Massive Sandstone Research Articles

The Upper Jurassic Blokelv-1 cored borehole in Jameson Land, East Greenland – an introduction

The Geological Survey of Denmark and Greenland (GEUS) successfully drilled the fully cored Blokelv-1 borehole in the central part of the Jameson Land Basin in East Greenland, targeting the Upper Jurassic, rich source-rock interval of the Hareelv Formation. The borehole achieved 100% core recovery from 1.72 m to a total depth of 233.8 m; the recovered Hareelv Formation section consists of interlayered black, laminated organic-rich mudstones, massive sandstones and heterolithic sandstone–mudstone intervals of the Katedralen Member, and amalgamated massive sandstones of the Sjællandselv Member. The core is of very high quality and has been subjected to an extensive sampling and analytical programme focused particularly on petroleum geological aspects, as presented in the following eight papers in this volume. This bulletin describes an important, previously poorly documented member of the ‘Kimmeridge Clay’ family of prolific petroleum source rocks in the North Atlantic area.

Identification of slip surface based on geoelectrical dipole-dipole in the landslides hazardous area of Gedangsari District, Gunungkidul Regency, Province of Daerah Istimewa Yogyakarta, Indonesia

Landslides problems that often occurred at Mertelu Village, Gedangsari District, Gunungkidul Regency, DIY are caused by several factors. In addition to the fact that the village is located in a fairly steep area, there is also a slip surface from the existing soil type. The purpose of this research is to gather the slip surface information based on resistivity method using Dipole-dipole configuration. The initial stage is done by taking 4 representative lines, which each line is 300 meters long, spaced 20 meters and using n = 1-8. The results showed that rock resistivity varied from 2 to 200 Ohm-m also divided into very low, low, medium and high resistivity. The interpretations are very low resistivity (2-8 Ohm-m) as claystones and or siltstones, low resistivity (8-20 Ohm-m) as muddy sandstones, medium resistivity (20-50 Ohm-m) as sandstones and high resistivity (> 50 Ohm –m) as massive sandstones. In general, the bedding begins with a very low resistivity at the top and high resistivity at the bottom. The slip surface is marked as a very low resistivity which lays above a higher resistivity. The landslide analysis indicates that the Gedangsari area is dominated by rotational landslide.

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.

Geophysical Study of Parts of Oru Area Imo State Nigeria Using Electrical Resistivity Method

Electrical resistivity method has been used in this research work to map the geological features in the Oru Area.Ten vertical electrical soundings were carried out within the study area. An Abem SAS 3000 terrameter and electrodes were used to acquire the resistivity data while a GPS system was used to obtain the co-ordinates of the survey points. The resistivity data was processed using IP2win software while surfer II was used to produce contours of the resistivity data at various depths. Field mapping shows that the northern part of the study area rests on Ogwashi-Asaba formation. The area has mudstone, claystone gritty claystone, and carboniferous mudstone massive sandstone facies whereas Benin formation is found to the southwest from Mgbidi. Also found are clay deposits. There are both shallow and deep seated Aquifers in the Area.

An unusual association of hadrosaur and therizinosaur tracks within Late Cretaceous rocks of Denali National Park, Alaska

We report details of a unique association of hadrosaur and therizinosaur tracks found in the Late Cretaceous lower Cantwell Formation, Denali National Park, central Alaska Range, Alaska. This rock unit is now well-documented as a source of thousands of fossil footprints of vertebrates such as fishes, pterosaurs, and avialan and non-avialan dinosaurs. The lower Cantwell Formation in this area consists of numerous fining-upward successions of conglomerates and pebbly sandstones, cross-stratified and massive sandstones, interbedded sandstones and siltstones, organic-rich siltstones and shales, and rare, thin, bentonites, typically bounded by thin coal seams, and it contains a diverse fossil flora. We report the first North American co-occurrence of tracks attributable to hadrosaurs and therizinosaurs in the lower Cantwell Formation. Although previously un-reported in North America, this association of hadrosaur and therizinosaur tracks is more characteristic of the correlative Nemegt Formation in central Asia, perhaps suggesting that parameters defining the continental ecosystem of central Asia were also present in this part of Alaska during the Latest Cretaceous.

