Outcrop Samples Research Articles

Palynomorphs of the Fezouata Shale (Lower Ordovician, Morocco): Age and environmental constraints of the Fezouata Biota

The present study documents new palynological investigations of the Fezouata Shale from the Anti-Atlas (Morocco). Palynomorphs were extracted from samples collected from both outcrops and drill cuttings. Outcrop samples were taken near Zagora, and include some that were collected during excavation of stratigraphic horizons where exceptionally well-preserved fossils of the Fezouata Lagerstätte occur. Subsurface samples were taken from the AZ-1 (Adrar Zouggar Mountain) borehole, which was extracted some 300km to the southwest of Zagora. The palynological samples yielded acritarchs, chitinozoans, scolecodonts, conodonts and fragments of graptolites. The abundance and quality of preservation of palynomorphs varies greatly, but rich and diverse assemblages were recovered from several samples. The diversity and composition of the assemblages points to an open shelf environment. Generally mixed preservation states suggest resedimentation or differential transport histories. The acritarchs can be assigned to the diagnostic messaoudensis-trifidum acritarch assemblage, which is typical of the Tremadocian/Floian boundary interval of the Gondwanan margin in high southern palaeolatitudes. The acritarch taxa present in some of the lower parts of the Fezouata Shale including levels of exceptional preservation can be attributed to sub-assemblages 1–2 of the messaoudensis-trifidum assemblage and thus point to a late Tremadocian age of the Fezouata Lagerstätte, confirming biostratigraphic data provided by graptolites of the Araneograptus murrayi graptolite biozone. Chitinozoans from the Fezouata Shale are from the E. symmetrica and E. brevis biozones and include various species that are well-known from several localities on the Gondwanan margin and from other palaeocontinents (Baltica, Laurentia, and South China), demarcating broad links between those regions. The coincidence between index fossils of these three groups, hitherto not all found in the same level, suggests that the age assignments of chitinozoan biozones may be in need of revision.

Geochronologic Constraints on the Permian–Triassic Northern Source Region of the Sverdrup Basin, Canadian Arctic Islands

Detrital zircon U–Pb ages are used to provide constraints on the geologic evolution of the sediment source area(s) north of the Sverdrup Basin from the middle Permian to Late Triassic. Previous research on facies relationships and sediment progradation patterns of late Paleozoic and Triassic strata from the northern portion of Sverdrup Basin indicate that substantial sediment was derived from north of the basin. Utilizing LA-ICP-MS U–Pb geochronology we have analyzed detrital zircons from these northerly derived strata, including sandstones of four Late Triassic (Norian) outcrop samples the northeast Sverdrup Basin, and two Triassic (Olenekian and Carnian) and two Permian (Roadian and Wordian) samples from wells in the northwestern Sverdrup Basin.The samples from northwestern Sverdrup Basin contain abundant Early Mississippian (350Ma) to Early Ordovician (460Ma), late Cambrian (500Ma) to Cryogenian (650Ma), and early Tonian (960Ma) to Orosirian (2050Ma) detrital zircon. The detrital zircon ages from these samples are similar to zircon age components of Late Devonian siliciclastic strata of the Franklinian foreland basin, and we suggest a similar source area, a low-lying landmass north of the Sverdrup basin, which included extensive Devonian foreland basin strata.The U–Pb detrital zircon age components of northerly-derived Late Triassic strata of northeastern Sverdrup Basin samples are similar to the Permian and Triassic Northwestern Sverdrup Samples, but also contain a substantial age component of Triassic (201Ma) to Middle Mississippian (340Ma) detrital zircons, suggesting an additional source area. The only well documented source for such zircons in the Arctic region is the Ural Orogen. Consequently, it is postulated that, in the Late Triassic, sediment was transported ~1500km from the northern Urals, across the northern landmass, all the way to the shoreline of northeastern Sverdrup Basin.

