Siltstone Lenses Research Articles

Efficiency and limitation of vertical electrical sounding in evaluation of groundwater potential in fractured shale terrain: a case study of Abakaliki Area Lower Benue Trough Nigeria.

Water supply in the Abakaliki Area of Southeastern Nigeria and its environs has been a source of worry. The area is marked by a series of abortive boreholes, sparsely productive boreholes, and failed water wells. These problems are a result of the direct and indirect function(s) of the prevailing geology of the area which is underlain by aquiclude (Abakaliki Shale, lenses of siltstone and sandstone) dominantly indurated shale. Sixteen (16) vertical electric sounding (VES) were acquired using a resistivity meter. The acquired data was plotted on a bi-log graph using INTERPEX and SURFER. Quantitative and qualitative interpretations were used in preparing geoelectric layers and layer parameter maps. Three (3) to five (5) geoelectric layers were delineated. The first layer is a compacted lateritic overburden. VES 1, 3, 4, 6, 11, and 15 were observed to have thin layers of clay with very low apparent resistivity values with an average of 2.642 Ωm and average thickness of 1.08m, and depth generally less than 10m. Fractured and non-fractured/baked shale layers were dominant in all points of the study area. The non-fractured consolidated shale has a high apparent resistivity value ranging from 180.3 Ωm to 770.42 Ωm with an average of about 339.53 Ωm while the fractured shale has an average resistivity value of about 21.36-68.79 Ωm and an average of 38 Ωm. The confinement of the aquifer implies that the indurated shale generally underly the Abakaliki Area. The low resistivity value of the fractured shale is an indication of the presence of fluid, possibly water. The results of this research implied that the application of exploration method(s) that could delineate the subsurface fractures should precede groundwater development in the area. Also, there is no specific depth to the water table in the area; however, the area has a generally shallow depth to groundwater on average.

GIS-Based Relief Compartment Mapping of Fluvio-Karst Landscape in Central Brazilian Highlands

The present study describes the preliminary findings of a research project aiming at creating a knowledge-base for the protection of caves heritage at Rio Vermelho preservation area in the central Brazilian highlands. A GIS-based relief compartment mapping was conducted using readily available data (e.g., satellite images, geological, and cave location maps). Four resultant geomorphological domains were identified, including (i) lowlands (282 km2) with a baselevel in silicates and carbonates, (ii) the karst terrains (994 km2) which were developed in carbonates trapped by siltstone lenses, (iii) the talus (1483 km2) having colluvial and alluvial units deposited by the escarpment retreat (Urucuia Formation) and (iv) the highlands (1143.7 km2) developed over the sandstone of the Urucuia Group. The intersection of landform and geological maps resulted in delineating two abrupt contacts, the first between lowland and karst terrains and the second between the talus and highlands that formed canyon escarpment. For sustainability perspective, this study proposed two types of cave systems in the region as superior/vadose (top-bottom) that collect floods from hillslopes and deep Epigene fluvial-karst (bottom-up).

Cenozoic sediments in the southern Tarim Basin: implications for the uplift of northern Tibet and evolution of the Taklimakan Desert

Abstract Cenozoic sedimentary successions along the southern margin of the Tarim Basin, western China, reach up to 10 km in thickness. The two studied sections, the Yecheng and Aertashi, comprise c . 4.5 km and c . 7.0 km of clastic sedimentary rocks respectively. The base of the Yecheng section has been dated palaeomagnetically to be about 8 Ma. Age control of the Aertashi section is based on 87 Sr/ 86 Sr measurements (for the basal marine bed), together with magnetostratigraphy and regional stratigraphic correlation. The lower part of each section is mainly composed of fine-grained mudstone and fine sandstone, which makes up the Wuqian Group (Miocene). The palaeoenvironment is low-energy, meandering and braided streams. The middle part is composed of red mudstone, sandstone with thin conglomerate beds, which make up the Artux Formation (Pliocene). The palaeoenvironment is a distal- to mid-fan environment. The uppermost part of the section, known as the Xiyu Formation (Plio-Pleistocene), consists of cobble and boulder conglomerate intercalated with massive siltstone lenses, which formed as proximal alluvial fan and aeolian deposits. Neogene red beds passing upward into upward-coarsening conglomerate and debris-flow deposits record the change in palaeoslope related to uplift of the northern margin of Tibetan Plateau. The formation of aeolian dunes at c . 8 Ma, and underlying playa lake deposits (as at Aertashi), may indicate an arid, enclosed basin in the southern Tarim after this time. Sedimentological characteristics, together with grain size distribution and geochemistry of siltstone bands in the Xiyu and Artux Formations, point to an aeolian origin. This indicates that the Taklimakan Desert and the regional climate regime may have been fully developed by the Early Pliocene. The onset of aeolian sedimentation in the southern Tarim Basin coincided with uplift of the northern Tibetan Plateau, as inferred from the lithofacies change. Tibetan Plateau uplift resulted in the shift of sedimentary environments northwards into the southern Tarim Basin, and could well have triggered the onset of full aridity in the Taklimakan region as a whole.