Enigmatic clastic pipe swarms and implications for fluidization dynamics in aeolian deposits

AbstractSoft‐sediment deformation of contorted and massive sandstone is common throughout much of the siliciclastic record, but clastic pipes represent a distinctive class of pressurized synsedimentary features. Remarkable centimetre to metre‐scale clastic pipe exposures in the Jurassic Navajo Sandstone of Utah (USA) establish a range of pipe sizes, expressions and relationships to the host rock in an erg margin setting, traditionally thought to be just a dry desert system. In particular, the field and laboratory characterizations of cylindrical pipes show internal concentric, annular rings that imply water fluidization, with alignment of long grain axes due to shear flow along pipe margins. Central interior parts of decimetre‐scale pipes appear massive in plan view, but display weakly developed pseudobedding from post‐pressure release, gravitational settling in the cross‐sectional view. Deformation features of conjugate fractures, ring faults, hypotrochoid patterns (geometric arcs and circles) and breccia in the host material reflect both brittle and ductile behaviour in response to the fluidization and injection of the clastic pipes. The stratigraphic context of individual pipes and the stratabound intervals of pipe features imply dynamic deformation nearly coincident with deposition in this Early Jurassic aeolian system related to multiple factors of groundwater expulsion, timing and local host sediment properties that influenced pipe development. Although the pipe features might be easily overlooked as a smaller scale feature of soft‐sediment deformation in dune deposits, these are valuable environmental indications of disrupted fluid pathways within porous, reservoir quality sands, associated with possible combinations of periodic springs, high water‐table conditions and strong ground‐motion events. These pipe examples may be important analogues where exposures are not so clear, with applications to diverse modern and ancient clastic settings internationally on Earth as well as in planetary explorations such as on Mars.

Impact of geo technical factors on strata behavior in longwall panels of Godavari Valley coal field-a case study

Understanding the cantilevers formed by thick, massive beds in the near-seam overburden above longwall panels and the associated loads and strata fracturing effects developed during caving (main and periodic weightings) are key elements for the successful implementation of longwalls. Such caving mechanisms rely on the geotechnical conditions within the panel. In India, the majority of longwall downtime and/or roof failures were caused by a lack of knowledge on overburden caveability, in particular when the main and periodic weightings will impact the face and longwall support selection to effectively mitigate such weightings. Godavari Valley Coal Fields is no exception as longwall faces were adversely affected due to the presence of thick, massive beds in the near-seam overburden at both Godavarikhani (GDK) 7 and 9 Incline mines. In contrast, overburden weightings were negotiated successfully in GDK10A and Adriyala Longwall Project (ALP) mines by detailed geotechnical studies, the use of adequate longwall support capacities, and effective operational practices. Thirteen longwall panels with varying face width, at different depths have been extracted under massive sandstone beds of 18 m to 28 m thickness at GDK 10A and ALP mines. This study elucidates that the main roof weighting interval decreases with an increase in face width and attains a constant value with further increases in face width under the same geo- mining conditions. In addition, this study also concludes that with increases in face width, the periodic roof weighting interval decreases and shield loads increase. Similarly with increasing panel width to depth ratio, the main and periodic roof weighting intervals decrease but shield loads again increase. Lastly, the strata behaviour of the longwall face retreated along up-dip direction is demonstrated. The results of this paper improves the mechanistic understanding of the impact of face width, depth and main roof thickness on periodic weighting and associated roof control problems on the longwall face.

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.

Subaqueous sandy mass-transport deposits in lacustrine facies of the Upper Triassic Yanchang Formation, Ordos Basin, Central China

