Carboniferous Basin Research Articles

Buffer properties in the Guadalquivir Estuary (SW Iberian Peninsula)

The Guadalquivir Estuary (main source of continental waters to the Gulf of Cadiz) has a carbonate basin, which enables the transport of inorganic carbon to adjacent coastal areas. Therefore, in order to study the dynamic of the carbonate system and its buffer capacity, a total of 12 samplings were carried out from 2017 to 2022. Samplings included longitudinal transects and tidal cycles in different seasonal and tidal conditions. Total alkalinity (TA) and dissolved inorganic carbon (DIC) showed increased values upstream, while calcium (Ca2+) presented the highest values in most of the marine samples. The ranges values obtained for these three variables were of 2180–5140 μmol kg−1, 430–3950 μmol kg−1 and 1295–10,855 μmol kg−1 for TA, DIC and Ca2+, respectively. Two buffer factors (βDIC and βH) were also calculated to study the variability of the buffer capacity of the Guadalquivir Estuary. These indicate that the estuary is well buffered for salinities above 10, while the inner part is more vulnerable to acidification effects. Using a non-linear 1D hydrodynamic model, net inorganic carbon system transports were calculated, showing that the Guadalquivir Estuary is exporting TA, DIC and Ca2+ to the Gulf of Cadiz.

Seismic quantitative interpretation of diagenetic processes: A study in Brazilian pre-salt carbonate reservoirs

The Brazilian pre-salt carbonate province is a scientific frontier that has been subject of extensive research and academic discussion. Santos basin carbonates show that reservoir quality is strongly conditioned by the characteristics of the depositional environment and its associated diagenetic history and alterations. Dolomitization and silicification are two of the most common diagenetic processes in Brazilian carbonates, and the combination of sedimentary and diagenetic complexity leads to a much more heterogeneous reservoir, especially complicated for geoscientists trying to mimic these geological features in terms of static and dynamic modelling. This study proposes a methodology for seismic derived diagenetic properties calculation through seismic quantitative interpretation and classification of inverted P- and S-impedance volumes applied to Brazilian Pre-Salt carbonate reservoirs. Our proposition is to establish relations between petroelastic properties and diagenetic features, first in the well-log domain and, later, in the seismic domain through different quantitative probabilistic techniques. Using the available seismic data and probabilistic approaches through stochastic inversion and Bayesian facies classification, we can interpret the occurrence of diagenetic silica and dolomite in 3D volumes. The volumetric analysis generated through the presented methodology can provide much more insights into the sedimentary history of the field, especially for static and dynamic porosity and permeability modelling.

Pre-Choiyoi volcanism at Cordillera del Viento, southwestern margin of Gondwana (∼37° S): Geological characterisation, geochronology and regional implications

This contribution provides a comprehensive description and classification of fifteen lithofacies within the Carboniferous rocks attributed to the Arroyo del Torreón Formation and Sofía Dacite in order to understand the eruptive dynamics and the evolution of volcanism associated with the onset of the Gondwanan Orogenic Cycle at the Cordillera del Viento (Argentina). The outcrops of Carboniferous volcanic and volcaniclastic rocks linked to this cycle are restricted to the Cordilllera del Viento range. In consequence, they offer a valuable opportunity to research the volcanic arc products of the pre-Choiyoi magmatism.The Arroyo del Torreón Formation lithofacies interpretation and its distribution indicate that the volcanism commenced with local andesitic lava flows followed by a volcano-sedimentary sequence formed by multiple pumice-rich quasi-steady concentrated pyroclastic density currents alternating with episodes of epiclastic sedimentation. The latter are covered ignimbrites developed by boiling over eruptions. Crystal-rich tuffs overlie the ignimbrites and represent a transition to a plinian eruption. This eruption style continued, developing concentrated pyroclastic density currents with highly unsteadiness conditions and scarce fall-out deposits. Conversely, the Sofía Dacite, represent a notable shift in the volcanism style, characterized by dacitic to rhyolitic lava flows with minor pyroclastic beds. Zircon dating of a pumice-rich lapilli-tuff from the Arroyo del Torreón Formation yielded a minimum age of 327.77 ± 1.79 Ma that was interpreted as the maximum depositional age for this unit. Similarly, zircons from a porphyritic dacite representing the Sofía Dacite provided a Concordia age of 329.11 ± 1.31 Ma that was interpreted as the crystallisation age of this rock.Consequently, we propose a new stratigraphic division of the Arroyo del Torreón Formation into two members. The Cerro San Pedro Member will comprise the pyroclastic rocks at the base of the sequence, while the Sofía Member will include the upper lava-dominated portion of the unit. In this sense, the whole lithostratigraphic unit represents a distinctive Carboniferous basin associated with arc-related volcanism representative from the pre-Choiyoi magmatism.

