Lowermost Part Research Articles

Stratigraphic palynology and micropaleontological study of the Cretaceous-Paleogene succession of the Nani-1 well of the Anambra and Niger Delta basins: Implications for hydrocarbon exploration

Integrated palynological and micropaleontological analyses were carried out on the Nani-1 well drilled into the Anambra and Niger Delta basins of Nigeria. The study is aimed at reconstructing biozones and paleoenvironments of deposition, as well as deducing the sequence stratigraphic framework of the Cretaceous-Paleogene successions of an area containing key elements for hydrocarbon exploration. Encountered lithofacies succession of sandstone, siltstone, dark-grey to black shale, and coal beds comprises six lithostratigraphic units, namely the Nkporo Group (Campanian-Maastrichtian), Mamu Formation (Middle Maastrichtian), Ajali Formation (Middle-Late Maastrichtian), Nsukka Formation (Late Maastrichtian), Imo Formation (Danian-Thanetian) and Ameki Group (Eocene). Fourteen dinoflagellate zones (A-N) and seven pollen and spore subzones (A1-G1) are recognized based on the first occurrence of two or more species. Two major stratigraphic events are documented: (1) dinoflagellate cyst (dinocyst) zone G at 880 m depth marked by first appearance of Danea aff. californica and Danea cf. mutabilis in association with Cordosphaeridium fibrospinosum, and the last occurrence of Danea aff. californica and Phelodinium magnificum place the Cretaceous-Paleogene (K/Pg) boundary in the lowermost part of the Imo Formation; and (2) a hiatus characterized by a starved section observed at 380 m directly overlain by the Early Eocene assemblages of the Ameki Group indicates a sequence boundary at Imo/Ameki Boundary. Thus, a chronostratigraphic chart is developed for parts of the Anambra Basin and the Niger Delta. Six depositional environments which include marginal to shallow marine, marshy lagoon to estuarine, shallow neritic and tidally influenced fluvial channel are identified, and palynostratigraphic evidences indicate that fresh water palynomorphs are present in the Lower Maastrichtian strata. Four sequence boundaries and four maximum flooding surfaces are also identified within the Maastrichtian–Early Eocene sediments. The paleoenvironmental reconstruction shows that possible hydrocarbon reservoirs in the basin are the marine sandstone facies of the Nkporo Group and Mamu Formation. Their shale members constitute potential source rocks, while the overlying shale units of the Nsukka and Imo formations may provide regional seals for hydrocarbon habitation.

Mixed deltaic and carbonate deposition in a tectonically restricted basin: An example from the lower and middle members of the Eocene Musawa Formation, Abat Basin, south‐eastern Oman Mountains

Mixed siliciclastic and carbonate sediments of the Eocene Musawa Formation were deposited in the Abat Basin in the south‐eastern part of the Oman Mountains when the rest of the Arabian Plate was experiencing extensive carbonate sedimentation. The Musawa Formation was deposited as mixed siliciclastic and carbonate sediments in the Abat Basin bounded by the Ja'alan and Qalhat strike‐slip faults. Movements along these bounding faults and extensive deformation in the source area provided an enormous amount of clastic sediments in a laterally restricted basin undergoing strong tectonic‐related subsidence and was fed by basin axis parallel drainage system. The lithofacies assemblage represents fluvial and wave‐dominated deltaic sediments that accumulated as a local siliciclastic feature in a carbonate‐dominated subtropical environment. The Musawa Formation is divided into three members, the lower, middle, and upper, based on lithological characteristics; however, this study focuses on the lower and middle members of the formation. The lower Musawa member is about 350 m thick, comprising laterally confined conglomerate (lithofacies GL) beds interbedded with Alveolina‐bearing sandstone in the lowermost part of the formation. These beds were deposited as fan‐delta on top of the underlying Ypresian limestone of the Abat Formation. The conglomerate beds grade up‐section into over 170 m thick medium‐ to thick‐bedded channelized sandstone lithofacies (lithofacies CSL), occasionally interbedded with mudstone and peat streaks. The sandstone sequence northwards of the study area passes into fine‐grain lithofacies of siltstone and mudstone (lithofacies ML). The sandstone (CSL) was deposited in a delta‐plain setting with coastline shifting northwards. The enormous thickness of the sandstone sequence is due to the location of the depocenter around Wadi Musawa area, from where the streams entered the basin and deposited their sediment load. The upper part of the lower Musawa member comprises interbedded clay, siltstone, and thin‐bedded fine‐grain sandstone (lithofacies association LFA3) deposited as mud‐flat accumulations. The middle Musawa member is about 650 m thick, comprising both carbonate (LFA4) and siliciclastic (LFA2 and LFA3) lithofacies associations. The carbonate lithofacies association (LFA4) was deposited during flooding events. The marl lithofacies (CM) comprising branching corals, gastropods, and oysters was deposited in a lagoonal setting, whereas thick‐bedded limestone lithofacies (CL) comprising Nummulites was deposited in open‐marine conditions. Occasional coarse siliciclastic influx resulted in the deposition of mouth bar and shoreface lithofacies association (LFA2), especially in the upper part of the middle Musawa member. The mouth bar and shoreface sandstone interbedded with occasional chert‐bearing conglomerate are laterally persistent across the Abat Basin outcrops. The uppermost part of the middle Musawa member is defined by ridge‐forming, thick‐bedded open‐marine limestone (CL) extending across the Abat Basin. The upper boundary of this limestone facies (i.e., CL) marks the boundary between the middle and upper members of the Musawa Formation. This study helped in understanding the mechanism of mixed siliciclastic–carbonate deposition in the Abat Basin.

