Limestone Deposits Research Articles

Geochemical Evaluation of Organic Matter Enrichment in the “Mississippian Limestone” Interval of the Anadarko Shelf of Oklahoma

Samples from a cored petroleum exploration well drilled in Kingfisher County, Oklahoma were studied using a combination of organic carbon stable isotopes (δ13Corg), and specific elemental geochemical proxies, to determine the effects of paleoproductivity and detrital input on organic matter enrichment in the Mississippian Limestone interval of the Anadarko Shelf. Total organic carbon (TOC) values are between 0 and 2.1 wt %, with an average of 0.4 wt % in the studied interval of the core, while δ13Corg values were between −38.6‰ and −24.7‰ (average −28.3 ± 2.9‰). Elemental proxies of detrital input and paleoproductivity are not enriched above average carbonate values, suggesting that there was low nutrient contribution to the study area, and consequent low organic matter productivity during deposition of Mississippian Limestone sediments. Together, insights from our geochemical tools indicate that the Mississippian Limestone interval of the Anadarko Shelf is unlikely to have generated liquid hydrocarbons because of lack of heightened productivity, and the largely terrestrial nature of organic matter preserved within the unit.

Morphological Characteristics and Mineral Content Analysis of Magnetic Minerals Based on River and Coastal Sand using SEM-EDX

This study aims to analyze the mineral content and morphological characteristics of magnetic minerals based on coastal and river sand. Analysis of minerals content uses Atomic Absorption Spectroscopy (AAS) to determine the content of Fe and Energy Dispersive X-Ray (EDX) to determine the elements of magnetic minerals based on coastal and river sand. While the morphological characteristics were analyzed using Scanning Electron Microscope (SEM). Based on the AAS analysis, magnetic mineral based on coastal sand has higher Fe content (9.03 mg/gram) compared to magnetic mineral based on river sand (8.03 mg/gram). This is also confirmed by EDX analysis where the Fe content of magnetic mineral based on coastal sand is 2.07 ± 0.21%. This value is greater than the Fe content of magnetic mineral based on river sand which cannot be measured by EDX. Morphological analysis using SEM shows that magnetic mineral based on coastal sand has a relatively uniform particle size compared to magnetic mineral based on river sand. The particle size of magnetic minerals based on coastal sand also smaller than magnetic minerals based on river sand. Coastal sand also has finer size compared to river sand. This is because coastal sand sediments are formed due to the energy of sea waves so that they have a smoother structure. While river sand sediments come from limestone deposits that have a fine and coarse structure.

Reducing Blasting-Induced Ground Vibrations at the Velkolom Čertovy Schody-Západ Quarry

The study discusses the use of the electronic initiation system and software modeling to reduce ground vibrations induced by blasting works. The main part compares non-electric and electronic initiation systems, namely how the system-type affects the peak vector sum (PVS). The study evaluates blasting works conducted between 2011 and 2020 at the Velkolom Čertovy schody quarry. KonĘprusy limestone deposit mined from a quarry Velkolom Certovy schody belongs to one of the most significant mining locations in the Czech Republic. The main mining technology used in breaking rock mass at the Velkolom Čertovy schody quarry is blasting (namely bench blasts and overburden blasts). Blasting generates ground vibrations that affect the surroundings of the quarry. The information on ground vibrations is continuously collected at the predetermined measurement sites through a monitoring network. The network constantly monitors peak particle velocity (PPV), PVS, frequency, and other parameters. The key measurement site appears to be Prošek Dome (M15) in the Koneprusy Caves. At this measurement site, the limit value of the PVS is stipulated at 3.0 mm s-1. If this value is exceeded, it is necessary to establish measures which lead to blasting restrictions (e. g. decrease in the weight of the deck charge, bench blast rows reduction). To meet the criteria, the Velkolom Čertovy schody-západ quarry started to use the electronic initiation system (E*STAR) along with the specialized software Paradigm for vibration modeling. This study, using data collected at the measurement sites Prošek Dome (M15) and KonĘprusy No. 19, compares the PVS generated by the non-electric initiation system (Shock*Star) without modeling and by the electronic initiation system (E*STAR) with modeling. As reference years for non-electric initiation were stipulated years 2011, 2012, 2013, and for electronic initiation years 2018, 2019, and 2020. An analysis of 467 bench blasts executed at the quarry was conducted - or rather, the analysis of the PVS values collected at the pre-selected measurement sites. The analysis shows that the average value of the PVS at the measurement site Prošek Dome (M15) decreased from 2.05 mm s-1 to 1.64 mm s-1 when using the electronic initiation system with vibration modeling. The decrease in the PVS value was observed at the measurement site KonĘprusy No. 19 as well, namely from 0.48 mm s-1 to 0.31 mm s-1. In addition, significantly fewer occasions of exceeding the PVS limit value were reported at the measurement site Prošek Dome (M15), specifically from 6.7 % to 2.7 % of the blasting works conducted within the selected reference years. The study also describes fundamental principles of work with the Paradigm software. Based on the vibration analysis, parameters of the bench blasts need to be adjusted: timing, number of deck charges or rows, etc. Finally, the study summarizes the benefits of the electronic initiation system with modeling.

