). They assumed that bicarbonate ion concentra- deposits are known from several formations dated c.2.8– tion exceeded twice that of calcium in Precambrian seawater 2.4 Ga (Table 11; Pope and Grotzinger, 2003). However, the (Grotzinger, 1989, see Rouchon et al., 2009, for more up-to- oldest ( 2250 Ma) saline giant, recognized by the presence of date information on contents of calcium and carbonate– copious pseudomorphs after gypsum and anhydrite within bicarbonate ions in the Archean seawater). This would cause 100 m thick interval of the section, occurs in Chocolay– the Ca ion to become exhausted during evaporite concentration Gordon Lake succession, on Superior craton, Canada and by calcite/aragonite precipitation well before the stage of United States, and is estimated as 4500 km3 of vanished evap- gypsum precipitation was achieved. Therefore, the precipita- orite salts (Table 9; Evans, 2006). The Gordon Lake Formation tion of gypsum was bypassed during early salinity rise, and in Ontario presumably contains the earliest preserved Ca halite precipitated directly after Ca carbonates in all the early sulfate deposits as thin beds of anhydrite nodules within lam- Precambrian marine evaporite successions (Eriksson et al., inated mudstone (Cameron, 1983; Huston and Logan, 2004). 2005; Pope and Grotzinger, 2003). According to Grotzinger Most of the pre-Ediacaran saline giants are known only from (1990), the rare occurrences of pseudomorphs after gypsum the accumulation of pseudomorphs within thick stratigraphic in earliest Precambrian were restricted to deltaic settings, where intervals and associated collapse breccias. The earliest well- locally higher concentration of calcium could appear. Grotzin- preserved sequence of extensive bedded evaporites, including ger and coauthors assumed that NaCl concentration was high, gypsum, occurs in the latest Paleoproterozoic to early Mesopro- in agreement with the presence of halite pseudomorphs. The terozoic ( 1.6 Ga) rocks of the McArthur Basin of Australia high chloride concentration, together with much other evi- (Tables 9 and 11; Walker et al., 1977). The younger mentioned dence, suggests that the seawater had relatively low pH at that Centralian Superbasin in Australia (800–830 Ma), about time (e.g., Foriel et al., 2004; Holland and Kasting, 1992; Pinti, 140000 km2 in size, contains the most extensive and relatively 2006; Rouchon et al., 2009; Sugisaki et al., 1995). This would well-preserved gypsum, anhydrite, and halite beds with typical explain why seawater was unable to precipitate Na carbonates thickness 800 m (Table 9; Evans, 2006, with references). (Grotzinger and Kasting, 1993), otherwise expected to form in The first recorded bedded Ca sulfate deposits occur the hypothetic soda ocean (Kempe and Degens, 1985). in Mesoproterozoic, proving that sulfate concentration in We would like to point out that the use of mineralogy as the water has been high enough for more abundant gypsum only evidence or the lack of evidence of the Usiglio sequence precipitation at least since that time (Kah et al., 2004). The might lead to significant misinterpretation in the case of lim- mentioned first recorded bedded Ca sulfate deposits in the ited data. Modern halite deposits can start an evaporite Mesoproterozoic McArthur Basin (1.6 Ga) also marks the sequence without or only with minor crystallization of earlier limit of the existence of the hypothetic early soda ocean accord- gypsum, as it is proved by both modeling of the marginal ing to the other concept of ocean chemistry evolution (Kempe marine evaporite basins (Sanford and Wood, 1991) and a and Kaz´mierczak, 1994). The assumed slow rise in sulfate similar record from some modern environments – for example, concentration in the Archean and Mesoproterozoic is consis- halite pans on supratidal flats or the Taxada halite from the tent with C isotope record from that time and with a presum- MacLeod basin (Logan, 1987). Indeed, evaporite sequences ed increase in oxygenation recorded in the biosphere (Kah can be modified by a replacement processes, which include Geochemistry of Evaporites and Evolution of Seawater 543

Period Era Eon

Geon Quaternary Neogene . r e C. T Paleogene 60 ± 0.5 Ma Cretaceous Gulf of Mexico evaporites, the largest saline giant on Earth, Jurassic 3 Common,

Mesoz. Triassic ~2 400 000 km 251 ± 0.1 Ma well Permian preserved Carboniferous evaporites Devonian Silurian Ordovician P h a n e r o z i c Paleozoic Cambrian 542 ± 1.0 Ma Ediacaran ~635 Ma ozoic Cryogenian Centralian superbasin, Australia, 800–830 Ma oter the largest preserved 850 pre-Ediacaran saline giant, 3 Tonian ~140 000 km Neopr 1000 43

