Composition, structure and formation conditions of the Arydzhangsky Formation of the Maimecha-Kotuy District of the Siberian Trap Province

We studied 6 sections of the Arydzhangsky lava formation (P2-T1) in the Kotuy river valley. The results of petrographic and geochemical studies of the composition of rocks of the Arydzhangsky, Khardaksky and Pravoboyarsky formations are presented. The stratigraphic columns of the sections were built and the composition of the rocks was additionally determined using a scanning electron microscope. In this regard, the relative position of these formations was established, the mantle and crust sources of magmas were confirmed. A geochemical identity of the rocks of the Khardaksky formation with the rocks of the Arydzhangsky formation was established, which suggests a similar age of their formation.

Siberian Trap volcanism, global warming and the Permian-Triassic mass extinction: New insights from Armenian Permian-Triassic sections: Comment

Joachimski et al. carried out geochemical investigations to study seawater temperature changes and their potential triggers across the Permian-Triassic Boundary (PTB). Unfortunately, in our opinion, an incorrect biochronology was applied to define the PTB, and the existing alternative was not considered, nor the reasoning explained. As a consequence, Joachimski et al. report diachronous temperature changes for the investigated Chanakhchi section with respect to the global stratotype section and point (GSSP) in Meishan, China. This discrepancy disappears when the, in our view, correct position of the PTB is adopted by using the proper biochronology.

Siberian Trap volcanism, global warming and the Permian Triassic mass extinction: New insights from Armenian Permian-Triassic sections: Reply

Horacek et al. (2021) commented on our publication arguing that we used an incorrect biochronology to define the Permian-Triassic (PT) boundary and that this inaccurate definition resulted in an erroneous interpretation of the oxygen isotope record in the studied Chanakhchi (former Sovestashen) section. Their comment gives us the opportunity to discuss in depth the identification of the PT boundary and to address some of the flawed arguments of Horacek et al.

The Influence of Trap Magmatism on the Geochemical Composition of Brines of Petroliferous Deposits in the Western Areas of the Kureika Syneclise (Siberian Platform)

—We present the results of study of the influence of trap magmatism on the geochemical composition of brines and on the geothermal regime of the Earth’s interior in the western areas of the Kureika syneclise. The Siberian trap province, which unites all cutting and layered tholeiite–basic magmatic intrusions and erupted basaltic lava, is the world’s largest Phanerozoic continental basalt province. Brines, hydrocarbon deposits, and organic matter of the sedimentary cover were subjected to a significant thermal impact as a result of the Permo-Triassic trap magmatism. During the trap intrusion, the maximum paleotemperatures in major Silurian (D’yavolskii), Ordovician (Baikit), and Cambrian (Deltula–Tanachi, Abakun, and Moktakon) productive horizons reached 650 °C. The Paleozoic and Proterozoic deposits of the study area contain brines with TDS = 50–470 g/dm3. By chemical composition, they are of Na, Na–Ca, Ca–Na, Ca–Mg, and Ca chloride types (according to the classification by S.A. Shchukarev), with mixed Ca–Na and Na–Ca chloride brines dominating. The studied brines can be divided into three groups according to the degree of metamorphism: low (S1), medium (S2), and high (S3). The first group includes mainly sodium chloride brines with TDS = 50–370 g/dm3 (rNa/rCl = 0.60–0.95; S ≤ 100). The second (dominating) group comprises Na–Ca, Ca–Na, Ca, and Ca–Mg chloride brines with TDS = 150–470 g/dm3 (rNa/rCl = 0.10–0.87; 100 ≤ S ≤ 300). The third group is Ca–Na and Ca chloride brines with TDS = 223–381 g/dm3 (rNa/rCl = 0.12–0.45; S ≥ 300). We have first established changes in the hydrogeochemical field (major- and trace-component and gas compositions) with distance from the contacts of intruded dolerite sills and dikes. Hydrocarbons (CH4, C2H6, C3H8, i-C4H10, n-C4H10, i-C5H12, n-C5H12, and C6H14) and water-soluble components I, B, and NH4 were most actively subjected to destruction. For example, at a distance of 100 m from the intrusion zone, the water-dissolved gases are dominated by CO2 (>90 vol.%), and CH4 amounts to 5 vol.%, whereas at a distance of 250 m, the concentration of CO2 decreases to 30 vol.%, and that of CH4 increases to 60–70 vol.%. In addition to the negative effect on the hydrocarbon preservation in the contact zone (≤400 m), the intrusive trap magmatism favored the formation of hydrocarbons in remote horizons. The reaction of intruding traps with brines of the sedimentary cover led to the saturation of the latter with iron, aluminum, and silica, which suggests extraction of metals in the form of salts from magmatic melts into an ore-bearing fluid.

