sedimentary environments
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Author(s):  
Fangting Wang ◽  
Ke Bao ◽  
Changsheng Huang ◽  
Xinwen Zhao ◽  
Wenjing Han ◽  
...  

Cadmium is a toxic element with a half-life of several decades, which can accumulate in the human body by entering the food chain and seriously harm health. The cadmium adsorption and desorption processes in the soil directly affect the migration, transformation, bioavailability, and ecotoxicity of this element in soil-plant systems. Coastal zones are located in the transitional zone between land and sea, and large amounts of terrigenous material input have important environmental effects on this ecosystem. The pH, hydrodynamic conditions, soil organic matter (SOM), and other factors defining the sea-land interaction within the sedimentary environment are significantly different from those defining land facies. In order to study the key factors affecting cadmium adsorption in soils at the sea-land interface in the Nansha area of the Pearl River Delta, a test was conducted on a column of undisturbed soil. The results showed that the adsorption constant KF and the Cd2+ adsorption capacity of marine soils were higher than those of terrestrial soils. However, the saturation adsorption of cadmium in terrestrial sediments was higher than in marine sediments. Soil pH was an important factor affecting cadmium adsorption capacity in both terrestrial and ma-rine sediments. Neutral and alkaline topsoil conditions inhibited the vertical migration of cadmium, while the acidic environment favored it. The higher the clay and SOM were, the stronger the Cd2+ adsorption capacity of the soil was. These findings suggest that the distribution of cadmium in marine and continental sedimentary soils is not only related to adsorption, but also to the physical and chemical processes occurring in different sedimentary environments.


2021 ◽  
Vol 38 (2) ◽  
pp. 63-78
Author(s):  
Ganapati Narayan Nayak

Estuaries are one of the major sub-environments of the coastal zone wherein freshwaters interact and mix with saline waters, and facilitate deposition of finer sediments, organic matter, and metals. Intertidal mudflat and mangrove sediment cores collected from estuaries along the central west coast of India were investigated for various sedimentological and geochemical parameters to understand the changes in the sedimentary depositional environments and various factors influencing the processes. Additionally, estuarine biota was examined to understand the bioaccumulation of metals with respect to bioavailability. The results indicated considerable changes in the depositional environments with time owing to sea-level changes; geomorphology of the estuaries; rainfall and river runoff; anthropogenic activities including construction of dams and bridges. The sediments in the estuaries are considerably polluted by metals and pose toxicity risks to the estuarine biota due to high metal bioavailability. Marine gastropods and mangrove plants act as prospective bio-indicators, and the bioremediation potential of mangroves for contaminated sediments was identified. Metal bioaccumulation in edible benthic biota can be harmful to the human health.


2021 ◽  
Author(s):  
Ari Koeppel ◽  
Christopher Edwards ◽  
Lauren Edgar ◽  
Amber Gullikson ◽  
Kristen Bennett ◽  
...  

MAUSAM ◽  
2021 ◽  
Vol 62 (4) ◽  
pp. 641-646
Author(s):  
DHRUV SENSINGH ◽  
RASIK RAVINDRA

Ny-Alesund, located in Svalbard, Arctic exhibits complex topography and geomorphic features evolved by various sedimentary environments under direct control of climate and tectonics. The controls of glacial and fluvial environments were analyzed on the basis of field documentation of geomorphic features evolved by small valley glaciers (Vestre brogger and Midre loven) and streams originating from it. These terrestrial valley glaciers are characterized by convex wrinkled surface, crevasses, bergchrunds, supraglacial streams, longitudinal debris strips, lateral moraines, recessional moraines, hummocky moraines, thrust moraines, convex longitudinal profile with breaks in slope, fractures and joints. The glacial deposits are made up of very poorly sorted clast to matrix supported boulders with varying sizes of clast, matrix and gravels. The matrix supported facies underlain by clast supported facies indicate the increasing energy of the glacier and so the cold climate. The bi-modal palaeocurrent pattern of moraines suggests two prominent directions for the movement of glaciers in the past under direct control of tectonic activity. The granulometric analysis of the streams indicate moderately sorted medium to coarse sand. The mean grain size decreases from origin to the middle reaches of the river and increases towards its mouth. The percentage of the finer sediments decreases and coarser fragments increases in the downstream direction. The results of the granulometric parameters which are contrary to the normal fluvial system are due to the control of tectonic activity. The present study provides the basic characteristics and activity of the glacial and fluvial environments the interpretation of, which explains the control of tectonic activity in this region.


2021 ◽  
Vol 48 (3) ◽  
Author(s):  
Alexandria Littlejohn-Regular ◽  
John D. Greenough ◽  
Kyle Larson

Rocks in the Late Proterozoic Horsethief Creek Group at Quartz Creek in British Columbia display rare ‘pinolitic’ textures resembling those described in some sparry magnesite deposits elsewhere in the world. Elongated white magnesite crystals up to 30 cm long occur in a contrasting, dark, fine-grained matrix of dolomite, chlorite, organic material, clay minerals and pyrite. The rocks are aesthetically appealing for use in sculpture and as dimension stone. The term ‘pinolite’ is derived from the superficial similarities between these unusual textures and pinecones. Petrographic examination indicates that these textures formed when metasomatic fluids replaced primary sedimentary dolomite with magnesite. Fluids moved along fractures and bedding planes with repeated fracturing yielding magnesite crystals oriented in opposite directions on either side of annealed fractures, and broken magnesite crystals adjacent to later fractures. Magnesite contains dolomite microinclusions and has elevated Ca contents that are consistent with its formation by replacement of dolomite. Low concentrations of Cr, Ni, Co, Ti, Sr, and Ba in magnesite also imply formation in a metasomatic rather than a sedimentary environment. The rare earth element (REE) concentrations in the Quartz Creek magnesite are higher than those in most evaporitic magnesite and REE patterns lack the Ce and Eu anomalies that characterize carbonate rocks from sedimentary environments. Enrichment in light REE relative to heavy REE, and the similarities between dolomite, chlorite, and magnesite REE profiles, imply that metasomatic fluids modified the original sedimentary geochemical signature of the dolostones during formation of the pinolite rocks. A Late Ordovician to Early Silurian U–Pb age (433 ± 12 Ma), for titanite in the black matrix surrounding the sparry magnesite is younger than the local host rocks, and also younger than the Mesoproterozoic to Middle Cambrian stratigraphic ages of the host rocks for nearby magnesite deposits. The ca. 433 Ma titanite overlaps the ages for numerous fault-associated diatremes and volcaniclastic deposits in the area. Possibly the igneous activity furnished heat for, and/or was the source for, metasomatic fluids that produced the pinolite deposits.


