Saline Basin Research Articles

Amun’s Userhat Boat and its Role in the Theban Festivals: Data from the Theban Royal Bank Archive Contextualized

This paper examines an undernoticed theme of the papyrus archive of the Theban royal bank, contextualizing data on Amun’s Userhat boat and the Theban religious festivals in the later Ptolemaic period. The bank archive reveals the fraudulent use of money deposits destined for the replacement of two iron anchors for the Userhat and for the maintenance of this sacred riverine ship which transported Amun’s sacred bark twice a year (during the Opet and the Valley Festivals). The Userhat is well attested in the pharaonic period, while the information for the Ptolemaic era, though scarce, shows that the main Theban festivals were still organized and that the Userhat still played a major role. The documentary evidence offers more detail on royal investment in the ship’s maintenance even during a civil war, its outer appearance, on the saline basin where it was moored and the storage place of its removable parts. The association of the Ptolemaic Userhat with the Opet temple, as suggested by the bank records, fits with a shift in focus towards this sanctuary in the later Ptolemaic period.

Mercury Sources and Fate in a Large Brackish Ecosystem (the Baltic Sea) Depicted by Stable Isotopes.

Identifying Hg sources to aquatic ecosystems and processes controlling the levels of monomethylmercury (MMHg) is critical for developing efficient policies of Hg emissions reduction. Here we measured Hg concentrations and stable isotopes in sediment, seston, and fishes from the various basins of the Baltic Sea, a large brackish ecosystem presenting extensive gradients in salinity, redox conditions, dissolved organic matter (DOM) composition, and biological activities. We found that Hg mass dependent fractionation (Hg-MDF) values in sediments mostly reflect a mixing between light terrestrial Hg and heavier industrial sources, whereas odd Hg isotope mass independent fractionation (odd Hg-MIF) reveals atmospheric inputs. Seston presents intermediate Hg-MDF and odd Hg-MIF values falling between sediments and fish, but in northern basins, high even Hg-MIF values suggest the preferential accumulation of wet-deposited Hg. Odd Hg-MIF values in fish indicate an overall low extent of MMHg photodegradation due to limited sunlight exposure and penetration but also reveal large spatial differences. The photodegradation extent is lowest in the central basin with recurrent algal blooms due to their shading effect and is highest in the northern, least saline basin with high concentrations of terrestrial DOM. As increased loads of terrestrial DOM are expected in many coastal areas due to global changes, its impact on MMHg photodegradation needs to be better understood and accounted for when predicting future MMHg concentrations in aquatic ecosystems.

Evidence for Groundwater Salinity Origin Based on Hydrogeochemical and Isotopic (2H, 18O, 37Cl, 3H, 13C, 14C) Approaches: Sousse, Eastern Tunisia

The key processes responsible for the rise in groundwater salinization in the Mio–Pliocene aquifer system of Sousse (Tunisia, eastern coastline) were identified through a multidisciplinary approach based on the use of geochemical, stable (2H, 13C, 18O and 37Cl) and radioactive (3H and 14C) isotope methods. In the study region, the mineralization of groundwaters is related to water–rock interaction ascribed to the dissolution of minerals in evaporite rocks, as well as to saltwater intrusion. Both processes explain the development of groundwaters in which Cl and Na dominantly determine the groundwater quality deterioration state. The isotopic and geochemical signatures of the studied groundwaters are clearly explained by the (i) occurrence of saline basins (sebkhas adjacent to the study region), (ii) type of rocks found below the ground surface, and (iii) cation exchange between clays and groundwaters.

