Cenozoic Age Research Articles

Study of petrophysical properties of deep-seated Meso-Cenozoic sediments within the North Apsheron system of uplifts

This article presents our research on the depth dependence of the reservoir properties oil and gas bearing deposits of the Meso- Cenozoic age within the Apsheron uplift. The petrophysical features and patterns of change at depth of the Meso-Cenozoic sediments of the deposits of the Apsheron Bank and Western Apsheron were studied. Despite the fact that the history of the discovery and processing of the abovementioned deposits dates back to the 1950s, some geophysical features associated with these deposits still remain relevant. In particular, from literary sources it is known that the clay content of oily reservoirs of the Apsheron Archipelago tends to grow in a southeast direction. Reservoirs consist mainly of rounded, semi-rounded and angular rounded grains of isometric shape. The average carbonate content in the Apsheron Bank is up to 16.2%, and the average carbonate content in Western Apsheron is up to 13.8%. The average porosity here is 22%, with slight differences in the lower and upper sections. Due to the presence of carbonate material as cement, carbonization in sand reservoirs varies between 2.9-31.8%, and the porosity coefficient is 6.8-25.6%. In general, in deposits of the Archipelago, sand reservoirs have high permeability, on average characterized by permeability coefficients of 139*10-15 m2. From the results of our study based on the core samples from wells drilled in the territory, the general porosity of rocks involved in the depth-section is characterized by unstable values. Nevertheless, in general, there is a tendency to decrease in porosity in depth. So, in particular, in the context of the Apsheron Bank with an average value of porosity of 8%, the pattern of its decrease is described by the linear equation Y = – 0.16x + 12.59 and is on average 0.6% for every 100 m. For Western Apsheron with a sharper the change in porosity in depth, the average value is 14.2%, and the tendency to decrease with increasing depth is weaker and is 0.25% per 100 m. To determine the causes of the observed variability of porosity at different depths, we studied the effect of the degree of carbonate content of various rock samples on porosity. As a result, in both deposits (Absheron Bank and Western Apsheron) the inverse proportion of the porosity of the rocks and the values of carbonate was confirmed. Although the separate carbonate contents negatively affect the porosity of reservoir rocks, the combined effect of carbonate and clay contents differs for the studied deposits.

Baddeleyite SK10‐3: A Natural Reference Material for Microbeam U‐Pb Geochronology and Hf Isotopic Measurements

Baddeleyite is an important U‐Pb geochronometer and Hf isotope tracer that commonly occurs as an accessory phase in silica‐undersaturated igneous rocks of terrestrial and extra‐terrestrial origin. Currently, very few well‐characterised, large sized reference materials are available for baddeleyite U‐Pb geochronology and Hf isotope measurement. In this study, we document a baddeleyite reference material (SK10‐3) of Cenozoic age. SK10‐3 is inclusion‐free and does not contain secondary alteration minerals. The baddeleyite has uniform U‐Pb ages and Hf isotope ratios, within analytical uncertainty, as demonstrated by multiple LA‐ICP‐MS spot analyses (weighted mean 206Pb/238U age: 31.59 ± 0.11 Ma, MSWD = 0.7, n = 197) and LA‐MC‐ICP‐MS analyses (arithmetic mean 176Hf/177Hf ratio: 0.282741 ± 59, 2s, n = 188). Seven ID‐TIMS analyses yielded a weighted mean 206Pb/238U age of 31.592 ± 0.020/0.022/0.040 Ma (n = 7, 2s, MSWD = 2.2). Nine aliquots of MC‐ICP‐MS analyses yielded an arithmetic mean 176Hf/177Hf ratio of 0.282742 ± 8 (2s). We further demonstrate that the method of shallow‐pit (~ 2 μm depth) ablation substantially improves the precision and accuracy of baddeleyite U‐Pb ages. SK10‐3 has a relatively high 176Yb/177Hf ratio (~ 0.007) compared with most other baddeleyites, allowing the precise measurement of βYb and may be useful in generating the βYb‐βHf relationship during LA‐MC‐ICP‐MS Hf isotope measurement. SK10‐3 may be a useful addition to previously distributed baddeleyite reference materials for microbeam‐based U‐Pb geochronology and Hf isotope measurements.