Stenian 42

ozoic 1200 39 40 41

oter Ectasian 1400 38 Calymmian 37 Mesopr 1600 36e

P r o t e z i c 36d 36b 36c Statherian 35 36a 1800 33 34 Saline giant with abundant traces 32 30 31 First common 29 of Ca-sulfates, Ca-sulfate

ozoic Orosirian 28 2.1 Ga Tulomozero Formation, evaporites Upper Jatulian Group,

oter 2050 27 Russia 2.06 Ga 25 26 Rhyacian 20 21 22 23 24 17 18 19 Great 15 16 Oxidation Paleopr 2300 First undisputable Event vanished saline giant 2.3 Ga Siderian with Ca-sulfates and halite, Gordon Lake Formation, 2.35 Ga 2500 Huronian Supergroup, Canada 14 and Kona Dolomite, 12 13 Chockolay Group, USA Neoarchean 11 8 9 10 Pseudomorphs after halite, 2.7 Ga Tumbiana Formation 2800 7 (lacustrine or marine), Fortescue Group, Australia ca 3.06 Ga Silicified pseudomorphs after nahcolite? Mesoarchean Farrel Quartzite, George Creek Group, Australia 6 Barite pseudomorphs after gypsum? 3200 Halite molds 3.4 Ga Witkop Formation, 3.4 Ga in chert, Nondweni Rocklea Dome, A r c h e a n Greenstone Australia Paleoarchean 2 3 4 5 Belt, S. Africa Silicified 1 pseudomorphs 3.4 Ga after nahcolite? 3600 ca 3.49 Ga Buck Reef Chert, Barite and/or Kromberg Formation, barite pseudomorphs Barberton Greenstone after gypsum? Belt, S. Africa Eoarchean Dresser Formation, Warrawoona Group, ca 3.4 Ga Australia Silicified pseudomorphs ~4000 4.03 Ga The oldest rocks; after evaporite mineral Acasta gneisses, (aragonite? gypsum? Canada nahcolite?) Strelley Pool Chert, Kelly Group, Australia H a d e a n

4.4 Ga The oldest minerals; detrital zircons from Jack Hills metaconglomerate, Australia (early hydrosphere)

~4600 1 Precambrian evaporites listed and numbered in Table 11

15 Saline giants with volume of evaporites ³1000 km3

Figure 22 Precambrian (pre-Neoproterozoic) record of evaporite deposits, after data by Bekker et al., 2006; Evans, 2006; Bekker and Holland, 2012, and other references in Table 11. Age of the Great Oxidation Event after Bekker and Holland, 2012; time scale after Ogg et al., 2008. 544 Geochemistry of Evaporites and Evolution of Seawater the early replacement of less soluble gypsum by more soluble 2. Prevalence of symmetrical (wave) ripples halite taking place in halite-producing environments having 3. Lack of unidirectional current structures supersaturated brine warmed to 35–50 C, which is typical of 4. Paucity of dolomite the heliothermal effect (Hovorka, 1992; Schreiber and Walker, 5. An evaporite succession that goes from carbonate directly to 1992; Schro¨der et al., 2003). halite (no sulfates were found)

His interpretations of this evidence are the following:

