Carboniferous Basin Research Articles

Pulmonary oxidative stress in wild bats exposed to coal dust: A model to evaluate the impact of coal mining on health.

This study aimed to verify possible alterations involving histological and oxidative stress parameters in the lungs of wild bats in the Carboniferous Basin of Santa Catarina (CBSC) state, Southern Brazil, as a means to evaluate the impact of coal dust on the health of wildlife. Specimens of frugivorous bat species Artibeus lituratus and Sturnira lilium were collected from an area free of coal dust contamination and from coal mining areas. Chemical composition, histological parameters, synthesis of oxidants and antioxidant enzymes, and oxidative damage in the lungs of bats were analyzed. Levels of Na, Cl, Cu, and Br were higher in both species collected in the CBSC than in the controls. Levels of K and Rb were higher in A. lituratus, and levels of Si, Ca, and Fe were higher in S. lilium collected in the carboniferous basin. Both bat species inhabiting the CBSC areas exhibited an increase in the degree of pulmonary emphysema compared to their counterparts collected from control areas. Sturnira lilium showed increased reactive oxygen species (ROS) and 2',7'-dichlorofluorescein (DCF) levels, while A. lituratus showed a significant decrease in nitrite levels in the CBSC samples. Superoxide dismutase (SOD) activity did not change significantly; however, the activity of catalase (CAT) and levels of glutathione (GSH) decreased in the A. lituratus group from CBSC compared to those in the controls. There were no differences in NAD(P)H quinone dehydrogenase 1 protein (NQO1) abundance or nitrotyrosine expression among the different groups of bats. Total thiol levels showed a significant reduction in A. lituratus from CBSC, while the amount of malondialdehyde (MDA) was higher in both A. lituratus and S. lilium groups from coal mining areas. Our results suggested that bats, especially A. lituratus, living in the CBSC could be used as sentinel species for harmful effects of coal dust on the lungs.

Santonian-Maastrichtian carbon-isotope stratigraphy and calcareous nannofossil biostratigraphy of the Zagros Basin: Long-range correlation, similarities and differences of carbon-isotope trends at global scale

Abstract A high-resolution study of carbon isotope stratigraphy and calcareous nannofossil biostratigraphy has been undertaken on the Upper Cretaceous sediments of the Gurpi Formation (Fm.) in the Bowan section (Zagros Basin, Iran). The integrated stratigraphy of the section allows for large-scale correlation with Upper Cretaceous reference sections (Gubbio, Italy; German Chalk; Shahneshin, Iran) and suggests the age of the Gurpi Fm. at Bowan to be latest Santonian to early Selandian. Correlation of the isotopic data from Bowan to the Shahneshin section in the central Zagros mountains shows remarkable similarity that may be related to effects specific to the peculiar stratigraphy of the area and, possibly, to the long-term evolution of seawater δ13C in the Zagros Basin. A sequence stratigraphic framework is proposed for both sections. Correlation of the two sections to data from the Boreal realm, Indian Ocean, equatorial Pacific Ocean, and other Tethyan sections suggests that it is possible to identify some of the previously defined major carbon isotope events in the Iranian sections. Significant differences, however, are observed in absolute values and overall amplitude of carbon isotope trends. In particular, our results show that the Santonian/Campanian boundary event (SCBE) which is a well-defined, double-peaked, positive excursion at Gubbio and in the Boreal realm is absent in the Zagros Basin, eroded by a major sequence boundary. Moreover, the most pronounced feature in Upper Cretaceous carbon isotope ratios of the Zagros Basin carbonates is an overarching maximum culminating in the early Campanian which correlates with a discrete, low-amplitude (0.25‰) positive excursion defined as the papillosa Zone event at Gubbio and in the Boreal realm. Our results thus reveal a contrasting evolution of carbonate δ13C during the early Campanian between different oceanic basins but also within the Tethys.

Pressure transient analysis of acid fracturing stimulated well in multilayered fractured carbonate reservoirs: A field case in Western Sichuan Basin, China

In this paper, we propose a novel analytical model to characterize the bottom-hole pressure (BHP) behavior of acid fracturing stimulated wells in the multilayered fractured carbonate reservoirs. The inter-porosity flow between fracture and matrix, and the crossflow in acid fracturing stimulated zone and unstimulated zone are simultaneously captured. The Bessel functions, Laplace transform, and inversion algorithm are deployed to solve the acid fracturing stimulated model for multilayered fractured carbonate reservoir. Nine flow regimes are identified in the type curves. Compared with current acid fracturing stimulation models for fractured carbonate reservoir, this model has additionally inner crossflow and outer crossflow regimes. Results show that the crossflow obviously affects the concave characteristics in the middle flow stage. The bigger the crossflow coefficient is, the earlier the crossflow regime appears. The pressure derivative value for outer radial flow is found as 0.5 times of the high-permeability layer (HLP) mobility ratio, which provides us a straightforward indication for the determination of acid fracturing stimulation degree. Finally, a field case from the Western Sichuan Basin carbonate reservoir are discussed in detail to validate the capabilities of our model.