Palynotaphofacies analysis applied to Jurassic marine deposits, Neuquén Basin, Argentina

Fil: Martinez, Marcelo Adrian. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Bahia Blanca. Instituto Geologico del Sur. Universidad Nacional del Sur. Departamento de Geologia. Instituto Geologico del Sur; Argentina

Terrane‐controlled crustal shear wave splitting in Taiwan

AbstractTaiwan is the result of arc‐continent collision associated with the convergence of the Philippine Sea plate with the eastern Eurasian plate continental margin. The locus of deformation is found in eastern Taiwan in the form of mountain building (Central Range) with underlying thickened lithosphere. Rapid tectonic exhumation in the Central Range has uncovered low‐to‐high‐grade metamorphic rocks marked by steep cleavage. We carried out a crustal seismic anisotropy study across Taiwan, producing a database of over 27,000 local earthquake shear wave splitting measurements. Additionally, we carried out rock physics measurements of metamorphic outcrop samples to quantify shear wave rock anisotropy. We produced a map of station‐averaged splitting measurements across Taiwan. Patterns of fast shear wave directions correlate with tectonic terranes produced by plate convergence. Deformation‐related mineral‐preferred orientation in the metamorphic rocks produces a significant amount of the crustal anisotropy in the Taiwan collision zone.

Post‐breakup burial and exhumation of the southern margin of Africa

AbstractDespite many years of study, the processes involved in the development of the continental margin of southern Africa and the distinctive topography of the hinterland remain poorly understood. Previous thermochronological studies carried out within a monotonic cooling framework have failed to take into account constraints provided by Mesozoic sedimentary basins along the southern margin. We report apatite fission track analysis and vitrinite reflectance data in outcrop samples from the Late Jurassic to Early Cretaceous sedimentary fill of the Oudtshoorn, Gamtoos and Algoa Basins (Uitenhage Group), as well as isolated sedimentary remnants further west, plus underlying Paleozoic rocks (Cape Supergroup) and Permian‐Triassic sandstones from the Karoo Supergroup around the Great Escarpment. Results define a series of major regional cooling episodes. Latest Triassic to Early Jurassic cooling which began between 205 and 180 Ma is seen dominantly in basement flanks to the Algoa and Gamtoos Basins. This episode may have affected a wider region but in most places any effects have been overprinted by later events. The effects of Early Cretaceous (beginning between 145 and 130 Ma) and Early to mid‐Cretaceous (120–100 Ma) cooling are both delimited by major structures, while Late Cretaceous (85–75 Ma) cooling appears to have affected the whole region. These cooling events are all interpreted as dominantly reflecting exhumation. Higher Late Cretaceous paleotemperatures in samples from the core of the Swartberg Range, coupled with evidence for localised Cenozoic cooling, are interpreted as representing Cenozoic differential exhumation of the mountain range. Late Cretaceous paleotemperatures between 60°C and 90°C in outcropping Uitenhage Group sediments from the Oudtshoorn, Gamtoos and Algoa Basins require burial by between 1.2 and 2.2 km prior to Late Cretaceous exhumation. Because these sediments lie in depositional contact with underlying Paleozoic rocks in many places, relatively uniform Late Cretaceous paleotemperatures across most of the region, in samples of both basin fill and underlying basement, suggest the whole region may have been buried prior to Late Cretaceous exhumation. Cenozoic cooling (beginning between 30 and 20 Ma) is focussed mainly in mountainous regions and is interpreted as representing denudation which produced the modern‐day relief. Features such as the Great Escarpment are not related to continental break up, as is often supposed, but are much younger (post‐30 Ma). This history of post‐breakup burial and subsequent episodic exhumation is very different from conventional ideas of passive margin evolution, and requires a radical re‐think of models for development of continental margins.

Investigation of Potential Loss of Injectivity and Formation Integrity Due to Pressure Cycling

Two tests were carried out on weak sandstone outcrop samples, in order to assess whether sequences of injection of a pore fluid and shut-in could have a destabilising effect on the borehole wall of the hollow cylinder specimen. The fluid injected was kerosene, at room temperature, from the borehole radially outwards, while maintaining confinement by inserting the specimen in a rubber sleeve, in a pressurized oil bath. Although no visible signs of any damage could be seen, cumulative deformation occurs at each injection cycle, with net effect of slight borehole enlargement. An analytic analysis suggested however that under the confining stress conditions of the tests, plastic deformation should cumulate in the opposite direction, with borehole diameter shrinkage. This is despite a very good match in terms of absolute deformation values. Further analyses should resolve the issue and allow one to predict whether cyclic injection may have an impact on permeability or formation integrity.

