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Journal articles on the topic "Unconformably"
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El-Arnauti, A., and M. Shelmani. "Stratigraphic and Structural Setting." Journal of Micropalaeontology 4, no. 1 (March 1, 1985): 1–10. http://dx.doi.org/10.1144/jm.4.1.1.
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Abstract. INTRODUCTIONThe material which forms the basis of this project was obtained from a number of wells in the study area in Cyrenaica, the northeastern part of Libya. The study area, which is located between latitudes 25° and 33°N and between longitudes 20° and 25° E, covers some 365,750 square kilometres (see Fig. 1). The area extends from the Egyptian border in the east to the eastern flank of the Sirte Basin in the west and is part of the stable Saharan Shield.Since Precambrian time several phases of epeirogenic movements have produced troughs, horst blocks or platforms which have in turn influenced the subsequent sedimentological history of the area. In the southern and southeastern part of the study area, the basement is unconformably overlain by a thick, partially marine Palaeozoic sequence which is in turn unconformably overlain by sediments of Jurassic or younger age. The basement in the central and southwestern parts of the area is unconformably overlain by non-marine clastics of Late Jurassic and Early Cretaceous age or by marine sediments of Late Cretaceous and Tertiary age. In the eastern and northeastern section the basement is overlain by a wedge of eastward thickening marine Palaeozoic rocks which are in turn unconformably overlain by marine sediments of Late Cretaceous and Tertiary age. In the most northerly part of the northeastern region of the study area, a thick paralic sequence of Triassic, Jurassic and Early Cretaceous deposits is unconformably overlain by Late Cretaceous and Tertiary sediments.PALAEOZOICRocks of Cambro-Ordovician . . .
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Cope, J. C. W., and A. W. A. Rushton. "Cambrian and early Tremadoc rocks of the Llangynog Inlier, Dyfed, South Wales." Geological Magazine 129, no. 5 (September 1992): 543–52. http://dx.doi.org/10.1017/s0016756800021701.
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AbstractUntil recently no Cambrian rocks were known in the Llangynog area. Detailed mapping has now revealed a succession of ?Lower and Upper Cambrian rocks overlain by Tremadoc rocks. The Allt y Shed Sandstones (new) rest unconformably on the Precambrian, but have yielded no diagnostic fossils and are tentatively assigned to the Comley Series. Succeeding with faulted or unconformable contact is an Upper Cambrian Merioneth Series succession which includes in ascending order: conglomerates, sandstones and siltstones with olenid trilobites and resembling the Treffgarne Bridge Beds of the Haverfordwest area; micaceous shales and siltstones referred to the Ffestiniog Flags Formation; and black mudstones with calcareous concretions and a rich olenid fauna referred to the Dolgellau Formation. Succeeding the latter with possible disconformity is a succession belonging to the lower part of the Tremadoc Series and earlier than any rocks of that series hitherto recorded from the area.
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Malak, Zaid A. "Stratigraphic and Microfacies Study of Kometan Formation (Upper Turonian-Lower Campanian), in the Dokan area, Northern Iraq." Iraqi Geological Journal 54, no. 1F (June 30, 2021): 51–68. http://dx.doi.org/10.46717/igj.54.1f.6ms-2021-06-26.
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The Kometan Formation is widely distributed in the northern (Kurdistan region) and central Iraq. The studied area is located near the Dokan Dam, about 58 km., to the Northwest of the Sulaymaniyah city, Northeastern Iraq. The Kometan Formation is exposed on the southwest flank of the Sarah anticline. The formation consists of limestone and dolomitic limestone, which have cherts nodules throughout the formation. The Gulneri Formation is recorded below the Kometan Formation with unconformable contact, while at the top is bounded by the Shiranish Formation unconformably too. Three microfacies are identified, these are lime mudstone, planktic foraminiferal lime wackestone-packstone, keeld planktonic foraminiferal lime wackestone-packstone microfacies. All the sedimentary and fossil evidence refer that the sedimentary environment of the formation is the outer shelf to upper bathyal at the lower and upper parts of formation and its extension to the middle bathyal in the middle part of the formation. Based on the stratigraphic ranges of the recorded Calcareous nannofossils biozones, the age of the Kometan Formation at Dokan area is Late Turonian-Early Campanian.
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Schwennicke, Tobias, Diana María Santisteban-Mendívil, José Antonio Pérez-Venzor, Mara Yadira Cortés-Martínez, and Elvia Plata-Hernández. "Evolución estratigráfica de la cuenca Los Barriles, Baja California Sur, México." Revista Mexicana de Ciencias Geológicas 34, no. 3 (November 29, 2017): 212. http://dx.doi.org/10.22201/cgeo.20072902e.2017.3.476.