Oil families in the eastern cordillera and llanos basin, Colombia: A comprehensive characterization using advanced geochemical technologies

Three major age-related oil families, clustered into seven groups, were identified in the Llanos basin based on advanced geochemical technologies that unveiled complex mixtures throughout the basin. The analyses included the conventional whole oil and biomarker analysis and the more refined and advanced GC-MS/MS analysis. The latter provided for terrestrial diterpane-based age-specific arrays that discriminated between Cretaceous and Cenozoic floral types. The analysis of asphaltene hydrous pyrolysates revealed the initial charges to the reservoirs, often of early maturity, but also strongly biodegraded and overprinted by fresh oil charges. Extensive analysis on diamondoids allowed the characterization of the late maturity charges, differentiation between mixed and singly-sourced oils and the ability to tie together earlier with later generated oil components of oil mixtures. Oils from Family A are the most widespread in the basin, found in the southern Llanos and in the Foothills and are derived from Lower Cretaceous to Cenomanian marine shale with a terrigenous input. Within Family B, of Upper Cretaceous age, two main source facies were identified, one with a siliciclastic marine input, corresponding to Groups 4 and 5. They have the highest concentrations of the C25 highly branched isoprenoid (HBI) and occur in the Northern and Eastern Llanos and in the Axial Zone of the Eastern Cordillera. The other facies has a more calcareous aspect, identified mainly in the Southern Llanos designated as Groups 2 and 3. Family C, of Cenozoic age, is restricted to the Foothills and two oil Groups were distinguished: Group 6 as the only endmember of a terrigenous Cenozoic facies, identified in Oil 7, and Group 7 shows a Cenozoic terrigenous facies and varying degrees of mixing with a marine Cretaceous input. These families are mixed in a variety of ways, having mixtures from different facies, while others show multiple charges from the same facies.

Metallogenic age of the world‐class giant huoshaoyun non‐sulphide Zn–Pb deposit in Karakoram Area, Xinjiang, Northwest China

AbstractMetallogenic geochronology plays a crucial role in the study of ore genesis and mineralization evolution. Unfortunately, accurately determining the metallogenic age of the non‐sulphide Zn–Pb deposits is difficult. Herein, we employed Rb–Sr dating of smithsonite and Sm–Nd dating of coexisting calcite to explore the mineralization ages of the Huoshaoyun Zn–Pb deposit. The Rb–Sr and Sm–Nd isotopic ratios yield isochron ages of 26.6 ± 1.7 and 27.5 ± 7.6 Ma, respectively. These obtained ages are identified as the metallogenic age of the Huoshaoyun deposit. Moreover, investigations into carbonate‐hosted Zn–Pb deposits in the East Tethys Metallogenic belt suggest they have formed in similar tectonic settings and yielded consistent Cenozoic ages. In sum, our research indicates that carbonate‐hosted Pb–Zn metallogenic ages in the East Tethys Metallogenic belt are principally concentrated in the late Palaeogene, and directly related to the collisional orogeny of the Tibetan Plateau during 40–26 Ma.

The Thermal Evolution of Western Norway Based on Multi‐Sample Models of an Elevation Transect: Implications for the Formation of High‐Elevation Low‐Relief Surfaces on an Elevated Rifted Continental Margin

AbstractThe post‐Caledonian thermal and geomorphological evolution of onshore Western Norway is poorly understood, including the formation and age of the high‐elevation low‐relief surfaces seen across the Norwegian landscape. We present new apatite fission track (AFT) and (U‐Th‐Sm)/He analyses from an elevation transect (ET) covering ∼1,800 m vertical distance below a high‐elevation low‐relief surface in the inner Nordfjord. The AFT ages increase with elevation from 159 ± 11 Ma to 256 ± 21 Ma and apatite (U‐Th‐Sm)/He ages increase with elevation from 80 ± 4 Ma to 277 ± 15 Ma. In order to test different possible thermal evolutions, we present the first multi‐sample thermal history models from Norway using HeFTy combining both AFT and (U‐Th‐Sm)/He ages along the ET, refining available thermal history models for the area considerably. The best modeling results are found for a thermal evolution with slow cooling throughout the Mesozoic and increased cooling rates from the Late Cretaceous until present, indicating a Cenozoic age for the low‐relief surface at the top of the transect. The models also allow for cooling to surface conditions in the Late Jurassic, but such an evolution must have been followed by rapid burial by 1.5–3 km Cretaceous sediments, and by re‐exhumation in the Cenozoic, indicating that the low‐relief surface cannot represent a simply uplifted Jurassic or Cretaceous peneplain. We compare our results with multi‐sample models from the wider North Atlantic region, supporting previous findings of Cenozoic exhumation and landscape forming processes within that region.