Nonuniversality of the Archie exponent due to multifractality of resistivity well logs

AbstractArchie's law expresses a relation between the formation factor F of porous media and their porosity ϕ, , where m is the Archie or the cementation exponent. Despite widespread use of Archie's law, the value of m and whether it is universal and independent of the type of reservoir have remained controversial. We analyze various porosity and resistivity logs along 36 wells in six Iranian oil and gas reservoirs using wavelet transform coherence and multifractal detrended fluctuation analysis. m is estimated for two sets of data: one set contains the resistivity data that include those segments of the well that contain significant clay content and one without. The analysis indicates that the well logs are multifractal and that due to the multifractality the exponent m is nonuniversal. Thus, analysis of the resistivity of laboratory or outcrop samples that are not multifractal yields estimates of m that are not applicable to well logs in oil or gas reservoirs.

The Effect of Dolerite Intrusions on the Hydrocarbon Potential of the Lower Permian Whitehill Formation (Karoo Supergroup) in South Africa and Southern Namibia: A Preliminary Study

Recent interest in the shale gas potential in the main Karoo Basin of South Africa has focused attention mainly on the carbonaceous Whitehill Formation (Ecca Group, Karoo Supergroup). To unravel the metamorphic effect of the Lower Jurassic Karoo igneous intrusions on the Lower Permian Whitehill Formation, outcrop samples were taken at various distances (ranging from 1 to >30 m) from the intrusive contacts of dolerite sills in the western part of the main Karoo Basin (Northern Cape, South Africa) and in the Karasburg Basin (southern Namibia). Furthermore, to establish the baseline petrological and geochemical composition of the Whitehill Formation, samples have also been collected at localities unaffected by dolerites in the southern main Karoo Basin. Mineral assemblages from all sample localities plot within the chlorite zone and show very low grade metamorphism. Mineral assemblages and illite crystallinity data indicate that the Whitehill Formation has undergone (a) anchizone metamorphism (250 to 300°C) in the southern main Karoo basin as well as in areas close to the dolerite intrusions, and (b) moderate burial diagenesis (~180°C) in areas away from the immediate effect of dolerites in the Northern Cape and southern Namibia. Regional evaluation of unconventional gas potential of the Karoo basins of southern Africa ought, therefore, to consider the subsurface thickness and spacing of Karoo intrusive bodies within the target carbonaceous formations.

Outcrop analogue study of Permocarboniferous geothermal sandstone reservoir formations (northern Upper Rhine Graben, Germany): impact of mineral content, depositional environment and diagenesis on petrophysical properties

