Geochemical Studies Research Articles

Petrogenesis of Miocene high Ba–Sr granitoids from the Central Pamir: Implications for continental growth

High Ba–Sr granitoids differ from the I-, S- and A-type granitoids, and their petrogenesis and role in the evolution of the continental crust remain enigmatic. This paper reports a study of whole-rock geochemistry, and Sr–Nd isotopes, zircon U–Pb geochronology, and Lu–Hf isotopes of the Zankan high Ba–Sr intrusion in the Central Pamir. U–Pb dating of zircons suggests that the pluton was emplaced during the Miocene (10.2 ± 0.1 Ma). The Zankan rocks have high contents of K2O (3.83 to 12.3 wt%), Rb (212–483 ppm), Ba (701–6910 ppm), and Sr (503–3371 ppm). They have several geochemical characteristics that are consistent with A-type granitoids, such as high Na2O + K2O (8.10–14.2 wt%) and Zr + Nb + Ce + Y (336–1393 ppm) contents. All samples have enriched Sr–Nd–Hf isotope compositions, with 87Sr/86Sri = 0.7097 to 0.7126, εNd(T) = −9.3 to −8.4, and εHf(T) = −12.2 to −4.0. Their isotopic compositions differ from those of mafic lower crust in the Central Pamir. Alternatively, the Zankan rocks may have been derived from an enriched lithospheric mantle. Combining our new isotopic results with data from the literature, we propose that a shift from isotopically juvenile to more isotopically evolved compositions in mantle-derived magmas took place from the Eocene to Miocene. The isotopic shift reveals that South Pamir lower crust was underthrusted beneath the Central Pamir lithosphere during the Miocene. Although high Ba–Sr granitoids generally exhibit “crust-like” isotopic characteristics, our data indicate that they play a role in continental growth.

Aliphatic Biomarker Signatures of Crude Oil from Tarakan Subbasin, Tarakan Basin, North Kalimantan, Indonesia

Organic geochemical studies of crude oil from Pamusian Field, Tarakan Subbasin, Tarakan Basin, North Kalimantan, have been done. Biomarker aliphatic hydrocarbon fractions were identified using a combined gas chromatography-mass spectrometer (GC - MS). Identified biomarkers consist of n-alkane groups, isoprenoids, bicyclic sesquiterpenoids, and pentacyclic triterpenoids. The most abundant aliphatic hydrocarbon biomarker is pristane followed by n-C19. The existence of n-alkanes shows a homologous (n-C16- n-C30) with a unimodal distribution type. The abundance of n-C19 is higher than other n-alkanes, supported by LHCPI value of 2.03, as an indicator of organic matter derived from microbial organisms. The amount of long chain n-alkanes (n-C25- n-C30) is almost the same as medium chain n-alkanes (n-C19 - n-C24) indicating the source of organic compounds is not only from microbial organisms, but also from terrestrial higher plants. The presence of 8β (H)-drimane compounds together with homodrimane shows the presence of bacterial input on the formation of oil from organic compounds. Ratio of Pr/Ph is 3.76, ratio of drimane/homodrimane is 1.058, ratio of Pr/n-C17 is 34.41, and ratio of Ph/n-C18 is 16.02 indicating the source of organic compounds came from terrestrial higher plants deposited in the oxic environment, and disposed to increase biodegradation. The CPI value is 0.95, and the highest amount of 17α (H), 21β (H)-hopane compounds suggest that Tarakan Subbasin oil was mature, and the source of organic compounds was derived from bacteria Keywords: Tarakan Basin, organic geochemistry, aliphatic hydrocarbon fraction, CPI

Main Ordovician–Silurian events in the South Ural and event stratigraphy regional tasks