Basin filling evolution of the central basins of Mallorca since the Pliocene

AbstractA new compilation of data from 436 drill cores using decompaction and backstripping techniques was used to reconstruct the basin filling history from the Pliocene until the present day in the Palma, Inca and Sa Pobla Basins on the island of Mallorca (Spain). Calcareous rocks dominate the source area and provide a limited amount of clastic input to the basins that has resulted in an average accumulation rate of between 5 and 20 m/Ma during the last 5.3 Ma. Carbonate sediment production dominated the basin filling history during early‐mid Pliocene, but during the Quaternary, the sedimentation processes in the Palma Basin were probably enhanced by an evolution in the drainage network that increased the sediment supply and the accumulated thickness caused by stream capture. However, the maximum sedimentation rate filling the depocentres of the three basins has been decreasing since the Pliocene, showing that not only the catchment transport efficiency but also the relative sea level have been controlling the sediment accumulation in these carbonate basins. The isopach cross‐sections support the idea that a palaeorelief was generated during the Messinian sea level drop and that heterogeneities were filled in from the Pliocene to the Quaternary. We conclude that the central basins of Mallorca were filled heterogeneously due to tectonic and geomorphic processes that controlled sediment transport and production, resulting in different average sedimentation thicknesses that decreased since the Pliocene as the accommodation space became filled and the relative sea level dropped.

Distribution of brachiopods in the Lower Visean deposits in the Eastern Urals

Subject. This paper is aimed at investigating the distribution of brachiopods across the stratotypes of the Lower Visean regional substages and formations, as well as of the Upper Visean Zhukovsky regional substage, which are presently located in the East Uralian and Magnitogorskian megazones of the Eastern Urals. Materials and methods. Brachiopods were one of the most numerous groups of benthic organisms inhabiting the Early Carboniferous marine basins now located in the eastern Urals. This paper presents information on the distribution of brachiopods across the carbonate and carbonate-terrigenous facies of the Middle (Pokrovskoe, Zhukovo, Smolino, Brod-Kljuchiki) and Southern (Nizhnyaya Gusikha, Verkhnyaya Kardailovka, Kipchak, Ust-Grekhovka and Khudolaz) Urals sections.Results. It is found that Delepinеа lebedevi, D. comoides, Ovatia markovskii and Composita sp. were the domineering species during the Early Visean period. The Ust-Grekhovsky time marked the appearance of migrant species, which resulted not only in a decrease in the proportion of Delepinеа and Ovatia but also significantly changed the entire structure of the local brachiopod communities. The evolutionary transformation of the Ovatia genus at the Ust-Grekhovsky–Zhukovsky time boundary led to the appearance of the Linoprotonia genus and subsequently to the Globosoproductus genus (the first representative of the Gigantoproductini). The Zhukovsky period was characterized by a continuing reorganization of the composition and structure of the communities, featuring a change in the dominant taxa. The Linoprotonia and Globosoproductus genera became widespread. Rare representatives of the Gigantoproductus, Datangia and Semiplanus genera appeared.Conclusions. A direct correlation between the diversity of brachiopod associations and abiotic factors is found. The most diverse associations represented by the taxa of several orders, including Gigantoproductini, inhabited shallow-water environments with carbonate sedimentation. The evolution of brachiopods over the Early Visean and Zhukovsky periods of the Late Visean was characterized by natural succession in the composition of genera and species, with the most significant alteration having occurred in the Ust-Grekhovsky and Zhukovsky periods.