New insights into the carbon cycle and depositional models of the Eocene saline lake, Jianghan basin, China

Geochemical characteristics and sedimentary processes of sediments, especially mixed sediments, have long been hot topics of research in basin systems, which can be used to infer runoff, evaporation, productivity, precipitation patterns of the paleoenvironment, as well as records of a diverse range of climate-related signs. However, compared with shallow marine mixed siliciclastic-carbonate sediments, the study of lacustrine mixed sedimentary systems in combination with geochemical information is relatively limited. Also, model-based study on the reconstruction of the lacustrine carbon biogeochemical cycle is defective, especially in saline lacustrine environments. In this work, a total of 26 mixed siliciclastic–carbonate sediment core samples from Well BX-7 in the Qianjiang Depression were sequentially selected for scanning electron microscope observation, major and minor element test, and isotope measurements (e.g., δ13Ccarb, δ18Ocarb, and δ34SCAS). Two types of mixed sediments were generated in the overall inflow/outflow balance of water within the saline basin during the Eocene: siliciclastic-dominated mixed sediment (SDMS) and carbonate-dominated mixed sediment (CDMS). The δ13Ccarb values of SDMS and CDMS samples range from −7.13‰ to −4.52‰ (average −5.82‰) and −9.00‰ to −6.11‰ (average −7.48‰), respectively. The δ18Ocarb values of SDMS and CDMS samples range from −10.26‰ to −1.40‰ (average −4.73‰) and −3.80‰ to −0.96‰ (average −1.55‰), respectively. In addition, combining the geochemical parameters of sedimentation rate, Mn2+ content in carbonate lattice ([Mncarb]), carbonate mass fraction, and [Mg2+]/[Ca2+] ratio, we established a lacustrine δ13C variation model at the sediment-water interface (SWI) with the aim of accurately reflecting δ13Ccarb changes during carbonate formation. Based on the sedimentary processes and geochemical characteristics, we established two depositional models for these two types of mixed sediments in a saline lacustrine basin in the overall inflow/outflow balance of water. Model I illustrates SDMS sedimentary processes with a relative low salinity, low FluxDIC-O, high water inflow, and the organic carbon oxidation is dominated by Fe (III) reduction. Model II demonstrates CDMS sedimentary processes with a high salinity, high FluxDIC-O, high water outflow, and the organic carbon oxidation is dominated by sulfate reduction.

Suggested solutions for the problems of salinity increase and cumulated pollution in lake Qarun, Egypt: Present and future (A review)

Lake Qarun is the third-largest natural lake in Egypt. The lake turned from a freshwater body to a saline basin. The lake receives up to 70% of the drainage water of Fayoum (i.e. agriculture drainage, sewage drainage, and industrial drainage). Drainage water is the only source of lake inflow while the evaporation of freshwater is the only outflow. At the present, the level of salinity concentration in the lake exceeds the global allowable level. This increase in salinity and cumulated pollution affected the ecosystem and reduced fish production to 25% of its value in 2014. This research aims to identify the problems of salinity increase and cumulated pollution in Lake Qarun and review the suggested solutions. Also, the efforts of the Fayoum governorate for developing the lake and the future projects planned to be implemented were reviewed. The development of Lake Qarun turned in an increase in national income.

Soils with dark subsurface horizons in saline basins in the Brazilian Pantanal

Soils in the Brazilian Pantanal classified as Espodossolos and registered in the literature diverge from the central concept of pedogenesis by podzolization, especially due to the high values of pH and basic cations, although the morphology is similar to that of spodic horizons. In this sense, this study hypothesized that the neutral to alkaline conditions along the edges of the saline basins in the Lower Nhecolândia region do not inhibit the podzolization process nor the development of spodic soils. [...]

Biomarkers reveal two paramount Pliocene-Pleistocene connectivity events in the Caspian Sea Basin