The main regional abiotic events of the Ordovician and Silurian of the Southern Urals are manifested in the restructuring of sedimentation in the paleobasin. Eustatic fluctuations and tectonic motions primarily cause changes in the lithological composition of strata. Geochemical events influence the isotopic composition of elements.
 Biotic events affect biodiversity in micro- and macrofauna complexes. The largest of the five Phanerozoic extinctions was the global extinction event at the Ordovician–Silurian boundary (LOME). The Ordovician biotic diversification event (GOBE) is divided into three phases. The Darrivillian level of manifestation of this event is noted in the Southern Urals.
 The location of the global biotic events GOBE, LOME, and the geochemical event HICE in the sections of the Southern Urals is substantiated. Based on the analysis of the connection between biotic and abiotic events in the Ordovician-Silurian deposits of the Southern Urals, the significant role of conodonts, graptolites, chitinosoans and their correlation potential were revealed. Insufficient knowledge of the sections makes it possible to correlate regional events with certain assumptions.
 In order to carry out global event correlations, in addition to the comprehensive biostratigraphic characteristics of the Ordovician and Silurian deposits of the Southern Urals, geochemical studies of a number of sections are necessary. The most promising sections for identifying event levels are the sections of the western slope of the Zilair synclinorium: Nabiullino, Maksyutovo, Gremyachiy, Kaga-V.Avzyan, Sermenevo.

Source rock potential and spatial distribution of the stratigraphic formations in the central Mediterranean Ridge: Evidence from mud volcanic deposits and 2D seismic data

Due to the lack of deep wells in the broader region, the mud volcanic deposits (mud breccia) are the only source of direct information for the deep stratigraphic units of the Mediterranean Ridge (MR), in the eastern Mediterranean. The study of this material, combined with the available seismic data, can improve the geological understanding of this frontier exploration area.In this paper, biostratigraphic and geochemical studies are performed on mud breccia deposits from five Mud Volcanoes (MVs) in the central MR, aiming to define the sediments’ stratigraphic origin and assess the source rock potential of the individual formations. In addition, regional seismic data is used to reveal the spatial distribution of the major lithostratigraphic formations in the subsurface.Results indicate an Eocene-Miocene origin for the mud breccia of Gelendzhik, Nice, Moscow and Dublin MVs, whereas a Paleocene (?) and Cretaceous origin is suggested for the Toronto MV deposits. Most clasts represent hemipelagic mudstones/marlstones. Regarding the source rock potential of the area, it is considered that: (a) nine clasts of Miocene, Eocene and undetermined age, reflect the presence of immature and early mature, gas-prone source rocks of poor to moderate potential; (b) a small clast discovered in the matrix of Dublin MV originates from an excellent quality oil-prone source rock; and (c) the discovered solid hydrocarbons and oil droplets point to an active petroleum system in the region.Seismic interpretation defines the spatial distribution of the Post-Evaporite, Evaporite and Pre-Evaporite formations. The burial depth of the Pre-Evaporite formation (source layers of MV deposits) significantly varies from 20 to 4970 m inside the study area and is largely dependent on Evaporite thickness.

Gley catagenesis of Devonian red-colored rocks on the Middle Timan

Research subject. The article presents the results of morphological, mineralogical, and geochemical studies into gley zones in the Devonian red-colored sediments of the Middle Timan. Aim. Determination of the timing of gleization processes in the formation history of the Devonian sedimentary strata; identification of morphological, mineralogical and geochemical features of gley zones. Methods. A macroscopic study of the morphology of gley zones in successive sections of the sediments was carried out in field conditions. Thin sections were studied using a Nikon eclipse LV100 ND polarization microscope with a Nikon DS Fi2 camera; polished samples were characterized using a TESCAN electron microscope VEGA3 with an Oxford instruments X-Max energy dispersion attachment; the chemical composition was determined by an X-ray fluorescent silicate method on a MESA-500W spectrometer; X-ray diffraction analysis was performed using a Shimadzu XRD-6000 diffractometer under the CuKα radiation. Results. In terms of size and morphological features, the gley zones under study are divided into four types: point, veined, lens-shaped, and bed-shaped. The similarity between the forms of gley zones and core organics fragments was established both in plan and vertically. The lithological heterogeneity of rocks (stratification) does not have any effect on the development of gley processes. Changes in the content of rock-forming elements during gleization are confined to intensive iron removal and a slight decrease in the potassium content; the silica content remains almost unchanged. An increase in the content of aluminum, titanium, and magnesium was observed. Among the contents of microelements, trends towards accumulation of Y and Yb, removal of Ga, V, Co, Ni are noticeable. Conclusions. Gleization processes proceeded for a very long time until the sedimentary sequence was completely formed and compacted; the main mechanism of chemical element migration was diffusion.

