Fluviatile Environment Research Articles

Sedimentology and Mineralogy of Sedimentary Sequences in Nanim Field in the Niger Delta basin, Nigeria.

A total of nineteen ditch cuttings from the sedimentary sequence of Nanim Field, were subjected to both sedimentological and mineralogical analysis with the aim of investigating the mineralogical composition of the studied section (1810 m - 2650m) in the study area. The shale samples were grinded, pulverized and sieved with less than 75μm and analyzed using X-ray diffraction techniques (XRD) for mineralogical composition. Results of the sedimentological analysis, suggests four lithofacies made up of sandstone, shaly sand, shale and sandy shale in he studied section. The studied section has been interpreted as a shallow marine environment  divided into two broad lithofacies sequences made up of beach sand (1810 m - 2290 m.) and upper shoreface (2300 m – 2650m) respectively. The beach sand sequences comprises thick sands, brownish, grey to black, fine to coarse grained, whereas the upper shoreface sequence is essentially a heterogeneous sequence of alternating sand medium to very fine grained sand and shale - grey. Results from the XRD analysis shows that the mineralogical composition of the basal part (upper shoreface) of the studied section is characterized by kaolinite a dominant in sediments of fluviatile environments and is known to concentrate in many near-shore sediments (shallow marine) with a decrease in abundance from the shoreline as other clay minerals increase basinward.

Facies Implication of GERCUS Formation with The Bathymetry and Tectonic Activity of Van-Pyrenean Phases in Haibat-Sultan Mountain, Iraqi Kurdistan Region

The Eocene red clastic strata are represented by molasses facies of Gercus Formation and well exposed at Haibat-Sultan Mountain . A sequence of about 88m thick of the formation is located in the middle part of the Mountain. Detailed investigations including field, petrographic investigations which are linked  between bathymetric fluctuation and depositional environment.  The sequence is generally found to be a shallowing upward facies which start from deep marine (Kolosh Formation) to continental environment passing through shallow marine. Petrographic studies revealed the presence of a high rate of terrigenous grains; the most abundant clasts are sedimentary rock fragments such as limestone and chert. There are less abundant clasts derived from igneous and metamorphic rocks like quartz, feldspar, and micain addition to  authigenic  grains of glauconite are also represented. The pore space between grains are filled by  red clay with carbonate cement. The provenance consisted mainly of  Balambo,Tanjiro,Shiranish,and Aqra Formations while the Igneous and metamorphic grains are reworked from ophiolte and metamorphic ource areas that cropped out on the Hinterland near Iraq-Iran border. Gercus Formation in this area is deposited in four  depositional environments: fluviatile environments( river environment ), alluvial fan (shore line) , delta, and shore face environments. The deposition and fluctuation  influenced by  paleo-slope and regional tectonism of Van–Pyrenean phases. The Middle Part of this Formation interfingers with the Avanah Formation (Carbonate Rocks)  which was deposited during the rising of sea level.

Petrotectonic framework of Siwalik Group in Khairi Murat-Kauliar area, Potwar Sub-Basin, Pakistan

The Khairi Murat-Kauliar area lies between the Salt Range Thrust (SRT) in the south whereas Main Boundary Thrust (MBT) in the north which is the part of the Potwar Sub Basin. Eocene to Recent succession is exposed in the study area. The selected siliciclastic Siwalik Group display various facies in a fluviatile environment, with different lithologies, and sedimentary features. The petrographic studies of Siwalik Group delineate different microfacies including feldspathic litharenite, litharenite and sub arkose. The provenance study of sandstones depicted the terrane of dissected arc and recycled orogeny, indicating that the detritus was received from sedimentary, metamorphic, plutonic and volcanic rocks from the northern domain of Indian Plate, Karakoram Ranges and Kohistan Island arc. The Siwalik sandstone also contains heavy mineral assemblage such as tourmaline, garnet, epidote, hornblende and chlorite. This heavy detritus assemblage depicted that the deposits were received from metamorphic and igneous origin. A modified dynamic depositional stages of the Siwalik Group with respect to Himalayan orogeny is further built using outcrop data, microfacies and heavy minerals analysis. According to this concept, the group was deposited along Himalayan uprising and thrusting, on the depository in targeted area. The Siwalik Group depicted different phase of Himalayan tectonics and these molasse sequence were deposited in a subsiding foreland basin under the conditions of rapid erosion and quick deposition.

