International Journal of Earth Sciences最新文献

Abstract

Within the Tethyan belt, the NW-Iranian block is bound by two sutures, the Sevan-Akera suture in the north, and the Zagros suture in the south, where the pre-Cambrian geology is poorly constrained. Lower-Middle Cambrian sandstone in NW Iran is represented by quartz and feldspar dominated sub-arkose and sub-litharenite with well-developed cross bedding structures. They are interlayered with shale and limestone and overlain unconformably by Middle Cambrian dolomite. Here we describe and present U–Pb ages of the detrital zircon and rutile together with in-situ ε-Hf data from Lower to Middle Cambrian sandstones. Some zircons are characterized by oscillatory zoning and Th/U ratios of 0.3 to 2.0, pointing to an igneous provenance. Ages of the detrital zircons range from 481 to 2762 Ma, whereby the majority of zircons have ages between 524 and 1000 Ma (Neoproterozoic), and small peaks at 1800–2000 and 2400–2600 Ma. Late Paleoproterozoic to Mesoproterozoic zircons (1100–1750 Ma) are absent in the detrital record which is a distinctive feature of Gondwana-related detrital zircons. Detrital rutile has elevated Cr contents and variable Zr content (88 to 1087 ppm), suggesting derivation mainly from amphibolite-facies meta-basic rocks. U–Pb rutile ages range from 561 to 1253 Ma. Initial ε-Hf values of the Neo-Proterozoic zircons range from -10 to 20, suggesting an association of highly depleted mantle and crustal magmas. Thus, the Lower-Middle Cambrian sandstones in Iranian Azerbaijan were supplied from a Neoproterozoic igneous and metamorphic provenance. Sandstone whole-rock major and trace elements are in accordance with a detrital material provenance from continental granitoids and Precambrian recycled sediments. These results support the hypothesis that Iranian Azerbaijan Cambrian detritus was supplied from repetitive recycling of the crystalline basement and related sedimentary cover of the Saharides and the Arabian-Nubian Shield and deposited in a passive-margin setting in northern Gondwana land. Our results show a close geological tie between Iranian Azerbaijan, Sanandaj-Sirjan, Zagros, Alborz, and other Gondwana-Land-derived units in terms of Early Paleozoic detritus sources. Northwest Iranian Block was probably a passive continental margin in Late Ediacaran-Cambrian after the so-called Cadomian orogeny.

Abstract

During the Late Permian Wuchiapingian–Changhsingian (W–C) transition, significant biotic and environmental changes occurred. These changes had the potential to greatly influence the type, accumulation, and preservation of organic matter within sediments during this period. The Wujiaping Formation, which acts as the contemporaneous heterotopic facie of the Longtan Formation, is regionally found in the Susong–Dongzhi stratigraphic subregion in the Lower Yangtze Platform (LYP). However, the variations in organic matter input and preservation during the Late Permian W–C transition in this specific area have not been comprehensively understood. Consequently, this study involved the collection of Upper Permian Wujiaping and Dalong shale samples in the LYP. Total organic carbon (TOC) content, vitrinite reflectance (R_o), maceral compositions, carbon isotope composition of kerogen, as well as the major and trace elements in the shale samples were all measured in this study. The results of R_o analysis indicate that the maturity levels of shale derived from the Dalong and Wujiaping Formations exhibit maturity levels exceeding 2%, which indicates an over-mature stage. The maceral compositions and carbon isotope analysis of kerogen reveal that the predominant source of organic matter within the Dalong shale is attributed to algal organism. Conversely, the organic matter in the Wujiaping shale primarily comes from higher plants. The major and trace element distributions provide insights into the depositional conditions of the Upper Permian shale, and significant variations in organic matter input and preservation are evident during the Late Permian W–C transition. The findings indicate that the Wujiaping Formation was characterized by a low paleo-productivity, high terrestrial influx intensity, low paleo-salinity, and a pronounced restricted setting under oxic conditions. However, the Dalong Formation is deposited under an anoxic environment, characterized by high paleo-productivity and paleo-salinity, limited terrestrial influx intensity, and increasing upwelling. In addition, the water mass restriction weakened within the Dalong Formation, attributable to a gradual rise in sea level. The shift of organic matter input and preservation was instigated by the persistent regional rise in the sea level during the Late Permian period. In summary, the great input and favorable preservation conditions of organic matter observed in the Dalong shale indicates a promising potential for shale gas exploration.

