Boundary Clay Research Articles

Nanoparticles of iridium and other platinum group elements identified in Chicxulub asteroid impact spherules – Implications for impact winter and profound climate change

The Chicxulub asteroid that ended the Cretaceous Era ~66.05 million years ago caused a prolonged time of global darkness – the impact winter – leading to mass extinctions. Elements from the asteroid, including the platinum group elements (PGEs) osmium, iridium and platinum are known from the globally distributed boundary clay but their carrier elements have so far been unknown. We identify, for the first time in detail, the presence of these PGEs within Chicxulub impact spherules and importantly, we identify their carrier elements. We show through synchrotron Nano-XRF how these PGEs occur in nanostructures as un-ordered cube- and/or needle-like crystals co-localizing with both siderophile and chalcophile elements including Co, Ni, Cu, Zn, and Pb, derived from the asteroid. These crystals are set within a matrix of iron-rich calcium and silica glass revealing the mix of vaporized target rock and the asteroid. The results provide insights into the combination of elements present in the spherules, indicating formation of new minerals. We argue that the nano-shards of unreactive elements such as platinum, iridium and copper acted as nuclei for aerosol formation and potentially contributed to a prolonged impact winter with darkness and cooling leading to a profound and long-term climate change.

Hyperspectral Reflectance Assessment for Preliminary Identification of Degraded Soil Zones in Industrial Sites, India

The study explores the potential of next-generation satellite hyperspectral imaging systems for screening and predicting surface‐soil contamination and degradation by exploiting various spectral indices and signature‐matching techniques at a heavily industrialized area in India. The soil moisture content, desertification and salinity status, clay or fine material content, heavy metal content, vegetation health status, and stress levels were assessed from continuum-removed spectral reflectance values. Results indicated the presence of water in two tailings ponds, high salinity, and desertification values in most of the tailings ponds and dump sites, clay boundary liner along four ponds, high heavy metal indices along three ponds and all dump sites, highly stressed vegetation near all tailings ponds and coal dump sites, and pollutants in nearby water channels. The results suggest a strategy for the initial identification of priority areas for ground-based investigations and an alternative rapid methodology to monitor large industrial hubs in India.

Fluid upwelling and alluvial controls on spring localization: An example from Sri Lanka

In water-scarce regions, perennial springs can be a valuable source of drinking water. However, to identify unreported springs and shallow water upwelling zones, it is essential to understand the factors that control spring localization. In a crystalline basement, as in Sri Lanka, without a sedimentary cover, faults and fractures provide the only far-reaching fluid pathways and springs commonly emerge at fault/fracture intersections. While surveying cold and hot water springs in Sri Lanka, it was observed that all springs probed were located at the edge of alluvium. In order to gain insight into this relationship, we performed a topographic and geomorphological analysis was conducted utilizing remote sensing, geological and soil maps, and geological mapping in the field. The results of our analysis of 27 springs indicate that their localization is controlled by fault intersections, non-permeable clay in the alluvium and laterite, and the chemically weathered surface of the bedrock. Furthermore, the constant discharge rates observed over the years and isotope analysis suggest that the springs are part of a tens-of-kilometer-wide regional groundwater system. Based on these results, we propose a conceptual model in which water rises at fault intersections from depth until it reaches the base of the alluvium where up to several meters thick clay with low to zero permeability further inhibits vertical flow forcing the water to spread laterally. Along the alluvium clay boundary with the more permeable weathered bedrock, the water continues its path to the surface. The localization of springs differs from that of fault intersection by tens of meters, with the potential for mixing between shallow and deep groundwater. This observed effect of alluvium and their contact boundaries on spring localization has not been reported for Sri Lanka. Consequently, discharge rates may be significantly increased if the fault intersections are specifically targeted by shallow drilling.