Abstract Subaqueous sandy mass-transport deposits (SMTDs), which are a type of sedimentary deposit formed in deep water environments, have attracted increased attention in recent years. Based on the analysis of outcrops, cores and thin sections using X-ray diffraction and scanning electron microscopy, numerous sandy mass-transport deposits or sandy debrites have been identified in the delta-front and deep lake environments recorded by the Chang 6-7 Member of the Yanchang Formation in the Ordos Basin; thus, a mass-transport model has been established in this paper. These sandy mass-transport deposits are characterized by two distinct features: first, sandstones are characterized by a low matrix content and are defined as massive clean sands; second, massive sandstones are characterized by the widespread development of a rimed chlorite cement with a two-layer structure, which is identical to that present in distributary channel sands of the delta-front environment of the Yanchang Formation. The occurrence of and components of clay minerals indicates that the isopachous rimed cements in the inner layer are related to the original sedimentary environment. Rimed chlorite cements are formed from isopachous clay films that originally adhered to the surfaces of the detrital particles and represent syn-depositional products. Further studies suggest that during the process of retransporting delta-front sediments and forming the sandy debris flows, this material, which was adhered to the surfaces of clastic particles as isopachous clay coatings, together with the small amount of clay-water matrix present in the flow, acted as an “adhesive agent” between particles during the subsequent remobilization of the deposits and the formation of sandy debris flows. The adhesion strength and local matrix support strength created by the clay-water matrix (gels), together with the frictional strength of the sediments, provided support strength for the subaqueous mass transport of the Yanchang Formation. The adhesion formed by the isopachous clay rim or the clay-water matrix is especially dominant and is considered to be the root cause holding the sandy debris flows together during their mass transport. This research may have global implications for better understanding analogous subaqueous mass-transport processes and the distribution of sandstone reservoirs in other locations.

Development of a palaeovalley complex on a Late Ordovician glaciated margin in NW Saudi Arabia

Abstract Late Ordovician glacial deposits are of great importance in North Africa and the Middle East as a result of their significance as reservoirs for hydrocarbons and groundwater. The sedimentary record of this glaciation in NW Saudi Arabia (the Sarah Formation) is generally preserved in meridionally oriented palaeovalleys cut beneath northward-flowing ice sheets. In the Tabuk region of NW Saudi Arabia, an apparently intersecting complex of north–south- and east–west-oriented palaeovalleys occurs in the Alwizam area. Field relationships show two generations of palaeovalley incision, suggesting that the north–south-oriented palaeovalley was cut subglacially, filled, subsequently deformed and then cross-cut by the east–west-oriented palaeovalley. Abundant facetted and striated quartzite clasts occur at the base of each palaeovalley, testifying to a subglacial origin. Detailed examination of the north–south-oriented palaeovalley shows it to be well-defined with symmetrical sides. Its fill is composed of nine lithofacies grouped into four facies associations. About 80% of the fill consists of three sandstone facies: a parallel-bedded massive sandstone, a stacked scoured sandstone and a massive sandstone. Centimetre-scale extensional faults developed in soft sediments are commonly found throughout the stratigraphy, along with a glacially striated surface seen mid-way through the succession. These features provide evidence for direct ice contact, synglacial fill, and consequent reworking, cannibalization and deformation by the fluctuating ice margin.

Petrology, lithofacies, and sedimentary environment of Upper Cretaceous Abu Roash “G” in the AESW Block, Abu Gharadig Basin, Western Desert, Egypt

The Cretaceous clastic rocks are main targets for petroleum exploration and development in the Abu Gharadig Basin. In this paper, the petrology, lithofacies, and sedimentary environment are studied based on the core samples, thin sections (TS), and scanning electron microscopy (SEM) data of Upper Cretaceous Abu Roash “G” (AR “G”) Member in the AESW Block, Abu Gharadig Basin, Western Desert, Egypt. Petrographic studies suggest that sandstones of the AR “G” are classified as sub-feldspathic arenites, quartz arenites, quartz wackes, and sub-feldspathic wackes. Based on rock textures and fabrics, eight lithofacies are identified within sandstones as gravelly sandstone (Sg), massive sandstone (Sm), cross bedded sandstone (Scb), laminated sandstone (Sl), laminated silty sandstone (Slz), ripple laminated sandstone (Srl), deformed laminated sandstone (Sdl), and bioturbated sandstone (Sb). Siltstone facies are classified as laminated siltstone (Zl), laminated sandy siltstone (Zls), laminated muddy siltstone (Zlm), lenticular siltstone (Zlt), and gravelly siltstone (Zg). Mudstone facies mainly consist of massive mudstone (Mm) and laminated mudstone (Ml). Petrographic study together with Lithofacies, typical sedimentary structures, palynomorphs, and biofacies suggest a tide-dominated coastal environment ranging from subtidal flat to intertidal flat in the study area. The tidal channels and tidal bars in the subtidal flat are the most favorable sedimentary microfacies for AR “G” sandstone reservoirs in the Abu Gharadig Basin, Western Desert, Egypt.