A new arthropod resting trace and associated suite of trace fossils from the Lower Jurassic of Warwickshire, England

Abstract: A new suite of arthropod trace fossils, attributed to a decapod crustacean, is described from the Lower Jurassic Saltford Shale Member of the Blue Lias Formation of Southam Cement Works Quarry, eastern Warwickshire, England. Solusichnium southamensis igen. et isp. nov. consists of small, isolated, bilaterally symmetrical, suboval hypichnia, comprising three regions. The concave anterior region contains imprints of chelate appendages, antennae and antennules. The elongate middle region contains abdominal appendage imprints that extend laterally, separated by a bifurcated medial imprint. The convex posterior region terminates in a globular V‐shaped telson imprint. The large sample size and range of trace morphologies allows identification of five morphotypes within a taphoseries. S. southamensis is found on the base of siltstone lenses in what is otherwise a dysaerobic laminated mudstone unit, associated with epichnial Rusophycus, and the suite of trace fossils is interpreted as the resting traces (Cubichnia) and escape reactions (Fugichnia) of small decapods that were trapped below a distal storm deposit. The producer of S. southamensis was possibly an Eryon‐like decapod, similar to those known from the slightly older Wilmcote Limestone Member of southwestern Warwickshire.

Earth's oldest liverworts— Metzgeriothallus sharonae sp. nov. from the Middle Devonian (Givetian) of eastern New York, USA

Liverworts are generally regarded as rare elements in Palaeozoic floral assemblages. However, a focus on dark gray to black shales and siltstones in the Middle–Late Devonian Catskill Delta of eastern New York shows that liverworts are locally quite common as well-preserved, apparently parautochthonous specimens in thin, lenticular, dark gray–black shale and siltstone lenses. These lenses are either dysoxic–anoxic lacustrine or estuarine facies deposited under oxygen-stratified water masses or rapidly deposited flood plain deposits that were not oxidized after deposition. Carbonized remains of the upper Middle Devonian (Givetian) liverwort Metzgeriothallus sharonae sp. nov. are locally common in these lenses. Well-preserved thalli (gametophytes) are only evident by projecting polarized light on the shale and siltstone surfaces. An associated sporophyte capsule is the first evidence of a reproductive structure in a Devonian liverwort. Metzgeriothallus sharonae sp. nov. is the oldest known liverwort. The age of the new species helps recalibrate chloroplast DNA studies that have led to proposals of the timing of liverwort diversification by showing that the evolutionary separations of the Jungermanniopsida and Marchantiopsida and of the Metzgeriidae and Jungermanniidae [previously thought to be Late Devonian and Late Carboniferous, respectively] were no younger than late Middle Devonian.

