Cross-bedded Sandstone Research Articles

Characterization of the salinity conditions of Cenomanian formations based on sedimentological and ichnological data of selected cores from Ivoirian offshore basin (septentrional Gulf of Guinea)

Detailed sedimentological and ichnological analysis of core material from selected wells were performed in order to fully characterize the range of facies encountered within Cenomanian formations of Ivorian offshore basin.Results indicate that the cored successions comprise four major groups of lithofacies: Pebbly (CS, PS), clean sandstone (S), muddy sandstone (S*M) and mudstone (HM, ML, MJ & M). These lithofacies groups were further sub-divided into component facies based mainly on sedimentary structures. The pebbly group comprises conglomerate sandy and pebbly sandstone. The clean sandstone group includes seven facies: massive sandstone, laminated sandstone, cross-bedded sandstone, bioturbated sandstone, deformed sandstone, wavy-bedded sandstone and rippled sandstone. The muddy sandstone group comprises bioturbated muddy sandstone, while the mudstone group comprises four main facies, namely wavy-bedded heterolithic/sandy mudstone, calcareous mudstone, silty mudstone and pure mudstone.A range of ichnofossils were identified in the cores including: Planolites isp, Palaeophycus isp, Lockeia isp, Phycosiphon isp, Thalassinoides isp, Rhizocorallium isp, Cylindrichnus isp, Chondrites isp and Teichichnus isp. Among these, the Phycosiphon isp Chondrites isp and Rhizocorallium isp reveal fully marine salinities in some intervals of these cores, although Chondrites isp usually used as proxy for disoxia and Rhizocorallium isp were sometimes associated with Glossifungites isp ichnofossils. Integration of the sedimentary data (lithofacies) and trace fossil ichnofossils data revealed several depositional environments ranging from coastal/deltaic to shallow marine settings within the Cenomanian cores.

Benthic foraminiferal fauna and sediment provenance of Eocene syn-rift sequences in Taiwan: implication for onset of Asian epi-continental marginal seas off China coast

Early Cenozoic rift basins developed commonly on the Mesozoic basement along the SE Asia Continent. However, Eocene–Oligocene sequences were only exposed widely onshore Taiwan. We study benthic foraminifera and determine U–Pb geochronology of detrital zircon grains in the Early Cenozoic sequence onshore Taiwan for understanding if there was any significant change in faunal content and sediment provenance between the Eocene syn-rift sequences and the overlying Oligocene post-rift strata across the breakup unconformity. The Eocene syn-rift sequences are mostly of thick, cross-bedded sandstones of fluvial-deltaic depositions without marine fauna. Intensive study on the Eocene stratigraphy in more than ten sections all over the Taiwan mountain belt in the last three decades, shallow marine benthic foraminifera of Gaudryina hayasakai-Hanzawaia asterizana-Planularia okinoshimaensis-Heterolepa praecinta assemblage were found only in very limited exposures in the Western Foothills, central Taiwan. This study shows that the Eocene benthic foraminiferal assemblage is similar to the Shihtsaoan fauna in the overlying Oligocene post-rift marine strata. This indicates no significant faunal break across the breakup unconformity. As a consequence, Gaudryina hayasakai Zone of the Shihtsaoan age can extend downward to the Eocene and the Shihtsaoan Stage would be equivalent to the Hsuehshanian Stage established previously from northern Taiwan. The Taiwan Eocene marine sequences could be deposited in a normal-fault bounded narrow seaway or gulf connecting southeastward to the open Huatung Basin. U–Pb geochronology of detrital zircons in the Taiwan Eocene syn-rift sandstones shows a prominent age peak centered in Yenshanian (100–155 Ma) similar to the Paleocene–Oligocene fluvial-deltaic deposits in the East China Sea and is also comparable to the U–Pb zircon age spectrum of modern river sands of the Fujian Province, SE China. Petrographic study also suggests a prevailing sediment provenance of the Cathaysia granites and volcanics. These Cathaysia detritals were transported to the Taiwan Eocene grabens through some SE-flowing rivers. Structural reconstructions in previous study indicated that the mountain belt with the Eocene sequences in NE Taiwan had been shortened by imbricated thrusting westward for 160–200 km wide during the arc-continent collision in the last 6.5 Ma. Integrating paleontology and sedimentology evidence reveal that the Eocene coast was located along the modern shelf break of the East China Sea ~ 350–400 km east off the modern Chinese coast line. This implies that in the Eocene time (~ 40 Ma) there was no wide Asian epi-continental marginal seas off Chinese coast until the onset sedimentation of the Oligocene post-rift strata during opening of the South China Sea in the Early Oligocene time (~ 33 Ma).

