Synthesis and characterization of K2Ca5(SO4)6· H2O, the equivalent of görgeyite, a rare evaporite mineral

Görgeyite, K2Ca5(SO4)6··H2O, is a very rare monoclinic double salt found in evaporites related to the slightly more common mineral syngenite. At 1 atmosphere with increasing external temperature from 25 to 150 °C, the following succession of minerals was formed: first gypsum and K2O, followed at 100 °C by görgeyite. Changes in concentration at 150 °C due to evaporation resulted in the formation of syngenite and finally arcanite. Under hydrothermal conditions, the succession is syngenite at 50 °C, followed by görgyeite at 100 and 150 °C. Increasing the synthesis time at 100 °C and 1 atmosphere showed that initially gypsum was formed, later being replaced by görgeyite. Finally görgeyite was replaced by syngenite, indicating that görgeyite is a metastable phase under these conditions. Under hydrothermal conditions, syngenite plus a small amount of gypsum was formed, after two days being replaced by görgeyite. No further changes were observed with increasing time. Pure görgeyite showed elongated crystals approximately 500 to 1000 µ m in length. The infrared and Raman spectra are mainly showing the vibrational modes of the sulfate groups and the crystal water (structural water). Water is characterized by OH-stretching modes at 3526 and 3577 cm–1 , OH-bending modes at 1615 and 1647 cm–1 , and an OH-libration mode at 876 cm–1 . The sulfate 1 mode is weak in the infrared but showed strong bands at 1005 and 1013 cm–1 in the Raman spectrum. The 2 mode also showed strong bands in the Raman spectrum at 433, 440, 457, and 480 cm–1 . The 3 mode is characterized by a complex set of bands in both infrared and Raman spectra around 1150 cm–1 , whereas 4 is found at 650 cm–1.

Geochemistry of evaporite in the Red Sea

One of the major shipboard findings during Leg 23 drilling in the Red Sea was the presence of late Miocene evaporites at Sites 225, 227, and 228. The top of the evaporite sequence correlates with a strong reflector (Reflector S) which has been mapped over much of the Red Sea (Ross et al., 1969, Phillips and Ross, 1970). This indicates that the Red Sea appears to be extent. Miocene sediments, including evaporites, are known from a few outcrops along the coastal plains of the Gulf of Suez to lat 14°N (Sadek, 1959, cited in Friedman, 1972; Heybroek, 1965; Friedman, 1972). Along the length of the Red Sea, the presence of Miocene salt is indicated by seismic reflection studies (Lowell and Genik, 1972) and confirmed by drilling. The recently published data from deep exploratory wells (Ahmed, 1972) demonstrate the great thickness of elastics and evaporites which were deposited in the Red Sea depression during Miocene time. The Red Sea evaporites are of the same age as the evaporites found by deep sea drilling (DSDP Leg 13) in the Mediterranean Sea. Therefore, Reflector S in the Red Sea is comparable to Reflector M in the Mediterranean. It is assumed that during Miocene time a connection between these two basins was established (Coleman, this volume) resulting in a similar origin for the evaporites deposited in the Red Sea and in the Mediterranean Sea. The origin of the Mediterranean evaporites has been discussed in great detail (Hsü et al., 1973; Nesteroff, 1973; Friedman, 1973). The formation of evaporites may be interpreted by three different hypotheses. 1) Evaporation of a shallow restricted shelf sea or lagoon which receives inflows from the open ocean. 2) Evaporation of a deep-water basin which is separated from the open ocean by a shallow sill (Schmalz, 1969). 3) Evaporation of playas or salt lakes which are situated in desiccated deep basins isolated from the open ocean (Hsü et al., 1973). The purpose of this study is to show whether one of these models might apply to the formation and deposition of the Red Sea evaporites. Therefore, a detailed petrographic and geochemical investigation was carried out.