The Permocarboniferous siliciclastic formations represent the largest hydrothermal reservoir in the northern Upper Rhine Graben in SW Germany and have so far been investigated in large-scale studies only. The Cenozoic Upper Rhine Graben crosses the Permocarboniferous Saar–Nahe Basin, a Variscan intramontane molasse basin. Due to the subsidence in this graben structure, the top of the up to 2-km-thick Permocarboniferous is located at a depth of 600–2900 m and is overlain by Tertiary and Quaternary sediments. At this depth, the reservoir temperatures exceed 150 °C, which are sufficient for geothermal electricity generation with binary power plants. To further assess the potential of this geothermal reservoir, detailed information on thermophysical and hydraulic properties of the different lithostratigraphical units and their depositional environment is essential. Here, we present an integrated study of outcrop analogues and drill core material. In total, 850 outcrop samples were analyzed, measuring porosity, permeability, thermal conductivity and thermal diffusivity. Furthermore, 62 plugs were taken from drillings that encountered or intersected the Permocarboniferous at depths between 1800 and 2900 m. Petrographic analysis of 155 thin sections of outcrop samples and samples taken from reservoir depth was conducted to quantify the mineral composition, sorting and rounding of grains and the kind of cementation. Its influence on porosity, permeability, the degree of compaction and illitization was quantified. Three parameters influencing the reservoir properties of the Permocarboniferous were detected. The strongest and most destructive influence on reservoir quality is related to late diagenetic processes. An illitic and kaolinitic cementation and impregnation of bitumina document CO2- and CH4-rich acidic pore water conditions, which are interpreted as fluids that migrated along a hydraulic contact from an underlying Carboniferous hydrocarbon source rock. Migrating oil and acidic waters led to the dissolution of haematite cements in the lower Permocarboniferous formations. During the Eocene, subsidence of the Upper Rhine Graben porosities and permeabilities of the sandstones of these formations were strongly reduced to 2.5 % and 3.2 × 10−18 m2. The second important influence on reservoir quality is the distinct depositional environment and its influence on early diagenetic processes. In early stage diagenesis, the best influence on reservoir properties exhibits a haematite cementation. It typically occurs in eolian sandstones of the Kreuznach Formation (Upper Permocarboniferous) and is characterized by grain covering haematite coatings, which are interpreted to inhibit cementation, compaction and illitization of pore space during burial. Eolian sandstones taken from outcrops and reservoir depths exhibit the highest porosities (16.4; 12.3 %) and permeabilities (2.0 × 10−15; 8.4 × 10−16 m2). A third important influence on reservoir quality is the general mineral composition and the quartz content which is the highest in the Kreuznach Formation with 73.8 %. Based on the integrated study of depositional environments and diagenetic processes, reservoir properties of the different Permocarboniferous formations within the northern Upper Rhine Graben and their changes with burial depth can be predicted with satisfactory accuracy. This leads to a better understanding of the reservoir quality and enables an appropriate well design for exploration and exploitation of these geothermal resources.

Facies and Diagenetic Level of the Upper Cibulakan and Parigi Formation, in Randegan and Palimanan Area

DOI:10.17014/ijog.2.3.157-166This research aims to determine the facies and diagenetic level of limestone of the Upper Cibulakan and Parigi Formations, and also aims to determine the structural correlation between surface and subsurface limestones. Based on thin section analyses taken from the core and outcrop samples, there are four types of lithofacies on the Upper Cibulakan Formation, i.e. mudstone-wackestone, wackestone-packstone, packstone-grainstone, and grainstone facies, and also four types of lithofacies on the Parigi Limestone Formation, i.e. mudstone-wackestone, wackestone-packstone, packstone-grainstone, and lower mudstone-wackestone facies. The analysis of surface and subsurface limestone facies of the Upper Cibulakan and Parigi Formations led to the knowledge of the proportionality and variation of the limestone characteristics on both positions. Limestone of the Upper Cibulakan Formation was deposited locally and discontinuously, whilst the Parigi Formation limestone was deposited evenly and continuously. The structural correlation between the surface and subsurface limestone indicates that these formations were uplifted/exposed due to a local force, likely caused by the intrusion of igneous rocks, as happened in the Kromong Complex. The presence of residual hydrocarbon on the surface of the limestone samples suggests the possibility of potential hydrocarbon trapped in the limestone beneath the surface.

Porosity and pore size distribution of deeply-buried fine-grained rocks: Influence of diagenetic and metamorphic processes on shale reservoir quality and exploration

Significant exploration risks are associated with the pursuit of deeply-buried shale gas reservoirs due to pore volume reduction and changes in pore size distribution. These changes in pore character result in decreases in gas in place and permeability. A suite of shale, low grade, pelitic metamorphic and a granite outcrop samples from various location in North America have been selected to span the later stages of diagenetic, epimetamorphic (epizone) and anchimetamorphic (anchizone) processes to evaluate the changes in the inorganic pore volumes and size distributions. Diagenetic/metamorphic ranking of samples were determined by the illite crystallinity method. Pore volumes reduce with increasing maturity/metamorphic grade. The loss of mesopore volume (2–50nm) with increasing maturity is the cause of the reduction in porosity. The reduction in mesopore volume is interpreted to be due to the authigenic recrystallization and growth of the clay minerals. As maturity/metamorphic grade increases there is a relative increase in the macropore (>50nm) and micropore (<2nm) size fractions. The increase in micropore volumes may be attributed to the development of secondary porosity within the kerogen. At higher maturity/metamorphic grade (i.e., illite crystallinity<0.2 Δ2θ) porosity values range between 0.9% and 3.6% indicating that fracture porosity is not the only mechanism of gas storage in deeply buried shale (and pelitic metamorphic rocks) reservoirs. Matrix porosities in these higher maturity/metamorphic samples are comparable to matrix porosities of the Horn River shales of British Columbia and other shale reservoirs. Similar to the Horn River and Doig–Montney shales, the reduction in mesopore volumes may reduce the matrix permeability of these rocks and fracture stimulation will be an integral component of the completions program to access hydrocarbons.