Structural and geodynamic modelling of the influence of granite bodies during lithospheric extension: Application to the Carboniferous basins of northern England

Intra-basinal highs within classic ‘block and basin’ style tectonic frameworks are underpinned by large granite bodies. This is widely believed to relate to the relative ‘rigidity’ and ‘buoyancy’ of granite in relation to accommodating basement. It has been suggested that during periods of tectonic extension, normal faulting around the peripheral regions of granite batholiths permits granite-cored blocks to isostatically resist subsidence, thus forming stable areas during periods of widespread faulting-induced subsidence. However, one-dimensional modelling indicates that relatively less dense crust is incapable of resisting subsidence in this way. Instead, when local isostasy is assumed, the occurrence of granite-cored, intra-basinal highs relates to initial isostatic compensation following granite emplacement. Differential sediment loading during extensional tectonism exaggerates this profile. An integrated two-dimensional lithospheric numerical modelling approach highlights the role of flexural rigidity in limiting the amplitude whilst increasing the wavelength of isostatic deflection. In light of these models, it is suggested that such a response leaves residual second-order stresses associated with the under-compensated buoyancy of the granite body and flexural tension. The observed basin geometries of the Carboniferous North Pennine Basin can be replicated by incorporating a density deficiency within the crust, flexural rigidity, simple shear deformation within the shallower subsurface and pure shear deformation within the deeper subsurface. In adopting this technique, the regional flexural profile in response to underlying granite bodies and large extensional faults can be reproduced and thus, to an extent, validated. It is proposed that the interaction of three factors dictate the tectonic framework within a partially granitic, brittle-ductile lithosphere and the occurrence of inter-basinal highs: 1) non-tectonic, ‘second-order’ stresses such as the flexural response of the lithosphere and residual, under-compensated buoyancy forces in relation to granite bodies; 2) extensional tectonic stress and importantly; 3) inherited basement fabric.

A Comparative Study of CO2-Flood Displacement Efficiency for Different CO2 Injection Strategies: Permian Basin vs. U.S. Gulf Coast

In CO2-EOR, there are two main field development strategies: water-alternating-gas (WAG) and continuous gas injection (CGI). The aim of our study is to compare these strategies in terms of their economic performance (from the basis of incremental oil recovery) and in terms of their environmental performance (from the basis of ultimate CO2 storage volumes). Within this framework and to demonstrate the efficiency of each strategy, we evaluate the distribution of Carbon Dioxide in oil, gas, and brine phases; the amount of total CO2 stored at the end of the project; the incremental oil recovery; and the CO2 utilization ratios. In this study, we model and compare two fields which represent two different reservoir settings: Cranfield (representative of the U.S. Gulf Coast sandstone reservoirs) and SACROC (representative of the Permian Basin carbonate reservoirs). CGI is the original operating strategy in Cranfield and WAG is the original operating strategy applied in the SACROC unit. High resolution geocellular models are used for both Cranfield and SACROC fields. The models are constructed based on wire-line logs, seismic surveys, core data, and stratigraphic interpretations. A comprehensive pressure-production history matching for primary, secondary, and tertiary recovery is conducted for both of the fields. Different operating strategies are designed for each field (e.g. CGI and WAG). After finishing the history-matching, CGI and WAG scenarios are simulated in both models to compare their performances. CO2 partitioning in oil, brine, and gas phase (mobile or residual) are compared for both scenarios (WAG and CGI). The partitioning of CO2 in oil results in CO2 miscibility in oil, the partitioning of CO2 in brine results in CO2 dissolution in brine, and CO2 partitioning in gas phase are divided into structural trapping and residual trapping of CO2. We plotted the contribution of different trapping mechanisms over a post injection period for WAG and CGI for both SACROC and Cranfield. Additionally, the total CO2 storage, the incremental oil recovery, and CO2 utilization ratios are compared in both scenarios for both fields. Although actual operating strategy in these two fields are different (CGI in Cranfield and WAG in SACROC), our numerical modelling results show that WAG could not only balance the CO2 storage, incremental oil recovery, and CO2 utilization ratio but also store the trapped CO2 with lower risk of leakage in both fields (by decreasing the amount of structurally trapped CO2). Because of multiple alternation of CO2 and water slugs in WAG, this approach reduces the viscous instability and therefore the efficiency of oil recovery. Our study shows that the distribution of CO2 in different phases is different for each field. Because of the lower minimum miscibility pressure (MMP) and lighter initial oil saturation in SACROC, the partitioning of CO2 in oil is much higher in SACROC than in Cranfield. The dissolution of CO2 in brine is much higher in Cranfield because of the presence of strong aquifer near injection wells. The present work provides valuable insights for optimizing oil production and CO2 storage in a CO2-EOR project. Additionally, this study clearly shows the impact of development strategies on the relative importance of different trapping mechanisms.