Recognizing different types of ocean plate stratigraphy in the southeastern South Qilian Accretionary Belt, northeastern Tibet Plateau

Dissection of relicts of ocean plate stratigraphy (OPS) in orogens could provide important insights into oceanic evolution, orogenic formation and continental growth. Here we describe a study of petrology, geochronology, geochemistry and Sr–Nd isotopes for OPS in the South Qilian Accretionary Belt with the aim of providing new constraints on the evolution of the Proto-Tethys Ocean (PTO). Three types of OPS units were recognized by their differing petrological, geochemical and isotopic features. Type 1 OPS, representing relicts of ocean islands or seamounts, comprises ocean island basalt and gabbro ( t = 525 ± 4 Ma, ( 87 Sr/ 86 Sr) i = 0.7035–0.7039 and ε Nd ( t ) = +3.63 to +4.16) and (siliceous) carbonate rocks. Type 2 OPS, representing fragments of normal oceanic crust, consists of normal mid-ocean ridge basalt (N-MORB) and basaltic andesite (( 87 Sr/ 86 Sr) i = 0.7059–0.7063 and ε Nd ( t ) = +6.33 to +7.44), chert and siliceous mudstone. Type 3 OPS could be oceanic plateau-derived and comprises enriched (E)-MORB and dolerite (( 87 Sr/ 86 Sr) i = 0.7051–0.7064 and ε Nd ( t ) = +4.81 to +6.24), carbonate–siliceous mudstone and carbonate rock. These OPS units witnessed evolution of the PTO. Using available studies on regional arc-type magmatism and U–Pb geochronological data for detrital zircon in this study, a model of ‘trench jam accompanying subduction flip induced by accretion of the OPS’ is put forward. Supplementary material : Zircon U–Pb data, whole-rock major and trace element data and a supplementary figure are available at https://doi.org/10.6084/m9.figshare.c.6764637 Thematic collection: This article is part of the Ophiolites, melanges and blueschists collection available at: https://www.lyellcollection.org/topic/collections/ophiolites-melanges-and-blueschists

Distribution features of mobile forms of heavy metals and magnetic properties of soils in the Dubravniy Forest recreational area of the city of Kazan, Russia

Aim. To compare the results of studying the magnetic properties and concentration of heavy metals in the soils of the Dubravniy Forest recreational zone of Kazan to justify the use of the petromagnetic method in conducting ecological and geochemical studies in urbanised areas.Material and Methods. The object of the study is the soil cover in the "Dubravniy Forest", using petromagnetic methods (magnetic susceptibility, differential thermomagnetic analysis) and atomic absorption spectrometry.Results. According to the results of the studies conducted into the lightgray forest soil, the measurements of magnetic susceptibility and concentration of mobile forms of heavy metals do not contradict each other and indicate the absence of magnetic minerals and heavy metals of technogenic origin.Conclusions. The results of magnetic susceptibility studies indicate the absence of soil contamination with heavy metal compounds, which was confirmed by the results of the determination of mobile forms of heavy metals by the atomic absorption method.

San Felipe Geothermal Prospect: A Previously Unrecognized Hydrothermal System on the Northeastern Coast of the Baja California Peninsula, México

Geophysical surveys discovered low resistivity values that, in combination with geochemical and structural data, indicate the presence of a previously unrecognized geothermal system with a possible maximum size potential similar to that of the presently installed capacity of the Cerro Prieto geothermal field. The only evidence of a hydrothermal system in the San Felipe Valley are warm groundwater wells and four intertidal hot springs. Exploration at San Felipe was part of a research project that included geological, geochemical and geophysical studies, which indicated the presence of low resistivity anomalies and high temperature at depth; the geological survey provided evidence of active fault systems that may act as channels for convective heat transport. Estimation of the energy potential of the San Felipe prospect using the heat in place method yielded a 50% probability of more than 300 MW that would add to the 570 MW of the Cerro Prieto geothermal field and can supply almost 40% of the state of Baja California electricity demand. The Baja California Peninsula is not connected with the national grid and has one of the highest electricity prices in Mexico, which should be an incentive to develop this clean energy source. The results of this work support the recommendation to pursue further advanced exploration of this prospect.

