Coal-bearing Beds Research Articles

Geochemical Characteristics and Sedimentary Paleoenvironment of the Coal-Bearing Strata in the Xishanyao Formation: A Case Study of the Yihua Coal Mine in the Zhundong Coalfield, Xinjiang

The eastern Junggar Basin in Xinjiang harbors abundant coal resources within the Middle Jurassic Xishanyao Formation. However, the formation environment associated with these coal-bearing strata remains unclear. Geochemical characteristics serve as crucial geological indicators of the sedimentary period. Therefore, it is imperative to explore the geochemical attributes and sedimentary context of the coal-rich layers within the Middle Jurassic Xishanyao Formation in the Zhundong region to enhance the prospects of coal extraction and utilization. The elemental compositions, both major and trace, of the Xishanyao Formation were analyzed through X-ray fluorescence spectrometry (XRF) and inductively coupled plasma mass spectrometry (ICP-MS). A comprehensive analysis was conducted on the sediment provenance, tectonic background, and depositional environment of the coal-bearing strata in the Xishanyao Formation. Moreover, through the utilization of a range of discrimination indices, including Sr/Cu, B/Ga, Sr/Ba, V/Cr, Ni/Co, and δCe, the paleo-depositional setting of the coal-containing layers was reconstructed. The findings suggest that the primary source rocks of the coal-bearing beds in the Xishanyao Formation consist of continental tholeiites, with the predominant material composition in the source region being felsic volcanic rocks originating from the upper crust. The tectonic backdrop of the source region is marked by a continental island arc environment. During the sedimentation period of the Xishanyao Formation, the depositional environment was characterized by a freshwater oxidizing setting. Additionally, it experienced a transition from arid-hot to humid-hot before returning to arid-hot conditions.

Types and Genesis of Siderite in the Coal-Bearing Beds of the Late Permian Xuanwei Formation in Eastern Yunnan, China

The Late Permian strata of the Xuanwei Formation in the eastern Yunnan region exhibit extensive diverse morphological features within siderite deposits. These variations in siderite deposits suggest potential differences in their formation processes. In this study, fieldwork and comprehensive indoor studies revealed four distinct forms of siderite deposits: stratiform-laminated, lens-like nodule, sandstone cementation, and fracture filling. The stratiform-laminated siderite, varying in color from bluish-grey to dark grey, is composed of uniformly sized microcrystalline to fine-grained siderite along with detrital matter, displaying precise layering and banding structures that suggest direct deposition from cyclic iron-rich seawater under reducing conditions. Lens-like-nodule siderite, which appears grey-yellow, is composed of mud microcrystalline siderite, medium to coarse-grained pseudo-ooids, and glauconite. It shows conformable distribution characteristics resulting from the diagenetic differentiation of iron-rich sediments under reducing conditions during the diagenetic and early diagenetic periods. Siderite as sandstone cementation exhibits a yellow-brown color and consists of dispersed colloidal siderite and cemented siderite clumps that fill intergranular pores of detrital particles. It precipitated under reducing conditions within those intergranular pores. Siderite filling fractures typically appear as vein-like or network-like structures intersecting bedding at large angles. They exhibit grain structures with significant variations in size. These siderite deposits exhibit exceptional purity and result from siderite dissolution during sedimentary periods, followed by reprecipitation within regional extensional fractures during the diagenetic phase. The primary occurrence of siderite deposits in the study area is within coal-bearing strata, as revealed by the integration of sedimentary profiles and sedimentary facies analysis. The coal-bearing strata, influenced by the Emeishan large igneous province, underwent iron enrichment during and after volcanic eruptions while developing a reducing environment, which was facilitated by abundant vegetation. Consequently, geological processes led to siderite layers, lens-like siderite nodules, and siderite cementation. The Yanshan orogeny induced extensive high-angle fracture development in epigenetic coal-bearing strata, facilitating fluid circulation and the redistribution of soluble siderite. This geological activity resulted in the formation of vein-like structures composed of siderite.

