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It is essential to identify marbles' petrographic and geochemical characteristics to determine the palaeo-environmental settings where their carbonate protoliths formed. The petrogenesis of massive Gimo marbles in the Gole area, Kurdistan Region of northeast Iraq, was investigated in this study through a combination of field mapping, petrographic, and geochemical techniques. Petrographic examination of these marbles reveals that mineral compositions are similar in all samples, with both homeoblastic and mosaic textures occurring, in addition to opaque grains that provide evidence of mineralization. Geochemical analyses show that the average calcium carbonate content of the marble is 94.96%; hence, the marble is lithologically characterized as a pure calcite marble. In most samples, the silica content was below 2 wt.%, with high values related to quartz veinlets. A range of geochemical indices and Post-Archean Australian Shale (PAAS–normalized rare earth element (REE) patterns) suggest that the limestone protolith was deposited in a shallow, near-shore marine environment on a continental margin, with very low input of detrital material. The negative Ce anomalies indicate that the protoliths of the Gimo marbles were carbonate rocks of a sedimentary origin.

The Middle to Late Eocene Mangahewa Formation in the Taranaki Basin has been evaluated for its petroleum system (source potential and reservoir qualities). The Mangahewa Formation is generally interpreted as an alternating marginal to shallow marine environment, with lithologies consisting of sandstone, siltstone, mudstone and bitumonius coal. The pyrolysis results show very good source rock generative potential with total organic carbon content of 0.8-90.02 wt. % and hydrogen index values in the range of 54- 491 mg HC/g TOC, with a predominance of oil- and/or gas-prone, mixed Type II-III kerogen. Organic petrographical data reveal that the humic nature of coals being rich in perhydrous vitrinite whereas shales are rich in alginite and bituminite desplaying frequent of migrabitumens. Biomarker analysis suggests predominantly terrigenous origin, whereas pyrolysis Tmax data (414–447°C) and other maturity indicators such as biomarkers and vitrinite reflectance indicates immature and mature samples. Petrographic analyses show that the occurrence of compaction and cementation is succeeded by leaching of feldspars and dissolution of calcite cement. The reservoir samples exhibit largely good reservoir quality with porosity being the dominant feature. The average porosity value is 15.7%, with 21.4% average water saturation. The source and reservoir units are part of a complete petroleum system of the Mangahewa Formation, with the overlying Turi Formation seal rock. The petroleum processes of maturation, generation, and migration which started since Lower Miocene (18.8 Ma) have been recorded in many stratigraphic traps within the Mangahewa Formation or other faulted structural traps due to migration. The generation process is expected to continue to the present day as the source continues to attain maturity while it does not yet reach the peak generation.

Fifteen samples of the Lower Cretaceous Balambo Formation from three sections in the Zagros Fold-Thrust Belt, Kurdistan Region of northern Iraq have been studied by means of organic petrography, in order to assess the type and the thermal maturity of the contained organic matter. The microscopic study revealed that most of the samples are poor in primary macerals but do contain frequent solid hydrocarbons. In terms of macerals, only bituminite-like particles, vitrinite, both indigenous and reworked, and fusinite are observed; additionally, three types of solid hydrocarbons occur, these of microgranular and homogenous migrabitumen, as well as pyrobitumen. The equivalent vitrinite reflectance (Eq.VR. %) of solid microgranular migrabitumen of the Baraw section ranges between 0.55 and 0.68%, of the Bn-1 section between 0.58 and 0.73%, and for the Sazan section, the Eq.VR. % value is 0.58%. The Eq.VR. % for solid homogenous migrabitumen was calculated for the Baraw and Sazan sections samples, ranging from 0.68 to 0.72% and from 0.65 to 0.67%, respectively, whereas the Eq.VR. % for the pyrobitumens of Baranan-1.G1 ranges from 0.87 to 0.96%. These values indicate that the organic matter of the Balambo Formation in the studied sections reached early mature to mature stage, and possibly, liquid hydrocarbons were generated.

Summary A new potential source rock formation was discovered in Ionian Zone, Epirus region, western Greece and its organic petrographic and organic geochemical characteristics were investigated. The formation lies between the overlying lower Liassic “Pantokrator Limestones” and the underlying Rhaetian “Pantokrator Dolomites”. It consists of alternating organic-rich black shale and less organic-rich gray dolomite/dolomitic sandstone beds. The organic geochemical results suggest high amounts (up to 35,56 wt.% TOC) of Type I and II/IIS organic matter, with a Hydrogen Index up to 790 mg HC/g rock and a high remaining generation potential (S2) of 237,4 mg HC/g rock. Based on the mean Tmax of 422⁰C and on %VRo-eq from solid bitumens, formation hasn’t entered the oil window in this part of the basin. Nevertheless, presence of Type IIS kerogen in some samples, indicate that certain intervals of the formation may already have entered oil window and produced liquid hydrocarbons. Relatively high clastic input may be indicative of a climatic shift towards seasonably controlled wetter conditions, as it is inferred from adjacent areas. This study suggests that the stratigraphic position and the geochemical characteristics are comparable to intervals in Albania and Italy, possibly indicating a source rock interval with regional significance.

