Shahab Varkouhi

This study reports on the occurrence of formerly bimineralic, ancient, calcitic coated grains, including half-moon ooids and micritic to microsparitic ooids in the Middle Anisian (Middle Triassic) grain flow from Hydra Island (Greece), and discusses their importance for palaeoseawater geochemical interpretations. The bi-partite fabric in half-moon...

Although anomalous compaction (dramatic physical property changes) is widely recognised from scientific drilling of sections of marine biosiliceous sediments that have undergone silica diagenesis, the precise mechanisms governing vertically abrupt compaction are poorly understood. To better understand relationships between silica diagenesis and ano...

67 Ocean Drilling Program and Deep Sea Drilling Project sites were investigated to determine the relationship between temperature and time for silica diagenesis. The selected sites cover a variety of settings where the opal-A to opal-CT transition zone lies in Cenozoic sediments. The opal-A to opal-CT transition leads to abrupt changes in the sedim...

Chemically oscillating reactions (COR) are abiotic processes that generate self-repeating circularly concentric morphologies during decarboxylation of organic acids. The geometry and millimetre to centimetre size dimensions of laminated quartz botryoids recorded in the Palaeoarchean Apex and Strelley Pool chert horizons in Western Australia simulat...

In this petrographic and geochemical study, we differentiated diverse quartz botryoids, including circular-concentric, twinned, columnar, wavy, and stromatolite-like structures versus synchronous biotic patterns of similar geometry and size dimensions (filamentous traits and stromatolites) in Precambrian cherts of Barberton, South Africa, and Gunfl...

Due to the lack of rainfall potential in Central Iran, the water scarcity is still the main problem of production in the country. Accordingly, the use of unconventional waters will be inevitable. This study presents the amount of water required by the Chadormalu mine from the water wells of the Sepidan Plain, as well as the deficit or excess for ex...

Biosiliceous cherts hosting the transformation of biogenic silica to paracrystalline opal-CT, deposited in the low-latitude realms of Jurassic to Neogene, were recently interpreted as developing during episodes of elevated primary productivity along upwelling areas in equatorial and sub-equatorial paleo-latitudes. Geographically widespread distribu...

The hydrate concentration model considerably affects elastic properties, including bulk and shear modulus. Defining seismic properties of sediments, such as compressional and shear wave velocity and density, provides valuable information to identify rock facies and fluid types. This information commonly results from pre-stack seismic inversion, whi...

The hydrate concentration model considerably affects elastic properties, including bulk and shear modulus. Defining seismic properties of sediments, such as compressional and shear wave velocity and density, provides valuable information to identify rock facies and fluid types. This information commonly results from pre-stack seismic inversion, whi...

The gas hydrate distribution model containing cement, or un-cement models, considerably affects elastic properties such as shear and bulk modulus. Thus, determining the distribution model in the hydrate-bearing sediments requires decreasing uncertainty in quantitative studies based on seismic velocities. Pre-stack seismic data include additional fl...

This paper evaluates previously proposed diagnostic criteria that can be used to determine whether or not there is active migration of the opal‐A to opal‐CT transition zone (TZA/CT). The criteria are based on the interpretation of 2D and 3D seismic surveys, and are therefore geometrical. They involve an assessment of the relationship of the TZA/CT...

This study calculated the dissolution rates of biogenic silica deposited on the seafloor and the silicic acid benthic flux for 22 Ocean Drilling Program sites. Simple models developed for two host sediment types—siliciclastic and carbonate—were used to explain the variability of biogenic silica dissolution and recycling under present-day low (−0.3...

Silica diagenesis leads to dramatic petrophysical variations in the host sediment across the depth of an opal-A to opal-CT transition zone. Predicting the present-day diagenetic status of opal-A to opal-CT transition zones, i.e., active versus fossilized fronts, is essential to constraining the drivers that control abrupt changes in the physical st...

Four aspects of biogenic silica diagenesis are researched under this project: signatures of ongoing silica diagenesis in pore water, drivers leading to anomalous compaction (abrupt petrophysical changes), bottom-water temperature controls on silica dissolution and recycling, and temperature-time relationships in silica later diagenesis. Results of...

Streambed-sediment samples were collected in the Veysian River Basin in Lorestan Province, west of Iran to characterize the occurrence and distribution of lead in natural and anthropogenic sites of the basin. The concentration of lead in streambed sediment is strongly affected by the particle-size distribution. The range in concentrations of lead a...

Streambed-sediment samples were collected in the Sarbaz River Basin in Sistan and Baluchestan Province, east of Iran, to characterize the occurrence and distribution of lead in natural and anthropogenic sites of the basin. During June and July 2008, stream sediment was collected at 30 sites, and the samples were analyzed for lead. Sites sampled rep...

Lead trace element was analyzed in streambed sediment samples collected from 30 sites in the Veysian River Watershed in Lorestan province, west of Iran. Sites sampled represented agricultural, mining, mixed, urban/rural, and recreation land uses and background conditions. Lead trace element was detected in streambed sediment samples collected at al...

Thirteen environmental elements were distinguished in the livers of various species of fish that have been sampled from 15 sites in a restricted area of the KhorramAbad River Basin in Lorestan province (west of Iran). Sites sampled represented agricultural, mining, mixed, and urban/recreation land uses and background conditions. Lithium and silver...

Thirteen trace elements were distinguished in liver of various species of fish that have been sampled from 15 sites in restricted area of Khorramabad River Watershed in Lorestan province, west of Iran. Sites sampled represent agricultural, mining, mixed, and urban/recreation land uses and background conditions. In the analyzed fish samples, Vanadiu...

Toxic trace elements were analyzed in recent wind-driven sediment samples collected from 40 various sites in the Zahedan catchment area, east of Iran, as part of the National Water/Soil Quality Assessment program. Sites sampled represented mining, agricultural, residential/recreation, and mixed land uses and background conditions. The results for 8...

Polrud River is a sandy-gravelly river with single bed load channel that springs from Alborz mountain ranges and flows toward Caspian Sea. In order to determination of main sedimentologic characteristics, textural properties of streambed sediments are discussed in this study. For such purpose, representative samples were collected from different si...

سازند آسماری از انواع مختلف سنگ های آهکی ( الیگوسن تا میوسن زیرین ) تشکیل شده است. برای تعیین تغییرات رخساره ها، محیط رسوبگذاری و دیاژنتیکی این سازند، برش مناسبی در جنوب غربی شهرستان خرم آباد، انتخاب و به تفصیل مورد بررسی قرار گرفت. سازند آسماری بین سازندهای پابده و گچساران قرار می گیرد. مرز زیرین آن با سازند پابده تدریجی و مرز بالایی آن با سازند گ...