Depositional environment, organic matter characterization and hydrocarbon potential of Middle Miocene sediments from northeastern Bulgaria (Varna-Balchik Depression)

AbstractThe depositional environments and hydrocarbon potential of the siliciclastic, clayey and carbonate sediments from the Middle Miocene succession in the Varna-Balchik Depression, located in the south-eastern parts of the Moesian Platform, were studied using core and outcrop samples. Based on the lithology and resistivity log the succession is subdivided from base to top into five units. Siliciclastic sedimentation prevailed in the lower parts of units I and II, whereas their upper parts are dominated by carbonate rocks. Unit III is represented by laminated clays and biodetritic limestone. Units IV and V are represented by aragonitic sediments and biomicritic limestones, correlated with the Upper Miocene Topola and Karvuna Formations, respectively. Biogenic silica in the form of diatom frustules and sponge spicules correlates subunit IIa and unit III to the lower and upper parts of the Middle Miocene Euxinograd Formation. Both (sub)units contain organic carbon contents in the order of 1 to 2 wt. % (median: 0.8 for subunit IIa; 1.3 for unit III), locally up to 4 wt. %. Based on Hydrogen Index values (HI) and alkane distribution pattern, the kerogen is mainly type II in subunit IIa (average HI= 324 mg HC/g TOC) and type III in unit III (average HI ~200 mg HC/g TOC). TOC and Rock Eval data show that subunit IIa holds a fair (to good) hydrocarbon generative potential for oil, whereas the upper 5 m of unit III holds a good (to fair) potential with the possibility to generate gas and minor oil. The rocks of both units are immature in the study area. Generally low sulphur contents are probably due to deposition in environments with reduced salinity. Normal marine conditions are suggested for unit III. Biomarker composition is typical for mixed marine and terrestrial organic matter and suggests deposition in dysoxic to anoxic environments.

The mechanical properties of shale based on micro-indentation test

Abstract In view of the difficulty to get mechanical characteristics of shale reservoirs, a quantitative evaluation method based on micro-indentation test technology was proposed to research the meso-mechanical properties of shale. Through micro-indentation test of shale outcrop samples from the Cambrian Longmaxi Formation in the Changning area, Sichuan Basin, the meso-mechanical properties of shale were analyzed, and the relationship between the macro-scale and meso-scale shale mechanical properties was evaluated. The analysis results of micro-indentation tests show that the mesoscopic elastic modulus and indentation hardness are heterogeneous in distribution. The comparison of macro and meso experiments shows that the statistical mean value of meso-elastic modulus is approximate to the value of the macro-elastic modulus. The relationship between composition and mechanical properties of shale was obtained based on the packing density model theory. The result shows that mesoscopic elastic modulus and indentation hardness increase nonlinearly with the increase of the packing density. Based on the hardness-packing density model, the reverse analysis of cohesion and friction angles shows that the mesoscopic value is slightly smaller than the macroscopic value. The micro-indentation test technology can evaluate shale meso-mechanical properties and predict the macro-mechanical properties effectively.

An experimental study on the mechanism of degradable fiber-assisted diverting fracturing and its influencing factors