Upper Jurassic Naokelekan Formation, being part of the intercepted strata of the well-known Miran oilfield in Kurdistan region of Northern Iraq, has been previously extensively evaluated as a potential/effective source rock, mainly by means of organic geochemistry. In the present study, a total of 60 samples were collected from four Naokelekan Fm. outcrops, those of Banik, Galy-Derash, Barsarin and Dwawa, in order to conduct organic petrographical study and organic geochemical assessment, including both biomarker and Rock-Eval analyses. The average recorded TOC content for Banik, Galy-Derash, Barsarin and Dwawa section is considerable to very high, corresponding to values of 27.5, 9.0, 3.5 and 5.2 wt%, respectively, with the highest values representing the notably organic-rich bottom part of the Formation, known as “coal layer”. According to the petrographical analysis, solid migrabitumens comprise the predominant component for all the analysed samples, whereas the maceral groups of vitrinite, liptinite and/or inertinite showcase a minor to trace occurrence. In terms of organic geochemistry, each of the four sections of interest shows a different biomarker profile. Nevertheless, a number of calculated parameters related to kerogen type and depositional conditions, including the isoprenoids/n-alkanes ratios, suggest a mixed terrestrial-marine organic matter. Furthermore, as indicated by the Ro (%) measurements along with Rock-Eval parameters and the vitrinite reflectance equivalent based on aromatic compounds, the maturity level is marginally mature in the cases of Banik and Galy-Derash, whereas in the cases of Dwawa and Barsarin sections it is mature to post-mature. A synthesis of the organic petrography and geochemical appraisal applied in the present study, suggests that the reported solid hydrocarbons in Naokelekan Fm., particularly at its basal layers are non-indigenous/migrated and the precursor organic matter was deposited in a marine environment, under oscillating conditions ranging from euxinic to well‑oxygenated. Accordingly, the organic features of the notably bitumen-rich “coal-bed” fit the profile of a reservoir and/or migration path., This research was supported by the University of Patras, Greece, the University of Soran, KRG-Iraq, INCAR, Spain, as well as from EU Erasmus + Programme.

A recent field study in Northeastern Iraqi Kurdistan revealed the extensive occurrence of fuchsite mineral in listvenite bodies within the Zagros Ophiolites. Mineralogical and geochemical analytical techniques were applied to describe the features of the fuchsite-rich phases in relation to the various listvenite lithotypes. Fuchsite occurs in two main types: (i) as pale green flaky form infilling intensively fractured zones (type I), and (ii) as pale to intense green primary mineral crystals within the listvenite (type II). The main paragenesis associated with fuchsite includes quartz and clinochlore with variable Cr content, calcite and/or dolomite, and spinel. The results of this study suggest that fuchsite and the associated Cr-rich clinochlore have been formed as a result of metasomatic reactions of Si- and K-rich fluids with Cr-rich serpentine and Cr-spinel due to hydrothermal alteration of serpentinized peridotite within the Zagros Ophiolites.

The characteristics of the source rocks in the early to late Miocene Belait Formation of Brunei Darussalam have been evaluated through the application of Rock-Eval and biomarker analyses, as well as by organic petrographical examination. Analyses have been performed on coal, coaly shale/carbonaceous claystones and shale samples from the Formation, retrieved from outcrops across the Brunei-Muara district, and covering a wide lateral extension of the Formation. The geochemical results indicate that the coal and some carbonaceous samples (with TOC from 14.1% to 67.7%) from the Belait Formation have “good to excellent” generating potential, quantity and quality, due to their high S2 and TOC values, which are consistent with the intermediate hydrogen index (HI) values ranging from 144 to 258 mg HC/g TOC. Organic material of “fair to good” quantity, quality and hydrocarbon generating potential is recorded for the coaly shale samples in the Belait Formation. Non-coal samples generally have the lowest potential as source rocks, due to their low TOC, HI and S2 values. Within the Formation, the coal layers together with a number of coaly shale and shale layers contain type III (gas prone) and type II-III (mixed oil and gas) kerogens. This is proven by the dominance of huminite, often of fluorescent varieties, which is confirmed though maceral analysis, as well as a trend of n-alkanes skewed towards heavier compounds. Evidence of the possible generation of liquid hydrocarbon is offered by the fact that liptinite is the second most abundant maceral group in most of the samples, as well as by the perhydrous nature of part of the huminite. Furthermore, kerogen type IV (dry gas) has been identified in a majority of the coaly shale samples. Facies analysis of the Belait Formation through the use of maceral indices and biomarkers data indicates that the coals were deposited in a mangrove setting in a lower delta plain, where mainly herbaceous and arboreal plants were growing. The depositional conditions were predominantly oxic, with a possible marine influence, and hence brackish conditions. All samples are found to be thermally immature to early mature, with Tmax values ranging from 356 °C to 441 °C, huminite reflectance values of up to 0.46% and high carbon preference index (CPI) values.