Rainfall-induced landslide in the active frontal fold–thrust belt of Northwestern Himalaya, Jammu: dynamics inferred by geological evidences and Ground Penetrating Radar

Landslides are the most established geological hazards in the frontal fold–thrust belt of Northwestern Himalaya comprising of Siwaliks and Murree strata. The continuous rainfall from 2 to 6 September, 2014 caused a massive landslide at village Sadal in Udhampur district of Jammu and Kashmir state. The landslide occurred in the early morning of September 6, 2014, destroying entire Sadal habitation comprising 45 houses, and killing 41 people and more than 500 domestic animals. Google earth images of pre and post-landslide events along with the field measurements show the kinematics of upper and lower parts of the slide. Horizontal and vertical components of displacement and mode of failure suggest the landslide as of complex nature. The shallow subsurface geophysical imaging through Ground Penetrating Radar (GPR) survey shows the failure plane composed of friable mudstone bed underlain by massive mudstone and overlain by cross-bedded sandstone. The depth of debris material above the failure plane ranges from 6 m at Site S1a-b to 10 m at Site-S2b and 20 m at Site S3a. The velocity analysis of Site-3 shows four thick layers represented from bottom to surface by L1—sandstone (V = 0.16 m/ns, travel time = 356.36 ns), L2—mudstone (V = 0.17 m/ns, travel time = 288.48 ns), L3—massive mudstone (V = 0.19 m/ns, travel time 220.68 ns), and L4—cross-laminated sandstone (V = 0.20 m/ns, travel time = 77.58 ns) overlaying the failure plane. The study shows the landslide occur along the western limb of a fold identified during the present work. We mapped an old landslide on the same limb which shows 5–6 m-thick subsurface debris material with thick rock fragments involved in the landslide process. The detailed geological and geophysical investigations suggest that both the landslides were triggered by extreme rain fall events.

Subsurface aquifer heterogeneities of Lower Triassic clastic sediments in central Germany

Abstract A combined study of facies and diagenesis variations was carried out with the aim to understand small-scale heterogeneities in porosity and permeability of sandstones within a 219 m completely cored Middle Buntsandstein succession from central Germany. The well Erfurt 1/12 (EF-FB 1/12) allows studying aquifer quality variations by taking 49 plug samples of fresh rock material for thin section analyses and petrophysical measurements. This potential Buntsandstein aquifer is composed of varying portions of sandstones, mudstones and sandstone-mudstone interlayers, which were deposited on a large terminal fan system and in a large playa-lake in the basin centre. A fluvial channel and a sandflat depositional environment can be distinguished. Both are composed of varying amounts of channel-, sandsheet- and floodplain sediments of mainly massive, cross-bedded, horizontally laminated and ripple cross-bedded sandstones. Best aquifer potential occurs in the horizontally laminated and cross-bedded sandstones within channels of the fluvial environment, and in the massive sandstones of channels in sandflat deposits. Aquifer quality does not decrease with increasing depth or stratigraphic position. Instead, it is controlled by grain size and diagenetic evolution. Four diagenesis types were distinguished: (1) cementation type (CT), (2) leaching type (LT), (3) illite type (IT) and (4) mixed type (MT). Best aquifer quality was found in the leaching type (LT) consisting of larger grain sizes (medium sand), which led to the formation of a large primary pore network. Our data suggest a strong relation of hydraulic parameters not only with different facies types, architectural elements and depositional environments, but particularly with compaction and cementation during burial, and dissolution by meteoric water during subsequent uplift history. Thereby, present horizons with good hydraulic properties relate to this complex interaction of sedimentary facies and diagenetic evolution, but are restricted to only very local areas with no relevance for basin-wide fluid flow in the subsurface.