Thermal studies on the lower Carboniferous basins of Khenifra and Qasbat-Tadla, Morocco: What do they teach us about the pre-Variscan stages in NW Africa?

Within the Variscan Belt of Morocco, the Central Massif preserves Early Carboniferous rift basins. The Lower Carboniferous Khenifra and Qasbat-Tadla basins are aborted rifts, developed just before the Variscan orogenesis in Morocco that occurred during the Pennsylvanian-Cisuralian in NW Africa. Due to both weak inversion of these basins during the Variscan orogeny and limited burial afterwards, these basins offer the opportunity to study the Early Carboniferous pre-orogenic thermal regimes. In the Khenifra basin, 77 samples collected across the basin and its basement's boundaries, allowed the determination of the maximal temperature reached during the rocks burial by means of Raman spectroscopic analyses. The Ordovician basement shows mean temperatures between 230 and 300 °C whereas the upper Visean/Serpukhovian infill has a wide range, from temperatures <160 °C to 250–260 °C. This thermal variation within the basinal series has been evidenced from west to east and cannot have been acquired during the Variscan events. The acquisition of these maximal temperatures occurred between Late Devonian to Upper Visean/Serpukhovian and is thought to result from the formation of an extended rift. In the Qasbat-Tadla basin, Rock-Eval data from Ordovician to Devonian source-rocks indicate significantly lower maximal temperatures reached by pre-Carboniferous samples that are within the oil window. Our results are in favor of a heterodox model for the Variscan belt in Morocco and NW African in general, suggesting that no pre-Variscan compressional events are needed. Instead, the development of the intraplate Variscan belt in NW Africa was permitted through the development of hot and weak Lower Carboniferous basins, subsequently inverted in a far-field stress field. The striking thermal differences between the Khenifra and Qasbat-Tadla basins suggest that important tectonic segmentation must have shaped the area during the Early Carboniferous extensional phase.

Defining Aspects of the New Economy in Valea Jiului Carboniferous Basin

Abstract The new economy of Valea Jiului Carboniferous Basin changes the economic profile of the six localities with urban status in Hunedoara County: Petroșani, Vulcan, Lupeni, Petrila, Uricani and Aninoasa. The changes in the new economic landscape occurred in a relatively short period of time (about 33 years) and created educational, social and political imbalances. The new economy proposes the reintegration of a significant part of the population by abandoning extractive operations, reducing the secondary sector of the economy and focusing on the tertiary sector, the service sector. The business environment in the Valea Jiului coalfield is going through a new stage, which began with the restructuring that began in 1990. It is influenced positively or negatively by technological advances, European Union policies, local, national and international political events and the evolution of demand and supply. Technology and strategic innovators have the opportunity to quickly enter competitive markets and replace or assimilate local players.