In this article, we report the discovery of a gossanite-type hematite and magnetite ore associated with sulfide mineralization in the Rayat area of NE Iraq. Detailed petrographic, mineralogical, and geochemical data define the features of the gossanite and the associated sulfide-rich rocks, providing an assessment of the mineralization and its relation to hydrothermal, microbial and alteration processes. The identified gossanite-like rocks are interpreted as part of a specific submarine gossan formed on the sulfide-rich serpentinite. In the uppermost part of the studied sequence, jasperite lithofacies occur, within which millimeter-thick layered iron oxide-silica alternations are also visible and comparable to the banded iron formation (BIF). Below the jasperite, an oxidized mineralized zone (OMZ) developed, representing gossanite that is exceptionally rich in iron oxides (up to 70%), chlorite, and quartz with some minor spinel content. The lowermost part of the studied sequence is the sulfide-rich reduced mineralized zone (RMZ) composed of silica, pyrite, chalcopyrite, pentlandite, Ni-chlorite, and siderite. The transition zone (TZ), approximately 1 m thick, between the OMZ and RMZ, contains chlorite, Fe-oxides, quartz, and partially altered sulfide minerals. The potential economic significance of the ore body in addition to Fe is the silver-nickel (Ag-Ni) and cobalt (Co) mineralization, with an average Ag concentration of 5.09 wt% per sulfide grain, which occurs as an exsolution phase within the sulfidic-cherts lithofacies. The Ni concentration ranged from 363 to 4,000 mg/kg, while that of Co ranged from 90 to 441 mg/kg, depending on the lithofacies. A thin lensoid coaly bed associated with the ore body, attributable to the Ophiolitic Melange, provides some initial clues for the epigenetic thermotectonic evolution of the studied strata. The overall data suggest that the Rayat gossanite, jasperite, and the underlying sulfide-rich zone were formed near the seafloor through a combination of initial hydrothermal alteration of serpentinites, which provided the sulfides, accompanied by the sedimentary deposition of Fe-Si-exhalatives along with the olistostromatic brecciated facies in the upper section, and the subsequent seafloor oxidation/weathering effects along microbial iron uptake. The discovery of gossanite and sulfides in the Rayat area, along with the already known chromitite deposits in the contiguous areas, highlights NE Iraq as a potential mineral-rich domain.

Upper Jurassic Naokelekan organic-rich strata are ubiquitous across the Kurdistan Region of Iraq. Laterally, continuous layers, of substantial thickness, outcrop in the highly folded and imbricated zones and in subsurface sections in the Low Folded Zone. In this study, 15 samples from 5 outcrops, viz., Barzinja, Sargelu, Barsarin, Karak, and Bnavya, were examined, which represent the entire lithological alternations of limestones and shales encountered in the Whole Naokelekan Formation. This study assesses the type, the thermal maturity and the petroleum generation potential of the organic matter contained in the upper Jurassic Naokelekan formation throughout the area. The qualitative petrographical evaluation of the studied samples revealed that the main organic constituents are solid hydrocarbons, in the form of microgranular migrabitumens, with minor amounts of pyrobitumens. Equivalent vitrinite reflectance estimations (0.59–1.12% Ro) indicate that the upper Jurassic sequence in the western part of the area is at a mature stage, while the same sequence in the eastern part is at late mature stage.

The aim of this study is to assess the type, thermal maturity and the petroleum generation potential of the Upper Jurassic Naokelekan Formation, occurring across the Kurdistan Region of Iraq, by applying organic petrographical methods and Rock-Eval analysis. The Rock-Eval data would indicate the presence of kerogen types III, IV and II as the main constituents. However, the qualitative petrographical evaluation revealed that the main organic constituents are solid hydrocarbons, in the form of microgranular migrabitumens, with minor amounts of pyrobitumens. These secondary particles have affected the results of the Rock-Eval analysis and would have led to misinterpretation of organic matter typification based on pyrolysis results only. The combined results of petrography and pyrolysis indicate an active petroleum system within the Upper Jurassic sequence, where hydrocarbons are generated and reservoired within suitable lithologies.