Lithostratigraphy, facies, mineralogy and diagenesis of the syntectonic late Oligocene and Neogene Barzaman Formation (Al-Khod, Sultanate of Oman)

This is the first comprehensive study of the >170-m-thick late Oligocene to Pliocene(?) Barzaman Formation from the northern side of the Oman Mountains. Our work closes a major gap in the understanding of a complex geological interval and region which was affected by regional doming, syndepositional thrusting, changing eustatic sea level and changing climate. The dynamic, and diverse setting is reflected by the formationʼs varied lithologies. Based on seven measured sections we subdivided the Barzaman Formation into five lithostratigraphic units which we correlated over a distance of 1.3 km. The lower three units are shallow marine, the remaining two units are terrestrial. The marine development was at first siliciclastic (near-shore; Unit 1), followed by coral limestone deposition with some associated siliciclastics (Unit 2) and then siliciclastic again (Unit 3). The limestones include a coral-bearing limestone debrite. Associated (or at least contemporary) with the debris flow, are coral limestone boulders which rolled downslope beyond the area of limestone deposition. The lower terrestrial unit (Unit 4) is marked by isolated lenticular claystone beds within weathered conglomerates. The claystone beds, which may be cellular, consist of palygorskite and commonly also of saponite. Their clay mineralogy, limited areal extend and association with conglomerates indicate their origin from evaporation of small ponds/pools between wadi gravel. Within the claystones and conglomerates, two slides were identified. These slides and the limestone debrite indicate slope instability which we attribute to syndepositional thrusting. Thrust deformation may explain the thickness variations of units 2–4. The uppermost Unit 5 is characterized by highly altered conglomerates whose primary features are largely obliterated by diagenesis such as (1) alteration and replacement of igneous ophiolite clasts, (2) local basal silica cementation and (3) mainly dolomite cement with some calcite cement. Based on the general geological setting (doming, falling eustatic sea level) and the involved near-surface diagenetic processes we interpret these conglomerates as terrestrial. Diagenesis of Unit 5 indicates an increasingly wet climate. Considering the foraminifer-constrained age of Unit 2, paleostress constraints and dated climatic change data, we conclude that the Barzaman Formation dates as late Oligocene to at least the mid-Miocene.

Selection of strategy and mining system for Mokulaevskoe limestone deposit

Implementation of many investment projects connected with large mineral deposits across Russia is essentially impeded by under-developed transport and public infrastructure, inefficient decisionmaking risks and insufficient case study of strategic scenarios of mining process and mine development. New mining projects in Russia involve integrated optimization of mine planning and design in difficult geological and geotechnical conditions. The correct strategy and optimized technology selected for the mining process can ensure sustainability of a mine for a long time. This article describes an authors’ approach to designing a quarry and selecting a mining system. The optimized and effective development strategy is presented as the case-study of Mokulaevskoe limestone deposit. Alternatives of pit wall parameters and structure are presented as 3D visualization of northern Mokulaevsky site. The calculation data on work content and transport infrastructure parameters depending on the chosen mining system are given. The change in the stripping ratio as a function of the mining advance alternative is described. The advantages and disadvantages of the mining advance scenarios are defined. The approach to the design decision-making is assessed. The sound design of the pit wall working zone and the optimized strategy of mining advance in difficult geological and geotechnical conditions make it possible to ensure higher productivity of mining and handling machines, to reduce stripping ratio and to enhance mining efficiency.