In the Late Permian Zechstein Sea of Central Europe, up to 2000 m of evaporitic rocks were deposited in at least four consecutive cycles. The age of these evaporitic rocks could not yet be precisely determined, because they are virtually fossil-free and do not contain radiometrically datable volcanic layers. A chemostratigraphic age of the succession can be determined by comparing ⁸⁷Sr/⁸⁶Sr ratios of marine gypsum and anhydrite to the worldwide marine strontium evolution curve. Unfortunately, published ⁸⁷Sr/⁸⁶Sr data of the Zechstein succession are characterized by frequent outliers towards higher ratios, making an age assignment challenging. The scatter in ⁸⁷Sr/⁸⁶Sr ratios might be induced by different processes like the contribution of meteoric water to the brine, in-situ Rb decay, or post-depositional hydrothermal or diagenetic overprint. Here, we present a dataset of 26 new gypsum and anhydrite ⁸⁷Sr/⁸⁶Sr ratios from drill cores situated at “Alter Stolberg” in the northernmost Thuringian Basin. Evaporites of the Werra-, Staßfurt-, and Leine cycles were sampled. The close proximity of the drillings allows a very accurate assignment of the stratigraphic position of each sample, so that trends and outliers in ⁸⁷Sr/⁸⁶Sr ratios can easily be recognized. While the entire Werra Formation obviously revealed non-marine ⁸⁷Sr/⁸⁶Sr ratios, the lowermost ⁸⁷Sr/⁸⁶Sr ratios in the Staßfurt and Leine Formations can be assumed to represent marine ratios and allow estimating a chemostratigraphic age of 257‒254 Ma. The combination of the ⁸⁷Sr/⁸⁶Sr data with the mineral composition of the samples suggests a contribution of meteoric water, probably river water, to the Zechstein Sea as the main reason for the observed increase in ⁸⁷Sr/⁸⁶Sr ratios. Additional in-situ Rb decay, related to the riverine input of clay minerals, cannot be excluded. Modelling the amounts of sea water and meteoric water in the brine indicates that 83‒99% of meteoric water would be necessary to explain the highest ⁸⁷Sr/⁸⁶Sr ratios observed in the Werra Formation.

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This study developed a novel, detailed sedimentological analysis for the complex interactions between rainout, iceberg rafting, tractional underflows, and settling of fines along a glacially influenced basin margin. The glaciomarine interval of the El Imperial Formation (Pennsylvanian, Serpukhovian–Bashkirian) in the San Rafael basin comprises massive to stratified diamictites, interpreted as rainout tills, thinly bedded diamictites, associated with cohesive debris flows, and mudstones containing ice-rafted debris (IRD), all capped by postglacial, transgressive, fine-grained sediments. The rhythmic intercalation of IRD-bearing (dropstone mudstones) and IRD-free (mudstones) intervals likely indicates variations in debris content within the ice margins, the on-and-off switching of ice streams, or dynamic oscillations of the ice terminus. The glaciomarine deposits exhibit soft sediment deformation on both large (metric to decametric) and small (centimetric) scales. This contribution refines previous interpretations of the soft sediment deformation, discerning between loading and slope triggered deformation. Large-scale deformation is characterized by coherent slump folds with low dispersion in the orientations of fold axial plane vergence and fold b-axes. Downslope-verging folds indicate a northward paleoslope, consistent with paleoflow indicators from flute casts found in sandstone turbidite beds. The diamictites affected by the large-scale soft sediment deformation are interpreted as rainout tills with a variable degree of gravity remobilization. Their association with thinly bedded diamictites and laminated mudstones with dropstones suggests that ice rafting played a significant role in the deposition of this succession.

Graphical abstract

Remarkably well-preserved crustal sections from the Eastern Hellenides offer the chance to evaluate the regional geodynamic evolution of continental crust. Here, we identify and geodynamically interpret eclogite facies metamorphism in the Triassic–Jurassic volcano-sedimentary series of the West Circum Rhodope zone in the eastern Hellenides. Equilibrium phase diagrams and measured mineral compositions were used to inform reconstructions of geodynamic evolution during the early Alpine period. We newly define the existence of the Eohellenic HP belt, consisting of pre-Alpine basement, continental volcano-sedimentary formations, and a Jurassic magmatic arc. We suggest that the Eohellenic HP-Belt was subducted in the late Jurassic to early Cretaceous beneath the European plate margin. Detailed geodynamic reconstructions such as ours provide a robust anchor for future computational models of long-term crustal evolution in the Eastern Hellenides.