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The Los Barriles basin, located north of the San José del Cabo basin, is part of the Gulf Extensional Province. It is a half graben bounded by the Los Barriles fault system on its western side. Our study confirms that this system is not part of the San José del Cabo fault but an independent structure. The basin fill includes three stratigraphic sequences: SE 1, SE 2, and SE 3. Los Barriles and Trinidad Formations constitute SE 1. The Los Barriles Formation is in contact with the marginal fault and on the eastern margin it rests unconformably upon the plutonic and meta- morphic basement. The unit is composed of conglomerate and sandstone formed in alluvial fans. The marine Trinidad Formation is composed of sandstone and mudstone. Both formations interfinger and constitute fan deltas without foresets, suggesting rapid subsidence along the Los Barriles fault. Calcareous nannofossils in SE 1 point toward an age in the nannofossil zone NN11 (Late Tortonian-Messinian). Thus, faulting and subsidence occurred since the late Miocene, indicating that the Los Barriles fault system is older than the San José del Cabo fault, which had been activated during the Pliocene. The Refugio Formation (SE 2) rests unconformably on the Trinidad Formation; it consists of fossiliferous sandstone and conglomerate originated in a shallow marine coastal set- ting. Laterally, it interfingers with younger portions of the Los Barriles Formation, forming a fan delta setting of probable Pliocene age. The El Chorro Formation unconformably covers all older units and, locally, even Los Barriles fault system. It comprises sandstone and conglomer- ate formed in an alluvial fan depositional environment. These deposits interfinger towards the present coastline with fossiliferous sandstone and conglomerate formed during the last interglacial period, representing SE 3.
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Zhou, Jian-Bo, Jie Han, Guo-Chun Zhao, Xing-Zhou Zhang, Jia-Lin Cao, Bin Wang, and Sheng-Hui Pei. "The emplacement time of the Hegenshan ophiolite: Constraints from the unconformably overlying Paleozoic strata." Tectonophysics 662 (November 2015): 398–415. http://dx.doi.org/10.1016/j.tecto.2015.03.008.
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Jefferson, C. W., and R. R. Parrish. "Late Proterozoic stratigraphy, U–Pb zircon ages, and rift tectonics, Mackenzie Mountains, northwestern Canada." Canadian Journal of Earth Sciences 26, no. 9 (September 1, 1989): 1784–801. http://dx.doi.org/10.1139/e89-151.
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Stratigraphic evidence suggests sporadic rifting began during deposition of the mainly platformal Mackenzie Mountains Supergroup: minor magnetite iron-formation in shale basins, lead–zinc in karsted and brecciated carbonates, red-bed and evaporite wedges, and basalts at the top. In the unconformably overlying Coates Lake Group similar climates and definite rifting are recorded by thin orthoconglomerates with thick red-bed and evaporite wedges containing stratiform copper deposits in paleovalleys. Unconformably above this, basal Windermere Supergroup records major climatic change and more emphatic rifting, with thick orthoconglomerates next to fault scarps overlain by glaciomarine deposits with volcanics and hydrothermal iron-formation.A quartz diorite plug, here dated by the U–Pb zircon method at [Formula: see text], is bounded by faults but is contained in a thrust panel together with Mackenzie Mountains Supergroup and is chemically similar to diabase sills previously dated at 766–769 ± 27 Ma (Rb–Sr). A diatreme intruding Coates Lake Group contains clasts of granite and gneiss from inferred basement. U–Pb systematics from a granite clast indicate inherited zircons about 1.6 ± 0.25 Ga in age and crystallization between 1100 and 1175 Ma, a maximum age for Mackenzie Mountains Supergroup.
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Strank, A. R. E. "Foraminiferal biostratigraphy of the Woo Dale Borehole, Derbyshire and the age of the Dinantian-Basement unconformity." Journal of Micropalaeontology 5, no. 1 (April 1, 1986): 1–4. http://dx.doi.org/10.1144/jm.5.1.1.
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Abstract. Detailed micropalaeontological analysis of the Woo Dale Borehole shows that Dinantian strata of Holkerian and Arundian age lie unconformably on top of the pre-Carboniferous basement beds. The Chadian and Tournaisian are missing. The chronostratigraphy here recognised is compared with that proposed by Cope (1973) and the differences in the two interpretations explained in the light of recent palaeontological and Midlands regional research.
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Lenhardt, N., W. Altermann, F. Humbert, and M. de Kock. "Lithostratigraphy of the Palaeoproterozoic Hekpoort Formation (Pretoria Group, Transvaal Supergroup), South Africa." South African Journal of Geology 123, no. 4 (December 1, 2020): 655–68. http://dx.doi.org/10.25131/sajg.123.0043.
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Abstract The Palaeoproterozoic Hekpoort Formation of the Pretoria Group is a lava-dominated unit that has a basin-wide extent throughout the Transvaal sub-basin of South Africa. Additional correlative units may be present in the Kanye sub-basin of Botswana. The key characteristic of the formation is its general geochemical uniformity. Volcaniclastic and other sedimentary rocks are relatively rare throughout the succession but may be dominant in some locations. Hekpoort Formation outcrops are sporadic throughout the basin and mostly occur in the form of gentle hills and valleys, mainly encircling Archaean domes and the Palaeoproterozoic Bushveld Complex (BC). The unit is exposed in the western Pretoria Group basin, sitting unconformably either on the Timeball Hill Formation or Boshoek Formation, which is lenticular there, and on top of the Boshoek Formation in the east of the basin. The unit is unconformably overlain by the Dwaalheuwel Formation. The type-locality for the Hekpoort Formation is the Hekpoort farm (504 IQ Hekpoort), ca. 60 km to the west-southwest of Pretoria. However, no stratotype has ever been proposed. A lectostratotype, i.e., the Mooikloof area in Pretoria East, that can be enhanced by two reference stratotypes are proposed herein. The Hekpoort Formation was deposited in a cratonic subaerial setting, forming a large igneous province (LIP) in which short-termed localised ponds and small braided river systems existed. It therefore forms one of the major Palaeoproterozoic magmatic events on the Kaapvaal Craton.
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Al-Husseini, Moujahed, and Robley K. Matthews. "Devonian Jauf Formation, Saudi Arabia: Orbital Second-order Depositional Sequence 28." GeoArabia 11, no. 2 (April 1, 2006): 53–70. http://dx.doi.org/10.2113/geoarabia110253.