TO THE QUESTION OF THE GENESIS OF THE LIMESTONE OF THE GUIDIRIM AND SEVERIN DEPOSITS

Problem Statement and Purpose. In Transnistria, the deposits of Sarmatian-age limestone are explored and exploited. These minerals are used as raw materials for cement production, as well as for the production of buta and rubble. The issues of genesis and facial transitions of these deposits remain under-studied. Data & Methods. The purpose of this work is to determine the genetic affiliation of the limestone deposits of the Gidirim and Severin deposits on the basis of facial and chemical analysis. The materials of the research are the limestones of two deposits of Transnistria. The object is the limestone of the Sarmatian age of the deposits of Transnistria. The subject of the study is the lithological and paleontological characteristic, the chemical composition of these limestones. Research methods: topical; biofacial, computer processing with GIS – programs; Laboratory quality diagnostics, chemical and physical-chemical methods of quantifying the main components of carbonate rocks. Results. The geological conditions of the Severin and Gidirim deposits were studied, and the place of productive layers of deposits in the stratigraphic scheme of Transnistria was determined on the basis of the lithological and paleontological characteristics of the rocks. Limestones mined at the Gidirim field belong to the May Day retinue, and the limestone of Severinovsky belongs to the Bessarabian reefs. Chemical analysis of limestone samples extracted from the deposits was carried out and differences in the chemical composition of the limestone of these deposits were determined. The limestone deposits in the content of calcium carbonate are clean. The concentration of silicon dioxide in the samples of the Severin field is higher than in the samples of the Giderim field, the content of one-and-a-half oxides, on the contrary, in Severinovka – 0.68%, in samples of the Giderim field – 1.04%. Analysis of the lithological composition and fauna of limestones has made it possible to distinguish within the Middle-Sarmatian basin of sedimentopulation: (a) accumulation of biogenic-chemogenic limestone of the near shelf, b) biogenic precipitation of the transition zone (reefs), c) silicate-terrigenous formations of the far shelf. The variety of phased conditions in the basin is associated with the position of the coastline and the inflection of the bottom on the boundary of the near and far shelf. The limestone of the studied deposits was formed in two different facial environments: the chemogenic-carbonate and the transient, which is associated with the formation of a strip of Bessarabian reefs. The study of paleontological residues, lithology and chemical composition of rhypogenic limestone showed the autonomy of this environment, as it has features of sedimentogenesis and near and far shelf.

A fish-parasitic isopod (Cymothoidae) on the pachyrhizodont Goulmimichthys roberti from the lower Turonian (Upper Cretaceous) Vallecillo plattenkalk, NE Mexico

The platy limestone (plattenkalk) deposit of Vallecillo in northeastern Mexico is widely known for its well preserved and diverse fish and marine reptilian assemblage dated to the early–middle Turonian (Late Cretaceous). A single specimen of the pachyrhizodont G. roberti revealed the first Cretaceous isopod (Crustacea, Arthropoda) attached to a fish host. Preservation allows for the interpretation of the entire body and most appendages. A parasitic lifestyle of the isopod is inferred based on the specimen's morphology including claw-like dactyli, but is also inferred based on the anoxic bottom conditions variously interpreted for the Vallecillo plattenkalk deposit, which excluded scavengers. The individual is here referred to the family Cymothoidae and described as Mothocya vallecillae n. sp.