Water seepage beneath dams on soluble evaporite deposits: a laboratory and field study (Caspe Dam, Spain)

The paper presents analytical methods and results for assessing the variation in the concentration of sulphate (and other ions) over space and time in groundwater flowing through a soluble evaporite terrain beneath a dam. The influence of effective porosity, groundwater flow velocity and the specific rate of dissolution (K′) are considered. The theoretical analysis was tested in a scale model simulating a dam constructed on heavily karstified bedrock. A simple and useful method for assessing how much material is lost through dissolution and how the rate of dissolution changes over time is considered in the context of the Caspe Dam, Spain.

(Table 3) Sulfur and oxygen isotopic composition of cold water soluble sulfate, and strontium content and isotopic composition of upper Miocene evaporite samples recovered from DSDP Site 23-227

The origin of three Red Sea submarine brine pools was investigated by analysis of the S and O isotope ratios of dissolved sulfate and Sr isotope ratios of dissolved Sr in the brines. Sulfur and O isotope ratios of sulfate and Sr isotope ratios of evaporitic source rocks for the brines were measured for comparison. The S, O and Sr isotope ratios of evaporites recovered from DSDP site 227 are consistent with an upper Miocene evaporites age. The Valdivia Deep brine formed by karstic dissolution of Miocene evaporites by overlying seawater and shows no signs of hydrothermal input. The Suakin Deep brines are derived from, or have isotopically exchanged with Miocene or older evaporites. There has been only minor dilution of the brine by overlying seawater. Strontium isotope ratios of Suakin brine may indicate addition of a minor (15%) amount of volcanic Sr to the brine, but there is no evidence of high temperature brine-rock interaction. The sulfate in the Atlantis II brine was apparently derived from seawater. The O isotope ratio of sulfate in the present Atlantis II brine could reflect isotopic exchange between seawater sulfate and the brine at approximately 255°C. Approximately 30% of the Sr in the Atlantis II brine is derived from the underlying basalt, probably by hydrothermal leaching. Atlantis II brine is the only known example from the Red Sea which has a significant high-temperature hydrothermal history.

Assessment of the molecular structure of the borate mineral boracite Mg3B7O13Cl using vibrational spectroscopy

Boracite is a magnesium borate mineral with formula: Mg3B7O13Cl and occurs as blue green, colorless, gray, yellow to white crystals in the orthorhombic – pyramidal crystal system. An intense Raman band at 1009 cm−1 was assigned to the BO stretching vibration of the B7O13 units. Raman bands at 1121, 1136, 1143 cm−1 are attributed to the in-plane bending vibrations of trigonal boron. Four sharp Raman bands observed at 415, 494, 621 and 671 cm−1 are simply defined as trigonal and tetrahedral borate bending modes. The Raman spectrum clearly shows intense Raman bands at 3405 and 3494 cm−1, thus indicating that some Cl anions have been replaced with OH units. The molecular structure of a natural boracite has been assessed by using vibrational spectroscopy.

Characterization of the sulphate mineral amarantite Fe3 2 3+ (SO4)O 7H2O using infrared, Raman spectroscopy and thermogravimetry

The mineral amarantite Fe23+(SO4)O∙7H2O has been studied using a combination of techniques including thermogravimetry, electron probe analyses and vibrational spectroscopy. Thermal analysis shows decomposition steps at 77.63, 192.2, 550 and 641.4°C. The Raman spectrum of amarantite is dominated by an intense band at 1017 cm-1 assigned to the SO42- ν1 symmetric stretching mode. Raman bands at 1039, 1054, 1098, 1131, 1195 and 1233 cm-1 are attributed to the SO42- ν3 antisymmetric stretching modes. Very intense Raman band is observed at 409 cm-1 with shoulder bands at 399, 451 and 491 cm-1 are assigned to the v2 bending modes. A series of low intensity Raman bands are found at 543, 602, 622 and 650 cm-1 are assigned to the v4 bending modes. A very sharp Raman band at 3529 cm-1 is assigned to the stretching vibration of OH units. A series of Raman bands observed at 3025, 3089, 3227, 3340, 3401 and 3480 cm-1 are assigned to water bands. Vibrational spectroscopy enables aspects of the molecular structure of the mineral amarantite to be ascertained.