Incomplete but intricately detailed: The inevitable preservation of true substrates in a time-deficient stratigraphic record

True substrates are defined as sedimentary bedding planes that demonstrably existed at the sediment-water or sediment-air interface at the time of deposition, as evidenced by features such as ripple marks or trace fossils. Here we describe true substrates from the Silurian Tumblagooda Sandstone of Western Australia, which have been identified by the presence of the surficial trace fossil Psammichnites. The examples are unexpected because they have developed along erosional internal bounding surfaces within a succession of cross-bedded sandstones. However, their seemingly counterintuitive preservation can be explained with reference to recent advances in our understanding of the time-incomplete sedimentary-stratigraphic record (SSR). The preservation of true substrates seems to be an inevitable and ordinary result of deposition in environments where sedimentary stasis and spatial variability play important roles. We show that the true substrates developed during high-frequency allogenic disturbance of migrating bedforms, forcing a redistribution of the loci of sedimentation within an estuarine setting, and subsequently permitting an interval of sedimentary stasis during which the erosional bounding surfaces could be colonized. These observations provide physical evidence that supports recent contentions of how sedimentary stasis and the interplay of allogenic and autogenic processes impart a traditionally underestimated complexity to the chronostratigraphic record of geological outcrop.

Fish assemblage and palaeoenvironment of Early Cretaceous (Barremian) neap-spring tidal rhythmites from Sidi Aïch Formation of the Chotts basin (Southern Tunisia)

The Khanguet Aicha Barremian Biota site (KABBS) has yielded five actinopterygian taxa, four of are shortly described in this paper. The fish assemblage comprises the ichthyodectiform Cladocyclus sp., indeterminate osteoglossiform, chanoidei and stem otophysan, plus an ellimmichthyiform previously described. The fish assemblage recorded in the KABBS corresponds to a mixture of mostly freshwater taxa, the osteoglossiform, with taxa that dwell in both marine and freshwater environments (Cladocyclus and the chanoidei) and a marine fish (the stem otophysan). The association of the fish specimens with both freshwater conchostracan and marine shrimp indicates that the paleoenvironment was characterized by the influence of freshwater input. The fish assemblage contains a mixture of taxa that are found along the southern margin of the Tethys and along both margins of the incipient South Atlantic Ocean.Sedimentary facies of the Sidi Aïch Formation, which encompasses the KABBS include channel intraformational clasts, cross-bedded sandstones with mud drapes, herringbone cross-bedding; and sigmoidal cross-bedding suggesting strong tidal influences. Tidal facies together with paucity of bioturbation and mixed freshwater to marine fossils indicate that sedimentation took place mainly in restricted tidal flat ponds. The clayey varved facies, which dominates the KABBS corresponds to dark organic-rich and white organic-poor laminae interpreted as cyclic rhythmites reflecting neap-spring tidal cycles interrupted by flood events. Excellent preservation biota within KABBS and like-varved facies suggest deposition in low-energy restricted environments like mixed marine and fresh-water ponds along the tidal flats of the tidal meandering channel. Organic geochemistry analysis supported the idea of rapid burial associated with short-period sub-anoxic condition.

Oligocene storm-induced lacustrine deposits in the Yaxi Area of the Jiuxi Basin, northeastern margin of the Tibetan Plateau

Storm-induced deposits in the sedimentary record can now be easily identified on account of a better understanding of processes of unidirectional and oscillatory flow. Thin-bedded sandstone, siltstone, and interlayered mudstone deposits of the Oligocene Jianquanzi Member in the Yaxi Area of the Jiuxi Basin along the northeastern margin of the Tibetan Plateau were formed by shallow lacustrine storm-generated flows. Petrologic analysis reveals that the sandstones exhibit moderate to high compositional maturity but are texturally sub-mature to immature. Based on investigation of drill cores, six storm-deposit lithofacies are identified, including massive or graded sandstone, parallel and trough cross-bedded sandstones, hummocky cross-stratified sandstone, wave-rippled sandstone and siltstone, massive or horizontal bedded mudstone, and structurally deformed sandstone and mudstone. In a vertical succession, these lithofacies occur as three fining-upward lithofacies associations, each of which represents different architectural elements (and depositional processes) of proximal to distal storm deposits. The relatively coarse proximal architectural element is formed by strong density flows and unidirectional-dominated combined flows; the transitional architectural element is dominated by unidirectional- and oscillatory-dominated combined flows to pure oscillatory flows, resembling Tb-e divisions of the classic Bouma sequence; the relatively fine distal architectural element is dominated by unidirectional-dominated combined flows with a very weak oscillatory flow component. The origin of storms responsible for these deposits is attributed to Asian winter monsoons associated with the paleoclimatic and paleogeographic setting.