Trend detection and depletion effects evidence in time series of groundwater levels in the southern sector of the left bank of the Tagus-Sado Basin (Portugal, Iberian Peninsula)

In the last 20 years in Portugal, water resources have been affected to the point that water storage has decreased by 20% since 2000. Creating strategies to manage water resources requires a comprehensive understanding of the factors influencing water storage and their effects over time. This study is focused on the evolution of Groundwater Deep Levels (GDL) by applying a two-phase trend analysis methodology to examine the dynamic changes in GDL within a series of monitoring wells located in the Central and Southern sectors of the Left Bank of the Tagus-Sado Cenozoic age Basin, situated in Portugal In the initial phase of trend analysis, Factorial Analysis of Mixed Data (FAMD) was employed and posteriorly the Hierarchical Classification Analysis (HCA). These techniques enabled us to identify distinct GDL trend profiles and generate interpretative maps illustrating their spatial distribution. In the second phase, the non-parametric Mann–Kendall Analysis (MKA) and Innovative Trend Analysis (ITA) were applied, allowing for a quantified confirmation of the different trend profiles previously detected. These techniques allowed the identification of positive and negative hydrodynamic trends in distinct sections of the Basin. In the SE sector they are characterized by a significative increase of GDL associated with overexploitation and in the Central sector with a decrease of GDL. Nevertheless, significant depletion effects can result from natural factors such as prolonged droughts, and in certain regions, changes in geological and hydrothermal dynamics, such as Alpine-age faults, graben, and horst structures, may account for these alterations.

Comment on: Fürsich et al., 2023, Miocene instead of Jurassic: the importance of sound fieldwork for paleontological data analysis

AbstractWe published a series of papers regarding the oldest turritellids, naticids, their paleoecological interaction, and gastropod biozonation, which are of Oxfordian in age, from the Jhura pond section, Kutch, western India. Recently, an Oxfordian age was challenged by Fürsich et al. (2023) and they argued for a Cenozoic age. The authors reproduced a local geological map based on regional data where the Jhura pond section sediments were overlying the Bhuj Formation. In the original regional data, there was no Bhuj Formation and the introduction of the Bhuj Formation served to show that Jhura pond section sediments were “allochthonous”. Other lines of argument against our conclusions (e.g., identification of associated bivalve fauna, foraminiferal assemblage, and geological context) were brought forward. There were additional inconsistencies, such as the reworking of Oxfordian fossils, in their comment/opinion pieces. The only hard evidence was the report of a microfaunal assemblage, but the taxa were identified at the generic level and most of the genera appear in the Jurassic or even earlier.Here we provide detailed and concrete evidence explaining features at the Jhura pond section, such as the subvertical nature of the beds, the ooid-bearing lithologies, the presence of various Oxfordian fossils, the difference in turritellids, naticid assemblages, and differences in the diversity curves between the present beds and the lower Miocene Chhasra Formation of Kutch. Detailed paleoecological analyses (both gastropods and bivalves) speak for two paleocommunities. We, therefore, reiterate that the present Jhura pond section sediments are Oxfordian in age and validate all the interpretations and conclusions that we have made in our previous papers.

Cenozoic Pb–Zn–Ag mineralization in the Western Alps

Abstract Metallogenic models of polyphase mountain belts critically rely on robust geochronology. We combine petrology with Rb–Sr and U–Th–Pb in situ geochronology, paired at thin-section scale, to date mineralization in deformed hydrothermal Pb–Zn–Ag deposits along an east-west transect in the Western Alps, France. The Pb–Zn–Ag veins occur in shear zones with kinematic structures consistent with the mylonitized host rocks. The ore consists mainly of galena in a quartz-phengite gangue. The paragenesis can be related to hydrothermal crystallization during periods of variable strain. Both isotope systems yield only Cenozoic ages (ca. 35 Ma and 15–20 Ma) without any pre-Alpine inheritance, clearly indicating orogenic mineralization. The metallogenic model proposed here includes significant fluid circulation along major tectonic contacts between basement and sedimentary cover during Alpine convergence.