Evolution of the Jurassic Comallo volcanic sedimentary complex in the western North Patagonian Massif, Rio Negro province, Argentina

ABSTRACT Here we define the Comallo volcanic sedimentary complex of the western North Patagonian Massif. It is composed by two members that include 9 lithofacies and 7 facies associations. The lower member is represented by massive and stratified lapilli tuffs, lithic and tuffaceous breccias, coherent andesite-dacite lava-flows, andesitic breccias, and massive crystalline limestones. The upper member consists of red conglomerates, parallel and cross-stratification sandstones, and mudstones. The lower member is interpreted as having been deposited by dilute and dense pyroclastic currents, block and ash deposits and lava-flow, and hypersaline lacustrine environments. The upper member is considered to have been deposited in fluviatile environments. A new U-Pb age of 192.0 ± 3.0 Ma (Sinemurian) was obtained for this complex. It is coeval with several volcanic sedimentary units that crop out along the western North Patagonian Massif, the Neuquén basin and the Extraandean Chubut in pull-apart or rift depocentres. The movements of the NW-SE strike-slip faults that border the northern and southern limits of the Comallo depocentre made possible the development of a pull-apart basin as well as the volcanism and the fluvial system. This and other coeval units were deposited in similar environmental conditions along the North Patagonian Massif, the Neuquén basin and the extraandean Chubut, indicating a similar tectonomagmatic setting, in a tensional rear-arc during Lower Jurassic times.

Geochemical, Mineralogical and Biological study of Holocene deposits in Almuthana province, southern Iraq

Fifteen samples were collected from recent sediments grouping at 80 km east Samawa City, southern Iraq. Three selected samples for grain size analysis and twelve samples for chemical and biofacies analysis. Grain size analysis indicated that the sediment is mainly composed of the silt and clay with a small amount of sand. Most of the samples considered to be as clayey silt. The dominated non clay minerals are Quartz, Calcite, and Dolomite, while the clay minerals are composed of mixed Montmorillonite- Chlorite, Palygorskite, Illite and Kaolinite. Chemical analysis showed that all samples have high concentrations of SiO2 and CaO in comparison with Al2O3, MgO, Fe2O3, K2O and N2O. The identified faunas consist of a number of groups such as Mollusca, Ostracoda and Charophyta, all diagnosed genera indicated of fresh water environments. The results from all collected data are indicated that the sediments belong to flood plain deposits which deposited in fluviatile environments.

Application of integrated clustering and petrophysical-microscopic methods for facies determination of Campanian–Maastrichtian and Danian–Thanetian reservoirs: Constraints for tectonostratigraphic influences on sedimentation across the NW Indian Plate margin