Theropod and other dinosaurian tracks from the upper Lower Cretaceous of northeastern China: Overlooked Fuxin Biota records reinvestigated

Dinosaur tracks have been known and reported sporadically from the coal-bearing beds of the Fuxin Formation (upper Aptian–Albian, upper Lower Cretaceous) of Liaoning Province, northeastern China for some time but have not been described in detail. Here available material is illustrated suggesting a diversity of theropod track morphotypes, including small grallatorid, eubrontid and possible Gigandipus-like forms, a Magnoavipes-like form and an isolated small ornithopod track. Some of the tracks show the characteristic distortion of flattened footprints. The ichnofauna supplements our knowledge of the Fuxin Biota by adding a more diverse dinosaur fauna, indicated by the footprint record.

Permian-Early Triassic tectonics and stratigraphy of the Karoo Supergroup in northwestern Mozambique

The Gondwana continent was the base of great basin inception, sedimentation and magmatism throughout the Cambrian to Middle Jurassic periods. The northwestern Mozambique igneous and metamorphic basement assemblages host the NW-trending Moatize Minjova Basin, which has great economic potential for coal and gas mining. This rift basin was activated by an S-SW stress field during the Early Permian period, as constrained by regional and field scale structural data. Tectonically induced subsidence in the basin, from the reactivation of NW-SE and NNE-SSW regional structures is well recorded by faults, folds and synsedimentary fractures within the Early Late Permian Moatize Formation. NW-SE, N-S and NE-SW field structures consist of post-Karoo reactivation patterns related to a NNE-SSW extension produced by the Pangea breakup and early inception stages of the Great East African Rift System. The Early Late Permian sequences of the Moatize-Minjova Basin are composed of fluvial meandering, coal-bearing beds of the Moatize Formation, which comprises mostly floodplain, crevasse splay and fluvial channel lithofacies associations, deposited in a cyclic pattern. This sequence was overlapped by a multiple-story, braided fluvial plain sequence of the Matinde Formation (Late Permian – Early Triassic). Lithofacies associations in the Matinde Formation and its internal relationships suggest deposition of poorly channelized braided alluvial plain in which downstream and probably lateral accretion macroforms alternate with gravity flow deposits. NW paleoflow measurements suggest that Permian fluvial headwaters were located somewhere southeast of the study area, possibly between the African and Antarctic Precambrian highlands.

Further contribution to the mega- and microfossil assemblages from the Johilla-Ganjra Nala confluence, South Rewa Gondwana Basin, Madhya Pradesh, India

The present paper deals with mega- and microfossils recovered from the Early Permian sediments of the Johilla-Ganjra Nala confluence of Johilla Coalfield, Madhya Pradesh. Megafossils include Gangamopteris major, G. cyclopteroides, Glossopteris indica, G. gigas, G. conspicua, G. mohudaensis, Noeggerathiopsis hislopii, Samaropsis goraiensis, Cordaicarpus zeilleri, Alatocarpus indicus, few platyspermic seeds and Equisetalean axes. The palynological studies reveal that coal-bearing beds contain dominance of monosaccate pollen (Parasaccites, Plicatipollenites and Pachysaccus) in association with Callumispora gretensis, Crucisaccites monoletus, Barakarites indicus, Faunipollenites varius, Lunatisporites diffusus and Crescentipollenites fuscus indicating an Early Permian age to the coal beds exposed near the confluence of Johilla River and Ganjra Nala. The mega- and microflora recorded from these beds indicate a transitional zone of the Upper Karharbari and Lower Barakar formations. The study further suggests that the climatic conditions of Son Valley were cooler than the Damodar Basin.

New observations on the Middle Fork Eel River coal-bearing beds, Mendocino County, California, USA