Coal layers up to 1 m thick, exposed mainly on river banks in the vicinity of Agbor, Okhuokhuo and Ubiaja, Southern Nigeria, were examined by means of organic petrology, mineralogy and geochemistry, in order to gain coal quality data and understand the palaeoenvironmental conditions during peat accumulation in the broad area of the Ogwashi-Asaba Formation. The obtained results show that coal is of low-rank C; it overlies mainly claystone derived from flooding of branches of the palaeo-Niger River. The precursor peat was accumulating in mires under mesotrophic to ombrotrophic, anoxic conditions. The peat-forming vegetation represented mainly herbaceous plants with minor tree contribution. Though the number of studied samples is low, the distribution of the lignite layers extends further towards N.NW of the known lignite-bearing area. Taking into consideration the low ash yields of some samples, there are encouraging indications for notable lignite deposits of high quality. The mineralogical composition and the activity concentrations of 238U, 226Ra, 232Th and 40K exclude any severe environmental effect from coal exploitation. Due to all these promising evidences, a detailed exploration in these and between these outcrops is recommended in order to estimate the lignite potential hosted in this area.

A recent geological field work in the Northeastern part of Iraqi Kurdistan and subsequent analytical studies showed that the previously reported metamorphosed limestone outcrops around Rayat area represent actually listvenite bodies. Field mapping and remote sensing applications were used to understand the spatial distribution of the listvenite; additionally petrographical, mineralogical and geochemical studies were applied in order to define the features of the listvenite and to provide an initial genetic model, as well as to assess potential mineralizations related to the listvenitization. Listvenitization occurred as a product of hydrothermal alteration of the Cr-rich serpentinised peridotite that extensively occurs in the area, and resulted in the formation of silica and carbonate listvenites, as well as transitional phases, with fuchsite mineralization being predominant along the sheared zones. The results of this study upgrade the broad area of Rayat as potential hydrothermal ore-forming system and provide a basis for future detail prospecting of the area.

Maceral analyses along with proximate and elemental analyses were undertaken in order to determine the features of the Amynteo coal deposit and its depositional environment. The Amynteo coal has an eu-ulminite B reflectance of Rr = 0.21%, and in terms of lithotype belongs to matrix lignite. Huminite is the most abundant maceral group, consisting mostly of detrohuminite. Inertinite has relatively low percentages whereas liptinite concentrations are rather high. A ternary plot was applied as an indication of the depositional paleoenvironment. The results from the majority of the samples indicate origin in a topogenous setting. The peat accumulation was governed by a high groundwater level (wet telmatic to limno-telmatic facies). The depositional environment can be characterized as a reed-marsh environment, with occasional establishment of forest swamps.

The low-grade base metal sulphide Cu–Zn–Pb and Fe mineralization of Qandil Series develop in shear zones that occur in formations of the north-western part of the Zagros Orogen. This sulphide mineralization occurs either as quartz vein type or disseminated type associated with metamorphic rocks (marbles and phyllites). This study aims to characterize these sulphide-rich ores by means of their mineralogical and geochemical features, including also the features of the corresponded host formations and those of marbles (calcitic and dolomitic) and phyllites. Petrographical data indicate the presence of Cu, Zn, Pb and Fe sulphides in hydrothermal quartz (±calcite) veins of different generations. Geochemical data of surface samples indicate enrichment of Cu and Fe in shear zones with low concentrations in Zn and Pb. The REE data indicate that the genesis of these sulphide ores took place in a hydrothermal system and was generally attributed to high temperature (> 250 °C).The mineralization seems to be fault-controlled, which is favoured by the significant tectonic deformation of the area.

Thermal maturity and palaeodepositional environment of the Taratu Formation has been studied by evaluating its geochemical properties and organic petrographical features. Geochemical properties of the Cretaceous-Palaeocene Taratu source rock that are identified through pyrolysis indicate that this formation has excellent organic matter quality, quantity and hydrocarbon generation potential. Only the Cretaceous-aged sequence from this formation is thermally mature, with Tmax values ranging from 429 °C to 459 °C, while Palaeocene samples are found to be thermally immature. Organic matter of the Taratu Formation comprises primarily of oil and gas prone kerogen type II-III and gas prone kerogen type III, which is reflected by high HI (165.0–327.5 mg HC/g TOC) and low OI (5.00–25.7 mg CO2/g TOC) values. Tissue Preservation Index (TPI) and Gelification Index (GI) indicates that the Taratu Formation was previously deposited in a limnic environment. Further assessment of the source rock's palaeodepositional environment through correlating cross-plots of various biomarker data and evaluation of organic petrography suggests that the formation was subjected to brackish water influx.