Multi‐mineral petrochronology on a high‐pressure mafic granulite reveals short‐lived high‐temperature metamorphism in the North China Craton

AbstractAccurately defining the peak ages and timescales of high‐temperature metamorphism is fundamental to unravelling tectonic dynamics. However, metamorphic constraints are frequently hampered by a large spread of zircon U–Pb ages without explicit textural relationships. Integrated garnet and zircon petrochronology may clarify ambiguous ages retrieved from ancient high‐temperature metamorphic rocks. There is a long‐standing debate on the interpretation of the spread of zircon ages from c. 2.5–1.8 Ga for the granulites of the North China Craton. In order to clarify the timing and duration of (ultra)high‐temperature metamorphism in the North China Craton, we investigated a mafic granulite and the adjoining gneiss from the Yinshan Block of the North China Craton using zircon and titanite U–Pb geochronology combined with garnet Lu–Hf and Sm–Nd geochronology. Pseudosection modelling and conventional thermobarometric calculations constrain the peak metamorphic conditions to be ~1.0 GPa and ~850°C. The near‐complete lack of major‐element zoning in garnet, aside from ~2 μm diffusion profiles at crystal rims, suggests complete re‐equilibration at peak temperatures followed by fast cooling from high temperatures. The Lu–Hf garnet age of 1870 ± 4 Ma and Sm–Nd age of 1870 ± 7 Ma, determined on the same garnet fractions, are indistinguishable from the zircon U–Pb age of 1866 ± 11 Ma obtained from zircon that grew contemporaneously with garnet, evidenced by the chemical equilibrium of coexisting garnet and zircon, and are additionally consistent with a titanite U–Pb age of 1876 ± 7 Ma. We interpret this close agreement of ages, within uncertainty, coupled to the existence of flat Sm–Nd–Hf profiles in garnet that also has well‐preserved Lu zoning, to reflect a short‐lived high‐temperature metamorphic event that was terminated by rapid exhumation and cooling. The short‐lived (<4 Myr) high‐temperature metamorphism may be generated in the lowermost parts of the crust through magmatic underplating/intraplating during extension that follows collision of the Ordos and the Yinshan Blocks.

Eruptive tempo of Emeishan large igneous province, southwestern China and northern Vietnam: Relations to biotic crises and paleoclimate changes around the Guadalupian-Lopingian boundary

Abstract The Emeishan large igneous province (LIP), southwestern China and northern Vietnam, is thought to have been a potential driver for the biotic crises and paleoclimate changes around the Guadalupian-Lopingian boundary (GLB; Permian), but the lack of high-precision radiometric dates to constrain the duration and eruption rates of the volcanism has limited the assessment of their relationship. We present new chemical abrasion–isotope dilution–isotope ratio mass spectrometry U-Pb zircon geochronology of three samples from the lowermost and uppermost parts of the volcanic succession in the central portion of the Emeishan LIP. The results demonstrate that Emeishan volcanism began by 260.55 ± 0.07 Ma and persisted until at least 257.22 ± 0.37 Ma. Combined with a previously published age of 259.1 ± 0.5 Ma for silicic ignimbrites, we estimate that ~85% of Emeishan LIP volume erupted within 1.45 ± 0.50 m.y. Our new results confirm that the Emeishan volcanism began slightly prior to the initiation of the associated mass extinction event and was contemporaneous with the associated warming interval. The new data support the hypothesis that the Emeishan LIP likely triggered the biotic crises and paleoclimate changes around the GLB.

Solid grain migration on hydraulic properties of fault rocks in underground mining tunnel: Radial seepage experiments and verification of permeability prediction