Psycho-Social Perspectives in the Educational System at the Level of the Valea Jiului Carboniferous Basin, in the Context of the New Economy

Abstract The research of the reality in the territory of Valea Jiului Carboniferous Basin focuses both on the peculiarities of social ideas regarding the position of education and learning in the value system of individuals in society, as well as on the psychological principles for strengthening values in socially unstable conditions. The conclusions reached in the process of determining the degree of integration of self-confidence in the value system of the adolescent personality, showed that the development of self-confidence at a high level influences the infusion of values and the formation of one’s own system. Changes in the subject’s attitude and tendency to ensure uniformity and consistency of information, attitude and behaviour can be observed.

A primary evaporite weld revealed in the late Paleozoic Antigonish sub-basin of Nova Scotia

The Antigonish sub-basin lies within the late Paleozoic Maritimes Basin of Atlantic Canada. Late Devonian to early Carboniferous basin development resulted in a basin-and-range topography, within which the clastic Horton Group was deposited in grabens and half-grabens. The overlying Viséan Windsor Group contains substantial evaporite units; later basin development was accompanied by expulsion of these evaporites. In the Antigonish sub-basin, a significant stratigraphic omission surface initially described as a thrust was subsequently reinterpreted as the extensional Ainslie Detachment. This surface can be examined in drill-core, where the halite-bearing interval is reduced to 3.8 m of halite-cemented breccia of sedimentary rock fragments. The halite cement is sub-horizontally foliated and lineated. At Lakevale, an outcrop section of the Windsor Group is reduced in thickness to tens of metres. Above a basal limestone unit containing pseudomorphs of gypsum, most of the Windsor Group is represented by sedimentary-clast breccias that resemble those seen in core, but with the halite removed by solution in the near-surface environment. The stratigraphic record within the sub-basin implies that expulsion of lower Windsor salt was initially toward the edges of the basin where rising diapirs blocked the deposition of middle Windsor group, but in the basin centre a second salt unit was deposited. Subsequently, during contractional inversion of basin-bounding faults, the middle Windsor salt was expelled into diapirs near the centre of the basin. The Ainslie Detachment is reinterpreted as a primary salt weld: a boundary between units formerly above and below expelled lower Windsor evaporites. The resulting stratigraphic omissions and structures match those seen above expelled evaporite layers on continental margins.

Regional assessment of the ultra-deep geothermal (UDG) reservoir quality and potential of the Dinantian Zeeland Formation, the Netherlands

Abstract Dinantian carbonates in the NW European Carboniferous Basin (NWECB) in the Netherlands form a target for ultra-deep geothermal (UDG) exploration. The NWECB was a deep water area with shallow water attached carbonate systems in the southwestern Netherlands and isolated carbonate platforms nucleated on horsts in the northern part of the Netherlands. Carbonate platforms in the SW Netherlands contain intra-Dinantian, sub-Namurian and sub-Cretaceous karst systems with irregular cavities, enlarged fracture systems and collapse breccias with relict porosity. Isolated carbonate platforms in the northern Netherlands were not affected by sub-Namurian or sub-Cretaceous karst but contain petrophysical anomalies interpreted as intra-Dinantian karst or fracture systems. The matrix reservoir quality of Dinantian limestones is generally poor but has been improved by a phase of regional dolomitization that affects the lower parts of both isolated and attached carbonate platforms. Dolomitization took place during burial and was associated either with late Carboniferous to early Permian burial or a thermal event during the middle to late Jurassic. Additional reservoir quality is present in a system of hydrofractures in late Tournaisian ramp carbonates in the SW Netherlands that post-date dolomitization; the fracture system may have formed during late Jurassic basin inversion. Present heat flow indicates that two isolated carbonate platforms in the northern Netherlands are buried to sufficient depth to be considered as potential UDG exploration targets. Attached carbonate systems in the SW Netherlands are too shallow to have been heated to the temperature required for industrial applications or for generating electricity from geothermal energy.