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ABSTRACT The Devonian Jauf Formation (Huj Group) froms part of a regional transgressive-regressive depositional sequence that extends more than 1,500 km across the Arabian Platform from the Al Jawf outcrops in northwest Saudi Arabia, to the subsurface of eastern Saudi Arabia and Oman (Misfar Group). The formation ranges in thickness from 200–335 m in eastern Saudi Arabia to about 300–330 m in northwest Saudi Arabia. It disconformably (?unconformably) overlies the continental to shallow-marine Tawil Formation, and is unconformably overlain by the continental Jubah Formation. The Jauf Formation consists of five members that are apparently conformable; from base-up: Sha’iba Shale, Qasr Limestone, Subbat Shale, Hammamiyat Limestone and Murayr. In the Al-Qalibah reference section, it is divided into 21 informal units. The Early Devonian Emsian Hammamiyat Member represents the main marine flooding event; it consists of Hammamiyat units 1–6 each characterized by a clastic section that is capped by limestone. The Jauf Formation is interpreted as an orbital second-order depositional sequence (denoted DS2 28), which is bounded by two second-order sequence boundaries: SB2 28 = Jauf/Tawil (c. 407.6 Ma) and SB2 27 = Jubah/Jauf (c. 393.0 Ma). The Jauf Formation appears to consist of six third-order depositional sequences (DS3 28.1 to 28.6) that were deposited in the Early Devonian, ?Pragian and Emsian stages The Hammamiyat Member (DS3 28.4) is interpreted to consist of six fourth-order orbital cycles (DS4 28.4.1 to 28.4.6) each deposited in 0.405 million years.
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Lavoie, Denis, and Esther Asselin. "A new stratigraphic framework for the Gaspé Belt in southern Quebec: implications for the pre-Acadian Appalachians of eastern Canada." Canadian Journal of Earth Sciences 41, no. 5 (May 1, 2004): 507–25. http://dx.doi.org/10.1139/e03-099.
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The post-Taconian units in the Quebec and northern New Brunswick Appalachians constitute the Gaspé Belt and geological studies have mostly focussed on its eastern Quebec segment. Biostratigraphic data indicate that the succession in southern Quebec is no older than Late Silurian and extends into the Early Devonian. Two distinct stratigraphic assemblages are present. The first assemblage (Saint-Luc, Cranbourne, and Lac Aylmer formations, and Glenbrooke Group) unconformably overlies the Humber and Dunnage zones. The units show a basal alluvial conglomerate that passes progressively to deeper marine facies upsection, which have recorded a post-Late Silurian transgressive event. The second assemblage (Saint-Francis Group and Frontenac Formation) is faulted against either Dunnage units or autochthonous post-Taconian units. It locally unconformably overlies units of the Dunnage Zone; the succession shows progressively deeper marine conditions upsection and also has recorded a post-Late Silurian transgressive event. The biostratigraphic framework suggests that some of the units that were assumed to be vertically stacked are rather laterally equivalent. Independant evidence supports the hypothesis that the Gaspé Belt in southern Quebec formed after the collapse of the Taconian orogen in Late Silurian time. This event is ascribed to the Salinian Orogeny. The framework from southern Quebec is incorporated in a regional scenario. The Gaspé Belt experienced a PridolianLochkovian sea-level rise. In Pragian time, shallower marine conditions were established in southern Quebec, whereas in the Gaspé Peninsula, the shallower conditions only occurred in early Emsian time.
Dissertations / Theses on the topic "Unconformably"
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Gore, R. J. "Geochronological and sedimentological constraints of the Srisailam Formation, S.E. India." Thesis, 2011. http://hdl.handle.net/2440/96125.
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This item is only available electronically.The Proterozoic Cuddapah Basin contains the poorly constrained Srisailam Formation, which presumably lies unconformably over the Nallamalai Group. The Cuddapah Basin is thought to have initiated as a rift basin > 1900 Ma before developing into a foreland basin due to uplift of the Eastern Ghats Belt (EGB) at ~1600 Ma. U-Pb geochronology indicates deposition of the Srisailam Formation commenced after 1660 Ma and ceased prior to the deposition of the Kurnool Group which was deposited < 1090 Ma. The Srisailam Formation was deposited in a tidal flat/shallow marine environment as it contains tidal and storms influences, glauconitic sandstones, along with bimodal east-west paleocurrents, which suggest links with an open seaway. Detrital zircon Hf isotope data combined with detrital zircon U-Pb data suggest the Dharwar Craton as a dominant source region with a mixed crustal evolution (ɛHf -11 to +8). Detrital zircon age peaks at ~3200 Ma, ~2700-2400 Ma and ~2300 Ma imply that sediments are dominantly sourced from 3400-3000 Ma tonalite-trondhjemite-granodiorite (TTG), 3000-2500 Ma volcanosedimentary greenstone belts and 2600-2500 Ma calc-alkaline to K-rich granitic intrusions. Trace element data suggests zircon grains are sourced from granitoids with zircon crystallisation at ~860˚C. This study reveals that the Srisailam Formation is quite possibly a lateral equivalent of the Nallamalai Group.
Thesis (B.Sc.(Hons)) -- University of Adelaide, School of Earth and Environmental Sciences, 2011
Books on the topic "Unconformably"
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Packer, Nancy Huddleston. In my father's house: Tales of an unconformable man. Santa Barbara: Stanford Alumni Association, 1988.