When fault fracture zones are encountered in the mining tunnel excavation, the water-conducting pathway is easily formed by the granular structure of the broken surrounding rock, probably resulting in water inflow hazards. Therefore, the configuration and hydrological characteristics of existing faults are key factors for the safe mining tunnel construction. In this paper, one-dimensional (1D) radial seepage experiments were carried out under variable grain size distribution (GSD) and water pressure (WP). Hydraulic properties were investigated, including porosity and permeability under the 1D radial grain migration. Experimental results show that the permeability and porosity increase with time, and the occurrence process of water inflow can divide into four stages, including the rapid increase, decelerated increase, slow climbing, and stable period. After the seepage experiment, the porosity of the sample increases gradually from the top to the bottom and reaches the maximum at the lowermost part (outlet), indicating that the spatial distribution of the porosity exhibits the non-uniform property. Through comparisons of grain migration under different conditions, it is concluded that, with the decrease of GSD and the increase of WP, more severe fine grain migration can be occurred, leading to great changes in hydraulic properties. In addition, three prediction models were verified by the testing results, and Carman-Kozoeny model shows the highest accuracy. In the same predictive model, if a sample has a smaller grain migration capacity, then there is a higher prediction accuracy of the sample. By means of Carman-Kozoeny model, it is predicted that there is a higher final permeability in the position closer to the water outlet. Based on the research results, a series of strategies were proposed to prevent and control water inflow in fault rocks.

Knowledge of Cervical Cancer Prevention and Screening Uptake Among Female Non-Health Care Providers in Two Selected General Hospitals in Lagos State

Cervical cancer is an abnormal growth of the cells of the cervix which is the lower-most part of the uterus. This cancer can spread to other parts of the body, including the lungs, liver, bladder, vagina, and rectum. Therefore, this research was aimed at assessing the knowledge of cervical cancer prevention and screening uptake among female non-health care providers working in various departments in two general hospitals in Lagos. Annually, in Nigeria 14,943 cases of cervical cancer are reported: out of these 10,403 women die leading to 28 deaths daily from cervical cancer. However, this needless death can be prevented if the cases are diagnosed early through the cervical screening, knowledge and uptake. The research adopted a descriptive cross-sectional survey. The population comprises of 350 female non-health care providers from two selected general hospitals in Lagos Island. The sample size of 165 was determined using Leslie Kish formula. A self-developed and validated questionnaire was used to collect data. Data collected were analysed using descriptive and inferential statistics at 0.05 level of significance. The results showed that 108 (65.5%) of the respondents knew that abnormal vagina bleeding and bleeding after intercourse are symptoms of cervical cancer while 102 (61.8%) showed that having multiple sexual partners is among the factors for acquiring cervical cancer. Furthermore 113 (68.5%) showed that cervical cancer is preventable while 118 (71.5%) believes that regular cervical screening can prevent cervical cancer and 148 (89.7%) were interested in participating in cervical cancer screening. The knowledge and prevention revealed that there was a positive and significant relationship between them. The research concluded that despite the adequate knowledge of cervical cancer screening as reported by the result, the level of screening is still low. It is hereby recommended that female non-health care providers should do cervical cancer screening regularly.

Disentangling climate signal from tectonic forcing: The Triassic Aghdarband Basin (Turan Domain, Iran)

The Middle–Upper Triassic Aghdarband Basin, NE Iran, consists of a strongly deformed marine and non-marine stratigraphic succession, deposited along the southern margin of Asia in a highly complex tectonic context related to a back-arc setting. The youngest deformed units of the Aghdarband area consist of a rather monotonous sequence of brown-colored shales, with intercalations of siltstones and fine-grained sandstones forming the Miankuhi Formation. The shale-dominated Miankuhi Formation rests on an unconformity surface, separating it from the underlying Sina Formation. A multidisciplinary study based on sedimentological, palynological, and paleobotanical data permits to reconstruct the depositional environments, sedimentary evolution, and paleoclimate conditions of the upper Sina and the lowermost Miankuhi formations. The palynological association of the lowermost part of the Miankuhi Formation yielded sporomorphs of the latest early Carnian to early late Carnian age. Qualitative and quantitative analyses document a shift from xerophytic associations in the upper Ladinian (upper Sina Formation) to hygrophytic assemblages in the Carnian (lower Miankuhi Formation). This increase in hygrophytic elements is also observed in coeval Tethyan outcrops at the same latitudinal belt, suggests a more humid climate in the lower part of the Miankuhi Formation, and correlates this part of the succession with a record of the Carnian Pluvial Episode. The sedimentological and stratigraphical analyses show an evolution from prodelta to delta setting in the upper Sina Formation, then an unconformity enhanced by an interval of fluvial deposits with histosol levels in the basal Miankuhi Formation, in correspondence with the hygrophytic assemblages. The unconformable boundary between the Miankuhi and the Sina formations is, consequently, interpreted as a result of the sea-level fall associated with the humid climate shift, occurring in close association with the first effects of the Eo-Cimmerian Orogeny along the suture zone, taking to a regional reorganization of the basins architecture and the end of volcanic activity in the back-arc region. The main deformations related to the Eo-Cimmerian event thus, correspond in the Aghdarband Basin to the tectonic event that deformed the Miankuhi Formation. This event is probably older than the middle Norian (217.1 ± 1.7 Ma) but younger than the late Carnian, testifying to a diachronicity in the record of collision along the Iranian Cimmerian blocks and Southern Laurasia according to the different considered structural positions. • Stratigraphical and sedimentological revision of Upper Triassic strata from NE Iran • Palynological studies assignm the basal Miankuhi Formation to the Carnian age • Paleobotanical data show clear evidence of the Carnian Pluvial Episode in Iran • The best available estimation of the onset of Eo-Cimmerian event in NE Iran