Storm and tide influenced depositional architecture of the Pliocene–Pleistocene Chad Formation, Chad Basin (Bornu Sub–basin) NE Nigeria: A mixed fluvial, deltaic, shoreface and lacustrine complex

Lithofacies analyses of the upper part of the Chad Formation (Bama Ridge Complex) in the Bornu Sub–basin of the Chad Basin indicated four facies associations; fluvial, deltaic, shoreface and lacustrine sequences. The fluvial sequences are composed of fining upward cycles with successive occurrence of planar crossbedded sandstone facies displaying unimodal paleocurrent system and rare mudstone facies typical of braided river system. The deltaic succession consists of both fining and coarsening upwards cycles with the former depicting fluvial setting of an upper delta plain while the later suggestive of mouth–bar sequences. The setting displays a polymodal current system of fluvial, waves, storms and tides that were primarily induced by complex interactions of seiches and lunar tides. Similar current systems devoid of fluvial patterns were reflected in the coarsening upward packages of the shoreface sequences. Lacustrine succession composed of thick bioturbated mudstone facies generally defines the base of these coarsening upward profiles, giving a fluvio–lacustrine geomorphic relief where complex interaction developed the deltaic and shoreface facies along its shorelines. Clay mineral fractions of the formation are dominantly kaolinitic, indicating a predominantly humid tropical–subtropical climatic condition during their deposition. This climatic regime falls within the African humid period of the early–mid Holocene that led to the third lacustrine transgression of the Lake Mega-Chad, whereas the subordinate smectite mineralization points to aridification that characterizes most of the post humid period to recent.

Classification and sedimentary characteristics of lacustrine hyperpycnal channels: Triassic outcrops in the south Ordos Basin, central China

Subaquatic channels are known as active conduits for the delivery of terrigenous sediments into related marine and lacustrine basins, as well as important targets for hydrocarbon exploration. Compared to submarine channels, lacustrine subaqueous channels created by hyperpycnal flows are understudied. Using well-exposed outcrops collected from three different locations in the southern Ordos Basin, central China, morphologies and architecture of a channelized hyperpycnal system were studied and classified. Six facies associations represent sedimentary processes from strong erosion by bedload dominated hyperpycnal flows, to transitional deposition jointly controlled by bedload and suspended-load dominated hyperpycnal flows, finally to deposition from suspended-load dominated hyperpycnal flows. On the basis of channel morphologies, infilling sediments and sedimentary processes, the documented channels can be classified into four main categories, which are erosional, bedload dominated, suspended-load dominated, and depositional channels. In very proximal and very distal locations, erosional channels and depositional channels serve as two end-members, while in middle areas, bedload-dominated channels and suspended-load dominated channels are transitional types. Erosional channels, as a response to strong erosion from bedload dominated hyperpycnal flows on upper slope, were mainly filled by mud interbedded with thin sand beds. As flow energy decreases, bedload dominated channels develop on middle slopes, which are characterized mainly by under- to balanced sediment infillings with cross-bedded sandstones and/or minor massive sandstones. Compared to bedload dominated channels, suspended-load dominated channels mainly develop in deeper water, and were filled mainly by massive or planar-laminated sandstones. Depositional channels, as a response to suspended-load dominated hyperpycnal flows in deep-water areas, are characterized by thin-medium bed classical turbidites with Bouma sequences and thin- to thick massive sandstones. Such evolution patterns of hyperpycnal channel systems are ascribed to the progressive decrease in flow capacity of hyperpycnal flows, and provide an adequate explanation for the basinward channelization behavior of hyperpycnal systems.