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Packer, Nancy Huddleston. In my father's house: Tales of an unconformable man. Santa Barbara: J. Daniel, 1988.
Find full textBook chapters on the topic "Unconformably"
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Tripp, Gerard I., Richard M. Tosdal, Thomas Blenkinsop, Jamie R. Rogers, and Scott Halley. "Chapter 33: Neoarchean Eastern Goldfields of Western Australia." In Geology of the World’s Major Gold Deposits and Provinces, 709–34. Society of Economic Geologists, 2020. http://dx.doi.org/10.5382/sp.23.33.
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Abstract Neoarchean greenstone-hosted gold deposits in the Eastern Goldfields Superterrane of the Yilgarn craton of Western Australia are diverse in style, timing with respect to magmatic activity, structural environment, host rocks, and geochemical character. Geologic constraints for the range of gold deposits indicate deposit formation synchronous with volcanism, synchronous with syn- and postvolcanic intrusion, synchronous with postvolcanic deformation in faults and shear zones, or some combination of superposed events over time. The gold deposits are distributed as clusters along linear belt-parallel fault zones internal to greenstone belts but show no association with major terrane boundary faults. World-class gold districts are associated with the thickest, internal parts of the greenstone belts identified by stratigraphic preservation and low metamorphic grades. Ore-proximal faults in those regions are more commonly associated with syn- and postvolcanic structures related to greenstone construction and deformation rather than major terrane amalgamation. Using the Kalgoorlie district as a template, the gold deposits show a predictable regional association with thicker greenstone rocks overlain unconformably by coarse clastic rock sequences in the uppermost units of the greenstone stratigraphy. At a camp scale, major gold deposits show a spatial association with unconformable epiclastic and volcaniclastic rocks located above an unconformity internal to the Black Flag Group. Distinct episodes of gold deposition in coincident locations suggest fundamental crustal structural controls provided by the fault architecture. Late penetrative deformation and metamorphism overprinted the greenstone rocks and the older components of many gold deposits and were accompanied by major gold deposition in late quartz-carbonate veins localized in crustal shear zones or their higher order fault splays.
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"unconformable." In Dictionary Geotechnical Engineering/Wörterbuch GeoTechnik, 1449. Berlin, Heidelberg: Springer Berlin Heidelberg, 2014. http://dx.doi.org/10.1007/978-3-642-41714-6_210106.
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"(structurally) unconformable." In Dictionary Geotechnical Engineering/Wörterbuch GeoTechnik, 1334. Berlin, Heidelberg: Springer Berlin Heidelberg, 2014. http://dx.doi.org/10.1007/978-3-642-41714-6_198351.
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Riggs, Nancy, Brian McConnell, and John Graham. "Sedimentary provenance of Silurian basins in western Ireland during Iapetus closure." In New Developments in the Appalachian-Caledonian- Variscan Orogen. Geological Society of America, 2022. http://dx.doi.org/10.1130/2021.2554(16).
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ABSTRACT Three Silurian basin fills, the Llandovery–Wenlock Croagh Patrick and Killary Harbour–Joyce Country successions and the Ludlow–Pridoli Louisburgh–Clare Island succession, overstep the tectonic contacts between elements of the Grampian (Taconic) accretionary history of the Caledonian-Appalachian orogeny in western Ireland. New U-Pb detrital zircon data from lower strata of these Silurian rocks provide insight into basin evolution and paleogeography. The shallow-marine Croagh Patrick succession unconformably overlies the Clew Bay Complex and the northern part of the Ordovician South Mayo Trough. Two samples have zircon populations dominated by Proterozoic grains typical of the Laurentian margin, with few younger grains. Up to 13% of the grains form a cluster at ca. 950–800 Ma, which is younger than known Grenville magmatism on the local Laurentian margin and older than known magmatism from Iapetan rifting; these may be recycled grains from Dalradian strata, derived from distal Tonian intrusions. The Killary Harbour–Joyce Country succession overlies the structural contact between the Lough Nafooey arc and the Connemara Dalradian block and records a transgressive-regressive cycle. Four samples of the Lough Mask Formation show contrasting age spectra. Two samples from east of the Maam Valley fault zone, one each from above Dalradian and Nafooey arc basement, are dominated by Proterozoic grains with ages typical of a Laurentian or Dalradian source, likely in north Mayo. One sample also includes 8% Silurian grains. Two samples from west of the fault overlie Dalradian basement and are dominated by Ordovician grains. Circa 450 Ma ages are younger than any preserved Ordovician rocks in the region and are inferred to represent poorly preserved arc fragments that are exposed in northeastern North America. Cambrian to late Neoproterozoic grains in association with young Ordovician ages suggest derivation from a peri-Gondwanan source in the late stages of Iapetus closure. The Louisburgh–Clare Island succession comprises terrestrial red beds. It unconformably overlies the Clew Bay Complex on Clare Island and is faulted against the Croagh Patrick succession on the mainland. The Strake Banded Formation yielded an age spectrum dominated by Proterozoic Laurentian as well as Ordovician–Silurian ages. Although the basin formed during strike-slip deformation along the Laurentian margin in Ireland and Scotland, sediment provenance is consistent with local Dalradian sources and contemporaneous volcanism. Our results support ideas that Ganderian continental fragments became part of Laurentia prior to the full closure of the Iapetus Ocean.