Dynamics of Saltwater Intrusion in a Heterogeneous Coastal Environment: Experimental, DC Resistivity, and Numerical Modeling Approaches

Saltwater intrusion (SWI) is a critical concern affecting coastal groundwater sources due to natural and anthropogenic activities. The health of coastal aquifers is deteriorated by excessive SWI, mainly caused by the disturbance of the freshwater–saltwater equilibrium due to the escalating population, climate change, and the rising demand for freshwater resources for human activities. Therefore, gaining insight into the dynamics of SWI is crucial, particularly concerning the various factors that influence the intrusion mechanism. The present study focuses on the experimental simulation of saltwater in freshwater aquifers, considering boundary conditions and density-dependent effects. Two geological scenarios within coastal environments were investigated: First, a uniform, homogeneous case consisting of only sand, and second, a heterogeneous case in which layers of sand, clay, and sand mixed with pebbles are used. During the experiment, DC resistivity sounding data, as part of a widely recognized geophysical method, were collected and subsequently inverted to determine the depth of the freshwater–saltwater interface (FSWI). A finite element analysis was employed to generate numerical models based on experimental feedback. Further, for validation purposes, electrical resistivity tomography (ERT) data were collected from two distinct locations: near the seacoast and an aquaculture area. The ERT results show the presence of salinity intrusion in the study area, attributed mainly to groundwater overpumping and fish farming practices. The experimental findings indicate that the advancement of saltwater is affected by the geological properties of the media they traverse. The porosity (ϕ) and permeability (k) of the geological layer play a crucial role during the passage of saltwater flux into freshwater aquifers. The FSWI deviated along the clay boundary and hindered the easy passage of saltwater into surrounding layers. The alignment of experimental, numerical, and geophysical data suggests that this integrated approach could be valuable for studying SWI and can be applied in different geological settings, including tidal flats and alluvial plains.

Engineering Geology and Slope Stability Analysis in Kendari-Andoolo Road Section, Wolasi District, South Konawe Regency, Southeast Sulawesi

This research presents the engineering geological features of the Kendari-Andoolo road section, Wolasi Sub-district, South Konawe Regency, Southeast Sulawesi, a vulnerable area for landslides. The slope factor of safety (FoS) was also determined using the limit equilibrium method on a single and overall slope. Hand auger drilling and Wenner-Schlumberger configuration geoelectric surveys were conducted to estimate the slope failure plane. The study area is composed of phyllite, mudstone, and sandstone. Discontinuities at the face of the slope are N45ºE and N105ºE shear fractures, N280ºE foliation, and N310ºE fault brecciation. The overburden is low plasticity organic silt (OL) with a density range of 16.92 kN/m3-18.01kN/m3 and a plasticity index of 8.64-10.57 (medium). The FoS values of the slopes assumed rotational and nonrotational slip failures. On a single slope assuming rotational failures, the FoS value was lower than the nonrotational plane but still above the threshold value. The critical FoS is on the rotational sliding plane on the overall slope model. The slope's landslide failure plane is the clay's boundary layers and weathered phyllite.

Can the initial phase of the K/Pg boundary fern spike be reconciled with contemporary models of the Chicxulub impact? New insights from the birthplace of the fern spike concept

Researchers at Tanis, North Dakota, U.S.A., cited faulting associated with soft sediment deformation of the K/Pg boundary clay at Madrid East in the Raton Basin, U.S.A., as additional evidence of “more-instantaneous effects” that preceded the longer-term, climatic effects of the Chicxulub impact. However, Madrid East is among numerous localities where the initial phase of the K/Pg boundary fern spike initiated within rather than above the K/Pg boundary clay crosscut by this fault. Accordingly, this phase of the K/Pg boundary fern spike must have preceded the cessation of seismic aftershocks of the Chicxulub impact—a conclusion also reached by researchers at the deep marine depositional setting of Gorgonilla Island in Colombia, South America. The observation that the Chicxulub impact winter was shorter in duration than post-impact seismicity need not signify a major dilemma for contemporary climate models of the Chicxulub impact, a dilemma originally exacerbated by the common perception that this phase of the fern spike was dominated by tropical tree ferns. Because tree ferns have exceptionally long generation times (ca. 100 y according to contemporary estimates), they could not have had ample time to reach sporing stage if they were killed back to rhizomes or other belowground reserves by a complete shutdown of photosynthesis and subsequent impact winter. Alternatively, the dennstaedtiaceous affinity of spores at Madrid East suggests that these ferns had a generation time of only 2–4 y, which better fits contemporary estimates on how long it took for the effects of Chicxulub to wind down.