ЗАКОНОМЕРНОСТИ РАСПРОСТРАНЕНИЯ ОСНОВНЫХ КОМПОНЕНТОВ И ТИПОВ ПОРОД БАЖЕНОВСКОЙ СВИТЫ ЗАПАДНОЙ СИБИРИ

The distribution regularities of the main components and types of rocks of the Bazhenov Formation are investigated. It is one of the largest black shale formations in the world. The results of the lithological and geochemical study revealed that the brittlest rocks of the formation are widely distributed in the Central region and are considered as potential reservoirs: siliceous mudstones, kerogenic siliceous mudstones, carbonated radiolarites (limestones and dolomites). In the South-Eastern region, thicknesses of silicites are noticeably reduced; kerogen-clay-siliceous mudstones (similar in silica content to siliceous mudstones) prevail, which are also reservoirs in a number of areas. These types of rocks are practically not typical for the Northern and Southern regions. Detailed distribution maps of the main components of rocks for the lower, middle and upper parts, as well as for the Formation as a whole, were constructed. It was revealed that the highest concentrations of siliceous material are observed in the lower and to a lesser extent in the middle parts of the Bazhenov Formation section in the Central region. By the nature of distribution, composition and thickness of potential reservoirs, the Central region can be considered as a highly promising region in terms of development for hydrocarbon raw materials, the South-Eastern is medium-promising one, the Northern and Southern are low-promising ones.

Early Famenian Trachyandesite Magmatism of the Pripyat Paleorift, East European Platform: U–Pb Age and Petrology

On the basis of the mineralogical-petrographic and geochemical study of igneous rocks of intermediate composition of the Pripyat complex of the Late Devonian Pripyat-Dnieper magmatism area, two subphases of the Pripyat magmatism phase have been definished: late Fransian (Chernin or Skolodino-Chernin) with potassium specification and early Famennian (Turov-Drozdov (Yelets)) with potassium-sodium specification. For the first time, the U–Pb age of titanite from trachyandesites of the parametric borehole Pribor was obtained for rocks of Pripyat-Dnieper magmatism area at 364 ± 1 Ma. These data confirm the Famennian age of the Yelets subphase of the Pripyat phase of magmatism and make it possible to determine the duration of the magmatic activity of this structure at least 14 Ma taking into account the isotope dating of the earliest phases of magmatism in the Pripyat-Dnieper-Donetsk Paleorift Structure as 388 ± 12 Ma, 383.3 ± 3.8, 384.7 ± 3.9 and 383.6 ± 4.4 Ma in the Azov Region and 381 ± 2 Ma in the Pripyat-Dnieper magmatism area.

Mineralogy and Geochemistry of Anah and Euphrates Formations and Their Suitability for Portland Cement and Noora Industry at Al-Baghdadi and Haditha Areas, Western Iraq

The current study including geochemical and mineralogical aspects of 12 rock samples from Anah and Euphrates formations in two outcrops, The first outcrop is at Haditha city, with 12.5 meters thickness, and the second location is at Al-Baghdadi city, with 21 meters thickness. The mineralogical study by X-ray diffraction indicated that calcite is the main mineral in the rocks of Anah Formation, while calcite and dolomite exist in Euphrates Formation, where calcite is concentrated in the lower part of Euphrates Formation, while dolomite is common in the middle and upper parts of this formation, in addition to other minor minerals such as quartz and feldspar. Geochemical study was carried out by XRF to determine the major oxides(CaO, MgO, Fe2O3, Al2O3, SiO2, SO3, K2O, Na2O, MnO) and the suitability of Anah and Euphrates rocks as raw material for Portland cement and Al-Noura (lime) cement industries. According to the results it is found that Euphrates Formation in the Al-Baghdadi and Haditha outcrops is not suitable for the Portland cement, because of high percentage of MgO as a result of the high percentage of dolomitic limestone. The chemical analysis of the samples of the Anah Formation in Haditha outcrop are suitable for the Noura cement (lime) industry according to the Iraqi standard. The high content of magnesium in the Euphrates Formation at Al-Baghdadi area used as indicator that the rocks deposited in shallow marine and warm condition, and the environment was mostly isolated with warm condition. Low Sr content indicates shallow carbonate rocks. Thus, the sedimentary environment of the Anah Formation at Haditha outcrop was relatively shallower than that of the Euphrates Formation.

