Non-marine Water Research Articles

The Messinian ‘Vena del Gesso’ evaporites revisited: characterization of isotopic composition and organic matter

Abstract The ‘Vena del Gesso’ (Gessoso-Solfifera Fm, Messinian) is a 227 m-thick ridge along the western Romagna Apennines (Italy) consisting of up to 16 selenite cycles separated by shales and minor carbonate. The total organic carbon values of these deposits range between 0.087–0.016% (gypsum) and 3% (shales). Organic matter is dominated by black debris associated with continental debris. Algae and dynocysts are rare (<1%). The amount of amorphous organic matter is low but it may reach up to c. 40%. The 87 Sr/ 86 Sr of gypsum and carbonate vary from 0.708890 to 0.709024, yielding non-oceanic values with several exceptions that plot within error of coeval oceanic values only in the upper part of the section (from the 6° bed). The sulphur isotope composition of gypsum range between δ 34 S =+21.8 and +23.7‰ and may represent precipitation of δ 34 S-enriched gypsum due to the fractionation effect or recycling of coeval gypsum with contributions of brine-sediment redox variations. The isotope values of carbonates show a large variability (−6.4<δ 18 O<+6.05‰; −14.68<δ 13 C<+2.5‰), suggesting a complex origin by mixing of marine and non-marine waters with a significant contribution of reduced organic matter. These data point to an evaporite basin dominated by continental waters which received significant phases of marine recharge in the upper part together with a marked facies change. Because seawater recharges and a similar facies change are present in other Messinian sections, it follows that we have new possible geochemical and facies markers to correlate the Lower Evaporites across the Mediterranean.

New phallodrilines (Annelida: Clitellata: Tubificidae) from Western Australian groundwater

Four species of phallodriline tubificids (Clitellata: Tubificidae) from karst aquifers and caves along the west coast of the state of Western Australia are the first records of this subfamily from nonmarine waters in the southern hemisphere. Aktedrilus parvithecatus (Erséus 1978) and Pectinodrilus ningaloo n. sp. occur in anchialine groundwater of Cape Range, along with other taxa of marine affinity. Aktedrilus leeuwinensis n. sp. and Aktedrilus podeilema n. sp. occur in caves of the Leeuwin-Naturaliste Ridge and Perth Basin respectively and are the first taxa of marine lineage to have been collected from these systems.

Post-evaporitic restricted deposition in the Middle Miocene Chokrakian-Karaganian of East Crimea (Ukraine)

In the Middle Miocene of East Crimea, gypsum evaporites formed in a shallow basin from mixed seawater–nonmarine waters are overlain by marl, siltstone and claystone which contain a few horizons of stromatolitic limestone. The thickness and abundance of the stromatolitic horizons increase up the section. In the siliciclastic portion of the section, a very poor and taxonomically impoverished assemblage of benthic foraminifers ( Jadammina, Nonion, Haynesina, Astrononion and Eponides) is recorded. It is typical for a shallow water marsh or lagoon environment with a lowered salinity. Accordingly, the brackish conditions prevailing during gypsum precipitation in East Crimea continued afterwards, although at the end of evaporite deposition the basin became desiccated and then it was rapidly reflooded by brackish water. The impoverished biota and the occurrence of microbialites in the Ptashkino section indicate extremely unfavourable conditions for most living organisms during the deposition of both the terrigenous and carbonate beds. The water salinity thus was probably not only lowered but also anomalous in composition if compared to normal marine water. The occurrence of carbonate stromatolitic horizons is probably related to the periodic shallowing of the basin caused by a drop of the lake water table driven by climatic factors. The resulted changes allowed for a growth of the bizarre microbial-serpulid communities that gave birth to most of the stromatolites. In Karaganian time, the Eastern Paratethys was a huge lake isolated from the Tethys. This lake responded to any climatic fluctuation that in turn might lead to water level oscillations. In humid climate periods, the lake could be open with a surface outflow and, when it was drier, it could be a closed system without surface outflow. Gypsum evaporites and stromatolitic carbonates are clear evidence of strong evaporation in a dry climate that probably induced water level fall in the whole basin. However, all the time the environmental conditions were predominantly brackish, even during gypsum precipitation as suggested by the chemical composition of fluid inclusions in gypsum. Similar conditions may be expected in other evaporite-hosted, predominantly brackish basins, such as some Messinian basins of the eastern Mediterranean, where some evaporites were deposited in the oligohaline to mesohaline conditions typical of the Lago Mare deposits.