Mid-19th century reports of “immense” coal outcrops in the Middle Fork Eel River (MFER) drainage near Round Valley in California's northern Coast Ranges fueled the early geological interest in this area, with mine development the primary focus of many studies. It was not until Samuel G. Clark's 1940 “Geology of the Covelo District, Mendocino County, California,” that the coal was placed in its regional geologic context and assigned to the Miocene, a determination that relied primarily on a Desmostylus hesperus molar found in shale overlying the coal and an associated equivocal, though Miocene-compatible, marine molluscan fauna. Our investigation of the MFER coal-bearing beds has provided new data from foraminifera, marine mollusks, fish remains, and the first reported fossil plants, which as a whole support Clark's Miocene age assignment. We also present an updated stratigraphy proposing under modern-day stratigraphic protocols that the informal name Sand Bank beds (SBb) be used in place of the Temblor Formation to refer to the SBb coal-bearing fluvial-marine unit. Analysis of the SBb stratigraphy and sedimentology reveals the presence of a fluvial system that flowed from a distal upland region southward toward the paleocoast of California. An abundant diverse palynoflora containing lycophytes, ferns, conifers, and mesic, thermophillic herbaceous and woody angiosperms indicates the drainage flowed through a coastal swampy forested bottomland and estuarine environment before emptying into a coastal basin. Presence of Taxodium-like wood, foliage, pollen, and other “hydrophiles” suggests the MFER coal was a local mire buried by the progradation of the SBb fluvial system during a regressive phase, an interpretation to be tested with future field work and detailed compositional analysis of the coal.

Growth of the Huoerguosi anticline (north Tianshan Mountains) by limb rotation since the late Miocene

The Huoerguosi anticline, located in the north Tianshan Mountains piedmont fold-and-thrust belt, is a trending east-west fault-related fold. In the cross section along the Jingou River, its south limb is composed of the pre-growth strata of the Anjihaihe (E2–3a), the Shawan ((E3-N1)s), the Taxihe (N1t) and the lower part of the Dushanzi (N2d) Formations, trending east-west and dipping to south 55°, and the growth strata of the upper part of the Dushanzi (N2d) and Xiyu ((N2-Q1)x) Formations, dips of which decrease from 55° at the base of the growth strata to 47° at the bottom of the Xiyu ((N2-Q1)x) Formation to ∼0° at the top of the Xiyu ((N2-Q1)x) Formation. The strata at the north limb of the anticline are vertical or over-turned, and are cut by the breakthrough thrusts to result in the drag fold. In the depth, the anticline is symmetric, and its core comprises the Cretaceous and the Jurassic coal-bearing beds. In the seismic profile, the seismic reflectors of pre-growth strata at the south limb of the anticline dip to south constantly, and ones of the growth strata fan southward, whose dips decrease upward. The geometry of the south limb growth strata outcropped along the Jingou River valley and the deep structure of the anticline shown in the seismic profile indicate that the Huoerguosi anticline is a detachment fold anticline growing by limb rotation. Based on the growth model and magnetostratigraphic age, during the growing process of the Huoerguosi anticline, the average shortening rate absorbed by the south limb is ∼0.46 mm/a, and the average uplifting rate of the anticline is ∼0.86 mm/a which exceeds the average deposition rate, which is in accordance with the fact that the top of the anticline is intensely eroded. Considering symmetric geometry of the Huoerguosi anticline and ignoring the breakthrough thrusts, the shortening of the whole anticline should be more than ∼0.92 mm/a, doubling the shortening rate determined from the growth at the south limb.

The geology and petroleum potential of the North Afghan platform and adjacent areas (northern Afghanistan, with parts of southern Turkmenistan, Uzbekistan and Tajikistan)