Complex Technologies of Brucitic Limestone Capitalization

Abstract The paper presents a synthesis of the research consisting in a complex capitalization of a brucitic limestone deposit from Romania, in environmental protection, respectively of the complex processing possibilities for using the final products could in a very well defined direction such as: the getting of MgO with 99% purity from a brucitic concentrate with 38-40% MgO content; the getting of a fertilizer containing struvite, limestone and microelements with benefit effects on the acid soils amelioration and on plants growth. The research allowed the establishing of a complex system of three technologies, respectively, one of brucitic limestone processing, the second of magnesia obtaining by brucitic concentrate leaching with carbon dioxide and the third, that of getting a double-role agricultural fertilizer (manure for plants growth and acid soils neutralizer).

Health Risk and Environmental Assessment of Cement Production in Nigeria

The cement manufacturing industry has played a fundamental role in global economic development, but its production is a major facilitator to anthropogenic CO2 release and solid waste generation. Nigeria has the largest cement industry in West Africa, with an aggregate capacity of 58.9 million metric tonnes (MMT) per year. The Ministry for Mines and Steel Development asserts that the nation possesses total limestone deposits of around 2.3 trillion MT with 568 MMT standing as established reserves and 11 MMT used. Cement industries are largely responsible for releasing air pollutants and effluents into water bodies with apparent water quality deterioration over the years. Air pollution from lime and cement-producing plants is seen as a severe instigator of occupational health hazards and work-related life threats, negatively affecting crop yields, buildings, and persons residing in the vicinity of these industries. World Bank observed in 2015 that 94% of the Nigerian populace is susceptible to air pollutants that surpass WHO guidelines. In 2017, World Bank further reported that 49,100 premature deaths emanated from atmospheric PM2.5, with children beneath age 5 having the greatest vulnerability owing to lower respiratory infections, thereby representing approximately 60% of overall PM2.5-induced deaths. Cement manufacturing involves the significant production of SO2, NOx, and CO connected to adverse health effects on humans. Sensitive populations such as infants, the aged, and persons having underlying respiratory ailments like asthmatics, emphysema, or bronchitis are seen to be most affected. Consequently, in addressing this challenge, growing interests in enacting carbon capture, usage, and storage in the cement industry is expected to alleviate the negative environmental impact of cement production. Still, no carbon capture technology is yet to achieve commercialization in the cement industry. Nonetheless, huge advancement has been made in recent years with the advent of vital research in sorption-enhanced water gas shift, underground gasification combined cycle, ammonium hydroxide solution, and the microbial-induced synthesis of calcite for CO2 capture and storage, all considered sustainable and feasible in cement production.

Tracing the Provenance of the Devonian Limestone of Telen River, East Kalimantan

H. Witkamp found an outcrop with Devonian Limestone in East Kalimantan in 1925. In 1989, an expedition run by Institute of Technology Bandung (ITB) reinvestigated the outcrop and concluded that the Devonian Limestones in Telen River were boulders within a Permian formation. This paper gives a wider overview on the distribution of Devonian rocks in Asia Pacific region and discusses their possible origin.Based on the distribution map of Devonian rocks in the region, the Devonian limestone in Borneo is very isolated. The closest Devonian limestones are about more than 2000 km away. Probably the Devonian limestone in Telen River has been separated away from its origin by significant tectonic movement. There are several theories and models related to the formation history of this area, which makes it very complex. To understand the origin of these limestones, the geology needs to be restored to their time and place of deposition of the Devonian limestone.

IDENTIFICATION OF ROCK LAYER CONTACTS IN THE SURROUNDING OF THE SUTAMI DAM USING GEOMAGNETIC METHODS

Research on rock layer contact at Sutami Dam, Karangkates Village, Sumberpucung District, Malang Regency, Indonesia was undertaken. This research was conducted to identify volcanic sediments layers' which contact with Limestone Sediments in the surrounding of Sutami Dam and to mitigate potential disasters in the dam's surrounding area. This research was conducted by a geomagnetic method. Data were collected using the Proton Precession Magnetometer G-856. The geomagnetic data acquisition started from the Kromengan District (112.494oE; 8.129oS) to the Sukorame District (112.358oE; 8.213oS). The radius of geomagnetic data acquisition was 15 km; the space between the points was 300 meters with 1372 measurement points. The value of the geomagnetic intensity ​​are between -210 nT to 514 nT. The northern part of the research location has a lower total geomagnetic intensity than the southern area. The northern part is thought to be volcanic sediment (Tuff Desposits and Butak Volcanic Sediments), which only covers the surface, while the southern part is (Limestone Sediments) Marine sediment, which is some parts thought to have been volcanoes in ancient times. The ancient volcanoes in the southern part are Mounts Golo, Selorejo, Selumban, Tretes, Soko, Pehlembun and Krowedul. The contact layer between volcanic sediments with Limestone Sediments is more difficult to consolidate, so that the buildings built on them are more vulnerable.