Landlocked basins like the Caspian Sea are highly sensitive to changes in their hydrological budget, especially at times of disconnection from the global ocean. Here, we reconstruct the Pliocene to Pleistocene palaeohydrological and palaeoenvironmental changes occurring in the South Caspian Basin between ~3.6 and ~ 1.9 Ma, using compound-specific hydrogen isotope (δ 2 H) data on long chain n -alkanes and alkenones. Additionally, we established a record of mean annual air temperature (MAT) and the source of organic matter, based on the relative distribution of branched and isoprenoid glycerol dialkyl glycerol tetraethers (BIT). The ~55‰ variation in the δ 2 H measured on the terrestrial plant long chain n -alkanes indicates significant continental hydrological changes in the region surrounding the Caspian Sea over the investigated 1.7 Myr interval. The MAT and BIT data show that the so-called Akchagylian marine incursion at around 2.75 Ma, marked by influx of marine biota into the Caspian Basin, originated from a cold region of the open ocean, endorsing a hydrological connection with the Arctic domain. The onset of the regional Apsheronian stage at ~2.13 Ma, identified by the invasion of Tyrrhenocythere sp. ostracods, coincided with a change towards constant δ 2 H n -alkane and is shortly followed by the occurrence of alkenones in the Caspian Basin. The relative distributions of alkenones and their δ 2 H values indicate that a connection with a saline basin, most likely the Black Sea, was established at the Akchagylian–Apsheronian transition. • 55‰ δ 2 H n -alkanes variation hint at hydrology changes in 3.6–1.9 Ma circum-Caspian. • Cooling at 2.75 Ma Akchagylian marine incursion caused by influx from Arctic. • Alkenones and their δ 2 H support a Caspian–Black Sea connection starting at ~2.13 Ma.

Discovery of shale oil in alkaline lacustrine basins: The Late Paleozoic Fengcheng Formation, Mahu Sag, Junggar Basin, China

A new type of shale oil in alkaline lacustrine sediments has been discovered in the Late Paleozoic Fengcheng Formation, Mahu Sag, Junggar Basin, China. The fine-grained sedimentary rocks deposited in this alkaline lacustrine environment can be divided into four types and eight sub-types: mudstone (with no alkali minerals), including massive dolomitic mudstone, and massive and laminated calcareous mudstone; dolomite, including massive argillaceous dolomite (with alkali minerals), and massive and laminated argillaceous dolomite (with no alkali minerals); evaporites; and pyroclastic rocks. The massive argillaceous dolomite (with alkali minerals) and pyroclastic rocks have the highest shale oil potential, with average oil saturation index (OSI) values of 344.67 and 124.65 mg HC/g TOC, respectively. Shale oil exploration in the representative well MY1 indicates that the Fengcheng Formation is thick and contains abundant natural fractures, brittle minerals, and mobile oil. The entire Fengcheng Formation is oil-bearing and contains three concentrated stratigraphic intervals of shale oil (i.e., sweet spots). Well MY1 indicates that, compared with source rocks developed in marine and sulfate-type saline basins, the fine-grained sedimentary rocks deposited in alkaline lacustrine environments can also have high shale oil potential. The co-existence and regular distribution of conventional and unconventional reservoirs in the Fengcheng Formation indicate that it is an ideal exploration target for multiple resource types.

Phytoplankton dynamics in relation to Red tide appearance in Qarun Lake, Egypt

Qarun Lake is a unique saline basin. Its phytoplankton species abundance and dynamics in relation to the Red Tide phenomenon is the focus of this study. Samples were collected from May 2015 to April 2016 in twelve successive cruises. Phytoplankton productivity attained the highest level on July with the bloom of Dinophyceae, while showing negative correlation with water transparency (r = −0.72) and positive correlation with DO (r = 0.84). The causative species was Gymnodinium lantzschii. Another incident of Dinophyceae bloom was observed in March when chlorophyll a recorded 158.4 mgm−3, chl. b was (92.7 mgm−3 and chl. c was 160 mgm−3. The causative species were Prorocentrum aporum and Prorocentrum micans and the lake’s water turned to red color; the “Red Tide phenomenon”. Chlorellavulgaris bloom was recorded for the first time in the lake on August at site (4) with green water discoloration.The water temperature of the lake was one of the main phytoplankton bloom’s drivers as the dominant species grew and flourished within a narrow range of temperature (30.4–34.9 °C). The results showed that there were strong correlations between carbonate, bicarbonate, DO and nutrients indicating that the dinoflagellate bloom was due to the high eutrophication of the lake. Finally, the Red tide phenomenon may influence the lake fisheries causing significant economic loss.