This paper focuses on reservoirs study in tectonostratigraphic perspective using soft computing multivariate statistical technique of clustering analysis (CA) to delineate electrofacies (EF) for rock typing. The EF knowledge was combined with petrophysics, rock fabric number (rfn) and application of microscopic studies comprising thin sections (TS), scanning electron microscopy (SEM), back scattered electron (BSE) and energy dispersive X-Ray spectroscopy (EDS) on fauna acquired from novel drill cuttings of selected wells. The methods were implemented on data of eight exploratory wells from eastern Sulaiman sedimentary basin (Pakistan) to investigate tectonostratigraphic influences and reservoir characteristics of the Campanian–Maastrichtian, and Danian–Thanetian reservoirs. The Danian-Thanetian (Upper and Lower Ranikot Formations) demonstrate good reservoir rocks in the Sulaiman Fold Belt (SFB) and the northern part of the Zindapir (ZA), however, in the Sulaiman Depression (SD), the Danian-Thanetian reservoirs are shale-rich bearing poor reservoir potential based on EF log correlation. The presence of glauconite (Gl) in the Paleocene Ranikot intervals suggests transgressive (TST) or early highstand system tract (HST) for this particular formation. This evidence is further supported by the occurrence of planktonic foraminifera (Pl), the abundance of which is indicative of late TSTs and early stage HSTs. The presence of Pl in the Campanian Parh Limestone indicates an open sea environment. The clay minerals (kaolinite, chlorite, montmorillonite) occurrence in Maastrichtian Pab Sandstone suggest the detrimental effect on reservoir quality, hindering permeability and fluid flow, proposing this particular formation as a tight reservoir. The kaolinite clay type in the Lower Ranikot Sands in the northern part of ZA characterize continental to near-shore sediments, indicative of fluviatile environment. The Maastrichtian Mughal Kot Formation in the SFB indicates arkosic sandstone (feldspar-rich) with some micaceous content and montmorillonite.The findings from the EF correlation of different wells demonstrate that the reservoir rocks in the SD to the southeast are more shale rich in comparison to those encountered in the SFB in the northeast and northwest. The rfn suggests class 1 type rock fabric (grain dominant) for the Cretaceous Parh Limestone. Due to incomplete logging data, it was not possible to derive rfn for Paleocene formations. The results validate the reservoir heterogeneities on microscopic and small-scale using drill cuttings and well logs.Geologically, active tectonics during the Cretaceous and Paleocene, local sea level fluctuations, diagenesis, clay mineralogy and paleo-topography have strongly affected the lateral variation of facies of Campanian–Maastrichtian, and Danian–Thanetian reservoirs. Moreover, regional active tectonics (Himalayan Orogeny) spanning the Cretaceous and Paleogene Periods also played a major role in crafting the reservoir architecture of various rock units. The results demonstrate the Campanian–Maastrichtian and Danian–Thanetian reservoirs as promising exploratory targets in the SFB. The comparison of the achieved outcomes showed a close agreement with the lateral facies variation in Cretaceous (Campanian–Maastrichtian) and Paleocene (Danian–Thanetian) across the study area.

Sedimentology and Depositional Environment of part of Lokoja Formation Exposed at Felele Junction, Southern Bida Basin

The exposed Campanian sedimentary sequence at Felele junction around Lokoja has been mapped, logged and sampled. The total thickness of the section is approximately 21.48m. The sediments consist of conglomeratic sandstones, coarse sandstones and mudstones. Grain size analysis performed on nineteen sandstone samples revealed the average values of mean, sorting, skewness and kurtosis as 0.6, 1.03, 0.53 and 0.76 respectively. These results show that the sandstones are coarse grained, poorly sorted, strongly fine skewed and platykurtic. This characteristic is typical of fluvial depositional environment. The plots of skewness against sorting, sorting versus kurtosis and mean against sorting suggest a fluvial depositional environment. Petrographic analysis of selected sandstones reveals the presence of quartz, feldspars (plagioclase and microcline) and mica (biotite and muscovite). Quartz (especially monocrystalline) dominates followed by feldspar with minor muscovite and biotite. Heavy mineral study revealed the presence of non-opaque mineral suites suggesting that the sediments are derived from the basement complex of igneous and metamorphic rocks. The heavy minerals observed include staurolite, rutile, kyanite, zircon and sphene. The samples are dominated by stauronite which signifies low grade metamorphism in the area. Integration of sedimentological and petrographical characteristics in this study suggest that the sandstone samples are derived from mixed origin and deposited in fluviatile environment under high energy setting not too far from the source. Hence it is a proximal deposit.