Key Events in the Ecological Radiation of the Ostracoda

Ostracodes are ecologically diverse at the present day, inhabiting marine, nonmarine and (semi)terrestrial environments. Modern benthic faunas are dominated by Podocopa (marine and nonmarine Podocopida, marine Platycopida, and extremely rare marine Palaeocopida), while the Myodocopa (Myodocopida and Halocyprida) are diverse in the marine pelagic realm, as well as having many nektobenthic taxa. Their excellent fossil record facilitates reconstructions of their phylogenetic relationships and ecological adaptations throughout their Phanerozoic history. The earliest known ostracodes are of Ordovician age, when representatives of the extant orders Podocopida, Platycopida and Palaeocopida were already present, together with (possible) early Myodocopa and extinct orders such as the Leperditicopida. Cambrian bivalved arthropods such as bradoriids and phosphatocopids are no longer regarded as Ostracoda.Ordovician ostracodes were predominantly marine meiobenthos, diversifying into depth-related assemblages dominated by palaeocopids. The beginnings of podocopan radiations in marginal marine environments (brackish and hypersaline waters) are seen in the Silurian, as is an ecological shift of nektobenthic myodocopans to form the first pelagic ostracode faunas. Of the diverse marine Paleozoic palaeocopids, only a single lineage, the puncioids, survived beyond the Permian and today live interstitially in high-energy shallow marine environments. Post-Paleozoic marine benthic ostracode faunas are dominated by cytheroidean podocopids which gave rise to several radiations in the Mesozoic and Cenozoic. The healdiid metacopines (podocopans), of Devonian origins, enjoyed a marine radiation in the Triassic and Early Jurassic and then became extinct. Marine platycopids were also significant components of Mesozoic marine faunas and are relatively diverse in warm, shallow carbonate environments today.Suggestions that the first freshwater ostracodes were Devonian leperditicopids are controversial; undoubted nonmarine / freshwater radiations developed during the Early Carboniferous, including darwinuloidean and carbonitoidean podocopids and possibly some platycopids, together with cytheroidean podocopids (limnocytherids) in the Late Carboniferous. Of these only the darwinuloideans and limnocytherids survived the end-Permian extinctions and are still found in modern nonmarine waters; however, the dominant freshwater ostracodes today are the cypridoidean podocopids, whose radiation began in the Triassic and attained explosive proportions in the Late Jurassic - Early Cretaceous (although there are controversial suggestions of Paleozoic origins for this group). In addition to the limnocytherids there have been several other, separate invasions of nonmarine waters by cytheroidean podocopids, notably the cytherideids and the commensal entocytherids. Radiations in damp terrestrial environments have been initiated by both marine and nonmarine groups, but such invasions lack a recognized fossil record; (semi)terrestrial cypridoideans and darwinuloideans may represent Late Mesozoic radiations, while the Terrestricytheroidea, with marine affinities, may be much older, possibly Late Paleozoic in origin.

Sr, S, and OSO4 Isotopes and the Depositional Environments of the Upper Miocene Evaporites, Spain