Petrographical and Geochemical Characteristics of Magmatic Rocks in the Northwestern Siberian Traps Province, Kulyumber River Valley. Part II: Rocks of the Kulyumber Site

The origin of the Siberian trap province is under discussion even though numerous models of its formation have been created over the last three decades. This situation is mainly due to lack of modern geochemical data on magmatic rocks around the province. These data are a very important tool to reconstruct of magmatic evolution within the province in time and space and to understand a mechanism of province formation. Geochemical study has only been carried out so far for the Norilsk and Meimecha–Kotuy areas. For the first time, we have studied the geochemical and mineralogical characteristics of magmatic rocks at the Kulyumber river valley located 150 km to south from the Norilsk ore district, in the junction of the Tunguska syneclise and Norilsk–Igarka zone. It comprises three sites, i.e., Khalil, Kaya, and Kulyumber. The geochemical data on the magmatic rocks of the Khalil and Kaya sites were published earlier (Part I). This article (Part II) regards geochemical and mineralogical data on igneous rocks at the Kulyumber site. Seventeen intrusive bodies (41 samples) and six samples of sedimentary rocks were studied by X-ray fluorescence (XRF) and inductively coupled plasma mass spectrometry (ICP-MS). Isotopes analyses (Sr, Nd, Pb) were conducted for 12 samples. These data were compared with data for intrusions of the Norilsk area, the Dzhaltulsky massif, Kureyka river, and intrusions in Angara river valley published earlier. The whole list of analyses includes 102 items. Three groups of intrusive rocks were recognized: (1) Mafic rocks with elevated K2O without negative Ta-Nb and Pb-positive anomalies, with (Gd/Yb)n = 2.0 and εNd = −1.0; attributed to a new Kulyumbinsky complex; (2) subalkaline rocks with elevated SiO2,TiO2, P2O5, and K2O with small negative Ta-Nb and positive Pb anomalies and (Gd/Yb)n = 1.8, εNd = −3.8; Ergalakhsky complex; and (3) mafic rocks with strong Ta-Nb and Pb anomalies and (Gd/Yb)n = 1.2–1.4, εNd = +0.4–+2.2. The third group is rather nonhomogeneous and includes intrusions of the Norilsk, Kuryesky, Katangsky, Ogonersky, and Daldykansky complexes differing in MgO content and trace element distribution (values of Ta-Nb, Pb, and Sr anomalies). Three groups of intrusive bodies had different magma sources and different condition of crystallization reflecting their origin in rift and platform regimes.