From widespread Mississippian to localized Pennsylvanian extension in central Spitsbergen, Svalbard

Abstract. In the Devonian–Carboniferous, a rapid succession of clustered extensional and contractional tectonic events is thought to have affected sedimentary rocks in central Spitsbergen, Svalbard. These events include Caledonian post-orogenic extensional collapse associated with the formation of thick Early–Middle Devonian basins, Late Devonian–Mississippian Ellesmerian contraction, and Early–Middle Pennsylvanian rifting, which resulted in the deposition of thick sedimentary units in Carboniferous basins like the Billefjorden Trough. The clustering of these varied tectonic settings sometimes makes it difficult to resolve the tectono-sedimentary history of individual stratigraphic units. Notably, the context of deposition of Mississippian clastic and coal-bearing sedimentary rocks of the Billefjorden Group is still debated, especially in central Spitsbergen. We present field evidence (e.g., growth strata and slickensides) from the northern part of the Billefjorden Trough, in Odellfjellet, suggesting that tilted Mississippian sedimentary strata of the Billefjorden Group deposited during active (Late/latest?) Mississippian extension. WNW–ESE-striking basin-oblique faults showing Mississippian growth strata systematically die out upwards within Mississippian to lowermost Pennsylvanian strata, thus suggesting a period of widespread WNW–ESE-directed extension in the Mississippian and an episode of localized extension in Early–Middle Pennsylvanian times. In addition, the presence of abundant basin-oblique faults in basement rocks adjacent to the Billefjorden Trough suggests that the formation of Mississippian normal faults was partly controlled by reactivation of preexisting Neoproterozoic (Timanian?) basement-seated fault zones. We propose that these preexisting faults reactivated as transverse or accommodation cross faults in or near the crest of transverse folds reflecting differential displacement along the Billefjorden Fault Zone. In Cenozoic times, a few margin-oblique faults (e.g., the Overgangshytta fault) may have mildly reactivated as oblique thrusts during transpression–contraction, but shallow-dipping, bedding-parallel, duplex-shaped décollements in shales of the Billefjorden Group possibly prevented substantial movement along these faults.

Extending the paleogeographic range and our understanding of the Neoarchean Monteville impact spherule layer (Transvaal Supergroup, South Africa)

AbstractThe Monteville spherule layer (MSL) was deposited in the Griqualand West Basin (GWB) on the Kaapvaal Craton approximately 2.63 Ga. The spherules were generated by a large impact and reworked by impact‐generated waves and/or currents. The MSL has been intersected in three previously undescribed cores. Two of the cores, GKF‐1 and GKP‐1, were drilled ~30 km west of the southernmost outcrop of the MSL. The third core, BH‐47, was drilled ~250 km south and east of the GWB. The MSL contains medium to coarse sand‐size spherules like those described previously in all three cores but each one was emplaced in a different way. In GKF‐1, the MSL is 90 cm thick and contains large rip‐up clasts of basinal carbonate and early diagenetic pyrite. In GKP‐1, the MSL is only 1.5 cm thick and consists largely of fine carbonate sand, yet it contains pyrite intraclasts up to ~1 cm long. In BH‐47, the MSL consists of a lower coarse sandy zone ~37 cm thick rich in spherules, carbonate peloids/ooids, pyrite intraclasts, and quartzose sand and an upper, finer sandy zone ~46 cm thick; neither zone contains any large intraclasts. The new occurrences triple the known extent of the MSL from ~15,000 to ~46,000 km2, support the oceanic impact model for the formation of the MSL, demonstrate that it is a persistent regional time‐stratigraphic marker, place new constraints on the Kaapvaal paleoshoreline at the time of impact, and support the existence of Vaalbara.

The Geological Evolution of the Variscan Jebilet Massif, Morocco, Inferred From New Structural and Geochronological Analyses

AbstractThe present work aims at understanding the tectonic evolution of the Jebilet massif, Morocco, during the Late Paleozoic as constrained by structural, metamorphic, and geochronological studies. From Late Devonian to Early Carboniferous, bordering faults controlled the opening of the Jebilet intracontinental basin (D0 stage) as shown by sedimentary infill. This episode was accompanied by a magmatic activity, newly dated between 358 ± 7 Ma and 336 ± 4 Ma. The first record of the Variscan event affected the Jebilet by the Late Visean‐Namurian and is represented by allochthonous superficial nappes emplaced at shallow depth in a moderately lithified sedimentary succession. D1 also developed regional‐scale recumbent folds trending E‐W that may suggest N‐S crustal shortening not generating crustal thickening nor contributing to metamorphism. The main Variscan D2 episode consists of a progressive evolution from bulk coaxial deformation to noncoaxial dextral transpression consistent with NW‐SE horizontal shortening, resulting in a moderate thickening. This episode was accompanied by HT‐LP metamorphism and syntectonic intrusions controlled by an inherited thermal anomaly in relation with the intracontinental rifting stage (D0). Based on previous age determinations from syntectonic leucogranite and metamorphic rocks, D2 is dated between 310 and 280 Ma. The tectono‐metamorphic evolution of the Jebilet massif can be correlated with a plate‐tectonic scenario evolving from, first a Late Devonian‐Early Carboniferous basin formation during stretching of the north‐Gondwana margin and initiation of the Paleotethys Ocean, and, second, to a Late Carboniferous‐Early Permian ocean closure (Rheic or Paleotethys Oceans depending of scenarios) that resulted in the final Variscan‐Alleghanian tectonics.