9.17.23.3 Nonmarine Evaporites in Precambrian 1. The interfingering relationships are unlikely to occur in According to Frimmel and Jiang (2001), most of the known marine transgressions. but scarce records of metamorphosed Proterozoic evaporites 2. Unidirectional sedimentary structures such as asymmetrical represent nonmarine playa lake environments in rift grabens. ripples and herringbone cross-bedding would suggest tidal They are recognized mainly because of mineralogical and geo- activity, but they are absent. chemical data such as their low 11B/10B ‘nonmarine’ ratios 3. Dolomite is very common in ancient marginal marine car- (Byerly and Palmer, 1991). These values are recorded in a bonates and is usually indicative of saline waters with high number of Proterozoic borate deposits, including the Mg/Ca ratios. The rarity of dolomite in the Tumbiana For- (2.1 Ga) of the Liaohe Group in Liaoning, China (Jiang et al., mation suggests nonmarine conditions consistent with a 1997; Peng and Palmer, 1995); the 1.7 Ga Thackaringa lacustrine depositional environment. Group in New South Wales, Australia (Slack et al., 1989); 4. Buick (1992) did not find gypsum, its pseudomorphs, or and the Neoproterozoic Duruchaus Formation in the Damara other sulfate evaporite evidence, but sulfates are known Belt in Namibia (Porada and Behr, 1988). Additionally, there from the Archean marine deposits elsewhere (Zharkov, are data from some other occurrences (Frimmel and Jiang, 2005). Its apparent absence from the Tumbiana Formation, 11 10 2.7 Ga, was conspicuous for Buick (1992) and was used 2001; Grew et al., 2011). On the other hand, high B/ B ratios in tourmalines associated with vanished silicified as strong evidence for the nonmarine origin of this deposit. Archean ( 3.5 Ga) evaporite deposits in Barberton greenstone By contrast, this and similar formations were treated by belt (Table 11) suggest derivation of the boron from marine Reddy and Evans (2009) as marine in origin. The halite pseu- evaporites (Byerly and Palmer, 1991). domorphs present within calcilutites, without any traces after Evaporites cannot help directly in recognition of the salinity dissolved gypsum in the underlying sequences – as expected in and chemistry of the Precambrian oceans because it is difficult the Usiglio sequence, were used as evidence of the anomalous to recognize truly marine evaporites in Precambrian, except for chemistry of the early ocean, following earlier interpretation by the saline giants described earlier. However, even the scale of a Grotzinger (1989), Pope and Grotzinger (2003). The origin of large basin, there is not universal criterion because the brine in this well-exposed formation – marine or nonmarine, tideless particular subbasins can evolve in its own pathway, as proved sea, or lake – is the subject of continuing debate (Awramik and by Garcı´a-Veigas et al. (1995) and Ayora et al. (2001). Only Buchheim, 2009; Bolhar and van Kranendonk, 2007; Sakurai carefully integrated, multimethodological geochemical studies et al., 2005). This is a good example of the weakness of any can lead to the recognition of the marine signal in halite fluid interpretations of the Precambrian seawater chemistry based inclusions (Garcı´a-Veigas et al., 2009, 2011). The separation of on a nonfossiliferous sedimentary record, lacking of clear diag- marine from lacustrine deposits in Precambrian settings, even nostic features of marine environment. by using the criteria listed by Kelts (1988) and Eriksson et al. (2004), is more difficult than in the Phanerozoic and requires complex analysis (Awramik and Buchheim, 2009; Brasier, 9.17.23.4 Pseudomorphs after Evaporite Minerals in 2011). Southgate et al. (1989) suggested the following criteria Precambrian helpful in the recognition of marine and lacustrine Precam- brian evaporites: Pseudomorphs after various salt minerals are common in the Precambrian (Table 11). The most common appear to be of 1. Arrangement of facies gypsum (in Neoarchean; Gandin et al., 2005) and halite (Pope 2. The assemblage of evaporite minerals or their pseudo- and Grotzinger, 2003). Microcline pseudomorphs (up to 10 cm morphs long) after shortite and gaylussite were recognized in the Call- 3. Any fossils that may have been present anna Group of the Willouran Ranges, Australia, late Proterozoic 4. Geochemical evidence 1.4–0.8 Gy. These are interpreted as evaporite playa lake deposits (Rowlands et al. 1980 in Muir, 1987). Silicified pseu- Buick (1992) argued that the Late Archean evaporite domorphs (up to 40 cm long) after bottom-grown evaporite sequences of the Tumbiana Formation in Western Australia crystals (nahcolite) occur in > 2.97 Ga Farrel Quartzite, in (Table 11), which pass from Ca carbonates to halite, without George Creek Group, Pilbara Craton, Australia (Sugitani et al., intercalated or present traces of gypsum, are different than the 2003, 2007). Possible pseudomorphs after shortite occur in Usiglio sequence and that this suggests a lacustrine environ- Corella Formation (1.74–1.54 Gy) in Australia (Muir, 1987). ment. Buick (1992) further supported lacustrine environments The Precambrian pseudomorphs interpreted as postevaporite for these deposits based on several lines of evidence: (after gypsum, nahcolite, etc.) in origin have been commonly 1. Interfingering relationships found between the nondetrital treated as evidence of the chemistry of the ancient oceans. Such sediments and the terrestrial basalts and between the allu- opinions seem to be invalid until two facts are proved: first that vial fan and fluvial sediments these are true pseudomorphs after the given evaporite mineral, Geochemistry of Evaporites and Evolution of Seawater 545 and second, that the evaporite crystal is marine in origin. In the squared terminal crystal apices (Peryt et al., 1990). Another case of Precambrian deposits, it is not easy, if ever possible. revisitation of these crystal pseudomorphs should be made Probably, the oldest well-recognized record of vanished evap- utilizing the results given by Riccioni et al. (1996) in which orites on Earth is silicified pseudomorphs of the bottom-grown aragonite crystals were examined closely and the hexagonal crystals, up to 40 cm long, interpreted as supposed nahcolite cross sections (in that deposit) were found to be the result of