Origin and evolution processes of hybrid event beds in the Lower Cretaceous of the Lingshan Island, Eastern China

ABSTRACTOn the basis of detailed sedimentological investigation, three types of hybrid event beds (HEBs) together with debrites and turbidites were distinguished in the Lower Cretaceous sedimentary sequence on the Lingshan Island in the Yellow Sea, China. HEB 1, with a total thickness of 63–80 cm and internal bipartite structures, is characterised by a basal massive sandstone sharply overlain by a muddy sandstone interval. It is interpreted to have been formed by particle rearrangement at the base of cohesive debris flows. HEB 2, with a total thickness of 10–71 cm and an internal tripartite structure, is characterised by a normal grading sandstone base, followed by muddy siltstone middle unit and capped with siltstones; the top unit of HEB 2 may in places be partly or completely eroded. The boundary between the lowest unit and the middle unit is gradual, whereas that between the middle unit and the top unit is sharp. HEB 2 may be developed by up-dip muddy substrate erosion. HEB 3, with a total thickness up to 10 cm and an internal bipartite structure, is characterised by a basal massive sandstone sharply overlain by a muddy siltstone interval. The upper unit was probably deposited by cohesive debris flow with some plant fragments and rare mud clasts. HEB 3 may be formed by the deceleration of low-density turbidity currents. The distribution of HEBs together with debrites and turbidites implies a continuous evolution process of sediment gravity flows: debris flow → hybrid flow caused by particle rearrangement → high-density turbidity current → hybrid flow caused by muddy substrate erosion → low-density turbidity current → hybrid flow caused by deceleration.

An Early Jurassic braided river system from Mehadia, South Carpathians, Romania

The Lower Jurassic (Hettangian–Sinemurian) continental deposits of the Mehadia area (Caras–Severin County) belong to the Presacina Basin, Upper Danubian Units of the South Carpathians, Romania. This un-named succession is exposed along large areas within the Greaţca Quarry where deposits of a complex braided river system can be seen. Nine clastic facies are identified within the Mehadia section and grouped into two facies associations reflecting two main sub-environments. (A) a fine-grained association, up to 6.5 m thick, composed of greyish black and dark grey massive and horizontally laminated mudstones interbedded with fine- to medium-grained sandstones showing ripple lamination, tabular low-angle large-scale cross-bedding and in some places massive sandstones. Within this association coarsening and fining-upward sequences are visible, while subordinate pensymmetrical-like sequences were observed. The sediments of the fine-grained association are interpreted as having been deposited along an alluvial plain from flood waters. The sandstone interbeds are interpreted as crevasse channel-fills and the thinner sandstone bodies as proximal crevasse splays. (B) a coarse-grained facies association represented by sandstones and conglomerates, both clast- and matrix-supported, from granule to pebble clast sizes. Almost all basal members of this association are underlain by erosional surfaces, while internal erosional surfaces occur at some levels. The coarse-grained facies association is interpreted as having been deposited within active river channels of a sandy braided river system. The occurrence of numerous erosional surfaces, the recurrence of the facies within this association (channel bodies), as well as the abundant mudstone and sandstone intraclasts all point to frequent conditions of erosion (including redeposition) of previously deposited sediments. The relatively low fine-grained sediment content (<25%) can be explained by two factors: (1) a creation rate for accommodation space was not enough for the accumulation of a large amount of overbank deposits; (2) a lack of larger quantities of fine-grained material being transported in the river system. Both factors may have operated independently or interacted.

Intrinsic vulnerability assessment of shallow aquifers of the sedimentary basin of southwestern Nigeria.

The shallow groundwater of the multi-layered sedimentary basin aquifer of southwestern Nigeria was assessed based on its intrinsic vulnerability property. The vulnerability evaluation involves determining the protective cover and infiltration condition of the unsaturated zone in the basin. This was achieved using the PI (P stands for protective cover effectiveness of the overlying lithology and I indicates the degree of infiltration bypass) vulnerability method of the European vulnerability approach. The PI method specifically measures the protection cover and the degree to which the protective cover is bypassed. Intrinsic parameters assessed were the subsoil, lithology, topsoil, recharge and fracturing for the protective cover. The saturated hydraulic conductivity of topsoil, infiltration processes and the lateral surface and subsurface flow were evaluated for the infiltration bypassed. The results show moderate to very low vulnerability areas. Low vulnerability areas were characterised by lithology with massive sandstone and limestone, subsoils of sandy loam texture, high slopes and high depth to water table. The moderate vulnerability areas were characterised by high rainfall and high recharge, low water table, unconsolidated sandstones and alluvium lithology. The intrinsic vulnerability properties shown in vulnerability maps will be a useful tool in planning and monitoring land use activities that can be of impact in groundwater pollution.