English

The intense exploitation of coal deposits in Southern Brazil has caused severe degradation problems in extensive areas. In order to recover such areas, the use of revegetation with species adapted to disturbed environments and with the capacity to establish mutual relationships with microorganisms have been of great value. The objective of this study is to characterize plant-root symbioses in two grass-legume (Calopogonium mucunoides with Brachiaria decumbens and Vicia sativa with Brachiaria decumbens) consortia inoculated with soil of the Carboniferous Basin in the state of Santa Catarina. Areas evaluated were at different stages of land reclamation and the influence of those consortia on the occurrence of rhizobia, arbuscular mycorrhizal fungi, and in the community of endophytic bacteria were evaluated. The study was done in two independent experiments in a completely randomized design, with five replications; done under greenhouse condition. There were seven treatments - five inoculated (with soil obtained from areas of 2, 4, 6 and 12 years of recovery, and a reference area) and two control treatments without inoculation (with low and high concentrations of mineral nitrogen). After 50 days of implantation, soil and plant material were collected to characterize root symbioses by nodule counting, nitrogen fixing bacteria isolation, mycorrhizal occurrence (%), and characterization of root endophytic bacterial communities. Only the calopogonium-brachiaria consortium was able to nodulate with rhizobia from the recovering coal mining areas. Arbuscular mycorrhizal fungi (AMF) and endophytic bacteria occur in the vetch-brachiaria and calopogonium-brachiaria consortia regardless of the time of recovery. The microbial communities present in soils with different stages of recovery are more efficient in promoting plant growth in the calopogonium-brachiaria consortium and this behavior may be associated with the calopogonium's ability to associate with autochthonous rhizobia. Key words: Environmental recovery, revegetation, plant-growth-promoting, rhizobia, arbuscular mycorrhiza.

The dismantling of the Apulian carbonate platform during the late Campanian – early Maastrichtian in Albania

The Apulian carbonate margin is widely preserved across the Adriatic domain and has been extensively studied in the south of Italy. In Albania, Oligocene–Pliocene fold-and-thrust tectonics led to widespread exposure of the Apulian Platform and associated Ionian Basin carbonates. However, the portion linking the platform to the basin is missing, preventing a direct reconstruction of the platform margin. Syn-sedimentary folding and faulting are recognized in the uppermost part of both the platform and basinal/slope series. Mass transport deposits (MTDs) occur within the platform succession incorporated into well-bedded intertidal (stromatolites) to shallow-subtidal (rudist packstones) sedimentary sequences. They display significant lateral variability which is accompanied by both rigid and soft deformation structures. Spectacular slumps made up of sediment density flow deposits are recognized in the adjacent Ionian Basin. The lateral extent of basal shear surfaces, syn-sedimentary faults and folds evidenced in the Ionian Basin points toward multiple regional tectonic triggering events affecting the Apulian Platform margin at that time. Bio- and chrono-stratigraphic analyses suggest that the triggers occurred during the late Campanian – early Maastrichtian. Beyond the obvious interest from a stratigraphic point of view, the study of these events recording the dismantling of the Apulian carbonate platform allows for a better understanding of the triggering mechanisms and the sedimentary characteristics of MTDs and slumps at a basinal scale.

Establishing a geochemical baseline for the Lower Carboniferous stratigraphy of the Rathdowney Trend, Irish Zn-Pb orefield

Carbonate-hosted Zn-Pb mineralisation within strata of the Irish Midlands can be subdivided between deposits forming on either Lower Carboniferous basin margin. Those on the southern side, known as the Rathdowney or Lisheen trend deposits, are hosted within the Waulsortian Mudbank formation and have been exploited for over 35 Mt of massive sphalerite-galena-pyrite ore since the 1960s. Additional occurrences of Irish-style mineralisation along the Rathdowney trend are numerous; however, questions remain regarding the extent and geochemical signature of the accompanying alteration haloes as, until now, no geochemical baseline was established.Preliminary results from Rapla, an exploration prospect 15 km northeast of the decommissioned Lisheen mine, show that an unaltered stratigraphical geochemical baseline can be distinguished using bulk 4-acid ICP-AES/MS data, thus a chemostratigraphic sequence can be derived from select major elements (Ca, Mg, Al) and ΣREE concentrations. With Eu and Ce anomalies and redox sensitive elements (Mo-U-V) providing environmental conditions during formation.pXRF analysis on the sample pulps show >95% precision of 15 elements. Of these 5 elements display >90% accuracy (Al, Ti, Fe, Cu, Rb), 4 elements >80% accuracy (K, As, Cd, U), and finally 6 elements at >50% accuracy (S, Ca, Mn, Zn, Se, Sr). Therefore confidence in data collected from powdered samples from rocks of this type by pXRF is high.