The Temperature of Halite Crystallization in the Badenian Saline Basins, in the Context of Paleoclimate Reconstruction of the Carpathian Area

Currently, fluid inclusions in halite have been frequently studied for the purpose of paleoclimate reconstruction. For example, to determine the air temperature in the Middle Miocene (Badenian), we examine single-phase primary fluid inclusions of the bottom halites (chevron and full-faceted) and near-surface (cumulate) halites collected from the salt-bearing deposits of the Carpathian region. Our analyses showed that the temperatures of near-bottom brines varied in ranges from 19.5 to 22.0 °C and 24.0 to 26.0 °C, while the temperatures of the surface brines ranged from 34.0 to 36.0 °C. Based on these data, such as an earlier study of lithology and sedimentary structures of the Badenian rock salts, the crystallization of bottom halite developed in the basin from concentrated and cooled near-surface brines of about 30 m depth. Our results comply with the data on the temperature distribution in the modern Dead Sea.

Depositional sequences in northern Peru: new insights on the palaeogeographic and palaeotectonic reconstruction of western Gondwana during late Permian and Triassic

Late Permian to Early Jurassic strata in northern Peru allow us to carry out a seismostratigraphic, lithotectonic and chemostratigraphic analysis connecting the Andean–Amazonian foreland basins of Huallaga, Ucayali, southern Marañón and the Eastern Cordillera. This analysis and data integration from Ecuador to western Brazil and southern Peru and Bolivia allow us to redefine the timing of the major documented tectonic phases and corresponding palaeogeographies of western Gondwana from the late Permian to the Triassic. Three lithotectonic sequences and four associated deformation stages are recognized: (1) A sequence, tectonic relaxation, during the late Permian; (2) A–B intra-sequence, folding-and-thrusting attributed to a continuation in time of the Gondwanide Orogeny, during the Early to Middle Triassic; (3) B sequence, rifting, attributed to Gondwana breakup during the Middle and late Triassic; (4) C sequence, thermal sag, during the Late Triassic. Evaporites and carbonates (A sequence) dominated a low-subsidence basin with southern restricted marine inflow at the Permian–Triassic boundary. A novel palaeogeographic model for these evaporites suggests that this saline basin extended up to 50 000 km 2 in a restricted environment area with a potential bullseye pattern. The last pulse of the Gondwanide Orogeny and associated fold and thrust belt (A–B intra-sequence) exhumed prior to the sequence, generating emerged areas with little to no sedimentation. Red beds (B sequence) characterize the rifting stage, representing the syn-depositional infill of continental grabens, likely extending to the Acre Basin in Brazil. Finally, during the thermal sag, a marine inflow likely from the northwestern part of Peru generated sedimentation of carbonates and evaporites (C Sequence) to the west and east of the Peruvian margin. This sediment differentiation was, in part, controlled by the existence of pre-existing grabens associated with the previous rifting stage. This interpretation, together with other evaporitic occurrences, attributed here to a Late Triassic epoch in south and north Peru and west Brazil, suggest the existence of an evaporitic basin filling an undeformed area of probably c. 170 000 km 2 . It is therefore suggestive of the existence of a Late Triassic (Norian to Rhaetian; 217 to 204 Ma) salt giant controlled by thermal sag in western Gondwana. Our results are of great relevance for any future interpretation related to mass extinctions, palaeoclimatic analysis and ocean dynamics during the Permian and Triassic as well as natural resource distribution between Ecuador and Bolivia.