Lithostratigraphy, petrography and facies analysis of the Late Cenozoic sediments in the foreland basin of the West Kunlun

The Yecheng profile, lying in the southwest Tarim Basin at the northern foot of the West Kunlun Mountains, comprises 4.5 km of conformable Miocene to Pliocene strata. The lower part of the section, the Wuqia Group, is composed of interbedded red mudstone and pale-coloured fine sandstone with a thickness of 1700 m. The Artux Formation is 800 m thick and composed of mudstone, sandstone with thin gravel and conglomerate beds. The upper part of the section, known as the Xiyu Formation, consists of 2000 m of cobble and boulder conglomerate intercalated with massive siltstone lenses. Compositional study of the sandstones in the Wuqia Group and Artux Formation indicates that they were sourced from low relief areas of the Kunlun region and probably further south from Tibet. The provenance of the conglomerate in the Xiyu Formation is the West Kunlun Mountains. Compositional trends within the conglomerate indicate that Upper Palaeozoic marine, and Mesozoic to Tertiary terrestrial silicic rocks were eroded first, along with the Proterozoic to Lower Palaeozoic Proto-Tethys metasedimentary rocks. Erosion into deeper levels of the Kunlun Mountains provided igneous and high-grade metamorphic sediment, which first appears 640 m above the base of the Xiyu Formation. Lithofacies change from fine-grained mudstone and sandstone to coarse clasts coincides with the onset of aeolian sedimentation, indicating major shift of regional palaeoclimatic regime. Although climatic changes may have played an important role in controlling the sedimentary regime worldwide, our study of the lithostratigraphy and petrography of the Yecheng section suggests that the lithofacies change recorded the progressive unroofing history of the source rocks in the West Kunlun Mountains.

Late Devonian acanthodians from Colombia

Acanthodian remains occur in micaceous siltstone lenses (presumed to have been deposited during a marine incursion) in the Cuche Formation (?Frasnian) of northeast Colombia. The acanthodians are represented by patches of scales from climatiidid Nostolepis sp. cf. N. gaujensis and a fin spine and scales from a new diplacanthid. Type material of N. gaujensis is from the Frasnian Sventoji regional stage in the Baltic, and Nostolepis sp. cf. N. gaujensis has been recorded in the Frasnian of Iran, as well as from Colombia. The new diplacanthid taxon shows affinity to Baltic and Antarctic diplacanthids. The fauna thus shows possible links to both Gondwanan and Euramerican acanthodian assemblages.

Clastic dykes of the Devono—Carboniferous Horton Bluff Formation, Nova Scotia: storm-related structures in shallow lakes

Clastic dykes are common in the Late Devonian to Early Carboniferous Horton Bluff Formation of Nova Scotia where they occur in wave-dominated shoreline deposits of lacustrine shoaling-upward cycles. The dykes, typically less than 25 cm wide and 40 cm in vertical extent, project downward into clayshale from broad loads at the base of elongate isolated lenses of hummocky cross-stratified siltstone. Ptygmatic folding of the dykes reflects a shale: siltstone compaction ratio of 2.3 times, and maximum depth of dyke penetration prior to compaction was > 1 m. Dyke orientation parallels the orientation of wave-ripple crests and the elongation direction of the siltstone lenses. Dyke formation was penecontemporaneous with sedimentation. Dyke and load formation was probably initiated in shallow water during storms which promoted sediment failure through cyclic wave loading, microseisms and rapid deposition of HCS-bearing siltstone lenses. Reversed-density gradient and uneven sediment loading from silt lenses probably promoted downward emplacement. Loads reflect ductile failure of surficial water-rich mud, whereas dykes reflect downward injection of silt following brittle failure of underlying, more compacted mud. The depositional slope provided a tensional stress that controlled the fracture direction (orthogonal to the slope) of the failed sediment.

Anatomy of a large-scale braid-plain quartzarenite from the Neoproterozoic Shaler Group, Victoria Island, Northwest Territories, Canada

The Neoproterozoic Kuujjua Formation is an up to 120 m thick, texturally submature quartzarenite typified by laterally persistent tabular planar cosets of simple and compound planar crossbedding, intercalated with rare, thin dolomitic siltstone lenses up to tens of kilometres wide. It is interpreted as the deposit of a big river, occupying a braid plain, at least 150 km wide, which flowed into the Amundsen Basin from the southeast. The dominant elements of this deposit are stacked tabular and laterally continuous compound crossbeds, interpreted as very large channel forms, which migrated mainly by lateral accretion of superposed small- to moderate-scale two-dimensional dunes. Simple planar crossbedding represents moderate to large two-dimensional periodic bedforms deposited in channels. Rare trough crossbedding represents three-dimensional dunes, which probably were deposited in narrow low-stage chutes that cut across the larger bedforms. Dolomitic siltstone lenses are interpreted as deposits of large flood basin playa lakes that were periodically rejuvenated by river floods. Unrestricted migration of the channels back and forth across the braid plain reworked many of the thin lake deposits and produced the observed multistoried sandstone sheet geometry. A prevailing arid climate is indicated by the occurrence of evaporite casts and pseudomorphs in the flood-basin deposits. The Kuujjua Formation shares features with deposits of the Brahmaputra River; however, there appear to be no modern analogues for the thick, large-scale braided-stream deposits that characterized many Proterozoic cratonic basins.