Infrared and Raman spectroscopic characterization of the borate mineral colemanite – CaB3O4(OH)3·H2O – implications for the molecular structure

Colemanite CaB3O4(OH)3 H2O is a secondary borate mineral formed from borax and ulexite in evaporate deposits of alkaline lacustrine sediments. The basic structure of colemanite contains endless chains of interlocking BO2(OH) triangles and BO3(OH) tetrahedrons with the calcium, water and extra hydroxide units interspersed between these chains. The Raman spectra of colemanite is characterized by an intense band at 3605 cm-1 assigned to the stretching vibration of OH units and a series of bands at 3182, 3300, 3389 and 3534 cm-1 assigned to water stretching vibrations. Infrared bands are observed in similar positions. The BO stretching vibrations of the trigonal and tetrahedral boron are characterized by Raman bands at 876, 1065 and 1084 cm-1. The OBO bending mode is defined by the Raman band at 611 cm-1. It is important to characterize the very wide range of borate minerals including colemanite because of the very wide range of applications of boron containing minerals.

Vibrational spectroscopy of the borate mineral chambersite MnB7O13Cl – Implications for the molecular structure

Chambersite is a manganese borate mineral with formula: MnB7O13Cl and occurs as colorless crystals in the monoclinic pyramidal crystal system. Raman bands at 902, 920, 942 and 963 cm-1 are assigned to the BO stretching vibration of the B7O13 units. Raman bands at 1027, 1045, 1056, 1075 and 1091 cm-1 are attributed to the BCl in-plane bending modes. The intense infrared band at 866 cm-1 is assigned to the trigonal borate stretching modes. The Raman band at 660 cm-1 together with bands at 597, 642 679, 705 and 721 cm-1 are assigned to the trigonal and tetrahedral borate bending modes. The molecular structure of a natural chambersite has been assessed using vibrational spectroscopy.

Vibrational spectroscopy of the borate mineral tunellite SrB6O9(OH)2·3(H2O) : implications for the molecular structure

Tunellite is a strontium borate mineral with formula: SrB6O9(OH)2∙3(H2O) and occurs as colorless crystals in the monoclinic pyramidal crystal system. An intense Raman band at 994 cm-1 was assigned to the BO stretching vibration of the B2O3 units. Raman bands at 1043, 1063, 1082 and 1113 cm-1 are attributed to the in-plane bending vibrations of trigonal boron. Sharp Raman bands observed at 464, 480, 523, 568 and 639 cm-1 are simply defined as trigonal and tetrahedral borate bending modes. The Raman spectrum clearly shows intense Raman bands at 3567 and 3614 cm-1, attributed to OH units. The molecular structure of a natural tunellite has been assessed by using vibrational spectroscopy.

A vibrational spectroscopic study of the sulphate mineral glauberite

The mineral glauberite is one of many minerals formed in evaporite deposits. The mineral glauberite has been studied using a combination of scanning electron microscopy with energy dispersive X-ray analysis and infrared and Raman spectroscopy. Qualitative chemical analysis shows a homogeneous phase, composed by sulphur, calcium and sodium. Glauberite is characterized by a very intense Raman band at 1002 cm-1 with Raman bands observed at 1107, 1141, 1156 and 1169 cm-1 attributed to the sulphate ν3 antisymmetric stretching vibration. Raman bands at 619, 636, 645 and 651 cm-1 are assigned to the ν4 sulphate bending modes. Raman bands at 454, 472 and 486 cm-1 are ascribed to the ν2 sulphate bending modes. The observation of multiple bands is attributed to the loss of symmetry of the sulphate anion. Raman spectroscopy is superior to infrared spectroscopy for the determination of glauberite.