Petrography, provenance, diaganesis and depositional environment of Murree Formation in Jhelum Valley, Sub Himalayas, Azad Jammu and Kashmir, Pakistan

The clastic sediments of the Murree Formation of Miocene age are exposed in Jhelum valley areas of Azad Jammu and Kashmir Pakistan. Field observations revealed the cyclic deposition in the Murree Formation. The sandstone, siltstone, and shale constitute a single cycle within the formation. This single unit is divided into five different lithofacies which constitute the Bouma sequence in the Murree Formation. The Murree Formation shows faulted contacts with Panjal Formation and Nagri Formation in the study area. The modal mineralogy data obtained from the petrography of sandstone indicates that sandstone is litharenite and lithic greywacke. The mineralogical and textural data suggests that sandstone is compositionally mature and poorly to moderately sorted. The dominantly angular to sub angular quartz grains show nearness of the source area. Fractured and sutured quartz grain reveals tectonodiagentic changes that occurred in Murree Formation. The sandstone experienced diagenetic changes. The pressure solution and cementation reduced the primary porosity of sandstone. However, alteration of feldspar and fractures in grains have produced secondary porosity. The X-ray diffraction (XRD) of the shale samples indicates that shale of the Murree Formation is argillaceous and dominated by illite clay mineral. The illite crystallinity values indicate very low grade metamorphism of Murree Formation in core of Hazara Kashmir Syntaxis. The petrographic data suggests that the provenance of sandstone is recycled orogen. Quartz is of igneous and metamorphic origin. Feldspar (albite and microcline) composition suggests its derivation from acidic igneous rocks. The rock fragments of volcanics, slate, phyllite, and schist suggest igneous and metamorphic provenance. The petrographic data suggests that at the time of deposition of Murree Formation, igneous and low grade metamorphic rocks were exposed. However, presence of some clasts of carbonates indicates that sedimentary rocks were also exposed in the source region. The quartz content and clay minerals in the shale revealed that source region was igneous and metamorphic rocks. Cyclic deposition, lithofacies, and various sedimentary structures like cross bedding, ripple marks, and calcite concretions suggest that deposition of Murree Formation occurred in fluviatile environment by meandering river system having decreasing turbidity current.

Geochemistry and petrology of Late Miocene-Pleistocene Dibdibba sandstone formation in south and central Iraq: implications for provenance and depositional setting

Major, trace, and some rare earth element compositions in clastic sediments of the Dibdibba Formation (Late Miocene-Pleistocene) in central and southern Iraq have been investigated to describe the sedimentary environment and provenance. These sediments are classified as subarkosic to arkosic with few sublithic arenite, lithic arenite, and gray wacke; they are mainly composed of quartz (Q) followed by feldspar (F) and rock fragments (L) with a petrologic composition of Q73-F21-L6. The Arabian Shield is a probable source of the studied sediments which are derived from multi-sources including igneous rocks (felsic to mafic) and metamorphic rocks and were transported by river currents towards the northeast. Eventually, the clastic sediments were deposited in a fluviatile environment covering a wide area in Saudi Arabia, Kuwait, Qatar, and Iraq during the Late Miocene-Pleistocene. They were developed on a passive continental margin under a semi-humid climate alternating with drought periods. The grain size analysis indicates that Basra in the south of Iraq is close to the source, but Karbala and Najaf in central Iraq are farthest from the source.