An introduction to the Bowland Shale Formation, UK: processes and resources

Abstract This volume showcases recent geological, geophysical and geochemical research on the Carboniferous Bowland Shale Formation. The Bowland Shale is a relatively thick and extensive Palaeozoic black shale unit with a long history of debate and controversy in the UK. The Bowland Shale is proven in many of the key Carboniferous basins in the Midlands, northern England and North Wales, and represents a significant, near-continuous temporal record spanning 16 Myr including the important mid-Carboniferous boundary (Mississippian–Pennsylvanian). Since the first geological surveys in the late nineteenth century, the Bowland Shale has been of interest for a variety of reasons, including the search for Irish-type Pb–Zn base metal mineral deposits, and as a source rock in conventional hydrocarbon systems. In the mid-2000s, attention turned to the Bowland Shale as a target for unconventional hydrocarbon extraction, shale gas, following success in the USA. This placed the Bowland Shale at the centre of a series of interconnected controversies and debates from the local to national scale. The geological credibility of the purported shale gas resource in the UK was – and continues to be – highly contentious. This volume contributes to a more updated view of the Bowland Shale, covering topics such as sedimentary, geochemical and physical properties and processes, basin-forming events, hydrocarbon prospectivity, mineralization and heat and fluid flow in the subsurface. The volume also includes a field guide to some of the key localities in the UK. With the benefit of hindsight offered by the latest generation of research, the early regional shale gas assessments failed to attach sufficient weight to the compositional heterogeneity, structural complexity, compartmentalization and highly variable exhumation, erosion and palaeo-heat flow history of the Bowland Shale. The following topics are identified as promising avenues for future research beyond shale gas: (1) the role of the Bowland Shale in the context of mineral systems; (2) the role of the Bowland Shale as a cap rock in the Lower Carboniferous limestone geothermal play and potentially as an analogue of CO 2 or radioactive waste storage in the UK; and (3) pathways and mechanisms for weathering, alteration and trace element release from the Bowland Shale into the surface and/or subsurface environment.

Late Ordovician and early Silurian virgianid and stricklandioid brachiopods from North Greenland: implications for a warm‐water faunal province

AbstractAn unusually rich and diverse suite of virgianid brachiopods, hitherto poorly known, is systematically described here for the first time from the Ordovician–Silurian boundary interval (late Katian – Aeronian) of North Greenland. The Late Ordovician virgianids comprise typical taxa of the warm‐water Tcherskidium fauna (e.g. Tcherskidium tenuicostatum, Proconchidium schleyi, Holorhynchus giganteus and Deloprosopus dawesi sp. nov.). Among the early Silurian taxa, Virgiana hursti sp. nov. occurs as abundant shell beds, similar to other congeneric species in Laurentia, but has somewhat larger internal skeletal structures, albeit not as extravagantly developed as in the late Katian virgianids; Borealoides balderi gen. et sp. nov. shows extreme thickening of the shell wall and internal structures, approaching the extravagant calcification of Katian virgianids. The highly distinctive mid‐Aeronian stricklandioid brachiopod genus, Kulumbella, characterized by a shell with criss‐cross (divaricate) ribbing, also occurs in North Greenland, represented by K. heimdali sp. nov., which has the largest and most strongly biconvex shells for the genus. Palaeogeographically, the Late Ordovician virgianid fauna of Laurentia was highly distinct, confined to the low–mid tropical latitudes north of the palaeoequator. In comparison, the early Silurian (Rhuddanian) Virgiana and some related taxa in Laurentia spanned the tropics of both hemispheres, forming extensive shell beds in carbonate basins, although Borealis and Borealoides gen. nov. remained confined largely to the northern hemisphere, suggesting a certain level of provincialism extending into the earliest Silurian. A palaeoecological preference for warm‐water carbonate settings would explain the unusual abundance and richness of the virgianid faunas in North Greenland.

Metataxonomy of acid mine drainage microbiomes from the Santa Catarina Carboniferous Basin (Southern Brazil).