A Maastrichtian insect assemblage from Patagonia sheds light on arthropod diversity previous to the K/Pg event

Insect faunas from the latest Cretaceous are poorly known worldwide. Particularly, in the Southern Hemisphere, there is a gap regarding insect assemblages in the Campanian-Maastrichtian interval. Here we present an insect assemblage from the Maastrichtian Chorrillo Formation, southern Argentina, represented by well-preserved and non-deformed, chitinous microscopic remains including head capsules, wings and scales. Identified clades include Chironomidae dipterans, Coelolepida lepidopterans, and Ephemeroptera. The assemblage taxonomically resembles those of Cenozoic age, rather than other Mesozoic assemblages, in being composed by diverse chironomids and lepidopterans. To the best of our knowledge, present discovery constitutes the first insect body fossils for the Maastrichtian in the Southern Hemisphere, thus filling the gap between well-known Early Cretaceous entomofaunas and those of Paleogene age. The presented evidence shows that modern clades of chironomids were already dominant and diversified by the end of the Cretaceous, in concert with the parallel radiation of aquatic angiosperms which became dominant in freshwater habitats. This exceptional finding encourages the active search of microscopic remains of fossil arthropods in other geological units, which could provide a unique way of enhancing our knowledge on the past diversity of the clade.

Marker Minerals in Volcanics and Xenoliths—An Approach to Categorize the Inferred Magmatic Rocks Underneath the Present-Day Volcanic Landscape of Tenerife, Spain (NW African Rare Mineral Province)

A mineralogical mapping (terrain analysis) based on micro-mounts has been performed in the Archipelago of the Canary Islands, Spain. The rare elements Be, F, Li, Nb, Ta, Zr, Hf, and rare earth elements (REE) were investigated on the largest island of the Canary Islands Archipelago, Tenerife, Spain. This study forms a contribution to the metallogenetic evolution of the offshore area of the NW African Rare Mineral Province. The finds made at Tenerife were correlated by means of minero-stratigraphy with the adjacent islands La Gomera, Gran Canaria and Fuerteventura, where typical critical element host rocks, e.g., carbonatites, are exposed. At Tenerife, these hidden rock types are only indicated by a wealth of 128 compositional first-order marker minerals hosting Be, F, Zr, Nb, Ta, Zr, Hf, Li, Cs, Sn, W, Ti and REE plus Y and another 106 structural second-order marker minerals describing the geodynamic and morpho-structural evolution of Tenerife (Mn, Fe, Pb, U, Th, As, Sb, V, S, B, Cu, Zn, Mo, Au). Based upon the quantitative micro-mineralogical mapping of lithoclasts and mineralogical xenoliths (foid-bearing monzodiorite/gabbro, (nepheline) syenite, phonolite trachyte) in volcanic and volcaniclastic rocks, hidden intrusive/subvolcanic bodies can be delineated that are associated with contact-metasomatic, zeolitic and argillic alteration zones, as well as potential ore zones. Two potential types of deposits are determined. These are pegmatite-syenites with minor carbonatites bound to a series of agpaitic intrusive rocks that are genetically interlocked with rift zones and associated with a hotspot along a passive continental margin. Towards the east, the carbonatite/alkali magmatite ratio reverses at Fuerteventura in favor of carbonatites, while at Gran Canaria and La Gomera, shallow hypogene/supergene mineral associations interpreted as a marginal facies to Tenerife occur and a new REE discovery in APS minerals has been made. There are seven mineralizing processes different from each other and representative of a peculiar metallogenic process (given in brackets): Protostage 1 (rifting), stages 2a to 2d (differentiation of syenite–pegmatite), stages 3 to 4b (contact-metasomatic/hydrothermal mineralization), stages 5a to 5b (hydrothermal remobilization and zeolitization), stage 6 (shallow hypogene-supergene transition and kaolinization), and stage 7 (auto-hydrothermal-topomineralic mineralization). The prerequisites to successfully take this holistic approach in economic geology are a low maturity of the landscapes in the target area, a Cenozoic age of endogenous and exogenous processes amenable to sedimentological, geomorphological, volcano-tectonic and quantitative mineralogical investigations. The volcanic island’s mineralogical mapping is not primarily designed as a proper pre-well-site study on the Isle of Tenerife, but considered a reference study area for minero-stratigraphic inter-island correlation (land–land) and land–sea when investigating the seabed and seamounts around volcanic archipelagos along the passive margin, as exemplified by the NW African Craton and its metallogenic province. This unconventional exploration technique should also be tested for hotspot- and rift-related volcanic islands elsewhere on the globe for mineral commodities different from the ones under study.