The Pera-Lakkos coal located on top of bauxite deposits in the Ghiona mining district (Central Greece), is the only known Mesozoic (Late Cretaceous) coal in the country. It was derived from herbaceous plants and algae growing in mildly brackish mires that formed behind a barrier system during a regression of the sea, on a karstified limestone partly filled in with bauxitic detritus. Petrological, mineralogical and geochemical data point to the predominance of reducing conditions and intense organic matter degradation in the palaeomires. O/C vs. H/C and OI vs. HI plots, based on elemental analysis and Rock-Eval data, characterize kerogen types I/II. This reflects the relatively high liptinite content of the coal. Besides kerogen composition, O/C vs. H/C plot for the Pera-Lakkos coals is in accordance with a catagenesis stage of maturation in contrast with vitrinite reflectance and T max from Rock-Eval pyrolysis, which indicate the onset of oil window maturation stage. Suppression of vitrinite reflectance should be considered and the high liptinite content corroborates this hypothesis. Despite some favourable aspects for petroleum generation presented by the Pera-Lakkos coal, its maximum thickness (up to 50 cm) points to a restricted potential for petroleum generation. Coal oxidation took place either during the late stage of peat formation, due to wave action accompanying the subsequent marine transgression, or epigenetically after the emergence of the whole sequence due to percolation of drainage waters. Both options are also supported by the REE shale-normalized profiles, which demonstrate an upwards depletion in the coal layer. Oxidation also affected pyrite included in the coal; this led to the formation of acidic (sulfate-rich) solutions, which percolated downwards resulting in bleaching of the upper part of the underlying bauxite.

The present study aims to elucidate the depositional environment of Seam I in the Megalopolis Basin, Southern Greece, using existing geological data supported by maceral and mineralogical analyses, as well as by natural radioactivity determinations. Very high pyrite and uranium contents and a very low tissue preservation index usually suggest a marine influence during deposition. In Seam I, however, these features are most probably the result of a karstic aquifer supplying the palaeomire with sulphate-rich, neutral to weakly alkaline water. The pyrite formation and the U precipitation are attributed to the anaerobic conditions, which prevailed during peat accumulation. The petrographic, mineralogical and geochemical data of the studied profile point to several changes in the surface runoff and the supply of clastic material during deposition.

Summarization: The Dahomey Basin, SW Nigeria, hosts a 3000-m-thick sedimentary succession of Cretaceous and Cenozoic age, of which the Turonian-Maastrichtian Afowo Formation includes sandstones, arkoses, shales, shelly limestones, unconsolidated sand, clay and most importantly, bituminous (tar) sand strata. Eighteen samples were picked up from outcrops exposed by streams and channels, and were examined applying sedimentological, mineralogical, petrographical, geochemical (inorganic and organic) and radiological techniques with the aim of assessing the origin and the thermal maturity of the organic facies. The samples represent mostly coarse-grained sands and subordinately shales, referred usually as ‘tar sands’; they consist of mainly quartz and kaolinite, with variable amounts of mixed clay layers of illite-montmorillonite, mica and pyrite, probably derived from weathering of the Migmatite Gneiss Complex exposed to the north of the basin; this can also explain the relative enrichment in the natural radionuclides 40K, 238U, 226Ra and 232Th for some samples, although the radioactivity falls within the range for world values for soils. The clastic material of Afowo Formation was deposited in a rather oxic shallow marine environment. The particulate organic matter of the bituminous sediments comprises solid hydrocarbons, coalified (huminite) and partially oxidized (inertinite) remnants of terrestrial plants, and minor amounts of both terrestrial and marine liptinite macerals. The random reflectance values of the indigenous huminite population ranges between 0.40 and 0.45% pointing to an immature stage for oil generation. The respective reflectance of the migrabitumens ranges from 0.49 to 0.59% corresponding to vitrinite equivalent reflectance values of 0.70–0.76% falling well within the oil window. This study concludes that the hydrocarbons contained in the Afowo Formation are upwards migrating from parts of the basin where Afowo Formation has subsided at depths corresponding well within the oil window; the source rock corresponds to the middle shale horizon, whereas the sandy horizons act as migration paths and/or reservoirs. Παρουσιάστηκε στο: Marine and Petroleum Geology