СОСТОЯНИЕ ЭКОСИСТЕМ ВОСТОЧНОГО И ЗАПАДНОГО БАССЕЙНОВ САКСКОГО ОЗЕРА (РЕСПУБЛИКА КРЫМ)

Sakskoe Lake is the most thoroughly studied water body in Crimea. Its therapeutic mud and brine are exploited by balneological treatment methods. During the two centuries, when the lake was used by humans, it was subdivided into seven water bodies by dams, with two of these bodies (Eastern and Western) being now utilized for medical purposes, and the other five being protective. The Eastern (currently exploited) basin is now used to produce therapeutic mud and brine. The bottoms of the saline basins are covered by sediments: an upper layer of black silt, which is underlain by gray, steel-gray, occasionally bluish silt, which is used as therapeutic mud. The lake is fed by surface and groundwaters. Retaining dams and flood embankments erected in nearby ravines preclude desalination of the lake with flood and rain waters. Seawater is pumped to the lake through channels to preclude its drying. A quay is now actively constructed around the lake and will likely notably affect its hydrological and ecological conditions. The aim of the present study was the comparative analysis of the chemical and physical characteristics of the Eastern and Western basins of the Sakskoe Lake at the period of intensive building activity on their coasts at the summer period of 2019. Brine samples were collected at two tested sites in each of the lakes. Water salinity was measured by a PAL-06S LTA GO (Japan) refractometer and was expressed in ‰. The pH and Eh of the waters and oxygen dissolved in them were determined in the laboratory by an Expert-001 (Econix-Expert Moexa CoLtd, Russia) analyzer, with the use of appropriate Volta (Russia) selective electrodes. Ions concentration was determined spectrophotometrically and by atomic absorption method. Various living stages of Artemia populations in two water bodies were studied according the standard microscopic methods. The obtained results demonstrated, that the total content of the cations in the brine of the Western basin was in 1,5-fold higher as compared with the data of the brine in the Eastern basin (108,4 and 71,2 g/l respectively). The values were directly correlated with the high salinity of the Western basin brine. The identical trend was shown for the anions concentration, which was significantly greatly in the Western basin related to Eastern one (193,14 and 125,41 g/l correspondingly), which was connected with the different hydrogeological conditions of the formation of the ecosystems of the tested water bodies. At the other hand, pH, salinity and Eh of the brine in the Eastern basin were lower than in the brine of the Western basin, while the concentration of dissolved oxygen was higher. In the brine of the Eastern basin of the lake all living stages of Artemia, including cysts, nauplia and adults were found, while in the Western basin only cysts were shown. Therefore, according the obtained results we could suggest, that anthropogenic processes which were taken place on the coasts of the Sakskoe Lake accompanied with the intensive building activity did not influence on the lake ecosystem. The further monitoring studies including the testing of the ions concentrations in the brine of two basins, Artemia populations state are required for the understanding the changes of the both ecosystems and the possible reasons of their changes. It is important for development of the optimization of the management of Sakskoe lake and its resources exploitation.

Geochemical Data and Fluid Inclusion Study of the Middle Miocene Halite from Deep Borehole Huwniki-1, Situated in the Inner Zone of the Carpathian Foredeep in Poland

The geochemical data and the study of fluid inclusions in primary halite are invaluable sources of saline basin information. Most of the previous analyses of salt from the Carpathian area have been obtained by studying the halite samples collected from depths not exceeding 1000 m (i.e., from salt mine outcrops or boreholes). In this article, for the first time, we present the results of samples obtained from a deep well where salt occurs below the frontal orogenic wedge at a depth of ~5000 m. The salt core’s petrological studies showed, quite unexpectedly, the presence of the chevron relics, typical for primary halite. Their geochemical data and fluid inclusion study can be used to reconstruct the environment of the salt sedimentation. The bromine, strontium, and rubidium content values indicated that primary brines were of marine origin, and salts may have undergone partial dissolution and redeposition under lower salinity water inflows. The main ions’ (K, Mg, SO4) ratios in the fluid inclusions were typical for those of the Badenian brines collected from the Carpathian Foredeep’s eastern part. Compared with modern seawater’s chemical composition, this brine contained a slightly lower content of sulfate ions. This was associated with evolutionary changes occurring in the contents of sulfate ions during the Cenozoic.