INTEGRATING REMOTE SENSING DATA WITH HYDROTHERMAL ALTERATION MAPPING AND GEOCHEMICAL CHARACTERISTICS OF PRECAMBRIAN ROCKS ACROSS MAMBILLA PLATEAU, NORTHEASTERN, NIGERIA

Mineral exploration must include the mapping of hydrothermally altered regions, which are typically connected to mineralization. This study presents a strategy for integrating remote sensing data with the geochemical characteristics of Precambrian rocks from the Mambilla Plateau in northern Nigeria. Tectonically, the lineaments were fractures with the following orientations: NE-SW, NW-SE, ENE-WSW, and N-S. The distinct spectral reflectance and absorption properties of remotely sensed Landsat 8 data in the visible, near-infrared, shortwave-infrared, and thermal infrared portions of the electromagnetic spectrum were exploited in various digital image processing approaches. Mapping hydrothermal alteration minerals was done effectively and efficiently using band ratios (red/blue, SWIR 2/NIR, SWIR 1/NIR), spectral band combinations (Kaufmann and Sabins ratios), and principal component analysis. Ferric, phyllic, propylitic, and argillic iron all underwent changes as a result of hydrothermal alteration. Regional metamorphism also resulted in important alteration processes such as epidotization, sericitization, muscovititization, kaolinitization, and chloritization. Geochemically, on average, the Al2O3, SiO2, Fe2O3, CaO, MgO, K2O, Na2O, Li2O content are 12.04 %; 54.83%; 4.76%, 7.16%, 3.02%, 10.22%, 4.53%, 1.35% while MnO, P2O5 and TiO2 are less than 1%. The average base metal composition revealed that 60% of them had positive anomalies, which indicate mineralization, and 40% had negative anomalies. About 50% of the samples had positive anomalies, which indicated strong potential for harbouring mineralization based on the makeup of trace elements. Geochemical studies revealed the presence of lithium, titanium, and silica oxides in substantial concentrations. The local mineralization is governed by structural factors.

Geochemical studies of the gold mineralization of Kodiarani-(Doko permit). Prefecture of Siguiri, Administrative region of Kankan, Republic of Guinea

West Africa is now a major player in world gold production with numerous gold deposits hosted in Birimien green belts (2.2-2.0 Ga). However, these belts and their geological formations remain unexplored, as does their evolution during the Eburnean orogeny. This is why, after acquiring its exploration Licence, TOROGOLD focused its work on Air Core drilling activities in the Doko-Kodiarani Licence in north-eastern Guinea. During these activities, geochemical studies will be carried out on rock samples taken from the six (6) boreholes pre-selected for this purpose. The aim of this research work is to carry out a geological study in order to determine the chemical associations between the mineralization, the nature of the host rock and others for future work. To achieve this objective, we used a number of methods, including a statistical approach, field reconnaissance, and macroscopic and lithogeochemical analyses. Geochemical studies reveal that the rocks studied are meta-sediments. They belong to the schist groups. Their protholites are moderately altered (60 < CIA < 80) and the source is thought to be andesitic and basaltic, emplaced in a geotectonic oceanic island arc. As for the various AC drilling sections, our observations reveal that the gold mineralization is found in two types of deposit: disseminated, present in all lithology’s, and vein-type, resulting from the filling of fracture zones, associated with the highest concentrations. We noted a strong discontinuity of mineralization in these veins, due to a tectonic phase that may have played an important role in the remobilization of gold in these structures.