High-resolution trace element chemistry across the Cretaceous-Tertiary boundary in Denmark

Closely spaced samples on millimeter scale across the Cretaceous-Tertiary boundary clay in Denmark were analyzed by instrumental neutron activation analysis. The results show a strong correlation between Cr and Ir while Co, Zn, As, Sb and Au are correlated with Fe. The elemental peaks for Ir-Cr and Fe are separated by 6 mm. The Fe peak is found in burrow-fillings at the lowermost part of the boundary clay. Chromite grains extracted from boundry clay in Denmark and New Zealand show a compositional common group. The composition points to an ultrabasic (kimberlitic) origin of the chromites. Tandem accelerator mass spectroscopy demonstrated, that there are no Ir carriers in addition to elemental carbon in the boundary clay from two localities in Denmark.

Lithostratigraphy and sedimentology across the Cretaceous/Tertiary boundary in the Flyschgosau (Eastern Alps, Austria)

Detailed lithological profiles across the Cretaceous/Tertiary boundary (K/T) in the flyschoid Gosau Formation at Gosau (Elendgraben) and Gams (Knappengraben) are presented. The revised low sediment accumulation rates in the lowermost Danian correspond to those calculated by Smit & Hertogen (1980) for the Caravaca section. The estimated longer time-span for the deposition of the K/T boundary layers of 6-11 ka seems to be more realistic. The sediment at the K/T in the Gosau area was deposited under reducing conditions (Reissner et al. 1985). Peak levels of the siderophile elements do not coincide at Gosau and Gams. A diachronism of events is therefore assumed. The gradual decline of CaCO3 and some major element oxides beginning 4 cm below the K/T boundary and also a 1 mm thin yellow clay layer 10 mm underneath the boundary clay at Gams suggest multiple events and could be the result of a period of increased volcanism.

The Permian–Triassic boundary section at Baghuk Mountain, Central Iran: carbonate microfacies and depositional environment

Sections at Baghuk Mountain, 45 km NNW of Abadeh (Central Iran), have excellent exposures of fossiliferous marine Late Permian to Early Triassic sedimentary successions. Detailed bed-by-bed sampling enables the analysis of microfacies changes of three successive rock units across the Permian–Triassic boundary. The Late Permian Hambast Formation is mainly the result of biogenic carbonate production. Its carbonate microfacies is dominated by biogen-rich and bioturbated nodular limestones, indicating a well-oxygenated aphotic to dysphotic environment. The biogen-dominated carbonate factory in the Permian ceased simultaneously with the main mass extinction pulse, which is marked by a sharp contact between the Hambast-Formation and the overlaying Baghuk Member (= ‘Boundary Clay’). The clay and silt deposits of the Baghuk Member with some carbonate beds show only a few signs of bioturbation or relics of benthic communities. The Early Triassic Claraia Beds are characterised by a partly microbially induced carbonate production, which is indicated by frequent microbialite structures. The depositional environment does not provide evidence of large amplitude changes of sea level or subaerial exposure during the Permian–Triassic boundary interval. The deposition of the Baghuk Mountain sediments took place in a deep shelf environment, most of the time below the storm wave base.

Baghuk Mountain (Central Iran): high-resolution stratigraphy of a continuous Central Tethyan Permian–Triassic boundary section

Abstract. Permian–Triassic boundary sections at Baghuk Mountain (Central Iran) are investigated with respect to their lithological succession, biostratigraphy (particularly conodonts, nautiloids and ammonoids) as well as chemostratigraphy (carbon isotopes). The rock successions consist of the Late Permian Hambast Formation, the youngest Permian Baghuk Member (new name for the “Boundary Clay”) and the Early Triassic Claraia beds. Correlation of the data allows the establishment of a high-resolution stratigraphy based on conodonts with seven Changhsingian zones. Abundant ammonoids enable the separation of ammonoid assemblages with the successive Wuchiapingian genera Prototoceras, Pseudotoceras and Vedioceras, as well as the Changhsingian genera Shevyrevites, Paratirolites, Alibashites, Abichites and Arasella. Griesbachian and Dienerian ammonoids are usually poorly preserved. Nautiloids occur predominantly in the Wuchiapingian part of the section with two successive assemblages dominated by the Liroceratidae and Tainoceratidae, respectively. Numerous Early Triassic strata contain microbialites of various outer morphology and microstructure. The carbon isotope curve (δ13Ccarb) shows a continuous late Changhsingian negative excursion continuing across the Baghuk Member with the lightest values at the base of the Triassic.