Late Oligocene macrofloras from fluviatile siliciclastic facies of the Köln Formation at the south-eastern border of the Lower Rhine Embayment (North Rhine-Westphalia, Germany)

Abstract The leaf remains described herein came from the oldest sites of the Cainozoic deposits in the Lower Rhine Embayment, located in the Siebengebirge Volcanic Field at the south-eastern border of this basin, in the area of Siebengebirge and vicinity. These revisited floras are bound to pre-volcanic siliciclastic facies of the Siebengebirge Mts., interpreted as marginal facies of the Köln Formation. Chronostratigraphically they are assigned to the late Oligocene (Chattian). The described leaf remains are partially compressions with preserved epidermal anatomy, and therefore highly useful for systematic determination of leaf impressions recovered from other localities of siliciclastic facies. On account of the epidermal characteristics of leaf compressions varying in gross morphology, the previously determined taxa Quercus goepperti, Laurus phoeboides, and Persea speciosa all fall into the abundantly represented Eotrigonobalanus furcinervis. The siliciclastic deposits originated in coastal and flood plain areas within fluviatile environments of variable deposition energy. Remains of Taxodium dubium, Eotrigonobalanus furcinervis, Populus germanica, and Daphnogene cinnamomifolia dominate among the recovered fossils. The general aspects of this plant assemblage correspond, together with their sedimentary settings, to riparian forest vegetation with mesophytic elements.

Near-field sea-level variability in northwest Europe and ice sheet stability during the last interglacial

Global sea level during the Last Interglacial (LIG, Marine Isotope Sub-stage 5e) peaked between c. 5.5 and 9 m above present, implying significant melt from Greenland and Antarctica. Relative sea level (RSL) observations from several far- and intermediate-field sites suggest abrupt fluctuations or jumps in RSL during the LIG highstand that require one or more episodes of ice-sheet collapse and regrowth. Such events should be manifest as unique sea-level fingerprints, recorded in far-, intermediate- and near-field sites depending on the source(s) of ice-mass change involved. To date, though, no coherent evidence of such fluctuations has been reported from near-field RSL studies in northwest Europe. This is an important problem because RSL fluctuations during the LIG are portrayed as warning signs for how polar ice sheets may behave in a future, warmer than present, world. Here we review the evidence for RSL change during the LIG using stratigraphic data from the best resolved highstand records that exist in the near-field of northwest Europe, from a range of settings that include lagoonal, shallow marine, tidal flat, salt marsh and brackish-water fluviatile environments. Consideration of previously published stratigraphic records from two sites in the Eemian coastal-marine embayment that existed in the central Netherlands, yields no clear indications for abrupt RSL change during the attainment of the near-field highstand. Nor do we find any such indications common to other records from countries bordering the North Sea, the Baltic Sea and the White Sea. Two modelling experiments that explore the global signal of hypothetical sea-level oscillations caused by partial collapse and regrowth of either the Greenland or Antarctic LIG ice-sheet, show that the North Sea region is relatively insensitive to mass changes sourced from Greenland but should clearly register events with an Antarctic origin, especially those that occur late in the LIG. The lack of evidence for abrupt sea-level fluctuations at this time in northwest Europe concurs with a lack of clear near-field evidence for ice sheet collapse.

Fluvial transport potential of shed and root-bearing dinosaur teeth from the late Jurassic Morrison Formation.

Shed dinosaur teeth are commonly collected microvertebrate remains that have been used for interpretations of dinosaur feeding behaviors, paleoecology, and population studies. However, such interpretations may be biased by taphonomic processes such as fluvial sorting influenced by tooth shape: shed teeth, removed from the skull during life, and teeth possessing roots, removed from the skull after death. As such, teeth may behave differently in fluvial systems due to their differences in shape. In order to determine the influence of fluvial processes on the preservation and distribution of shed and root-bearing dinosaur teeth, the hydrodynamic behaviors of high-density urethane resin casts of shed and root-bearing Allosaurus and Camarasaurus teeth were experimentally tested for relative transport distances at increasing flow velocities in an artificial fluviatile environment. Results show that tooth cast specimens exhibited comparable patterns of transport at lower velocities, though the shed Camarasaurus teeth transported considerably farther in medium to higher flow velocities. Two-Way ANOVA tests indicate significant differences in the mean transport distances of tooth casts oriented perpendicular to flow (p < 0.05) with varying tooth morphologies and flow velocities. The differences exhibited in the transportability of shed and root-bearing teeth has important implications for taphonomic reconstructions, as well as future studies on dinosaur population dynamics, paleoecology, and feeding behaviors.