Mining activities generate large quantities of wastes that significantly alter the biogeochemistry and ecological structure of entire river basins. Microbial communities that develop in these areas present a variety of survival and adaptation mechanisms. Knowing this diversity at the molecular level is strategic both for understanding adaptive processes and for identifying genomes with potential use in bioremediation and bioprospecting. In this work, prokaryotic and eukaryotic communities were evaluated by meta-taxonomics (16S and 18S amplicons) in sediments and water bodies impacted by acid mine drainage in an important coal mining area in southern Brazil. Five sampling stations were defined on a gradient of impacts (pH 2.7-4.25). Taxon diversity was directly proportional to pH, being greater in sediments than in water. The dominant prokaryotic phyla in the samples were Proteobacteria, Actinobacteria, Acidobacteria, OD1, Nitrospirae, and Euryarchaeota, and among the eukaryotes, algae (Ochrophyta, Chlorophyta, Cryptophyceae), fungi (Basidiomycota, Ascomycota, and Cryptomycota), and protists (Ciliophora, Heterolobosea, Cercozoa). The prokaryotic genera Leptospirillum, Acidithiobacillus, Acidiphilium, Thiomonas, Thermogymnomonas, and Acidobacterium, and the eukaryotic genera Pterocystis and Poteriospumella were associated with more acidic conditions and higher metal concentrations, while the prokaryotic genera Sediminibacterium, Gallionella Geothrix, and Geobacter were more abundant in transitional environments.

On understanding mountainous carbonate basins of the Mediterranean using parsimonious modeling solutions

Abstract. The study aims to demonstrate that an effective solution can be implemented for modeling complex carbonate basins, in the situation of limited data availability. Considering the alternative modeling approaches under circumstances of data shortage is more significant knowing the vulnerability and effectiveness of these kinds of basins to drought and climate change conditions. In this regard, a hybrid approach that combines time series analysis and reservoir modeling is proposed to describe behavior in carbonate basins. Time series analysis estimates the contributing area and response time of the fractured carbonate system beyond the catchment's hydrographic boundaries. The results obtained align with previous literature-based field surveys. This information is then used to develop a conceptual reservoir system using the GEOframe modeling system. The model is validated using in situ discharge observations and Earth observations (EO) data on evapotranspiration and snow. Model reliability is assessed using traditional goodness of fit indicators, hydrological signatures, and a novel statistical method based on empirical conditional probability. This approach enables detailed analysis and investigation of water budget components in Mediterranean carbonate catchments, highlighting their response to significant precipitation deficits. Overall, our results demonstrate that flows from carbonate rock areas outside the hydrographic boundaries significantly impact the water budget of the upper Nera River. The storage capacity of the carbonate basin plays a crucial role in sustaining river discharge during drought years. In a single dry year, meteorological drought is considerably attenuated, while in subsequent dry years, it is slightly intensified. Multi-year droughts result in slower recovery due to the time required for precipitation to replenish the depleted storage that supported river discharge in previous dry years. This unique behavior makes these basins particularly vulnerable to the more severe and frequent drought episodes expected under future climate change.