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Whitmore, Ross J., Patricia H. Cashman, and Daniel M. Sturmer. "Structures at Buck Mountain, Nevada: Establishing the Southeastern Extent of Mid-Pennsylvanian Tectonism." In Late Paleozoic and Early Mesozoic Tectonostratigraphy and Biostratigraphy of Western Pangea, 102–13. SEPM (Society for Sedimentary Geology), 2022. http://dx.doi.org/10.2110/sepmsp.113.06.
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This paper reports the structural and stratigraphic history of Buck Mountain, Nevada, and its regional significance in the development of southwestern Laurentia during the late Paleozoic. The two distinct generations of folding have similar style and/or timing to other fold sets in late Paleozoic strata of northern Nevada. Unconformities in the upper Paleozoic strata at Buck Mountain are consistent with unconformities documented in northern and east-central Nevada. Northwest-vergent folds (F1) in the Morrowan–Atokan Ely Limestone are erosionally truncated and unconformably overlain by the middle Desmoinesian Hogan Formation and middle Wolfcampian (Sakmarian) Upper Strathearn Formation. This upper Paleozoic stratigraphic package was subsequently refolded by the Buck Mountain Syncline and associated mesoscale folds (F2). F2 folds lack tight age control but are interpreted to be associated with the Cretaceous central Nevada thrust belt. Critically, none of these structures are localized above or below low-angle faults. The unconformity between the Ely and Hogan formations is consistent with the C5 regional unconformity. Importantly, it constrains the age of northwest-vergent deformation on Buck Mountain. West-vergent folds and west-directed thrusts are documented at several locations in northern and east-central Nevada, but because of the dominance of the C6 unconformity and/or lack of robust age control, the age of these structures has not been tightly constrained. The evidence at Buck Mountain indicates that west-vergent structures predate the C5 unconformity. Buck Mountain is important because it: (1) precisely brackets the age of west-vergent deformation in Nevada to pre–mid-Desmoinesian (sub C5-unconformity) and (2) defines a southeastern edge to the late Paleozoic west-vergent deformation in northern and east-central Nevada.
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Rovey, Charles W., Damon J. Bassett, and Matthew P. McKay. "Ordovician and Mississippian stratigraphy in southwestern Missouri, USA." In Field Excursions from the 2021 GSA Section Meetings, 181–200. Geological Society of America, 2021. http://dx.doi.org/10.1130/2021.0061(08).
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ABSTRACT A succession of Ordovician and Mississippian carbonates, separated unconformably, is exposed across the southern flank of the Ozark Dome in southwest Missouri. Deposits of both periods exemplify typical facies of the Midwestern United States: carbonate tidal-flat assemblages for the Early Ordovician and carbonate shelf environments for the Early–Middle Mississippian. The basic stratigraphic sequence of these deposits has been known for over a century, but interesting features remain to be addressed. Thin discontinuous sandstones are present within the Early Ordovician Cotter Dolomite, but the informal Swan Creek sandstone member seems anomalous. This sandstone can exceed 5 m in thickness and is fairly continuous across southwest Missouri. Most Ordovician sandstones in Missouri mark major transgressions above regional unconformities, but not the Swan Creek, and there is no obvious source of the sand. Therefore, we hypothesize that the Swan Creek represents reworked eolian dunes blown across the broad peritidal environment. Clastic sandstone dikes, apparently sourced from the Swan Creek, cut across beds of Cotter Dolomite near faults. We propose that these dikes are evidence of local faulting and seismicity during the Early Ordovician. Early and Middle Mississippian limestones comprise a sequence of shelf deposits, although mud mounds and other facies changes near the Missouri-Arkansas line mark the edge of the Mississippian shelf and the transition to a ramp setting. Early Mississippian carbonate deposition was interrupted by a short and localized influx of siliciclastic sediment comprising the Northview Formation. The Northview has additional characteristics consistent with a river-dominated deltaic deposit, which we suggest as its origin. If correct, this hypothesis implies that the history of tectonic features in the Midwest is more complicated than yet known. Finally, facies changes within and between the local Mississippian formations may record an early crustal response to the impending Ouachita orogeny farther to the south.
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Murphy, J. B., and J. D. Keppie. "The Late Precambrian Antigonish Terrane (a periarc basin) unconformably overlain by Paleozoic overstep rocks typical of the Avalon Composite Terrane, near Antigonish, Nova Scotia." In Centennial Field Guide Volume 5: Northeastern Section of the Geological Society of America, 421–26. Geological Society of America, 1987. http://dx.doi.org/10.1130/0-8137-5405-4.421.
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Ogawa, Yujiro, and Shin’ichi Mori. "Gravitational sliding or tectonic thrusting?: Examples and field recognition in the Miura-Boso subduction zone prism." In Plate Tectonics, Ophiolites, and Societal Significance of Geology: A Celebration of the Career of Eldridge Moores. Geological Society of America, 2021. http://dx.doi.org/10.1130/2021.2552(10).