Kinetics of shale oil generation from kerogen in saline basin and its exploration significance: An example from the Eocene Qianjiang Formation, Jianghan Basin, China

In this study, confined pyrolysis experiments were performed on kerogen from the Qianjiang Formation in the Jianghan Basin, China, to investigate hydrocarbon evolution in the inter-salt shale deposited in the basin. Kinetic parameters obtained from the pyrolysis experiments were applied to reconstruct the history of hydrocarbon generation in the Eq34–10 cyclothem inter-salt shale reservoir. The results indicate the following: (a) The source rock deposited in the salt basin has a high hydrocarbon potential and a low activation energy for hydrocarbon generation. Petroleum can be generated at a lower maturity stage, and the maximum yield is reached at an EasyRo% of approximately 0.75 %. (b) Hydrocarbon generation from the Eq34–10 cyclothem inter-salt shale reservoir started at approximately 36–33 Ma. The current conversion rates (total oil) for the shale are approximately 0.59, 0.97, 0.97, and 0.88 in wells designated A, B, C, and D, respectively. (c) Deeper shale oil characterized by a high proportion of saturated hydrocarbons migrated laterally and were concentrated in the anticlinal area with shallow burial depth. In regions where structural traps form, lateral up-dip oil migration along variably deformed shallow shale laminates are conducive to the formation of shale oil systems. In thermally mature source kitchens, continuous shale oil accumulation in structurally undisturbed areas still provides attractive shale oil drilling targets.

Origin and circulation of saline springs in the Kuqa Basin of the Tarim Basin, Northwest China

It is widely accepted that hydrogeochemistry of saline springs is extremely important to understand the water circulation and evolution of saline basins and to evaluate the potential of potassiumrich evaporites. The Kuqa Basin, located in the northern part of the Tarim Basin in Northwest China, is a saline basin regarded as the most potential potash-seeking area. However, the origin and water circulation processes of saline springs have yet to be fully characterized in this saline basin. In this study, a total of 30 saline spring samples and 11 river water samples were collected from the Qiulitage Structural Belt (QSB) of the Kuqa Basin. They were analyzed for major (K+, Ca2+, Na+, Mg2+, SO42−, Cl− and HCO3−) and trace (Sr2+ and Br−) ion concentrations, stable H-O-Sr isotopes and tritium concentrations in combination with previously published hydrogeochemical and isotopic (H-O) data in the same area. It is found that the water chemical type of saline springs in the study area belonged to the Na-Cl type, and that of river water belonged to the Ca-Mg-HCO3-SO4 type. The total dissolved solid (TDS) of saline springs in the QSB ranged from 117.77 to 314.92 g/L, reaching the brine level. On the basis of the general chemical compositions and the characteristics of the stable H-O-Sr isotopes of saline springs, we infer that those saline springs mainly originated from precipitation following river water recharging. In addition, we found that saline springs were not formed by evapo-concentration because it is unlikely that the high chloride concentration of saline springs resulted in evapo-concentration and high salinity. Therefore, we conclude that saline spring water may have experienced intense evapo-concentration before dissolving the salty minerals or after returning to the surface. The results show that the origin of salinity was mainly dominated by dissolving salty minerals due to the river water and/or precipitation that passed through the halite-rich stratum. Moreover, there are two possible origins of saline springs in the QSB: one is the infiltration of the meteoric water (river water), which then circulates deep into the earth, wherein it dissolves salty minerals, travels along the fault and returns to the surface; another is the mixture of formation water, or the mixture of seawater or marine evaporate sources and its subsequent discharge to the surface under fault conditions. Our findings provide new insight into the possible saltwater circulation and evolution of saline basins in the Tarim Basin.