Colliding cratons: linking the Variscan Orogeny in West Africa and North America

Abstract The Variscan Orogen was formed during the closure of the Rheic Ocean and the final collision between the North American and West African cratons in the Late Paleozoic. This collision led to the multistage building of the Mauritanide Belt to the east of the Variscan suture and to the building of the well-known Appalachian Belt to the west. Both led to opposite vergences in this part of the Variscan belt. The earliest records of the main collision episode begin at ∼360 Ma and end about 250 myr ago, while a late extensional phase lasted until ∼190 Ma. Three distinct stages are recognized in West Africa. The first stage ( c. 350–300 Ma) records the indentation of the Reguibat Shield into the central Appalachian margin of Laurentia. This indentation led to thrusting of the Souttoufide and Akjoujt ‘nappes’ onto the Reguibat Shield, to southward motion of the Senegalese block (SB), and to strike-slip motion in the Appalachians. The motion of the SB to the south is coeval with: (1) folding of the northern part of the Bové Basin, (2) north–south sinistral strike-slip motions in the central Mauritanides, and (3) the end of sedimentation in the Bové and Taoudeni Basins by the Late Devonian. The second stage ( c. 300–250 Ma) involves the eastward motion of the Western Thrust Block (WTB) against the SB and, likely, some of the westward thrusts in the Appalachians. This second ‘Variscan’ event includes: (1) closure of parts of the lower Diourbel Carboniferous basin, which is now concealed beneath the Senegalo-Mauritanian Basin, (2) thrusting to the east of the Simenti Group over the Koulountou Group in the Bassaride Belt, (3) thrusting to the east of the Wa-Wa Group, (4) thrusting of the Mauritanide Belt onto the Taoudeni Basin in the central Mauritanide Belt, and finally (5) thrusting of the Agualilet Group over the Akjoujt nappes and eastward motion of the western units over the Dhloat Ensour (Late Ordovician to early Devonian) autochthonous unit in the Souttoufides. West of the supposed ‘Variscan’ suture, Appalachian thrusting affected parts of Appalachian Belt. The third stage ( c. 250 to 190 Ma) began with the opening of Triassic rift basins in the Senegalo-Mauritanian basin and also in the north of Florida. As numerous previous correlations across the Variscan system do not include the West African part, our sythesis is intended to enhance these correlations.

Phytotoxicity of coal waste elutriates (Douro Coalfield, North Portugal) in Lactuca sativa.

One of the most important mining areas in the Douro Carboniferous Basin is the Pejão Coalfield. In the summer of 2017, a wildfire promoted the ignition and self-burning some of the coal waste piles in the area and caused important environmental changes, promoting a new heterogenic pedological zonation. This study aims to assess the ecotoxicological effects of 25 soil elutriates from these different soil types in seed germination and individual (emergence, growth, and morphologic alterations) and subindividual parameters in Lactuca sativa. The different evaluated endpoints were differently affected regarding the soil elutriate revealing the high heterogeneity of soil characteristics. The presence of different potentially toxic elements (e.g., Cd, Cr, Pb, Zn) in soil elutriates, even in low concentrations, caused effects on L. sativa development. Unburned coal wastes and downhill soil elutriates were able to inhibit the germination of L. sativa and affect them individually and sub-individually (decrease in size, biomass, and presence of morphological alterations). Additionally, it was observed that all soil elutriates induce a decrease in root size. The results highlight the importance of using elutriate samples in phytotoxicity studies of coal mining waste, since the tailings lixiviate may reduce plant establishment and growth, affecting the terrestrial ecosystems. The integrated use of seed germination assays with the analysis of morphological and biochemical alterations in plants proved to be sensitive parameters to evaluate the phytotoxicity of coal mining wastes.

Carboniferous to Early Permian tectono-sedimentary evolution in the western Junggar Basin, NW China: implication for the evolution of Junggar Ocean

The discovery of Carboniferous hydrocarbon source rocks in the Mahu-Shawan Sag has implied considerable exploration potential in the Carboniferous strata in the western Junggar Basin. However, controversy has long surrounded when and how the Junggar Ocean was eventually closed, leading to a poor understanding of the Carboniferous basin evolution and the continental growth of the Central Asian Orogenic Belt. We performed stratigraphic and geochronologic studies to establish the chronostratigraphic framework of the western Junggar Basin to better understand its tectonic-sedimentary evolution during the Carboniferous-Early Permian. Three tectonostratigraphic units in the southern West Junggar region have been identified as Early Carboniferous shallow-deep marine sequences, Late Carboniferous coast-shallow marine sequences, and Early Permian continental sequences. The Carboniferous strata are similar to forearc and backarc-rift sequences in the Western Fault Belt and the Mahu-Shawan Sag, respectively. The Lower Permian strata in the southern West Junggar region are all continental sequences. Seismic profiles indicate extensional settings in the early stage of Late Carboniferous and Early Permian but a compressional setting at the end of Late Carboniferous. Geochemical data have suggested a Carboniferous continental arc setting and an Early Permian within-plate extensional setting. Meanwhile, calc-alkaline arc magma migrated from the Zhongguai High to the Western Fault Belt at the end of the Late Carboniferous. Collectively, the tectonic-sedimentary evolution in the Carboniferous-Early Permian of the southern West Junggar region can be divided into three stages: 1) Early Carboniferous subduction, 2) Late Carboniferous slab roll-back, and 3) Early Permian intra-continental evolution stage. This model constrains the closure of the Junggar Ocean at the Late Carboniferous.