Sedimentological, petrophysical, and geochemical controls on deep marine unconventional tight limestone and dolostone reservoir: Insights from the Cenomanian/Turonian oceanic anoxic event 2 organic-rich sediments, southeast Constantine Basin, Algeria

The Cenomanian/Turonian period is characterized by the deposition of organic-rich and fine-grained sediments that form important source rocks and unconventional reservoir units in North Africa and other parts of the world. The Lower Turonian deposits of the Djebel Darmoun Field, southeast Constantine Basin, Algeria, comprise a thick carbonate succession that has potential as an unconventional reservoir unit. This research aims to investigate the Lower Turonian succession in terms of microfacies, diagenesis, petrophysical, and geochemical characteristics, which were previously unknown. Sedimentological and diagenesis analyses were performed based on the core and thin section observations. Furthermore, geochemical and petrophysical analysis methods were carried out to assess the resource potential based on geochemical measurements, core measurements, and well logging evaluation in an arrangement. Based on sedimentological investigation, the Lower Turonian carbonate section is composed of tight limestone and dolostone rocks characterized by four bioclastic limestones and two dolomicrite microfacies, while paleontological investigation indicates that the faunal content is dominated by planktonic assemblages, revealing a pelagic deep marine setting environment. The primary pores of the Lower Turonian carbonate rocks are seldom preserved due to multi-stage diagenetic alteration (i.e., cementation, compaction, fracturing, dolomitization, dissolution, asphaltene), while dominant secondary pores are represented by dissolution-enlarged and open fractures/fissures, while intercrystal pores might be added in dolostone intervals. Dissolution and fracturing diagenetic events play a major role in enhancing the pore network, while compaction, cementation, and asphaltene diagenesis processes share in the obliteration of the petrophysical properties. Dolomitization played a dual role in the dolostone intervals, where it tended to develop the porosity at the early stages of diagenesis, while it tended to decrease the porosity at the latest diagenesis stages. The geochemical analysis indicated high amounts of organic matter in these intervals, where the higher estimated organic richness reaches a maximum TOC of 7.8% at the lowermost part. The petrophysical analysis inferred that the Lower Turonian carbonate sediments are characterized by low porosity (avg. 4%), very low permeability (<0.01mD), with dominant micro and meso porosities, and therefore they can be classified as tight carbonate unconventional resources. This study provides an insight into factors controlling the pore system network (microporosity) of fine-grained carbonate rocks as an excellent analog of the deep marine unconventional tight limestone and dolostone reservoirs and improves the knowledge and modeling of these unconventional resources. The study sheds light on the organic-rich sediments that are associated with oceanic anoxic events (OAEs) across the North African region and other parts elsewhere, forming high quality source rocks that might be neglected as excellent unconventional resources.

Fossil-bearing Citalang Formation, Sumedang-Majalengka, West Java

The Citalang Formation in Sumedang-Majalengka area comprises of various lithological units, including coarse-grained sandstones to conglomerates, greenish grey to dark grey claystone with sandstone and tuff interbeds, and pumice-bearing tuffaceous sandstones and tuff. All these units occur in the lower part of the formation and the contacts with older, underlying rock units are unconformable in several places.Vertebrate fossil fragments are frequently found in the lowermost part of the formation, especially within the coarse-grained sandstones to conglomerates unit. This unit also holds stone tools artefacts, which were made from different kind of stones and show quite simple or primitive shape. The age of Citalang Formation is not yet resolved and still needs to be researched. Some published literatures suggest Pleistocene while there are others that suggest Pliocene.

Sedimentological and paleontological analysis of the Lower Jurassic part of the Zatrnik Formation on the Pokljuka plateau, Slovenia

The uppermost Ladinian to Lower Jurassic Zatrnik Formation is the lithostratigraphic unit of the Mesozoic deeper marine Bled Basin. The uppermost part of the Zatrnik Formation and the transition into the overlying Ribnica Breccia was logged at the Zajamniki mountain pasture on the Pokljuka mountain plateau in the Julian Alps. The lowermost part the section belongs to the “classical” Zatrnik Formation and is dominated by beige micritic limestone and fine-grained calcarenite. Foraminifers Siphovalvulina, ?Everticyclammina, ?Mesoendothyra and ?Pseudopfenderina are present, indicating Early Jurassic age. The beige limestone is followed by light pink limestone of the uppermost Zatrnik Formation. Slumps are common in this interval, and crinoids are abundant. Alongside some species already present in beds lower in the succession, Meandrovoluta asiagoensis Fugagnoli &amp; Rettori, Trocholina sp., Valvulinidae, small Textulariidae, Lagenida, and small ?Ophthalmidium also occur in this interval. Resedimented limestone predominates through the studied part of the Zatrnik Formation, indicating deposition on the slope or at the foot of the slope of the basin. The switch to crinoid-rich facies within the slumped interval of the Zatrnik Formation may reflect accelerated subsidence of the margins of the Julian Carbonate Platform in the Pliensbachian. The Zatrnik Formation is followed by the formation of the Pliensbachian (?) Ribnica Breccia. Impregnations of ferromanganese oxides, violet colour, and an increase in clay content are characteristic. The foraminiferal assemblage consists of Lenticulina, small elongated Lagenida, and epistominids. Individual beds of the Ribnica Breccia were deposited via debris flows. Enrichments in ferromanganese oxides point to slower sedimentation.