Astronomical control on organic matter enrichment of lacustrine mudstones in the first member of the Late Cretaceous Qingshankou Formation, the Songliao Basin, NE China

Astronomical forcing has an important effect on organic matter enrichment in marine mudstones, but this effect remains poorly constrained in lacustrine mudstones. Here, we investigate the astronomical control of organic matter enrichment in lacustrine black mudstone from the first member of the Qingshankou Formation in the Songliao Basin. Detailed mineralogical, lithological, geochemical, and cyclostratigraphic studies were carried out. The results show that there are high-frequency variations in the organic matter content in the mudstones of the Qingshankou Formation. The upper and lower sections are further divided according to the organic matter content level and the variation frequency. The organic matter content in the lower section is high, up to 6.08 wt%, with long-period variation and individual cycles around 10 m. The organic matter content in the upper section is relatively low, the highest organic matter content is only 2.91 wt%, with short-period variation and individual cycles mostly less than 5 m. Cyclostratigraphic studies indicate that significant astronomical signals are recorded in the mudstone stratigraphy. 100 kyr short eccentricity and 38 kyr obliquity strongly control the variation of organic matter content in the lower and upper sections, respectively. Organic matter enrichment has a closely synchronized phase relationship with paleoproductivity, preservation conditions, and dilution indicators. Astronomical cycles influence the depositional conditions of organic matter enrichment by controlling climate change, which eventually forces organic matter enrichment. At high values of eccentricity and obliquity, enhanced insolation, monsoon, precipitation, and river runoff caused lake expansion, increased input of terrestrial nutrients, and increased bottom water reduction conditions, which are conducive to organic matter enrichment. On the contrary, the depositional conditions for organic matter enrichment become poor.

Origins and evolution of two types of Late Triassic granitic magmas in the Caolong-Xiangkariwa area of central-eastern Songpan-Ganze terrane, northern Tibet: Implications for pegmatite lithium mineralization

Pegmatite-type lithium (Li) deposits are an important source of the low-carbon energy metal, which is generally considered to be formed by the high degrees of differentiation of strongly peraluminous granitic magma. However, the question of whether the parental rocks of these peraluminous magmas are igneous or sedimentary has been widely debated. Recent studies have identified a world-class pegmatite-type Li deposit belt (up to 2800 km long) closely associated with the Late Triassic granitoids and (meta)sedimentary rocks along the West Kunlun and Hoh Xil-Songpan-Ganze terranes in northern Tibet. This study presents a comprehensive petrological, geochronological, and geochemical study on the two types of Late Triassic granitoids in the Caolong-Xiangkariwa area of the Yushu region of central-eastern Hoh Xil-Songpan-Ganze terrane in northern Tibet: type A includes the Tongtianhe-Zhenqin-Zhaduo-Zhaya-Xiangkariwa (TZX) diorites and granodiorites (218−212 Ma), and type B includes the Caolong two-mica and muscovite granites (213−205 Ma), as well as ore-barren, beryl-bearing, and spodumene-bearing pegmatite dikes (209−196 Ma). The TZX diorites and granodiorites contain variable amounts of amphibolite and biotite. They are metaluminous to slightly peraluminous with variable SiO2 (54.4−71.3 wt%), MgO (0.72−7.26 wt%) contents, and Mg# values (40−70). Some samples with low SiO2 (54.4−58.5 wt%) contents have geochemical features similar to high-Mg andesites: e.g., high MgO contents (5.24−7.26 wt%) and Mg# values (61−70). The TZX diorites and granodiorites exhibit less enriched (86Sr/87Sr)i (0.7080−0.7118) and εNd(t) (−4.8 to −8.0). By contrast, the Caolong two-mica and muscovite granites are characterized by the occurrence of abundant muscovite (plus tourmaline and garnet) and are strongly peraluminous. The Caolong granites and pegmatites are geochemically characterized by high SiO2 contents (68.8−79.8 wt%) and low MgO contents (0.01−0.10 wt%) and Mg# values (4−23). They have εNd(t) values (−8.8 to −11.4; granites: −8.8 to −10.8; pegmatites: −9.2 to −11.4) that are more enriched than the TZX diorites and granodiorites but similar to those of Songpan-Ganze (meta)sedimentary rocks (−7.4 to −12.9), and the Caolong two-mica granites have high zircon δ18O values (11.6−12.1). In addition, decreasing K/Rb ratios correspond to increasing Cs contents in K-feldspar and muscovite from the Caolong granites and pegmatites. Taking into account the Late Triassic granitoids and (meta)sedimentary rocks in the Hoh Xil-Songpan-Ganze terrane, we suggest that the TZX diorites and granodiorites were most probably formed by the partial melting of metasomatized lithospheric mantle that subsequently underwent extensive fractional crystallization. Conversely, the Caolong two-mica and muscovite granites were likely generated purely by the partial melting of (meta)sedimentary rocks rather than via the evolution of dioritic-granodioritic magmas. In summary, there were two kinds of granitic magmas with different sources in the Caolong-Xiangkariwa area. Finally, the Caolong pegmatites were most likely formed by the extreme differentiation of two-mica granitic magmas rather than the dioritic-granodioritic magmas. Therefore, the evolution of magmas derived from (meta)sedimentary rocks were most likely to have formed the Li-rich pegmatites. Moreover, these (meta)sedimentary rocks representing the ultimate Li source must have undergone strong chemical weathering, resulting in significant Li enrichment.