Fiber-laden fluid systems have been successfully applied for reorientation fracturing in tight gas and shale gas reservoirs around the world. Although many successful cases have been reported in the literature, there is a lack of a deep understanding of the mechanical mechanism of fiber-assisted diverting fracturing. Hence, this paper presents a systematic study of the fracture diversion mechanisms of the fiber-diverting fracturing technique. A series of laboratory experiments is conducted with a real tri-axial stress simulation system. Degradable fibers are applied to large-size natural outcrop samples (300 mm × 300 mm × 300 mm) under true triaxial stress conditions. The dynamic filtration experiment to test the temporary plugging ability showed that the fractures were effectively plugged by fiber fluids. A variety of factors related to the fracture reorientation are tested and compared, including injection rate, fracture width and horizontal principal stress difference. The additional pressure drop caused by the fiber filtration cake is calculated and used to quantitatively analyze the effects on fracture reorientation. The net pressure increase is the driving force of the fracture diversion and formation of the fracture network. The conclusions were used to guide carbonate reservoir stimulations in the Tarim oil field, in northwest China. The phenomenon of fracture diversion was evident as the pumping pressure increased considerably after injecting the degradable fiber. The hydraulic fracturing treatment and production results showed substantial pressure responses and excellent hydrocarbon production.

Shale oil potential and thermal maturity of the Lower Toarcian Posidonia Shale in NW Europe

A suite of drilling cores and outcrop samples of the Lower Toarcian Posidonia Shale (PS) were collected from multiple locations including the Swabian Alb and Franconian Alb of Southwest-Germany, Runswick Bay of UK and Loon op Zand well (LOZ-1) of the West Netherlands Basin. In order to assess the thermal maturity and quantify the petroleum generation potential of the rocks, elemental analysis, Rock-Eval pyrolysis, organic petrographic investigations and molecular hydrocarbon analyses were performed. Available literature data of the Posidonia Shale from Luxembourg and northwest Germany were used for comparison in the discussion.The Lower Toarcian Shale is more carbonate-rich (about 30% on average) in SW-Germany, NW-Germany and Luxembourg, and is instead more silicate-rich in UK and NL with carbonate contents of about 15% on average. This coincides with the relative distances of the depositional settings to the clastic source areas on the continents during the early Jurassic. However, HI values are similar, approx. 500–700mgHC/g TOC on average at all sampling localities, exhibiting typical type II kerogen with excellent hydrocarbon generation potential. Differences in relative abundance of terrigenous organic matter input are deduced from molecular indicators, Rock-Eval data and organic petrography. The highest abundance of terrigenous organic matter is evident for Runswick Bay, UK.Samples from outcrops of the Lower Toarcian Shale from Runswick Bay, UK, have reached the early stage of the oil window, with quite uniform Tmax values (425–438°C, avg. 433°C) and a narrow range of PI (production index) values (0.10–0.19), substantiated by mature fluorescing characteristics of telalginite and lamalginite and vitrinite reflectance values of 0.6–0.7%. Wider ranges of Tmax values (421–443°C, avg. 427°C), vitrinite reflectance (0.4–0.8%) and production indices (0.06–0.29) suggest more variable thermal maturation ranging from immature to almost peak oil generation at the LOZ-1 well, NL, although only some intervals indicate advanced thermal maturity there. In contrast, the Lower Toarcian marlstones from the Swabian and Franconian Alb of SW-Germany are clearly immature, similar to the samples from Luxembourg. In NW-Germany, the Posidonia Shale covers a wide spectrum of maturity ranging from immature to overmature.Source potential index (SPI) indicates the highest value in the LOZ-1, NL followed by Wickensen, NW-Germany and Esch-sur-Alzette, LU, mainly due to differences in thickness of the studied sections. The lowest value was observed in SW-Germany. The Lower Toarcian (Jet Rock) in Runswick Bay, UK, is assumed to have a high shale oil potential because of its advanced thermal maturity, although its SPI is not high due to the limited thickness of the section studied. The PS in SW-Germany has low shale oil potential due to low thermal maturity and limited thickness.

Quantitative determination constraints on dolomitization model for the Upper Permian Changxing reservoir dolomites of Northeastern Sichuan Basin, Southwestern China