Effects of paleo sedimentary environment in saline lacustrine basin on organic matter accumulation and preservation: A case study from the Dongpu Depression, Bohai Bay Basin, China

The Dongpu Depression has abundant oil and gas resources, but the distribution of hydrocarbon resources and enrichment degrees of organic matter (OM) in the northern and southern Dongpu Depression have significant differences due to the diverse sedimentary environment. To gain deep insight into the effects of sedimentary environment on OM accumulation and preservation, a series of experiments including element geochemistry, organic geochemistry and isotope geochemistry were performed on core samples collected from the fresh, brackish and saline regions of the third member of the Eocene Shahejie Formation (Es3). The lacustrine closure, paleo-salinity, redox conditions, hydrodynamic conditions, paleo-climate and paleo-productivity were quantitatively evaluated. Controlling factors and OM enrichment models were evaluated and established. The results show that the Es3 Formation was deposited as the lake experienced closed saline to transitional and then fresh lake stages. The lacustrine deposits were accompanied by climate changes from dry to humid and strongly rifting during Es3 deposition. The weak hydrodynamic conditions (Zr/Rb) and paleo climate indices (δ18O, climate index, Fe/Mn, Sr/Cu and Al/Mg) imply that moderate humid and dry climate can encourage OM development and preservation. The paleo productivity indices (δ13C, P/Al, P/Ti and P content) are positively related to TOC indicating that high productivity promotes OM accumulation. All the paleo salinity indices (Z value, Sr/Ba and B/Ga) have positive correlations with TOC content, suggesting that OM enrichment increases with salinity to some extent. The positive relationships between the redox indices (V/Cr, V/Sc, U/Th, and δU) and TOC indicate that redox conditions are the most important for OM preservation. This study not only advances the theory of OM enrichment mechanism in saline basins, but also provides guidance for predicting the distributions of high-quality source rocks in the Dongpu Depression.

Hydrothermal origin of early Permian saddle dolomites in the Junggar Basin, NW China

Hydrothermal-related saddle dolomites widely exist in the lower Permian Fengcheng Formation in the northwestern Junggar Basin, and this formation is a set of carbonate-rich deposits in an alkaline saline basin. Core and thin section observations, cathodoluminescence (CL) imaging, and carbon and oxygen isotope composition analyses have been used to study the origins of saddle dolomites with various occurrences. Hydrothermal fluids include Si-rich and Si-poor fluids, and saddle dolomites occur, along with siliceous bands, as debris and assemblages in fragmented rocks and as cements filling pores and microfractures. Different types of dolomites in the Fengcheng Formation have similar δ13C values, while the δ18O values differed from each other, which demonstrated that the dolomites originated from the same primary carbonates and underwent multiple stages of recrystallization. The δ18O values were extremely negative, which was caused by fractionation at high temperatures from hydrothermal fluids. Dolomites are directly or indirectly affected by hydrothermal diagenetic fluids. According to the diagenetic stages, the types of migration paths for hydrothermal fluids, and the patterns of hydrothermal fluids acting on the dolomites, a model was proposed to illustrate the origins and evolution of the dolomites, and three paths were utilized. Path I occurred during the contemporaneous diagenetic stage, when the carbonate particles were still free and could be captured by high-density bottom hydrothermal flows and distorted. Path II occurred during the long diagenetic history after the carbonate-bearing sediments had consolidated. Saddle dolomite assemblages and saddle dolomite debris occurred with the aid of compressive tectonic forces. Path III also occurred in the long diagenetic history, and the host rocks were not fragmented. The saddle dolomites reprecipitated as cements in the pores, stylolites, fractures/microfractures or laminated seams.