Facies and Depositional Environments of the Energy Shale Member (Pennsylvanian) and their Relationship to Low-sulfur Coal Deposits in Southern Illinois

ABSTRACT Thick deposits of Energy Shale (Carbondale Formation, Desmoinesian) are associated with low-sulfur coal deposits in the underlying Herrin (No. 6) Coal Member in southern Illinois. The Energy Shale consists of wedges up to at least 26 m thick, which thin away from the Walshville channel (interpreted as a major channel deposit), and local pods or lenses which occur farther from the channel. Facies recognition and interpretation of depositional environments are based on paleoecology, lithology, sedimentary structures, vertical and lateral relationships, and geometry. Supplementary evidence was obtained from total sulfur content and boron content. Six facies are recognized in the areas studied. The thickest and coarsest facies is adjacent to the Walshville channel and is characterized by numerous fining-upward channel-fill sandstones, siltstones, and silty shales. This facies is interpreted as a series of crevasse-distributary channel-fill, levee, and interchannel deposits formed in the proximal portions of the splays. The proximal splay facies grades laterally into a distal splay facies, which consists of shale with abundant plant remains, thin coal beds (splits from the Herrin Coal), rare siderite concretions, and siltstone lenses. The distal splay facies grades laterally into or overlies shale with laterally persistent siderite layers, interpreted as a nonmarine bay facies. The nonmarine bay facies grades vertically and late ally into shale, which is bioturbated and contains euryhaline bivalves and is interpreted as a brackish to marine bay facies. The brackish to marine bay facies grades vertically into shale, containing a moderately diverse marine fauna with some small, possibly stunted, individuals. This facies is interpreted as a marginal marine deposit. Local lenses of organic-rich, dark gray to black shale underlie isolated pods of the marginal marine facies and probably were deposited in freshwater ponds developed on the Herrin peat swamp. The Walshville channel, the proximal and distal crevasse-splay facies of the Energy Shale, and possibly the black shale pond facies of the Energy Shale were partly contemporaneous with Herrin peat deposition. The sulfur content of the Herrin Coal is highest beneath the proximal splay and marginal marine facies of the Energy Shale and is lowest (less than 1.5%) beneath the distal splay facies and the nonmarine bay facies. The sulfur content of the Herrin Coal is related to the thickness, permeability, and environment of deposition of the facies of the overlying Energy Shale.

Geochemical Effects and Efficiency of Primary Petroleum Migration in Interbedded Sand/Shale Sequences: ABSTRACT

Expulsion of petroleum from mature shale source rocks is not an exhaustive process. Invariably, some of the oil generated remains in the pore system of the source rock. The problems are to determine expulsion efficiency and to understand the type and magnitude of compositional fractionation associated with expulsion. To solve these problems a mass balance approach was used based on geochemical analysis of closely spaced core samples from interbedded sand/shale sequences. The content and molecular composition of extractable hydrocarbons from the center of thick shale units were compared to those from the edges of the units and from thinly interbedded shales. The main case histories for this study were two shale/sand sequences of Tertiary and Lower Cretaceous age from Svalbard, Norway, and one of Upper Carboniferous Westfalian age from the Ruhr area, Federal Republic of Germany. In each example, the shales had adequate organic matter contents (Type III kerogens) and maturity levels for hydrocarbon generation, and the interbedded sands had migrated hydrocarbon shows. Petroleum expulsion is higher from the edges of shale units and from thinly interbedded shales. N-alkaline expulsion shows pronounced compositional fractionation with greater expulsion of shorter chain-length molecules. Expulsion efficiencies reach 80-90% at peak generation. Pristane andmore » phytane are expelled to a lesser degree than n-alkane isomers, which increases the pristane/n-C/sub 17/ ratios in depleted samples. Expulsion efficiencies are not uniform; they vary as a function of proximity to migration avenues, such as sandstones, siltstone lenses, and fractures. Expulsion efficiencies are controlled by source rock richness and the extent of hydrocarbon generation. At equal maturity, Type II kerogen source rocks have higher expulsion efficiencies than Type III source beds.« less