Florinanthus bussacensis sp. nov., a new cordaitalean cone from the Upper Pennsylvanian of Portugal

A new species of adpression cordaitalean cone is described from the Stephanian C (Upper Pennsylvanian) Vale da Mó “Formation” of the Buçaco Carboniferous Basin, central western Portugal. The macro- and micro-morphology of the new species, named Florinanthus bussacensis sp. nov., is described and its ontogenetic and palaeoecological significance assessed. The new cone species is erected on the basis of three primary axes with secondary fertile shoots with fimbriate apices. The number, linear-filiform shape and small size of the structures preserved on the distal parts of the scales suggests they represent pollen sacs, thus the new species F. bussacensis is considered to represent a male fructification. The new species is characterized by pollen sacs grouped in 4 to 5 clusters, composed of 4–7 basally fused sacs, and ovate to lanceolate-shaped sterile scales. The new cone seems to present different maturation states (mature to overmature) of its shoots, and its association with Cordaites leaves and Carpolites and Cardiocarpus seeds/ovules, suggests the new species was probably produced by the same parent plant species. The morphological and taxonomic diversity of the Pennsylvanian Cordaitaceae fructifications in western Variscan Euramerica remains largely unclear, due to the difficult recognition of these structures in the fossil record. This is the second record of a cordaitalean cone in the Carboniferous of Portugal, despite the abundance of cordaitalean remains (mainly of leaves, seeds, stems and roots) in its sequences. The difficult recognition of these structures in poor preservation conditions can easily make them go unnoticed and is more likely to be this the cause of their poor knowledge than a hypothetical limited record.

"Carbonífero de Puertollano" Natural Monument (Puertollano basin, Spain): a window for the knowledge of Early Vertebrates

Coal mining at the Puertollano Carboniferous basin has led to the discovery and study of numerous fossiliferous layers, rich in chondrichthyan, actinopterigyan and tetrapod remains. The end of the mining operations and closure of the mines could also represent complete cease of paleontological prospections and field work at the Puertollano basin. Fortunately, three quarries, called María Isabel, La Extranjera and La Tejera, have been declared a Natural Monument. Consequently, they are protected by law and reserved for geological and palaeontological scientific research. In this paper, we describe the geology of the Natural Monument and its vertebrate fossil record. The outcrops of the three quarries show the most superficial part of the stratigraphic series so that they inform about the latest stages of the sedimentological and palaeogeographical evolution of the Puertollano basin. The actual coal basin appears to represent a remnant of a much larger basin which opened eastward to the Paleo-Tethys. The diverse chondrichthyan assemblage (acanthodians, xenacanths and euselachians) and euryhaline actinopterygians, and the presence of tidal rhythmites, indicate an estuarine-deltaic environment. Future sedimentological and paleontological studies at the Natural Monument will inform about the degree of marine influence in the basin and the changes of the vertebrate communities.