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ABSTRACT Discrimination between gravity slides and tectonic fold-and-thrust belts in the geologic record has long been a challenge, as both have similar layer shortening structures resulting from single bed duplication by thrust faults of outcrop to map scales. Outcrops on uplifted benches within the Miocene to Pliocene Misaki accretionary unit of Miura-Boso accretionary prism, Miura Peninsula, central Japan, preserve good examples of various types of bedding duplication and duplex structures with multiple styles of folds. These provide a foundation for discussion of the processes, mechanisms, and tectonic implications of structure formation in shallow parts of accretionary prisms. Careful observation of 2-D or 3-D and time dimensions of attitudes allows discrimination between formative processes. The structures of gravitational slide origin develop under semi-lithified conditions existing before the sediments are incorporated into the prism at the shallow surfaces of the outward, or on the inward slopes of the trench. They are constrained within the intraformational horizons above bedding-parallel detachment faults and are unconformably covered with the superjacent beds, or are intruded by diapiric, sedimentary sill or dike intrusions associated with liquefaction or fluidization under ductile conditions. The directions of vergence are variable. On the other hand, layer shortening structure formed by tectonic deformation within the accretionary prism are characterized by more constant styles and attitudes, and by strong shear features with cataclastic textures. In these structures, the fault surfaces are oblique to the bedding, and the beds are systematically duplicated (i.e., lacking random styles of slump folds), and they are commonly associated with fault-propagation folds. Gravitational slide bodies may be further deformed at deeper levels in the prism by tectonism. Such deformed rocks with both processes constitute the whole accretionary prism at depth, and later may be deformed, exhumed to shallow levels, and exposed at the surface of the trench slope, where they may experience further deformation. These observations are not only applicable in time and space to large-scale thrust-and-fold belts of accretionary prism orogens, but to small-scale examples. If we know the total 3-D geometry of geologic bodies, including the time and scale of deformational stages, we can discriminate between gravitational slide and tectonic formation of each fold-and-thrust belt at the various scales of occurrence.
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Zhang, Y., H. Ji, J. Wang, and J. Ye. "Optimization of mining parameters for coal mining under unconformable overlying stratums." In Rock Mechanics: Achievements and Ambitions, 1019–23. CRC Press, 2011. http://dx.doi.org/10.1201/b11438-201.
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Miller, Elizabeth L., Mark E. Raftrey, and Jens-Erik Lund Snee. "Downhill from Austin and Ely to Las Vegas: U-Pb detrital zircon suites from the Eocene–Oligocene Titus Canyon Formation and associated strata, Death Valley, California." In Tectonic Evolution of the Sevier-Laramide Hinterland, Thrust Belt, and Foreland, and Postorogenic Slab Rollback (180–20 Ma). Geological Society of America, 2022. http://dx.doi.org/10.1130/2021.2555(14).
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ABSTRACT In a reconnaissance investigation aimed at interrogating the changing topography and paleogeography of the western United States prior to Basin and Range faulting, a preliminary study made use of U-Pb ages of detrital zircon suites from 16 samples from the Eocene–Oligocene Titus Canyon Formation, its overlying units, and correlatives near Death Valley. The Titus Canyon Formation unconformably overlies Neoproterozoic to Devonian strata in the Funeral and Grapevine Mountains of California and Nevada. Samples were collected from (1) the type area in Titus Canyon, (2) the headwaters of Monarch Canyon, and (3) unnamed Cenozoic strata exposed in a klippe of the Boundary Canyon fault in the central Funeral Mountains. Red beds and conglomerates at the base of the Titus Canyon Formation at locations 1 and 2, which contain previously reported 38–37 Ma fossils, yielded mostly Sierran batholith–age detrital zircons (defined by Triassic, Jurassic, and Cretaceous peaks). Overlying channelized fluvial sandstones, conglomerates, and minor lacustrine shale, marl, and limestone record an abrupt change in source region around 38–36 Ma or slightly later, from more local, Sierran arc–derived sediment to extraregional sources to the north. Clasts of red radiolarian-bearing chert, dark radiolarian chert, and quartzite indicate sources in the region of the Golconda and Roberts Mountains allochthons of northern Nevada. Sandstones intercalated with conglomerate contain increasing proportions of Cenozoic zircon sourced from south-migrating, caldera-forming eruptions at the latitude of Austin and Ely in Nevada with maximum depositional ages (MDAs) ranging from 36 to 24 Ma at the top of the Titus Canyon Formation. Carbonate clasts and ash-rich horizons become more prevalent in the overlying conglomeratic Panuga Formation (which contains a previously dated 15.7 Ma ash-flow tuff). The base of the higher, ash-dominated Wahguyhe Formation yielded a MDA of 14.4 Ma. The central Funeral Mountains section exposes a different sequence of units that, based on new data, are correlative to the Titus Canyon, Panuga, and Wahguyhe Formations at locations 1 and 2. An ash-flow tuff above its (unexposed) base provided a MDA of 34 Ma, and the youngest sample yielded a MDA of 12.7 Ma. The striking differences between age-correlative sections, together with map-based evidence for channelization, indicate that the Titus Canyon Formation and overlying units likely represent fluvial channel, floodplain, and lacustrine deposits as sediments mostly bypassed the region, moving south toward the Paleogene shoreline in the Mojave Desert. The profound changes in source regions and sedimentary facies documented in the Titus Canyon Formation took place during ignimbrite flareup magmatism and a proposed eastward shift of the continental divide from the axis of the Cretaceous arc to a new divide in central Nevada in response to thermal uplift and addition of magma to the crust. This uplift initiated south-flowing fluvial systems that supplied sediments to the Titus Canyon Formation and higher units.
Conference papers on the topic "Unconformably"
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Pisarev, Denis Yurievich, Ildar Fanurovich Sharipov, Artur Michailovich Aslanyan, Danila Nikolaevich Gulyaev, and Anastasiya Nikolaevna Nikonorova. "Oil Production Enhancement by EOR Candidates Optimization." In SPE Russian Petroleum Technology Conference. SPE, 2021. http://dx.doi.org/10.2118/206498-ms.