The North Afghan platform has a pre-Jurassic basement unconformably overlain by a Jurassic to Paleogene oil- and gas-bearing sedimentary rock platform cover, unconformably overlain by Neogene syn- and post-orogenic continental clastics. The pre-Jurassic basement has four units: (1) An ?Ordovician to Lower Devonian passive margin succession developed on oceanic crust. (2) An Upper Devonian to Lower Carboniferous (Tournaisian) magmatic arc succession developed on the passive margin. (3) A Lower Carboniferous (?Visean) to Permian rift–passive margin succession. (4) A Triassic continental magmatic arc succession. The Mesozoic–Palaeogene cover has three units: (1) A ?Late Triassic to Middle Jurassic rift succession is dominated by variable continental clastics. Thick, coarse, lenticular coal-bearing clastics were deposited by braided and meandering streams in linear grabens, while bauxites formed on the adjacent horsts. (2) A Middle to Upper Jurassic transgressive–regressive succession consists of mixed continental and marine Bathonian to Lower Kimmeridgian clastics and carbonates overlain by regressive Upper Kimmeridgian–Tithonian evaporite-bearing clastics. (3) A Cretaceous succession consists of Lower Cretaceous red beds with evaporites, resting unconformably on Jurassic and older deposits, overlain (usually unconformably) by Cenomanian to Maastrichtian shallow marine limestones, which form a fairly uniform transgressive succession across most of Afghanistan. (4) A Palaeogene succession rests on the Upper Cretaceous limestones, with a minor break marked by bauxite in places. Thin Palaeocene to Upper Eocene limestones with gypsum are overlain by thin conglomerates, which pass up into shales with a restricted brackish-water ?Upper Oligocene–?Lower Miocene marine fauna. The Neogene succession consists of a variable thickness of coarse continental sediments derived from the rising Pamir mountains and adjacent ranges. Almost all the deformation of the North Afghan platform began in the Miocene. Oil and gas traps are mainly in Upper Jurassic carbonates and Lower Cretaceous sandstones across the entire North Afghan block. Upper Jurassic carbonate traps, sealed by evaporites, occur mainly north of the southern limit of the Upper Jurassic salt. Lower Cretaceous traps consist of fine-grained continental sandstones, sealed by Aptian–Albian shales and siltstones. Upper Cretaceous–Palaeocene carbonates, sealed by Palaeogene shales are the main traps along the northern edge of the platform and in the Tajik basin. Almost all the traps are broad anticlines related to Neogene wrench faulting, in this respect, like similar traps along the San Andreas fault. Hydrocarbon sources are in the Mesozoic section. The Lower–Middle Jurassic continental coal-bearing beds provide about 75% of the hydrocarbons; the Callovian–Oxfordian provides about 10%; the Neocomian a meagre 1%, and the Aptian–Albian about 14%. The coal-bearing source rocks decrease very markedly in thickness southwards cross the North Afghan platform. Much of the hydrocarbon generation probably occurred during the Late Cretaceous–Paleogene and migrated to structural traps during Neogene deformation. Since no regional structural dip aids southward hydrocarbon migration, and since the traps are all structural and somewhat small, then there is little chance of very large petroleum fields on the platform. Nevertheless, further studies of the North Afghan platform should be rewarding because: (a) the traps of strike–slip belts are difficult to find without detailed exploration; (b) the troubles of the last 20 years mean that almost no exploration has been done; and, (c) conditions may soon become more favorable. There should be ample potential for oil, and particularly gas, discoveries especially in the northern and western parts of the North Afghan platform.

The Jurassic system in the Qinshui Basin, Shanxi Province, with notes on the bivalve province of North China

There are two kinds of Jurassic strata in Shanxi Province of China: fluvial-lacustrine coal-bearing beds distributed in the Luliang-Taihang fault-block depression, and volcanic-sedimentary clastic rocks scattered in the Yanshan fault-block depression. The Jurassic in the Qinshui Basin belongs to the former, which yields a Ferganoconcha-Yananoconcha-Margaritifera (FYM) bivalve fauna. The fauna is very close to the Yan'an Formation bivalve fauna in the Shaanxi-Gansu-Ningxia Basin and intimately associated with bivalve fauna of the Eadat Formation of Siberia, in Chulim-Yenisei Basin, all of them belonging to the Paleo-Asian Province. The characteristics of the Middle Jurassic bivalves of Siberia and some typical elements of the Yorkshire flora of Britain suggest that the coal-bearing Jurassic of Shaanxi Province and the Qinshui Basin of Shanxi Province should belong to the Middle Jurassic; while the coal-bearing strata containing some elements of the FYM fauna in the Yanliao area are Early Jurassic in age, as evidenced by the fact that many Upper Triassic and Liassic elements, Thaumatopteris-Cladophlebis assemblage, exist in the strata. Thus the Jurassic coal-bearing beds in North China show a diachronous phenomenon from east to west. The FYM fauna was composed of ecologic communities in shallow lakes and meandering rivers of hilly areas under a warm-humid climate.

Environmental and diagenetic analyses of Lower Permian epiclastic and pyroclastic fan deposits—their role for coal formation and uranium metallogeny in the Stockheim Trough (F.R.G.)