Experimental study of the influences of different factors on the acid-rock reaction rate of carbonate rocks

The Sichuan Basin's carbonate gas reservoirs require stimulation. Non-uniform etched fractures are created as a result of the violent interaction between reservoir cores and an acidic fluid, and these fractures provide pathways for the flow of oil and gas. Focusing on the long distance and high conductivity of acid fracturing, in this study, based on the geological characteristics of the carbonate rocks in the Sichuan Basin and engineering requirements, a rotary disc instrument was used to conduct an experimental study of the acid-rock reaction rate under different temperature (40 °C, 65 °C, 90 °C, 115 °C, 150 °C), acid concentrations (12 %, 16 %, 20 %, 24 %), rotation speeds (125 rpm, 208 rpm, 291 rpm, 375 rpm), common ion effect values, and types of acid (conventional acid, gelled acid, diverted acid, cross-linked acid), focusing on the changes in the acid-rock reaction rate with the various parameters. The research shows that conventional acid had the fastest acid-rock reaction rate, which was 1.85 times that of the gelled acid, 1.94 times that of the diverted acid, and 3.03 times that of the cross-linked acid. To obtain a correct understanding of the acid-rock reaction kinetics, experimental investigation of the effects of the various parameters on the reaction rate is essential.

Prestack Seismic Velocity Ratio Evaluation of a Mixed Siliciclastic–Carbonate Formation: Case Study from the Strawn Group on the Eastern Shelf Texas

Although a mixed carbonate–siliciclastic system of the Strawn Group on the Eastern Shelf in King County, Texas, USA provides excellent hydrocarbon reservoirs, facies variability and reservoir properties within such systems are not well understood. We conducted prestack, simultaneous seismic inversion, and high-level petrophysical analysis to derive elastic properties of rocks to facilitate lithology identification and determination and distribution of the different carbonate facies. Our results show that (1) the Strawn Group in King County is dominated mostly by carbonates and (2) given the ratio of P- and S-wave velocity (Vp/Vs ratio), the carbonates can be separated into three facies: (a) high-Vp/Vs-ratio shelf-edge reef carbonates, in which the Vp/Vs ratio decreases linearly as porosity increases and the Vp/Vs ratio varies from ~2.1 to ≤2.6; (b) moderately low-Vp/Vs-ratio shelf (platform) carbonates, in which the Vp/Vs ratio also decreases as porosity increases and in which the Vp/Vs ratio ranges from ~1.75 to ≤2.15; (c) extremely low-Vp/Vs-ratio slope and basin carbonates, in which the Vp/Vs ratio, although appearing to be almost constant for a wide range of porosity, increases as porosity increases, and in which most Vp/Vs-ratio values appear to range from ~1.5 to ≤2. Results of a through c can be summarized thusly: the Vp/Vs ratio of reef carbonates &gt;the Vp/Vs ratio of platform carbonates and &gt;the Vp/Vs ratio of slope and basin carbonates in the study area.

Seminal infrared-based chemometric analysis of oxygen-bearing structural groups in vitrain samples from ten successive coal seams (Sydney Coalfield, Canada)

Reported are seminal results of a systematic application of infrared spectrometry to a succession of coal seams in a Carboniferous basin from Sydney Coalfield, Nova Scotia, Canada. Fifty-four lithotypic vitrain samples from ten successive coal seams were analyzed by solid-state (potassium-bromide pellet method) Fourier transform infrared spectroscopy and evaluated using principal-component analysis to explore chemical fingerprints of vitrain structural-group contents and distributions. At this level of sampling, the 3D principal-component analysis and ANOVA tests identified chemical structural-group changes related to relatively low contents of aliphatic and oxygen-bearing compounds. These probably confirm, for data represented by “younger” seams, the moderate thermal histories (0.75–0.90 Ro %) from which minimal diagenetic alterations are inferred in the preservation of fossils in the roof rocks of the coal seams. It is concluded that, throughout the lithostratigraphic column, the continual vertical changes in vitrain structural-group composition are related to some changes in the species diversity of the associated macroflora that filled niches in the peat-producing lower flood plains.