ABSTRACT Upper Miocene evaporites in the Nijar Basin, southeastern Spain, contain thick, massive and coarse-crystalline selenites of the middle Messinian Yesares Formation. On the basis of their sedimentary fabrics and structures, such as euhedral terminations of crystals, well preserved algal filament inclusions, and standing-growth orientations, these selenites are interpreted to be primary, bottom-growth deposits. Most of these selenites have Sr concentrations of about 1000 ppm (range from 700 to 1800 ppm). 87Sr/86Sr values of Yesares selenites vary between 0.70890 and 0.70896 (n = 18), which are all within the known range of Messinian seawater, suggesting a marine origin. However, quantitative modeling of 87Sr/86Sr vs. Sr/Ca of fluids demonstrates that a minor amount of admixed nonmarine fluid (e.g., 20%) might have contributed to the Yesares marine brines. 34S and 18OSO4 values of Yesares selenites range from 21 to 24‰ CDT and from 10 to 16‰ SMOW, respectively. These ranges are more variable and most values are heavier than those expected for normal Miocene marine gypsum. On the basis of quantitative modeling, these heavy 34S and 18OSO4 values have most likely resulted from reduction and oxidation reactions of sulfur species that occurred in brines rather than from contributions of nonmarine water or from reservoir (crystallization) effects. The use of Sr, S, and O isotopes provides a possible means of distinguishing whether an ancient evaporite was deposited by marine, nonmarine, or hybrid brines. Sr isotopes, however, are insensitive to minor nonmarine contributions on the basis of quantitative modeling, and consequently marine Sr isotopes for evaporites (e.g., gypsum) do not necessarily indicate pure marine depositional environments. Compared to Sr isotopes, 34S and 18OSO4 of marine gypsum are even more insensitive to minor nonmarine contributions because of much higher SO4 concentrations in seawater and seawater-evaporated brines than in most freshwaters. Therefore, Sr, O, and S isotopes should be used with caution to interpret depositional environments and to determine parent fluids of ancient evaporites.

Sr/Ca, Mg/Ca ratios and Sr and stable isotopes of biogenic carbonates from the Late Miocene Velona Basin (central Apennines, Italy) provide evidence of unusual non-marine Messinian conditions

The Sr/Ca and Mg/Ca ratios of fossil ostracod and mollusc shells from a Late Miocene (Early Messinian) lacustrine sequence in the Velona Basin (central Apennines, Italy) were used to calculate the Sr/Ca and Mg/Ca of waters in which these taxa lived. Sr/Ca of these waters were always higher than the Sr/Ca calculated for the Messinian seawater, despite the broad salinity ranges (fresh water-oligo/mesohaline) inferred from the paleontological analyses. The estimated Mg/Ca water from the Velona samples are below the Mg/Ca value for coeval seawater even though they represent relatively high values when compared with many non-marine waters. The salinity variations of the Velona lacustrine system, recorded by changes in faunal assemblages, are linked to variable inputs of Na–Cl from deep groundwaters and are not reflected in significant changes in Sr/Ca and Mg/Ca of the waters calculated from shell chemistry. The combination of δ 18O signatures and Sr isotopic ratios from molluscs from the Velona Basin suggests a non-marine environment. During some episodes of the lake history, given the saline inputs, the waters in the lake would attain a large solute concentration (oligo to mesohaline), although they retained the meteoric δ 18O signature. We compare the paleohydrochemical inferences from the studied sequence with other Messinian records, and we show the importance of combining paleoecological and geochemical proxies to obtain consistent paleoenvironmental reconstructions.

Effects of genotype and environment on phenotypic variability in Limnocythere inopinata (Crustacea: Ostracoda)

Limnocythere inopinata (Baird) is a Holarctic species, widely distributed in non-marine waters, and mainly occurring in unisexual populations. It displays polymorphic traits which could be useful for taxonomical and (palaeo)ecological purposes, if the origin of these traits could be better understood. Three clones of L. inopinata were cultured in the laboratory under various temperature and salinity conditions (i.e. temperature 15, 20 and 25 °C, salinity expressed as electrical conductivity 400, 2000, 5000 and 8000 μS cm−1). Morphological traits for both the valves (shape and size) and soft parts (11 limb setae) were observed. Field populations from Chinese salt lakes and from Austrian lakes were also compared. The freshwater population from Mondsee and its derived clone M develop larger valves than those of the other two clones, clone N (from Neusiedlersee) and clone S (from Seewinkel, Oberer Stinkersee), which live exclusively in saline (alkaline) water. Parthenogenetic specimens from the freshwater lake Mondsee and sexually reproducing females from the Chinese salt lakes both have sub-rectangular valves with straight dorsal margin; the saline clones and populations have highly arched valves with rounded dorsal margin. No direct effects of temperature or salinity on valve ornamentation (reticulation, nodation) have been found. At least for nodation, a genetic factor seems apparent, as the saline clones N and S are never nodose, while the freshwater animals from Mondsee and the sexual animals from the Chinese salt lakes can be both with or without nodes. In the former case, number and position of nodes are variable. Both absolute and relative length of limb setae can be affected by environmental factors and by genotype, and this is the first time that this has been demonstrated in non-marine ostracods. Based on the present observations and experiments, it is concluded that L. inopinata is a variable, polymorphic species, consisting of a (semi-) continuous morphological cluster, in which both clonal genotypes and sexual haplotypes are nested. Therefore, Limnocythere sappaensis Staplin and L. binoda Huang are considered synonyms of L. inopinata; L. mongolica Daday is a possible synonym; L. sanctipatricii sensu Huang and L. dubiosa sensu Huang from Lake Qinghai are most likely erroneous identifications. Apparently recognisable clones with typical ecologies cannot be allocated a taxonomic rank, as this does not reflect a phylogenetic reality. Such links between recognisable morphologies and typical ecological ranges are useful for palaeoenvironmental reconstructions, but are applicable at a regional scale only.