Evolution of Depositional Environments in Response to the Holocene Sea-Level Change in the Lower Delta Plain of Nakdong River Delta, Korea

The Nakdong River delta, located in southeastern Korea, preserves thick and wide sediments, which are suitable for the high-resolution study of the evolution of depositional environments in the lower delta plain area. This study traces the Holocene evolution of the Nakdong River delta using deep drill core (ND-3; 46.60 m thick) sediments from the present delta plain. Sedimentary units of the sediments were classified based on grain size compositions and sedimentary structures: (A) alluvial zone, (B) estuarine zone, (C) shallow marine, (D) prodelta, (E) delta front, and (F) delta plain. The weathered sediment, paleosol, was observed at 43.16 m below the surface. There is an unconformity (43.10 m) to separate a Pleistocene sediment layer in the lowermost part differentiating from a Holocene sediment layer in the upper part of the core. The shallow marine sedimentary unit (32.20~23.50 m), in which grain size decreases upward is overlain by the prodelta unit (23.50~15.10 m), which consists of fine-grained sediments and relatively homogeneous sedimentary facies. The boundary between the delta front unit (15.10~8.00 m) and the delta plain unit (8.00~0.00 m) appears to lie at 8.0 m, and the variation in grain size is different; coarsening upward in the delta front unit and fining upward in the delta front unit, respectively. These sediments are characterized by a lot of sand–mud couplets and mica flakes aligned along with cross-stratification, which may be deposited in relatively high-energy environments. Until 13 cal ka BP, the sea level was 70 m below the present level and the drilling site might be located onshore. At 10 cal ka BP, the sea level was located 50 m below the present level and the drilling site might be moved to an estuarine environment. From 8 to 6 cal ka BP, a transgression phase occurred as a result of coastline invasion by the rapid rise of the sea level. Thus, the drilling site was drowned in a shallow marine environment. After 6 cal ka BP, the sea level reached the present level, and, since then, progradation might begin to form, primarily by more sediment input. After this period, the progradation phase continues as the sediments have advanced and the delta grows.

The explosive, basaltic Katla eruption in 1918, south Iceland, II: Isopach map, ice cap deposition of tephra and layer volume

Due to poor preservation and lack of proximal tephra thickness data, no comprehensive isopach map has existed for the tephra layer from the major eruption of the Katla volcano in 1918. We present such a map obtained by combining existing data on the thickness of the 1918 tephra in soil profiles with newly acquired data from the 590 km² Mýrdalsjökull ice cap which covers the Katla caldera and its outer slopes. A tephra thickness of 20–30 m on the ice surface proximal to the vents is inferred from photos taken in 1919. The greatest thicknesses presently observed, 30–35 cm, occur where the layer outcrops in the lowermost parts of the ablation areas of the Kötlujökull and Sólheimajökull outlet glaciers. A fallout location within the Katla caldera is inferred for the presently exposed tephra in both outlet glaciers, as estimates of balance velocities imply lateral transport since 1918 of ∼15 km for Kötlujökull, ∼11 km for Sólheimajökull and about 2 km for Sléttjökull. Calculations of thinning of the tephra layer during this lateral transport indicate that the presently exposed tephra layers in Kötlujökull and Sólheimajökull were respectively over 2 m and about 1.2 m thick where they fell while insignificant thinning is inferred for the broad northern lobe of Sléttjökull. The K1918 layer has an estimated volume of 0.95±0.25 km³ (corresponding to 1.15±0.30×1012 kg) whereof about 50\% fell on Mýrdalsjökull. About 90\% of the tephra fell on land and 10\% in the sea to the south and southeast of the volcano. The volume estimate obtained contains only a part of the total volume erupted as it excludes water-transported pyroclasts and any material that may have been left on the glacier bed at the vents. While three main dispersal axes can be defined (N, NE and SE), the distribution map is complex in shape reflecting tephra dispersal over a period of variable wind directions and eruption intensity. In terms of airborne tephra, Katla 1918 is the largest explosive eruption in Iceland since the silicic eruption of Askja in 1875.