DETRITAL PLATINUM-GROUP MINERALS IN RIVERS DRAINING THE GREAT DYKE, ZIMBABWE

The present work focuses on the description of the assemblage of detrital platinum-group minerals (PGM) found in rivers draining the Great Dyke. This PGM assemblage distinctly contrasts with the suite of PGM in the pristine, sulfide-bearing Main Sulfide Zone (MSZ) of the Great Dyke, the assumed source of the detrital PGM. Specifically, PGE-bismuthotellurides and -sulfarsenides, common in the MSZ ores, and PGE-oxides or -hydroxides present in the oxidized MSZ, are missing in the assemblage of detrital PGM in the fluvial environment. Instead, conspicuously high proportions of grains of Pt-Fe alloy are common in the sediments, followed by sperrylite, cooperite, braggite, laurite, rare Pd-Sb-As compounds, and Os-Ir-Ru alloys. Possibly, some of the Pt-Fe alloy grains originate from the MSZ, but the majority appear to represent true neo-formations that formed in the course of weathering of the MSZ ores and concomitant supergene redistribution of the ore elements. Sperrylite, cooperite/braggite, and laurite appear to be direct descendants from the primary MSZ. Rare Pd-dominated minerals (Pd-Hg ± As and Pd-Sb ± As) are considered to be neo-formations that probably formed from dispersed elements during supergene processes. Os-Ir-Ru alloy grains, present in the samples from the Umtebekwe River in the Shurugwi area, possibly originate from the Archean chromitite deposits of the Shurugwi greenstone belt and not from the Great Dyke. Geochemically, the Pt/Pd proportions increase from pristine via oxidized MSZ ores to the fluviatile environment, corroborating earlier findings that Pd is more mobile than Pt and is dispersed in the supergene environment. Detrital PGM can be expected to be present in rivers draining PGE-bearing layered intrusions, and economic placers may form under particular sedimentological conditions. Therefore, the work also highlights the fact that simple field methods have their value in mineral exploration, especially if they are combined with modern micro-analytical methods. Furthermore, it is established that the PGE-bismu thotel lurides, PGE-sulfarsenides, and PGE-oxides, dominating the PGM assemblages in the pristine and oxidized MSZ, are components that are unstable during weathering and mechanical transport. Including the genetically somewhat disputed Pt-Fe alloys, the order of decreasing stability in the supergene environment is as follows: (1) Pt-Fe and Os-Ir-Ru alloys (very stable) → (2) sperrylite (stable) → (3) cooperite/braggite (variably stable/”metastable”) → (4) PGE-bismuthotellurides, PGE-sulfarsenides, and PGE-oxides (unstable).

Sedimentology of Quaternary calcareous tufas from Gafsa, southwestern Tunisia

Well-preserved tufa deposits exhibit a diversity of field fabrics along the major structural feature in Gafsa area and extent between Jebel El Mida in the southeast and Sidi Ahmed Zarrouk and Jebel Ben Younes in northwest. The deposition history of the tufa is defined by three major stages; the first occurred in a perched springline or slope system with dominance of the autochthonous facies (stromatolitic tufa facies, i.e. boundstone sheets of micrite and peloids, and phytoherm framestone facies) in the proximal zone and microdetrital tufa in distal sites. The second stage occurred in a mixture of perched springline and poorly drained paludal environments that characterized by the abundance of allochems and chalk and marl. The third deposition stage occurred in a mixture of paludal and braided fluviatile environments with allochthonous tufa facies (oncoidal cyanolith tufa facies, phytoclast tufa facies and lithoclast and intraclast tufa facies). Tufas are of particular interest since their occurrences are linked to tectonic activity and extensional fault systems. Gafsa strike-slip fault, in addition to its tectonic role in creating fluid paths to the surface through flowing springs, it acts as a major regional sill that controlled paleoflow directions, discharge locations, volume, rate and fluctuations of the water supply. Tufa cessation could be explained by increasing aridity during late Holocene and subsequent reduced rainfall, increased evaporation and water table falling, which reduce the amount of recharge and its subsequent dissolution in the recharge area.