Isotopic biogeochemistry of dissolved organic nitrogen: A new technique and application

We present a new technique for isolating and isotopically characterizing dissolved organic nitrogen (DON) for non-marine waters, δ 15N values for DON from lacustrine samples and data suggesting that this technique will be applicable to marine samples. Our technique involves preconcentration of DON via rotary evaporation and removal of dissolved inorganic nitrogen (DIN) via dialysis using a membrane that retains material above 100 Da. Results demonstrate quantitative removal of DIN, complete recovery of DON (95% or greater) and retention of isotopic integrity (isotope effect less than 0.4‰) for a solution containing a DON standard (tripeptide) and DIN in deionized water. Reproducibility of carbon and nitrogen isotope values and elemental concentrations is demonstrated for DOM from Chefswet Basin, Lake Superior and Grand Traverse Bay, Lake Michigan. The applicability of this technique to marine samples is suggested by demonstrating 99% removal of DIN from a sample of Gulf Stream water amended with ammonium and nitrate.

The historical East African freshwater algae collection at the Botanical Museum Berlin-Dahlem (B)

Jahn, R.: The historical East African freshwater algae collection at the Botanical Museum Berlin-Dahlem (B). — Willdenowia 26: 333–340. 1996. — ISSN 0511-9618.More than 100 samples of East African non-marine waters of almost 100 years ago were rediscovered at B. They contain original material for the names of about 200 algal taxa, among them the diatom genera Gomphocymbella and Rhopatodia by O. Müller, the bluegreen genera Chondrogloea, Myxoderma as well as the green algal genera Botryomonas, Chaetonella and Characiella by W. Schmidle.

Brine Inclusions in Halite and the Origin of the Middle Devonian Prairie Evaporites of Western Canada

ABSTRACT Brines were extracted from fluid inclusions in Lower Salt halite of the Middle Devonian Prairie Formation in Saskatchewan, Canada. The brines were analyzed by ion chromatography and were found to be of the Na-K-Mg-Ca-Cl type. They do not fall along a simple evaporation trend. Brines from clear, diagenetic halite are significantly lower in Na+ and higher in Mg2+, Ca2+, and Cl- than brines from cloudy, subaqueously formed halite with chevron structures. The isotopic composition of strontium and sulfur in anhydrite associated with the halites was found to be the same as that of Middle Devonian seawater. The composition of the inclusion brines can be derived from that of modern seawater by evaporation, extensive dolomitization of limestone, a d albitization of clay minerals. Other evolution paths are, however, also feasible, and it is impossible to rule out effects due to the addition of nonmarine waters (hydrothermal solutions, surface runoff, and groundwater), or dissolutional recycling of existing evaporites within the Prairie evaporite basin. Our analyses and published data on brine inclusions in halite from a number of Phanerozoic evaporite deposits show that the Na-K-Mg-Ca-Cl type brine is more common than the Na-K-Mg-Cl-SO4 type, which is expected from evaporation of modern seawater.