Sponge Takeover from End-Permian Mass Extinction to Early Induan Time: Records in Central Iran Microbial Buildups

The end-Permian mass extinction was the most severe biotic crisis in Earth’s history. In its direct aftermath, microbial communities were abundant on shallow-marine shelves around the Tethys. They colonized the space left vacant after the dramatic decline of skeletal metazoans. The presence of sponges and sponge microbial bioherms has largely gone unnoticed due to the sponges’ size and the cryptic method of preservation. In addition to sponge dominated facies recently described in South Armenia and Northwestern Iran, we describe here sponge-microbial bioherms cropping out in two well-known Permian-Triassic boundary localities: the Kuh-e Hambast section, south-east of Abadeh city and the more distal Shahreza section, near Isfahan. In both sections, the extinction horizon is located at the top of an upper Changhsingian ammonoid-rich nodular limestone, calledParatiroliteslimestone. At Kuh-e Hambast, the overlying decimetric thick shale deposit called “boundary clay,” the latest Permian in age, is conformably overlain by well-dated transgressive basal Triassic platy limestone containing four successive levels of decimeter to meter scale, elongated to form cup-shaped mounds made of branching columnar stromatolites. Sponge fibers from possibly keratose demosponge, are widely present in the lime mudstone matrix. At the Shahreza section, above the extinction level, the boundary clay is much thicker (3 m), with thin platy limestone intervals, and contains two main levels of decimeter to meter scale mounds of digitate microbialite crossing the Permian-Triassic boundary with similar sponge fibers. Three levels rich in thrombolite domes can be seen in the overlying 20 m platy limestone of earliest Triassic age. Sponge fibers and rare spicules are present in their micritic matrix. These sponge fibers and spicules which are abundant in the latest Permian post-extinction boundary clay, followed microbial buildups during the Griesbachian time.

Evidence for fungal proliferation following the Cretaceous/Paleogene mass-extinction event, based on chemostratigraphy in the Raton and Powder River basins, western North America

The presence of the amino acid α-aminoisobutyric acid (Aib) within Cretaceous/Paleogene (K/Pg) boundary clay in the Raton and Powder River basins in Colorado and Wyoming, respectively, has been described as compelling evidence that extraterrestrial Aib survived the high-energy Chicxulub impact. Based on contemporary experiments and simulations, however, it is highly unlikely that extraterrestrial Aib survived the impact, which had peak impact pressures and temperatures in excess of 600 GPa and 10,000 K, respectively. In other words, the amino acid signature of the carbonaceous chondritic asteroid that impacted Chicxulub was undoubtedly destroyed upon impact during formation of the vapor plume or so-called “fireball.” The only organisms known to produce Aib are the suite (more than 30 genera) of cosmopolitan saprotrophic filamentous fungi that include Trichoderma Pers., which has recently been hypothesized to have thrived during the K/Pg mass-extinction event. Therefore it is proposed that the Aib horizon in the K/Pg boundary clay in the Raton and Powder River basins correlates with the K/Pg boundary fungal spike, which thus far has only been observed in New Zealand (Southern Hemisphere). This proposition is based upon superimposing the Aib horizon on the well-known iridium and fern-spore spikes, as its stratigraphic position precisely matches that predicted by the fungal spike. If correct, this hypothesis alters the conventional perspective on the tempo and mode of terrestrial ecosystem recovery in western North America, as the heavily sampled K/Pg boundary section in the Raton Basin was instrumental in shaping the traditional narrative of the rapid recolonization of a denuded landscape by ferns via wind-blown spores in the immediate wake of regional deforestation caused by the K/Pg impact event. Perhaps more importantly, it could present an alternative to traditional palynological approaches for locating the fungal spike in other terrestrial K/Pg boundary sections and could provide additional support for the generalization that global mass-extinction events are frequently accompanied by fungal spikes.

Landscape evolution across the Cretaceous/Paleogene boundary in southwestern North Dakota, U.S.A.