Prospects of oil and gas potential of the Indigiro-Zyryansky trough based on direct geochemical data

Within Eastern Yakutia, certain prospects for oil and gas potential are associated with a number of negative structural elements of the Mesocainozoic age. Given the presence of a powerful sedimentary cover and a relatively calm tectonic situation, the Indigiro-Zyryansky trough is considered the most promising territory for oil and gas. According to the results of deep drilling conducted in the late 1980s and early 1990s, the presence of sufficiently powerful Cenozoic age strata was established. After joint processing of the drilling data with the seismic survey materials, the thickness of Cenozoic sediments in the trough is estimated at 2 – 2.5 km. The expediency of rethinking the materials of geochemical testing together with the data obtained during deep drilling is noted. According to the peculiarities of the composition of gases obtained during deep drilling and testing of wells in the section of the Indigiro-Zyryansky deflection, there are two types of natural gas. The first type is associated with Paleogene deposits and, judging by its composition, has a microbial genesis (wells No. 272-01 and 272-02). The second type of gas obtained from Upper Jurassic deposits appears to be catagenetic and heavier in composition (well No. 272-05). An analytical review of the results of direct geochemical testing is made, which also confirms the presence of at least two different types of gases. At the same time, the gas characterized as deep has clear features similar to the gases of collapsing oil accumulations. It is assumed that near-surface gases enriched with nitrogen and carbon dioxide may be associated with carbonaceous deposits of the Upper Jurassic and Lower Cretaceous. It is recommended to conduct areal geochemical testing using artificial sorbents for aromatic hydrocarbons.

Spatiotemporal Evolution of Central Qilian Shan (Northwest China) Constrained by Fission-Track Ages of Detrital Grains from the Huangshui River

The emergence of the Tibetan Plateau is one of the most significant geological events in East Asia. The Central Qilian Shan connects North and South Qilian Shan in the northeastern part of the Tibetan Plateau. However, the exhumation history of the Central Qilian Block from the Mesozoic to Cenozoic remains unclear. Determining the cooling ages of detrital zircon and apatite in modern river sediments is an ideal method for tracing the evolutionary processes of orogenic belts. In this study, we present the first single-grain detrital apatite (153) and zircon fission-track (108) data for the Huangshui River sediments from the Central Qilian Shan. The decomposition of the dataset revealed major Mesozoic and Cenozoic age peaks at ca. 145–93, and 11 Ma. The Central Qilian Shan entered the intracontinental orogeny stage dating back to the Cretaceous (ca. 145–93 Ma) and Late Cenozoic (ca. 11 Ma) caused by the subduction of the Neo-Tethys and Indian–Asian collision. Therefore, we propose that the geomorphic framework of the northeastern margin of the Tibetan Plateau was initially established during the Mesozoic and further consolidated in the Late Miocene.

DEFORMATION REGIMES AND LOW-RANK PALEOTECTONIC STRESSES OF THE WESTERN TIAN SHAN IN THE MESOZOIC – CENOZOIC

There is a description of the results of studies of deformation regimes and reconstruction of stress fields of certain time intervals of the Mesozoic – Cenozoic history of the western part of the Tien Shan based on the geological and structural data and earthquake focal mechanisms. The relevance of research is determined by the existing difficulties in the age reference of paleostress fields, which is associated with the retrospective nature of the initial data and the features of geological evolution, as well as the existence of controversial, unresolved issues regarding the development of the western periclinal part of the Tien Shan in the Mesozoic – Cenozoic. The aim of the research is to reconstruct the rank components of paleostresses in the earth’s crust in the western part of the Tien Shan at separate stages of the Mesozoic – Cenozoic development. The time intervals for which the stress field diagrams were obtained represent cyclically manifested phases of the first-rank rhythms, which are characterized by alternation of different deformation modes. The method for reconstructing paleostresses was based on the concept of the formation of superimposed systems of cracks of various generations, which were sequentially manifested at various stages of the development of deformation processes. Analysis of the data showed that with increasing age of rocks the number of different fracture systems actually increases – the earlier systems are superimposed by the later. At the same time, the characteristic elements in Quaternary rocks manifest themselves in different ways in the older rocks. This allows them to be used for the reconstruction of the Late Cenozoic stress field based on mass measurements of fracturing in rocks of earlier Mesozoic – Cenozoic ages. Based on the step-by-step identification of the heterochronous cracks system and determination of a pair of maxima of the fracture density with asymmetric scattering, region-based diagrams of the first-rank stress fields were obtained for different stages of manifestation of Mesozoic – Cenozoic deformation regimes: 1 – from the Permian-Triassic to the Middle Jurassic; 2 – Middle-Late Jurassic; 3 – Late Jurassic – Early Cretaceous; 4 – Late Cretaceous – Paleocene – Eocene; 5 – Oligocene – Quaternary. The results obtained indicate the alternation of compression and extension phases, first-rank for the region, and give an idea of the main trends in its geodynamic evolution. They can be used in the development of a tectodynamic model of the region.