Integrated Radiolarian and Conodont Biostratigraphy of the Middle to Late Permian Linghao Formation in Northwestern Guangxi, South China

AbstractThe Permian radiolarian zones and their correlations with conodont zones or other chronostratigraphic schemes are still under debate. In this study, four genera, 21 species and two subspecies of radiolarians together with one genus and six species of conodonts were recovered from the Linghao Formation cropping out at the Longwangpo (LWP) section, northwestern Guangxi, South China. Six radiolarian interval zones and one abundance zone are recognized in the section, namely in ascending order, the Follicucullus scholasticus, Albaillella cavitata, A. protolevis, A. levis, A. excelsa, A. triangularis Interval zones and A. yaoi Abundance Zone. They are correlated with the Clarkina dukouensis, C. guangyuanensis and C. orientalis conodont zones recognized at the same section. Based on our data, the F. scholasticus Interval Zone and the lowermost part of A. cavitata Interval Zone are recognized to be upper Capitanian age, whereas the four Albaillella Interval zones are of Lopingian age (Wuchiapingian to the late Changhsingian). Two previously known Changhsingian radiolarian zones, namely the A. triangularis and A. yaoi Interval zones, should be extended down to the uppermost Wuchiapingian in this studied section.

The middle Permian pyrophyllite-rich ferruginous bauxite, northwestern Iran, Irano–Himalayan karst belt: Constraints on elemental fractionation and provenance

The pyrophyllite-rich ferruginous (PRF) bauxites in northwestern Iran from the Irano–Himalayan karst belt are deposited on the paleokarst of the middle Permian carbonate sequence of the Ruteh Formation. They were selected from the lowermost part of weathered profiles from 9 karst bauxite deposits, belonging to different stratigraphic positions. These bauxite deposits share similar mineralogical and geochemical features. Powder-XRD analyses show that the bauxites consist of diaspore, hematite, and pyrophyllite, with lesser amounts of goethite, rutile, anatase, illite, and clinochlore. Among minor constituents, single crystals, such as monazite, florencite, and zircon, were detected by SEM–EDS analyses. The positive Ce anomaly of the PRF bauxites (1.0–2.2), the relevant depletion of mobile elements, and values of the La/Y ratio (1.0–3.2) indicate that the PRF bauxites formed in a well-drained environment, characterized by a prevailing alkaline environment, promoting the stability of Fe (oxyhydr)oxides. The mineralogical composition of the PRF bauxites affects the distribution of trace elements: the redox-sensitive trace elements Ni, Cr, Co, Ce, U, and V are probably controlled by Fe (oxyhydr)oxides, whereas most of high field strength elements, such as critical metals Hf and Nb, are hosted in the pool of resistant minerals. Gallium co-varies with Al2O3, indicating this critical trace metal is distributed by diaspore. Phosphate-bearing minerals probably played an efficient role in concentrating light (LREE: LaSm) and heavy (HREE: EuLu plus Y) rare earth elements during the generation of the PRF bauxites. The mineralogical control on the distribution of LREE and HREE, coupled with the preferential complexation of HREE in an alkaline environment clearly affect the (La/Yb)ch and (LREE/HREE)ch fractionation ratios. Based on the ThZr and TiO2–Zr binary diagrams, the concentration of trace elements Zr, Cr, and Ga, bivariate plots of Ta (ppm) versus Al2O3 (wt%) and TiO2 (wt%), and the discriminant function 3 against discriminant function 4 variation diagram, basalt rocks within carbonate bedrocks of the Ruteh Formation have considered to be a probable provenance for the PRF bauxites, similar to some bauxite deposits from the Mediterranean-type karst bauxite belt of different ages, especially northern and northwestern Iran and western India.

Transgressive nature and chilled margins of the Upper Zone in the western Bushveld Complex, South Africa

ABSTRACT The Upper Zone of the Bushveld Complex has long been known to have formed from a major influx of magma into the chamber that caused large-scale erosion of the chamber floor cumulates. The most dramatic manifestations of this process are two major gap areas (Northern and Southern) in the western Bushveld Complex in which the Upper Zone appears to have eroded away the underlying cumulates down to the very base of the Complex. However, due to almost complete lack of outcrops in the gap areas, no direct field observations have ever been reported to confirm the transgressive nature of the Upper Zone. Here, we present for the first time such observations from the Kameelhoek chromite mine located at the margin of the Northern Gap. In the open pit we have documented several transgressive depressions (up to 40 m in width) in the orthopyroxenite and chromitites of the Lower Critical Zone that are filled in with magnetite gabbro of the Upper Zone. The magnetite gabbro is chilled against the sidewalls of the depressions, forming glassy and fine-grained textured rocks with plagioclase laths arranged in radial clusters. Mineralogically and chemically, the magnetite gabbro correlates with cumulates from the lowermost part of the Upper Zone at its normal position in the complex. Three major points that have emerged from this study are: (1) the Critical Zone has been eroded away by magma that was parental to the Upper Zone, (2) this eroding magma was not the one that initiated formation of the Pyroxenite Marker, but rather the evolved melt that replenished the chamber at some later stage, and (3) the melt was phenocryst-free and likely derived from a deep-seated staging chamber. Our study thus supports a recent notion that even during the formation of the Upper Zone, the Bushveld chamber had still been operating as an open system that was replenished by melts from deeper magma sources.