Origin of the Atrevida Vein (Catalonian coastal ranges, Spain); mineralogic, fluid inclusion, and stable isotope study

Atrevida is a Ba-F base metal vein located in the Catalonian coastal ranges of Spain about 100 km southwest of Barcelona. The vein cuts Paleozoic metasediments and granites of the Hercynian basement and Triassic red beds at the base of an overlying transgressive sequence. The Atrevida vein can be divided into three parts on the basis of mineralogy. The lower level contains sugarlike quartz + fluorite + minor barite. The middle level contains a breccia of banded barite + basement rocks cemented by a complex sulfide-arsenide assemblage with galena, Ni sulfide, Ag sulfosalt, and native silver veinlets. The upper level contains symmetrical bands of white barite. Late calcite and marcasite are found in geodes. The only alteration observed is quartz + sericite + chlorite after K feldspar and biotite where the vein cuts granite host rocks.Fluid inclusions in fluorite homogenize at 110 degrees C and have salinities of 21 wt percent NaCl equiv. Inclusions in sphalerite homogenize at 90 degrees C and have salinities of 22 wt percent NaCl equiv. Eutectic results in both minerals are as low as -59 degrees C, indicating that the trapped fluids are complex CaCl 2 -bearing polysaline brines. Fluid inclusions in late calcite homogenize at -0.3 degrees C, indicating that low-salinity waters invaded the vein system during calcite deposition.Sulfur and oxygen isotope analyses reveal that vein barites have delta 34 S values of 14 to 17.9 per mil (CDT) and delta 18 O values of 9.5 to 12.2 per mil (SMOW). Barite also occurs as cement in the Triassic red beds with delta 34 S = 15.3 per mil and delta 18 O = 10.6 per mil. Both the sulfur and the oxygen isotope compositions are within the ranges reported for Lower Triassic- to Lower Jurassic-age evaporites.Banded galena from the middle level of the vein has delta 34 S values between -6.3 and -8.9 per mil, and rimming anglesite has delta 34 S values of -21 to -30.9 per mil. Galena from the central breccia has delta 34 S values of -14.9 to -16.1 per mil and coexisting sphalerite is about -10 per mil. Quartz in the lower level of the vein has delta 18 O in the range 20.7 to 22.7 per mil.We infer that sulfate in the vein was derived directly from seawater or from a solution which dissolved evaporites as it descended through the Triassic section along the fault zone. Barite and sulfides were precipitated where the sulfate-bearing solution mixed with an ascending, Ba-rich brine. The reduced sulfur found in the vein may have been carried by the ascending brine (banded galena) and may also have been produced by bacterial reduction of sulfate from a surficial source (galena in breccia). Oxidizing, nonmarine waters were introduced into the hydrothermal system giving rise to anglesite rims on galena.Mineralization took place in the Late Triassic during an extensional tectonic regime characterized by a high-geothermal gradient. Atrevida, and similar barite veins found throughout the Catalonian coastal ranges, formed along basin margin faults near a paleosurface formed on Hercynian basement. On a broader scale, low-temperature veins are known to occur throughout western Europe and northern Africa. If Atrevida is representative of the group, then the formation of these veins may be linked to Mesozoic extensional tectonics.

The Alpine Haselgebirge Formation, Northern Calcareous Alps (Austria): Permo-Scythian evaporites in an alpine thrust system

Multiphase-deformed and weakly metamorphosed Permo-Scythian evaporites of the Northern Calcareous Alps (Eastern Alps) of Austria were deposited in an aborted rift arm of the northwest Tethys. They represent marine precipitates laid down in a basin surrounded by alluvial fans and mudflats. Mean bromide values of halite (13 ± 53 ppm) as well as S-isotope ratios of sulphate minerals ( +14 ± 0.9ℵ CDT ) indicate that the contribution of non-marine waters to the marine brine composition was insignificant. The most striking feature is the Haselgebirge structure, a chaotic mélange of shales, silt and sandstones, anhydrites, carbonates and scarce magmatites (Kirchner, 1980) embedded in a clayey halite matrix. This mélange resulted from severe tectonization caused by a variety of deformational processes (halokinesis, diapirism, gravitational sliding and alpine thrust tectonics).