Natural gas was found in Upper Permian Changxing dolomite reservoirs of the NE Sichuan Basin, China. Researching the mechanisms for dolomitization was essential for petroleum exploration. Outcrop samples from Upper Permian Changhsingian Panlongdong and Yanggudong sections were studied using statistical work, cathodoluminescence (CL), electron microprobe, major element analysis and isotope studies (δ18O and δ13C), in an attempt to determine the migration pathway and origin of the dolomitizing fluids. The dolomite content, average dolomite size, δ18O values and Mg/Ca ratios were all decreased downwardly in the two sections, indicating that the Changxing dolomitizing fluid migrated downwardly from the top of Changxing Formation (sediments). The Mg, Na, Fe, Mn and Sr elements were uniformly distributed in dolomite crystals which proved that the dolomites were formed in the same fluid without time interval. The element content in Changxing dolomites was similar to that of the Feixiangan sakbha dolomites and the δ18O values of Changxing dolomite were much higher than those of the Changxing limestone, which suggested that the dolomitizing fluid was originated from evaporative seawater. In conclusion, we concluded that the coeval Changhsingian evaporative seawater caused dolomitization.

Roles of Thermophiles and Fungi in Bitumen Degradation in Mostly Cold Oil Sands Outcrops.

Oil sands are surface exposed in river valley outcrops in northeastern Alberta, where flat slabs (tablets) of weathered, bitumen-saturated sandstone can be retrieved from outcrop cliffs or from riverbeds. Although the average yearly surface temperature of this region is low (0.7°C), we found that the temperatures of the exposed surfaces of outcrop cliffs reached 55 to 60°C on sunny summer days, with daily maxima being 27 to 31°C. Analysis of the cooccurrence of taxa derived from pyrosequencing of 16S/18S rRNA genes indicated that an aerobic microbial network of fungi and hydrocarbon-, methane-, or acetate-oxidizing heterotrophic bacteria was present in all cliff tablets. Metagenomic analyses indicated an elevated presence of fungal cytochrome P450 monooxygenases in these samples. This network was distinct from the heterotrophic community found in riverbeds, which included fewer fungi. A subset of cliff tablets had a network of anaerobic and/or thermophilic taxa, including methanogens, Firmicutes, and Thermotogae, in the center. Long-term aerobic incubation of outcrop samples at 55°C gave a thermophilic microbial community. Analysis of residual bitumen with a Fourier transform ion cyclotron resonance mass spectrometer indicated that aerobic degradation proceeded at 55°C but not at 4°C. Little anaerobic degradation was observed. These results indicate that bitumen degradation on outcrop surfaces is a largely aerobic process with a minor anaerobic contribution and is catalyzed by a consortium of bacteria and fungi. Bitumen degradation is stimulated by periodic high temperatures on outcrop cliffs, which cause significant decreases in bitumen viscosity.

Unraveling crustal growth and reworking processes in complex zircons from orogenic lower-crust: The Proterozoic Putumayo Orogen of Amazonia

High-grade basement massifs exposed in the northern Andes and the buried basement of the adjacent Putumayo foreland basin contain a record of Amazonia's involvement in the supercontinent Rodinia. Metasedimentary granulites and orthogneisses, strongly deformed during at least one metamorphic episode dated at ca. 0.99Ga, provide critical information on the pre-collisional history of the Mesoproterozoic continental margin. Here, new U–Pb, Lu–Hf, Sm–Nd and O isotopic data from outcrop samples of the Garzón and Las Minas Cordilleran basement massifs as well as fragments of drill-core recovered from the Putumayo basin basement are reported. We explore the application of a dual-ICP-MS approach to obtain concurrent U–Pb and Lu–Yb–Hf information on complexly zoned zircon from orogenic lower-crust, and demonstrate its use to retrieve reliable pre-metamorphic information despite possible complexities introduced by mixed-domain ablation and isotopic disturbance of the U–Pb system by thermally induced recrystallization. In combination with δ18O compositions from the same zircon growth domains, and bulk-rock Nd isotope information, we reconstruct segments of the tectonic and crustal evolution of a long-lived accretionary orogen that developed along the (modern) NW margin of Amazonia during most of the Mesoproterozoic. Inherited zircons in metaigneous samples from the Cordilleran massifs, with protolith crystallization ages in the range from ca. 1.47 to 1.15Ga, have Hf–O compositions that indicate significant crustal reworking in their source region, but denote a trend of increasing 176Hf/177Hf with decreasing age that can be attributed to rejuvenation by progressive addition of radiogenic components during this time interval. Detrital zircons within this same age range found in metasedimentary granulites of the Garzón massif also follow this trend, further supporting previous inferences that their protoliths were deposited in arc-proximal basins with little to no coarse-grained detritus delivered from an older cratonic domain. A shift in orogenic deformation style starting at ∼1.15–1.10Ga, inferred to be associated with the accretion of fringing-arc terranes against the continental margin, triggered an early amphibolite-grade metamorphic episode; this was accompanied by pervasive partial melting and migmatite development in fertile metasedimentary units and is interpreted to be responsible for enhanced crustal reworking evidenced from the shallowing of 176Hf/177Hf vs. age trends in detrital and metamorphic zircons from the Garzón and Las Minas massifs. Convergent tectonism along the Putumayo margin came to an end during the final incorporation of Amazonia to the core of the Rodinia supercontinent, possibly during collision against the Sveconorwegian segment of Baltica at 0.99Ga. Although the position and role of Amazonia within Rodinia remains controversial, the new Nd and Hf isotope data provide additional evidence to link the evolution of this orogenic segment with the basement of Oaxaquia, as well as continue to draw fundamental differences with the timing and nature of the tectonic processes associated with the development of the Sunsás-Aguapeí Orogen of SW Amazonia.