Sedimentology and ichnology of the mid-Cretaceous succession of Ouled Nail Mounts (Eastern Saharan Atlas, Algeria)

Shallow marine deposits characterize the upper Albian – lower Cenomanian deposits of Northern Algeria. In Djebel Azzeddine (Ouled Nail Mounts), the corresponding sediments have been subdivided into three distinctive units A to C. The first discovered ammonite fauna from the Bou Saada area allowed the attribution of a part of the mid-Cretaceous post-Continental Intercalaire deposits to the upper Albian. The ammonite-bearing level indicates a maximum flooding surface and could be correlated with similar levels from Northern Algeria. The studied succession is characterized by a low ichnodiversity containing eight ichnotaxa with abundant Thalassinoides, common Skolithos, and rare Gyrolithes, Oichnus, Planolites and cf. Tisoa. This ichnoassemblage is dominated by domichnion, fodinichnion and praedichnion trace fossils, and is attributed to the Skolithos and Glossifungites ichnofacies. These traces are produced mainly by decapod crustaceans, polychaetes and naticid gastropods. The sedimentological and ichnological data suggest shoreface to backshore environments with mixed tide/storm energy, and long subaerial exposures indicated by Lofer cyclothems in the lowermost part and dinosaur footprints in the upper part of the section.

Degradation of Arable Soils in Central Yakutia: Negative Consequences of Global Warming for Yedoma Landscapes

Global warming, which is especially intensive (up to 0.08°C yr−1) in permafrost area of Central Yakutia, has dramatic consequences for scarce arable land resources in this region. In Yedoma landscapes, intense permafrost thawing on arable fields unprotected by forest vegetation transforms the surface microtopography with the formation of residual thermokarst mounds (byllars) of 6–10 m in diameter surrounded by a polygonal network of hollows of 0.3–1.5 m in depth above melting ice wedges. This process also takes place on former croplands abandoned in the recent decades because of socioeconomic reasons. It is accompanied by a significant transformation of the previously highly likely homogeneous soil cover composed of Cambic Turbic Cryosols (Sodic) into differentiated complexes of permafrost-affected Stagnic Cambisols or Calcic Solonetzes (Turbic) on the mounds and Calcic Stagnic Solonetzes (Turbic) in the microlows. Surface soil horizons on the mounds have a strongly to very strongly alkaline reaction (pH 8.5–9.5) and low (&amp;lt;2%) organic carbon content; a wavy line of effervescence is found at a depth of 15–30 cm. Soils in the microlows have a close to neutral reaction in the upper horizons (pH 6.2–7.5); higher organic carbon content (2–3%); more pronounced textural differentiation of the profile with the formation of typical natric Btn and, in some cases, overlying eluvial E horizons; deeper (50–60 cm) line of effervescence; and clear stagnic features in the lower part of the profile. In the case of shallow embedding by ice wedge, the lowermost part of the soil in the microlow is characterized by the low bulk density (1.04 g cm−3) because of the appearance of hollows after thawing of the ice-rich transient layer and melting of the top of ice wedges. This may be indicative of the further soil subsidence in the future and the appearance of initial thermokarst lakes (dyuedya) within the Yedoma terrain with its transformation into the alas type of landscape. Rapid thermokarst-driven development of microtopography followed by differentiation of the soil cover with increasing soil alkalinity on the microhighs and soil textural differentiation and overmoistening of deep layers in the microlows prevents the return of abandoned arable land to agriculture in Yedoma landscapes.

Origin of Critical Metals in Fe–Ni Laterites from the Balkan Peninsula: Opportunities and Environmental Risk

As the global energy sector is expected to experience a gradual shift towards renewable energy sources, access to special metals in known resources is of growing concern within the EU and at a worldwide scale. This is a review on the Fe–Ni ± Co-laterite deposits in the Balkan Peninsula, which are characterized by multistage weathering/redeposition and intense tectonic activities. The ICP-MS analyses of those laterites indicated that they are major natural sources of Ni and Co, with ore grading from 0.21 to 3.5 wt% Ni and 0.03 to 0.31 wt% Co, as well as a significant Sc content (average 55 mg/kg). The SEM-EDS analyses revealed that fine Fe-, Ni-, Co-, and Mn-(hydr)oxides are dominant host minerals and that the enrichment in these elements is probably controlled by the post-formation evolution of initial ore redeposition. The paucity of rare earth element (REE) within the typical Fe–Ni laterite ore and the preferential occurrence of Co (up to 0.31 wt%), REE content (up to 6000 mg/kg ΣREE), and REE-minerals along with Ni, Co, and Mn (asbolane and silicates) towards the lowermost part of the Lokris (C. Greece) laterite ore suggest that their deposition is controlled by epigenetic processes. The platinum-group element (PGE) content in those Fe–Ni laterites, reaching up to 88 μg/kg Pt and 26 μg/kg Pd (up to 186 μg/kg Pd in one sample), which is higher than those in the majority of chromite deposits associated with ophiolites, may indicate important weathering and PGE supergene accumulation. Therefore, the mineralogical and geochemical features of Fe–Ni laterites from the Balkan Peninsula provide evidence for potential sources of certain critical metals and insights to suitable processing and metallurgical methods. In addition, the contamination of soil by heavy metals and irrigation groundwater by toxic Cr(VI), coupled with relatively high Cr(VI) concentrations in water leachates for laterite samples, altered ultramafic rocks and soils neighboring the mining areas and point to a potential human health risk and call for integrated water–soil–plant investigations in the basins surrounding laterite mines.