Conglomerate-silt/mudstone successions are of widespread occurrence within Permian riftogenic troughs from mid Europe. Commonly these beds are abundant in volcanic detritus which was partly derived by weathering of volcanic cones, and partly from directly related certain eruptive pulses. The volcanic influence on sedimentation processes in the course of basin evolution decreases. The lowermost units contain abundant ignimbrites and lahars, whereas the overlying strata exhibit a gradual change from debris flow into more stream-dominated fan deposits. The outer-fan depositions built up by silty sediments, locally mixed with air-fall tuffs, contain coal seams. The coal-bearing host rocks may be categorized into four classes: (1) grey siltstones made up of prevalently non-volcanic detritus; (2) grey to black layers consisting of epiclastic and pyroclastic components; (3) silicified coal seams; and (4) brick-red petrified wood. Ore concentrations in these carbonaceous rocks result from the mobilization of elements from parent material containing large quantities of labile constituents. Four modes of strata-bound U concentration may be encountered: (1) U-bearing petrified wood remains; (2) U-bearing coal lenses; (3) U-bearing carbonaceous volcaniclastic conglomerates; and (4) U-bearing carbonaceous fine-grained tuffites (“fish eyes”). These U accumulations are produced during the course of early diagenesis of volcaniclastic material and coal-bearing beds. The reason for the very high prospectivity of these Permian mid-European sediments is the close intertongueing of carbonaceous matter-bearing rocks and volcaniclastic rocks necessary for the U supply (“uraniferous dirty coal”), in basins of rapid subsidence, which causes the bimodality of those clastic deposits.

Plant fossils from the Talchir and coal-bearing Formation of South Rewa Gondwana Basin, India and their Biostratigraphical significance

Plant fossils belonging to the Talchir and coal-bearing formations (Lower Permian) of four areas, namely Umaria, Birsinghpur Pali, Anuppur and Chirimiri of the South Rewa Gondwana Basin are described. The Talchir flora is represented by a few species of Gangamopteris and Noeggerathiopsis, while the megafossils from the coal-bearing formation are represented by various species of Glossopteris, Gangamopteris, Noeggerathiopsis and Vertebraria. A new species of Noeggerathiopsis, N. minor, has been recognized. It has also been observed that the flora of the coal-bearing beds in these areas is characterized by the dominance of Gangamopteris and Noeggerathiopsis. This suggests that these beds of the South Rewa Gondwana Basin are equivalent to the Karharbari ‘Stage’ of Peninsular India.

REGIONAL LITHOFACIES AND PALAEOGEOGRAPHY OF THE GIDGEALPA GROUP

The Permian Gidgealpa Group contains major reserves of gas and minor amounts of oil in fluvial to marginal marine sandstone reservoirs within coal measures in the Southern Cooper Basin. Lithofacies analysis of a sequential set of palynologically defined time-rock units through the Gidgealpa Group has clarified depositional trends, identified regions of maximum channel development, located positions of shore-lines and shown directions of marine transgressions and regressions.Braided streams deposited the oldest unit, the Tirrawarra Sandstone, on a possibly glacially scoured land surface. As topographic gradients declined, rivers began to meander, and sandstone, shale and coal deposits of the Patchawarra Formation encroached over Tirrawarra Sandstone. Northwards flowing rivers gradually filled pre-Permian valleys with detrital sediments.During uppermost Patchawarra Formation deposition, the Cooper Basin was invaded from the east by a restricted sea, which then deposited the Murteree Shale. As this sea retreated, shoreline sediments of the Epsilon Formation prograded towards the east. A second transgression inundated the land, and the Roseneath Shale was deposited. Finally, delta deposits forming the Daralingie Beds prograded eastwards in the wake of the retreating sea.A period of erosion followed, during which time the present structural grain was imposed on the basin. Subsequently, eastward flowing meandering rivers deposited sandstone, shale and coal of the Toolachee Formation on an essentially flat topography, with only minor hills. The Toolachee Formation grades upwards into non -coal bearing beds, which perhaps register a climate change.