Ramp-Style Deposition of Oligocene Marine Vedder Formation, San Joaquin Valley, California: ABSTRACT

The Oligocene Vedder formation consists of well-sorted medium to fine-grained marine sand and shale in the subsurface of the eastern San Joaquin Valley. Updip, this formation interfingers with nonmarine/lagoonal facies known as the Walker Formation. This relationship appears to be transgressive because the marine Vedder generally overlies the Walker Formation. Downdip, the Vedder sands interfinger with middle to lower bathyal shale in a progradational manner, forming upward-coarsening patterns in well logs. Depositional water depths for the shale were determined from benthic foraminifera assemblages. The Vedder formation is approximately 750 ft thick along its updip part, and gradually thickens to 1500 ft downdip. Overall deposition geometry, determined from well-log correlations and seismic data, is generally parallel and downlapping. A prominent shelf-slope break is not evident. Rather, depositional surfaces are tabular or broadly lobate, with a depositional slope of 5/sup 0/-10/sup 0/. This geometry of constant slope between nonmarine and deep marine water depth is termed a ramp. The depositional style and geometry are similar to that of the Oligocene upper Pleito Formation, which crops out in the San Emigdio Mountains on the southern margin of the San Joaquin Valley. The Vedder formation was deposited subsequent to a period of rapid subsidencemore » (about 50 cm/1000 years), as determined from geohistory analysis of well data on the Bakersfield arch. This rapid subsidence may have induced deposition in a ramp geometry, rather than a shelf-slope configuration.« less

Stable isotope study through the Permian-Triassic boundary in East Greenland

A survey of stable isotope ratios in sediments spanning the Permian-Triassic boundary in East Greenland shows Upper Permian evaporites to have b34S = + 10.6 ± 1.6%o and limestones to have b13Cmb = +4.5 ± 0.4%o, in conformity with similar values from probable correlative formations in Europe and North America. Most values of both isotopes in Triassic formations are lower and scattered, apparently reflecting varying inputs of non-marine waters including the oxidative erosion of isotopically light sulfur. This transition in the East Greenland section has obscured any clear detection of chemical events recorded elsewhere: a drop in marine b13C.,.,b near the Penman-Triassic boundary, and a sharp rise in b34S,1t in latest Scythian time.

Geochemistry of Regionally Extensive Dolomites, Burlington and Keokuk Formations (Mississippian), Iowa and Illinois: ABSTRACT

The Burlington and Keokuk Formations (Mississippian) contain 2 major generations of dolomite throughout the several ten-thousand square kilometers of study area. Dolomite I (oldest) is luminescently zoned, Ca-rich, Fe- and Mn-poor, and has Mississippian 87Sr/86Sr; dolomite II is unzoned, nearly stoichiometric, Fe- and Mn-rich, and has radiogenic 87Sr/86Sr; dolomite III, a minor zone, is nonluminescent and very Fe-rich. Dolomites I and II formed before nonmarine calcite cements, and all 3 dolomites formed before Late Mississippian under shallow burial conditions. Stable isotopes of dolomite I average +2.3 ^pmil ^dgr13C and -0.3 ^pmil ^dgr18O PDB. Dolomite I is slightly depleted in 13C and 18O with respect to estimated Mississippian marine dolomite. Thus, dolomite I may have formed in waters only slightly depleted in 18O and 13C compared with seawater at low temperatures (~ 25°C). Dolomite II averages -4.1 ^pmil ^dgr18O PDB, +2.8 ^pmil ^dgr13C PDB, and has a wide range of ^dgr18O (-0.5 to -6.6 ^pmil PDB) and a narrower range of ^dgr13C (+1 to +4 ^pmil). These data suggest that temperatures of precipitation were less than the 80°C-110°C ranges implied by the contained 2-phase fluid inclusions, unless the waters were isotop cally heavy (~ +3 to 11 ^pmil ^dgr18O SMOW). Dolomite II shows a regional geographic trend of decreasing ^dgr18O and increasing ^dgr13C from north to south. This trend can be accounted for by either a northward decrease in temperature or in 18O content of diagenetic waters. We suggest a model in which dolomite I precipitated in marine-dominated mixed waters at low temperatures, the bulk of the dissolved constituents being derived intraformationally. Dolomite II formed as a replacement of dolomite I in a system dominated by nonmarine waters and/or slightly elevated temperatures, deriving much of their constituents from sub-Burlington strata. End_of_Article - Last_Page 236------------

Clay diagenesis as a function of marine and nonmarine water flow, Niger Delta, Nigeria