Metro Doha Green Line: Fibre reinforced tunnel linings – Design and construction experience

AbstractThe Design and Build project ”Metro Doha Green Line Underground“ has been awarded to a joint venture composed of Porr, the Saudi Bin Ladin Group and HBK in summer 2013. It contains the ”ready to use“ construction of the underground part of the Green Line with 2 × 17 km tunnels, six stations, switching areas as well as cross passages and emergency exit shafts. The 34 km of tunnelling, realized with six EPB machines simultaneously, have been completed in only 18 months. The main impact on the determination of the design and build specification in terms of the segmental ring design is based on the extraordinary geological environment properties of the project area of Doha City. The geology is characterized by a dominating 3‐rocklayers system comprising massive upper and lower limestone deposits, which are commonly separated by a thin shale layer. Additionally, and in regard to the nearby located sea‐side the type of identified aggressive exposure conditions relevant to the concrete segment lining in terms of significant sulphate and chloride impact requires a durable reinforcement solution fit for required 120‐year service life. Especially due to chloride attack an ordinary steel bar reinforcement system including a projected 90 mm nominal concrete cover at lining's intrados and extrados turns out statically difficult and constructionally non‐practicable. Therefore, steel fibres are chosen to meet the strict design constraints.

Grain-size control in coal and carbonate rock mining

The prime cost of coal and carbonate market products depends on grain size composition and strength characteristics of minerals produced. The grain size composition of mineral products is governed by geological structure of deposits and by mineral mining technology. The volumes of geological blocks and grain size distribution in bedded deposits are conditioned by density of natural joints. Blastless mining technologies applied in coal and carbonate deposits produce block sizes which are much less than natural block sizes in rock mass. It is possible to change the actual/natural block size ratio by selective preparation of different mineral layers to extraction with appropriate choice of mining and handling equipment. The grain-size control and preservation of strength characteristics of rocks is possible using specialpurpose blasting techniques and improved extraction-and-loading technologies. In particular, buried blasts at a powder factor of 0.10–0.15 g/m3 make it possible to split a rock mass layer along a system of natural joints. The buried blasting experience is gained in mining operations in Ekibastuz and Shubarkol coal fields, in Dobryatinsky and Kasimov limestone deposits, and in other mineral extraction projects. In order to simplify extraction of heterogeneous layers, it is suggested to reduce the height of an extraction panel to 1.5–5 m and to employ hydraulic rear shovels with special-design buckets in extraction-and-loading.

The Silurian Transgression of a Palaeoshoreline: The Area between Old Radnor and Presteigne, Welsh Borderlands

AbstractQuarries between Old Radnor and Presteigne, Welsh Borderlands, expose a Silurian nearshore succession, which onlaps a rocky palaeotopography of the Neoproterozoic basement that had been uplifted along the Church Stretton Fault Zone. The succession documents the Aeronian to Sheinwoodian transgression of an island or islands, with the following sequence of events: deposition of shallow marine sandstones (Folly Sandstone Formation), regional uplift, preservation of a rocky shoreline and associated deposits (Dolyhir Rudite Member), deposition of limestones characterized by a profusion of coralline algae and the abundant remains of reefs (Dolyhir and Nash Scar Limestone Formation), and finally deposition of trilobitic silty mudstones (basal Coalbrookdale Formation). Facies analysis, carbon isotope (δ13Ccarb) values, sequence stratigraphy, and collections of bryozoans, conodonts, thelodonts, and trilobites have been used here as a means of refining our stratigraphic understanding of this unique succession. The revised stratigraphy demonstrates many similarities with the adjoining Midland Platform and the wider Silurian world. Notable features include the globally recognized early Sheinwoodian carbon isotope excursion and sea-level changes of regional and global extent. As one of the best examples of its kind, the palaeoshoreline and nearshore succession of Old Radnor and Presteigne acts as a depositional model for ancient rocky shores worldwide.