On the Possible Mechanisms for Saltening of the Bay of Bengal


 
 
 The Bay of Bengal (BoB) is a low saline basin owing to large influx of freshwater from precipitation and river runoff. To maintain the salt balance of the BoB, the incessant lowering of salinity is to be balanced by the inflow of saltier water into the basin. In the present work, various processes that contribute to the saltening of the BoB, viz. coastal upwelling, eddies and their interaction, lateral advection from Arabian Sea and tropical cyclones are discussed. In the near-shore regions, the coastal upwelling due to wind induced Ekman transport plays a dominant role in increasing the surface salinity. On the other hand, in the open ocean, the divergence induced by eddies and their mutual interaction contributes significantly to the salt water pumping. In the southern BoB, the advection from the Arabian Sea increases the salinity. The formation of cyclones in the BoB also leads to an increase in the surface salinity. However, the magnitude of saltening of the Bay due to these processes varies from north to south. The uplift of saltier water from subsurface levels increases the salinity in the surface layers thereby creating a salinity gradient and a salinity front.
 
 

High-frequency redox variations of the Eocene cyclic lacustrine sediments in the Yingxi area, western Qaidam Basin, China

The mineral assemblages of lacustrine mixed sediments have vital significance for reconstructing paleo-lake environments, and typical lacustrine mixed sediments deposited during the Eocene are distributed throughout the Yingxi area in the western Qaidam Basin. Accordingly, the framboid size distributions and sulfur isotope (δ34Spy) characteristics of pyrite in addition to the carbon isotope (δ13Ccarb) characteristics and redox-sensitive element ratios (Th/U, V/(V + Ni) and V/Cr) of authigenic carbonates were investigated to reconstruct the high-frequency redox variations in cyclic lacustrine sediments.Corresponding to different redox conditions, three types of mixed sediments developed during transgression and regression stages within the saline basin in the Yingxi area during the Eocene: mixed terrigenous clasts formed in oxic-dysoxic water column conditions during lake transgression, mixed carbonates formed in anoxic water column conditions during early-stages lake regression, and mixed evaporites formed in anoxic-sulfidic water column conditions during middle-late-stage lake regression. The redox proxies correlate well with the water salinity, exhibit little or no correlation with the water temperature, and show an incongruity with the water depth, suggesting that the redox conditions were predominantly controlled by the water salinity rather than the water depth or temperature. Therefore, based on the water redox condition variations and the salinity, three dynamic formation models of the high-frequency sedimentary cycles in a saline basin are established: a deep-water, low-salinity, oxic-dysoxic model (Model I), a medium-water, medium-salinity, anoxic model (Model II) and a shallow-water, high-salinity, anoxic-sulfidic model (Model III). Because the climate gradually turned dry and hot from lake transgression to regression, the continued closure of the basin enhanced evaporation and salinization. In addition, mixed terrigenous clasts, mixed carbonates and mixed evaporites deposited successively. Correspondingly, salinity stratification gradually developed within the lake water, increasing the extent of bacterial sulfate reduction in the bottom water.

Wide-azimuth seismic and potential field data integration for salt recognition in the southern Gulf of Mexico

In the recently opened exploration frontier area of the deepwater Saline Basin in the southern Gulf of Mexico, we successfully applied a multiphysics workflow to integrate wide-azimuth seismic and potential field data. In areas of poor signal-to-noise ratio, subtlety and variation in structural style due to salt kinematics and deep-seated thrusting impose challenges for seismic imaging. High-velocity (impedance) contrasts at the interfaces between salt and carbonate rafts within the background sediments result in strong reflection and refraction at small angles of incidence, diffractions with complex wave patterns, and lack of illumination near and below these features. This creates high noise levels in the seismic image resulting in high uncertainty in the salt interpretation. To reduce the uncertainties of salt interpretation, a multiphysics workflow is devised to integrate gravity data with the seismic measurements. The multiphysics workflow employs a jointly collected suite of wide-azimuth, long-offset, broadband seismic data and potential field data. The process consists of conventional processing steps to enhance the salt-related signal and a full 3D seismogravity modeling. Velocity model building, petrophysical link estimation for domain conversion, and gravity forward modeling are hence used to interactively assess the scenario testing. The geophysical integration enables definition of a better constrained earth model of velocity and density distributions with improved geometries and reduced uncertainties.