The vesiculated layer in the anomalous diogenite Northwest Africa 12973

AbstractDiogenites, which are part of the howardite–eucrite–diogenite (HED) group, are considered to represent rocks from the lower crust and mantle of a differentiated planetary body, likely the asteroid 4 Vesta. The Northwest Africa 12973 (NWA 12973) meteorite was classified as an anomalous diogenite due to the occurrence of a vesiculated layer. This work reports on the petrographic and geochemical study of two fragments of this meteorite, aiming to better constrain the origin of the vesiculated layer. Whereas the interior of NWA 12973 (here called host) presents the typical characteristics of an olivine diogenite, that is, coarse‐grained pyroxene, olivine ribbons, chromite, and accessory phases, the vesiculated layer presents a fine‐grained pyroxene groundmass with local rounded relics of olivine and interstitial chromite and metal, and is characterized by abundant large vesicles. The contact between the vesiculated layer and the host is sharply defined. The composition of individual minerals does not show any significant differences between the host and the vesiculated layer, suggesting in situ melting. Geothermobarometry indicates a slightly higher crystallization temperature at lower pressure for the vesiculated layer, consistent with melting and crystallization under lower crustal conditions upon exhumation. The trigger for the local melting was likely a large impact event, which was responsible for adiabatic decompression in the central area or deep faulting and frictional melting.

The great catastrophe: causes of the Permo-Triassic marine mass extinction.

The marine losses during the Permo-Triassic mass extinction were the worst ever experienced. All groups were badly affected, especially amongst the benthos (e.g. brachiopods, corals, bryozoans, foraminifers, ostracods). Planktonic populations underwent a fundamental change with eukaryotic algae being replaced by nitrogen-fixing bacteria, green-sulphur bacteria, sulphate-reducing bacteria and prasinophytes. Detailed studies of boundary sections, especially those in South China, have resolved the crisis to a ∼55 kyr interval straddling the Permo-Triassic boundary. Many of the losses occur at the beginning and end of this interval painting a picture of a two-phase extinction. Improved knowledge of the extinction has been supported by numerous geochemical studies that allow diverse proposed extinction mechanisms to be studied. A transition from oxygenated to anoxic-euxinic conditions is seen in most sections globally, although the intensity and timing shows regional variability. Decreased ocean ventilation coincides with rapidly rising temperatures and many extinction scenarios attribute the losses to both anoxia and high temperatures. Other kill mechanisms include ocean acidification for which there is conflicting support from geochemical proxies and, even less likely, siltation (burial under a massive influx of terrigenous sediment) which lacks substantive sedimentological evidence. The ultimate driver of the catastrophic changes at the end of the Permian was likely Siberian Trap eruptions and their associated carbon dioxide emissions with consequences such as warming, ocean stagnation and acidification. Volcanic winter episodes stemming from Siberian volcanism have also been linked to the crisis, but the short-term nature of these episodes (<decades) and the overwhelming evidence for rapid warming during the crisis makes this an unlikely cause. Finally, whilst the extinction is well studied in equatorial latitudes, a different history is found in northern Boreal latitudes including an earlier crisis which merits further study in order to fully understand the course and cause of the Permo-Triassic extinctions.