Siberian Trap volcanism, global warming and the Permian-Triassic mass extinction: New insights from Armenian Permian-Triassic sections

Permian-Triassic boundary sections from Armenia were studied for carbon isotopes of carbonates as well as oxygen isotopes of conodont apatite in order to constrain the global significance of earlier reported variations in the isotope proxies and elaborate the temporal relationship between carbon cycle changes, global warming and Siberian Trap volcanism. Carbon isotope records of the Chanakhchi and Vedi II sections show a 3–5‰ negative excursion that start in the Clarkina nodosa (C. yini) conodont Zone (latest Permian) with minimum values recorded in Hindeodus parvus to Isarcicella isarcica conodont zones (earliest Triassic). Sea surface temperatures (SST) reconstructed from oxygen isotopes of conodont apatite increase by 8–10 °C over an extrapolated time interval of ∼39 ka with the onset of global warming occurring in the C. iranica (C. meishanensis) Zone of the latest Permian. Climate warming documented in the Armenian sections is comparable to published time-equivalent shifts in SST in Iran and South China suggesting that this temperature change represents a true global signature. By correlating the Armenian and Iranian section with the radiometrically well-dated Meishan GSSP (Global Stratotype Section and Point) section (South China), the negative shift in δ13C is estimated to have occurred 12–128 ka prior to the onset of global warming. This temporal offset is unexpected given the synchrony in changes in atmospheric CO2 and global temperature as seen in Pleistocene ice core records. The negative δ13C excursion is explained by the addition of emission of isotopically light CO2 and CH4 from thermogenic heating of organic carbon-rich sediments by Siberian Trap sill intrusions. However, the observed time lag in the δ13C and δ18O shifts questions the generally assumed cause-effect relationship between emission of thermogenically produced greenhouse gases and global warming. The onset of temperature rise coincides with a significant enrichment in Hg/TOC (total organic carbon) ratios arguing for a major volcanic event at the base of the extinction interval. Whether global warming was a major factor for the Late Permian mass extinction depends on the duration of the extinction interval. Warming only starts at the base of the extinction interval, but with the extinction encompassing a time interval of 60 ± 48 ka, global climate warming in conjunction with temperature-related stressors as hypoxia and reduced nutrient availability may have been one of the major triggers of the most devastating biotic crisis in Earth history.

Unique PGE–Cu–Ni Noril’sk Deposits, Siberian Trap Province: Magmatic and Tectonic Factors in Their Origin

The unique and very large PGE–Cu–Ni Noril’sk deposits are located within the Siberian trap province, posing a number of questions about the relationship between the ore-forming process and the magmatism that produced the traps. A successful answer to these questions could greatly increase the possibility of discovering new deposits in flood basalt provinces elsewhere. In this contribution, we present new data on volcanic stratigraphy and geochemistry of the magmatic rocks in the key regions of the Siberian trap province (Noril’sk, Taimyr, Maymecha-Kotuy, Kulyumber, Lower Tunguska and Angara) and analyze the structure of the north part of the province. The magmatic rocks of the Arctic zone are characterized by variable MgO (3.6–37.2 wt %) and TiO2 (0.8–3.9 wt %) contents, Gd/Yb (1.4–6.3) and La/Sm (2.0–10.4) ratios, and a large range of isotopic compositions. The intrusions in the center of the Tunguska syneclise and Angara syncline have much less variable compositions and correspond to a “typical trap” with MgO of 5.6–7.2 wt %, TiO2 of 1.0–1.6 wt %, Gd/Yb ratio of 1.4–1.6 and La/Sm ratio of 2.0–3.5. This compositional diversity of magmas in the Arctic zone is consistent with their emplacement within the paleo-rift zones. Ore-bearing intrusions (the Noril’sk 1, Talnakh, Kharaelakh) are deep-situated in the Igarka-Noril’sk rift zone, which has three branches, namely the Bolsheavamsky, Dyupkunsky, and Lower Tunguska, that are prospected for discovering new deposits. One possible explanation for the specific position of the PGE–Cu–Ni deposits is accumulation of sulfides in these long-lived zones from the Neoproterozoic to the Mesozoic era during magmatic and metamorphic processes. Thus, trap magmatism, itself, does not produce large deposits, but mobilizes earlier formed sulfide segregations in addition carrying metals in the original magmas. These deposits are the results of several successive magmatic events, in which emplacement of the traps was the final event.