Carbonate seismic sedimentology: A case study of Cambrian Longwangmiao Formation, Gaoshiti-Moxi area, Sichuan Basin, China

This study applied seismic-sedimentological workflow to deeply buried marine carbonate sequences in western China. The workflow aimed at integrating core, wire line log and 3D seismic data to investigate the paleogeomorphology qualitatively and reservoir thickness quantitatively in the carbonate systems. In Gaoshiti-Moxi area of Sichuan Basin, the Longwangmiao Formation was formed in sedimentary environment of carbonate platform facies. Lithofacies vary from dolomitized grainstone to mudstone, which formed shoal, lagoon, and deep shelf sub-facies. The high-porosity (porosity > 4%) reservoir rocks are related to shoal sub-facies. Seismic geomorphology was employed to restore paleostructure of Longwangmiao Formation in the study area by methods of cast and isopach, which were calibrated by well data. It was found that the paleogeomorphology and depositional facies were largely controlled by a syndepositional, en echelon fault system. Following the strategy of seismic lithology, quantitative distribution of reservoir rocks and sedimentary facies was assessed by applying principle component analysis on amplitude attributes generated from multiple frequency panels. Seismic prediction of diagenetic facies (selective dissolution) was achieved by interpreting similarity variance, a seismic geometric attribute. In summary, the procedure, combining seismic geomorphology and seismic lithology, is effective and can be used as a reference for seismic-sedimentological study in other carbonate basins in China and elsewhere.

Reconstruction of a Late Jurassic–Early Cretaceous carbonate platform margin with composite biostratigraphy and microfacies analysis (western Sakarya Zone, Turkey): Paleogeographic and tectonic implications

During Late Jurassic–Early Cretaceous the Pontides were the site of a wide carbonate platform facing the Tethys ocean in the south. In the western Pontides the Upper Jurassic–Lower Cretaceous shallow marine carbonates abut the Tethyan İzmir-Ankara suture with no evidence for platform margin deposits. The Sivrihisar klippe 50 km south of the İzmir-Ankara suture preserves a record of the missing platform margin. In the Upper Jurassic–Lower Cretaceous carbonates exposed in this Sivrihisar klippe, two coeval but dissimilar rock packages, separated by a thrust fault, have been detected. The lower succession is composed of Kimmeridgian–Valanginian slope to basin deposits. Within these carbonates the following biozones are defined: Globuligerina oxfordiana – Mohlerina basiliensis Zone (Kimmeridgian), Saccocoma Zone (lower Tithonian), Protopeneroplis ultragranulata Zone (upper Tithonian), Crassicollaria Zone (massutiana Subzone – uppermost Tithonian), Calpionella Zone (alpina, Remaniella, elliptica Subzones – lower Berriasian), Calpionellopsis Zone (simplex, oblonga Subzones – upper Berriasian) and Calpionellites Zone (darderi Subzone – lower Valanginian). These slope to basin deposits are overthrust from north to south by Kimmeridgian shallow marine carbonates. Within this unit Labyrinthina mirabilis – Protopeneroplis striata Zone (Kimmeridgian) is recognized. Based on the distribution of microfacies types and fossil assemblages, a Kimmeridgian–Valanginian depositional model is proposed for the western Sakarya Zone Carbonate Platform (SCP). The position of the studied sections with respect to the SCP, biofacies and microfacies associations suggest that the studied basin and slope deposits represent the remnants of the southern margin and slope of this carbonate platform largely truncated by erosion. The slope and basinal carbonates overthrusted by the coeval shallow marine deposits in a region situated to the south of the main İzmir-Ankara suture indicates an important imbrication and shortening related to the closure of the Tethys ocean.