No phylogenomic support for a Cenozoic origin of the "living fossil" Isoetes.

The isoetalean lineage has a rich fossil record that extends to the Devonian but the age of the living clade is unclear. Recent results indicate that it is young, from the Cenozoic, whereas earlier work based on less data from a denser taxon sample yielded Mesozoic median ages. We investigated node ages in Isoetes using two genomic datasets (plastome and nuclear ribosomal cistron) analyzed using three different clock models implemented in MrBayes (ILN, WN and TK02 models) and a conservative approach to calibration. While topological results are consistently resolved in Isoetes estimated crown group ages range from the latest Paleozoic (mid-Permian) to the Mesozoic depending on datatype and clock model. The oldest estimates were retrieved using the autocorrelated TK02 clock model. An (early) Cenozoic age was only obtained under one specific condition (plastome data analyzed with the uncorrelated ILN clock model). That same plastome dataset also yielded the oldest (mid-Permian) age estimate when analyzed with the autocorrelated TK02 clock model. Adding the highly divergent recently established sister species Isoetes wormaldii to the dataset approximately doubled the average median node depth to the Isoetes crown group. There is no consistent support for a Cenozoic origin of the living clade Isoetes. We obtained seemingly well-founded, yet strongly deviating, results depending on datatype and clock model. The single most important future improvement is probably to add calibration points, which requires an improved understanding of the isoetalean fossil record or alternative bases for calibration. This article is protected by copyright. All rights reserved.

Segmentation and fault–monocline relationships in the Lapstone Structural Complex, Sydney Basin, New South Wales

The 95 km-long Lapstone Structural Complex is a segmented structural association consisting of north-trending faults and monoclines in the western Sydney Basin between the Cumberland Basin to the east and lower Blue Mountains to the west. It has developed in a compressional regime. At depth, the Lapstone Structural Complex is most likely a deeply penetrating, west-dipping thrust fault that is seismogenic in the brittle middle crust. This structure has propagated upwards into the overlying Sydney Basin in the top ∼3 km of the crust and formed a suite of distinct fault and fault–monocline structures, including: (a) in the north, inferred imbricate faults at depth in the lower Sydney Basin dying out upwards into a well-displayed, major east-facing monocline (central limb has an overall consistent <20°E dip); (b) in the middle part of the complex, an east-facing monocline with dips increasing from west to east formed as a fault-propagation fold; and (c) as found in the south, a single thrust fault (Bargo and Nepean faults). The complex has a probable late Cenozoic age and has played a role in landscape development as shown by topography, uplifted river gravels and knick points along lower order streams. Therefore, it has formed late in the uplift history of the southeastern Australian highlands postdating uplift in the Cretaceous and uplift associated with basaltic eruptions in the Cenozoic. KEY POINTS The Lapstone Structural Complex is an association of segmented faults and monoclines formed at the tip of a deep-seated thrust fault. The largest structure in the complex is a gently east-dipping monocline formed above an inferred imbricate fault system in the lower Sydney Basin succession. Much of the middle and southern parts of the complex are single faults and a fault-propagation monocline related to a thrust fault at depth. The Lapstone Structural Complex is of late Cenozoic age and is most likely seismogenic.