Geochemical Biodegraded Oil Classification Using a Machine Learning Approach

Chromatographic oil analysis is an important step for the identification of biodegraded petroleum via peak visualization and interpretation of phenomena that explain the oil geochemistry. However, analyses of chromatogram components by geochemists are comparative, visual, and consequently slow. This article aims to improve the chromatogram analysis process performed during geochemical interpretation by proposing the use of Convolutional Neural Networks (CNN), which are deep learning techniques widely used by big tech companies. Two hundred and twenty-one chromatographic oil images from different worldwide basins (Brazil, the USA, Portugal, Angola, and Venezuela) were used. The open-source software Orange Data Mining was used to process images by CNN. The CNN algorithm extracts, pixel by pixel, recurring features from the images through convolutional operations. Subsequently, the recurring features are grouped into common feature groups. The training result obtained an accuracy (CA) of 96.7% and an area under the ROC (Receiver Operating Characteristic) curve (AUC) of 99.7%. In turn, the test result obtained a 97.6% CA and a 99.7% AUC. This work suggests that the processing of petroleum chromatographic images through CNN can become a new tool for the study of petroleum geochemistry since the chromatograms can be loaded, read, grouped, and classified more efficiently and quickly than the evaluations applied in classical methods.

Сomparative analysis of oils from carbonate sediments of Upper Usolskaya subformation and ediacarian-cambrian productive horizons in central part of Nepsko-Botuobinskaya anteclise

The focus in study of the central part of Nepsko-Botuobinskaya anteclise is concentrated on the subsalt oil and gas bearing horizons of group B (Osinsky, Upper Ust-Kutsky, Lower Ust-Kutsky, Preobrazhensky horizons) and V (terrigenous formations of Vendian age). However, higher, in the Lower-Middle Cambrian carbonate-halogen deposits, there are also promising horizons of group A (Kelorsky, Atovsky, Khristoforovsky, Balykhtinsky), oil and gas presence of a sufficient amount of the Angara-Lena stage, the northern part of the Nepsko-Botuobinskaya anteclise and adjacent structures. The paper examines the results of geochemical studies of oil samples from the Osinsky horizon (layer B1) and the nameless dolomite layer located between the salts in the lower part of the Upper Usolskaya subformation, previously considered gas-bearing at best. The conducted studies by the method of chromatography-mass spectrometry and comparison of the geochemical parameters of oils from different reservoirs show the similarity of hydrocarbon fluids of the Upper Usolskaya subformation and lower productive horizons, which makes it possible to attribute them to a single oil and gas bearing system.

An integrated petrographical and geochemical study of the Tredian Formation in the Salt and Trans‐Indus Surghar ranges, North‐West Pakistan: Implications for palaeoclimate

AbstractThe Middle Triassic Tredian Formation is well exposed in the western region of the Salt Range. It is mostly composed of sandstone with minor alternations of shales and dolomite. This is the first integrated attempt using petrographical and geochemical features to reveal palaeoclimate during deposition of the Tredian Formation. This work sheds light on the petrographical and geochemical properties of the Tredian sandstone in order to date various layers and evaluate the palaeoclimate. The formation was sampled at two distinct stratigraphic layers for petrographic and geochemical analysis of major and trace elements. The sandstone of the Tredian Formation is sub‐feldspathic to feldspathic arenite with sub‐angular to rounded grains that are moderately to extensively sorted. The relative proportions of the quartz, feldspars and lithoclasts in the examined sandstone samples shows that the Tredian sediments originated from the interior of the craton during a transitional continental regime. Chemical index of alteration values of 59, chemical index of weathering values of 67, and plagioclase index of alteration values of 74.5 indicate a low to moderate degree of weathering in the Tredian sediment source region. Based on the silica content, SiO2/Al2O3 ratios (2.7–6.1; mean 4.1), and chemical maturity index, it is deduced that the Tredian Formation was deposited in chemically immature to sub‐mature and dry to semi‐arid conditions. Geochemical proxies indicate the acidic source of sediment and deposition on the passive margin of the Indian Plate. The trace element characteristics of the sediments, especially the Rb/Sr, Cu/Zn, Ni/Co, V/Cr and Sr/Ba ratios, indicate that the sediments originated from the first weathering cycle and support the notion that they were deposited in an oxidising continental environment. A semi‐arid to arid palaeoclimate predominated through the Middle Triassic at the north‐western passive continental margin of the Indian Plate in the south‐eastern Neo‐Tethys.