Diagenetic influence on reservoir quality evolution, examples from Triassic conglomerates/arenites in the Edvard Grieg field, Norwegian North Sea

Abstract The Utsira High (Southern Norwegian North Sea) has been a petroleum exploration target since the late 1960s. The southwestern part of the Utsira High complex (Haugaland High) attracted new interest when in 2007 Lundin Norway AS and partners Revus Energy ASA and RWE Dea Norge AS discovered commercial hydrocarbon reservoirs in Triassic to Early Cretaceous formations (Edvard Grieg field). In the present study, four siliciclastic cores from the Edvard Grieg field have been investigated sedimentologically, including core logging, optical mineralogy, X-ray powder diffraction (XRD) and scanning electron microscope (SEM). Quantification and characterization of the different mineralogical phases in thin section have been executed to better understand porosity evolution through time. Intergranular volume (IGV) and cement volume were also compared in order to estimate the most important factors effecting porosity loss within the studied samples. The results show that through time the various diagenetic events and phases, such as dissolution of unstable grains and precipitation of clay minerals and cements, strongly influenced reservoir quality in the Edvard Grieg field. Two main lithology groups are identified within the cored intervals, conglomerates and sandstones. These two groups can further be sub-divided into four units: 1) sandy conglomerate, 2) silty conglomerate, 3) interbedded sandstone, 4) large scale cross-bedded sandstone. Most of the reservoir quality reduction in the conglomerate matrix can be related to poor sorting, carbonate cement and pore-filling/pore-lining authigenic clay minerals. Better reservoir quality characterizes the sandstone-dominated alluvial fan intervals, which generally are associated with a greater degree of sorting that led to higher intergranular porosities. Large scale cross-stratified sandstone units, interpreted to be of aeolian origin, have the highest reservoir quality. These deposits are moderately to well sorted with only minor occurrences of patchy carbonate cement and generally low proportions of authigenic minerals. However, locally abundant kaolinite has been observed, filling the pore space and reducing the porosity, predominantly by blocking interconnected primary pores.

Barremian synrift sedimentation in the Oliete sub-basin (Iberian Basin, Spain): palaeogeographical evolution and distribution of vertebrate remains

A review of the onset of the synrift sedimentation and synsedimentary extensional tectonics of the Oliete sub-basin (northwestern Maestrazgo basin, East Spain) is presented here based on new data acquired after extensive sedimentological, structural and palaeontological analysis of the Barremian Blesa Fm. The lower boundary of the Blesa Fm is a prominent basal synrift unconformity overlying Jurassic units. This formation has been divided into three genetic stratigraphic sequences bounded by sub-basin-wide unconformities. The lower Blesa sequence (LBS) is characterized by distal alluvial to palustrine marls/clays grading upward to palustrine–lacustrine limestones. The LBS is bounded on top by a planar to irregular transgressive, hardened ferruginous surface, locally encrusted by oysters. Above this discontinuity, the middle Blesa sequence consists of oyster-rich limestones and marls deposited in a shallow restricted bay, which grade to distal alluvial and palustrine–lacustrine marls/clays and limestones towards the marginal areas of the basin. The boundary between the middle and upper Blesa sequence (UBS) is a regressive surface outlined by the local presence of an erosive conglomeratic bed. The UBS generally starts with red clays deposited in distal alluvial fan environments, which grade upwards to palustrine and lacustrine carbonates and marls/clays. The local presence of heterolithic alternations of clay with fine-to-medium sandstone and of cross-bedded sandstones indicates the local occurrence of siliciclastic coastal environments in the UBS. The upper boundary of the Blesa Fm is marked by widespread transgression, giving rise to the bioclastic limestones of the Alacon Fm. In the present paper, the stratigraphic position and palaeoenvironmental context of the abundant vertebrate remains found across the defined sequences within the Blesa Formation is reviewed. The results obtained are relevant for a further understanding of the tectosedimentary evolution of the studied basin. Successive stages of evolution are distinguished, including the initial uplift, breakup and erosion of the earlier Jurassic carbonate platform that took place during the Tithonian–Hauterivian; the onset of synrift sedimentation during the early Barremian, which was highly controlled by extensional faulting and differential block subsidence; the homogenization of the basin subsidence accompanied by the incursion of marine waters (sourced from southeastern areas) during the middle part of the Barremian; and the significant fall in base level, of possible climatic origin and also involving significant siliciclastic input in the northern areas of the Oliete sub-basin around the middle part of the late Barremian.