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The study field is located in the Nizhnevartovsk district of the Khanty-Mansi autonomous region. The deposit is located in the Nizhnevartovsk crest zone. The geological section of this deposit features a thick layer (2740-2870 meters) of Meso-Cenozoic era sedimentary rocks starting from the Jurassic period up to and including the Quaternary period, and rests unconformably on the surface of the deposits of the folded Paleozoic basement. The pay zones of study oil and gas fields features mainly sandstone-siltstone reservoirs. The study formation XX11-2 features interleaved rocks with a high clay content. In the west and south-west of the field, the oil-saturated thicknesses vary on average from 5-10 m, and in the north, the thickness increases to 10-20 m. This field has a long-lasting production history as a result of drilling vertical and horizontal wells but is currently at production decline stage. The existing reservoir pressure support system assumes that the water-cut trend at the wells will increase. In recent years, there has been advanced flooding in some areas, resulting in a drop in oil production, while the reasons for the advanced flooding are not always clear. This is often due to the progressing spontaneous fracturing in the injector wells (Aslanyan, Akimov et al., 2020).
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Rezig, Drifa, Imane Ouarda Hadjar, Ferhat Nettari, Matthew Hertz, Messaoud Boukhenifra, Djamil Bouacida, Hedi Hadjarab, and Omar Salmi. "Integration of Borehole Image Analysis, Open Hole Logs and Core Data to Unlock Stratigraphic & Sedimentological Analysis of a South Eastern Algeria Field." In International Petroleum Technology Conference. IPTC, 2022. http://dx.doi.org/10.2523/iptc-21879-ms.
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Abstract The identification of the depositional environment is critical to the delineation and prediction of the best quality reservoir. It often starts with a detailed core description, which is based on number of features. Borehole image augments the core data by providing important information for orienting features, filling in gaps between cores, recognizing sedimentary structures and sorting for facies analysis and identifying depositional environments. Oil-Based Micro-resistivity Images and Ultra-sonic Borehole Images were successfully applied to reservoir modeling by introducing a statistically correct model that obeys facies association rules and facies contacts and improves the dynamic history match. The principal hydrocarbon reservoir of field-A in the South Eastern Algeria basin, TAGI, is part of a fluvial system. The microfacies were analyzed with a pseudo-grain size profile and textural analysis of the borehole resistivity and ultrasonic images. The TAGI sits unconformably on the Paleozoic rocks, it consists of variable sequences which have been sub-divided into four fluviatile cycles. The depositional environments are mainly amalgamated channels passing laterally to flood plain, crevasse splay and sheet flood deposits. The correlation of the cycles combined with empirical functions enabled estimating the geometry of the sandstone bodied for each deposition element. This is required input for object modeling. This study showed the value of borehole image logs in sedimentology analysis, which progressed from single-well borehole image interpretation to conceptual model construction and channel dimension estimation.
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Chowdhury, Manabesh, Arun Babu Nalamara, VR Sunder, Pankaj Kumar, Pinakadhar Mohapatra, and Savitri Roy. "Utilization of Spectral Gamma Ray Logs to Ascertain Stratigraphic Surfaces in Carbonate Reservoir and Integration with Seismic Interpretation: An Integrated Case Study from Eocene-Oligocene Carbonate Reservoirs, D31 Cluster, Mumbai Offshore Basin, India." In SPE/IATMI Asia Pacific Oil & Gas Conference and Exhibition. SPE, 2021. http://dx.doi.org/10.2118/205709-ms.
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Abstract D31 cluster is located in the prolific Mumbai Offshore Basin, Western part of India. B-192Afield is part of this cluster, where Bassein (Middle Eocene),Mukta and Panvel (Early Oligocene)Formations are the main reservoirs. The reservoirs are complex in terms of reservoir heterogeneity. They were deposited in a shallow marine carbonate platform.Sea level fluctuations andchange in depositional environment impacted the porosity development. The main objective of this study was to integrate spectral gamma ray signatures with seismic interpretation for demarcating significant stratigraphic surfaces and differentiating depositional environments for robust reservoir characterization. Regionally, Bassein Formation (Middle Eocene) is characterized by thick foraminiferal and algal wackestone, packstone and occasional grainstone facies.The Mukta Formation (Early Oligocene),which unconformably overlies the Bassein Formation, is characterized by presence of fossiliferous limestone with shale intercalations. In the present study, data from four exploration wells data have been analyzed, where spectral gamma ray log patterns in carbonate reservoirs appear to have a distinctive relationship to depositional facies and stratigraphic surfaces in the Bassein and Mukta Formations. Different cross plots have also been utilized for analyzing the depositional conditions (i.e. oxic or anoxic).Later, the spectral log interpretations have been integrated with seismic interpretation. This study is part of a larger effort for reservoir characterization, as a basis for seismic interpretation and integrated reservoir modelling. The spectral gamma ray signatures demarcated significant stratigraphic surfaces. In BasseinFormation, three different units have been marked as Upper, Middle and Lower Bassein. The major lithological boundary between the Bassein and Mukta Formation is also well demarcated with spectral GR signature. The carbonate strata of Bassein & Mukta Formation have also been subdivided with U-Th-K abundance.The "Low Th-Low U" units indicative of pure carbonate and deposition in oxidizing environment whereas "Low Th-High U"is indicative ofreducing environment, which gave a relative sea level fluctuation in the area.The major stratigraphic boundaries identified from these spectral GR logs has been incorporated in the seismicinterpretation and used for regional seismic mapping.As porosity development is governed by thesea level fluctuations,this study also gave an indication of the possibility of porous zonein the reservoir section. These results can be useful as a basis for applying spectral GR signature as a tool for stratigraphic interpretation in un-cored heterogenous carbonate sections. Along with the petrophysical interpretation, integration of core analysis, biostratigraphy and seismic attribute are critical for detailed carbonate reservoir characterization incorporating depositional environment.This approach can be applied to support commercial development of the complex carbonate reservoirs.