Paleomagnetic study of impactites from the Karla impact structure suggests protracted postimpact hydrothermalism

AbstractWe present a paleomagnetic study of the ~10 km diameter Karla impact structure in Russia. We sampled the target carbonate rocks, and a yet undocumented fragmental melt‐bearing lithic breccia layer. This impact breccia, which contains carbonate melt, is enriched in stoichiometric magnetite by a factor of ~15 compared to the target lithologies, and carries a stable natural remanent magnetization. The weak remanent magnetization and the presence of both normal and reverse polarities down to the centimeter scale indicate that the breccia does not carry a thermoremanent magnetization (TRM), but rather a chemical remanent magnetization (CRM). The presence of stoichiometric magnetite and the absence of TRM suggest that the magnetite was formed during relatively low‐temperature postimpact hydrothermalism that affected the porous impact breccia layer. During this process, the breccia acquired a CRM. The paleomagnetic direction is compatible with a Cenozoic age for the impact event, but cannot bring more precise constraint on the age because of the stable position of the Eurasian plate over the last 60 Myr. However, the presence of both polarities indicates that mild hydrothermalism took place over a period of time long enough to span at least one reversal of the geomagnetic field, that is, over a time scale of the order of 100 kyr. This confirms that protracted hydrothermal systems associated with impact craters are long lived, even in relatively small craters such as Karla, and are key features of the geologic and environmental effects of impacts on Earth.

Metalliferous Coals of Cretaceous Age: A Review

Critical elements in coal and coal-bearing sequences (e.g., Li, Sc, V, Ga, Ge, Se, Y and rare earth elements, Zr, Nb, Au, Ag, platinum group elements, Re, and U) have attracted great attention because their concentrations in some cases may be comparable to those of conventional ore deposits. The enrichment of critical elements in coals, particularly those of Carboniferous-Permian and Cenozoic ages, have generally been attributed to within-plate (plume-related) volcanism and associated hydrothermal activity. However, Cretaceous coals are not commonly rich in critical elements, with the exception of some (e.g., Ge and U) in localised areas. This paper globally reviewed metalliferous coals from Siberia, the Russian Far East, Mongolia, South America, the United States and Mexico, Canada (Alberta and British Columbia), China, Africa, and Australasia (Victoria, Queensland, New South Wales, South Australia, Northern Territory, New Zealand, Nelson, West Coast, Canterbury, Otago, and Southland). The world-class Ge-U or Ge deposits in North China, Mongolia, and Siberia are the only commercially significant representatives of the Cretaceous metalliferous coals, which are related to bio-chemical reduction of oxidized meteoric, hydrothermal, or sea waters by organic matter of the peat bogs. The common Cretaceous coals worldwide are generally not rich in critical elements because intensive igneous activity led to extensive acidification of terrestrial and marine waters, which are responsible for the low coal metallogenesis during the Cretaceous period, especially the Early Cretaceous time.

Origin of an antifreeze protein gene in response to Cenozoic climate change

Antifreeze proteins (AFPs) inhibit ice growth within fish and protect them from freezing in icy seawater. Alanine-rich, alpha-helical AFPs (type I) have independently (convergently) evolved in four branches of fishes, one of which is a subsection of the righteye flounders. The origin of this gene family has been elucidated by sequencing two loci from a starry flounder, Platichthys stellatus, collected off Vancouver Island, British Columbia. The first locus had two alleles that demonstrated the plasticity of the AFP gene family, one encoding 33 AFPs and the other allele only four. In the closely related Pacific halibut, this locus encodes multiple Gig2 (antiviral) proteins, but in the starry flounder, the Gig2 genes were found at a second locus due to a lineage-specific duplication event. An ancestral Gig2 gave rise to a 3-kDa “skin” AFP isoform, encoding three Ala-rich 11-a.a. repeats, that is expressed in skin and other peripheral tissues. Subsequent gene duplications, followed by internal duplications of the 11 a.a. repeat and the gain of a signal sequence, gave rise to circulating AFP isoforms. One of these, the “hyperactive” 32-kDa Maxi likely underwent a contraction to a shorter 3.3-kDa “liver” isoform. Present day starry flounders found in Pacific Rim coastal waters from California to Alaska show a positive correlation between latitude and AFP gene dosage, with the shorter allele being more prevalent at lower latitudes. This study conclusively demonstrates that the flounder AFP arose from the Gig2 gene, so it is evolutionarily unrelated to the three other classes of type I AFPs from non-flounders. Additionally, this gene arose and underwent amplification coincident with the onset of ocean cooling during the Cenozoic ice ages.