Vibrational spectroscopic characterization of the sulphate–halide mineral sulphohalite – implications for evaporites

The mineral sulphohalite – Na6(SO4)2FCl is a rare sodium halogen sulphate and occurs associated with evaporitic deposits. Sulphohalite formation is important in saline evaporites and in pipe scales. Sulphohalite is an anhydrous sulphate–halide with an apparent variable anion ratio of formula Na6(SO4)2FCl. Such a formula with oxyanions lends itself to vibrational spectroscopy. The Raman band at 1003 cm−1 is assigned to the (SO4)2− ν1 symmetric stretching mode. Shoulders to this band are found at 997 and 1010 cm−1. The low intensity Raman bands at 1128, 1120 and even 1132 cm−1 are attributed to the (SO4)2− ν3 antisymmetric stretching vibrations. Two symmetric sulphate stretching modes are observed indicating at least at the molecular level the non-equivalence of the sulphate ions in the sulphohalite structure. The Raman bands at 635 and 624 cm−1 are assigned to the ν4 SO42− bending modes. The ν2 (SO4)2− bending modes are observed at 460 and 494 cm−1. The observation of multiple bands supports the concept of a reduction in symmetry of the sulphate anion from Td to C3v or even C2v. No evidence of bands attributable to the halide ions was found.

Extraordinarily thick-boned fish linked to the aridification of the Qaidam Basin (northern Tibetan Plateau)

Scattered with numerous salt lakes and approximate to 2,700-3,200 m above sea level, the giant Qaidam inland basin on the northern Tibetan Plateau has experienced continuing aridification since the beginning of the Late Cenozoic as a result of the India-Asia plate collision and associated uplift of the Tibetan Plateau. Previous evidence of aridification comes mainly from evaporite deposits and salinity-tolerant invertebrate fossils. Vertebrate fossils were rare until recent discoveries of abundant fish. Here, we report an unusual cyprinid fish, Hsianwenia wui, gen. et sp. nov., from Pliocene lake deposits of the Qaidam Basin, characterized by an extraordinarily thick skeleton that occupied almost the entire body. Such enormous skeletal thickening, apparently leaving little room for muscles, is unknown among extant fish. However, an almost identical condition occurs in the much smaller cyprinodontid Aphanius crassicaudus (Cyprinodonyiformes), collected from evaporites exposed along the northern margins of the Mediterranean Sea during the Messinian desiccation period. H. wui and A. crassicaudus both occur in similar deposits rich in carbonates (CaCO3) and sulfates (CaSO4), indicating that both were adapted to the extreme conditions resulting from the ariclification in the two areas. The overall skeletal thickening was most likely formed through deposition of the oversaturated calcium and was apparently a normal feature of the biology and growth of these fish.

鄂尔多斯盆地东部地区奥陶系马家沟组沉积相与储层特征研究

Ordos Basin is one of the primary bases for petroleum exploration in our country. A series of Ordovician large gas fields were discovered, which suggest that the Lower Paleozoic carbonate, especiallly for Ordovician carbonate rocks, preserve plenty of hydrocarbon resources. Well Longtong 1 is studied as the typical exploration well. Acorrding to the specific research on the type of lithology, texture, structure and sedimentary sequence in Ordovician Majiagou Formation as well as additional data from another 20 wells, the sedimentary model has been built in Majiagou Formation. The sedimentary characteristics for each Member in Majiagou Formaiton and the feature of distribution are well understood as below: It suggests that period of Member 1, Member 3 and Member 5 in Majiagou Formation characterize with dry and hot climate as well as drop of the sea level. The area of Well Longtan 1 in the eastern basin is abundant of platform evaporite lithofacies with the depositional anhyrock and salt rock, whereas yield a suite of dolomite intercalated by the thin layers of anhyrock from the anhyrcok-dolomite platform sediment. It deposits muddy dolomite, dolomitic limestone and fine-grain dolomite in limestone-dolomite platform and restricted sea. During the stage of Member 2 and Member 4 in Majiagou Formation, the climate is wet and hot with increasing sea level. The study region occurs limestone with little dolomite in the open sea environment; but the margin area is the restricted sea settings with interbeding dolomite and limestone. Based on the thin section identification, element and isotope analysis as well as the study of texture and structure, it sugguests that the main reserviors are dolomite while the gypsum are major cap rocks. The Member 2 in Majiagou Formation is both the source rocks and the resveroirs; gypsum rocks widely occur in Member 3 as the better cap; similar to the Member 2, the Member 4 in Majiagou Formation is both the source rocks and the resveroirs; there are two source-reservoir-cap assemblages in the Member 5 alone and the cap is gypsum with high quality and great thickness, which is a favorite source-reservoir-cap assemblage.