Lithologic Environments: The Controlling Factor for Green Mountain-Type Uranium Deposits: ABSTRACT

Much has been written about Wyoming's roll-front uranium deposits, but little has been published about what is hereafter referred to as the Green Mountain-type uranium deposits. They occur in the Eocene Battle Spring Formation, a sequence of continental fluvial deposits over 5000 ft thick. This sequence consists of arkosic sandstones, conglomeratic sandstones, and siltstones. The Granite Mountains, an ancient crystalline high now partially buried in part by material eroded from it, supplied both the detritus and the uranium for the Battle Spring and the Wind River Formations, the latter being the host for uranium of the Gas Hills district. Both the similarities and dissimilarities of the Green Mountain-type vs. the roll-front-type uranium occurrences are discussed. Most of the Battle Spring Formation is a leaky aquifer devoid of consistent aquicludes, which explains the lack of high-grade uranium concentrations at the frontal or closure redox boundary. Instead, the high-grade mineralization occurs at the interface between carbonaceous debris-rich siltstone lenses and the permeable arkosic sandstone and conglomeratic sandstone. Economically significant deposits occur where mineralizing fluids penetrate a high frequency of these interfaces. Published minable reserves of Atlantic Richfield's Round Park deposit are 42 million lb U/sub 3/O/sub 8/ with an average grade ofmore » 0.23%. These and other deposits are examples of Green Mountain-type uranium deposits.« less

Trace fossils in upper cretaceous argillaceous marine facies of the U.S. Western interior

Argillaceous strata of the Greenhorn and Niobrara depositional cycles contain an extensive, though spottily developed, record of tracemaking organisms. These beds are assignable to five facies, four of which represent the gradation from nearshore sandy shales to far offshore calcareous shales, the fifth representing anoxic or nearly anoxic bottom conditions. In strata studied by us the best potential for trace fossil preservation was in deposits characterized by pronounced textural variation, such as shales with sandstone interbeds, shales with thin lenses of siltstone or sandstone, or sandy and silty shales (= mudstones). In pure clayey shales and calcareous shales, trace fossils are preserved best in concretionary structures. Our study suggests that except for shales rich in organics, trace-making organisms were common and widespread in argillaceous muds of the Western Interior. Initial fluidity, high degree of compaction, and textural homogeneity are principal reasons for the poor record of trace makers in pure, clayey shales.

Stratigraphy, sedimentology and structure of the Ihungia decollement, Raukumara Peninsula, North Island, New Zealand

The 75 km2 Ihungia catchment, in the extreme northeast of the North Island of New Zealand, includes part of the northeast-trending, complex belt of Cretaceous and Tertiary rocks forming the eastern continental margin sequence of New Zealand (the East Coast Deformed Belt). Upper Cretaceous “autochthonous” rocks, exposed in the north of the region, are mapped as extensions of the Ngaterian Hikurangi Beds(formation)and overlying Teratan–Haumurian calcareous flysch of Tapuaeroa Formation. The Hikurangi Beds contain 2 new units—the lower Mangarakeke lithofacies(300 m thick, alternating noncalcareous sandstone and mudstone), and the Rangikohua lithofacies(200 m thick, massive, noncalcareous sandstones separated by thin siltstone lenses). These rocks were deformed by north–southtrending isoclinal folding before becoming a repository area for 3 thrust sheets, emplaced by gravity sliding from the north over the “autochthonous” material. The lowest thrust sheet, emplaced following Late Oligocene time, is composed predominantly of Mokoiwi Formation mudstones, including blocks of Taitai Sandstone Member (Motuan, Albian age), and blocks of Mangatu Group lithologies, including Whangai and Weber Formations (Dannevirke–Landon, Paleogene),enclosed in bentonite. New lithologies in the Mangatu Group are divided into sandstone, flysch, or greensand lithofacies. The middle thrust sheet contains thick Upper Tertiary mudstone and flysch of the Ihungia Formation, including a 10-15 m thick, normally graded, igneous conglomerate lithofacies, and a 100 m thick, laminated bryozoan, coquina limestone lithofacies. Emplacement postdates the emplacement of the lowest thrust and occurred later than Middle Miocene. Mangatu Group lithologies recur in the uppermost thrust sheet, emplaced after the middle thrust. All lithologies have been influenced by multiphase ENE-WSW to east-west faulting and folding episodes.