(NaHCO3) from the Kromberg Formation (3.416–3.334 Ga), penetration twinning (aragonite is orthogonal) and commonly Barberton Greenstone Belt, South Africa (Table 11; Lowe and show diagnostic indentations on some faces. Worrell, 1999). The authors were not sure about that interpreta- One of the seafloor crystal crusts, from the 2.6 Ga Carawine tion based on the measurements of interfacial angles with “an Dolomite in Australia (Table 11; Simonson et al., 1993), rep- error of from 2 , where the faces were well preserved, to resents carbonate pseudomorphs after crystals, considered as Æ as much as 10 between poorly preserved faces” (Lowe and the earliest unquestionable gypsum precipitates (Eriksson Æ Worrell, 1999, p. 180). They concluded that the silicified pseu- et al., 2005). Hardie (2003) and Gandin et al. (2005) ques- domorphs “most closely resemble nahcolite” (Lowe and Worrell, tioned at least one of the ‘aragonite’ interpretations (from 1999, p. 181). Nahcolite is a typical evaporite mineral of the soda Neoarchaean Kogelbeen and Gamohaan formations of the lakes (Batalin et al., 1973; Warren, 2010). Campbellrand Subgroup, South Africa, 2.5 Ga), suggesting The other comparable example of equally old ( 3.4 Ga) that the pseudomorphs can represent selenite crystals creating vanished evaporites are barite and quartz pseudomorphs after large domal structures similar to those known from the Messi- gypsum, as well as negative crystals of that mineral, forming nian of the Mediterranean. Hardie further noted that careful stellate aggregates and single euhedral forms in the Witkop measurements of interfacial angles are needed to support these Formation, the Nondweni Group, Kaapvaal Craton, South interpretations. Indeed, at least three minerals with elongated Africa, well documented by measurements of interfacial angles habit can show very similar hexagonal cross sections: arago- of the crystals (Wilson and Versfeld, 1994). nite, gypsum, and nahcolite. The distinction requires very care- The primary mineralogy of many pseudomorphs is com- ful measurements of interfacial angles, which however not monly identified by a superficial comparison of crystal habit, always bring the conclusive results. Sumner (2004) stated which can lead to serious mistakes. Many lens-shaped pseudo- that “measurements of interfacial angles are consistent with morphs interpreted as postgypsum forms could mimic many either an aragonite or gypsum precursor due to the sensitivity other salt minerals: ikaite, gaylussite (Warren, 2006), or glauber- of results to small errors in cross section orientation.” “Errors ite. In particular, glauberite is remarkably similar in morphology were estimated to be 5–10, which are too high to aid in to gypsum (Salvany et al., 2007). Trona and gypsum are both primary mineral identification” (Sumner, 2004). The addi- monoclinic and form radial sprays (Smoot and Lowenstein, tional misinterpretation can result from vicinal character of 1991). The following groups of minerals can form similar natural crystal faces or unnoticed compactional or tectonic pseudomorphs: ikaite–gypsum–gaylussite-glauberite, barite– deformation, particularly acting during replacement process siderite–gypsum, aragonite–gypsum, pyrite–halite-sylvite, and (Hovorka, 1992). anhydrite–gypsum (Warren, 2006, supplemented). Hydrohalite The proper identification of primary minerals forming pseu-