Diagenetic evolution and reservoir potential of the Barremian–Cenomanian Debre Libanose Sandstone, Blue Nile (Abay) Basin, Ethiopia

The Blue Nile Basin is located in the Central Plateau of Ethiopia. The basin consists of Precambrian basement, Palaeozoic and Mesozoic sedimentary rocks and Tertiary volcanic rocks. The sedimentary successions and Debre Libanose Sandstone reach a maximum thickness of 3000 and 310 m, respectively. The Debre Libanose Sandstone is composed of mudstone, finely laminated siltstone, fine-to medium-grained sandstone, massive to crudely cross-bedded gravely sandstone and massive to crudely bedded conglomerate. In the Blue Nile Basin it was deposited in a fluviatile environment, predominantly in braided and meandering rivers. The sandstone has a complex diagenetic history and is cemented by silica, calcite, kaolinite, hematite with minor amounts of illite and chlorite. Depositional environment, burial and thermal history, pore water composition and circulation, and diagenetic processes are the major factors that control the porosity and permeability of the sandstone. Minor amounts of primary porosity are preserved owing to framework grain stability. Dissolution of feldspar grains and calcite cement created a certain amount of secondary porosity in the sandstones. The fine-to medium-grained sandstones are porous and have good reservoir potential.

Effects of adjacent mud rocks on CO2 injection pressure: Model case based on a typical U.S. Gulf Coast salt diapir field under injection

Abstract Geological carbon storage aims at long-term storage of carbon dioxide (CO 2 ) in deep geological formations to reduce anthropogenic CO 2 emissions into the atmosphere. The viability of CO 2 storage hinges on how much of the CO 2 can be injected into the storage formation. However, the rate of CO 2 injection can be limited by low injectivity of the storage formation and limits placed on the injection pressure to maintain seal integrity. Therefore, pressure evolution during CO 2 injection is an important consideration for CO 2 storage operation and is investigated in this study. We use geological characteristics of a typical oil field near a salt diapir in the Gulf Coast basin in the Southern United States. In this case CO 2 is injected into a complex sedimentary rocks deposited in a fluviatile environment, juxtaposing volumes of high- and low-permeability rocks. The rock volume in which CO 2 injection is taking place can be modelled, for the purpose of this study, as a simple reservoir surrounded by mud rocks which exhibit small, but finite, permeability and high compressibility. The mud rock is expected to behave as a capillary seal preventing upward CO 2 migration, but may allow significant pressure dissipation. This pressure attenuation can be important from an operational standpoint as a fault in the vicinity of the injection well requires an accurate estimate of pressure evolution to avoid leakage along the fault. Most numerical simulations of geological CO 2 storage have focused on the behavior of fluids within a storage formation and assumed that overlying and underlying rocks are impermeable and incompressible. Such a reservoir model has immediate pressure buildup and drawdown corresponding to start and end of injection. Numerical simulations using reservoir parameters and a simple geomechanical model based on rock and fluid compressibilities were performed with the commercial simulator GEM from CMG. They show that overlying and underlying mud rocks attenuate pressure build-up within a reservoir during injection and extend the period of pressure recovery after the end of injection. The attenuation of pressure propagation within a target formation can reduce the probability of creation and/or reactivation of geological discontinuities. In addition, strong pressure gradients detected just outside the storage formation require high numerical resolution at the boundaries between the storage formation and mud rocks, otherwise extensive numerical diffusion will lead to unphysical pressure dissipation. It is therefore not just important to include the surrounding rocks but also to discretize them appropriately, and this is currently not standard practice.