Analyses of samples of surface sediments from 30 localities in the Niger Delta showed that the distribution and nature of clay minerals are related to source and hydro-dynamic processes. The major mineral assemblages are: o (1) Kaolinite and halloysite (2H 2O) in the central delta. (2) Highly aluminous smectites (beidellites), illite, mixed layer illite-smectite, and kaolinite in calcareous shale of eastern delta and (3) Montmorillonite and nontronite in coastal regions of the delta. The central delta with permeability > ID has the highest groundwater flow rates and constant meteoric water flushing. The young volcanics of the eastern delta are the sources for the Mg-deficient smectites. The coastal delta is sea water influenced. The clay mineral distribution is interpreted as consequences of severe leaching, rapid rate of infiltration, permeability, shale dewatering and marine, nonmarine water influence.

Factors influencing the geochemistry of surface sediments in the supratidal Niger Delta

Abstract Chemical data for major and trace elements are presented for 54 samples from surface sediments of the Niger Delta. Over most of the delta, intense leaching leaves a product soil essentially in the system SiO 2 -Al 2 O 3 -H 2 O (−Fe 2 O 3 ) and severe depletion in the major oxides MgO, CaO, K 2 O and Na 2 O. Except in the smectite-rich eastern and coastal areas of the delta, the major minerals of the soils are quartz, kaolinite, gibbsite and goethite. The chemistry of these sediments is interpreted as consequences of severe leaching, rapid rate of infiltration, clay mineralogy, permeability and marine, non-marine water influence. Factor analysis on the bulk chemical data confirms this severe depletion and identifies trace element concentration mainly in the clay or the non-soluble refractory minerals.

The study of a natural hypersaline lagoon in a desert area (the Bardawil Lagoon in Northern Sinai)

The hypersaline Bardawil Lagoon, situated on the Mediterranean coast of the Sinai Peninsula, was studied. Seven environmental parameters (water temperature, salinity, pH, calcium and magnesium ion concentrations, content of dissolved oxygen and micronutrients) were monitored. The magnesium/salinity and calcium/salinity ratios of the brines of the Bardawil Lagoon (0·0386 8 ±0·0002 7 and 0·0114 2 ±0·0002 2 g l −1 (S ‰) −1 , respectively) are equal to the ratios for Mediterranean seawater and are in good agreement with literature values for other oceans and seas. The process of the formation of the Bardawil Lagoon water body was modelled in laboratory conditions. The results of this study, the constancy of the magnesium/salinity and calcium/salinity ratios and their identical values to those of Mediterranean sea water show that the brines of the Bardawil Lagoon were formed by mere evaporation of Mediterranean seawater without the interference of other non-marine water sources except rain water.

Petrology of Buckner Member of Haynesville Formation in Adjacent Parts of Texas, Louisiana, and Arkansas: ABSTRACT

The Buckner Member of the Haynesville Formation is an evaporitic mudstone unit of Late Jurassic age that is present only in the subsurface around the margin of the Gulf Coast embayment. It has been divided informally into two parts, lower and upper. The most common rock types in the Buckner are nodular anhydritic mudstone and nodular anhydrite. The nodules consist of swirls of lathy anhydrite in a matrix of blocky to anhedral crystals. The mudstone matrix consists of a red or gray non-laminated or poorly laminated mixture of silt and clay minerals. The clay minerals are mostly illite and chlorite. The next most common rock type is light gray crypto- to micrograined laminated anhydrite that is largely confined to the lower part. This type contains scattered minute rounded dolomite grains, clay mineral grains, and fine-grained sand and silt. Some less common rock types in the Buckner are oolitic and detrital limestone, oolitic-micritic and detrital-micritic limestone, rock salt, micrograined dolomite, and medium-grained dolomite. > The member was deposited around the margin of the Gulf Coast embayment in linear basins. Contemporaneously growing salt-cored anticlines along the seaward margin caused restricted circulation with the open sea. The lower part was deposited mainly in standing bodies of water and the upper part was deposited on a tidal mud flat that was, from time to time, flooded by both marine and non-marine water. The sea generally was regressing during deposition of the Buckner. Micrograined anhydrite is associated with rock salt and is considered to be primary. Nodular anhydrite is associated with brackish-water fossils and was probably deposited as gypsum. End_of_Article - Last_Page 461------------