The Hell Creek Formation and overlying Fort Union Formation record a geologically rapid base-level rise that was approximately contemporaneous with the K/Pg extinction and deposition of Chicxulub-impact indicators. An outstanding question that remains is whether this base-level rise is attributable to: 1) a multi-thousand-year transgression adjacent to a relatively low-relief coastal plain, causing a rise in the water table; or 2) catastrophic flooding due to upland denudation, rapid channel accretion, and hydrologic reorganization resulting from wildfires/deforestation consequential of the impact. Herein we aim to address which of these hypotheses is most consistent with a paleolandscape reconstruction at Mud Buttes, a locality where the boundary clay (BC) is coincident with the Hell Creek-Fort Union contact. One hundred twenty-seven trenches were examined laterally across ∼2 km transect of K/Pg boundary. The uppermost Hell Creek is comprised of three pedotypes: Pale-Silt Inceptisol (PSI), Olive-Clay Vertisol (OCV), and Chocolate-Clay Vertisol (CCV), which range from moderately well-drained, to variable to poorly drained, to very poorly drained, respectively. All of the BC occurs superjacent to the CCV, despite this pedotype accounting for only ∼50% of the pre-event landscape. The edaphic features preserved in the CCV pedotype are not attributable to Paleogene overprinting, which indicates that hydromorphic conditions began prior to the impact. Furthermore, 46% of BC is overlain by lignite, despite lignite occurrence on 17% of the earliest Paleogene landscape. This reveals that the poorest-drained landscape positions of the latest Cretaceous persisted across the boundary. These relationships are most consistent with a non-catastrophic base-level rise.

A sediment-mixing process model of till genesis, using texture and clay mineralogy data from Saginaw lobe (Michigan, USA) tills

AbstractWe present a sediment-mixing process model of till genesis based on data from surface tills of the Saginaw lobe terrain in lower Michigan. Our research uses a spatial approach to understanding glacial landsystems and till genesis. We sampled calcareous till at 336 upland sites and at 17 sites in lacustrine sediment of the Saginaw Lake plain. The loamy tills have bimodal grain-size curves, with a fine-texture mode near the silt–clay boundary and a sand mode. Spatial grouping analysis suggests that tills can be divided into six groups, each with different textures and clay mineral compositions that vary systematically down-ice. The similarity among groups with respect to the silt–clay mode and clay mineralogy argues for a common origin for the fines—illite-rich lacustrine sediment of the Saginaw Lake plain. Fine-textured sediments were probably entrained, transported, and deposited down-ice as till, which also becomes sandier and enriched in kaolinite, reflecting increasing mixing with shallow sandstone bedrock with distance from the lacustrine clay source. Clayey tills on the flanks of the Saginaw terrain may reflect proglacial ponding against nearby uplands. A process model of progressive down-ice mixing of preexisting fine lake sediments with crushed/abraded sandstone bedrock helps to better explain till textures compared with a purely crushing/abrasion process model.

Enrichment of chalcophile elements in seawater accompanying the end-Cretaceous impact event

AbstractChalcophile elements are enriched in the Cretaceous–Paleogene (KPg) boundary clays from Stevns Klint, Denmark. As the concentrations of Cu, Ag, and Pb among several chalcophile elements such as Cu, Zn, Ga, As, Ag, and Pb are correlated with those of Ir, we suggest that these elements were supplied to the oceans by processes related to the end-Cretaceous asteroid impact. Synchrotron X-ray fluorescence images revealed that Cu and Ag exist as trace elements in pyrite grains or as 1–10-µm-sized discrete phases specifically enriched in Cu or Ag. The difference in carrier phases might depend on the materials that transported these elements to the seafloor. Based on their affinities with Cu, Ag, and Ir, iron oxides/hydroxides and organic matter were identified as the potential carrier phases that supplied these elements to the seafloor. Chalcophile elements adsorbed on iron oxides/hydroxides might have been released during reductive dissolution of iron oxides/hydroxides and incorporated into the pyrite produced simultaneously with the reductive dissolution of iron oxides/hydroxides. Both iron oxides/hydroxides and chalcophile elements were possibly released from the KPg target rocks (i.e., sedimentary rocks and/or basement crystalline rocks) by impact heating.Elements with a high affinity to organic matter would have been released upon its degradation and then converted into discrete minerals because of the deficiency in Fe ions. As such discrete minerals include the elements that form acid soluble sulfides such as Cu, Ag, and Pb, enrichment of these elements might have been induced by the intense acid rain just after the end-Cretaceous asteroid impact.

