Distribution of diagenetic alterations in glaciogenic sandstones within a depositional facies and sequence stratigraphic framework: Evidence from the Upper Ordovician of the Murzuq Basin, SW Libya

The spatial and temporal distribution of diagenetic alterations has been constrained in relationship to depositional facies and sequence stratigraphy of the Upper Ordovician glaciogenic quartzarenite sandstones in the Murzuq Basin, SW Libya, which were deposited during the Haritanian glaciation when the basin was laying along the continental margin of Gondwana. Eogenetic alterations encountered include: (i) replacement of detrital silicates, mud matrix and pseudomatrix by kaolinite in paraglacial, tide-dominated deltaic, in foreshore to shoreface (highstand systems tract; HST) and in post-glacial, Gilbert-type deltaic (lowstand systems tract; LST) sandstones, particularly below the sequence boundaries (SB). Kaolinite formation is attributed to the influx of meteoric water during relative sea level fall and basinward shift of the shoreline. (ii) Cementation by calcite (δ¹⁸O_VPDB = − 3.1‰ to + 1.1‰ and δ¹³C_VPDB = + 1.7‰ to + 3.5‰) and Mg-rich siderite in the paraglacial, tide-dominated deltaic and foreshore to shoreface HST sandstones, in the glacial, tide-dominated estuarine (transgressive systems tract; TST) sandstones and in the post-glacial, shoreface TST sandstones is interpreted to have occurred from marine pore-waters. (iii) Cementation by Mg-poor siderite, which occurs in the post-glacial, Gilbert-type deltaic LST sandstones and in the paraglacial, tide-dominated deltaic and foreshore to shoreface HST sandstones, is interpreted to have occurred from meteoric waters during relative sea level fall and basinward shift of the shoreline. (iv) Pervasive cementation by iron oxides has occurred in the glacial, shoreface–offshore TST sandstones and post-glacial, shoreface TST sandstones immediately below the maximum flooding surfaces (MFS), which was presumably enhanced by prolonged residence time of the sediments under oxic diagenetic conditions at the seafloor. (v) Formation of grain-coating infiltrated clays mainly in the glacial, fluvial incised-valley LST sandstones and in the post-glacial, Gilbert-type deltaic LST sandstones as well as, less commonly, in the paraglacial, foreshore to shoreface HST sandstones and in the tide-dominated deltaic HST sandstones below the SBs.

Mesogenetic alterations include mainly the formation of abundant quartz overgrowths in the glacial, fluvial incised-valley LST sandstones, post-glacial, Gilbert-type deltaic LST sandstones and glacial, shoreface TST sandstones, in which early carbonate cements are lacking. Illite, chlorite and albitized feldspars, which occur in small amounts, are most common in the glacial, tide-dominated estuarine TST sandstones and paraglacial, shoreface HST sandstones. This study demonstrates that the spatial and temporal distribution of diagenetic alterations and their impact on reservoir-quality evolution in glacial, paraglacial and post-glacial sandstones can be better elucidated when linked to the depositional facies and sequence stratigraphic framework.     

Facies Analysis and Sequence Stratigraphy of the Qal’eh Dokhtar Formation (Middle–Upper Jurassic) in the West of Boshrouyeh, East Central Iran

The study area is located in the east Tabas Block in Central Iran. Facies analysis of the Qal’eh Dokhtar Formation (middle Callovian to late Oxfordian) was carried out on two stratigraphic sections and applied to depositional environment and sequence stratigraphy interpretation. This formation conformably overlies and underlies the marly-silty Baghamshah and the calcareous Esfandiar formations, respectively. Lateral and vertical facies changes documents low- to high energy environments, including tidal-flat, beach to intertidal, lagoon, barrier, and open-marine. According to these facies associations and absence of resedimentation deposits a depositional model of a mixed carbonate–siliciclastic ramp was proposed for the Qal’eh Dokhtar Formation. Seven third-order depositional sequences were identified in each two measured stratigraphic sections. Transgressive systems tracts (TSTs) show deepening upward trends, i.e. shallow water beach to intertidal and lagoonal facies, while highstand systems tracts (HST) show shallowing upward trends in which deep water facies are overlain by shallow water facies. All sequence boundaries (except at the base of the stratigraphic column) are of the no erosional (SB2) types. We conclude eustatic rather than tectonic factors played a dominant role in controlling carbonate depositional environments in the study area.     