Rare earth element geochemistry of outcrop and core samples from the Marcellus Shale.

In this work, the geochemistry of the rare earth elements (REE) was studied in eleven outcrop samples and six, depth-interval samples of a core from the Marcellus Shale. The REE are classically applied analytes for investigating depositional environments and inferring geochemical processes, making them of interest as potential, naturally occurring indicators of fluid sources as well as indicators of geochemical processes in solid waste disposal. However, little is known of the REE occurrence in the Marcellus Shale or its produced waters, and this study represents one of the first, thorough characterizations of the REE in the Marcellus Shale. In these samples, the abundance of REE and the fractionation of REE profiles were correlated with different mineral components of the shale. Namely, samples with a larger clay component were inferred to have higher absolute concentrations of REE but have less distinctive patterns. Conversely, samples with larger carbonate fractions exhibited a greater degree of fractionation, albeit with lower total abundance. Further study is necessary to determine release mechanisms, as well as REE fate-and-transport, however these results have implications for future brine and solid waste management applications.Electronic supplementary materialThe online version of this article (doi:10.1186/s12932-015-0022-4) contains supplementary material, which is available to authorized users.

Outcrop reservoir analogous and porosity changes in continental deposits from an extensional basin: The case study of the upper Oligocene Sardinia Graben System, Italy

Several recent hydrocarbon discoveries were detected in extensional areas located around fault-bounded tectonic highs. These tectonically-controlled mini-basins are diffusely characterised by terrestrial and shallow-marine successions with complex geometrical relationships. The degree of seismic resolution and the punctual well-log lithostratigraphic data do not allow suitable reconstructions of these plays and, thus, the use of good outcrop analogues is crucial in their reservoir characterisations.In this paper, we present the results of a sedimentological study carried on continental deposits filling a segment of the Oligo-Miocene south-eastern basin margin of the Sardinia Graben System, in the central-western Mediterranean. This well-exposed terrestrial succession results from the erosion of Palaeozoic metamorphic and magmatic basement rocks exposed along the basin margin. Continental, coarse-grained eluvio-colluvial, alluvial and fluvial sediments exhibit changes both in thickness and lateral extensions due to the existence of several endorheic depocentres, which were aligned along major normal faults.Based on the stratigraphic and sedimentological analysis of a number of exposed stratigraphic sections, the main depositional processes are identified for each specific facies association. Due to the grain-size of the dominant deposits, porosity is estimated by using an image analysis software on high-resolution digital photographs from a number of outcrop samples. The results show how porosity changes dramatically across the reconstructed sections due to the complexity of the reciprocal geometrical passages among all these lithofacies.The dominance of colluvial/alluvial fans or river braidplain systems and the different nature of sediment occupying each depositional areas are interpreted as the response to the interplay between the capacity generated by the vertical tectonic displacement of major normal-faults and the interception of the base-level with the topography of these mini-basins. Our observations suggest six possible depositional scenarios that resume as many reservoir types in fault-controlled half-grabens with dominant continental lithofacies.