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.

Sedimentary processes and architecture of Upper Cretaceous deep-sea channel deposits: a case from the Skole Nappe, Polish Outer Carpathians

AbstractDeep-sea channels are one of the architectonic elements, forming the main conduits for sand and gravel material in the turbidite depositional systems. Deep-sea channel facies are mostly represented by stacking of thick-bedded massive sandstones with abundant coarse-grained material, ripped-up clasts, amalgamation and large scale erosional structures. The Manasterz Quarry of the Ropianka Formation (Upper Cretaceous, Skole Nappe, Carpathians) contains a succession of at least 31 m of thick-bedded high-density turbidites alternated with clast-rich sandy debrites, which are interpreted as axial deposits of a deep-sea channel. The section studied includes 5 or 6 storeys with debrite basal lag deposits covered by amalgamated turbidite fills. The thickness of particular storeys varies from 2.5 to 13 m. Vertical stacking of similar facies through the whole thickness of the section suggest a hierarchically higher channel-fill or a channel complex set, with an aggradation rate higher than its lateral migration. Such channel axis facies cannot aggrade without simultaneous aggradation of levee confinement, which was distinguished in an associated section located to the NW from the Manasterz Quarry. Lateral offset of channel axis facies into channel margin or channel levee facies is estimated at less than 800 m. The Manasterz Quarry section represents mostly the filling and amalgamation stage of channel formation. The described channel architectural elements of the Ropianka Formation are located within the so-called Łańcut Channel Zone, which was previously thought to be Oligocene but may have been present already in the Late Cretaceous.

Dinosaur behaviour in an Early Jurassic palaeoecosystem – uppermost Elliot Formation, Ha Nohana, Lesotho

The Ha Nohana palaeosurface in southern Lesotho preserves tridactyl and tetradactyl tracks and trackways attributable to Early Jurassic bipedal, theropod-like dinosaurs. Complementary sedimentological and ichnological observations along the palaeosurface and in the strata below and above it allow detailed interpretations of climatically driven changes in this southern Gondwana palaeoecosystem. Sedimentological evidence suggests trackmaking under a semi-arid climate with heavy storms and episodic flash flooding that induced ephemeral, unconfined sheetwashes. The palaeosurface is overlain by rhythmically bedded, organic-matter rich mudstones that formed in a deep, stratified lake indicative of a longer and wetter period in the history of the site. The unique morphological details of the Ha Nohana tracks help refine the properties of the substrate during track making, the ichnotaxonomic affinities of the footprints and the interpretation of the foot movement relative to the substrate. Two footprint morphotypes, ~ 300 m apart, are defined on the palaeosurface. Tracks of morphotype I are tridactyl, shallow, contain digital pad impressions and were impressed on a firm, sand rippled substrate that underwent desiccation. Conversely, tracks of morphotype II are tetradactyl, deep, and have an elongated posterior region. These tracks are preserved on the surface of a massive sandstone and are associated with soft sediment collapse structures related to the animal’s foot sinking into the water-saturated, malleable sediment layer. Morphotype II tracks show that as the animal waded across the substrate, the liquefied sediment lost its cohesive strength and could only partially support the weight of the animal. In so doing, the animal’s foot sunk deep enough into the sediment such that the impression of the metatarsal and digit I (hallux) are now visible. Thus, the palaeosurface was walked on by small-to-medium sized theropods that traversed over ripple marks in firmer moist sand, as well as a larger theropod that tottered through water-logged sand.