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Fankhauswer, S. D., and E. A. Erslev. "Unconformable and cross-cutting relationships indicate major Precambrian faulting on the Picuris-Pecos Fault System, Southern Sangre de Cristo Mountains, New Mexico." In 55th Annual Fall Field Conference. New Mexico Geological Society, 2004. http://dx.doi.org/10.56577/ffc-55.206.
Full textReports on the topic "Unconformably"
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Cecile, M. P., B. S. Norford, G. S. Nowlan, and T. T. Uyeno. Lower Paleozoic stratigraphy and geology, Richardson Mountains, Yukon (with stratigraphic and paleontological appendices). Natural Resources Canada/CMSS/Information Management, 2022. http://dx.doi.org/10.4095/329454.
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The Richardson Trough was a rift basin on the southern margin of an ancestral Iapetus Ocean. It was part of a complex paleogeography that included at least two major rift basins on western Franklinian and northern Cordilleran continental shelves. This paleogeography included the Ogilvie Arch, Porcupine Platform, Blackstone 'supra-basin', Babbage Basin, Husky Lakes Arch, Richardson Trough, Mackenzie Arch, Lac des Bois Platform, and the White Mountains and Campbell uplifts. The Richardson Trough was the failed arm of a triple rift system that formed when an early Paleozoic Iapetus Ocean developed north of the trough. The Richardson Trough displays a classic 'steer's head' profile with two rift fill cycles. The first features late early to middle late Cambrian rifting and late late Cambrian to late Early Ordovician post-rift subsidence; the second, late Early Ordovician to early Silurian rifting and late early Silurian to early Middle Devonian post-rift subsidence. Lower Paleozoic strata exposed in the Richardson Trough range in age from middle Cambrian to early Middle Devonian and are similar to strata in their sister rift, the Misty Creek Embayment. Before this study, the stratigraphic units defined for the Richardson Trough were the Slats Creek Formation and the Road River Formation. Here, the Slats Creek Formation and a new Road River Group are recognized. In order, this group consists of the middle and/or late Cambrian to Early Ordovician Cronin Formation; the early Early Ordovician to latest early Silurian Mount Hare Formation; the early Silurian to late Silurian Tetlit Formation; and the late Silurian to early Middle Devonian Vittrekwa Formation. These Road River Group strata are unconformably overlain by the late Middle to Late Devonian Canol Formation (outcrop) and by the Early Devonian Tatsieta Formation (subsurface).
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Salad Hersi, O., and D. Lavoie. The unconformable character and paleogeographic significance of the Chazy-Black River group contact, Montréal area, southwestern Quebec. Natural Resources Canada/ESS/Scientific and Technical Publishing Services, 2001. http://dx.doi.org/10.4095/212157.
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MacNaughton, R. B., and K. M. Fallas. Neoproterozoic-Cambrian stratigraphy of the Mackenzie Mountains, northwestern Canada, part IV: a stratigraphic reference section for the Ediacaran-Cambrian transition in NTS 95-M (Wrigley Lake map area). Natural Resources Canada/CMSS/Information Management, 2021. http://dx.doi.org/10.4095/329217.
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A composite reference section for the upper Ediacaran and lower Cambrian is documented for a location near Moose Horn River in Wrigley Lake map area (NTS 95-M), Mackenzie Mountains, Northwest Territories. Four measured stratigraphic sections cover, in ascending order: the uppermost Sheepbed Formation; the informal Sheepbed carbonate; the lower, middle, and upper members of the Backbone Ranges Formation; the Sekwi Formation; and the lowermost beds of the Rockslide Formation. The uppermost Sheepbed Formation is dominated by dark-weathering shale and siltstone. The Sheepbed carbonate (440 m) lies conformably on the Sheepbed Formation and consists of limestone, dolostone, and dolomitic siltstone, including several horizons of rudstone with clasts up to boulder size. The upper surface of the Sheepbed carbonate has been eroded and the unit thins to a zero edge to the east. The lower member of the Backbone Ranges Formation (253 m) is heterolithic, including interbedded quartzose siltstone and quartzose sandstone, quartz arenite (locally with horizons of quartz pebbles), and dolostone to dolomitic sandstone. The middle member of the Backbone Ranges Formation (93 m) consists mainly of pink to grey-weathering limestone with red mudstone partings. The upper member (501.5 m) is dominated by quartz arenite, but also contains intervals of siltstone. Partway through the upper member there is a marker unit of dolostone to dolomitic sandstone that previous work suggests is a tongue of the Ediacaran Risky Formation. Based on regional correlations, the top of this marker may approximate the Ediacaran-Cambrian boundary in this section. The Sekwi Formation lies abruptly upon the Backbone Ranges Formation. The contact is unconformable at this locality and mapping in the area indicates eastward erosional removal of the upper member of the Backbone Ranges Formation beneath the Sekwi Formation. The Sekwi Formation here consists of variegated siltstone with lesser dolostone, limestone, and quartz sandstone. An abrupt contact with nodular limestone and grey shale of the overlying Rockslide Formation approximates the base of Cambrian Series 3.