Palaeobotany and stratigraphy of the coal bearing beds of the Daltonganj coalfield, Bihar

The present paper deals with the plant fossils and the miospores recovered from the coal-bearing beds of the Daltonganj Coalfield. On basis of these plant fossil evidences the stratigraphical positions of these beds in the Lower Gondwana succession are discussed.

Two miospore assemblages from the Argada sector south Karanpura coalfield, Bihar, with remarks on their probable age

Two miospore assemblages from the South Karanpura Coalfield are for the first time systematically described. Of these, one is from the shale associated with the Argada 'S' seam; and the other is from another shale about 70 feet above the Argada 'S' seam. The present study throws some light on the controversial question whether the basal coal-bearing beds including the Argada 'S ' seam of this area belong to the Karharbaris or the Barakars.

Studies in the Glossopteris Flora of India- 37. Further Contribution to the Miospore Assemblage of the Coal-Bearing Beds of the Umaria Coalfield, Madhya Pradesh

15 species of miospores belonging to twelve genera are described from the shales of the coal-bearing beds of the Umaria Coalfield. The evidences of miospores further substantiates the fact that the coal-bearing beds are homotaxial to the Karharbari Stage of the Giridih Coalfield.

Geology of Late Cretaceous Mesaverde and Paleocene Fort Union Oil Production, Birch Creek Unit, Sublette County, Wyoming

Birch Creek Unit is on the La Barge arch in the western Green River basin, and is part of the Big Piney-La Barge producing complex. Oil and gas in this area come from rocks ranging in age from Jurassic through Paleocene. This paper is concerned with the trap geometry and the source of hydrocarbons in the shallower productive units of the Upper Cretaceous Mesaverde Formation and Paleocene section. The Mesaverde and upper Hilliard Formations together form a regressive sequence which consists, from northwest to southeast, of lagoonal coal-bearing siltstone and thick sandstone beds, a littoral sandstone complex, and a sequence of marine siltstone and shale. Uplift along the La Barge arch during the Late Cretaceous or very early Paleocene resulted in the erosion of part of this sequence and of an unknown thickness of younger Cretaceous rocks. Truncated, upturned littoral sandstone beds at the Late Cretaceous-Paleocene unconformity, lateral permeability changes, and the gentle structure of the La Barge arch together form the traps within the Mesaverde Formation. The Paleocene sequence is composed of terrigenous clastic sedimentary rocks derived from two separate and distinctive source areas. The basal unit is a relatively thin one. It is a conglomerate and varicolored shale and siltstone sequence that was derived from a sedimentary terrane, probably in the rising thrust belt on the west. The unit, tentatively assigned to the Chappo, is characterized by pebbles and cobbles of limestone and quartzite. The major (upper) part of the Paleocene rocks at Birch Creek was derived from a granitic source on the east, probably in the vicinity of the Wind River Mountains, and is characterized by abundant mica and feldspar. The upper unit forms a regressive lacustrine sequence of: (1) lacustrine shale; (2) marginal-lacustrine sandstone; (3) paludal shale, siltstone, and thin sandstone; and (4) variegated mudstone and thick sandstone probably deposited in a fluvial environment. This sequence is assigned to the Fort Union Formation. Most of the oil and the major part of the gas produced from the Paleocene at Birch Creek and surrounding fields are from reservoirs within the marginal-lacustrine sandstone facies. Traps formed as a result of updip and lateral pinchouts of individual sandstone bodies into lacustrine shale along the east flank and crest of the La Barge arch. In some nearby fields, such as La Barge, these traps have been modified by subsequent structural movements. The close association of the oil production and the greater part of the gas production with the Paleocene Fort Union lacustrine shale body strongly suggests that this shale is the source of the hydrocarbons produced from the associated reservoirs. The close association of production in Mesaverde reservoirs with the unconformity above it and with the overlying shale body, the absence of a distinct chemical difference between oils from Cretaceous and Paleocene reservoirs, and the lack of significant production from areas where the shale is absent or poorly developed suggest that the source of hydrocarbons produced from Mesaverde reservoirs also may be the Paleocene lacustrine shale rather than the underlying Cretaceous marine shale and siltstone.