The term ‘marble’ in eighteenth-century encyclopaedic literature: from colourful and exclusive to grainy and popular

This article reports on findings concerning the use and understanding of marble in the eighteenth century, as uncovered by a team of geologists and conservators at the Department of Engineering Technology at the Technical University of Munich. While researching a group of marble objects in Bayreuth in order to devise suitable conservation methods, it became apparent that the eighteenth-century understanding of ‘marble’ was different to how we define the stone today. This earlier definition of marble was based on colour, pattern and the ability to shine when polished. However, by the end of the eighteenth century, there was a shift to a focus on the different grain sizes of the stones, while the previously defining quality of colour became less important. Such developments advanced towards the recognition of limestone and marble as two different types, enabling the distinction between sedimentary limestone and its metamorphic product marble to be drawn in the first half of the nineteenth century. At the same time, the exploration of local sources caused the exclusivity of marble to dwindle. Once a building and decorative material for the elite, it now became more widely available. Marble was still the material of sovereigns - proudly presented as locally found - but it simultaneously became accessible to a wider market for household utensils or collectors’ items. This is demonstrated through the exploration of a range of German sources, including encyclopaedias and lexicons with their inherent aim of accumulating the universal knowledge of their time, a ‘marble’ compendium, and a description of the prison and workhouse in St Georgen in Bayreuth, which had marble works on its premises.

Comment on Strauss et al., 2020: Subsidence analysis of salt tectonics‐driven minibasins (Northern Calcareous Alps, Austria)

Comment on Strauss et al., 2020: Subsidence analysis of salt tectonics‐driven minibasins (Northern Calcareous Alps, Austria)

Durability Performance Evaluation of Rubberized Geopolymer Concrete

Unfortunately, the production of cement impacts pessimistically on environments since it emits CO2—a principal Green House Gas (GHG)—encouraging the earth-heating dilemma. Moreover, it necessitates not only high temperature produced by the devouring of narrow natural mineral coal resources to obtain very high amounts of energy, but it also gulps down natural limestone deposits as a raw material that is found confined in nature to obtain intense energy. Quite recently, geopolymerisation—an exothermic process, through which geopolymeric binders can be produced by synthesis of a pozzolanic precursor rich in Alumina and Silica, for an instant, Fly Ash, with alkali solution for activation in an alkali medium at a low temperature and low operational energy—is recognized as a brilliantly promising alternative to conventional cement. That means, no elevated temperature and higher energy consuming reactions are essential any more as found associated with contemporary cement production. This research paper moves towards fulfilling the performance evaluation of durability studies viz., water permeability, sorptivity, sulphate resistance, acid resistance, salt resistance, chloride diffusion, drying shrinkage, and corrosion of fly ash based user and eco-friendly rubberized (containing rubber tyre fibres) geopolymer concrete. Comparisons of the outcomes have been made with its counterpart, which has unearthed that Rubberized Geopolymer Concrete proved to better concerning all the above-mentioned parameters than Rubberized OPC-Concrete.

Nannoplankton and 13C and 13O stable isotope stratigraphy record of the mid Cretaceous sequences, Zagros Basin (western Iran)