2021 ◽  
Vol 91 (11) ◽  
pp. 1166-1187
Author(s):  
Mollie Patzke ◽  
J. Wilder Greenman ◽  
Galen P. Halverson ◽  
Alessandro Ielpi

ABSTRACT Reconstructing Precambrian sedimentary environments over broad cratonic regions often relies on a combination of facies, structural, and provenance analyses. The Mesoproterozoic (ca. 1270–1090 Ma) Fury and Hecla Group, exposed on the Melville Peninsula and northern Baffin Island (Nunavut, Canada), is considered broadly correlative with strata of the Borden, Hunting–Aston, and Thule basins (together referred to as the Bylot basins). We present the results of updated mapping and the first high-resolution sedimentologic and stratigraphic analysis of the lowermost unit in the Fury and Hecla Group, the Nyeboe Formation. The Nyeboe Formation comprises five distinct facies associations: alluvial to fluvial, eolian-backshore, marine-intertidal, marine foreshore to shoreface, and marine-offshore. Thin mafic units are interbedded within the marine shoreface facies and are interpreted to represent volcanic flows. Lateral relationships between facies associations are complex, but generally, facies associations transition from a terrestrial environment at the base to a nearshore marine environment at the top, indicating a transgression. Considering both the along-strike and -dip thickness trends, the presence of mafic volcanic rock units, and possible syndepositional fault orientations crosscutting the deposits, we infer that the Fury and Hecla Group was deposited in a regime of crustal thinning in a half-graben setting. Our results from the Nyeboe Formation suggest a lithostratigraphic correlation to the Nauyat and Adams Sound formations of the Borden Basin. Therefore, this study establishes a geodynamic link between the opening of the Fury and Hecla Basin to the other Bylot basins and contributes to the understanding of a large late Mesoproterozoic intracontinental-basin system.


Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-10
Author(s):  
Zhiming Yan ◽  
Jinlong Wang ◽  
Xuetian Wang

The Dananhu coalfield, at the southern margin of Turpan-Hami Basin, Xinjiang, has good coal-forming geological conditions. Due to the low research level on the depositional environment and coal accumulation, the comprehensive coal mining is restricted. Based on drilling and sectioning outcrop data, the depositional characteristics, lithofacies, paleogeography, and coal accumulation of the coal-bearing formations in western Dananhu coalfield are analyzed. The middle member of the Xishanyao Formation is the major coal-bearing strata of the Dananhu coalfield, composed of conglomerate, sandstone, siltstone, mudstone, and combustible organic rock, which can be further subdivided into 14 lithofacies according to substance composition, sediment texture, and structure. During the early Middle Jurassic coal-accumulating period, alluvial fan, fluvial plain, fluvial delta, and shallow lacustrine deposits were developed from northeast to southwest in the western Dananhu mining area. Coal accumulation was most developed in the center regions of the study area extending from northeast to southwest, which were primarily concentrated in margin fans, floodplains, interdeltaic bays, and lakeshore environments, especially the transitional zone between the fluvial plain and the delta plain in the west of No. 1 mining area. This coal accumulation was mainly controlled by synsedimentary tectonic subsidence and clastic sediments supply or sedimentary environment, where tectonic subsidence was the primary controlling factor and the source supply was the secondary controlling factor for coal accumulation, which provided theoretical support for the coal prediction and geological exploration in western Dananhu coalfield.


2021 ◽  
Vol 251 ◽  
pp. 698-711
Author(s):  
Grigorii Cherdantsev ◽  
Aleksander Zharkov

The article discusses the prospects for the oil and gas content of the Upper Permian deposits in the southwestern marginal part of the Vilyui syneclise. In this margin, the Permian terrigenous complex with proven oil and gas productivity in the central part of the syneclise, pinches out. The study area, represented by the monoclinal slopes of the Vilyui syneclise, is considered a promising area for the exploration of non-structural hydrocarbon traps in the Upper Paleozoic sediments. The objectives of the study include identifying general patterns of sediment formation, associated mainly with the development of the alluvial complex, and substantiating the potential opportunities of migration and accumulation of hydrocarbons in the predicted traps. The research is based on the interpretation of the latest seismic surveys and prior-years geological and geophysical data. Authors carried out structural and paleo-structural analysis, identified lithofacies in the well log, generalized and analyzed the geochemical conditions of the oil and gas content of the Upper Permian deposits, traced the pinching out of the Upper Permian deposits on the southwestern margin of the syneclise, and also outlined areas of river valleys development that form zones of advanced reservoirs. The results of the studies have validated promising oil and gas accumulation zones on the southwestern slopes of the syneclise associated with non-anticlinal hydrocarbon traps. Authors also drew up a diagram of the oil and gas potential of the Upper Permian deposits. The obtained results are of interest for prospecting for oil and gas in the area under study.


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