(NaCl • 2H2O) crystallizing in temperatures below 0 C shows domorphs requires the statistical measurement of interfacial hexagonal shape that can be attributed to many minerals includ- angles of the pseudomorphs and their comparison with the ing gypsum (Roberts et al., 1997). ideal crystal form (Smoot and Lowenstein, 1991). This was rarely The Precambrian and Permian marine deposits are famous made in the case of Precambrian evaporite pseudomorphs. The for their seafloor crystal crusts showing grasslike structures rare exceptions concern pseudomorphs after gypsum (Walker (radial bundles) and interpreted as calcite pseudomorphs et al., 1977; Dunlop, cited in Lambert et al., 1978; Wilson and after primary bottom-grown aragonite (e.g., Sumner, 2002). Versfeld, 1994), after the aragonite (Winefield, 2000), and after Many of these crusts were formerly interpreted as calcitized nahcolite (Lowe and Worrell, 1999; Sugitani et al., 2003). grasslike gypsum deposits, based in part on the large crystal Nevertheless, even such measurements in case of barite crystals sizes (Cassedanne, 1984; references in Sumner and Grotzinger, being supposed pseudomorphs after gypsum gave conflicting 2000; Riding, 2008). Some occurrences were interpreted as results (Buick and Dunlop, 1990; Lambert et al., 1978; Runne- pseudomorphs after trona (Jackson et al. 1987 cited by gar, 2001; Runnegar et al., 2001). These include the Archean Winefield, 2000). Recently, the majority of such crusts have (3.47 Ma) North Pole Chert, Warrawoona Group, Australia been interpreted and/or reinterpreted as aragonite, based, (Figure 23; Buick and Dunlop, 1990; Lambert et al., 1978; among other reasons, on the high amount of strontium present Runnegar, 2001; Runnegar et al., 2001; Shen and Buick, 2004; (up to 4169 ppm; Grotzinger, 1989; Peryt et al., 1990; Sumner Shen et al., 2001, 2006; see comments by Buick, 2008; Warren, and Grotzinger, 2000). Aragonite commonly contains a great 1997, 2006, pp. 106, 559). Barite is, however, apparently also deal of strontium, whereas gypsum and calcite typically incor- primary in these Archean deposits (Nijman et al., 1998). porate less strontium because the strontium partition coeffi- Runnegar (2001) and Runnegar et al. (2001) proved it by mea- cient for aragonite is much larger (1.13) than strontium surements of the interfacial angles in some crystals. These partition coefficients for calcite and gypsum (<0.2). These authors used X-ray computer tomography (CT) and questioned crystal pseudomorphs reach centimeter to decimeter in length the occurrence of primary gypsum in these beds (the documen- (some upright crystals attain 1.60 m in length, Sumner and tation of these studies was not published, however). Shen et al. Grotzinger, 2000), and show elongated rodlike habit (‘rays in (2009) commented, “X-ray CT only images density contrasts in 2D view’) with hexagonal cross sections. The aragonite miner- the sample, so this technique cannot reveal original crystal alogy also is suggested by squared-off growth-off zones and morphology in partially silificified sediments where the 546 Geochemistry of Evaporites and Evolution of Seawater

postrift passive margins, and (4) continental collision zones and foreland basins. Hudec and Jackson (2007, their Figures 1–4) showed the distribution of these evaporite basins on Earth. The evaporites are important in Earth history and some of their selected significant features are as follows.