Subsurface Paleoenvironmental Analysis of Gas-Producing Medina Group (Lower Silurian), Chautauqua County, New York: ABSTRACT

A paleoenvironmental interpretation of the gas-producing Medina Group from the subsurface of Chautauqua County, New York, was made by making a lithologic study of a core from Panama, New York, and analyzing over 140 gamma-ray well logs. The oldest formation, the Whirlpool, is a light gray sandstone interbedded with thin lenses of siltstone. Isopach patterns reveal that the Whirlpool Formation was deposited in elongate parallel thick areas trending NE-SW which are similar to the patterns produced by modern tidal current ridges. The Whirlpool Formation is interpreted to be deposited as a tidally influenced sublittoral sheet sandstone. The Power Glen Formation is a medium dark gray shale interbedded with a light gray siltstone. It is interpreted as being deposited in: (1) a arine shelf and prodelta environment; and (2) as distal bar deposits. The Grimsby Formation has a light gray basal sandstone followed by medium red sandstone and interbedded with blackish red shales. The isopach patterns indicate that it was deposited in elongated dendritic areas that trend nearly north-south. The Grimsby is interpreted as a tidal-dominated delta, analogous to the modern Ord River delta of western Australia. There are four sub-environments: (1) channel and distributary mouth bars, (2) overbank splay deposits, (3) tidal channel, and (4) tidal flat. A regional correlation was made with the northeastern Ohio White Clinton sands to the basal light gray section of the subsurface Grimsby of northwestern Pennsylvania and Chautauqua County, New York. The Red Clinton of Ohio is c rrelated with the upper sections of the subsurface Grimsby. End_of_Article - Last_Page 606------------

Lithology, Reservoir Properties, and Burial History of Portion of Gammon Shale (Cretaceous), Southwestern North Dakota

In the northern Great Plains, large quantities of biogenic methane are contained at shallow depths in Cretaceous marine mudstones. The Gammon Shale and equivalents of the Milk River Formation in Canada, which comprise most sediments deposited offshore during the Eagle-Telegraph Creek regression, are typical of such gas-bearing rocks. At Little Missouri field, southwestern North Dakota, Gammon reservoirs consist of discontinuous lenses and laminae of siltstone, less than 10 mm thick, enclosed by silty clay shale. Large amounts of allogenic clay, including highly expansible mixed-layer illite-smectite cause great water sensitivity and high measured and calculated water-saturation values. Reconstructed burial depths, clay mineralogy, and organic matter maturation studies show that the Gammon has not undergone thermal conditions sufficient for oil or thermal gas generation. Scarce authigenic minerals such as pyrite, siderite, and calcite probably formed as a result of bacterial metabolism early in the burial history. The scarcity of authigenic silicates suggests that diagenesis has been inhibited during much of the burial history by the presence of free methane. Shale layers are practically impermeable whereas siltstone microlenses are porous (30 to 40%) and have permeabilities on the order of 3 to 30 md. Reservoir continuity between siltstone layers is poor and, overall, reservoir permeability is probably less than 0.4 md. Connecting passageways between siltstone lenses are 0.1 µm or less in diameter. Organic matter in the low-permeability reservoirs served as the source of biogenic methane, and capillary forces acted as the trapping mechanism for gas accumulation. At Little Missouri field, reservoirs and non-reservoirs cannot be distinguished on the basis of lithology, and much of the Gammon interval is potentially economic. Future research should be directed toward determining the physical basis of log response in the low-permeability reservoirs and toward the development or application of water-free recovery technology.