ЭВОЛЮЦИЯ ГИДРОГЕОХИМИЧЕСКОГО ПОЛЯ СЕВЕРНЫХ И АРКТИЧЕСКИХ РАЙОНОВ ЗАПАДНО-СИБИРСКОГО ОСАДОЧНОГО БАССЕЙНА В МЕЗОЗОЕ

Актуальность исследования состоит в выявлении фундаментальной роли палеогидрогеологических факторов в эволюции гидрогеохимического поля северных и арктических районов Западно-Сибирского осадочного бассейна в мезозойскую эру. Впервые предложен механизм, объясняющий их вклад в формирование гидрогеохимических аномалий в оксфордском резервуаре (верхнеюрском водоносном комплексе) изучаемого региона, где широко развита гидрогеохимическая инверсия. Цель: выявить особенности состава сингенетичных вод, захораниваемых одновременно с осадком на элизионных и инфильтрационных этапах развития осадочного бассейна на основе установленной цикличности гидрогеологической истории северных и арктических районов Западно-Сибирского осадочного бассейна; выполнить сравнительных анализ состава современных и сингенетичных вод и установить природу гидрогеохимических аномалий. Методы. Использованы методические приемы А.А. Карцева, С.Б. Вагина, Е.А. Баскова и других исследователей по палеогидрогеологическим реконструкциям осадочных бассейнов, выполнена периодизация гидрогеологической истории с выделением основных гидрогеологических циклов и инфильтрационных и элизионных этапов. На основе методики восстановления солевого состава вод древних морских и озерно-аллювиальных бассейнов, палеогеографических карт на юрский и меловой периоды, составленных сотрудниками ИНГГ СО РАН, информационного банка данных лаборатории гидрогеологии осадочных бассейнов Сибири ИНГГ СО РАН по арктическим районам Западно-Сибирского осадочного бассейна проведены палеогидрогеохимические реконструкции юрско-мелового разреза. Результаты. Приводятся результаты палеогидрогеологических реконструкций северных и арктических районов Западно-Сибирского осадочного бассейна. Установлено, что в гидрогеологическом разрезе исследуемого региона доминируют седиментогенные воды, в некоторых случаях разбавленные инфильтрогенными, проникшими при регрессии морского бассейна. Сравнительный анализ захороненных сингенетичных вод оксфордского бассейна и данных по современной гидрогеохимии подземных вод выявил ряд отрицательных и положительных аномалий. Отрицательные аномалии закономерно трассируют границу глинизации оксфордского регионального резервуара и связаны с развитием процессов элизионного водообмена. Геостатическая (литостатическая) водонапорная система на глубинах 2‒2,5 км переходит в термодегидратационную, что сопровождается аномально высокими пластовыми давлениями и появлением в водонапорной системе пресных химически-связанных вод. Большинство положительных аномалий приурочены к структурам Южно-Надымской и Предъенисейской мегамоноклиз, где широко проявлены процессы вертикальной разгрузки подземных вод нижне-среднеюрского и палеозойского водоносных комплексов в зонах тектонических нарушений. Системе «вода–порода–газ–органическое вещество» принадлежит ключевая роль в процессах формирования химического состава подземных вод нефтегазоносных отложений.

Paleohydrogeochemistry of the Upper Jurassic Deposits of the Arctic Regions of the West Siberian Megabasin

The paper considers the paleohydrogeochemistry of the Upper Jurassic sediments of the Arctic regions of Western Siberia. On the territory under investigation during the late Jurassic marine sedimentation was predominate, the sea depths reached 400 m in the Volga time. Under these conditions, syngenetic sodium thalassogenic chloride waters were buried, in some places with a high content of magnesium, the salinity of which reached 35-40 g/dm3. A comparative analysis of the buried syngenetic waters of the Oxford basin and data on the modern hydrogeochemistry of groundwater of the Upper Jurassic aquiferous complex revealed very significant differences. The analysis of distribution value the total mineralization allowed to establish areas of positive and negative anomalies. In the first case, most of the anomalies are associated with the processes of vertical discharge of groundwater of the Lower Middle Jurassic and Paleozoic aquifers in the zones of tectonic disturbances. Negative anomalies regularly trace the clay boundary of the Oxford regional reservoir, expanding significantly in the north-east direction. Their nature is associated with the development of processes of elision water exchange and thermal dehydration of clay minerals.