9.17.24.1 Paleogeographic Indicators Evaporite formation requires a relatively restricted climate, supporting a negative water balance. Ancient saline giants also needed specific paleogeography related to tectonic pulses of Earth and accommodation space for deposition. The evaporite deposits form and are preserved mainly in areas of limited Figure 23 Laminated chert draping the bottom-grown barite crystals rainfall and elevated evaporation. Today, they are largely con- interpreted as pseudomorphs after gypsum by Buick and Dunlop (1990) and as primary barite by Runnegar et al. (2001); North Pole Chert centrated within two ‘dry’ subtropical high-pressure belts (3.47 Ga), Warrawoona Group, Australia, scale in centimeters. Photo between 15 and 35 latitude from the equator (Borchert and courtesy Roger Buick. Muir, 1964; Lotze, 1938). Compilation by Ziegler et al. (2003), Zharkov (1998, 2001), and Chumakov and Zharkov (2003) proved that from the Permian until now, the evaporite depo- microquartz–barite boundary is within the original crystal sition prevailed within the two belts 10–40 N and 10–40 S, boundary along barite cleavage planes. By contrast, the apparently related to hot and dry climate conditions created by universal-stage petrographic technique used in previous studies the descending branches of the Hadley cells. This appears to (Buick and Dunlop, 1990; Lambert et al., 1978) differentiates indicate that global atmospheric circulation was approximately between the inclusion-rich microquartz of the surrounding silic- the same as today at least since Permian. In particular, Ziegler ified sediment and the inclusion-poor microquartz of the silici- et al. (2003) noted that the distribution of evaporites in time fied sulfate crystals, thus yielding accurate interfacial angle was related to availability of epeiric and shelf sea basins within measurements” (Shen et al., 2009, p. 384). lower latitudes rather than to global events of dry climate. Buick (2008), similar to earlier authors (Lambert, 1978; Some ancient evaporite basins, like the giant Permian Shen et al., 2006), believed that the necessary sulfate ions basins of north hemisphere, extended up to 50 latitude were produced from H2S by anaerobic photosynthesizers, (Trappe, 2000; Ziegler et al., 2003). The evaporites are good being a part of ancient sulfuretum ecosystem, and using this paleogeographic indicators suggesting the position of the gas as their electron donor. This view, however, is highly con- Phanerozoic basins did not extend beyond 35–50 latitude troversial – inorganic origin of sulfates (by photochemical and (Briden and Irving, 1964; Parrish et al., 1982; Rees et al., other reactions in atmosphere and surface of the hydrosphere 2004; Zharkov, 1998). They can be used for the correction of from volcanic emanations of hydrogen sulfide and sulfur diox- paleogeographic reconstructions based on paleomagnetic data ide, see, e.g., Grotzinger and Kasting, 1993; Holland, 2002; (e.g., Drewry et al., 1974; Evans, 2006). Huston and Logan, 2004; Lambert, 1978; Walker, 1983) is equally or more probable (according to Johnston, 2011, with 9.17.24.2 Seals for Hydrocarbons and More references). These probably are the oldest recorded bottom- (Evaporites and Hydrocarbons) grown sulfate crystals and remain one of the most important and intensively studied objects in pursuit of an understanding Unlike the other sedimentary rocks, evaporite deposits, particu- the Archean sulfur cycle and chemistry of the Archean atmo- larly halite, lose their porosity very early and rapidly, mostly due sphere and ocean, despite the fact that it is unclear if they are to early cementation (Garrett, 1970). Casas and Lowenstein lacustrine or ‘modified’ marine deposits (Grotzinger, 1989). (1989) have shown that saline pan halite is nearly entirely Irrespective of the primary mineralogy of these precipitates cemented by the burial depth of 10 m, where porosity is less (barite or gypsum), they indicate that the Paleoarchean seas or than 10%. Halite cementation is promoted by evaporative con- lakes “were at least locally sulfate bearing” (Golding et al., centration of groundwater brines and/or cooling of sinking 2010, p. 42). surface NaCl-saturated brines. This very important feature enables the evaporites to create the seal necessary for hydrocarbon accumulations (Warren, 2006). This also enables the study 9.17.24 Significance of Evaporites in the Earth of halite in underground mines in galleries, most of each is dry History or nearly devoid of water, which is an unusual feature in mines excavated in sedimentary rocks. Large exploration chambers There are many evaporite deposits present among the sedimen- appear to be devoid of any influence of underground waters tary rocks on Earth. Kozary et al. (1968) estimated that approx- and therefore considered as perfect sites for the storage of radio- imately 25% of continental areas are underlain by ancient active waste (Roedder, 1984). However, the other specific evaporite deposits and more large salt deposits have been feature – the ability of salt to flow due to its ‘halokinetic’ discovered since that time, for example, the Messinian saline properties – decides that such potential sites may not be safe. giant at the bottom of the Mediterranean. Evaporites are This flow property can be rapid, in human terms, requiring only encountered in (1) cratonic basins, (2) synrift basins, (3) months or years, and can compromise any valid seal safety. Geochemistry of Evaporites and Evolution of Seawater 547