Geophysical Study of the Weathered and Near Surface Zone in Parts of Oru Area, Imo State Nigeria Using Seismic Refraction Method

Seismic refraction method has been used to map the near surface geological features in parts of the Oru Area. Ten seismic refraction profiles were surveyed within the Area. The instruments used were a 10 kg sledge hammer, Mark 6 digital 12-channel seismograph, Reflexw software was used to process the seismic data. A GPS system was used to obtain the co-ordinates of the profiles. Surfer 11 software was used to produce contours of the seismic velocities within the study Area. This research has established that the distribution of p-wave velocities within the subsurface of this area show a general increase of velocity with depth and velocity varying from 400 m/s to 770 m/s for the weathered layer. The thickness of the weathered layer is on the average 20.4 m. Field mapping shows that the Northern part of the study area rests on Ogwashi-Asaba formation. The area has mudstone, claystone, gritty claystone, carboniferous mudstone, massive sandstone facies whereas Benin formation is found to the southwest from Mgbidi. And also clay deposits are found within the boundary between the weathered layer and the consolidated layer. This research shows the presence of shallow and deep seated aquifers within the area. There are traces or channels of less dense materials which may be conduits for fluid movement within the consolidated layer. These channels suggest a defect in engineering capacity of this layer. Hence cutting and filling may be adopted even at great depths in the study area for the purpose of infrastructural development. The clay deposits within the Area can be exploited for industrial purposes. Also discovered in this research is a Batholitic structure along Nempi-Ibiasoegbe which permits the possibility of quarrying for crushed rocks along the section.

Sedimentary response to tectonic uplift of the Dukla basin margin recorded at Skrzydlna – the Menilite Beds (Oligocene), Outer Carpathians, S Poland

The Menilite Beds (Oligocene of Polish Flysch Carpathians) at Skrzydlna crops out in a structurally complex zone of the Fore-Magura Unit, which is tectonically overridden by Magura Nappe thrust form the S. The exposed sedimentary suite, representing the Dukla Basin, consists of fine-grained, well organised strata deposited in a low-energy, deep marine basin, which are abruptly overlain by poorly organised, coarse sandy conglomerate that forms a Mass Transport Deposit (MTD) complex. The MTD contains large boulders of extrabasinal rocks, massive sandstone beds with intrabasinal mudstone clasts, and slump sheets of sandstones. Above rests a fining- upwards sequence of sandstone beds interlayered with mudstones. The fine-grained facies reappear above to terminate the exposed succession. Erosional contacts and rapid facies changes, both vertical and lateral, are characteristic for the MTD unit. The sandstone-mudstone unit above contains laterally migrating erosional channels filled with massive sandy conglomerate in the lower part. Turbidites of varying density and completeness of internal structures that occur above are accompanied by an association of mixed facies including large-scale dune cross-bedding. Mineralogically, the sandstones are quartz arenites, sub-lithic arenites and wackes. Calcarenite grains – bioclasts, micrite and marl occur in substantial proportions only in the uppermost part of the succession. The point-counting data plotted on Qm-F-Lt diagram are clustered within the recycled fields: quartzose and transitional. Mineralogical maturity of the sandstones has the tendency to decrease from the sub-MTD strata upwards via the MTD unit to the lower part of the sandstone-mudstone complex; then it increases to the youngest sandstone beds with carbonate grains. These tendencies, associated with sedimentary features of the succession, reflect rapid uplift, emergence and progressive erosion of the terrigenous detritus source area, followed by tectonic stabilisation reflected by the appearance of the “carbonate factory”.

Morphotectonic and sedimentological aspects in describing the relationship with ancient failure surfaces in southern part of Aizawl anticline, Mizoram, India

Population growth in Aizawl city has caused urban areas to expand into landslide-prone areas. These areas comprised of Bhuban Formation rocks of Surma Group and have geological features that frequently generate ground instabilities. The present study integrated with morphotectonic analysis, geotectonic characterization, role of litho-units including their sedimentological aspects and analyses of precipitation time series reveals that the southern part of Aizawl city is tectonically active and lithologically vulnerable towards landslide disaster. Greater surface slope and similar bed attitude enhance the risk of failure. The massive sandstone overlies upon weak clay surfaces that are regularly lubricated by high down pour. Even moderate rainfall can trigger the landslides. The clay layers can mobilize the geological litho-sequences as a combined result of the tropical humid climate and observed weak slope stability conditions. A catastrophic landslide had killed more than 80 people and many other sliding events have been recorded in adjacent areas. Therefore, this study presents tectonic and geologic conditions which can help to predict future slides.