Low-temperature thermochronology of Anticosti Island: A case study on the application of conodont (U-Th)/He thermochronology to carbonate basin analysis

Abstract The Ordovician to Silurian carbonate succession preserved on Anticosti Island is a near continuous record of the changing depositional and tectonic history of the Early Paleozoic Laurentian margin. These strata are a prime natural laboratory to test the applicability of conodont apatite (U-Th)/He thermochronology (CAHe) for carbonate basin analysis in a setting with a well-understood burial history and abundant paleotemperature constraints. We report 63 CAHe dates from seven samples collected from two boreholes. X-ray micro-computed tomography (XR-μCT) was used to assess individual conodont element size, volume and alpha ejection correction. CAHe dates are negatively correlated with effective uranium concentration (eU), with single conodont dates enigmatically older than the age of deposition to conodont dates as young as 2.7 ± 0.2 Ma. We rationalize this dispersion as a product of several factors, including diagenetic processes and pervasive conodont crystalline porosity and permeability. Additionally, one basement and two sandstone samples were collected for apatite and zircon (U-Th)/He (AHe, ZHe) and apatite fission track (AFT) thermochronology. In the Precambrian basement, ZHe dates range from 581.7 ± 46.5 Ma to 761.2 ± 60.9 Ma (n: 4) and AHe dates range from 26.7 ± 1.6 to 48.4 ± 2.9 Ma (n: 4). AHe dates from two Lower Ordovician sandstones (n: 8) are positively correlated with eU, increasing from 13.7 ± 0.8 Ma to 105.2 ± 6.3 Ma over a range of 186 ppm eU. Thermal history modeling of these data suggests two plausible thermal histories, both of which are novel as they imply that far-field effects related to the opening of the Atlantic Ocean have influenced the thermal history of Anticosti Island. Ultimately, these data highlight the complexities associated with, and necessity of, low-temperature thermochronology in carbonate basins.

Internal architecture of mass‐transport deposits in basinal carbonates: A case study from southern Italy

AbstractSubmarine mass‐transport deposits represent important stratigraphic heterogeneities within slope and basinal sedimentary successions. A poor understanding of how their distribution and internal architecture affect the fluid flow migration pathway may lead to unexpected compartmentalization issues in reservoir analysis. Studies of modern carbonate mass‐transport deposits mainly focus on large seismic‐scale slope failures; however, the near‐platform basinal depositional environment often hosts mass‐transport deposits of various dimensions. The small‐scale and meso‐scale (metres to several tens of metres) carbonate mass‐transport deposits play a considerable role in distribution of sediment and therefore have an impact on the heterogeneity of the succession. In order to further constrain the geometry and internal architecture of mass‐transport deposits developed in near‐slope basinal carbonates, a structural and sedimentological analysis of sub‐seismic‐scale mass‐transport deposits has been undertaken on the eastern margin of the Apulian carbonate platform in the Gargano Promontory, south‐east Italy. These mass‐transport deposits, that locally comprise a large proportion (50 to 60%) of the base of slope to basinal sediments of the Cretaceous Maiolica Formation, typically display a vertically bipartite character, including debrites and slump deposits of varying volume ratios. A range of brittle and ductile deformation styles developed within distinct bed packages, together with the presence of both chert clasts, folded chert layers and spherical chert nodules, suggest that sediments were at different stages of lithification prior to downslope movement associated with mass‐transport deposits. This study helps elucidate the emplacement processes, frequency and character of subseismic‐scale mass‐transport deposits within the basinal carbonate environment, and thereby reduces the uncertainties in the characterization of subsurface carbonate geofluid reservoirs.

Along strike behavior of the Tizi n’ Firest fault during the Lower Jurassic rifting (Central High Atlas Carbonate basin, Morocco)

The purpose of this study is to document the along-strike early syn-rift history of the Lower Jurassic Carbonate basin of the Central High Atlas (Morocco) by combining sedimentological observations and high-resolution biostratigraphy. Six sections, each from the Sinemurian to the Upper Pliensbachian, were investigated along a 75 km-long transect at the hanging wall of a major fault of the Lower Jurassic Basin (i.e. the Tizi n’ Firest fault). Depositional geometries of the early syn-rift deposits were reconstructed from the correlation between eight main timelines dated by biochronological markers for a time span covering about 6 Ma. Depocentre migration was examined and accommodation rates were calculated at the sub-zone timescale to discuss the along-strike-fault behavior of the Lower Jurassic basin formation. The early stages of extension are marked by contrasted along-strike variations in depositional geometry thickness, depocentre migration and accommodation rates, leading to the growth of three independent sub-basins (i.e. western, central, and eastern), ranging in size from 30 to 50 km, and displaying three contrasted tectono-sedimentary histories. Our results suggest that, during the early rifting phase, tectonic activity was not a continuous and progressive process evolving towards a rift climax stage, but rather a series of acceleration periods that alternated with periods of much reduced activity. The length of active fault segments is estimated at about 15–20 km, with a lifespan of a few ammonite sub-zones (> 2–3 Ma).