9.17.24.3 Halotectonics Borchert and Muir, 1964). Sometimes, incongruent dissolution of hydrated minerals, such as carnallite, releases water (Harville When during burial, halite deposits reach the depth where the and Fritz, 1986). Due to the high solubility and reactivity, the density of overlying sediments surpasses the density of the evaporites themselves do not survive long in the zone of meta- halite, the halite may deform plastically and move slowly as a morphism. In some cases, however, both anhydrite and halite fluid, unless that overlying sediment is already cemented and (that are part of well known sedimentary sequences) are known rigid, acting as a cap to salt movement. Particularly, significant to remain preserved in thick beds up to temperatures well over effects of salt deformation may occur in areas where the over- 300 C (Lugli, 1996a,b), preserving primary isotopic signals lying load is unevenly distributed or the slope of the deposits (Boschetti et al., 2011a), and when these data are pressure- gradually changes during subsidence. The moving salt is a corrected, the actual temperatures were closer to 380–400 C powerful tectonic force able to completely modify the structure (Lugli et al., 2002). However, hydrothermal salts, formed from of overlying sedimentary cover. The salt becomes mobilized, hot circulating waters, may precipitate to infill voids but do not and deforms or creeps downslope, out from beneath the over- appear as bedded sequences along with layers of dolomites and lying load, and may destroy or create entire sedimentary mudstones. In the metamorphic realm, the evaporites usually are basins. In areas of rising salt diapirs, the salt is able to move completely remobilized and create high-salinity subsurface to the Earth’s surface (diapiric structures), and in the zones fluids or brines. These and related fluids, on the other hand, are of dry climate, the salt may flow out and build salt mountains. able to carry and precipitate sedimentary metallic ore deposits as At the surface, in such zones, the rising salt (forced out by for example in the Mississippi Valley-type Zn–Pb deposits. diapirism) even may begin flowing down the mountain slopes The deep subsurface basinal fluids are nearly entirely repre- as namakiers or ‘salt glaciers’ (Talbot et al., 2009; Talbot and sented by high-salinity Ca–Na–Cl brines (e.g., Carpenter, Pohjola, 2009). In a similar way, the huge masses of salt 1978; Lodemann et al., 1997). Although the origin of these together, with their overlying sedimentary cover, are able to brines remains controversial, one of the accepted explanations flow down the slope of the basins and inclined continental is the infiltration of NaCl-rich evaporite brines and their inter- shelves. actions with Ca-rich rocks (e.g., Derome et al., 2007; Mo¨ller Flowing salt, squeezed out from below and between such et al., 2005, with references). The quantitative Ca–Na relations flows, may form salt walls and canopies, as in the Gulf of in these brines may be explained by dolomitization or albi- Mexico, where such processes are responsible for creating tization of plagioclases (Boschetti, 2011; Carpenter, 1978; numerous traps for hydrocarbons (see the review in Warren, Davisson and Criss, 1996). Recently, Lowenstein et al. (2003) 2006). Similar huge-scale structures occur in many areas suggested that these brines represent a true relic of evaporated of Earth and possibly on Mars (Hudec and Jackson, 2007; ancient seawater of the Ca chloride type, but the concept Montgomery et al., 2009). remains highly controversial as pointed out by Kharaka and Halite also has another feature in that it has a very high heat Hanor (2003) and Hanor and McIntosh (2006). That view is a capacity. Salt diapirs that rise toward the surface from great logical implication of the halite inclusion studies, which depths are, perforce, much warmer than nearer surface sedi- strongly suggested that there were long periods in the Phaner- ments (Mello et al., 1995) and conduct heat upward from ozoic history of the ocean when its halite brines were nearly depth. This process has two disparate results. First, the subsalt devoid of sulfates and that oceans producing sulfate brines, sediments are kept cooler than a regional geothermal gradient such as today, were possibly rare events in the Earth history. would suggest (slowing maturation of organic matter), and In recent studies, Lowenstein and Timofeeff (2008) showed second, the rising salt brings warmth and migrating fluids that this concept of relic Ca chloride brines is only partly true. through the sediment through which it passes, raising rates of diagenesis. Regionally, these two aspects of the effect of mobilized halite are rarely considered, but certainly, they may prove 9.17.25 Summary very important in many areas. Marine evaporites are the chemical deposits, which represent the direct record of the chemistry of ancient oceans and the 9.17.24.4 Diagenesis and Metamorphism of Evaporites soluble ionic load present in their waters. Crucial to our under- In surface and subsurface, evaporites are prone to dissolution standing of the origin of these evaporites is the order of salts and are typical rocks responsible for development of karst. Sub- precipitated from evaporated modern seawater: the Ca carbon- surface dissolution of evaporites, particularly chloride salts, is ates Ca sulfates Na chlorides Mg–K sulfates and ! ! ! considered as the main sources of saline fluids in many buried chlorides. This mineralogical order is usually preserved in the sedimentary basins (Carpenter, 1978; Hanor, 1994), and the Phanerozoic evaporites, although Mg–K salts are rarely present. composition of these fluids depends