Late Campanian-Maastrichtian foraminiferal biostratigraphy and paleoecology at Wadi Tarfa (North Eastern Desert, Egypt)

The upper Campanian-Maastrichtian (from Globotruncanella havanensis to Plummerita hantkeninoides zones) foraminiferal assemblages at the Wadi Tarfa section in the Egyptian North Eastern Desert are studied to infer paleoenvironments and relative sea-level changes. The multivariate R-mode hierarchical clustering and the Q-mode Nonmetric Multi-Dimensional Scaling (NMDS) of the benthic foraminiferal dataset have been attempted to quantify the vertical variations in paleobathymetry, oxygenation, and trophic conditions. The inferred foraminiferal-based sea-level curve reveals paleodepth fluctuations ranging from middle neritic to upper bathyal and distinguishes five 3rd order sequences, two in the upper Campanian and three in the Maastrichtian. The development of the inferred relative sea-level curve expresses greater control of the eustasy. Also, the regional impact of the Syrian Arc Orogeny (SAO) subordinately led to amalgamation and repositioning of some sea-level events. The lowermost part (Gl. havanensis Zone) was deposited under stressed, low oxygenated, weakly eutrophic bottom-water conditions. However, well‑oxygenated oligotrophic conditions occurred around the level of the Campanian/Maastrichtian (C/M) boundary, as inferred from the predominance of heavily calcified epibenthic oxic species. We attributed this oligotrophy to the oceanic circulation change and the accompanying climatic cooling experienced at that time. The remainder of the early Maastrichtian through late Maastrichtian experienced an environmental shift toward mesotrophic conditions without considerable oxygenation change. The latest Maastrichtian, however, reveals low-oxic mesotrophic-weakly eutrophic bottom-water conditions, which is likely owed to the Deccan volcanism induced food detritus enrichment.

Paleoenvironmental and paleoclimatic changes during the Late Cretaceous and Cretaceous–Paleogene (K/Pg) boundary transition in Tattofte, External Rif, northwestern Morocco: implications from dinoflagellate cysts and palynofacies

This paper presents a quantitative study of dinoflagellate cysts (dinocysts) and palynofacies of the Campanian–Danian marly succession at the village of Tattofte (western External Rif, northwestern Morocco). The paleoenvironmental and paleoclimatic interpretations, inferred from this palynologic analysis, are compared to coeval sequences of other areas in the Northern Hemisphere. Changes in the relative abundances of dinocyst taxa, which are paleoenvironmental indicators, throughout the section suggest a deposition in a marine inner to outer neritic setting. The upper Campanian dinocyst assemblage is characterized by the presence of outer neritic-oceanic and low productivity indicator taxa (e.g., Spiniferites spp., Odontochitina spp.) and cold-water taxa (e.g., Manumiella spp., Chantangiella spp., Laciniadinium spp.), whereas, the lower Maastrichtian assemblage is characterized by inner neritic, high productivity and warm-water indicator taxa (e.g., Palaeocystodinium spp., Andalusiella spp.). The upper Maastrichtian dinocyst assemblage displays a return to an outer neritic environment under a transgressive regime, but with a cooling pulse and a moderate productivity. However, the Cretaceous–Paleogene (K/Pg) boundary interval records remarkable changes in the relative abundances of dinocyst taxa, indicating an inner neritic (coastal) setting, which is the most proximal in the study section; such changes reflect instable paleoenvironmental conditions which may be related to global cooling periods, likely caused by the Deccan volcanism in India and/or the Chicxulub asteroid impact in Mexico at the K/Pg boundary. In the Danian, the dinocyst relative abundances indicate a gradual return to stable environmental conditions.A quantitative analysis of the kerogen plots (palynomorphs, phytoclasts and amorphous organic matter (AOM)) reveals five types of palynofacies, generally indicating oxic to suboxic marine environments. The upper Campanian and upper Maastrichtian (lowermost part) strata are characterized by a playnofacies (V), indicating a distal shelf, while the lower Maastrichtian and lower Danian (uppermost part) strata record a playnofacies (III), reflecting an intermediate inner-outer neritic environment. However, the K/Pg boundary transition is characterized by playnofacies types (I) and (II), indicating a proximal (coastal) environment.