Chemical and Isotopic Constraints for Recrystallization of Sedimentary Dolomites from the Western Canada Sedimentary Basin

Mississippian shoal carbonates of Western CanadaSedimentary Basin are important hydrocarbon hosts.Dolomitization plays a major role in the evolution ofreservoir porosity in these carbonates. This processvaries across the basin and reflects, in part, divergentsources and chemistry of pore fluids. Dolomites fromseveral petroleum reservoirs were analyzed formineralogical, geochemical and isotopic variation. Thedata clearly demonstrate the progressive and complexrecrystallization of dolomite during shallow and deepburial in modified marine, meteoric and burial fluids.These data include: change in crystal size,stoichiometry, cathodoluminscence characteristics,stable oxygen and carbon isotopic shifts and changesin radiogenic Sr isotopic composition. However,regional geology, tectonic history and fluid flowevolution play important roles in the diageneticimprints and the degree of recrystallization.Early microcrystalline dolomite formed in normalmarine and evaporative conditions in Mississippiancarbonates from Western Canada Sedimentary Basinhave undergone variable degrees of recrystallization, frompristine dolomite akin to Holocene sabkha dolomitewith preserved mineralogical and chemical attributesto highly recrystallized mesodolomite, however stillnonstoichiometric, but with highly altered chemicalsignatures. Careful attention should be made to localgeology, hydrodynamics and fluid flow when investigatingdolomite recrystallization in sedimentary basins.     

Correction to: Landslide susceptibility mapping of the Sera River Basin using logistic regression model

Natural Hazards - The article “Landslide susceptibility mapping of the Sera River Basin using logistic regression model,” written by Nussaïbah B. Raja, Ihsan Çiçek, Necla...     

Spatial modeling of Dengue prevalence and kriging prediction of Dengue outbreak in Khyber Pakhtunkhwa (Pakistan) using presence only data

Stochastic Environmental Research and Risk Assessment - During the span of August–October, 2017 a major outbreak of Dengue fever happened in Khyber Pakhtunkhwa province of Pakistan. Cases...     

Distribution and significance of hydrothermal alteration minerals in the Tuzla hydrothermal system, Çanakkale, Turkey

Hydrothermal alteration zones have been investigated by X-ray diffraction, mineralogical–petrographical techniques, and geochemical analysis. Examination of cores and cuttings from two drill sites, obtained from a depth of about 814–1020 m, show that the hydrothermal minerals occuring in the rock include: K-feldspar, albite, chlorite, alunite, kaolinite, smectite, illite, and opaque minerals.In the studied area, silicified, smectite, illite, alunite, and opal zones have been recognized. These alteration mineral assemblages indicate that there are geothermal fluids, which have temperatures of 150–220°C in the reservoir.The distribution of the hydrothermal minerals shows changes in the chemical composition of the hydrothermal fluid, which are probably due not only to interaction with host rock, but also to dilution of the Na–K–Cl-rich hydrothermal fluid of the deep reservoir by cold sea water at shallow levels. Geochemical analyses of the solid and liquid phases indicate that the hydrothermal fluids of the Tuzla geothermal system are in equilibrium with alteration products.The tectonic structure of the studied area is caused by NW–SE and NE–SW directional forces. The volcanic rocks where hydrothermal zones are observed in the studied area are of Lower–Middle Miocene age comprise latite, andesite, dacite, rhyolite-type lavas, tuff, and ignimbrites.     