on the mineralogy of van- This sequential relationship is the cornerstone of the wide- ished buried and/or metamorphosed evaporite deposits spread idea that the chemistry of the ocean was stable and (Lowenstein et al., 2003). Such fluids are particularly active in remained constant throughout Phanerozoic time and presum- the areas of salt diapirs (McManus and Hanor, 1993). During ably was similar to today’s ocean even earlier, in the Protero- burial, hydrated salts and particularly the most common gypsum zoic and possibly the Archean. The advance of studies over the undergo dehydration and gypsum passes into anhydrite releas- past few decades led to the emergence of the new and evolving ing large volumes of water (Jowett et al., 1993), which is then an picture of the ocean. active agent in diagenetic transformations of surrounding (over- What was previously expressed by a few forgotten investi- lying) evaporites, carbonates, and other rocks (Borchert, 1969; gators appeared to be the true and we are now quite certain that 548 Geochemistry of Evaporites and Evolution of Seawater the chemistry of the ancient oceans changed with time, and the Argento DC, Stone JO, Fifield LK, and Tims SG (2010) Chlorine-36 in seawater. Nuclear changes were profound and relatively rapid. The pair of ions Instruments and Methods in Physics Research Section B: Beam Interactions with 2 2 Materials and Atoms 268: 1226–1228. Mg þ and Ca þ apparently was crucial in the evolution of the Armstrong RL (1991) The persistent myth of crustal growth. Australian Journal of Earth sedimentary record. In the Phanerozoic, the molar ratio of Sciences 38: 613–630. 2 2 these ions Mg þ/Ca þ changed with time, varying from a min- Arthurton RS (1973) Experimentally produced halite compared with Triassic layered imum estimated value of about one in Cretaceous (Aptian) to halite-rock from Cheshire, England. Sedimentology 20: 145–160. today’s maximum known value 5. The change in the ratio of Arvidson RS, Guidry MW, and Mackenzie FT (2011) Dolomite controls on Phanerozoic seawater chemistry. Aquatic Geochemistry 17: 735–747. these ions, as well as the other remaining ions (particularly Aspler LB and Chiarenzelli JR (2002) Mixed siliciclastic-carbonate storm-dominated 2 SO4 À), had an oscillating character and is unmistakably ramp in a rejuvenated Palaeoproterozoic intracratonic basin: Upper Hurwitz Group, reflected in the clear changes in the depositional record of Nunavut, Canada. In: Altermann W and Corcoran PL (eds.) Precambrian potassium and magnesium salt deposits. Such KCl salts, dom- Sedimentary Environments: A Modern Approach to Ancient Depositional Systems. Special Publication of the International Association of Sedimentologists, No. 33, inant in much of the Phanerozoic, alternated with two (or pp. 293–321. UK: Blackwell Science. three) phases of magnesium sulfate salt deposition: first (con- Attia OE, Lowenstein TK, and Wali AMA (1995) Middle Miocene gypsum, Gulf of Suez: troversial) in late Neoproterozoic, then in the Permian and Marine or nonmarine? Journal of Sedimentary Research A 65: 614–626. Cainozoic. The last period appears to be the most peculiar Awramik SM and Buchheim HP (2009) A giant, Late Archean lake system: The considering the well-documented extremely high rate of these Meentheena Member (Tumbiana Formation; Fortescue Group), Western Australia. 2 2 Precambrian Research 174: 215–240. changes, the fact that Mg þ/Ca þ ratio has approached the very Ayllo´n-Quevedo F, Souza-Egipsy V, Sanz-Montero ME, and Rodrı´guez-Aranda JP high value (5.2 – the highest recorded in Phanerozoic), and (2007) Fluid inclusion analysis of twinned selenite gypsum beds from the Miocene that the driving forces of these changes remain controversial. of the Madrid basin (Spain). Implication on dolomite bioformation. Sedimentary Evaporites cannot help much in our understanding of the Geology 201: 212–230. Ayora C, Cendo´n DI, Taberner C, and Pueyo JJ (2001) Brine-mineral chemistry of early Precambrian oceans; they were removed reactions in evaporite basins: Implications for the composition of ancient from the fossil record and are mostly known from poorly oceans. Geology 29: 251–254. preserved pseudomorphs, commonly of a controversial deriva- Ayora C, Garcia-Veigas J, and Pueyo JJ (1994) The chemical and hydrological tion. True, well-preserved marine evaporites are unrecognized evolution of an ancient potash-forming evaporite basin as constrained by mineral from that early, very long time interval. Many facts suggest that sequence, fluid inclusion composition and numerical simulation. Geochimica et Cosmochimica Acta 58: 3379–3394. the Precambrian ocean was different than today. It is however Ayora C, Taberner C, Pierre C, and Pueyo JJ (1995) Modeling the sulfur and oxygen highly possible that it behaved like that of the Phanerozoic and isotopic composition of sulfates through a halite-potash sequence: Implications for the chemical changes in evaporite composition were even the hydrological evolution of the Upper Eocene Southpyrenean Basin. Geochimica et more rapid and drastic, and possibly also oscillating in nature. Cosmochimica Acta 59: 1799–1808. Ba˛bel M (2004a) Models for evaporite, selenite and gypsum microbialite deposition in ancient saline basins. Acta Geologica Polonica 54: 219–249. Ba˛bel M (2004b) Badenian evaporite basin of the northern Carpathian Foredeep as a drawdown salina basin. Acta Geologica Polonica 54: 313–337. Acknowledgments Ba˛bel M (2007) Depositional environments of a salina-type evaporite basin recorded in the Badenian gypsum facies in northern Carpathian Foredeep. In: Schreiber BC, Lugli S, and Ba˛bel M (eds.) 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