Deposition of black shales and dark argillaceous limestones across the Cenomanian to Turonian interval has been recorded in many parts of the world. In this regard, a stratigraphic section in the Iran's hydrocarbon field in the Kermanshah region in the Zagros Basin has been studied in detail to reconstruct palaeoceanographic conditions under a reliable biostratigraphic framework. Biostratigraphy based on calcareous nannofossils integrated with high resolution carbonate and oxygen stable isotope analyses were carried out on the Cenomanian-early Turonian interval of the upper part of Garau Formation. In this formation, 24 species of calcareous nannofossils were identified in the pelagic marine deposits. Our study allowed the definition of nannoplankton bio zones from the upper part of Eiffellithus turriseiffelii Zone to the lower part of Quadrum gartneri Zone in the mid Cretaceous. This research first recorded the upper part of the Garau Formation at site and it is consistent with the previous bio zones identified in the Tethyan domain in the region. The middle Cretaceous events of calcareous nannofossils proposed here correlate with the isotope global profile for the early Cenomanian-earliest Turonian interval and with those, reported for the southeastern France and south England reference curves, represented by the positive Cenomanian to Turonian δ13C excursion. Thus, the sequences of dark argillaceous limestone rich in organic matter in Kermanshah region can be considered as a continuation of the global trend in the Tethyan domain, where the Cenomanian-Turonian Oceanic Anoxic Event constrained to about 91.5 ± 8.6 millions of years, occurred in an anoxic pelagic sedimentary environment correlates with both, global and local sea-level rises, represented in this study by the characterization of the nannoflora assemblage reflected in a variety of widespread paleoenvironmental changes that coincides with significant shifts in the stable carbon and oxygen isotope signature.

Niobium mineralization of sedimentary carbonates, Lewisian Complex, UK

ABSTRACT Proterozoic limestone in a north British terrane contains a newly recognised occurrence of Nb-REE minerals. The mineralized Loch Shin Limestone is in the Lewisian Complex of the Northern Highlands of Scotland, intruded by alkaline plutons above a Caledonian (∼0.43 Ga) subduction zone. The mineral assemblage includes columbite, calcium niobate minerals, and niobian rutile and also includes W- and Sn-bearing phases. The interval between limestone deposition and mineralization was over a billion years. Other limestones in the Lewisian Complex that were not affected by alkaline plutons are not mineralized by Nb. The occurrence indicates that there may be exploration potential for Nb in limestones mineralized by hydrothermal activity above subduction zones with alkaline intrusions.

Controls and timing of Cenomanian-Turonian organic enrichment and relationship to the OAE2 event in Morocco, North Africa

The Cenomanian-Turonian Oceanic Anoxic Event (OAE2) is a significant global event that has been linked to major source rock development in marine environments. The aim of this study is to integrate biostratigraphic, sedimentological and geochemical data (including stable carbon isotopes and trace elements) to document the timing and controls of organic matter enrichment across the Cenomanian-Turonian boundary.Morocco has excellent exposures of Tethyan carbonate platform and basinal facies and this paper details a high-resolution analysis of organic-rich Late Cretaceous intervals exposed in the Errachidia-Goulmima Basin, to investigate their relationship to the OAE2. Integrating planktic foraminiferal and ammonite biostratigraphy with carbon isotope correlations indicate that organic-rich black mudstones identified were deposited from latest Cenomanian to early Turonian, suggesting a late-OAE2 to post-OAE2 age.The sedimentology, redox water conditions and palaeoproductivity of the palaeoenvironments were studied to characterise the lithofacies and geochemical signatures, and to analyse the controlling factors for organic–enrichment. In the study area during the lower OAE2 interval, a shallow water mid-ramp environment prevailed, with predominantly bivalve-rich limestone deposition. Subsequent organic-rich mudstone development can be correlated with the latest Cenomanian (late OAE2 interval) and early Turonian (post-OAE interval) transgression, which allowed development of anoxic to euxinic conditions in the outer-ramp environment, characterized by high TOC values, from 2.7 to 17 wt%. Shallow platform locations continued to experience limestone deposition with no organic enrichment.Trace and major element data from the C/T black mudstones show an extremely high concentration in palaeoproductivity-sensitive (P, Zn, Ni and Cu) and redox-sensitive elements (V, Mo, and U). The redox environments evolved from dysoxia to anoxia and sulfidic euxinia, which is interpreted to have provided optimum conditions for organic carbon preservation in the Errachidia area.The results highlight the important interplay of local paleogeography and eustatic sea-level (the late Cenomanian/early Turonian transgressions) as the main controls on organic mudstone deposition, rather than simply global OAE2 control. The development of organic-rich mudstones reflects both increased productivity at this time and enhanced organic matter preservation due to the change in redox bottom water conditions.