Blooms of aberrant planktic foraminifera across the K/Pg boundary in the Western Tethys: causes and evolutionary implications

AbstractWe report a detailed study of the different categories and types of abnormal morphologies in planktic foraminifera recognizable in the lowermost Danian, mainly from the El Kef and Aïn Settara sections, Tunisia. Various types of abnormalities in the test morphology were identified, including protuberances near the proloculus, abnormal chambers, double or twinned ultimate chambers, multiple ultimate chambers, abnormal apertures, distortion in test coiling, morphologically abnormal tests, attached twins or double tests, and general monstrosities. Detailed biostratigraphic and quantitative studies of the Tunisian sections documented a major proliferation of aberrant planktic foraminifera (between approximately 5% and 18% in relative abundance) during the first 200 Kyr of the Danian, starting immediately after the Cretaceous/Paleogene (K/Pg) boundary mass extinction (spanning from theGuembelitria cretaceaZone to the lower part of theP. pseudobulloidesZone). This contrasts with the proportionately low frequency of aberrant tests (generally <2%) identified within the uppermost Maastrichtian, suggesting more stable environmental conditions during the last ~50–100 Kyr of the Cretaceous. Two main pulses with abundant aberrant tests were recognized in the earliest Danian, the one recorded in the well-known K/Pg boundary clay being the more intense of those (maxima of >18%). These main pulses of aberrants coincide approximately with relevant quantitative and evolutionary turnovers in the planktic foraminiferal assemblages. In this paper, we explore the relation of these high values of the foraminiferal abnormality index with the environmental changes induced by the meteorite impact of Chicxulub in Yucatan, Mexico, and the massive eruptions of the Deccan Traps, India.

The Cretaceous-Paleogene transition at Galanderud (northern Alborz, Iran): A multidisciplinary approach

We investigated the Cretaceous-Paleogene (K/Pg) transition at the Galanderud section, northern Alborz (Iran) to identify the pattern of mass extinction of planktic foraminifera and to unravel the associated paleoenvironmental changes in a little-studied area of the eastern Tethys. We applied a high-resolution quantitative and multidisciplinary study based upon benthic and planktic foraminiferal assemblages, clay mineralogy, rock magnetic properties, stable isotopes, and geochemistry. In this section, the K/Pg boundary is marked by an abrupt change in lithology from marl to a clay boundary layer, a marked decrease in magnetic susceptibility, a negative 2.2‰ δ13C excursion, and a peak in iridium. In the uppermost Maastrichtian, foraminifera are well preserved and diversified suggesting a stable, mesotrophic environment. By contrast, the K/Pg boundary and basal Danian is marked by high values of epifaunal benthic morphogroups, low planktic diversity, and high percentages of opportunistic species (Guembelitria cretacea and Cervisiella operculata) suggesting highly stressed and variable conditions, partly due to the dramatic collapse of calcareous primary producers. Benthic foraminiferal assemblages indicate outer neritic-uppermost bathyal depths with slight bathymetric variations. The most peculiar and unique aspect of the Galanderud section is the occurrence of the three thin chalk layers interbedded within clays above the K/Pg boundary, each marked by positive shifts in δ13C and δ18O values, and consisting of >80% carbonate. We propose that the chalk/clay deposits in the basal Danian reflect changes in seawater chemistry and dynamic changes in circulation (upwelling) alternating with episodes of enhanced weathering and runoff. This section on the northern margin of eastern Tethys provides new clues about the pattern of the K/Pg mass extinction and the paleoenvironmental changes occurring during the biotic recovery phase.

Special aspects of catagenetic sulfate accumulation in Permian sedimentary sequences of Central Russia

The scope and the role of the secondary (catagenetic) processes in sedimentary-rock formation belong to the category of incompletely resolved and, therefore, the urgent problems of lithological science. The purpose of this work was to show, by means of stadium analysis, the huge “hidden” potential of catagenetic processes in the transformation of the mineral composition of sedimentary strata on the example of sulphate complexes. Boundary clay and carbonate sediments of Urzhumskiy and Sakmarskiy stage of Western limit of the pre-Ural trough were selected as the objects of study. It was found that their lithological appearance has been largely shaped by secondary (diaand catagenetic) processes of sulfate mineralization. And, if the first is reflected in the development of scattered concretionary nodules of gypsum, the latter manifested in large-scale metasomatism with the formation of large anhydrite-gypsum and gypsum-anhydrite lens and tabular bodies, stretching for hundreds of meters. It’s possible that metasomatic solutions were very reactive and moved with underground waters. Those solutions were as aggressive as lateritic weathering, and replaced not only the carbonates, but clay and ferrous minerals as well as quartz and feldspar detritus. All of this points to the high alkalinity and to the reducing atmosphere of sulphate of metasomatic solutions.