Studies in the Glossopteris flora of India - 33. Fossil plants and miospores from the coal bearing beds of the Umaria coalfield with some remarks on the age of the beds

The age of the coal-bearing beds of the Umaria coalfield is an stratigraphical controversy in Indian Lower Gondwana System. Views have been expressed in the past by several workers to consider them as equivalent to the Barakar stage, however, others opined it to be Karharbari in age. The present investigations of the paleobotanical content of these beds suggest that they are more or less homotaxial to the Karharbari beds of the Giridih coalfield.

Petrography and Derivation of Jurassic-Cretaceous Clastic Rocks, Southern Rocky Mountains, Canada

Late Jurassic and early Cretaceous sediments in the southern Rocky Mountain region consist of three lithologic divisions; in ascending order these are: (1) the Fernie Formation, consisting mainly of shale of Jurassic age, (2) the Kootenay Formation, consisting of shale and coal-bearing beds with subordinate sandstone, at least partly of Jurassic age, and (3) the Blairmore Group, consisting of a basal conglomeratic member of unknown age overlain by sandstones with subordinate shales of Early Cretaceous (Aptian) age. The precise position of the Jurassic-Cretaceous contact remains controversial. Toward the west, sections appear to be most complete, and a hiatus, or unconformity, increases in magnitude toward the east. Thus in the westerly sections coal-bearing Kootenay beds grade into the coarse-grained Blairmore clastics by increase in frequency, thickness, and grain-size of the sandstone and conglomeratic units. In the easterly sections there is no such gradation, and conglomeratic beds of the Blairmore cut into and overstep siltstones and coal-bearing beds of the Kootenay Formation. In the Mount Allan section (the source of most of the analyzed material), the cliff-forming conglomerate is composed of a series of interdigitating lenses of conglomerate with sandstone, and shale with sandstone. The majority of rock types analyzed are lithic or rock-fragment sandstones and conglomerates, the components of which consist of clastic mineral and rock fragments with clays, and authigenic minerals. The mineral and rock fragments are grouped into four suites which apparently originate from four distinct sources: (1) the Metamorphic Suite, from the Selkirks metamorphic province, (2) the Stable Detritals Suite, reworked from a Paleozoic and possibly pre-Paleozoic source, (3) the Pyroclastics Suite, from the Pennsylvanian-Permian volcanic province, and (4) the Phosphorite-Bitumen-Carbonate Suite from the uppermost Paleozoic and lowermost Mesozoic sedimentary sequence. Uplift and erosion of the distributive province in the west apparently began at the close of Permian time and continued intermittently into Jurassic time. The proportions of the components of the four suites are related to the grain-size of the sediments (an observation which is confirmed by statistical analysis) and thus to abrasion and sorting during the entire period of erosion of the distributive province. Sedimentary differentiation of the clastic material is related to sorting (or lack of sorting) by the transporting agent during a geologically short period of time. Rapid alternation of high- and low-velocity transporting media caused scouring of underlying beds and, with loss of transporting power, these media deposited poorly sorted coarse-grained material and ultimately moderately sorted fine-grained material. There was no sorting after deposition to complete sedimentary differentiation. Depositional features, such as festoon- and cross-bedding, and poorly sorted, bimodal sediments indicate that the clastics were laid down in a continental or alluvial environment. Late Jurassic uplift in the west resulted in increased erosion and rate of transport, culminating in the deposition of the basal Blairmore conglomerate and followed by the quieter estuarine and flood-plain conditions of middle Blairmore time. The course of the various rivers and their tributaries shifted laterally, so that the gross effect achieved is of one, homogeneous conglomeratic unit extending from northern Alberta and British Columbia to the United States. The Kootenay-Blairmore clastics are thus transitional between one type of sedimentary environment in the Jurassic and another in the Cretaceous and are indicative of one of a series of orogenies in the western hinterland which began at the close of the Paleozoic Era and culminated during the Tertiary Laramide orogeny.

Basin-Study Approach to Oil Evaluation of Parana Miogeosyncline, South Brazil

Basin-Study Approach to Oil Evaluation of Parana Miogeosyncline, South Brazil

PALEOGEOGRAPHY OF SOUTH AMERICA

PALEOGEOGRAPHY OF SOUTH AMERICA