Tectonic evolution of syn- to late-orogenic sedimentary–volcanic basins in the central Norwegian Caledonides

We present new structural, geochemical and U–Pb zircon data from syn- to late-orogenic sedimentary–volcanic basins in the southwestern part of the Trondheim Nappe Complex, central Norwegian Caledonides. In this area, a succession of enriched mid-ocean ridge basalt type metabasalt, jasper, ribbon chert with associated sandstone and conglomerate, and green siltstone is interpreted to represent volcanism and sedimentation in a hitherto little-known spreading-dominated tectonic environment. This environment is different from the suprasubduction-zone ophiolite setting dominating the Iapetus rock record elsewhere in the Scandinavian Caledonides. This volcanic and sedimentary succession was overturned and isoclinally folded in a pre-427 Ma orogenic phase. Post-427 Ma cross-bedded sandstones were deposited on the eroded surface of the previously deformed rocks, representing a rare example of a late Silurian or younger sedimentary basin within the Scandinavian Caledonides. The cross-bedded sandstones are intercalated with and/or overlain by post-427 Ma intermediate volcanic or subvolcanic rocks of calc-alkaline composition, representing a hitherto unknown volcanic phase within the Trondheim Nappe Complex and elsewhere within the Scandinavian Caledonides. Their particular geochemical signature could be the result of late-stage subduction-zone volcanism just prior to the onset of continent–continent collision between Baltica and Laurentia, or much younger post-collisional extensional melting with inherited subduction signatures. Supplementary material: A description of analytical methods and a table of geochronological data from LA-ICP-MS analysis of zircons are available at https://doi.org/10.6084/m9.figshare.c.3994605 .

One diamictite and two rifts: Stratigraphy and geochronology of the Gataga Mountain of northern British Columbia

Neoproterozoic glacial diamictites and rift-related volcanics are preserved throughout the North American Cordillera, yet the nature and timing of both glaciation and rifting are poorly constrained. New geochronological, geochemical, and stratigraphic data from the Cryogenian Gataga volcanics and bounding units at Gataga Mountain, in the Kechika Trough of northern British Columbia, better constrain the age of these rift-related volcanics and suggest that they erupted during glaciation. At Gataga Mountain, three informal sequences are exposed; a basal quartzite, the Gataga volcanics, and an overlying mixed carbonate-siliciclastic succession. The basal quartzite is dominated by cross-bedded sandstone with an intertidal facies assemblage including bidirectional cross-stratification and mud-cracks, indicative of non-glacial deposition. The overlying Gataga volcanics are over one kilometer thick, comprising both mafic and felsic units, with volcaniclastic breccia and interbedded sedimentary units including iron formation and matrix-supported diamictite with exotic clasts. Magmatic ages in the upper Gataga volcanics span 696.2 ± 0.2 to 690.1 ± 0.2 Ma, and detrital zircon from the underlying non-glacial quartzite provide a maximum age constraint on the onset of glaciation

The Coconino Sandstone (Permian, Arizona, USA): Implications for the origin of ancient cross-bedded sandstones

The Permian Coconino Sandstone is one of the most prominent layers of rock in the Grand Canyon and is important to creationists because it has often been used by conventional scientists to discredit the Bible since it is a supposed wind-blown (eolian) deposit. Their argument is that deposits like this would be impossible to form in the midst of a global flood as described in Genesis. Over the past forty years, new data has been collected by us and others that we believe indisputably identifies the Coconino as a subaqueous sandstone--data that will be difficult for our critics to counter. These data include evidence from petrology, fossil footprint studies, sedimentology, regional stratigraphy and soft sediment deformation features. In our studies we found that there are many misconceptions or “urban myths” about the Coconino Sandstone including its grain roundness, grain sorting, grain frosting and angle of cross-bed dips. There are no modern analogs that match the precise sedimentology of the Coconino, but we believe that subaqueous sand waves may be a start in the right direction to understand how the Coconino was deposited. Instead of the Coconino being a problem for creationists, it can be one of our most powerful arguments in support of the biblical account of the Flood. There are many other similar cross-bedded sandstones around the world; the Coconino may be the key to unlocking their origin as well.