Über die tektonisch-mechanischen Folgerungen aus den großen anatolischen Erdbeben des letzten Dezenniums

Ohne Zusammenfassung     

Fuzzy robust process capability indices for risk assessment of air pollution

Air pollution is one of the most important threats for the humanity. It can damage not only human health but also Earth’s ecosystem. Because of the harmful effects of air pollution, it should be controlled very carefully. To do the risk assessment of air pollution in Istanbul, the process capability indices (PCIs) which are very effective statistics to summarize the performance of process are used in this paper. Fuzzy PCIs are used to determine the levels of the air pollutants which are measured in different nine stations in Istanbul. Robust PCIs (RPCIs) are used when air pollutants have correlation. Fuzzy set theory has been applied for both PCIs and RPCIs to have more sensitive results. More flexible PCIs obtained by using fuzzy specification limits and fuzzy standard deviation are used to evaluate the air pollution’s level of Istanbul. Additionally some evaluation criteria have been constructed for fuzzy PCIs to interpret the air pollution.     

Distribution of diagenetic alterations in fluvial and paralic deposits within sequence stratigraphic framework: Evidence from the Petrohan Terrigenous Group and the Svidol Formation, Lower Triassic, NW Bulgaria

Elucidation of diagenetic alterations in the Petrohan Terrigenous Group (fluvial; highstand systems tract HST) sandstones and Svidol Formation (tide-dominated deltaic and tidal flat, transgressive systems tract TST and highstand systems tract HST, respectively) sandstones and calcarenite, Lower Triassic, NW Bulgaria was constrained within a sequence stratigraphic framework. Eogenetic alterations in the fluvial HST sandstones include (i) formation of grain-coating infiltrated clays as a result of percolation of mud-rich surface waters into underlying coarse-grained and permeable channel-fills and crevasse splay sandstones; (ii) formation of pseudomatrix by mechanical compaction of mud intraclasts that were incorporated into the coarse-grained channel sandstones during their lateral avulsion; and (iii) cementation by calcite (δ¹⁸O_VPDB = − 6.5‰ to − 3‰; δ¹³C_VPDB = − 5.1‰ to + 0.6‰) and dolomite (δ¹⁸O_VPDB = − 6.1‰ to − 0.3‰; δ¹³C_VPDB = − 7.2‰ to − 5.8‰) in the crevasse splay and floodplain sediments. Mesogenetic alterations that are encountered in the fluvial HST sandstones include (i) illitization of grain-coating clays, mud intraclasts, and mica, possibly because of simultaneous albitization of feldspars; (ii) cementation by calcite (δ¹⁸O_VPDB = − 14.5‰ to − 8.4‰; δ¹³C_VPDB = − 7.7‰ to + 0.6‰) and dolomite (δ¹⁸O_VPDB = − 15.8‰ to − 5‰; δ¹³C_VPDB = − 7.9‰ to + 1.5‰); and (iii) limited amounts of quartz overgrowths in the channel sandstones owing to occurrence of thick grain-coating clays.

Conversely, the tide-dominated deltaic TST sandstones and the tidal flat HST calcarenite were pervasively cemented by calcite (δ¹⁸O_VPDB = − 6.6‰ to − 3.1‰; δ¹³C_VPDB = − 5.1‰ to + 0.6‰) and siderite (δ¹⁸O_VPDB = − 7.2‰ to − 5.7‰; δ¹³C_VPDB = + 0.3‰ to + 0.9‰) particularly below marine and maximum flooding surfaces, due to the presence of abundant bioclasts and prolonged residence time of the sediments under certain geochemical conditions along these surfaces. The remaining open pores were cemented during mesodiagenesis by calcite (δ¹⁸O_VPDB = − 6.6‰ to − 3.1‰ and δ¹³C_VPDB = − 5.1‰ to + 0.6‰) and dolomite (δ¹⁸O_VPDB = − 6.6‰ to − 3.1‰ and δ¹³C_VPDB = − 5.1‰ to + 0.6‰).

This study shows that constructing a conceptual model for the distribution of diagenetic alterations is possible by integration of diagenesis with sequence stratigraphy. The model shows that tide-dominated deltaic TST sandstones and tidal flat HST calcarenite were pervasively cemented by carbonates during near-surface eodiagenesis, owing to the presence of abundant bioclasts. Conversely, fluvial LST sandstones remained poorly cemented during near-surface eodiagenesis due to the lack of bioclasts, but were cemented by mesogenetic calcite, dolomite and quartz overgrowths instead.