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Situated in the western Sierras Pampeanas of San Luis, the Nogolí Metamorphic Complex has become a key geological locality for unraveling the construction of the western Gondwana margin on the South American tectonic plate. This study presents a comprehensive analysis, encompassing new petrological and geochronological data, along with a meticulous structural examination of two distinct regions within the Nogolí Metamorphic Complex. Our primary aim is to assess the age and provenance of the protoliths, thereby shedding light on their geodynamic evolution. Detrital zircon U–Pb ages, obtained from a quartz–feldspathic-schist paleosome within a metatexite exposure in the La Barranquita area, disclosed a polymodal distribution. The predominant age population, centered around 616 ± 11 Ma, suggests a late Neoproterozoic source (Brasiliano–Pan African orogen). A secondary, yet significant, age peak at 542 ± 12 Ma points to a late Ediacaran to Early Cambrian origin (Pampean orogen). Additionally, a peak ranging from 930 to 1144 Ma indicates contributions from an early Neoproterozoic source (Grenvillian–Sunsas orogen). The maximum depositional age was determined to be 533 ± 14 Ma, based on the calculation of the youngest grain cluster at 2σ uncertainty. This polymodal zircon-age spectrum indicates that the sedimentary protolith of the Nogolí Metamorphic Complex derived from a Cambrian-age crystalline basement situated along the western margin of Gondwana. Contrary to models invoking continent–continent collision in western Gondwana during the early Cambrian, our findings better support a ridge–trench collision as the most plausible hypothesis for the origin of the Pampean orogeny.

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The majority of Greek lignite fields and coal-fired power plants is accumulated in the centre of Western Macedonia in the Ptolemais-Amynteo region of Northern Greece (Ptolemaida basin). The corresponding environmental impact dominantly caused by the mining process itself but also due to the burning process of lignites needs to be considered. Therefore, this study aimed at assessing the potential of PAHs to trace the environmental impact of power plant and coal mining emissions on soil pollution in the Ptolemaida basin. Noteworthy, the study area exhibits some special features (e.g. geomorphological and meteorological conditions, well-defined emission sources) that allow to prove the suitability of PAHs as indicators for specific petrogenic contaminations. The different sets of PAH emission sources followed in this study (fly ashes, lignite dust, charred woody material) reflected the pollution as derived from the coal mining activities as well as agricultural measures. Different approaches from simple (total amount) to more complex fingerprinting (ring member classification; profiles of sulphur-/nitrogen- and oxygen-containing PACs) as well as the application of established specific PAH ratios revealed no significant correlation with the detected soil contamination or rather soil PAH profiles. However, the microscopic analyses contradicted this assumption, since relevant particle concentrations were evident for fly ash as well as lignite particles. Hence, a huge superimposition by a further PAH emission source is assumed, probably the exhaust fumes of car traffic. In general, the study demonstrated that the application of PAHs as source indicators in soil systems is very complex and needs a very thorough interpretation. Hence, the need of using additionally complementary parameters for an unambiguous emission source apportionment seems obvious.

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Understanding geochemical zoning, including major components, minor components, and trace elements, in ore deposits can significantly improve Au exploration. Therefore, in this study, we focus on the geochemical characteristics of ore and alteration zones in the largest low-sulfidation (LS) epithermal Au–Ag deposit in Thailand, namely Chatree deposit. The occurrence of metal and metalloids can be distinguished into three groups: (1) major components in ore minerals (e.g., As, Cu, Fe, Pb, Sb, and Zn), (2) trace elements in ore minerals (e.g., As, Cd, Hg, and Mn), and (3) trace elements in gangue minerals (e.g., Mn). This study suggests that the ore minerals of a shallow system of the epithermal LS deposit are enriched in As, Sb, and Hg compared to the deeper system. Hydrothermal alteration leads to enrichment of K₂O and depletion of Na₂O and CaO. Besides major oxides, some low-field strength elements (e.g., Rb, and Ba) show the same behavior as K₂O, whereas Sr is similar to CaO. In addition, positive Eu anomalies are associated with hydrothermal alteration. For metals and metalloids, arsenic is an important pathfinder element because its content is associated with the electrum occurrence and significantly increases toward the ore zone. Mn, Pb, and Cd are prominent in the ore zone; whereas, Ti, Al, and Cr decrease toward the ore zone due to dilution from silicification. Furthermore, even though the concentrations of As, Cd, Cr, Pb, and Ni in the ore and alteration zones are lower than Thailand's Total Threshold Limit Concentration (TTLC) for waste, the mine should still implement critical monitoring of these elements.

Graphical abstract