The significance of micas in ancient cross-bedded sandstones

The significance of micas in ancient cross-bedded sandstones

Improved reservoir characterisation using fuzzy logic platform: an integrated petrophysical, seismic structural and poststack inversion study

There is a tendency for applying different integrated geophysical approaches for better hydrocarbon reservoir characterisation and interpretation. In this study, petrophysical properties, seismic structural and poststack seismic inversion results are integrated using the fuzzy logic AND operator to characterise the Tensleep Sandstone Formation (TSF) at Powder River Basin (PRB), Wyoming, USA. TSF is deposited in a coastal plain setting during the Pennsylvanian era, and contains cross-bedded sandstone of Aeolian origin as a major lithology with alternative sabkha dolomite/carbonates. Wireline logging datasets from 17 wells are used for the detailed petrophysical evaluation. Three units of the TSF (A-sandstone, B-dolomite and B-sandstone) are targeted and their major rock properties estimated (i.e. shale/clay volume, Vsh; porosity, φEff; permeability, K; fluid saturations, Sw and SH; and bulk volume water, BVW). The B-sandstone zone, with its petrophysical properties of 5–20% effective porosity, 0.10–250 mD permeability and hydrocarbon potential up to 72%, is considered the best reservoir zone among the three studied units. Distributions of the most important petrophysical parameters of the B-sandstone reservoir (Vsh, φEff, K, Sw) are generated as GIS thematic layers.The two-dimensional (2D) and three-dimensional (3D) seismic structural interpretations revealed that the hydrocarbons are entrapped in an anticlinal structure bounded with fault closures at the west of the study area. Poststack acoustic impedance (PSAI) inversion is performed on 3D seismic data to extract the inverted acoustic impedance (AI) cube. Two attribute slices (inverted AI and seismic amplitude) were extracted at the top of the B-sandstone unit as GIS thematic layers. The reservoir properties and inverted seismic attributes were then integrated using fuzzy AND operator. Finally, a fuzzy reservoir quality map was produced, and a prospective reservoir area with best reservoir characteristics is proposed for future exploration. The current study showed that integration of petrophysical, seismic structural and poststack inversion under a fuzzy logic platform can be used as an effective tool for interpreting multiple reservoir zones.

The oldest known paleosol profiles on Earth: 3.46 Ga Panorama Formation, Western Australia

Subaerial volcanic flank and floodplain facies of the 3.46Ga Panorama Formation have been recognized on the basis of trough cross-bedded sandstones, lapilli tuffs, and abundant nodularized barite sand crystals, like those noted in other Archean non-marine facies. These barite-nodular layers are interpreted as alluvial paleosols for the following reasons. They show different degree of bedding disruption scaled to nodule size beneath a sharp upper boundary, like desert soil profiles. They show multiple generations of cracking, clay skins, and up-profile destruction of feldspar and rock fragments, compatible with weathering of labile constituents of the parent material. Loss of alkali and alkaline earth elements and phosphorus up profile are also features of chemical weathering. Geochemical mass balance calculations (tau analysis) shows that the profiles lost mass and labile elements, unlike unaltered sediments and tuffs. Rare earth element analysis also shows light rare earth retention as in weathering, as opposed to sedimentation or hydrothermal alteration. Barite of nodules in the paleosols is mobilized to concentration under very acidic conditions (pH<3) and is very stable under less acidic conditions. These Archean alluvial paleosols may have formed by acid sulfate weathering by sulfuric acid, rather than the currently more common hydrolysis by carbonic acid. This archaic system of widespread acid sulfate weathering has since been marginalized to a few playa lakes, deep water tables, and sulfur springs.

Late Ordovician glacial and glacio-fluvial paleovalley architecture and sedimentation in southeast Jordan and northwest Saudi Arabia