Lithostratigraphic subdivision of the Kuhlan Formation in Yemen

The lithostratigraphic subdivision of the Kuhlan Formation in Yemen is reviewed based on the previous literature and new examination of five widely spaced outcrops in the Kuhlan Affar, Jabal Maswar, Jabal Salab, Wadi Hajar, and Ras Falanj areas. Following the guidelines set by the North American Commission on Stratigraphic Nomenclature, Kuhlan Formation, with an age as latest Triassic to the Middle Jurassic, includes three members, Azzan, Souq, and Hesn, in an ascending order. Azzan member consists mainly of about 40 m of whitish coarse grained sandstone with many conglomeratic horizons. The Souq member is characterized by its reddish to brownish sandstones as well as the presence of polygonal structures at in the central part of this member, with a thickness of about 70 m. The Hesn member consists dominantly (80 m) of whitish sandstones with some marl intercalations at its topmost part. The Kuhlan Formation was deposited in a fluviatile environment.

Late Ordovician (Sandbian) brachiopods from the Mweelrea Formation, South Mayo, western Ireland: stratigraphic and tectonic implications

AbstractA Late Ordovician (Sandbian), Scoto‐Appalachian brachiopod fauna from the Mweelrea Formation in western Ireland confirms a location for the South Mayo Trough adjacent to the Laurentian margin, characterized at this time by a succession of marine excursions over fluviatile environments. The new, younger biostratigraphical data help to constrain the timing of late Grampian folding of this part of the South Mayo Trough. Copyright © 2010 John Wiley &amp; Sons, Ltd.

Organic petrographical, mineralogical and geochemical features of the Achlada and Mavropigi lignite deposits, NW Macedonia, Greece

Abstract The Achlada and Mavropigi lignite deposits in northern Greece provide the main coal source for the next generation of Greek power plants. A comparative characterization of these two lignite deposits is presented, covering the coal rank and the features of the maceral components, based on detailed coal petrography, and the mineralogical and geochemical features of the coals and their ashes, based on XRF and XRD analyses. The data are used to interpret the palaeoenvironments of the lignite beds, as well as factors that may affect their burnout behavior. Both deposits have a lignite C rank. The Mavropigi lignite is mainly a matrix lignite lithotype, whereas the Achlada deposit consists both of matrix and xylite-rich lithotypes. The Achlada lignite was formed in a fluviatile environment, mainly in the abandoned channels of a meandering river system during flooding periods; hence it is enriched in inorganic matter, with ash values > 30 wt.%. The Mavropigi lignite formed in a reed-marsh environment under limno-telmatic conditions, and displays ash values The inorganic matter of the two deposits is different in composition due to the contrasting environments, and these differences should be taken into account in optimizing their utilization for power production. A preliminary assessment indicates that the Achlada lignite may have more favorable slagging and fouling properties than the Mavropigi lignite, although experimental studies are required for more solid conclusions to be reached.

Paleodepositional environmental diagnosis of the Nsugbe area and environs, Anambra state, southeastern Nigeria: an application of pebble Morphometric studies.

The application of pebble morphometric studies in diagnosing the paleodepositional environment of Nsugbe area and environs was carried out using one hundred and seventy (170) vein quartz recovered from seventeen (17) outcrops widely distributed in the studied area. Results show that the pebbles are rounded to subrounded and dominantly compact to compact-bladed. Computed mean values for the flatness index (FI), elongation, maximum projection sphericity index (MPSI) and oblate-prolate index (OPI) are 0.47, 0.74, 0.67 and 0.40 respectively. When these values were integrated with bivariate plots of MPSI versus OPI and mean roundness versus elongation ratio, a dominantly fluviatile depositional environment with subordinate beach/littoral setting are indicated for the Nsugbe area and environs. KEY WORDS: Pebble morphometry, Paleodepositional environment, Fluviatile, Nsugbe, Anambra basin.