U-Pb age of a late Cenozoic ultra-high temperature metamorphic event under Central Mexico, as inferred from granulite xenoliths from Cerro El Toro, Mexico

ABSTRACT Cerro El Toro, a Pliocene scoria cone that carried abundant lower crust xenoliths to the surface, is located in the Mesa Central (MC), Mexico, where mafic alkalic intra-plate volcanism has occurred since the early Miocene (end of the Sierra Madre Occidental volcanism). Early studies of El Toro xenoliths showed that the feldspathic granulite equilibrated at P = 0.9–1.4 GPa and T = 900−1100°C under anhydrous conditions (ternary feldspars calculations). A young (Oligocene-Quaternary?) pulse of ultra-high temperature (UHT) metamorphism was thus proposed for the region, without a strict age constrain. Zircon crystals recovered from a set of nine xenoliths (7 Grt-Sil bearing metapelites, a Px-bearing meta-quartz diorite, and a Grt-Opx bearing orthogneiss) were selected for LA-(MC)-ICPMS U-Pb geochronology. Palaeozoic to Neoproterozoic zircon crystals are scant, whereas Mesozoic to Cenozoic ages are more abundant. Based on their chondrite-normalized REEs all Neoproterozoic to Mesozoic zircons are interpreted as igneous, whereas those of late Oligocene to late Miocene age (ca. 27–6 Ma) are mostly metamorphic and grew during a protracted pulse of UHT metamorphism in the lower crust. The presence of Cenozoic metasediments in the lower crust under Cerro El Toro is indicative of the action of the subducted Farallon plate, coupled with tectonic erosion of continentally derived sediments, either from a forearc basin and/or an accretionary prism that were relaminated to the lower crust by sediment diapirism. Similarities among the xenolith zircon ages with those from modern sediments belonging to Central Mexico Pacific coast point towards a NW-SE 100 km long coast stretch across Zihuatanejo as a possible sediment source. The paucity of Grenville-age detrital zircon grains in the recovered xenoliths suggests that the El Toro area is not underlain by a Proterozoic basement, thus implying a substantial reduction of Oaxaquia extension beneath Central Mexico and presence of the younger Guerrero terrane.

ІНТРУЗИВНО-МАГМАТИЧНІ УТВОРЕННЯ АРХІПЕЛАГУ ВІЛЬГЕЛЬМА ЗАХІДНОЇ АНТАРКТИКИ (ЧАСТИНА 2 – ГІПАБІСАЛЬНІ ТА СУБВУЛКАНІЧНІ ДАЙКОВІ ПОРОДИ)

The second part of the work "Intrusive-magmatic complexes of Wilhelm Archupelago, West Antarctica" is devoted to dykes. The authors studied dyke rocks in the Ukrainian Antarctic Station area in order to specify their petrographic diversity as well as to clarify the spatial distribution of the dykes, their geological position, age and geological relationships with other igneous formations in the region. It was found that hypabyssal and subvolcanic dykes of the Mesozoic-Cenozoic age are widespread on the Wilhelm Archipelago. The most common composition are mafic and intermediate rocks namely microgabbros, diabases, basalts and microdiorites. Felsic dykes are subordinate. Typically, studied rocks occur as small dykes that can concentrate in extended swarms. Sill-like intrusions are less common. The spatial distribution of dykes is controlled by the Lemaer – Penola fault zone of northeastern strike. Their greatest concentration was found on the Argentine Islands. The geological relationships of the dykes with isotopically dated granitoids as well as the sequence of intrusion of individual dyke bodies, which is established in the places of their distribution, allowed to distinguish, at least, two stages of dyke formation - namely Mesozoic and Cenozoic. The most ancient dyke formations of the Argentine Islands are hypabyssal dykes and sill-like intrusions of the Mesozoic age. They intruded after the accumulation of the Jurassic-Cretaceous volcanic strata of the Argentine Islands, but before the formation of the Paleogene granitoids on the Barchans and Forge Islands. The petrographic diversity of Mesozoic dyke rocks is represented by microdiorites and microgabbros, as well as their contact-metamorphosed equivalents. All hypabyssal and subvolcanic dykes intruding the Paleogene granitoids on Barchans and Forge islands are of Cenozoic age. Among them, the most common are diabase and basalt dykes. Microdiorites are of subordinate importance. The characteristic petrographic features of the Cenozoic dykes allow to identify their age analogs outside of the Barchans-Forge granitoid intrusion.