Four recently discovered glacio-fluvial paleovalleys in southeast Jordan and northwest Saudi Arabia are described for the first time. The paleovalleys formed as a result of glacial erosion by series of sub-parallel valley glaciers during the Late Ordovician (Hirnantian) southern hemisphere glaciation on the Arabian Plate. The southwest-northeast orientation of the paleovalleys, Proterozoic erratic clasts and paleocurrent vectors indicate the advance of glaciers and subsequent glacio-fluvial siliciclastics emanating from a paleo-ice sheet located to the south on the Arabian Shield. U-shaped, paleovalley cross-sectional morphologies and gently inclined longitudinal profiles indicate initial glacial erosion of the ‘finger-like’ paleovalleys, probably as wet-based valley glaciers, eroded up to 250 m depth into Late Ordovician marine bedrock formations. Paleovalley-fill sequences comprise a tripartite upwards succession: (a) basal sandstone-dominated tillite with well-rounded, grooved and striated granitoid and metamorphic basement clasts derived from the Proterozoic Arabian Shield together with locally derived, rounded and elongate boulders eroded from the local bedrock at the margins of the paleovalleys (Retrogradational Lowstand Sequence); (b) green chloritic siltstone (Zarqa Formation) deposited during a progradational sea-level rise with marine influence (Transgressive Sequence); (c) coarse-grained, trough cross-bedded sandstone (Sarah Formation) attributed to progradational fluvial sedimentation as glacial outwash. Rapid sea-level rise during latest Hirnantian to Early Llandovery time resulted in marine flooding of the glacio-fluvial alluvial plain and deposition of organic-rich mudstones representing transgressive and high-stand sequences.

Generic hierarchy of sandstone facies quality and static connectivity: an example from the Middle-Late Miocene Miri Formation, Sarawak Basin, Borneo

A significant percentage of the world’s hydrocarbon reserves are found in shallow marine sandstone rocks. Understanding reservoir connectivity and quality of shallow-marine sandstones from outcrop analysis and facies characteristics is a challenging task. Here, we analyze well-exposed outcrops of the Miri Formation, Sarawak Basin, Borneo, to characterize reservoir properties (grain-size, petrography, pore-perm, and static connectivity) of different sandstone facies and to construct a 2D intermediate-scale model of sandstone distribution and connectivity. The outcrops, with lateral extent of ∼200–500 m, consist of mostly sandstone with mud-rich deposits including some isolated sand bodies. Field description in terms of facies distribution and dimensions of sand bodies and rock sampling for grain-size (Folk and Ward methods), petrographic (point count method for porosity, sorting, grain-size, and sand-mud %), and poro-perm (for porosity and permeability) analyses were performed to quantify and examine seven different types of sandstones facies, i.e., (i) hummocky cross-stratified sandstones (HCSS, ∼0.5–4 m thick), (ii) herringbone cross-bedded (HBCBS, ∼0.5–3 m thick), (iii) trough cross-bedded sandstones (TCBS, ∼0.5–2 m thick), (iv) wavy- to flaser-bedded (W-FBS, ∼1–3 m thick), (v) cross-bedded sandstone (CS), ∼0.5–3 m thick), (vi) bioturbated sandstone (BS, ∼1–5 m thick), and (vii) massive sandstone (MS, ∼0.5–2 m thick). Our results show that compared to other sandstone facies, sandstones of HCSS and HBCBS are better sorted, have minimal mud content, and display increasing vertical and lateral connectivity due to depositional patterns even in bioturbated rich sand. Sandstones of BS and CB are of poor quality in terms of grain sorting and poro-perm, while TCB and MS sandstone facies are of less lateral and vertical extent. On the basis of these results, a 2-D outcrop-based model is constructed that provide additional insights into the significance of small-scale heterogeneity and static connectivity of shallow marine sandstone deposits which can be an analogue for subsurface reservoir quality analysis.

Composition, provenance and tectonic setting of Eze-Aku Sandstone facies in the Afikpo Synclinorium, Southern Benue Trough, Nigeria

Field study, petrographic and major element geochemical composition of the Eze-Aku Sandstone facies outcropping in the Afikpo Synclinorium, southeastern Nigeria, were utilized in this study. The aim is to interpret the provenance and tectonic setting for sandstones in the sedimentary basin. Field observation shows alternating sequence of parallel sandstone ridges trending NE-SW and shales which represent the low-lying plains in the area. Four major sandstone facies were identified: massive conglomeritic sandstone facies, laminated sandstone facies, bioturbated sandstone facies and cross-bedded sandstone facies. Ternary plots for framework elements (quartz, feldspar and rock fragments) from petrography of the sandstones indicate the sandstones as arkosic and subarkosic arenites. Tectonic setting discrimination diagrams plotted based on major element oxides revealed continental block provenance dominantly in a passive continental margin. Petrographic and geochemical results indicate large amounts of detritus were derived principally from plutonic igneous rocks with minor contribution from metamorphic source region, probably from Obudu Plateau, Oban and Cameroon Massifs.