A comparison of the relationship between measured acoustic response and porosity in carbonates across different geologic periods, depositional basins, and with variable mineral composition

Recent work has shown that there is a predictable inverse relationship between laboratory-measured sonic velocity response and porosity in carbonates, which can be reasonably approximated using the empirical Wyllie time-average equation (WTA). The relationship was initially identified in late Cretaceous to Cenozoic age samples collected from the Great Bahama Bank and the Maiella Platform, an exhumed Cretaceous carbonate platform in Italy. We have compared older carbonate samples from different basins and different geologic ages to determine the applicability of this relationship and subsequent correlations to key petrophysical properties to other carbonate basins and other geologic time periods. The data set used for the comparison shows this relationship to be relatively consistent in other depositional basins (Michigan Basin, Paradox Basin) and with samples from older geologic periods (Pennsylvanian, Ordovician, and Mississippian). However, this basic relationship is also observed to vary significantly within a reservoir system and within a depositional basin in samples from different geologic periods (e.g., Silurian- versus Ordovician-age rocks in the Michigan Basin). Although the empirical WTA can generally be applied as a first-order estimate across a wide range of sample ages in carbonates, limited data suggest the relationship between velocity and porosity to be moderately more complex. For instance, in unconventional carbonate reservoirs characterized by predominantly micro- to nanoscale porosity, it is observed that the WTA should be applied as an upper data boundary. In addition, this study has shown that the relationship to the dominant pore type is less direct than in a macropore system in which it can be assumed that the dominant pore type also has the greatest effect on the effective permeability.

Proterozoic carbonates of the Vindhyan Basin, India: Chemostratigraphy and diagenesis

The Vindhyan Basin of north-central India contains a thick, areally extensive, largely unmetamorphosed succession of sedimentary rocks deposited during the Proterozoic Eon. Despite a wealth of studies aimed at using Vindhyan Basin strata as an archive for Proterozoic global events, fundamental questions persist about basic aspects of Vindhyan Basin stratigraphy. Specifically, we lack detailed age constraints for units within the Upper Vindhyan succession, discrete correlation of units across the basin, and critical understanding of the extent to which diagenetic processes have compromised primary geochemical signals. Here, we focus on Vindhyan Basin carbonates—their chemostratigraphy and diagenesis. We present a new petrographic and geochemical dataset—including carbon isotopes, oxygen isotopes, and trace element signatures—for a variety of carbonate units exposed within the Vindhyan Basin, both in the Son Valley and Rajasthan sectors. Results of our diagenetic assessment indicate a range of preservation states in strata of the Lower Vindhyan sequence. The Bhagwanpura Limestone is pervasively dolomitized (largely fabric-destructive), and has been subjected to multiple generations of burial diagenesis in the presence of iron-rich, reducing fluids that altered oxygen isotope and trace element trends. By contrast, the Nimbahera Limestone is dominantly composed of micritic to microsparitic calcite that preserves largely marine isotopic and trace element signatures. The Tirohan Limestone is also pervasively dolomitized, but unlike the Bhagwanpura Limestone, dolomitization potentially occurred during early marine diagenesis, preserving seawater-like isotopic and trace element trends, with the exception of Sr depletion. Upper Vindhyan sequence carbonate units (the Lakheri and Bhander limestones) are largely characterized by micritic to microsparitic fabric-retentive microstructure, as well as isotopic and trace element trends that suggest diagenetic stabilization in the presence of marine fluids.Carbon isotope chemostratigraphy builds on previous work, and when interpreted in the context of recent geochronology, provides new information on the age of the Upper Vindhyan sequence. In the Lakheri Limestone, a stratigraphically coherent pattern of δ13C values between +2 and +3‰ with a minor negative excursion down to +1‰ is observed. This isotopic profile is consistent with global patterns of muted isotopic variability during the late Mesoproterozoic to earliest Neoproterozoic eras, thus supporting recent geochronology that suggests a much older age for the Upper Vindhyan sequence than traditionally thought, at least in the Rajasthan sector. Similar age revisions have recently been proposed for other ‘Purana’ basins in India. In Son Valley, however, strongly positive δ13C values (between +4 and +6‰) are recorded in the Bhander Limestone, suggesting that the Lakheri and Bhander limestones are not stratigraphic equivalents and that the Bhander Limestone may be fully Neoproterozoic in age. Ultimately, our data provide new diagenetic and chemostratigraphic information that will inform future studies of Vindhyan Basin strata.